Arthur J. Banister

Electron spin resonance study of CH3CNSSN˙, C6H5CNSSN˙, and SNSSN˙+ free radicals

Isotropic and powder e.s.r. spectra have been recorded for CH3[graphic omitted]˙, C6H5[graphic omitted]˙, and [graphic omitted]˙+. Isotropic labelling with nitrogen-15 and sulphur-33 has been accomplished for [graphic omitted]˙+ and it has been possible to prepare 33[graphic omitted]˙+. Sulphur-33 satellites have been observed for C6H5[graphic omitted]˙. MNDO and Gaussian 76 calculations have been used to calculate the minimum-energy structures of the radicals, while INDO calculations have provided values for the hyperfine coupling constants. Unfortunately, poor agreement was obtained between the latter and the corresponding experimental values. All the radicals dimerise in solution at low temperatures and we have been able to measure the energetics of dimerisation for C6H5[graphic omitted]˙ and [graphic omitted]˙+. The dimers exist as crystalline solids which contain readily detectable amounts of the monomeric free radical.

The high yield preparation, characterisation, and gas phase structure of the thermally stable CF3CSNSCCF3·, 4,5-bis(trifluoromethyl)-1,3,2-dithiazolyl and the X-ray crystal structure of benzo-1,3,2-dithiazolyl

The very thermally stable, but photochemically sensitive radical, 4,5-bis(trifluoromethyl)-1,3,2-dithiazolyl has been prepared, isolated, and fully characterised including a gas phase structure, and found to be paramagnetic in the liquid state at room temperature; the X-ray structure of benzo-1,3,2-dithiazolyl has been obtained for comparison.

Crystal structure of 4-phenyl-1,2-dithia-3,5-diazole dimer

4-Phenyl-1,2-dithia-3,5-diazolium chloride on reduction with thiocyanate ion gives the black air-sensitive title compound, (PhCN2S2)2. Crystals have been studied by means of X-ray diffraction at room temperature. The compound crystallizes in the space group P212121(no. 19) with a= 16.061(1), b= 32.984(5), and c= 5.774 0(4)A, and Z= 8. The crystal structure has been solved using 2 513 reflections and refined to a final R value of 0.082. Each asymmetric unit contains two (PhCN2S2)2 molecules. Within each dimer the bridging mean S ⋯ S distance is 310.9(5)pm. The two half-molecules within each dimer are nearly parallel and are slightly twisted with respect to each other. The short (mean) CN2S2 ring distances (dCN= 133, dSN= 162, dSS= 209 pm) and the PhCN2S2 coplanarity suggest that the rings are aromatic with one electron pair delocalized at the four (disulphide) sulphur atoms.

DITHIADIAZOLYLS AS HETEROCYCLIC CHELATORS : A RADICAL APPROACH TO COORDINATION CHEMISTRY ?

The ability of heterocyclic compounds to act as chelating ligands via the cleavage of a heterocyclic E–E (or E–E′) bond with concomitant formation of M–E (and M–E′) bonds is described with particular reference to the 7π heterocyclic dithiadiazolyl radicals, R Figure options Download full-size image Download as PowerPoint slide . These electron-rich ring systems form a diversity of structural bonding types in which the heterocyclic ring can formally act as a 2e−, 3e−, 5e− or 6e− donor ligand. These structural bonding modes are described through examples in which the heterocyclic ring interacts with halide anions, N atoms and particularly metal centres, forming monometallic, dimetallic and trimetallic complexes. The structural features which determine which compounds are likely to act as cyclic chelators are discussed and examples of thiadiazole, diselenadiazolyl and dithiole rings acting as cyclic chelators are given.

Preparation of salts of the 5,5′-(1,4-phenylene)bis(1,3,2,4-dithiadiazolylium) dication and of its 1,2- and 1,3-phenylene analogues. Preparation and crystal structure of the stacked, neutral 5,5′-(1,4-phenylene)bis(1,3,2,4-dithiadiazole)

Reactions of o-, m- and p-C6H4(CN)2 with [SNS][AsF6] in liquid SO2 produced the AsF6– salts of o-, m- and p-[C6H4([graphic omitted])2]2+ in high yield. The para-phenylene AsF6– salt was readily converted (>75%) into other salts (Cl–, Br–, SbCl6– or S3N3–) by anion metathesis. Reduction of [p-C6H4-([graphic omitted])2]Cl2 with SbPh3 gave the bis(dithiadiazole), p-C6H4([graphic omitted])2, which crystallises in the triclinic space group P, with a= 5.772(1), b= 6.382(1)c= 7.491(1)A, α= 79.21(1), β= 82.86(1), γ= 70.25(1)°, Z= 1; R= 0.077 for 678 observed reflections. The structure shows equidistant molecular stacking of the trans isomer with weak S ⋯ S (3.214 A) and S ⋯ N (3.346 A) intermolecular interactions.

Adducts of tetrasulphur tetranitride

Abstract Reactions in inert solvents between tetrasulphur tetranitride and Lewis acids have given new adducts S 4 N 4 ·A (A = PhBCl 2 , TiI 4 , HfCl 4 , NbF 5 , TaF 5 , WBr 4 ), S 4 N 4 ·2A′ (A′ = AlBr 3 , GaCl 3 , InCl 3 , FeCl 3 ) and S 4 N 4 ·4TiF 4 . IR spectra and possible structures of the adducts are discussed.

Novel S–N ring contractions using the 4-phenyl-1,2,3,5-dithiadiazole dimer, the synthesis and X-ray crystal structures of [(PhCN2S2)2Cl][S3N3], [PhCN2S2][S3N3], and [PhCN2S2][S3N2]Cl, and an ab initio molecular-orbital study of the bonding in [PhCN2S2][S3N3]

When the 4-phenyl-1,2,3,5-dithiadiazole dimer (1) dehalogenates [S5N5]Cl a novel ring contraction occurs producing [(PhCN2S2)2Cl][S3N3], (2), in acetonitrile, and a mixture of (2) and [PhCN2S2][S3N3], (3), in pentane. The salt [S4N3]Cl is also dehalogenated by (1) in acetonitrile giving [PhCN2S2][S3N2]Cl, (4). The X-ray crystal structures of (2)–(4) provide an insight into the electronic state of the CN2S2 rings in these three compounds by comparison of the S–S bond length with the known lengths in compound (1), [PhCN2S2][AsF6], and [PhCN2S2]Cl. Extended-Huckel and ab initio molecular-orbital calculations were carried out on compound (3) and high-yield preparations of (2)–(4) are also described. The reactions of [S5N5]Cl or [S5N3]Cl with (1), in acetonitrile, produced in both cases the new e.s.r.-active compound [PhCN2S2]2Cl, whose solid-state preparation is described. The reaction between the vapours of (SN)x and (1) produced (3) providing further evidence for S3N3˙ being the major vapour-phase species above (SN)xin vacuo at ca. 160 °C.

X-Ray crystal structures of some lithium aryl thiolates: monomeric [o-MeC6H4SLi·(NC5H5)3], chain [PhSLi·(NC5H5)2]∞, and the unique folded ladder of [PhCH2SLi·NC5H5]∞ with Li–S rungs

The X-ray crystallographic study of the title compounds has shown a remarkable structural variation induced by minor changes in the anion, [PhCH2SLi·NC5H5]∞ forming an infinite folded ladder polymer with Li–S rungs, removal of the CH2 group to give [PhSLi·(NC5H5)2]∞ resulting in a polymer containing an infinite Li–S chain, while the introduction of an Me group into the ortho-position in [o-MeC6H4SLi·(NC5H5)3] prevents association; all three structures have tetrahedral lithium whereas the co-ordination around sulphur varies from 2 to 4.

Direct insertion of a nitrogen atom into the S–S bond of a 1,2,3,5- dithiadiazole ring in a direct current nitrogen glow discharge, and X-ray crystal structure of 4-methyl-1,2,3,5-dithiadiazole

Dimeric aryldithiadiazoles (R[graphic omitted])2(R = Ph or p-ClC6H4,) were treated with atomic nitrogen, generated in a cool direct current plasma, to form the corresponding dithiatriazine dimers by nitrogen insertion into the S–S bonds; alkyl derivatives (R = Me, Pr, or But) gave polymeric products. Dithiadiazolylium salts [R[graphic omitted]]+ X–(R = Ph or p-ClC6H4; X = I, Br, CN, or S3N3) also reacted with nitrogen plasma to give high yields of the respective dithiatriazine (RCN3S2)2. Structural criteria for the reaction are discussed. The crystalline methyldithiadiazole contains planar [graphic omitted] rings with S–S 2.076(2), S–N 1.636(3), C–N 1.324(5)A, N–S–S 94.5(1), C–N–S 114.5(3), and N–C–N 122.2(4)°(all average values). Within the dimer unit the parallel monomer rings are linked via one weak S ⋯ S bond (3.10 A). The crystals are triclinic, space group P, with a= 11.296(1), b= 12.498(1), c= 14.647(2)A, α= 72.06(1), β= 77.85(1), γ= 77.30(1)°, and Z= 8.

Spectroscopic studies on sulphur—nitrogen compounds

Abstract The infra-red stretching frequencies of sulphur—nitrogen bonds are summarised and discussed. It is shown that the wavelength of the absorption band is related in a linear manner to the bond length. In the case of compounds containing the NSO group it is shown that the symmetric and asymmetric stretching frequencies are linearly related.