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

Abstract

The complexes [Cu 2(ox)(phen) 2(H 2O) 2](NO 3) 2 ( 1), [Cu 2(sq)(pmdien) 2(H 2O) 2](ClO 4) 2 ( 2) and {[Cu 3(pdc) 3(4,4′-bipy) 1.5(H 2O) 2.25] · 2.5(H 2O)} 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)(H 2O)-(4,4′-bipy)-Cu(pdc)(H 2O) 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 ) .