Formation of polymeric assemblies of six-coordinate metal complexes with mixed bridges of dicarboxylato-azido moieties

New biscarboxylato zwitterionic ligands, namely bis(N-carboxylatoethyl)-4,4′-dipyridinum) L1 and bis(N-carboxylatopropyl)-)-4,4′-dipyridinum) L2, were synthesized from the reaction of 4,4′-dipyridine with 3-bromopropanoic acid and 4-bromobutanoic acid, respectively. The reaction of these ligands and the azido coligand with some metal ions resulted in the formation of polymeric complexes of general formulae [Cr2(Ln)(N3)4]Cl2·H2O and [M2(Ln)(N3)4] xH2O, where (M=Mn (II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II); n=1, 2; x=1, 1, 1, 1, 0, 1, and 1, respectively.) The oxygens of the carboxylato group are coordinated to the metal ion in a bidentate fashion. The mode of bonding and overall geometry of the complexes were determined through IR, UV–VIS, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, chloride content and conductance. These studies revealed the formation of polymeric assemblies of six-coordinate complexes with distorted octahedral geometries about metal centers.