Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies

Three, PO 4 3- /HPO 4 2- and AsO 4 3- -incorporated, new tetranuclear complexes of copper(II) and zinc(II) ions have been synthesized and fully characterized. In methanol-water, reactions of H 3 cpdp (H 3 cpdp = N , N '-Bis[2-carboxybenzomethyl]- N , N '-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II) chloride in the presence of either NaOH/Na 2 HPO 4 ·2H 2 O or KOH/Na 2 HAsO 4 ·7H 2 O lead to the isolation of the tetranuclear complexes Na 3 [Cu 4 (cpdp) 2 (μ 4 -PO 4 )](OH) 2 ·14H 2 O ( 1 ) and K 2 [Cu 4 (cpdp) 2 (μ 4 -AsO 4 )](OH)·16 2 / 3 H 2 O ( 2 ), respectively. Similarly, the reaction of H 3 cpdp with zinc(II) chloride in the presence of NaOH/Na 2 HPO 4 ·2H 2 O yields a tetranuclear complex, Na(H 3 O) 2 [Zn 4 (cpdp) 2 (μ 4 -HPO 4 )]Cl 3 ·12 1 / 2 H 2 O ( 3 ). All complexes are characterized by single-crystal X-ray diffraction and other analytical techniques, such as Fourier transform infrared and UV-vis spectroscopy, thermogravimetric and electrochemical studies. The solid-state molecular framework of each complex contains two monocationic [M 2 (cpdp)] + (M = Cu, Zn) units, which are exclusively coordinated to either phosphate/hydrogen phosphate or arsenate groups in a unique mode. All three complexes exhibit a μ 4 :η 1 :η 1 :η 1 :η 1 bridging mode of the PO 4 3- /HPO 4 2- /AsO 4 3- groups, with each bridging among four metal ions. The thermal properties of all three complexes have been investigated by thermogravimetric analysis. Low-temperature magnetic studies of complexes 1 and 2 disclose moderate antiferromagnetic interactions mediated among the copper centers through alkoxide and phosphate/arsenate bridges. Electrochemical studies of complexes 1 and 2 in dimethylformamide using cyclic voltammetry reveal the presence of a fairly assessable one-electron metal-based irreversible reduction and one quasireversible oxidation couple.