FIVE- AND SIX-COORDINATE COMPLEXES OF TRIVALENT MANGANESE AND COBALT WITH BENZOYL HYDRAZONES

Abstract

The five- and six-coordinate dimeric manganese(III) and cobalt(III) complexes derived from benzhydrazide and salicylaldehyde(BSH), 0-hydroxyacetophenone(BAH), o-hydroxypropiophenone(BPH), o-hydroxybutyrophenone (BBH) and 2-hydroxy-1-naphthaldehyde(BNH) having the general formulae [Mn(L)X]₂ and [Co(L)(OH)H₂O]₂ (X = Cl, Br or CH₃ COO) are described. These complexes have been characterised by elemental analyses and by conductance, molecular weight, magnetic, electronic and infrared spectral measurements. The complexes of Mn(III) involve phenolic oxygen, while in Co(III) complexes hydroxyl groups are present as bridges between metal atoms as revealed by i.r. spectra. Each unit of dimeric Mn(III) complexes possesses distorted square-pyramidal shape and anions are present on the axial position. The ν(Mn-X) values are consistent with penta-coordinate stereochemistry. These complexes have subnormal magnetic moments (3.40–3.52 BM) explained in terms of antiferromagnetic exchange coupling between two adjacent paramagnetic Mn(III) atoms. The assignments in the electronic spectra of Mn(III) and Co(III) complexes have been made in terms of effective C_4v and D_4h symmetry, respectively. In both the cases the degree of distortion (DT/DQ) has been calculated by the application of Normalised Spherical Harmonic (NSH) Hamiltonian theory and discussed.