2∞[Cu2(μ5-btb)(μ-OH)(μ-H2O)]: a two-dimensional coordination polymer built from ferromagnetically coupled Cu2 units (btb = benzene-1,2,3-tricarboxylate)

Hydrothermal reaction of Cu(NO3)(2).3H2O, Cd(OH)2 or Zn(OH)2 with benzene-1,2,3-tricarboxylic acid (H3btb, hemimellitic acid) produced the 2D coordination polymer (MOF) (infinity)(2)[Cu2(mu5-btb)(mu-OH)(mu-H2O)] (1) and the 2D hydrogen-bonded complexes [Cd(H2btb)2(H2O)4].2H2O (2) and [Zn(H2O)6](H2btb)(2).4H2O (3) which are characterized by single-crystal X-ray diffraction, X-ray powder diffraction and thermoanalysis. Magnetic susceptibility measurements between 1.9-300 K for 1 revealed three magnetic active exchange pathways that link the copper(II) ions through a long mu-aqua bridge, an anti-syn carboxylate bridge [j2 = 0.161(1) cm(-1)], and through a mixed mu-hydroxo + syn-syn carboxylate bridge [J = 83(1) cm(-1)]. At temperatures higher than 30 K the system behaves as isolated Cu2 units with strong ferromagnetic Cu-Cu coupling through the mu-hydroxo and syn-syn carboxylate bridge. The strong ferromagnetic coupling is explained with Hoffmann's approach by means of the concept of counter-complementarity introduced by Nishida et al.[Chem. Lett., 1983, 1815-1818].