Chemical significance of normalised spherical harmonic(NSH) hamiltonian and angular overlap parameters in some five- and six-coordinated trivalent chromium complexes with terdentate benzoyl hydrazones

Abstract

The five- and six-coordinate chromium(III) complexes derived from benzoylhydrazine and salicylaldehyde (BSH), o-hydroxyacetophenone (BAH), o-hydroxypropiophenone (BPH), o-hydroxybutyrophenone (BBH) and 2-hydroxy-1-naphthaldehyde (BNH) having the general formulae [Cr(L)X] 2 and [Cr(L) 2] Cl (XCl, Br or NO 3) are described. The complexes have been characterised by elemental analyses and by electrical conductance, magnetic and spectral (electronic and IR) measurements. The five-coordinated complexes are dimeric having phenolic oxygen bridges as revealed by ▪ ring vibrations in the IR. spectra at 730–745 cm −1. The v(M-X) values are consistent with five-coordinate geometry of the complexes. The low magnetic moments of five-(2.95–3.25 BM) and six-coordinate (3.80–3.90 BM) complexes have been explained in terms of antiferromagnetic exchange coupling and low symmetry components. The electronic spectra of six-coordinate complexes are consistent with tetragonal geometry of the molecule while five-coordinate complexes appear to have trigonal bipyramidal shape. Various ligand field parameters viz. Ds, Dt, Dq L and Dq Z have been evaluated and in turn have been used to calculate NSH parameters, viz. DS, DT, DQ, DQ, L and DQ Z and the degree of distortion in terms of (DT/DQ)(0.156–0.185). The electronic spectra of six-coordinate complexes have also been interpreted in terms of McClure's semi-empirical molecular orbital and orbital angular overlap model and the parameters d σ , d π , e′ σL , e′ πL , e′ σZ , e′ πZ and the ratio ( e′ σZ / e′ πZ ) pertaning to these theories have been calculated. An attempt has been made to correlate these parameters with each other and to find out their chemical significance.