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Correlations between solid state structure and vibrational spectra previously derived by the authors, and based upon full structure determination by X-ray methods, have been applied to the following 1:1 complexes which have not hitherto been adequately characterised structurally: HgX 2 (PPr 3 ) [X = Cl, Br or I (α- and β-forms)], HgX 2 (PPh 2 Me) [X = Cl (α and β-forms), Br or I], HgX 2 (PPhMe 2 ) [X = Cl, Br or I], HgX 2 (PEt 3 ) [X = Br or I], HgX 2 (PBu 3 ) [X = Br or I] and HgI 2 (PMe 3 ). In the case of the HgX 2 (PPr 3 ) series, the studies were augmented by far-infrared, NMR and relative molecular mass data on solutions. While for some complexes structures have been proposed with a reasonable measure of confidence, for others only general indications of structural features can be made, and in a few cases entirely new (but uncharacterised) structures are probable. There is remarkable spectral variety even within such closely related series.

The synthesis and properties of some nitroimidazole complexes of platinum and palladium starting from the MCl42- salts are described. Both 5-NO2-imidazole and metronidazole give cis-[MCl2L2] complexes whereas trans-[MCl2L2] is obtained for 2-NO2-imidazole and misonidazole. The crystal structure of trans-dichlorobis(misonidazole)platinum(II) was determined by three-dimensional X-ray methods. The compound crystallized in space group P21/c in discrete monomeric units with a = 11.303(5), b = 13.002(5) and c = 8.125(3) A, B = 91.39(3)°, Z = 2 and the observed and calculated densities are 1.83 and 1.859 respectively. The final full-matrix least-squares refinement gave values of R1 = 0.037 and R2 = 0.045 for 142 variables. The complex is square-planar with Pt-Cl and Pt-N distances of 2.294(3) and 2.016(9) A respectively. The mean plane of the misonidazole ring is twisted 56° with respect to the PtCl2L2 square plane and the Cl-Pt-N angles are 89.4(3) and 90.6(3)°; the nitro group also lies out of the plane of the misonidazole ring. The closest nonbonded contact between non-hydrogen atoms in the unit cells is 2.80 A suggesting hydrogen bonding between the hydroxyl proton and the ether oxygen in the misonidazole side-chain, i.e. O-H⋯O. Aspects of the chemistry of these species in relation to their biological activity are discussed.

A discrete dimeric form of the 1:1 adduct of mercury(II) chloride with tributylphosphine, β-HgCl2(PBu3), has been characterised by full single-crystal X-ray diffraction analysis. In contrast to the previously reported α-form, which has been described as ‘tetrameric’, β-HgCl2(PBu3) consist of centrosymmetric halogen-bridged dimers with no indication of any further association; the far-i.r. and Raman spectra may readily be assigned on this basis. The spectra of the α-form are markedly different to those of the β-isomer, yet these too are best interpreted in terms of a dimeric structure, albeit one significantly distorted by weak inter-dimer interactions rather than the ‘tetrameric’ structure previously advocated.

Complete crystal structure analyses have been carried out for 1:1 adducts of mercuric chloride with triphenylphosphine and 1,2,5-triphenylphosphole. In each case the structure consists of discrete centro-symmetric chlorine-bridged dimers, with mercury atoms in distorted tetrahedral environments, but with different HgCl bridge distances. Preliminary single-crystal X-ray photographs indicate that HgX2(PPH3) [X = Br or I] and HgBr2)1,2,5-triphenylphosphole) are isostructural with their chloro analogues. A full X-ray study has shown that the α-form of HgCl2(PBu3) comprises a discrete tetrameric unit, in which two unsymmetric dimers, related by a centre of symmetry, are loosely linked by further HgCl bridges.

The crystal structures of the complexes HgCl 2 (PMe 3 ) and HgCl 2 (PEt 3 ) have been completely characterised by single crystal X-ray analysis. In each case the structures are polymeric, with mercury atoms in distorted trigonal bipyramidal environments, but the actual arrangements are different. Whereas HgCl 2 (PEt 3 ) may be regarded as an extended chlorinebridged chain with essentially covalent bonding throughout, a very larg PHgCl angle, and other structural features, characterise the trimethylphosphine complex as being of ionic formation, HgCl(PMe 3 ) + CL − . Preliminary single crystal photographs show that HgBr 2 (PMe 3 ) is isostructural with chloride, but HgI 2 (PMe 3 ) is apparently structurally different. The structures found are thus in marked contrast to those previously reported for 1:1 adducts of mercuric chloride with bulker phosphine, and the origins of the differences are discussed.

A critical appraisal has been made of the far-infrared and Raman spectra (40–450 cm −2 ) of the complexes HgX 2 (PR 3 of crystallographically known structure: HgX 2 (PPh 3 ) [X = Cl, Br or I, [XgX 2 (1,2,5-triphenyphosphole) [X = Cl or Br], α- and β-HgCl 2 (PBu 3 ), HgCl 2 (PCy 3 ) [Cy = cyclohexyl], HgCl 2 -(PEt 3 , and HgX 2 (PMe 3 ) [X = Cl or Br]. Remarkably, although the known structures are apparently quite varied, and the spectra similarly diverse, it is shown that the gross features of the spectra can be explained, to the first order, in terms of a common centrosymmetric halogen-bridged dimeric unit. However, there are subtleties in the structures which can have very significant influence on the spectral patterns, and this makes structural elucidation from spectroscopic data fraught with difficulty.