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

Three, PO43–/HPO42– and AsO43–-incorporated, new tetranuclear
complexes of copper­(II) and zinc­(II) ions have been synthesized and
fully characterized. In methanol–water, reactions of H3cpdp (H3cpdp = 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/Na2HPO4·2H2O or KOH/Na2HAsO4·7H2O lead to the isolation of the tetranuclear complexes Na3[Cu4(cpdp)2(μ4-PO4)]­(OH)2·14H2O (1)
and K2[Cu4(cpdp)2(μ4-AsO4)]­(OH)·162/3H2O (2), 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 (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 [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 PO43–/HPO42–/AsO43– 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.