Xanthate complexes nickel structures

Among the recent reports on metal xanthate chemistry the following are mentioned, dealing with the structural diversity of nickel(II),213 zinc(II),214 mercury(II), 15 and tellurium(II) bis (xanthate) complexes,216 based upon different coordination patterns and supramolecular self-assembly. 

With P-donors a variety of different structures are formed. Two complexes (359a,b) with a five-coordinate square pyramidal geometry and one S-donor in the apical position are reported.934,933 In a related complex (360) the nickel center reveals a distorted square planar geometry, because one xanthate ligand switched to a monodentate coordination mode. 6 By reaction of [NiL2] complexes with Ph2P(CH2)2P(Ph)(CH2)2PPh2, compound (362) is formed, which consists of a five-coordinate cation and a hexacoordinate anion. 7... 

Substituted dithioformate anions as ligands R C(S)S are usually called dithiocarbamates (R = R2N), alkyl and aryl dithiocarbonates or xanthates (R = RO), alkyl and aryl trithiocar-bonates or thioxanthates (R = RS). Dithioacid anions (R = alkyl, aryl) have been rarely used as ligands of nickel(II) because of their instability. Structural properties of selected nickel(II) complexes with substituted dithioformate, dithiolene and related ligands are shown in Table 90. 

The ligand field strength of the ligands is between that of the dithiocarbamates and water.49 IR studies show characteristic bands near 1250, 1100, 1020 and 550 cm-1.93 The contribution of the resonance form (85) in transition metal complexes is less than that of the analogous structure in the dithiocarbamates.60 The electron density on the metal is not very high, which accounts for the fact that abnormal high oxidation states are exceptional and a strong interaction of bases with the square planar nickel (and some other metal) xanthates is found.94... 

Of the transition metals, the nickel triad has been the most studied in terms of xanthate structures, especially nickel xanthates. Thus, binary xanthate structures are known for all elements with no less than 15 binary nickel xanthate structures known and these aggregate in the solid state in six distinct supramolecular architectures. There is also a rich diversity of adducts as well as mixed-ligand complexes, in particular for nickel. 

Earlier structural studies of carbohydrates by CD involved introduction of suitable chromophores into the sugar molecule thereby affording derivatives which exibit Cotton effects. These include, among others, xanthates (4-8) or azides (9). Later it was found that some metal ions (10), i.e. copper (11,13), vanadate (14), chromium (15), molybdate (16-22), nickel (23) or cobalt (24,25) ions form complexes with carbohydrates, which show appreciable Cotton effects. 

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