Metal-to-ligand ratio-controlled assembly of two Ca(II) complexes: Synthesis, structures, reactant-induced reversible transformation, and catalytic properties

Hydrothermal reactions of Ca(NO3)2·4H2O and topiroxostat with different metal-to-ligand ratios yielded two new complexes {[Ca2(L)2(H2O)6]·H2O}n (1) and Ca(HL)2(H2O)4 (2) [H2L = 4-(3-(pyridine-4-yl)-1H-1,2,4-triazol-5-yl)picolinic acid], involving ligand in situ formation by hydrolysis of topiroxostat. X-ray structural analysis revealed that complex 1 has a 1D coordination polymeric structure while complex 2 displays a 0D discrete molecule. Both complexes exhibit interesting reactant-induced reversible structural transformation properties. Thermogravimetric analysis and temperature-dependent PXRD patterns indicated that the network of 1 keep high thermal stability up to 400 °C. The catalytic performance of the complexes for the solvent-free ring-opening polymerization of ε-caprolactone has been investigated.