Synthesis, chemical characterization and crystal structure of the (oxalato-O,O′)bis(1,10-phenanthroline)copper(II) pentahydrate

Abstract

Violet single-crystals of the complex [Cu(ox)(phen) 2]·5H 2O ( 1), where ox 2− is oxalate and phen is 1,10-phenanthroline, were obtained by slow evaporation of a solution previously prepared by dissolving Cu(ox)·1/3H 2O in a water–acetonitrile solution of phenantroline. Its crystal structure consists of neutral mononuclear [Cu(ox)(phen) 2] units and crystallization water molecules which are held together by face-to-face stacking interactions between the phenantroline aromatic rings and an extensive three-dimensional network of O w–H⋯O/O w hydrogen bonds. The copper atom is hexaco-ordinated to two oxygen atoms of a bidentate oxalato ligand and to four nitrogen atoms belonging to two phen ligands in a distorted octahedral cis arrangement. The e.p.r. Q-band spectrum of 1 shows an axial-type signal with g-tensor values of g ∥=2.28 and g ⊥=2.06, which is consistent with the axially elongated octahedral geometry of the copper(II) chromophore found in the structural work. The relation g ∥≫ g ⊥>2.0 indicates a d( x 2− y 2) ground state. Variable temperature susceptibility measurements (5–300 K) reveals the occurrence of magnetically isolated paramagnetic centers in the crystal structure. Thermal degradation of the compound 1 under synthetic air atmosphere starts between 50 and 110°C with an endothermic process attributable to the release of the crystallization water molecules.