Seven rings, eight-coordinated binuclear chelate: [Ca2(SCZ)4(NO3)2(H2O)2]Cl2 (SCZ = semicarbazide)

A novel eight-coordinated nitrate alkaline-earth metal coordination compound [Ca-2(SCZ)(4)(NO3)(2)(H2O)(2)]Cl-2 (1, SCZ = semicarbazide) was synthesized and characterized by elemental analysis and FTIR spectroscopy. Single-crystal X-ray diffraction analysis revealed that 1 crystallizes in the monoclinic space group P2(1)/n. In 1, Ca2+ was octacoordinated with three SCZ groups, one nitrate anion and a water molecule. Noticeably, SCZ presents typical bidentate coordination and unusual tridentate coordination modes, which provides a new insight into the SCZ based coordination compounds. The nitrate anion is also coordinated with the central calcium in a bidentate fashion. Differential scanning calorimetry (DSC) indicated that 1 is thermally stable with an onset decomposition temperature of more than 600 K. The non-isothermal kinetic parameters were calculated by the Kissinger's method and Ozawa-Doyle's method. The critical temperature of thermal explosion, the entropy of activation (Delta S-not equal), the enthalpy of activation (Delta H-not equal), and the free energy of activation (Delta G(not equal)) were calculated as 646 K, 202.7 J K-1 mol(-1), 314.9 kJ mol(-1), and 185.6 kJ mol(-1), respectively. Sensitivity tests revealed that 1 is insensitive to mechanical stimuli.