Octahedral complexes bond-length distortion

The ground-state distortion (Table I) from the normal octahedral geometry, i.e., the displacement of the central metal atom by up to 0.34 A toward the oxo from the plane formed by the four cyano carbon atoms, is in further agreement with this reasoning, indicative of more reactive complex with an increased metal-oxygen bond length. 

Let us start with the Ni(II) complexes of the already mentioned scorpiand diammac (6,13-diammino-6,13-dimethyl-1,4,8,11-tetraazacy-clotetradecane) in its two cis and trans conformations. In contrast to the previously mentioned chromium-, iron-, and cobalt-diammac complexes, in which the geometry of [M(fra s-diammac)]" + was substantially octahedral and that of the [M(cw-diammac)]" + was substantially trigonal prismatic, in the case of both [Nif/raws-diammac)]2+ and [Ni(m-diammac)]2 + the structural differences are attenuated and both can be viewed as more or less distorted octahedral geometries, with two sets of averaged Ni-N bond lengths of 2.07 A and 2.13 A, respectively.161 162 This is reflected by the fact that both the two complexes exhibit in aqueous solution a chemically reversible Ni(II)/Ni(III) oxidation ([Nif/raws-diammac)]2 + E° = + 0.67 V vs. SHE [Ni(m-diammac)]2 + ... 

Rhodium, Iridium. Considerable advances in the chemistry of rhodium 1,1-dithio chelates have taken place in the last 10 years. The structural prototypes for the Rh(R2Dtc)3 and Ir(R2Dtc)3 complexes are now available in x-ray structural determinations of these complexes with R2 = Et2 and Morpho. In the Rh(Et2 Dtc)3 structure (540, 537a) the RhS6 core shows only trivial deviations from D3 symmetry (Table XXI). The same distorted octahedral structure is found for the RhS6 core in the bis benzene solvate of the Rh(MorphoDtc)3 complex (96b). The mean Rh-S bond lengths in the two structures are identical (Table XXI). 

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