Polynuclear diorgano-phosphato and -phosphonato metal complexes: Characterization studies and physicochemical correlations

Abstract

A series of new and previously reported M(III) ( M = Al, Ti, V, Cr, Fe, Dy) and M(IV) ( M = Th, U) polynuclear (-O-P-O-bridged) complexes with several diorgano-phosphato and -phosphanato ligands ( n- and iso-alkyl-, aralkyl- or aryl-substituted) were prepared and characterized by means of spectral, magnetic and X-ray powder diffraction studies. Spectral data ( V POO, V M−O , Dq) were correlated to the σδ substituent constant (Hammett constants, as modified by Kabachnik for organophosphorus compounds). Linear V POO (asym) vs σδ plots were obtained; the V POO (asym) frequency increases with decreasing ligand-field strength. The V M−O vs σδ plots are considerably more complicated in the cases of 3 d metal ion than in Al(III) or Dy(III) complexes; Dq vs σδ plots for Ti(III) and V(III) complexes are also complicated. The non-linear trends observed in 3 d metal ion V M−O or Dq vs σδ plots are discussed in terms of the combination of inductive and steric effects in determining the degree of metal-ligand back-donation. The subnormal magnetic moments of several M(III) ( M = Ti, V, Cr, Fe) and U(IV) complexes suggest that the 3 d or 5 f electrons of these metal ions participate in magnetic exchange. The Dy(III) complexes are magnetically normal, as expected.