Synthesis and Magnetism of Copper(II) Binuclear Complexes with Squarate as Bridging Ligand

The study of magnetic exchange interaction propagated by multi-atom bridging is of current interest due to insights into the pathway of electron transfer in biological systems and obtaining some useful information about designing molecule-based magnets [1]. Many papers dealing with squarate as multi-atom bridging ligand have been published [2–14], in which most squarates bridge metal ions in cis-oxygen atoms or trans-oxygen atoms. But only a limited number of articles have focused on Schiff bases as the terminal ligands [15–18]. In order to understand the influence of Schiff bases as the terminal ligands on the magnetism of the bridging metal ions, we synthesized the complex [Cu2Sq(HNAQ)2] 3H2O (Sq = squarate, HNAQ = o-hydroxyl-naphthaldehyde-8-aminoquinoline) with new Schiff base HNAQ as terminal ligand. Here we describe the complex and its magnetic property. All the starting materials were of analytical grade.Terminal ligand HNAQ was prepared according to the general method for preparing Schiff bases. The complex of [Cu2Sq(HNAQ)2] 3H2O was prepared as follows: An ethanol solution of squarate (0.0408 g, 0.358 mmol) was added to an ethanol solution of piperidinium (0.720 mmol), HNAQ (0.2136 g, 0.716 mmol) and hydrated copper perchlorate (0.2653 g, 0.716 mmol). After the mixture has been stirred and refluxed for 4 h, fine brown microcrystals were obtained, filtered and washed several times with absolute ethanol and dried under vacuum. (Found: C, 59.21; H, 3.14; N, 6.22; Cu, 14.50%. Calcd. For C44H32N4O9Cu2 : C, 59.52; H, 3.41; N, 6.31; Cu, 14.32%). C, H and N analyses were carried on a Carlo-Erba elemental analyzer, Model 1106. The copper content was determined on an Atomic absorption spectrophotometer, Model Z-8000. IR spectra were recorded with a Shimadzu-Corporation 408 IR spectrophotometer using KBr discs.The measurement of the molar conductance and the electronic reflection spectrum were performed using a DDS-11A conductometer and a UV-265 spectrophotometer, respectively. The variable temperature magnetic susceptibility was measured on a magnetic property measurement system, model MPMS-7. The elemental analyses indicated that the reaction of squarate with hydrated copper perchlorate and HNAQ yielded a binuclear complex. Polish J. Chem., 74, 729–731 (2000) COMMUNICATION