Cadmium complexes sulfur ligands

Biirgi studied also a series of five coordinated cadmium complexes, 38, that contain three equatorial sulfur ligands, but in which the fourth and fifth, axial ligands, X and Y, are sometimes iodine, sometimes sulfur, and sometimes oxygen (84). The structural correlations have a clear interpretation in terms of the ligand exchange reaction and are reminiscent of the kind of process that is believed to occur in S 2-type nucleophilic substitution reactions ... 

Zinc and cadmium complexes of the novel tripod ligand (145) have also been described.1087 The reaction of Hg(HL)2 (HL = 2-mercaptobenzoic acid, 146) with cadmium nitrate leads to the novel CdHgL species, in which the cadmium is bonded to the carboxylate oxygen atom, and the mercury to the thiolate sulfur.1088... 

No compound with five-coordinate carbon as the central atom has yet been crystallized. Burgi, however, has studied a series of trigonal bipyramidal complexes of divalent cadmium with three equatorial sulfur ligands and with axial ligands iodide, hydroxyl, or sulfur groups ( Y and X). 

There are two types of neutral complexes homoleptic and heteroleptic. The former are generally dimers, with two cadmium atoms penta-coordinated by two molecules of dithiocarbamate, which acts as an anisobidentate ligand (Figure 31). One sulfur atom from one of the molecules coordinated to the cadmium ion acts as a bridge to the other cadmium atom, bringing about a distorted square pyramidal coordination geometry with the axial position occupied by the bridging sulfur atom [117]. 

The other general characteristic feature of cadmium(ll) complexes with thiol derivatives is the formation of di- or trinuclear species, in which thiol sulfur atoms behave as bridging ligands. The existence of polynuclear species was observed in nickel(ll)- and zinc(ll)-cysteine systems with similar stoichiometry, but cadmium(ll) complexes have usually an octahedral geometry, while in the nickel(ll) complexes this coordination mode results in four-coordinated square planar complexes. 

The complexes, [Fe(py>4]X2 (X = Br, 1), have been prepared by oxidation of metallic iron with bromine or iodine in methanol. Pyridine is added to the resultant solution and the pyridine complexes precipitated.22 Interaction between metallic zinc or cadmium and an excess of arsenic pentafluoride in liquid sulfur dioxide leads to the formation of solvento-complexes containing two or four SO2 ligands depending on the experimental conditions.23/24 The reactions studied are summarized as follows, Eq.4.4 ... 

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