Home Physical Sciences Synthesis and purification of metallooctachlorophthalocyanines
Article Publicly Available

Synthesis and purification of metallooctachlorophthalocyanines

  • Tobias Rüffer EMAIL logo , Dinara Nurpeisova , Zhanar Jakupova , Ayezkhan Tashenov , Nell Uhlig , Ahmed Khalladi , Lutz Mertens , Andreas Gonser , Michael Mehring and Heinrich Lang
Published/Copyright: August 5, 2017
Download Article (PDF)
Become an author with De Gruyter Brill
Author Information Explore this Subject
Zeitschrift für Naturforschung B
From the journal Zeitschrift für Naturforschung B Volume 72 Issue 8

Abstract

A detailed synthetic procedure based on the use of urea, dichlorophthalic acid, respective transition metal halides and [NH4]2[MoO4] as a catalyst in the melt or by using 1,2,4-trichlorobenzene as a high-boiling inert solvent is described to gain 2,3,9,10,16,17,23,24-metallooctachlorophthalocyanines (MPcCl8 compounds with M=Mn, Fe, Co, Ni, Cu). In cases that a first purification by subsequent treatment of the crude materials with HCl, NaOH and HCl would not give rise to analytically pure compounds, a second novel purification by using pyridine is described. The degree of purity, exceeding always 98%, is determined by thermogravimetric analysis. Comparative IR, UV/Vis and PXRD studies of the MPcCl8 compounds are reported.

Keywords: IR spectroscopy; powder X-ray diffraction; thermogravimetric analysis; urea melt method; UV/Vis spectroscopy

1 Introduction

Metallophthalocyanines (MPcs) are a class of materials which have been known for decades. They have found so many different applications that a simple enumeration of them would be beyond the volume of even an individual report. Nevertheless, our motivation to synthesize MPcs and to deliver them without detectable impurities is as follows: novel organic sensors based on electrically detected magnetic resonance [1] as well as devices like spin-organic field effect transistors [2] or spin-organic light-emitting diodes [3] have been developed since first reports on organic spin valves appeared [4, 5]. Thereby, various diamagnetic molecules [6] or individual single molecule magnets [7] were integrated into such spintronic devices. However, it still remains puzzling to understand the principles of the spin-polarized transport in organic spin valves in detail as well as the function/effect of suitable molecules deposited on respective (ferromagnetic) contacts. Sanvito has already coined the term “spinterface” to describe the spin manipulation at the interface between deposited (paramagnetic) molecules on (ferromagnetic) contacts [8]. It could be shown that a “… spin-active interface purely made from organic components (metal phthalocyanines) …” [9] is accessible and can be produced by the successive and/or co-deposition of MnPc and CoPcF16 on suitable substrates [9]. Thus, the two different MPcs became involved in mutual intermolecular contacts after deposition, giving rise to charge transfer ensembles of the type MnPcδ+/CoPcF16δ− [9]. Those MnPcδ+/CoPcF16δ− stacks were the subject of theoretical and spectroscopic characterization [10], whereby the MnPc is the electron donating and CoPcF16 the electron accepting part. Certainly, the MnPcδ+/CoPcF16δ− stack represents only one out of several different possibilities to place different MPcs onto each other. Consequently, related pairs were theoretically studied, and the energy levels, the ionization potentials and electron affinities (EA) were calculated [11].

The above-mentioned aspects show that MPcs having either electron-withdrawing or -donating substituents are of importance. Besides pristine MPcs, full series of substituted MPcs with M=Mn, Fe, Co, Ni, Cu are not commercially available. Furthermore, MPcs are usually traded with certified purities below 98% and the number of certified analytically pure MPcs (purity>99%) is very small. To mention one example, CuPc in its “triple-sublimed quality” can be purchased in a purity>99.95% (Sigma Aldrich). Such high purities of MPcs are conventionally produced by sublimation [or, alternatively, organic molecular beam deposition (OMBD)] techniques in ultra-high vacuum, surely costly at least in terms of time. A recent example is given by an exciting report of the group of Heutz, who aimed to produce pure thin films of CoPc for subsequently performed magnetic studies [12]. In order to avoid an impact of impurities from commercial CoPc, it was purified by temperature gradient sublimation [12]. Thus, in case that MPcs are required to be deposited in the form of thin films by means of OMBD, it would thus be desirable to have direct access to them in certified purities above 99%. In such a case just one time-costly OMBD step is required to avoid any impact of impurities to (thin) film properties.

With respect to the need of MPcs having electron-withdrawing substituents for further experimental studies [10], we became interested in the synthesis of metallo-2,3,9,10,16,17,23,24-octachlorophthalocyanines, MPcCl8, with M=Mn, Fe, Co, Ni, Cu. In the literature two reports by the group of Safari and Shaabani describe the synthesis of MPcCl8 compounds with M=Fe, Co, Ni, Cu, Zn [13] and with M=Mn, Fe, Co, Ni, Cu [14]. Within [13] a mismatch (ca. 6%) between the masses (m) and corresponding molar amount (n) of [Cu(SO4)·5H2O] and the diammonium salt of 4,5-dichlorophthalic acid (4,5-DPA), respectively, is obvious, and it is surprising that the molar ratio between these two starting materials is 1:9. Furthermore, the reaction equation given in Fig. 1 in [13] is in contrast to the description of the experiments which suggest the use of the diammonium salt of 4,5-DPA but not the utilization of 4,5-dichlorophthalic anhydride. According to [13], a novel purification method was developed, because the purification of the MPcCl8 compounds by “… extreme treatment … with acids and bases, using literature reported methods, results in partial demetalation, substitution of sulfate in the macrocycle ring …” and thus the authors “… were not able to get good elemental analysis data by conventional methods. …” [13]. According to the novel purification method, the MPcCl8 compounds should be refluxed in degassed dimethyl sulfoxide (DMSO) under inert atmosphere at 110°C for 7 h [13]. This is confusing as DMSO has a b.p. of 189°C [15]. In addition, we refer to the subsequently published report on the synthesis of MPcCl8 compounds by the following citation: “… The separated solid was heated in 0.1 N HCl and 0.1 N NaOH for 10 min, respectively. …”; thus the authors abstained from the use of the purification methodology reported before [14]. As the authors put much emphasis on the results of the elemental analysis, we compared the respective entries for CoPcCl8, NiPcCl8 and CuPcCl8, synthesized and purified via two different methodologies and found them to be fully identical to each other [13, 14]. That makes the choice of the synthetic and purification procedure difficult. The synthesis of CoPcCl8 is described in a further report [16]. Despite some mismatch between the mass and molar amount of [Co(SO4)·7H2O] of ca. 5% the molar ratio between 4,5-DPA and [Co(SO4)·7H2O] is ca. 3.5 [16]. Certainly, four equivalents of the (substituted) phthalic acid (PA) are required to convert one equivalent of the transition metal salt to theoretically one equivalent of the MPc under study by following the urea method. The authors give an 88% yield of CoPcCl8, without referring to which starting material the yield is calculated and without giving the weighted amount of CoPcCl8 [16]. In that case, due to the molar ratio of the two above-mentioned starting materials, a theoretical yield of only (3.5/4)×100%=87.5% could be achieved. That might indicate that the isolated CoPcCl8 of [16] was not pure [17].

Fig. 1: IR spectra of pure Nujol (top), CA (cyanuric acid) in Nujol (middle) and CoPcCl8 in Nujol (bottom) in the range of 750 to 4000 cm−1. IR absorptions belonging to Nujol, CA and CoPcCl8 have been marked in black, blue and pink, respectively. IR absorptions of CO2 have been indicated as such.
Fig. 1:

IR spectra of pure Nujol (top), CA (cyanuric acid) in Nujol (middle) and CoPcCl8 in Nujol (bottom) in the range of 750 to 4000 cm−1. IR absorptions belonging to Nujol, CA and CoPcCl8 have been marked in black, blue and pink, respectively. IR absorptions of CO2 have been indicated as such.

Keeping in mind that we aimed to deliver MPcCl8-type compounds in a very high purity allowing us to deposit them directly by means of OMBD techniques, we refrain from using already reported synthesis/purification methodology. Thus, the urea method was selected to prepare pristine MPcs (M=Mn, Fe, Co, Ni, Cu) first and to get detailed information on how to run their synthesis. Certainly, the method has been reviewed and (pristine) MPcs are accessible by this method using PAs, phthalic anhydrides, phthalimides or phthalamides, urea, the (transition) metal salt of choice, and often by using catalysts. It is rather common to run such reactions in high boiling solvents including nitrobenzene or 1,2,4-trichlorobenzene. The knowledge obtained out of such experiments should next be applied to synthesize/purify MPcCl8-type compounds (M=Mn, Fe, Co, Ni, Cu). We further aim to report in detail on the characterization of the MPcCl8 compounds using IR and UV/Vis spectroscopy, elemental analysis, powder X-ray diffraction studies (PXRD), and thermogravimetric analysis (TG).

2 Results and discussion

The synthetic and purification procedures described here can be summarized according to Scheme 1. In the following sections the individual steps are explained and discussed in detail.

Scheme 1: Synthesis and purification MPcCl8 compounds.
Scheme 1:

Synthesis and purification MPcCl8 compounds.

2.1 Synthesis and purification of pristine MPcs and MPcCl8 compounds (M=Mn, Fe, Co, Ni, Cu) by the urea (melt) method

2.1.1 Synthesis of the crude materials

We decided to apply the urea melt method according to a textbook description to synthesize pristine MPcs first [18]. This description does not differ significantly from related ones reported elsewhere [19]. According to [18] the use of CuCl2·2H2O and PA in a molar ratio of 1:5.2 is required as well as the use of a large excess of urea, and [NH4]2[MoO4] as catalyst. After mixing all components the mixture should be heated to 180°C and this temperature should be held for 6 h. This implies that the mixture should be heated ad hoc and not in certain intervals. As no further information is given, one would thus not expect to notice any severe changes of the mixture and no mentionable peculiarities. This is, however, not the case. Therefore, we will describe here in some more detail our observation to synthesize both pristine MPcs and MPcCl8 compounds (M=Mn, Fe, Co, Ni and Cu) by the urea melt method (cf. Scheme 1). Thereby, we worked with the same masses and molar ratios given in [18] and modified only the nature of the PA and the transition metal salts. Our applied modifications and their impact on the obtained yields and purities are described and discussed as given in Chapter 1S in the Supplementary Information. Pristine MPcs and MPcCl8 compounds were synthesized via (a) the urea melt method and (b) the urea method and by applying 1,2,4-trichlorobenzene (TCB) as an inert solvent. The crude materials obtained via (a) or (b) can both be purified to give very pure (>99%) compounds in about the same yields. We prefer the use of TCB as an inert solvent as it allows running the reactions more easily, but this is not a prerequisite.

2.1.2 First purification procedure using HCl and NaOH

The weights of the crude materials made as described above range from 11 and 20 g, and the colors of these solids appear from dark purple (CuII/NiII/CoII) via black (FeII) to dark green (MnII), indicating that they contain metallophthalocyanines. The IR spectra of the crude materials reveal the presence of mainly cyanuric acid (CA). Additional and much less intensive vibrations indicate the presence of further compounds. That observation calls for a reliable and reproducible purification methodology and we decided to carry out the work-up in relation to comments made in reference [18]. Hence, purification was done with diluted HCl, next with diluted NaOH and finally again with diluted HCl, although some modifications were necessary.

The first refluxing with should be at least 2 h. After the filtration the filter cake is washed neutral and next ice-cold NaOH is used. The filtrates are intensively colored and one can notice a significant volume reduction of the filter cake. The material obtained after the second refluxing with HCl and subsequent filtration is air-dried in a fume hood under aerobic conditions. In case that the materials did not contain other residues, especially CA as judged by IR spectroscopic measurements, TG studies were performed. In the absence of any mass decline below ca. 220°C, the material is >99% pure. If that was not the case, we subsequently performed pyridine purification.

2.1.3 Second purification procedure using pyridine

About 1 g of the sample was heated in 15 mL degassed DMSO under inert atmosphere for 7 h to 110°C. The compounds did then precipitate as the DMSO solutions cooled down. However, we did not observe significant purification. Heating of impure samples (ca. 30 mg) in [D6]DMSO (0.8 mL) in a NMR tube to 80°C under simultaneous sonication for 1 h showed the formation of intensively colored mixtures of which the MPcs precipitated rapidly after ca. 1 h. In selected cases the full precipitation took up to 2 days. 1H NMR measurements of the supernatants revealed the presence of CA, phthal- or 4,5-dichloro-phthalimid with other unknown impurities. By adding internal standards to the [D6]DMSO supernatants before heating and sonication, the amounts of CA liberated by that treatment were judged to be below 0.1 mg and thus below 0.5% of the MPc. Thus, such a treatment is not suited for purification purposes.

Since Robertson’s single crystal X-ray diffraction studies of (metallo)phthalocyanines [20] the packing motifs became obvious. For example, pristine MPcs as flat and aromatic molecules form chains due to mutual dispersion interactions. One can furthermore suppose that flat (and aromatic) molecules like CA as well as phthal- and 4,5-dichloro-phthalimid can be incorporated into these chains by replacing an individual MPc molecule. Any soxhlet extractions cannot help to purify, as the materials must be dissolved in order to “liberate” the impurities. One thus needs a purification method which “breaks” the contact between individual MPcs and their impurities in order to solvate them. A striking example to verify this hypothesis is given by Hanack and Thies [21], who reported on the synthesis of [tetra(2,3-pyrido)porphyrazinato]eisen(II) (TPyPFe) by the urea method. It is obvious that the dissolution of the crude material in ice-cold H2SO4 and its reprecipitation, even its extraction with ethanol and acetone, are not suitable to give analytically pure TPyPFe [21]. Instead, TPyPFe was reacted with two equivalents of isocyanides to allow recrystallization from CHCl3. The bis(adducts) could be purified and characterized [21]. Thus, if one aims to get rid of the impurities in MPcs, one should apply suitable organic donor molecules, which can be axially coordinated to the MPc and thus solvate both the MPc and the impurity. Upon screening appropriate organic donor molecules in combination with an organic solvent we came across a remark that “… magnesium phthalocyanine which has been crystallized from pyridine … is not contaminated …” [22].

Hence, 1 g of the impure MPc was added to 25 mL pyridine and purification was carried out as described in the Experimental Section. From solely stirred and subsequently sonicated mixtures of pyridine and the impure MPc we could never isolate pure materials. After refluxing [15] the mixtures of the reprecipitated/recrystallized MPcs were usually pure for 2 h. If not, the procedure had to be repeated.

Note: In case that the MPc/MPcCl8 compound subjected to pyridine purification contains ≥3% CA out of the filtrates, large and colorless needles (ca. 0.5×0.08×0.8 mm3) were formed overnight. The needles became immediately brittle after removing the solvent. Single crystal X-ray diffraction studies revealed the formation of [CA·3pyridine]. Interestingly, this composition is different from the one obtained after crystallizing CA from pyridine, namely [CA·pyridine], according to Sivashankar [23].

2.2 Characterization of MPcCl8 compounds (M=Mn, Fe, Co, Ni, Cu)

2.2.1 IR spectroscopy

IR spectroscopic studies are a well-suited tool to characterize MPcs, as these materials have several strong absorptions. In comparison with certified materials the identity of the individual MPc can be determined. In that context, the entries of the IR spectra of the pristine MPcs (M=Mn, Fe, Co, Ni, Cu) in the SDBS database [17] were extremely helpful.

The IR spectra of pristine MPcs were usually measured out of KBr disks [17, 24], but CoPcCl8 reported in [16] was measured in Nujol. For comparison, we measured our CoPcCl8 in Nujol as well (cf. Fig. 1). It is obvious that the CoPcCl8 reported in [16] was not free of CA while the one reported here is (cf. Fig. 1).

The IR spectra of MPcCl8 (M=Fe, Co, Ni, Cu; KBr disk) were reported twice [13, 14], whereas the IR spectrum of MnPcCl8 (KBr disk) was reported once [14]. By comparing the wavenumbers of individual entries of MPcCl8 compounds (M=Fe, Co, Ni, Cu) given in [13] with those of [14] differences of up to 6 cm−1 can be noted. Unfortunately, the experimental IR spectra are not presented and further comparison with respect to the shape, the pattern or the intensity of a specific absorption is impossible. To avoid this, a part of all IR spectra of the MPcCl8 compounds reported here is depicted in Fig. 2. Shaded areas belong to related absorptions and are numbered. The wavenumbers of these absorptions are summarized in Table 1. The full range IR spectra (750–4000 cm−1) are given in Figs. S1–S5 in the Supplementary Information. We abstain from assigning the IR vibrations and refer here to a forthcoming report comparing the IR and Raman spectra of MPc and MPcCl8 compounds (M=Mn, Fe, Co, Ni, Cu) with additionally performed quantum chemical calculations.

Fig. 2: IR spectra (KBr) in the range from 500 to 1800 cm−1 of MPcCl8 compounds.
Fig. 2:

IR spectra (KBr) in the range from 500 to 1800 cm−1 of MPcCl8 compounds.

Table 1:

Wavenumbers of shadeda IR vibrations of MPcCl8 compounds in the range from 500 to 1800 cm−1.

MPcCl8 entryaCuPcCl8CoPcCl8NiPcCl8FePcCl8MnPcCl8
1661661661660660
2705708708703706
3732742739734730
4745751750748747
5783784784781782
6845850852842849
7889888888890890
8955966967953959
910711074107510711071
10108810881088––
1111341137113711261127
1211961201120111961200
1312911293129312871288
1413381341134413211328
1513841389139013811383
1614151418141814151417
1715061524153315001507
1816031604160416011605

  1. aEntry refers to numbers given in Fig. 2 by acknowledging the applied color code.

Purity remark: In case that the IR spectra did not indicate the presence of CA or the respective phthalimides [17] we carried out TG analyses. If the individual TG analyses did not indicate significant mass loss below ca. 210°C, and if the first derivative did not show temperature maxima below 400°C, the sample was declared as pure by ≥99%. However, if the first criterion is not fulfilled but only the second, the sample was declared as pure by 100 – x%, where x refers to mass losses up to 400°C.

2.2.2 Powder X-ray diffraction studies

For all MPcCl8 compounds reported here PXRD studies have been performed at room temperature in the range 3<2θ<60° (Fig. 3). For CoPcCl8 the PXRD pattern has already been reported [16]. Its pattern is in agreement with the one reported here, although the degree of crystallinity is higher in the present case.

Fig. 3: PXRD patterns of the MPcCl8 compounds under study. Values refer to θ angles in deg.
Fig. 3:

PXRD patterns of the MPcCl8 compounds under study. Values refer to θ angles in deg.

Any calculations of crystallographic data were not carried out. We want to emphasize that especially the two reflections observed for Cu, Ni, CoPcCl8 at 14.0/14.5°, 14.0/14.7°, 14.0/14.5°, respectively, compared to related θ values of Fe, MnPcCl8 with only a single reflection at 14.8 and 15.0°, may indicate the presence of different packing motifs and/or phases. The PXRD patterns (Fig. 3) reveal that MPcCl8 compounds have been obtained in the form of microcrystalline powders. The degree of crystallinity can, however, be increased (pyridine treatment) or decreased (H2SO4 treatment) as described in the Experimental Section. A typical example for an MPcCl8 compound in two different states of crystallinity is shown in Fig. 4 for CuPcCl8.

Fig. 4: PXRD pattern of CuPcCl8 before (below) and after (top) H2SO4 treatment.
Fig. 4:

PXRD pattern of CuPcCl8 before (below) and after (top) H2SO4 treatment.

2.2.3 Elemental analysis

We could never get acceptable values for the CHN contents of our pristine MPcs and MPcCl8 compounds determined via combustion (cf. Experimental Section). According to the literature the elemental analysis of CoPcCl8 was performed with a Vario EL III CHNS analyzer [16] or a Heraus CHN-O Rapid analyzer [13, 14]. For MPcCl8 compounds (with the exception of FePcCl8 [13, 14]) the EA seems to be reliable to determine the CHN contents within ca. ±0.5% absolute deviation. We noticed that the experimentally determined CHN contents reported for CoPcCl8, NiPcCl8 and CuPcCl8 are identical to each other, when comparing entries from [13] with those of [14].

Additionally, we performed CHN combustion analysis of amorphous and/or less crystalline samples with the vario Micro cube analyzer for the two different samples of CuPcCl8 displayed in Fig. 4. The obtained CHN contents did in no case deviate by more than ±0.1% absolutely, when compared to each other. The following CHN contents were determined: CuPcCl8 before “H2SO4 treatment”=C: 43.3%, H: 0.9%, N: 12.9%. CuPcCl8 after “H2SO4 treatment”=C: 43.2%, H: 1.0%, N: 12.8%. For 100% pure CuPcCl8 (M=851.639 g mol−1) the CHN contents calculate to C: 45.13%, H: 0.95%, N: 13.16%. Obviously, especially the experimentally determined carbon content is too low and thus combustion temperatures of even 1800°C at the moment of the sample injection [25] are not sufficient to convert all carbon atoms to CO2.

On the other hand, one may ask if an EA with ±0.5% accuracy is suited to determine whether MPcCl8 compounds reported here are pure. To check this, the following example is given: for 100% pure CuPcCl8 (M=851.639 g/mol) the CHN contents calculate to C: 45.13%, H: 0.95%, N: 13.16%. Suppose that the experimentally obtained material is composed of CuPcCl8 (97.5%) and CA (2.5%, M=129.07 g mol−1); the calculated CHN contents modify to C: 44.70%, H: 0.98%, N: 13.64%. The differences to 100% pure CuPcCl8 are within ±0.5% absolute deviation only, and we regard thus the CHN analysis as not suitable to determine whether the compounds reported here are analytically pure.

2.2.4 Electronic spectra

The electronic absorption spectra of CoPcCl8 in context with those of CoPc, CoPcCl4 and CoPcCl16 were determined in pyridine and displayed and discussed in [16]. Three absorption maxima are reported for CoPcCl8, of which two have the same intensity [λmax in nm (lg ε)=356 (4.31) and 682 (4.31)] and a third one appears as a shoulder of the Q band [λmax in nm (lg ε=620 (4.19)] [19]. It is noticeable that neither the concentration of CoPcCl8 in pyridine nor any kind of sample treatment such as, for example, a brief sonication, is given [16]. Furthermore, the electronic spectrum of CoPcCl8 in pyridine does not display any fine structure but broad absorptions only [16].

Data of UV/Vis measurements of, for example, CoPcCl8 have been reported in [13, 14], where H2SO4 was used as a solvent. Unfortunately, no ε values and no concentrations and/or sample treatments are given and it remains speculative whether the H2SO4 used was concentrated or diluted [13, 14]. The data reported in [13] agree well with those reported in [14] within a deviation of ±2 nm. For CoPcCl8 in H2SO4 four absorption bands at 319.0, 434.5, 706.5 and 793.0 nm were noticed by the authors [14]. A comparison with the UV/Vis data reported for CoPcCl8 in H2SO4 [13, 14] and in pyridine [16] reveals some differences. This prompted us to carry out further measurements.

We investigated first whether electronic absorption spectra of CoPcCl8 in pyridine can be determined reproducibly. A detailed description of the experiments which we performed is summarized in Chapter 3S (Supplementary Information). Here, we aim to state that in our opinion CoPcCl8 is not soluble in pyridine in the form of solvated single molecules and that only aggregates of it with unknown aggregation number are dispersible.

We also performed UV/Vis measurements of the MPcCl8 compounds reported here in H2SO4(conc.) in a range of concentration as our preliminary UV/Vis measurements of CoPcCl8 revealed some differences with respect to reported λmax values [13, 14]. Additionally, concentration-dependent UV/Vis measurements were performed as it has already been reported that the nature (cofacial, face-to-face, tilted) and degree (dimer, oligomer, polymer) of mutual interactions of (metallo)phthalocyanines might modify their optical absorption significantly [26]. When starting with these measurements we were aware of a comment in [16] that “ … CoPcCl8 and CoPcCl16 are soluble in 33.0 N sulfuric acid with degradation. …” As displayed in Fig. 4 exemplarily for CuPcCl8, all MPcCl8 compounds reported here are well soluble in H2SO4 (conc.), and can be repeatedly precipitated without any degradation. That statement is verified further by IR studies. Additionally, we measured for each individual MPcCl8 compound at least six different concentrations, whereby originally prepared solutions were used for dilution. In certain limits (cf. below), the striking similarity of the UV/Vis spectra verifies that all compounds are stable in H2SO4 (conc.) in a time span of at least 12 h.

The UV/Vis spectra of the MPcCl8 compounds are shown in Fig. 5. The spectra for the whole series of concentrations of CuPcCl8, NiPcCl8, CoPcCl8, FePcCl8 and MnPcCl8 are given in Figs. S6–S10 in the Supplementary Information. The λmax and lgε values of the spectra displayed in Fig. 5 are summarized in Table 2. Tables S1–S5 in the Supplementary Information summarize λmax and lgε values of all measurements.

Fig. 5: Electronic absorption spectra of MPcCl8 compounds in H2SO4(conc).
Fig. 5:

Electronic absorption spectra of MPcCl8 compounds in H2SO4(conc).

Table 2:

Values for λmax (nm) and lgε (L·mol−1·cm−1) for MPcCl8 compounds under studya.

MPcCl8λmax lgɛ
CuPcCl8224.5246278314356413445.5646675.5712762.5803.5
4.6934.6144.6184.6214.2074.2014.3343.7363.9884.4734.5795.295
NiPcCl8b222246274.5313.5–410.5432.5636668699746785.5
4.5674.5934.5694.656–4.1414.1833.7433.9934.4184.4165.182
CoPcCl8224242–304.5––435––707.5–795
4.6524.598–4.866––4.352––4.466–5.084
FePcCl8224247304.5326–––631–716752787.5
4.6864.9304.3914.323–––3.728–3.7163.8214.008
MnPcCl8222.5249–314––446–680721/763/810/850
4.3084.603–4.048––3.540–3.3753.61/3.91/4.0/3.80

  1. aData refer to the spectra displayed in Fig. 5.

  2. bThe shoulder at 298 nm (lgε=4.538) and the absorption at 858 nm (lgε=3.65) are not included.

The systematic study has revealed that the intensity of the Q band of Cu, Ni and CoPcCl8 exceeds the one of the B band, while for Fe and MnPcCl8 this situation is reversed. For Cu and NiPcCl8 the intensity of the Q band is about twice as intense as the Q band of CoPcCl8, while for MnPcCl8 three bands were observed. With respect to the remarks given in [26] it is striking to observe that dilution of the H2SO4 (conc.) solution of the MPcCl8 compounds did modify the λmax values by maximum ±2 nm only, if at all. On the other hand, we observed that the energetically highest absorption belonging to the B band is severely prone to dilution, with the exception of CuPcCl8. The increase in intensity in the measured range of concentrations amounts for NiPcCl8@228 nm to 1.5, for CoPcCl8@223/306 nm to 2.5/1.25, for FePcCl8@247 nm to 2.5 and for MnPcCl8@223/248 nm to 1.5/1.5. The question if these values are due to any differences in the nature and/or degree of mutual interactions (cf. [26]) of the (metallo)phthalocyanines in H2SO4 (conc.) solutions is out of the scope of this report and is reserved for additional quantum chemical calculations, for example.

2.2.5 Thermogravimetric analysis

TG studies of (metallo)phthalocyanines performed so far, including those of CoPcCl8 (under air), have shown that these compounds are thermally stable up to temperatures exceeding at least 300°C [16]. For CoPcCl8 a “decomposition temperature (maximum decomposition temperature)” of 411 (484°C) is given, which surely reflects the high thermal stability of this species [16]. Unfortunately, the TG trace is not given, which does not allow unambiguously to address the two temperatures to Ton as well as whether this reported CoPcCl8 was TG-pure (cf. e.g. with Fig. 1).

The TG traces of MPcCl8 compounds reported here are summarized in Fig. 6. Individual TG traces together with their first derivative for each compound are displayed in figs. S11–S15 in the Supplementary Information. The Ton and Tmax temperatures have been determined. As expected, all compounds are thermally stable up to 400°C.

Fig. 6: TG traces of MPcCl8 compounds; gas flow N2 60 mL min−1, heating rate, 10 K min−1. Ton denotes the onset temperature of mass loss and Tmax the maximum of the first derivative of the TGA trace.
Fig. 6:

TG traces of MPcCl8 compounds; gas flow N2 60 mL min−1, heating rate, 10 K min−1. Ton denotes the onset temperature of mass loss and Tmax the maximum of the first derivative of the TGA trace.

The TG traces are well suited to determine the purity of the compounds. For CuPcCl8 and MnPcCl8 there is no reason to argue about the purity, as in the TG traces including their first derivatives no conspicuous features were observed. As a representative, Fig. S12a in the Supplementary Information contains a TG trace/first derivative of NiPcCl8 which is regarded as being >97.5% pure, as a mass loss in the temperature range between ca. 210°C and ca. 360°C was observed. The origin of that impurity remains unknown. The presence of remaining CA can be ruled out, as the melting point of CA is reported to be 320–330°C [17]. It should be emphasized that the reaction time to obtain this material was shorter as required (cf. Experimental Section and the caption of Fig. S11a). Another TG trace, included in Fig. 6, and its first derivate of an independently synthesized NiPcCl8 are given in the Supplementary Information. This sample is regarded as >99% pure, although a permanent mass loss from 40°C upwards was observed in the TG trace. The first derivate did not display any temperature maximum other than the one corresponding to the decomposition at 627°C. For CoPcCl8 the TG trace displays a mass decline of ca. 2% up to 430°C, accompanied by a maximum in the first derivative at 175°C. That material had been subjected to the pyridine purification four times, but no significant differences in the TG traces/first derivatives could be observed. Thus, the purity of CoPcCl8 is regarded as ≥98%. The first derivate indicates a second mass loss at ca. 785°C (cf. Fig. S13, Supplementary Information), which was not followed further in the context of this work. For FePcCl8 the TG trace/first derivative are not different from those of, for example, CuPcCl8 (cf. Fig. 6). A mass loss is indicated from ca. 420°C upward, accompanied by a maximum in the first derivative at ca. 500°C (Supplementary Information) before the decomposition of FePcCl8 is observed. The TG trace of FePcCl8 shown in Fig. 6 refers to a material that was subjected to two pyridine purifications. After a third and even a fourth pyridine purification the TG traces/first derivatives were not different to the one displayed. A comparison of the IR spectra and PXRD pattern of MnPcCl8, which is >99% pure, with those of FePcCl8 does not display conspicuous features which could be attributed to any impurities of FePcCl8. Compared to observations made for NiPcCl8 and CoPcCl8 (cf. above), the presence of less temperature stable impurities including CA (cf. [17, 27]), can be ruled out for the FePcCl8 case. From our point of view the FePcCl8 reported here is regarded as being free of detectable impurities, although it should likely not be assigned as >99% pure.

3 Discussion

The synthesis of pristine MPcs and MPcCl8 compounds (M=Mn, Fe, Co, Ni, Cu) can be easily and conveniently performed by following the synthetic procedure reported here. Moreover, it has been shown that out of the originally obtained crude materials the desired compounds are accessible in high purity. One aspect for the discussion is to identify the pros and cons of the urea (melt) method and to set them in context with other synthetic methods for phthalocyanines. The most common way to synthesize (substituted) phthalocyanines, with respect the number of reports per year, is the path from phthalonitriles as starting materials. Just recently this synthetic method has been comprehensively reviewed by Nemykin and Lukyanets [28]. What are the benefit(s) to use 4,5-dichlorophthalic acid and not the commercially available 4,5-dichlorophthalonitrile as a precursor? One benefit is the price of the starting materials. At the time of this report the price ratio between both commercially available compounds is about 1:40, with respect to molar amounts. The present synthesis of MPcCl8 compounds is surely more time-consuming compared to the synthetic route via 4,5-dichlorophthalonitrile, as judged with respect to information given in [28], but this synthetic route has another disadvantage. According to the review of Nemykin and Lukyanets [28] and other recent examples [29, 30] the use of phthalonitriles requires anaerobic working conditions, contrary to the present synthesis. In contrast, here reported syntheses refer to aerobic working conditions and no specific precautions are required, even not in case of the synthesis of MnPcCl8. As one might expect that the procedure reported here cannot give rise to non-oxidized species, especially Mn(II)-containing phthalocyanines, we will briefly discuss this.

The air (oxygen) sensitivity of pristine MnPc in the form of its adduct [Mn(II)Pc(py)2] is well described [31]. While crystals of [Mn(II)Pc(py)2] are reported to be moderately stable in air, pyridine solutions are not. In case that such solutions are exposed to air, an oxidation process to [Mn(III)Pc(py)2]O has been recorded [31]. For Mn(II)-containing phthalocyanines [32], and as observed for [Mn(II)Pc(py)2] [31], the Q-bands are split and are thus less intense if compared to the ones of related, for example, Cu(II)-containing phthalocyanines (cf. Fig. 5).

That phenomenon can be, with respect to quantum chemical calculations [32], attributed to the Jahn–Teller effect [33], which reduces the symmetry of MnPc. The electronic absorption spectrum of MnPcCl8 reported here (cf. Fig. 5) reveals an analogous situation. Upon oxidation of [Mn(II)Pc(py)2] to [Mn(II)Pc(py)2]O, and thus due to the presence of Mn(III) ions in [Mn(III)Pc(py)2]O, the Q-band is no longer split [31].

We come back to the comparison of the two different synthetic strategies to synthesize (substituted) phthalocyanines. If phthalonitriles are used as precursors, one has to purify obtained crude materials. Column chromatography is excellently suited for purification purposes and has usually been applied (cf. [28]). The purification requires that the phthalocyanines are soluble in organic solvents. That is not the case for pristine MPcs and MPcCl8 compounds reported here and thus independent of whether phthalonitriles or phthalic acid (derivatives) are used for their syntheses, another purification procedure is required. If the HCl/NaOH/HCl treatment reported here does not give pure compounds, there is a straightforward procedure which makes use of pyridine.

4 Experimental section

All starting materials were used as commercially obtained, unless stated. The specific chemical compound is given, as well as its purity and its commercial supplier. The German term “p.a.” or “z.A.” refers to chemicals delivered in certified qualities together with certified amounts of impurities, whereby “p.a.” or “z.A.” refers to per analysis or zur Analyse, respectively. In case that those chemicals were used, the term “p.a.” is thus added. Urea (99%, Grüssing GmbH), 1,2,4-trichlorobenzene (99%, Acros Organics), [NH4]2[MoO4] (99.99%, Carl Roth), 4,5-dichlorophthalic acid (99%, Sigma Aldrich), CuCl2·2H2O (99%, Grüssing GmbH), NiCl2·6H2O (>99%, p.a., VWR International), CoCl2·6H2O (98%, Alfa Aesar), FeCl2·6H2O (>99%, p.a., Merck), MnCl2·4H2O (>99%, p.a., FERAK Berlin). Indicator paper in the form of “Unitestpapier” (Carl Roth, Code AX01.1) for pH detection in the range 1≤pH≤14 was used. In the following a general procedure to obtain MPcCl8-type compounds (M=Cu, Ni, Co, Fe, Mn) in the analytically pure state is described.

Note: In case that we refer to literature-described MPcCl8-type compounds the respective metals M are written in black. In case that we refer to our synthesized and/or purified materials we referred to them as follows: CuPcCl8, NiPcCl8, CoPcCl8, FePcCl8 and MnPcCl8.

4.1 Synthesis of the crude materials

One gram of MCl2·nH2O salts (M=Cu, n=2; Ni, Co, Fe, n=6; Mn, n=4), but never more than 6 mmol, not more than 5.2 equivalents (with respect to the MCl2·nH2O salt used) of 4,5-dichlorophthalic acid, 50.0 mg of [NH4]2[MoO4] and 25.0 g of urea (416.2 mmol), were finely ground in a mortar and transferred into a 500 mL one-neck (ground glass joint, NSH 29) round bottom flask including a magnetic swizzle stick. Next, 250 mL 1,2,4-trichlorobenzene were added and the whole mixture was stirred for ca. 5 min for homogenization. After mounting a ca. 30 cm long reflux condenser (NSK 29) which does not need water cooling and under permanent stirring the temperature was raised slowly (within minimum 1 h) to ca. 125°C by making use of an oil bath. Note: All temperatures given refer to oil bath temperatures.

In dependency of the nature of the MCl2·nH2O salt used, multiple color changes were observed in all experiments. All reactions have in common that starting from temperatures of ca. 100°C H2O condensed inside the air-cooled reflux condenser. At approximately the same temperature a weak gas evolution of the stirred 1,2,4-trichlorobenzene suspension (bubbling) was noticed. By reaching 125°C the gas development, identified as ammonia, became stronger and one needs to inspect the progress of the reaction carefully in order to avoid boiling retardation. The temperature was raised very slowly (within minimum 30 min) up to ca. 135°C until the NH3 evolution was finished. Afterward, the temperature was raised quickly (within ca. 30 min) to ca. 165°C and then slowly (minimum 2 h) up to ca. 185°C as a further NH3 development occurred. When no further NH3 development was observed, the temperature was raised quickly to ca. 220°C with the 1,2,4-trichlorobenzene starting to reflux. The mixtures were refluxed as long as NH3 development was noticed. Refluxing may take up to 4 days, but is required in order to get the MPcCl8-type compound pure.

After the NH3 development had ceased, the reaction mixtures were allowed to cool down to room temperature. The round bottom flask was next sonicated for ca. 5 min to give a suspension with a finely distributed powder and filtered and washed several times with CH2Cl2 (ca. 5×35 mL). We exclusively used for all filtration purposes Buchner funnels with sintered glass discs (porosity grade: G4, volume ca. 50 mL), mounted on Buchner flasks with appropriate rubber bungs in order to allow, if required, vacuum suction with a water aspirator. The filter cake was removed from the G4 filter to a conventional filter paper and dried in air within a fume hood (ca. 30 min). The obtained crude materials amounted to ca. 15 g (cf. below). For further details and observations we refer to the chapter “1S Synthesis of the crude material” in the Supplementary Information.

4.2 HCl/NaOH/HCl treatment

Ten grams of the respective crude material was placed in a 250 mL round bottom flask together with HCl (10%, 120 mL), sonicated for 5 min and refluxed for minimum 2 h. After cooling down to room temperature, the suspension was filtered and the filter cake was washed first with water (ca. 5×35 mL). Next, ice-cold NaOH (2 N, 300 mL) was used to wash the filter in portions of 50 mL until the filtrate became colorless. Thereby, the NaOH solution was poured into the Buchner funnel and the filter cake was homogenized within the NaOH solution with the help of a spatula for no longer than 1 min. Afterward, the NaOH solution was vacuum sucked as quickly as possible through the Buchner funnel. Next the filter cake was washed neutral with water and that material was boiled again with HCl as described above, after which it was filtered, washed neutral with water, next with MeOH and finally with THF. The MPcCl8 material was dried overnight in air in a fume hood and its IR spectrum was measured. We refer to the masses obtained at that stage as follows: x.xxx g after HCl/NaOH/HCl treatment. For further details, observation and accompanying explanation we refer to the chapter “2S HCl/NaOH/HCl treatment” in the Supplementary Information.

4.3 Pyridine purification

Approximately 1.0 g of the respective MPcCl8 compound was added to 25 mL pyridine in a 100 mL round bottom flask. (The pyridine itself should have a purity of >99% and was used as-received from different commercial suppliers.) The suspension was sonicated for 5 min for homogenization and afterward refluxed for 2 h. Under continuous stirring heating was stopped after 2 h refluxing by removing the oil bath and the suspension was left stirring overnight. On the following day the suspension was filtered through a G4 Buchner funnel, washed with MeOH (2×25 mL) and THF (2×25 mL) and dried in a fume hood under ambient conditions. In case that the IR spectrum of the product still reveals the presence of further impurities, the pyridine purification is to be repeated. With the exception of CoPcCl8 all other MPcCl8-type compounds reported here were obtained pure after the second pyridine purification.

As reported for FePcCl8 and CoPcCl8, 1.0 g of the raw material in 25 mL of pyridine is refluxed for 2 h. The resulting suspensions are stirred overnight and filtered, washed and dried accordingly. In doing so one loses each about 20% of the material. The filtrates are intensively colored, and after slow evaporation of the pyridine microcrystals of either FePcCl8 or CoPcCl8 are formed. Isolated material corresponds to FePcCl8 or CoPcCl8 and not to their pyridine adducts. That might be surprising, although difficulties to synthesize pyridine adducts of MnPc (cf. [31]), and of CoPc and FePc are well documented [34]. In order to obtain [MnPc(pyridine)2] [31], [CoPc(pyridine)2] and [FePc(pyridine)2] [34], one should apply hydrothermal methods, cool down very slowly and usually work with much larger volumes of pyridine as reported here. The pyridine purification procedure reported here is not only suited to deliver pristine MPcs and MPcCl8 compounds analytically pure but it is also applicable for at least those metallophthalocyanines having small substituents R at the 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25 positions (R=H, F, Cl, Br, Me, OMe, …), although one should work for at least Mn(II)-containing samples under anaerobic conditions.

4.3.1 Modification of the degree of crystallinity

In order to increase crystallinity, after refluxing the respective MPcCl8 compound in pyridine the heating power was switched off, but the flasks remained in the hot oil bath and were stirred overnight. After isolation the degree of crystallinity of such materials was usually higher, although this statement is rather qualitative.

In order to decrease the crystallinity another procedure can be applied. A sufficiently large amount, at least 500 mg, of the respective MPcCl8 compound was dissolved in ice-cold and concentrated H2SO4 (10 mL) under stirring. After stirring for 10 min, the solution should be poured with caution into a 1000 mL beaker containing ca. 500 mL water ice, whereby the MPcCl8 compound precipitates immediately. The thus re-precipitated MPcCl8 compound in a mixture of H2SO4/water/ice can be left staying undisturbed overnight. Afterward, it was filtered (Buchner funnel), washed neutral with water and finally with THF.

4.4 Compound details

CuPcCl8: CuCl2·2H2O (1.007 g, 5.903 mmol), 4,5-dichlorophthalic acid (7.076 g, 30.109 mmol). Mass of crude material: 16.596 g. Ten grams of crude material gave 2.059 g after HCl/NaOH/HCl treatment. IR spectroscopy and TG showed the material to be pure CuPcCl8. Yield: ca. 70% based on CuCl2·2H2O and based on the use of ca. 60% of crude material.

NiPcCl8: NiCl2·6H2O (1.003 g, 4.220 mmol), 4,5-dichlorophthalic acid (3.955 g, 16.829 mmol). Mass of crude material: 18.553 g. Ten grams of crude material gave 0.831 g after HCl/NaOH/HCl treatment. IR spectroscopy and TG revealed that material is pure NiPcCl8. Yield: ca. 43% based on NiCl2·6H2O and based on the use of ca. 54% of crude material.

CoPcCl8: CoCl2·6H2O (1.408 g, 5.918 mmol), 4,5-dichlorophthalic acid (7.078 g, 30.114 mmol). Mass of crude material: 18.049 g. Ten grams of crude material gave 2.208 g after HCl/NaOH/HCl treatment. IR spectroscopy and TG revealed that material is impure. After pyridine purification of the whole amount 1.710 g were obtained, being impure (TG). After another pyridine purification of the whole amount 1.196 g CoPcCl8 was obtained which was >98% TG-pure. Yield: ca. 43% based on CoCl2·6H2O and based on the use of ca. 55% of crude material.

Comment: Higher purities were never achieved, independent of whether lower masses of CoCl2·6H2O were used and/or precisely four equivalents of 4,5-dichlorophthalic acid. Performing a third and even a fourth pyridine purification did not have an impact on the TG behavior.

FePcCl8: FeCl2·4H2O (1.159 g, 5.830 mmol), 4,5-dichlorophthalic acid (7.073 g, 30.096 mmol). Mass of crude material: 14.669 g. Ten grams of crude material gave 1.323 g after HCl/NaOH/HCl treatment. IR spectroscopy and TGA showed the material to be impure. After a first pyridine purification of the whole amount 1.303 g were obtained, being impure (TG). After a second pyridine purification of the whole amount 1.106 g FePcCl8 were obtained and judged according to TG to be pure. Yield: ca. 33% based on FeCl2·4H2O and based on the use of ca. 68% of crude material.

MnPcCl8: MnCl2·4H2O (0.835 g, 4.220 mmol), 4,5-dichlorophthalic acid (3.971 g, 16.896 mmol). Mass of crude material: 12.766 g. Ten grams of crude material gave 1.256 g after HCl/NaOH/HCl treatment. IR spectroscopy and TG revealed that material is pure MnPcCl8. Yield: ca. 45% based on MnCl2·4H2O and based on the use of ca. 78% of crude material.

4.5 Physical measurements

4.5.1 PXRD measurements

These experiments were carried out with a STOE-STADI-P diffractometer equipped with germanium(111)-monochromatized CuKα1 radiation (λ=1.540598 Å, 40 kV, 40 mA).

4.5.2 TG measurements

TG experiments were performed using a Mettler Toledo 1100 system with a UMX1 balance. For all experiments a gas flow of N2 of 60 mL min−1 and a heating rate of 10 K min−1 were adjusted. N2 in 99.999% purity [Air Liquide. Impurities (max): H2O<2.0 ppm mol−1. O2<2.0 ppm mol−1. Hydrocarbon<0.2 ppm mol−1].

4.5.3 Elemental analysis

Elemental analysis for C, H and N was made with a Thermo FlashAE 1112 series analyzer and a Vario Micro Cube from Elementar and has been performed as it is often required [35]. CHN analyses with a Thermo Flash EA 1112 analyzer were performed under standard measurement conditions for compounds reported here (oven temperatures: 950°C, 2.5 mg of material, Sn capsule, no oxidizing agents, O2 injection time: 5 s). However, CHN contents with up to –33% deviations were obtained. For comparison, commercially available samples of pristine MPcs with certified purities of >95% were measured to give related deviations. We repeated these measurements and used a vario Micro cube analyzer (elementar, Elementar Analysensysteme GmbH, Germany, www.elementar.de). These measurements (2 to 3 mg samples) were carried out in the presence of 10 to 15 mg of WO3 as an oxidizing agent (Sn capsule, oven temperature: 1150°C, O2 injection time 5 s). For those samples which we declared before as being pure (cf. above), the application of such CHN combustion analyses measurement conditions gave H and N contents with absolute deviation below ±0.4%. On the other hand and despite this, the C contents were always lower than expected and did deviate by more than –1.5% absolutely. For commercially available pristine MPcs related results were obtained.

4.5.4 Further devices

FT-IR spectra were recorded in the range of 400–4000 cm−1 on a Perkin-Elmer spectrum 1000 FT-IR spectrophotometer in the form of KBr pellets. UV/Vis absorption spectra were recorded with a Spectronic GENESYS 6 UV-Visible spectrophotometer (Thermo Electron Corporation) between 200 and 1000 nm.

5 Supplementary information

The following material is available online (DOI: 10.1515/znb-2017-0068). Additional comments for the synthesis of the crude materials in Chapter 1S. Additional comments for the HCl/NaOH/HCl treatment in Chapter 2S. IR spectra, UV/Vis spectra and TG charts of CuPcCl8, NiPcCl8, CoPcCl8, FePcCl8 and MnPcCl8. Chapter 3S summarizes observation with respect to the “solubility” of CoPcCl8 in pyridine, including a brief discussion.

Acknowledgments

This work has been supported by the Deutsche Forschungsgemeinschaft through project FOR 1154 “Towards Molecular Spintronics”. We thank Dipl.-Chem. Natalia Rüffer and Dipl.-Chem. Julian Noll for carrying out TG experiments.

  1. Author contributions: TR and HL conceived and designed the experiments and wrote the paper; DN performed experiments to synthesize, purify and characterize repetitively all pristine MPcs and MPcCl8 compounds reported here by the urea melt method and in part by using 1,2,4-trichlorobenzene as an inert solvent, whereby ZJ and AT analyzed the data; NU and AK synthesized, purified and analyzed repetitively MPcCl8 compounds by using 1,2,4-trichlorobenzene as an inert solvent under various reaction conditions; AG conceived, designed and carried out experiments to modify the crystallinity of pristine MPcs and MPcCl8 compounds reported here; LM measured PXRD data and created corresponding figures accordingly; MM analyzed PXRD data and is thanked for fruitful comments on the paper.

  2. Conflicts of Interest: The authors declare no conflict of interest.

References

[1] W. J. Baker, K. Ambal, D. P. Waters, R. Baarda, H. Morishita, K. van Schooten, D. R. McCarney, J. M. Lupton, C. Boehme, Nat. Commun.2012, 3, 898.10.1038/ncomms1895Search in Google Scholar

[2] T. Reichert, T. P. I. Saragi, Appl. Phys. Lett.2011, 98, 063307.10.1063/1.3554388Search in Google Scholar

[3] T. D. Nguyen, E. Ehrenfreund, Z. V. Vardeny, Science2012, 337, 204.10.1126/science.1223444Search in Google Scholar

[4] Z. H. Xiong, D. Wu, Z. V. Vardeny, J. Shi, Nature2004, 427, 821.10.1038/nature02325Search in Google Scholar

[5] V. Dediu, M. Murgia, F. C. Matacotta, S. Barbanera, C. Taliani, C. Solid State Commun.2002, 122, 181.10.1016/S0038-1098(02)00090-XSearch in Google Scholar

[6] B. Göhler, V. Hamelbeck, T. Z. Markus, M. Kettner, G. F. Hanne, Z. Vager, R. Naaman, H. Zacharias, Science2011, 331, 894.10.1126/science.1199339Search in Google Scholar PubMed

[7] M. Urdampilleta, S. Klyatskaya, J.-P. Cleuziou, M. Ruben, W. Wernsdorfer, Nat. Mater.2011, 10, 502.10.1038/nmat3050Search in Google Scholar PubMed

[8] S. Sanvito, Nat. Phys.2010, 6, 562.10.1038/nphys1714Search in Google Scholar

[9] S. Lindner, M. Knupfer, R. Friedrich, T. Hahn, J. Kortus, Phys. Rev. Lett.2012, 109, 027601.10.1103/PhysRevLett.109.027601Search in Google Scholar PubMed

[10] For example, S. Lindner, B. Mahns, A. König, F. Roth, M. Knupfer, R. Friedrich, T. Hahn, J. Kortus, Chem. Phys.2013, 138, 024707.10.1063/1.4774060Search in Google Scholar

[11] R. Friedrich, B. Kersting J. Kortus, Phys. Rev. B2013, 88, 155327.10.1103/PhysRevB.88.155327Search in Google Scholar

[12] M. Serri, W. Wu, L. R. Fleet, N. M. Harrison, C. F. Hirjibedehedin, C. W. M. Kay, A. J. Fisher, G. Aeppli, S. Heutz, Nat. Commun.2014, 5, 3079.10.1038/ncomms4079Search in Google Scholar PubMed PubMed Central

[13] N. Safari, P. R. Jamaat, M. Pirouzmand, A. Shaabani, J. Porphyrins Phthalocyanines2004, 8, 1209.10.1142/S1088424604000556Search in Google Scholar

[14] N. Safari, P. R. Jamaat, S. A. Shirvan, S. Shoghpour, A. Ebadi, M. DarVishi, A. Shaabani, J. Porphyrins Phthalocyanines2005, 9, 256.10.1142/S1088424605000320Search in Google Scholar

[15] DMSO=dimethyl sulfoxide. CAS: 67-68-5. According to, for example, the “Gestis Stoffdatenbank” under http://gestis.itrust.de/nxt/gateway.dll?f=templates&fn=default.htm&vid=gestisdeu:sdbdeu the b.p. of DMSO is 189°C. From here on the action to be performed assigned as “to reflux” indicates: To heat a solvent to its boiling point to such an extent that the evaporated solvent condenses on a reflux condenser and drops back to the solution.Search in Google Scholar

[16] B. N. Achar, T. M. M. Kumar, K. S. Lokesh, J. Coord. Chem.2007, 60, 1833.10.1080/00958970701194090Search in Google Scholar

[17] As described later on in this report, one byproduct of the synthesis of MPcs via the urea method is 1,3,5-triazine-2,4,6-triol (CAS: 108-80-5), conventionally referred to as “cyanuric acid” (CA). According to: https://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-DE-Site/de_DE/-/EUR/ProcessMSDS-Start;pgid=1YpMKfaYduNSRpEoLGRgbI7200006zq7dkH1;sid=X-TZtCtxc5e1tHMm-xHJPMUk5mIb627aBjjiZfoVPFjFhKMfhybWJ4sZcG3_-HtNlBL3rfgHnNkgHAO_dVKrkgVXPUVdvThYUPLRyfTNPewtdiEKhD2emPhP3DpS-N2swfJR2vOz14oBduhMpkzTz_Co?PlainSKU=MDA_CHEM-820358&Origin=PDP, the melting point is ca. 320–330°C. IR spectra of CA in nujol mull can be found in the online freely available Spectral Database for Organic Compounds (SDBS) either under the CAS or SDBS number (SDBS No.: 2043) via the link http://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_index.cgi. Further SDBS numbers: CuPc (4418), NiPc (17185), CoPc (24499), FePc (5223), MnPc (17255).Search in Google Scholar

[18] K. H. Thiele in Lehrwerk Chemie, Arbeitsbuch 7, Reaktionsverhalten und Syntheseprinzipien, 3. unveränderte Auflage; VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1989; p. 218. “5 g phthalic acid, 1 g CuCl2·2H2O, 25 g urea and approximately 50 mg [NH4]2[MoO4] as catalyst are accurately mortared. The mixture is heated next in a round bottom flask with the help of an oil or sand bath for six hours to an internal temperature of 180°C. After cooling down the mixture is cooked with 2 M HCl and vacuum-sucked. The filter cake is treated for approximately 10 min with cold 2M NaOH and again vacuum-sucked. The obtained blue material is cooked again with 2 M HCl, filtrated and washed until the filtrate is free of chloride ions and dried in an exsicattor.”Search in Google Scholar

[19] C. C. Leznoff in Synthesis of Metal-Free Substituted Phthalocyanines in Phthalocyanines: Properties and Applications, Vol. 1 (Eds.: C. C. Leznoff, A. B. P. Lever), VCH, Weinheim, 1989, chapter 1, p. 16, and references cited there.Search in Google Scholar

[20] For example, J. M. Robertson, J. Chem. Soc.1935, 615.10.1039/jr9350000615Search in Google Scholar

[21] M. Hanack, R. Thies, Chem. Ber.1988, 121, 1225.10.1002/cber.19881210704Search in Google Scholar

[22] F. H. Moser, A. L. Thomas, Phthalocyanine Compounds, American Chemical Society, Monograph Series, Reinhold Publishing Corporation, New York, 1963, p. 34.Search in Google Scholar

[23] K. Sivashankar, Proc. Indian Acad. Sci. (Chem. Sci.)2000, 112, 607.10.1007/BF02704368Search in Google Scholar

[24] A. A. Ebert Jr., H. B. Gottlieb, J. Am. Chem. Soc.1952, 74, 2806.10.1021/ja01131a031Search in Google Scholar

[25] Cf.: http://www.elementar.de/de/produkte/organische-elementaranalyse/vario-micro-cube.html “Quantitative decomposition up to 1200°C – with 10 years warranty on the furnace. (1800°C at the moment of combustion and by using tin capsules.) This is pre-requisite for 100 % retrieval and analytical accuracy also for difficult combustable samples. The jet injection of oxygen realizes a high local concentration at the decomposition spot together with an economical gas consumption” Citation taken accessed 24 July 2017.Search in Google Scholar

[26] N. B. McKeown, Phthalocyanine Materials Synthesis, Structure and Function, Cambridge University Press, Cambridge, 1998, chapters 4.1 to 4.3.Search in Google Scholar

[27] K. Huthmacher, D. Most, Cyanuric Acid and Cyanuric Chloride in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.Search in Google Scholar

[28] V. N. Nemykin, E. A. Lukyanets, ARKIVOC2010, (i), 136.10.3998/ark.5550190.0011.104Search in Google Scholar

[29] P. Zimcik, A. Malkova, L. Hruba, M. Miletin, V. Novakova, Dyes Pigm.2017, 136, 715.10.1016/j.dyepig.2016.09.039Search in Google Scholar

[30] P. M. Reintanz, R. Guthardt, C. Bruhn, F. Mohr, U. Siemeling, Eur. J. Inorg. Chem.2016, 36, 5610.10.1002/ejic.201601115Search in Google Scholar

[31] J. Janczak, R. Kubiak, M. Sledz, H. Borrmann, Y. Grin, Polyhedron2003, 22, 2689.10.1016/S0277-5387(03)00361-9Search in Google Scholar

[32] R. Friedrich, T. Hahn, J. Kortus, M. Fronk, F. Haidu, G. Salvan, D. R. T. Zahn, M. Schlesinger, M. Mehring, F. Roth, B. Mahns, M. Knupfer, J. Chem. Phys.2012, 136, 064704.10.1063/1.3683253Search in Google Scholar

[33] H. A. Jahn, E. Teller, Proc. R. Soc. London, Ser. A1937, 161, 220.10.1098/rspa.1937.0142Search in Google Scholar

[34] J. Janczak, R. Kubiak, Inorg. Chim. Acta2003, 342, 64.10.1016/S0020-1693(02)01060-5Search in Google Scholar

[35] Cf. for example the Author guides of the ACS Journal Inorganic Chemisty: http://pubs.acs.org/paragonplus/submission/inocaj/inocaj_authguide.pdf.Search in Google Scholar

Supplemental Material:

The online version of this article (DOI: https://doi.org/10.1515/znb-2017-0068) offers supplementary material, available to authorized users.

Received: 2017-4-20
Accepted: 2017-5-18
Published Online: 2017-8-5
Published in Print: 2017-8-28

©2017 Walter de Gruyter GmbH, Berlin/Boston

Articles in the same Issue

  1. Frontmatter
  2. In this Issue
  3. Rubidium chalcogenido diferrates(III) containing dimers [Fe2Q6]6− of edge-sharing tetrahedra (Q=O, S, Se)
  4. Cu(II)-CMC: a mild, efficient and recyclable catalyst for the oxidative alkyne homocoupling reaction
  5. Crystal structures and thermal decomposition of permanganates AE[MnO4]2·n H2O with the heavy alkaline earth elements (AE=Ca, Sr and Ba)
  6. Mg(OCH3)2-mediated one-pot synthesis of α-aminophosphonate derivatives of cytosine under mild conditions
  7. A coordination polymer of mercury(II) formed by triazole-based and chloride linkers
  8. Two 1D zinc coordination polymers based on tris(p-carboxylphenyl)phosphine oxide: syntheses, structures and photoluminescence properties
  9. A Cd complex with a di(imidazolyl)benzene ligand: synthesis, structural characterization, and fluorescence properties
  10. Synthesis and purification of metallooctachlorophthalocyanines
  11. The platinum-rich scandium silicide Sc2Pt9Si3
  12. Gallium-containing Heusler phases ScRh2Ga, ScPd2Ga, TmRh2Ga and LuRh2Ga – magnetic and solid state NMR-spectroscopic characterization
  13. Synthesis and crystal structures of non-symmetric 1,3-di(alkyloxy)imidazolium salts
  14. Note
  15. Crystal structure and theoretical investigation of bis(cis-1,2-diaminocyclohexane)zinc(II) tetrachloridozincate(II)
https://doi.org/10.1515/znb-2017-0068
Keywords for this article
IR spectroscopy; powder X-ray diffraction; thermogravimetric analysis; urea melt method; UV/Vis spectroscopy

Articles in the same Issue

  1. Frontmatter
  2. In this Issue
  3. Rubidium chalcogenido diferrates(III) containing dimers [Fe2Q6]6− of edge-sharing tetrahedra (Q=O, S, Se)
  4. Cu(II)-CMC: a mild, efficient and recyclable catalyst for the oxidative alkyne homocoupling reaction
  5. Crystal structures and thermal decomposition of permanganates AE[MnO4]2·n H2O with the heavy alkaline earth elements (AE=Ca, Sr and Ba)
  6. Mg(OCH3)2-mediated one-pot synthesis of α-aminophosphonate derivatives of cytosine under mild conditions
  7. A coordination polymer of mercury(II) formed by triazole-based and chloride linkers
  8. Two 1D zinc coordination polymers based on tris(p-carboxylphenyl)phosphine oxide: syntheses, structures and photoluminescence properties
  9. A Cd complex with a di(imidazolyl)benzene ligand: synthesis, structural characterization, and fluorescence properties
  10. Synthesis and purification of metallooctachlorophthalocyanines
  11. The platinum-rich scandium silicide Sc2Pt9Si3
  12. Gallium-containing Heusler phases ScRh2Ga, ScPd2Ga, TmRh2Ga and LuRh2Ga – magnetic and solid state NMR-spectroscopic characterization
  13. Synthesis and crystal structures of non-symmetric 1,3-di(alkyloxy)imidazolium salts
  14. Note
  15. Crystal structure and theoretical investigation of bis(cis-1,2-diaminocyclohexane)zinc(II) tetrachloridozincate(II)
Sign up now to receive a 20% welcome discount
Institutional Access
How does access work?
Have an idea on how to improve our website?
Please write us.
© 2025 De Gruyter Brill
Downloaded on 15.12.2025 from https://www.degruyterbrill.com/document/doi/10.1515/znb-2017-0068/html
Scroll to top button