Chromium(III), manganese(II) and iron(III) O,O'-bonded complexes of the para- and meta-substituted benzeneseleninic acids

A number of complexes of chromium(III), manganese(II) and iron(III) with para- and meta-substituted benzeneseleninic acids, XC6H4SeO2H (X = H, p-Cl, m-Cl, p-Br, m-Br, p-Me), are reported. The newly prepared compounds are characterized on the basis of near-i.r. and far-i.r. spectroscopy, electronic spectra and conductivity measurements, as well as by magnetochemical evidence. The wavelengths of the principal absorption peaks have been accounted for quantitatively in terms of the crystal field theory for chromium(III) and manganese(II) derivatives. The nephelauxetic parameters are all indicative of an appreciable metal-ligand covalency. The i.r. spectral data suggest that the ligands act as bidentate in seleninato-O,O' complexes and we can propose octahedral geometries with D3 symmetry for the chromium(III) and iron(III) derivatives and octahedral geometries, distorted towards D4h, for the manganese(II) complexes, in which the water has been shown to be coordinated to the metal.