Anisobidentate ligands, dithiocarbamates

The Sn Mossbauer spectra of a number of tin dithiocarbamate complexes have been reported (89, 91, 94, 108, 118, 147, 178, 180) Data are collected in Table IV. The Mossbauer spectral parameters have been used to infer the coordination number of the Sn atom. The isomer shift (IS) of tin species decreases as the i-electron density at the Sn atom decreases thus the isomer shift would generally be expected to decrease on increasing coordination number or increasing electronegativity of the ligands. These two factors are difficult to separate, since the anisobidenticity of dithiocarbamate ligands generally decreases as the Lewis acidity of the metal moiety increases. 

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]. 

Anisobidentate dithiocarbamate ligand. f Five-membered chelate ring. 

Homoleptic dithiocarbamate complexes of both teUurium(II) (215, 293, 294, 296, 302-311) and tellurium(lV) (293, 294, 296, 302, 304-306, 309, 310, 312-315) are well known. The molecular structures of the bis(dithiocarbamate)tel-lurium(II) compounds, [Te(S2CNR2)2], are analogous to those of the corresponding Se compounds The Te atom exhibits a planar trapezoidal coordination geometry, with the two dithiocarbamate ligands bound in an anisobidentate fashion [Te—S(ave) = 2.52 (short) and 2.83 A (long)]. Tellurium(II) has a tendency for pentacoordination and, with the exception of [Te(S2CNCy2)2], which is monomeric (311), there is a short intermolecular Te-- S contact (av... 

In the perchlorate complex [Te(p-C6H40CH3)(S2CNMe2)2(C104)] (353), an oxygen atom of the perchlorate coordinates to the Te in an equatorial position so that, with the exception that the dithiocarbamate ligands are anisobidentate (ATe—S = 0.29 A), it is structurally similar to the [TeXR(S2CNR2)2] complexes. 

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