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(μ-cbdca)(H2O)]n (1) (cbdca = cyclobutanedicarboxylate), [Cu2(μ-cbdca)2(μ-bipy)2]n (2) (bipy = 4,4‘-bipyridine), [Cu(μ-cbdca)(μ-bpe)]n (3) (bpe = 1,2-bis(4-pyridyl)ethane), [Cu(μ-cbdca)(bpy)]2 (4) (bpy = 2,2‘-bipyridine), [Cu(terpy)(ClO4)]2(μ-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 π−π 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.