Bis(micro-ethyl pyridine-2,6-dicarboxylato)bis[diaquachlorocadmium(II)] dihydrate

The reaction of cadmium chloride with pyridine-2,6-dicarboxylic acid (PDA) and 98% H2SO4 in ethanol led to the formation of the title compound, bis[mu-6-(ethoxycarbonyl)pyridine-2-carboxylato]-1:2kappa4O6,N,O2:O2;1:2kappa4O2:O2,N,O6-bis[diaquachlorocadmium(II)] dihydrate, [Cd2(C9H8NO4)2Cl2(H2O)4].2H2O. PDA is esterified to monoethyl pyridine-2,6-dicarboxylate (MEPD) by the catalysis of H2SO4 during the reaction. The dinuclear Cd(II) complex lies about an inversion centre and the unique Cd atom has a pentagonal-bipyramidal geometry. The two Cd atoms are bridged by two carboxylate O atoms, forming a planar Cd2O2 unit. Stair-like chains are formed via O-H.Cl hydrogen bonds and these are further arranged into two-dimensional layers via hydrogen bonds involving solvate water molecules.