Copper(II) carboxylates with 2-aminopyridine. Synthesis, cahracterization and a study of the dimer-monomer equilibrium in acetonitrile solutions by VIS-spectroscopic and microcalorimetric titrations

摘要

A series of COpper(II) carboxylates with 2-aminopyridine was prepared. In all cases typical dinuclear complexes with a paddle-wheel type structure, CU_2X_4L_2 , as well as mononuclear complexes of type CuX_2L_2 were obtained (X = hexanoate, heptanoate, octanoate or nonanoate, L = 2-aminopyridine). The structures of monoclinic CU_2(O_2CC_7H1S)_4(CsH_6N_2h, I, and CU(O_2CC_7H1Sh(CsH_6N_2h ,2, were determined by X-ray diffraction. VIS-absorption spectroscopic and isothermal calorimetric titrations, were employed to investigate the dimer-monomer equilibrium in acetonitrile solutions. The results were analysed on the basis of the mass-action model to obtain the equilibrium constants of monomer formation (KM ~ 104 L mol-l). The thermodynamic analysis shows that for all studied systems monomer formation is an enthalpy-driven process (#DELTAH_M~o approx= -14 kj mol~(-1)). The observed exothermic #DELTA#H~ovalues result most likely from the attractive coordinative interactions between CU~(2+) ion and 2-aminopyridine.