Carboxylato-bridged polymeric complexes of chromium(III) with the hexadentate (±)-1,3-pentanediamine-N,N,N′,N′-tetraacetate ligand carrying different counter ions. Stereospecific formation and crystal structures of Na[Cr(1,3-pndta)]·H2O, K[Cr(1,3-pndta)]·H2O and Ca[Cr(1,3-pndta)]2·4H2O

Abstract

A series of Na+, K+ and Ca2+ salts of chromium(III) complexes with the hexadentate (±)-1,3-pentanediamine-N,N,N′,N′-tetraacetate (1,3-pndta) ligand was evaluated. The extent of distortion exhibited in the geometry of these octahedral complexes was computed and related to the configuration at the metal center and the ligand stereogenic center. The materials have been used to investigate the effect of the counter ion and the diamine ring substitution on the self organization and degree of hydration of these molecules in crystals. Various modes of carboxylate binding to metal atoms have been related to the formation of 3D, 2D and 1D polymeric structures. The electronic absorption and 1H NMR spectra of 1,3-pndta-Cr(III) complexes are discussed in relation to those of 1,3-pdta-Cr(III) complex (1,3-propanediamine-N,N,N′,N′-tetraacetate ion) of known structure.