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

The complexes [Cu2(ox)(phen)2(H2O)2](NO3)2 (1), [Cu2(sq)(pmdien)2(H2O)2](ClO4)2 (2) and {[Cu3(pdc)3(4,4′-bipy)1.5(H2O)2.25] · 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 π–π 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 × 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 × 10−6 (2) and J = −1.34 cm−1 ± 0.1, g = 2.14 ± 0.01, R = 1.2 × 10−6 (3) (R defines as ∑ [ ( χ M ) obs - ( χ M ) calc ] 2 / ∑ ( χ M ) obs 2 ) .