Calcium coordination compounds of anionic forms of hydrogen dipicolinate and quinolinate: synthesis, characterization, crystal structures and DFT studies

Two calcium coordination compounds [Ca(2,6-Hpdc) 2 (H 2 O) 2 ] 1 and [Ca 2 (2,3-pdc) 2 (H 2 O) 6 ] n 2 (where 2,6-H 2 pdc = 2,6-pyridinedicarboxylic acid and 2,3-H 2 pdc = 2,3-pyridinedicarboxylic acid) were grown at room temperature. The compounds were characterized using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis, powder X-ray diffraction and single crystal X-ray crystallographic analysis. The structures of both compounds are stabilized by a network of hydrogen bonds arising from coordinated water molecules and carboxylate groups. Computational analysis revealed that compound 1 has a large energy gap (9.221 eV), suggesting high excitation energies and chemical hardness making it a better electron acceptor while compound 2 displayed a smaller energy gap (5.156 eV), which is indicative of a softer molecule with better polarizability and reactivity.