86785-19-5Relevant articles and documents
Coordination chemistry of microbial iron transport compounds. 25. Proton-dependent cobalt (III) spin states. Structure of the sodium salt of trans-tris(benzohydroximato)cobaltate(III)
Abu-Dari, Kamal,Barclay, Susan J.,Riley, Paul E.,Raymond, Kenneth N.
, p. 3085 - 3089 (2008/10/08)
Complexes of cobalt(III) with hydroxamic acids [RC(O)N(OH)R′] are described. Coordination occurs through the two oxygen atoms after the loss of the NOH proton. For tris(hydroxamate) complexes with R′ = alkyl the complexes are low spin; when R′ = H or when R contains an electron-withdrawing group, the complexes are paramagnetic. However, the tris(hydroximato)cobaltate(III) trianion complexes, which result from further deprotonation of the hydroxamate complexes when R′ = H, are low spin. Thus there is a reversible, proton-dependent transition between low- and high-spin states in the hydroximate and hydroxamate complexes. An unusual feature of the Co(III) complexes is that, while the low-spin hydroximato [CoL3]3- complex is thermally stable, the high-spin hydroxamato [Co(HL)3]0 complex ultimately undergoes an internal redox reaction resulting in oxidation of the ligand by the metal ion. The structure of the (nitrogen deprotonated) trans isomer of tris(benzohydroximato)cobaltate(III), as the salt Na3[Co(C7H5NO2) 3]·8H2O·C2H5OH, has been determined by single-crystal X-ray diffraction techniques with data obtained by counter methods. The material crystallizes as dark green prisms in the monoclinic space group P21/n with a = 10.360 (1) A?, b = 11.118 (2) A?, c = 28.403 (5) A?, β = 93.64 (1)° and is isostructural with the previously reported Cr(III) complex. The Co(III) complex possesses a trans geometry in which the OC and ON atoms of one chelate ring are trans to an OC and an ON atom of one of the other two chelate rings. The coordination geometry about Co(III) approximates that of a trigonally distorted octahedron. As in the structure of the Cr(III) complex, the lengthening of the C-O bonds and the shortening of the C-N bonds indicate that much of the negative charge on the deprotonated nitrogen atoms is delocalized over the N-C=O portions of the ligands. The calculated (1.47) and measured (1.44 g cm-3) densities are consistent with four formula units of the salt per unit cell. Full-matrix least-squares refinement of the structure with use of the 3906 reflections with F02 > 3σ(F02) have converged with R and Rw indices of 0.035 and 0.048, respectively.
