Growth, crystal structure and thermal properties of calcium bis(malate) dihydrate

A new coordination compound crystal of calcium with malic acid is prepared by gel aided solution growth. Single crystal X-ray diffraction studies revealed that the structural formula of the compound is Ca(C4H4O5)2·2H2O. It crystallizes in the monoclinic system with space group C2/c, Z = 4, with unit cell parameters a = 15.916(9) Å, b = 5.886(3) Å, c = 13.046(6) Å and β = 90.678(4)°. Data were collected by oscillation method and full-matrix least squares refinement was applied to the model converging to final R indices R1 = 0.0416 and ωR2 = 0.1255. Compound forms a layer-type polymeric structure, stabilized by intermolecular hydrogen bonding. Ca2+ is eight-fold coordinated. Malate is coordinated to Ca2+ tridendate-bidendate through two carboxylates and monodendate through oxygen atom of the hydroxyl group. Thermal behavior investigated using TG and DTA studies is in conformity with the proposed structure.