A Novel Mineral-like Copper Phosphate Chloride with a Disordered Guest Structure: Crystal Chemistry and Magnetic Properties

Abstract

Novel copper phosphate chloride has been obtained under middle-temperature hydrothermal conditions. Its crystal structure was established based on the low-temperature X-ray diffraction data: Na2 Li0.75 (Cs,K)0.5 [Cu5 (PO4)4 Cl]·3.5(H2 O,OH), sp. gr. C2/m, a = 19.3951(8) Å, b = 9.7627(3) Å, c = 9.7383(4) Å, β = 99.329(4)◦, T = 150 K, MoKα (λ = 0.71073 Å), R = 0.049. The crystal structure includes tetrameric copper clusters as the main building blocks, which are built of four CuO4 Cl pyra-mids sharing apical Cl vertices. The clusters are combined through phosphate groups and additional copper-centered polyhedra to form two mostly ordered periodic layers. between the layers and inside the framework channels, alkali ions, H2 O molecules, or OH groups are statistically distributed. Na2 Li0.75 (Cs,K)0.5 [Cu5 (PO4)4 Cl]·3.5(H2 O,OH) is a synthetic modification of a sampleite-polymorph of the lavendulan mineral group and represents a new member in a mero-plesiotype series of copper phosphates and arsenates, for which the crystal structures contain two-periodic [Cu4 X(TO4)4 ]∞ modules (T = As, P; X = Cl, O). Magnetically, this phase exhibits the phase transition at TC = 6.5 K, below which it possesses a weak ferromagnetic moment. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.