Volume 44, Issue 7

The crystal structures of the isotypic monoclinic fluorides Na 2 CuF 4 (a = 326.7(1), b = 937.0(2), c = 561.2(1) pm, β = 92.49(1)°; V = 171.63 x10- 30 m 3 ) and Na 2 CrF 4 (a = 334.8(1), b = 954.9(2), c = 566.5(3) pm, β = 92.85(3)°; V = 180.89 × 10 -30 m 3 ) have been redetermined by single crystal X-ray methods. The compounds are Jahn-Teller distorted variants of the orthorhombic Sr 2 PbO 4 type (space group Pbam) and crystallize with Z = 2 in space group P2 1 /c, a subgroup of Pbam. They form a chain structure of edge-sharing octahedra which are strongly elongated. The following distances were obtained: Cu-F = 190.4/193.8/235,7(2) pm and Cr-F = 199.1/199.7/241.7(4) pm. The geometry is compared to that of the corresponding distorted rutile type difluorides; relations to further compounds are discussed.

Graphite intercalation compounds (GICs) of mercuric chloride have been synthesized by four different methods: via the vapour phase, from melts of pure HgCl 2 , from melts of HgCl 2 , and alkali metal chlorides, and from solutions in concentrated aqueous HCl. Compounds of stages 4, 3 and 2 were obtained, respectively. GICs prepared from solution always show staging disorder. Pure stage compounds of stage three and four exhibit the following repeat distances along the c⃗ axis: c (3) = 1632 pm; c (4) = 1968 pm. Further structural analysis is hindered by the disorder phenomena common to GICs. Rather surprisingly, monochromatic Laue photographs probing the in-plane order of the intercalate reveal that - regardless of the preparation method - the diffraction patterns of all compounds are identical. The main phase possesses a monoclinic in-plane lattice with cell dimensions: a = 390(4) pm, b = 412(4) pm, γ = 108.6(3)°. A structure which resembles certain features of the structure of pristine HgCl 2 is proposed for this phase. Another unidentified phase seems to stabilize this structure in spite of different amounts of chlorine excess probably occurring in compounds prepared in different ways.

Anodic oxidation of graphitic materials in aqueous electrolytes is a complex process which may yield e.g. higher stage intercalation compounds and lamellar graphite oxides, acidic surface or defect oxides and gaseous or colloidal decomposition products. Kind and concentration of the electrolyte solution are the most important parameters to control this wide-spread distribution of products. Based on electrochemical and microscopic studies on HOPG and carbon fibres, a mechanistic concept of electrolyte effects is proposed: In dilute aqueous solutions, attack of OH • radicals formed in the primary electrochemical step is the dominant reaction pathway leading to formation of covalent carbon-oxygen bonds. Due to their reactivity, OH • radicals are able to attack basal plane carbon sites and also to create 3-dimensional defect oxides. Dissociation or capture of OH • radicals - which is favoured in basic and in most concentrated neutral solutions, respectively, - results in less active radical species and limits the attack to thermodynamically less stable carbon atoms at edge sites which may be either oxidized or removed. Due to acidification of the diffusion layer of anodes even in neutral aqueous electrolytes, direct current oxidation always yields higher stage acid intercalation compounds and lamellar graphite oxide as by-products. This can be almost prevented by alternating current oxidation.

TlCl 3 and TlCl 3 -TlCl mixtures have been prepared and investigated by Raman spectroscopy in the solid and molten state. Already at 50°C TlCl 3 starts to decompose according to TlCl 3 → TlCl + Cl 2 . TlCl generated reacts with TlCl 3 to give TlCl 4 - , Tl 2 Cl 7 ~ and possibly Tl n III Cl 3n+1 - units with n ≧ 2, respectively. Molten TlCl 3 , can be described best by the equilibrium TlCl 4 - + TlCl 3 ⇄ Tl 2 Cl 7 - . In solid TlCl 3 -TlCl mixtures the following species could be identified Tl 3 (Tl III Cl 6 ), Tl 3 1 (Tl 2 III Cl 9 ) and TlCl 4 ). TlCl 4 - and TlCl 5 2- complex units dominate in the molten state. In the melt, species are in dynamic coupled equilibria depending on temperature and stoichiometry.

Photooxidation of PET fibres or films creates fluorescent by-products which are separated in wavelength from the intrinsic fluorescence of PET. An experimental technique is described which allows the study of the dependence of photooxidation on wavelength by the fluorescence of only a single specimen. Furthermore, using polarized fluorescence, the conservation of photoselected orientation can be investigated if the photooxidation is carried out with linearly polarized light. Evidence is presented that photooxidation of PET films takes place under partial conservation of the photoselected molecular orientation.

In the pyrochlor system Ln 2-x Cu x Ru 2 O 7-z a partial substitution of Pr bv Cu is observed for x ≾ 0.375. With increasing x a gradual semiconductor-metal transition occurs. The change of sign of TCR from negative to positive is observed for ρ ∾ 6 × 10 -3 Ω cm (x = 0.2). The presence of variable range hopping in the insulating regime strongly suggests that the metal-semiconductor transition is of Anderson type. For the pyrochlores of type Ln 1.625 Cu 0.375 Ru 7-z with the smaller rare earth ions Sm, Eu, Gd, Dy the metallic conductivity is absent and localization of Anderson type occurs.

Metal dihalide low-volatility is the major characteristic slowing down their intercalation into graphite (GICs: graphite intercalation compounds). An original synthesis using volatile heterocomplexes between metal dihalide (CoCl 2 ) and gaseous dimer Al 2 Cl 6 increases strickingly CoCl 2 intercalation rate but entails cointercalation of significative amount of AlCl 3 in the compounds MGICs (mixture graphite intercalation compounds). Structural studies along c-axis, in plane and out the plane (3 D stacking) display a similar behaviour as in the CoCl 2 containing binary compounds. Microstructural studies confirm the separation of CoCl 2 and AlCl 3 in distinct domains. Other ternary phases with alternate CoCl 2 and AlCl 3 layers and characterized by a similar AlCl 3 /CoCl 2 ratio can be obtained using biintercalation method: (GBICs: graphite biintercalation compounds). X-Ray diffraction shows that the biintercalation involves a complete lost of correlations in the successive CoCl 2 or graphite layers. Transport studies of ternary phases (MGICs and GBICs) display an anomalous behaviour as T is lowered below the magnetic ordering temperature T c especially for in plane resistivity.

Bonds between metals (especially copper) and a protein fraction (18,100 g/mol) of a soya bean flour extract have been investigated. The binding capacity (304 nmol Cu/mg protein) and the binding stability (K = 1,046·10 3 in an ammonia buffer system) were determined by polarographic investigations. Changes in the polarogram caused by spiking the protein with metal ions were compared with effects in model substances. Cysteine, ethylenediamine, oxalic acid and derivatives of benzoic acid were used as chelating agents. The effects of functional groups on the metalprotein bonds were estimated by the determination of their different binding stabilities.

HNO 3 , HClO 4 , HReO 4 and CF 3 COOH have been intercalated into graphite by anodizing pieces of HOPG. Attempts to intercalate ClCH 2 COOH have failed. CV measurements and pulsed galvanostatic experiments were performed to ascertain possible side reactions as well as the reversibility of the intercalation process. Whereas the intercalation reaction proved to be fast in the cases of HNO 3 , HClO 4 and HReO 4 , it was slow and superposed by side reactions when CF 3 COOH was used.

[Ag(MeOC 6 H 4 N 3 C 6 H 4 OMe)] 2 (1) is formed in THF from AgNO 3 , and the triazenide anion, as obtained from the corresponding triazene and Na. 1 crystallizes from pyridine in the form of orange-yellow , air stable crystals with the com position 1·2/3 C 5 H 5 N: space group P 1̅ with a = 1468.0(5), b = 1514.1(6), c - 1316.1(3) pm, a = 113.45(3)°, β = 1 1 4 .8 1 (2 )°, γ = 66.78(3)°, Z - 3. The triazenide ion functions as a bridging ligand forming planar (AgN 3 ) 2 heterocycles. The unit cell contains two symmetry-independent dinuclear complexes, one of which is centrosymmetrical. The short Ag -Ag distances of 268.0 and 269.8 pm suggest Ag -Ag bonding. The pentaazadienido complexes Ag(RN 5 R) with R = p -MeO - C 6 H 4 (2), p -EtO - C 6 H 4 (3), p-Cl -C 6 H 4 (4), p -F -C 6 H 4 (5), are obtained from saturated solutions of the pentaazadiene in conc. NH 3 and AgNO 3 , as explosive, red precipitates which are stable in air. Crystals of 2 and 3 · C 5 H 5 N are obtained from pyridine. 2 crystallizes in the monoclinic space group P2 1 /c: a - 583.7(6), b = 1705.1(9), c = 1489.6(9) pm. β = 96.2(1)°, Z = 2; 3 · C 5 H 5 N is triclinic (space group P 1̅) with a = 1160.4(4). b = 1671.0(6), c = 509.0(1) pm. a = 97.51(2)°, β = 97.36(2)°, γ = 81.51(3)°, Z = 1. The complexes 2 and 3 are dinuclear with the pentaazadienide ion as a (N1)-η 1 ,(N5)-η 1 bridging ligand in 2 and a (N1)-η 1 , (N3)-η 1 bridging ligand in 3. The bridging mode in 3 results in a short Ag -Ag contact of 283.44 pm. The Ag -N distances range from 210.8 to 215.7 pm in 1 and from 215.0 to 220 pm in (2) and (3).

The structure of the first stable silaneimine ′Bu 2 Si=N—Si′Bu 3 (1) (i.e. a compound containing a silicon nitrogen double bond) has been determined by X-ray crystallography (monoclinic, space group P2 1 /n, a = 8.962(1), b = 18.361(1), c = 14.658(1) Å, β = 90.98(1)°, V = 2411.6 Å 3 .Z = 4, wR = 0.043, w = 1/σ 2 (F o ) for 208 refined parameters and 2610 observed structure factors. It is monomeric in the solid state and has a nearly linear Si=N—Si skeleton (Si—N—Si 177.8(2)°) with drastically different Si=N and Si—N bond lengths (1.568(3) and 1.695(3) A, respectively). The benzophenone adduct of ′Bu 2 Si=N—Si′Bu 3 and the tetrahydrofuran (THF) adduct of the closely related silaneimine Me 2 Si=N—Si′Bu 3 contain the donor molecules being coordinated exclusively to the unsaturated silicon atoms, which adopt a distorted tetrahedral coordination geometry upon coordination with characteristically elongated Si=N double bonds. The solid state structure of the benzophenone adduct strongly suggests that [2+2] cycloadditions of Si=N double bonds with aldehydes or ketones proceed in a non-concerted manner via prior formation of donor-Si bonds. ((THF) • Me 2 Si=N—Si′Bu 3 (2): P2 1 /n, a = 18.480(4), b = 14.209(2), c = 18.683(5) Å, β = 115.11(2)°, V = 4442.2 Å 3 , Z = 8, wR = 0.094 for 397 parameters and 3432 observables; (Ph 2 C=O) · ′Bu 2 Si=N—Si′Bu 3 (3): P2 1 ,/n, a = 13.247(2), b = 15.689(2), c = 17.073(2) Å. β = 110.53(1)°, V = 3323.0 Å 3 , Z = 4, wR = 0.039 for 379 refined parameters and 3789 observables.)

According to an X-ray structure analysis 1,5-bis(di-tert-butylmethylsilyl)-2,2,4,4,6,6,7,7-octamethyl-3-oxa-2,4,6,7-tetrasilabicyclo[3.1.1]heptane (1) is a rigid bicyclic molecule consisting of a 1,3-disilacyclobutane ring whose 2,4 positions are bridged by a Me 2 Si—O—SiMe 2 fragment. The four-membered ring is non-planar with a dihedral angle of 33.8° along the C—C axis. The intraring valence angles at carbon are significantly smaller than those at silicon leading to a transannular Si ··· Si distance of only 2.558(1) Å (triclinic, space group P 1̄ with a = 9.125(2), b = 12.668(2), c = 15.499(3) Å, α = 101.25(1), β = 87.87(1), γ = 96.88(1)°, V = 1744.4 Å 3 R (wR) = 0.044 (0.051) for 316 refined parameters and 5156 observables).

Controlled hydrolysis at low temperatures of (trimethylphosphito-P){tris[2-(diphenylphosphino)ethyl]phosphine-P,P′,P″,P″′}platinum(II)-dichloride, [Pt(PP 3 )(P(OMe) 3 )]Cl 2 (2), leads to the title compound (1) in nearly quantitative yield. The 31 P NMR spectrum of 1 shows an AMX 3 pattern consistent with the formulation as [Pt(P(O)(OMe) 2 )(PP 3 )]Cl. 1 has been further characterized by an X-ray structure analysis, which shows a trigonal-bipyramidal stereochemistry with the (dimethylphosphito)-ligand occupying an axial position. NMR and X-ray results of 1 and [PtH(PP 3 )](BPh 4 ) (3) are compared.

The treatment of acetylated Δ 5 -steroids with chromyl diacetate at low temperature afforded the 5β,6β-epoxy derivatives with stereoselectivity greater than 90 per cent.

Several 2,3- (and 3,4)-dihydroxybenzoyl-dipeptides (5) have been obtained as new ligands able to interact with therapeutically important metalloproteases. Some of them appeared to be strong inhibitors of leucine aminopeptidase [EC 3.4.11.1].

The complete amino acid sequences of the hemoglobins from the adult European polecat (Mustela putorius) are presented. The erythrocytes contain two hemoglobin components and three globin chains (α I, α II and β). The primary structure of globin chains and of the tryptic peptides determined in liquid- and gas-phase sequantors. Comparing the sequences of the globin chains of the polecat with that of human Hb-A, 17 (23.9%) substitutions were recognized in the α I, 16 (22.5%) in the α II and 14 (20.4%) in the β chain. A high degree of homology observed with other representatives of the family Mustelidae.

The synthesis of Thiafarfugin A via an intramolecular Diels-Alder reaction of a 6-alkenyl thieno[2,3-c]furan is described.

An efficient, regioselective synthesis of substituted bicyclo nonenes and decenes of type (4a, b) and the tricyclic tetradecadiene (5) is described. The key step is the regioselective dialkylation of cyclic 1,3-diketone-dimethylhydrazones (la—e) with 4-chlorobutane-2-one.

1-Chloro- and 1,3-dichloro-vinamidinium salts react with potassium cyanide to afford 1-cyanoand 1,3-dicyano-vinamidinium salts. The former add nucleophiles at the C-3 position. MNDO calculations, competitive hydrolysis experiments and cyclic voltammetry reveal the following sequence of stabilities of vinamidinium salts: 1,3-(NMe 2 ) 2 > 1-NMe 2 > 2-Aza > H > 2-(p-MeOC 6 H 4 ) > 2-OMe > 2-Cl > 2-CN > 1,3-(SMe) 2 > 1-Cl > 1-CO 2 Et > 2-NO 2 > 1-CN > 1,3-(CN) 2 . Interestingly enough, reduction potentials show that a 1,3-dicyanovinamidinium salt is more stable than a 1,3-dichlorovinamidinium salt, whereas a 1-chlorovinamidinium salt is more stable than a 1-cyanovinamidinium salt.

The selenostannate(IV) Cs 4 Sn 2 Se 6 has been prepared by methanolothermal reaction of Cs 2 CO 3 with SnSe 2 at 160°C and 13 bar. The [Sn 2 Se 6 ] 4— anions contain two edge-bridged SnSe 4 tetrahedra and display crystallographic C 2h symmetry. The bridging Sn—Se distances of 2.587(1) are markedly longer than the terminal Sn—Se distances of 2.447(1) and 2.452(2) Å.

The title compound, C 18 H 33 B 2 N 3 S, isolated from the reaction of 3,5-bis(diisopropylamino)-1,2,4,3,5-dithiazadiborolidine with elemental sodium, crystallizes in space group P1̅ with cell constants a = 1034.3(6), b = 1230.4(8), c = 1728.5(12) pm, α = 97.50(6), β = 97.95(5), γ = 90.17(5)° and Z = 4. X-ray structure refinement converged at R = 0.087, wR = 0.085, w -1 = σ 2 (F 0 ) + 0.004 F o 2 . The fourmcmbered ring B 2 NS is planar, the angle B—S—B being 70°.

The title compound has been prepared as a byproduct of the reaction of Se 2 Cl 2 with Ν,Ν,N′-Tris(trimethylsilyl)benzamidine in CH 2 Cl 2 solution. [SeCl 2 (HNC 2 N 2 Ph 2 )] 2 was characterized by an X-ray structure determination. Space group P2 1 /n, Z = 2, 2979 observed independent reflexions, R = 0.032. Lattice dimensions (-65 °C): a = 1050.1(4), b = 1018.9(4), c = 1402.1(6) pm; β = 99.78(3)°. The compound forms centrosymmetric dimeric molecules with SeCl 2 Se bridges (bond lengths 241.6(1) and 339.3(1) pm), the selenium atoms being members of nearly planar [xxx] selenatriazine rings with Se—N bond lengths of 182.2(2) and 181.5(2) pm.

[2.4]Paracyclophane crystallizes in the orthorhombic space group Pbca with cell constants (at —95°C) a = 1151.5(5), b = 1832.9(7), c = 1304.1(4) pm. The structure was refined to R = 0.053 for 1626 unique observed reflections. The aromatic ring systems are inclined to each other at an angle of 21°. The longer bridge is capable of more relaxation than the shorter, as is reflected in the non-bonded distances 279, 386 pm between bridgehead atoms and in the smaller displacements of the associated benzylic carbon atoms from the aromatic ring planes. The central bond length of the longer bridge (151.8 pm) is shorter than would be expected for a single bond.

The methylation of the pyrimidine bases of nucleic acids by dimethyl carbonate is described compared to dimethyl sulphate. The reaction needs higher temperature, a base and the help of 18-crown-6 and DMF as cosolvent.

Racemic 1-[(ethyl)(methyl)amino]-8-[(hydroxy)-di(phenyl)methyl]-naphthalene was resolved by column chromatography. The enantiomers are stable at room temperature.