Supramolecular networks of dinuclear copper(II): Synthesis, crystal structure and magnetic study

The complexes [Cu-2(ox)(phen)(2)(H2O)(2)](NO3)(2) (1), [Cu-2(sq)(pmdien)(2)(H2O)(2)](ClO4)(2) (2) and {[Cu-3(pdc)(3)(4,4'-bipy)(1.5)(H2O)(2.25)]center dot 2.5(H2O)}(n) (3) [phen = 1,10-phenanthroline; pmdien = N,N,N',N',N-pentamethyldiethylenetriamine; 4,4'-bipy = 4,4'-bipyridine; ox = oxalate dianion; sq = squarate dianion and pdc = pyridine 2,6-dicarboxylate] have been synthesized and characterized by X-ray single crystal structure determination, low. temperature magnetic measurement and thermal study. Structure determination reveals that 1 and 2 are dinuclear copper(II) complexes bridged by oxalate and squarate dianions, respectively, while 3 is a hexanuclear species formed by three Cu(pdc)(H2O)-(4,4'-bipy)-Cu(pdc)(H2O) fragments, connected through long Cu-O(pdc) bonds in a centrosymmetric arrangement. In complex 1 H-bonds occurring between the coordinated water molecules and lattice nitrate anions result in eight-membered ring clusters with the concomitant formation of 1D supramolecular chain. The adjacent chains undergo pi-pi stacking forming a 2D architecture. In the crystal of 3 an extensive H-bonding scheme gives rise to a 3D supramolecular network. Low temperature magnetic study shows a strong antiferromagnetic coupling in 1 (J = -288 +/- 2 cm(-1), g = 2.21 +/- 0.01, R = 1.2 x 10(-6)); and a very weak interaction in 2 and 3, the best-fit parameters being: J = -0.21 cm(-1), g = 2.12 +/- 0.01, R = 1.1 x 10(-6) (2) and J = -1.34 cm(-1) +/- 0.1, g = 2.14 +/- 0.01, R = 1.2 x 10(-6) (3) (R defines as Sigma[(chi(M))(obs) - (chi(M))(calc)](2)/Sigma(chi(M))(obs)(2)). (C) 2007 Elsevier B.V. All rights reserved.