Combined effects of diamines and carboxylate bridges on structural and magnetic properties of a series of polynuclear copper(II) complexes with 1,1-cyclobutanedicarboxylic acid

Six new copper(II) complexes of formula Cu(mu-cbdca)(H2O)]n (1) (cbdca = cyclobutanedicarboxylate), Cu2(mu-cbdca)2(mu-bipy)2]n (2) (bipy = 4,4'-bipyridine), Cu(mu-cbdca)(mu-bpe)]n (3) (bpe = 1,2-bis(4-pyridyl)ethane), Cu(mu-cbdca)(bpy)]2 (4) (bpy = 2,2'-bipyridine), Cu(terpy)(ClO4)]2(mu-cbdca).H2O (5) (terpy = 2,2':6',2' '-terpyridine), and Cu(cbdca)(phen) (H2O)].2H2O (6) (phen = 1,10-phenanthroline) were obtained and structurally characterized by X-ray crystallography. Complex 1 is a two-dimensional network with a carboxylate bridging ligand in syn-anti (equatorial-equatorial) coordination mode. Complexes 2 and 3 are formed by chains through syn-anti (equatorial-apical) carboxylate bridges, linked to one another by the corresponding amine giving two-dimensional nets. Complexes 4 and 5 are dinuclear, with the copper ions linked by two oxo (from two different carboxylate) bridging ligands in 4 and with only one carboxylate showing the unusual bis-unidentate mode in complex 5. Complex 6 is mononuclear, with the carboxylate linked to copper(II) in a chelated form. Intermolecular hydrogen bonds and pi-pi stacking interactions build an extended two-dimensional network. Magnetic susceptibility measurements of complexes 1-5 in the temperature range 2-300 K show the occurrence of weak ferromagnetic coupling for 1 and 4 (J = 4.76 and 4.44 cm(-1), respectively) and very weak antiferromagnetic coupling for 2, 3, and 5 (J = -0.94, -0.67, and -1.61 cm(-1), respectively). Structural features and magnetic values are compared with those reported for the similar copper(II) malonate and phenylmalonate complexes.