Synthesis and characterization of diethylmethylene diphosphonato metal complexes

Abstract

Reactions of tetraethylmethylene diphosphonate (TEMDP) with metal chlorides at elevated temperatures lead to the formation of complexes of the types M( L)( LH)( M = Al, Ti, V, Cr, Fe, Dy); M( L)( LH) 2( M = Th, U) and M 2( L)( LH) 2 ( M = Co, Ni), where L is the diethylmethylene diphosphonato (DEMDP) ligand. The new complexes are insoluble in all common organic solvents and do not melt or decompose at temperatures up to 300–350°C; furthermore, the Ti(III), V(III), Cr(III), Fe(III) and U(IV) complexes exhibit subnormal magnetic moments. These properties are strongly in favor of polynuclear structures. Spectral and magnetic studies suggest that the M(III) complexes are distorted octahedral, the M(II) compounds pentacoordinated, with a low symmetry square pyramidal configuration, and the M(IV) complexes octa- or ennea-coordinated. DEMDP acts as a tridentate bridging ligand, involving an uncoordinated PO group, whereas its monoprotonated derivative also acts as tridentate in the M(III) complexes; in the M(II) and M(IV) complexes one LH ligand acts as tridentate, while the other is, most probably, bidentate. Possible structures for the new complexes and the nature of the synthetic reactions are discussed.