Substituted benzeneseleninic acids as bidentate ligands. Synthesis and spectroscopic studies of manganese (II) and iron (II) complexes

The para- and meta-substituted seleninato anion, XC6H4SeO−2, forms complexes with manganese(II) and iron(II) of the type [M(XC6H4SeO2)2(H2O)2], which have been shown to contain the bidentate ligand in seleninato-O, O′ derivatives, the water molecules being coordinated to the metals. From the electronic absorption spectra and from the magnetic susceptibility data we have proposed for all the complexes a distorted octahedral D4h symmetry. The structure of the anhydrous para- and meta-substituted benzeneseleninato complexes of manganese(II) and iron(II) have been investigated by means of electrical conductance measurements, spectral (electronic and i.r.) studies and magnetic susceptibility measurements. The anhydrous complexes are always of the seleninato-O, O′ type with the ligands tetrahedrally coordinated to the central atom. The wavelengths of the principal absorption peaks have been accounted for quantitatively in terms of the crystal field theory for manganese(II) derivatives. The nephelauxetic parameters are all indicative of an appreciable metal-ligand covalency