Volume 48, Issue 7

The 1,3,5-trimethyl-1,3,5-triaza-2-oxo-2λ 4 -phosphinane-4,6-diones 7 and 8 were obtained from the 6,8,10-trimethyl-2,2,3,3-tetrakis(trifluoromethyl)-6,8,10-triaza-1,4-dioxa-5 λ 5 -phosphaspiro[4.5]decane-7,9-diones 3 and 5, either by reaction with water or on heating; in the latter case we assume that tetrakis(trifluoromethyl)oxirane was eliminated. The hydrolysis of 2-(β-chloroethyl)amino-1,3,5-trimethyl-1,3,5-triaza-2-[p-nitrobenzoylimido]-2A 4 -phosphinane-4,6-dione 4 and of 5-bis-(β-chloroethyl)-amino-6,8,10-trimethyl-2,3-perchlorobenzo-6,8,10-triaza-1,4-dioxa-5λ 5 -phosphaspiro[4.5]decane-7,9-dione 6, in the same manner, gave the products 7 and 8. The synthesis of the perfluoropinacolyl spirophosphorane 3 is described. The compounds 3,7 and 8 were characterized from their 1 H, 13 C and 31 P NMR spectra, mass spectra and through the X-ray structure determination of 8, in which the ring displays a flattened envelope conformation.

The phosphoryl(III)(λ 4 P) and thiophosphoryl(III)(λ 4 P) derivatives, 1,3,5-trimethyl-2-hydro-1,3,5-triaza-2-oxo-2λ 4 -phosphinane-4,6-dione 2 and 1,3,5-trimethyl-2-hydro-1,3,5-triaza-2-thio-2λ 4 -phosphinane-4,6-dione 3 were obtained from 2-chloro-1,3,5-trimethyl-1,3,5-triaza-2λ 3 -phosphinane-4,6-dione 1, by reaction either with water or with hydrogen sulphide. The reactions of 2 and 3 with the fluorine-containing ketones, hexafluoroacetone and trifluoroacetophenone, led to the compounds 4-7 with the P(:O)–O or P(:S)–O structural element. The compounds 2-6 were characterized via their 1 H, 13 C and 31 P NMR spectra, mass spectra and through the X-ray structure determination of 4. Compound 7 was characterized from its 1 H and 31 P NMR spectrum and mass spectrum, only.

The reaction of salicylic acid with phosphorus trichloride furnished the previously known 2-chloro-5,6-benzo-1,3,2-dioxaphosphorinan-4-one heterocycle 1 which was unambiguously characterized, for the first time, by NMR spectroscopy and mass spectrometry. The fluorine and bromine analogues of 1, 2 and 3 were synthesized from 1, using exchange reactions. The iodo derivative, 4, owing to its instability, could be identified only in the reaction mixture by 1 H and 31 P NMR spectroscopy. The amine derivatives 5-8 were obtained from 1 using standard exchange reactions, either with silylated amines or with secondary amines in the presence of base. There was no evidence by 1 H NMR spectroscopy for intramolecular Me 2 N→P coordination in 6. The 31 P NMR investigation of 7 revealed the presence of two rotational isomers, presumably as a result of steric hindrance at the P–N bond by the methyl substituent of the piperidine group. The reaction of 6 with methyl iodide led to methylation at the nitrogen atom of the Me 2 N group, producing the ammonium iodide, 9. The reactions of 5,6 and 8 with norbornadiene tetracarbonyl molybdenum failed to furnish isolable products.

The reaction of lithiated precursors with PCl 2 F led to a number of monofluorophosphines, including the known di-tert-butylmonofluorophosphine, 1. Bis(phenylethinyl)monofluorophosphine (2) was accessible only via this route (the classical method of synthesizing 2 by chlorine/fluorine exchange is impossible, because the corresponding chlorophosphine is unknown). Bis(2-methoxyphenyl)fluorophosphine (5) was prepared via the organolithium/PCl 2 F route. The NMR results for 5 thus prepared were inconsistent with previous reports, implying that the previously reported synthesis of 5 is in error. From 5 a cis-dichloroplatinum(II) complex (6) was synthesized and subjected to a single crystal X-ray structure analysis, confirming the expected planar coordination. From bis(2,3-dimethoxynaphthyl)monofluorophosphine (7) a rhodium(I) (8) and an iron(0)tetracarbonyl complex (9) were prepared. An iron(0)tetracarbonyl complex (11) was synthesized from bis(9-anthryl)monofluorophosphine (10) which was found to be stable to redox disproportionation.

Single crystals of CsPr 2 (CH 3 COO) 7 were obtained from an acetic acid solution of Pr(CH 3 COO) 3 • H 2 O and Cs 2 CO 3 in a molar ratio of 4:1 at 120°C. It crystallizes in the triclinic system, PĪ (no. 2), Z = 2, a = 1028.1(5), b = 1034.6(5), c = 1199.4(6) pm, α = 84.82(2), β = 67.07(3), γ = 76.01(2)°, V m = 343.3(3) cm 3 /mol, R = 0.031, R w = 0.027. The crystal structure contains infinite chains, 1 ∞ [Pr 2 (CH 3 COO) 6 ], running along the [110] direction. The chains are built up by bridging acetate ions coordinated to two crystallographically different Pr 3+ ions which are both surrounded by 9 oxygen ligands. These chains are linked by “intercalated” Cs(CH 3 COO) to layers parallel (100). Cs + has contacts to oxygen atoms of neighbouring layers, such that a three-dimensional network is formed.

The complex [Na(15-crown-5)][N(SO 2 CH 3 )2] crystallizes at —25°C from a methanol solution containing equimolar amounts of NaN(SO 2 CH 3 ) 2 and 15-crown-S. Its crystallographic data at —95°C are: monoclinic, space group P 2 1 /c, a = 852.1(5), b = 2731.9(12), c = 909.2(4) pm, β = 115.53(4)°, V = 1.910 nm 3 , Z = 4, D x = 1.445 Mgm 3 . The structure in the solid state consists of ion pairs. The sodium cation is coordinated to the five oxygen atoms of the crown ether, one oxygen atom of the anion, and to the nitrogen atom of the anion. The bond distances are Na—O(crown) 238.7-247.2, Na—O(sulfonyl) 234.9, Na—N 275.8 pm. The sodium ion lies 78 pm out of the plane of the crown ether oxygen atoms. The conformation of the coronand is described.

The new cubic compound Na 8 TiAs 4 , a = 1376.7(1) pm, space group Fd 3 m, is isostructural to Na 8 SnSb 4 [1]. The structure is characterized by ideal isolated TiAs 4 tetrahedra. The compound is in agreement with the Zintl concept.

A modified method for the preparation of (ClSN) 2 (ClS(O)N) (1) and (ClSN)(ClS(O)N) 2 (2) as well as the crystal structures of 1 and 2 are reported.

Reaction of Na 2 PdCl 4 with N-ferrocenylmethylidene-2,4,6-trimethylaniline yields the dimeric, chloro-bridged Pd(II) complex [Pd{(C 5 H 5 )FeC 5 H 3 C(H)=N-2,4,6-(CH 3 ) 3 C 6 H 2 }Cl] 2 . The title complex (1) is obtained by substitution of the chloro-bridges with acetate. 1 crystallizes in the orthorhombic space group Pbca with the lattice parameters a = 1346.4(4), b = 2876.6(2), c = 2472.8(5) pm and Z = 8. In the dimeric complex each Pd 2+ cation exhibits a square-planar coordination by the N atom and an ortho-C atom of the cyclopentadienyl ring of the Schiffbase and two oxygen atoms of two different bridging acetato groups.

To characterize the stability of dithiophosphinate complexes of silver the value of their ion product (IP) has been determined by potentiometry. Complexes with ethyl-, n-propyl-, and phenyl- radicals have been studied. The composition of the complexes (Ag + : L = 1:1) has been determined using the relationship E/lgC L .

The addition of highly active magnesium hydride to α-olefines, hydromagnesiation, is a well known reaction. The use of cheap magnesium hydride exhibiting a lower reactivity is highly desirable for industrial purposes. In a combination of chemical and mechanical activation the low reactivity of high temperature magnesium hydride could be overcome thereby making a broad variety of magnesium alkyls accessible.

We have studied the ligand properties of cis-Ph 2 PCH=CHPPh 2 at nickel(0). Several homoleptic nickel(0) alkene complexes react with the twofold molecular quantity of cis-Ph 2 PCH=CHPPh 2 to afford the red crystalline homoleptic 1:2 complex Ni(cis-Ph 2 PCH=CHPPh 2 ) 2 (1). The reactions of Ni(cdt) or Ni(C 2 H 4 ) 3 with equimolar amounts of cis-Ph 2 PCH=CHPPh 2 yield orange-yellow crystals of the homoleptic 1:1 complex {(μ-cis-Ph 2 PCH=CHPPh 2 )Ni} n (2). Sparingly soluble 2 is presumably oligomeric with the (PCH=CHP)Ni moiety π-bonded to another nickel(0) center. The π bridges are rather stable and are only cleaved by strong π acceptors. For example, 2 reacts with CO to yield the known carbonyl complex (cis-Ph 2 PCH=CHPPh 2 )Ni(CO) 2 (3). In contrast to the above synthesis of 2, the 1:1 reaction of Ni(cod) 2 with cis-Ph 2 PCH=CHPPh 2 affords orange-red crystals of the alkene complex (cis-Ph 2 PCH = CHPPh 2 )Ni(cod) - THF (4) in moderate yield. Ni(1,5-hexadiene) 2 reacts readily with cis-Ph 2 PCH=CHPPh 2 (1:1) to give yellow (cis-Ph 2 PCH=CHPPh 2 )Ni(rac-η 2 ,η 2 -C 6 H 10 ) (5, 77%), which exhibits a fluxional diene coordination. That these thermally labile alkene complexes are formed at all, is ascribed to the chelate effect of the dienes. From the reaction of 2, 4 or 5 with ethyne, yellow microcrystals of (cis-Ph 2 PCH = CHPPh 2 )Ni(C 2 H 2 ) · Et 2 O (6) are obtained.

Determination of the first structure of a chain-like polysulfane with five sulfur atoms in the chain has been attempted. Bis(triphenylmethyl)pentasulfane forms monoclinic crystals containing disordered solvent molecules preventing an accurate solution of the structure. The (Ph 3 C) 2 S 5 molecules consist of a helical C–S–S–S–S–S–C backbone (all torsion angles of same sign) and triphenylmethyl groups of normal conformation. The analogous (Ph 3 C) 2 S 6 forms triclinic crystals; the molecular conformation of the C–S 6 –C chains is not helical, but the motif of torsion angles is + + – – +. In both compounds the C– S bonds are considerably longer (191 pm) than comparable C–S single bonds as in cyclo-C 2 H 4 S 7 . The latter forms monoclinic crystals consisting of ring molecules of C 1 symmetry which can formally be derived from the crown-shaped S 8 ring by substituting one sulfur atom by a C 2 H 4 group of approximate C 2h symmetry.

Dimethylaminobis(trifluoromethyl)borane, (CF 3 ) 2 BNMe 2 (A), reacts with epoxides of the general formula to yield five-membered heterocycles (CF 3 ) 2 , R = Me (1), CH,F (2), CF 3 (3), Et (4), Bz (5). With R = Ph a 1:2 mixture of the isomers (CF 3 ) 2 O (6a) and (CF 3 ) 2 (6b) is obtained. To the contrary, and A form the borane-dimethylamine adduct (H 2 C=CMe—CH 2 -O)(CF 3 ) 2 B • NHMe 2 (7). The compounds have been characterized by elemental analyses, multinuclear NMR, IR and mass spectra.

A series of tin(IV) compounds containing ferrocenyl chalcogenate (FcE) and ferrocenylene dichalcogenate (fcE 2 ) ligands (E = S, Se, Te) has been synthesized for a systematic study of the NMR spectra with particular emphasis on 13 C, 119 Sn, 77 Se and 125 Te NMR. All compounds are formally derived from tetramethylstannane, SnMe 4 , by stepwise replacement of methyl by either FcE or fcE 2 ligands. Starting from lithioferrocene the products are tetrasubstituted stannanes Me 4-n Sn(EFc) n (n = 1 and 2, E = S, Se, Te; n = 3 and 4, E = S, Se). Starting from 1,1′dilithioferrocene, the products are 1,1′-disubstituted ferrocenes such as fc(E-SnMe 3 ) 2 (E = S, Se, Te), although 1,3-dichalcogena[3]ferrocenophane rings are formed whenever possible to give [3]ferrocenophanes fcE 2 SnMe 2 (E = S, Se, Te) and fc[E-Sn(Me)E 2 fc] 2 (E = S, Se) or tin spiro compounds Sn(E 2 fc) 2 (E = S, Se, Te). Whereas all (8) possible sulfur-containing and all (8) selenium-containing products were accessible, some of the tellurium-rich compounds could not be isolated due to preferred formation of either Fc 2 Te 2 or fcTe 3 . All compounds were characterized on the basis of their 1 H, 13 C, 119 Sn and, if possible, 77 Se and 125 Te solution NMR spectra. In many cases, coupling constants such as 2 J( 119 Sn 1 H), n J( 119 Sn 13 C) (n = 1,2,3), 1 J( 119 Sn 77 Se) and 1 J( 125 Τe 119 Sn), 1 J( 77 Se 13 C) and 1 J( 125 Te 13 C) could be determined. The δ 119 Sn chemical shifts of analogous phenyl and ferrocenyl compounds, Me 4-n Sn(EPh) and Me 4-n Sn(EFc) n (n = 0-4, E = S, Se, Te), are discussed, and for a microcrystalline sample of tetrakis(ferrocenylselenolato)stannane, Sn(SeFc) 4 , the 119 Sn and 77 Se CP/MAS NMR spectra are reported and compared with the solution spectra.

The reaction of Cp′ 2 ZrCl 2 (1) (Cp′ = C 5 H 4 Me) with Li(THF) 2 P(SiMe 3 ) 2 yields the zirconoocene monophosphido complex Cp′ 2 Zr(Cl){P(SiMe 3 ) 2 } (2) in good yield. 2 reacts with diphenylcarbodiimide with insertion of the heterocumulene into the Zr–P bond to give (3). 2 and 3 were characterized spectroscopically (IR, NMR), and an X-ray structure determination was carried out on 1 and 3 (crystal data: 1, a = 6.803(3), b = 12.008(6), c = 15.480(12) Å, space group Pnma (No. 62), Z = 4, 1685 observed independent reflexions, R = 5.4%, 3, a = 9.210(7), b = 11.491(13), c = 31.279(15) Å, β = 95.32(4)°, space group P2 1 /n (No. 14), Ζ = 4, 6408 observed independent reflexions, R = 6.2%). The crystal structure of 3 revealed η 2 -bonding (N,N′) of the phosphaguanidene ligand N(Ph)C{P(SiMe 3 ) 2 }N(Ph) ⊖ to the Zr atom (Zr–N 1 2.309(5) Å, Zr–N 2 2.348(5) Å). The ligand can not be obtained from the reaction of Li(THF) 2 P(SiMe 3 ) 2 with diphenylcarbodiimide, which instead affords

A discrete ammonium catecholate hydrate of the composition NH 4 [C 6 H 4 (OH) 2 ][C 6 H 4 (OH)O] · 0.5 H 2 O has been isolated and characterized by a single-crystal X-ray structure analysis. The crystals are monoclinic, space group C 2/c (No. 15), Z = 8, a = 24.613(3), b = 8.706(1), c = 11.890(2) Å, β = 110.56(1)°. The crystal lattice features a network of hydrogen bonds, which clearly contribute significantly to the overall stability of the lattice. The water molecule is engaged as a donor and an acceptor in as many as four hydrogen bonds. Surprisingly, the crystalline compound is air-stable, while anhydrous ammonium catecholate, as obtained by dissolving catechol in dry liquid ammonia, is quickly oxidized in air.

A discrete zinc bis[orotate(1—)] complex of the composition Zn(OrH) 2 ·8 H 2 O has been isolated and characterized by a single-crystal X-ray structure analysis. The crystals are monoclinic, space group P2 1 /c (No. 14), Z = 2, a = 10.884(2), b = 12.896(1), c = 6.954(1) Å, β = 98.27(1)°. The crystal lattice features hexaquo complexes of zinc, the Zn(H 2 O) 6 2+ cations being associated with two hydrated OrH - ions only through hydrogen bonds. The results are relevant for applications of zinc orotates in medical treatment.

Single crystals of NaZnAsO 4 were grown in a sodium molybdate flux. The compound crystallizes monoclinically, space group P2 1 /n, with a = 8.951(1), b = 8.2085(9), c = 15.699(2) Å, β = 90.153(6)° and Ζ = 12. The structure was refined to R = 0.036, R w = 0.035 for 3355 independent, absorption-corrected reflections. NaZnAsO 4 belongs to the beryllonite (NaBePO 4 ) structure type.

Crystals of the complexes [CdI 2 · C 6 H 12 S 3 ] 2 (1) and [Hg(C 6 H 12 S 3 ) 2 ](HgI 3 ) 2 (2) were obtained by diffusion of 1,4,7-trithiacyclononane (9 S 3) in ethanol into aqueous solutions of cadmium iodide and mercuric iodide/potassium iodide, resp. Both compounds crystallize monoclinically,1: space group P2 1 /n, Z = 4, a = 1207.1(5), b = 909.9(2), c = 1240.3(7) pm, β = 92.59(9)°; 2: P2 1 /c, Z = 2, a = 804.7(6), b = 934.0(6), c = 2167.9(4) pm, β = 94.34(7)°. 1 is dimeric, consisting of two [CdI 2 · 9S3] units, connected via iodine bridges. Crystals of 2 contain sandwich-like cations [Hg(9S3) 2 ] 2+ and [HgI 3 ] - anions, forming chains via Hg ··· S and Hg ··· I bridges.

The 2-selenoimidazolines 5 are obtained from the reaction of the imidazol-2-ylidenes 4 with selenium in very good yields. The ylidic nature of the carbon selenium bond (2) is revealed both by NMR and by X-ray analysis. On comparison with the corresponding tellurium compounds 3, reduction of the carbon chalcogen bond order in 5 is suggested.

X-ray structure analyses of crystalline [NMe 4 ][B 5 O 6 (OH) 4 ] · nH 2 O with n ≈ 0.25-0.50 (1), [NEt 4 ][B 5 O 6 (OH) 4 ] (2), [NPhMe 3 ][B 5 O 6 (OH) 4 ] (3), and [pipH][B 5 O 6 (OH) 4 ] (4) reveal that these materials are novel clathrates with closely related three-dimensional host structures built up of hydrogen-bonded oligomeric pentaborate [B 5 O 6 (OH) 4 ] - ions. The organic cations and water molecules (in 1) occupy as guest species large straight channel-like voids of nearly rectangular cross-section. Compound 1 crystallizes monoclinically with space group P2,/c (Z = 4); the compounds 2,3 and 4, which possess the same host-structure topology, crystallize triclinically with space group P1̄ (Z = 2). 11 B-MAS NMR spectra allow the detection of small angular distortions in the pentaborate anions caused by the specific hydrogen bonding in the host frameworks. Upon heating the compounds on a thermobalance in a dynamic inert gas atmosphere dehydration occurs at temperatures of 563 K (1), 543 K (2), 558 K (3) and 523 K (4) before degradation of the organic cations starts at temperatures of 633 K (1), 623 K (2), 623 K (3) and 613 K (4).

The 35 C1 NQR spectra of the chlorochalcogenide complexes of iridium (SCl 3 ) 2 [IrCl 6 ] 1, (TeCl 3 ) 2 [IrCl 6 ] 2, (SeCl 3 ) [IrCl 6 ] 3, [IrCl 3 (SCl 2 ) 2 ] 2 4, (SCl 3 ) [IrCl 4 (SCl 2 ) 2 ] 5 and [IrCl 3 (SeCl 2 ) 2 ] 2 6 have been studied. The spectra were recorded by pulse spectrometry. They consist of two mul tiplets, widely separated in frequency. The high-frequency multiplet belongs to the chlorine atoms bonded to sulfur, selenium and tellurium, respectively, in the ligand. A high-frequency shift is observed, which is typical for the coordination of the molecules ACl 2 (A=S, Se) and ACl 4 (A=S, Se, Te). The low frequencies in the multiplets of 4 and 6 are attributed to additional bonds formed between chalcogen atom and chlorine in the coordination environment of iridium. In the spectral region 18-24 MHz lie the NQR frequencies of 35 Cl bonded to iridium. For 2 the frequencies are close to those of [IrCl 6 ] 2- , which confirms the Ir oxidation state IV. The unexpectedly high frequencies for Ir III in the case of 4 and 5 are explained by the influence of ACl 2 molecules, which are weaker σ-donors than the chloro ligands. This promotes electron density transfer from neighbouring chlorine atoms. The 18 MHz frequency is assigned to the bridge chlorine atoms in dimeric molecule 4. This assignment is confirmed by the positive value of d v/dT = +0,2.

The crystal structures of two zinc(II) 5,15-dioxo-porphyrins (porphodimethenes) have been determined to investigate the coordination chemistry of porphyrins with interrupted conjugation system. Both compounds have a five-coordinated zinc center with pyridine as axial ligand and show overall structural parameters very similar to porphyrins. The oxidized meso-positions are, however, easily identified by longer C m –C a bond lengths and smaller C a –C m –C a angles. The macrocycles exhibit a small degree of conformational distortion, and the etioporphyrin I derivative shows evidence for π-stacking in the crystal. Crystal data: 1 – C 41 H 47 N 5 O 2 Zn. Triclinic, a = 10.052(3) Å, b = 14.139(4) Å, c = 14.635(5) Å, α = 105.17(2)°, β = 108.62(3)°, γ = 106.29(2)°, V = 1745.3(9) Å 3 , CuKα radiation, λ = 1.54178 Å, space group P1̅, Z = 2. R = 0.089. 2 – C 37 H 39 N 5 O 2 Zn. Triclinic, a = 12.122(3) Å, b = 12.383(3) Å, c = 12.759(4) Å, α = 61.77(2)°, β = 72.19(2)°, γ = 70.32(2)°, V = 1563.8(8) Å 3 , CuKa radiation, λ = 1.54178 A, space group PĪ, Z = 2, R = 0.076.

As part of our total synthesis of thymosin β 4 an optimized synthesis of the C-terminal part of thymosin β 4 is described. Side chain functional residues of the tridecapeptide are masked by tert-butyl and the α-amino residues are protected by Z groups. The fully protected peptide derivative was obtained by WSCI/HOBt coupling of three fragments representing the segments [31-35], [36-37] and [38-43].

[{Cp(CO) 2 Fe}SnCl 3 ] reacts with Na 2 Se in THF to form the compound [{Cp(CO) 2 Fe} 3 ClSn 3 Se 4 ] 1. 1 crystallizes in the monoclinic space group P2 1 /n with 4 formula units per unit cell. The lattice constants are α = 1435.2(7), b = 1124.4(4), c = 1972.7(12) pm, β = 94.59(4)°. According to the X-ray structure determination 1 contains a bicyclic Sn 3 Se 4 framework.

The title compounds were prepared in crystalline form and characterized analytically and spectroscopically.

Single crystals of Ba 2 [TaN 3 ] (monocl., C2/c (Nr. 15); a = 613.0(3), b = 1181.5(4), c = 1326.3(5) pm; β = 91.1(1)°; Ζ = 8) were prepared from mixtures of Li and Ba (molar ratio 1:1) in tantalum crucibles and by reaction with nitrogen (1 atm) at 1000°C. The crystal structure (an isotype of Ba 2 [ZnO 3 ]) contains infinite tetrahedral anions ∞ 1 [TaN 2 N 2/2 4- ] (Ta–N: 192.2(13)– 198.8(9) pm) which can be described as “Zweier-Einfach-Kette”. Sr 2 [TaN 3 ] (monocl., C2/c (Nr. 15); a = 600.5(3), b = 1131.3(7), c = 1260.3(7) pm; β = 91.71(6)°; Ζ = 8) was obtained as a yellow powder containing excess Sr 2 N by reaction of Sr 2 N and Ta (molar ratio Sr: Ta = 4.5:1) with nitrogen (1 atm) at 1000°C. The isotypic relationship to Ba 2 [TaN 3 ] was confirmed by X-ray powder investigations.

The crystal structure of [ReCl 4 (PhC = CPh)(OPCl 3 )] was solved with X-ray methods. Space group P1̄, Z = 2, 2085 observed unique reflections, R = 0.029. Lattice dimensions at -70°C: a = 857.0(2), b = 937.9(2), c = 1249.6(2) pm, α = 87.43(3)°, β = 83.48(3)°, γ = 89.80(3)°. [ReCl 4 (PhC ≡ CPh)(OPCl 3 )] has a molecular structure with the alkyne ligand bonded side-on (bond lengths Re-C 198.9(8) and 198.6(7) pm). The oxygen atom of the solvating POCl 3 molecule is coordinated in trans position to the ReC 2 unit of the alkyne ligand (bond length Re-O 226.7(5) pm).

A reinvestigation of the previously determined structures of two polymorphs of pyridinium chloride shows that both polymorphs contain several aromatic C– H-H···Cl hydrogen-bond interactions. These hydrogen bonds, hitherto unrecognized, may play a significant structural role, both in solution and in the solid-state.