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

A series of copper(ii) carboxylates with 2-aminopyridine was prepared. In a ll cases typical dinuclear complexes with a paddle-wheel type structure, Cu 2X4L2, as well as mononuclear complexes of type CuX2L2 were obtained (X=hex anoate, heptanoate, octanoate or nonanoate, L=2-aminopyridine). The structu res of monoclinic Cu-2(O2CC7H15)(4)(C5H6N2)(2), 1, and Cu(O2CC7H15)(2)(C5H6 N2)(2), 2, were determined by X-ray diffraction. VIS-absorption spectroscop ic and isothermal calorimetric titrations, were employed to investigate the dimer-monomer equilibrium in acetonitrile solutions. The results were anal ysed on the basis of the mass-action model to obtain the equilibrium consta nts of monomer formation (K(M)approximate to 10(4) L mol(-1)). The thermody namic analysis shows that for all studied systems monomer formation is an e nthalpy-driven process (DeltaH(M)(degrees)approximate to -14 kJ mol(-1)). T he observed exothermic DeltaH(M)(degrees) values result most likely from th e attractive coordinative interactions between Cu2+ ion and 2-aminopyridine .