Cadmium complex, bond length

The coordination modes of the nitrate ligand in the complexes [TpBut]M(N03) (M = Cu, Ni, Co, Zn) are summarized in Fig. 46. (171, 184). Evidently, the coordination mode varies from unidentate for Zn to symmetric bidentate for Ni and Cu, with the cobalt derivative exhibiting an anisobidentate coordination mode. Moreover, the related cadmium derivative [TpBut,Me]Cd(N03) also exhibits bidentate coordination of the nitrate ligand, with Cd-0 bond lengths of2.272(6) A and 2.295(7) A (91). Such symmetric bidentate coordination contrasts with the significantly different Zn-0 interactions [1.978(3) A and 2.581(3) A] in unidentate [TpBut]Zn(N03). The coordination modes for a variety of [TpRR ]M(N03) complexes are summarized in Table VIII. 

Structurally, complexes of malonaldehyde and acetylacetonate with Zn(R) ion show very similar Zn—O bond lengths . The cadmium complexes have similar structures but... 

For the cadmium-ethylenediamine complexes, the lengths of the M-N bonds are practically independent of the coordination number of the cadmium ion. The values of enthalpy changes of each step of the reactions are also invariable (-14 kJ mol for each Cd-N bond), which are the same as that of the Cd(NH3) complex. Therefore, the Cd-N bond strength of these complexes are almost the same, irrespective of their structures. 

Cd-Cd- and Hg-Hg-bonded complexes can also be synthesized by reacting diaryl cadmium or diaryl mercury with the intermetallic Zintl phases K Pb, or Kj As, respectively (method xiii. Scheme 12.5) [30]. In both cases, a Zind duster anion ([Pb CdCdPh,] " or [As HgHgAs ] ") is formed in which the metal atoms are connected by a single bond (16-17, Scheme 12.9). Complex 16 crystallized as two crystallographically independent molecules in which the Cd-Cd bond length is 2.697(1) and 2.715 (2) A, respectively, while the Hg-Hg bond distance in 17 is 2.6792(9) A. 

In Table V are shown overall changes of enthalpies and entropies of formation of the ammine and ethylenediamine complexes of zinc(II), cadmium(II) and copper(II) ions, together with the lengths and frequencies of the totally symmetric vibration of the M N bonds. 

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