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

Three, PO₄^3–/HPO₄^2– and AsO₄^3–-incorporated, new tetranuclear complexes of copper­(II) and zinc­(II) ions have been synthesized and fully characterized. In methanol–water, reactions of H₃cpdp (H₃cpdp = <i>N</i>,<i>N</i>′-Bis­[2-carboxybenzomethyl]-<i>N</i>,<i>N</i>′-Bis­[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper­(II) chloride in the presence of either NaOH/Na₂HPO₄·2H₂O or KOH/Na₂HAsO₄·7H₂O lead to the isolation of the tetranuclear complexes Na₃[Cu₄(cpdp)₂(μ₄-PO₄)]­(OH)₂·14H₂O (<b>1</b>) and K₂[Cu₄(cpdp)₂(μ₄-AsO₄)]­(OH)·16²/₃H₂O (<b>2</b>), respectively. Similarly, the reaction of H₃cpdp with zinc­(II) chloride in the presence of NaOH/Na₂HPO₄·2H₂O yields a tetranuclear complex, Na­(H₃O)₂[Zn₄(cpdp)₂(μ₄-HPO₄)]­Cl₃·12¹/₂H₂O (<b>3</b>). 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 [M₂(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 μ₄:η¹:η¹:η¹:η¹ bridging mode of the PO₄^3–/HPO₄^2–/AsO₄^3– 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 <b>1</b> and <b>2</b> disclose moderate antiferromagnetic interactions mediated among the copper centers through alkoxide and phosphate/arsenate bridges. Electrochemical studies of complexes <b>1</b> and <b>2</b> in dimethylformamide using cyclic voltammetry reveal the presence of a fairly assessable one-electron metal-based irreversible reduction and one quasireversible oxidation couple