Three-dimensional iron-series coordination networks based on antiferromagnetic and ferromagnetic dinuclear motifs with mixed carboxylate and aqua bridges

Three coordination polymers of the iron-series transition metal ions with 4-(3-pyridyl)benzoic acid (4,3-Hpybz) ligand were synthesized and structurally and magnetically characterized. They have the formulas [M-2(4,3-pybz)(4)(H2O)] (M = Fe, 1; Co, 2; and Ni, 3). In these isomorphous compounds, octahedrally coordinated metal ions are linked by the mixed (mu-syn, syn-COO)(2)(mu-H2O) triple bridges to give dinuclear motifs, which serves as tetrahedral building units and are further linked by 4,3-Hpybz to give rise to diamond networks. Magnetic studies demonstrated that the (COO)(2)(H2O) triple bridges induce antiferromagnetic coupling between metal ions in 1 and 2, but compound 3 with the same mixed triple bridges exhibits ferromagnetic coupling, which may be related to orbital countercomplementarity. (C) 2010 Elsevier B. V. All rights reserved.