Cadmium Heterometallic Compounds: Classification and Analysis of Crystallographic and Structural Data

Abstract

Cadmium chemistry is an important area of research from both an industrial and environmental point of view. This review surveys the structural determination of almost ninety heterometallic complexes of cadmium. The cadmium atom is found mostly in the oxidation state of +2, but there are also examples of +1 and zero. The coordination numbers observed range from two to eight, with six occurring most frequently. The heterometal atoms include both transition and non-transition metals. A range of derivatives from dimers to polymers contain two or more metal atoms, however, there appears to be no evidence to suggest the existence of a direct Cd-Cd metal bond.Each metal atom is four coordinate, almost tetrahedral but with distortion towards a trigonal bipyramid. The other derivative [6] has an almost planar [Οά(μl) 2 Hg] ring, with the metals being four coordinate Cdl 4 and Hgl 2 P 2) respectively. The former is a slightly distorted tetrahedron while the latter is highly irregular. In particular, the P-Hg-P angle of 152.8(1)° may be attributable to the strong s-donor abilities of triphenylphosphine coupled with the tendency of mercury(ll) to adopt linear coordination [2]. The mean Cd-I(bridge) bond distance of 287.4(1) pm is about 19.3 pm shorter than that of the Hg-I(bridge) distance of 306.7(1) pm (Table 1A). HETEROTRIMERIC COMPOUNDSThe structural and crystallographic data for nine heterotrimetallic derivatives of cadmium are given in Table 1B. The orange yellow compound (NMe 4 ){Na[Cd(PhCOS) 3 ] 2 } [7] has at the centre a sodium atom, and the two cadmium atoms are part of the ligand system around it. This is illustrated in Figure 2. The anion has a crystallographicaliy imposed centre of symmetry, with the Na(l) atom sitting at the inversion centre. It is bonded to each of the PhCOS ligands via oxygen which gives it a distorted octahedral NaO e environment. Each Cd(ll) atom is S-bonded to three thiobenzoate ions and also interacts weakly with three oxygen atoms at distances of 265.9 to 282.8(5) pm. The Cd-Na separation is 355.7(1) pm and does not involve any direct metal-metal bonding. C23 FIGURE 2. Structure of {NalCdiPhCOSJalJ [η There are four orange-red derivatives of composition LCd[Mn(CO) 5 ] 2 [8-10] in which cadmium is the central atom and the two Mn(CO) 5 moieties are part of the ligand 424 Brought to you by | Purdue University Libraries system. In two of these [8,10] the cadmium atom is coordinated by a terdentate ether [8], or terpyridyl [9] molecule (Cd-0 range from 254.1(7) to 269.6(7) pm [8] and Cd-N range from 240.5(12) to 249.3(14) pm [9]), and two Mn(CO) s units (Cd-Mn, 270.7(2) and 271.4(2) pm [8] and 276.0 and 279.9(5) pm [9]) in a very distorted trigonal bipyramidal arrangement. There is considerable distortion of the octahedral manganese coordination (MnC 5 Cd) as seen in Table 1B. Two structures LCd[Mn(CO) s ] z (L is 2,2'-bipyridyl or 1,10-phenanthroline [9]) are very similar. The cadmium atom is coordinated by two nitrogen atoms of L and two manganese atoms creating a distorted tetrahedral arr...

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