A Series of Enthalpy/Entropy-Driven Reversible Dissolution/Reorganization Equilibriums in the System of Cu(NO3)2–HL–GdX3–H2O (HL=5-methylpyrazine-2-carboxylic acid; X=Cl, Br, NO3, ClO4)

Abstract

Five coordination polymers, [Cu(L)2]n (1), {[Cu(L)(Cl)(H2O)]·H2O}2n (2), [KCu(L)(μ-Cl)2]n (3), [Cu(L)(Br)H2O]n (4), and {[Cu0.5(HL)(H2O)](NO3)·H2O}2n (5) (HL = 5-methylpyrazine-2-carboxylic acid) were obtained by reactions of a pyramidal CuII-containing ligand, {[Cu(L)2(H2O)]·3H2O}n (LCu), with Gd(ClO4)3·6H2O, GdCl3·6H2O, GdCl3·6H2O/KCl, GdBr3·6H2O, or Gd(NO3)3·6H2O in water. Structural analysis reveals that the structures of these compounds range from a 0D block to a 2D network with modification of the environment of the CuII ions compared with LCu. Interestingly, there occurred a series of reversible dissolution/reorganization equilibriums between the initial reactants and the final products 1–5, which were determined as enthalpy/entropy driven chemical equilibriums by single crystal X-ray diffraction and microcalorimetry. In addition, the thermal stability of 1–4 and the magnetic property of 2 are discussed.