Synthesis and Characterization of a New Quasi-One-Dimensional Copper(II) Phosphate, Ba2Cu(PO4)2

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Abstract
Crystals of Ba2Cu(PO4)2 have been grown in a low-temperature eutectic flux of 32% KCl and 68% CuCl (mp = 140 °C). The X-ray single-crystal structure analysis shows that this barium copper(II) phosphate crystallizes in a monoclinic lattice with a = 12.160(4) Å, b = 5.133(4) Å, c = 6.885(4) Å, β = 105.42(4)°, and V = 414.3(4) Å3; C2/m (No. 12); Z = 2. The structure has been refined by the least-squares method to a final solution with R = 0.020, Rw = 0.026, and GOF = 1.05. The framework of the title compound consists of [Cu(PO4)2]∞ linear chains with Ba2+ cations residing between these parallel chains. The chains are composed of an array of Cu2+ cations that are doubly bridged by PO4 anions. Each pair of bridging PO4 tetrahedra are in a staggered configuration above and below the CuO4 square plane, resulting in a linear chain with a long Cu---Cu separation distance, 5.13 Å (≡b). This quasi-one-dimensional framework is unusual among the Cu2+-based phosphates. Magnetic susceptibility data shows Curie−Weiss paramagnetic behavior in the range of ca. 190−300 K and a possible antiferro-to-ferromagnetic transition at ∼8 K. In this paper, the synthesis, structure, and properties of the title compound are presented. A structural comparison to a closely related vanadyl (VO)2+ phosphate, Ba2(VO)(PO4)2·H2O, as well as Na2CuP2O7 will be discussed.

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