Metal complexes of vitamin B6related compounds. Crystal and molecular structures of aqua(5′-phosphopyridoxylideneglycinato)copper(II) trihydrate and bis(pyridoxylideneglycinato)nickel(II) hexahydrate

Abstract

The crystal structures of two Schiff-base metal complexes, aqua (5′-phosphopyridoxylideneglycinato)copper(II) trihydrate, [Cu(P-Pxd-Gly)(H2O)]·3H2O (1), and bis(pyridoxylideneglycinato)nickel(II) hexahydrate, [Ni(Pxd-Gly)2]·6H2O (2), have been determined using single-crystal X-ray diffraction methods. Compound (1) crystallizes in space group P with a= 8.394(4), b= 9.819(8), c= 10.884(7)A, α= 101.85(6), β= 97.48(5), γ= 112.60(5)°, and Z= 2; compound (2) crystallizes in space group Pnna with a= 20.233(3), b= 19.423(3), c= 13.956(3)A, and Z= 8. The structures were solved by the heavy-atom method and refined to R values of 0.064 and 0.129 respectively. The CuII ion has a square-pyramidal geometry in compound (1) with phenolic oxygen, imine nitrogen, and carboxylate oxygen atoms of the Schiff-base ligand and a water molecule as basal donors. The compound is a one-dimensional polymer due to the axial coordination of one of the phosphate oxygens of a neighbouring molecule. The two tridentate Schiffbase ligands provide an octahedral geometry around the NiII ion in compound (2).The nearplanarity of the ligand in compound (1) and non-planarity in compound (2) are discussed in terms of the relative reactivities.