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)

Five coordination polymers, [Cu(L)(2)](n) (1), {[Cu(L)(Cl)(H2O)]H2O}(2n) (2), [KCu(L)(-Cl)(2)](n) (3), [Cu(L)(Br)H2O](n) (4), and {[Cu-0.5(HL)(H2O)](NO3)H2O}(2n) (5) (HL=5-methylpyrazine-2-carboxylic acid) were obtained by reactions of a pyramidal Cu-II-containing ligand, {[Cu(L)(2)(H2O)]3H(2)O}(n) (L-Cu), with Gd(ClO4)(3)6H(2)O, GdCl(3)6H(2)O, GdCl(3)6H(2)O/KCl, GdBr(3)6H(2)O, or Gd(NO3)(3)6H(2)O 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 Cu-II ions compared with L-Cu. 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.