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: Na2Li0.75(Cs,K)0.5[Cu5(PO4)4Cl]·3.5(H2O,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 CuO4Cl pyramids 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, H2O molecules, or OH groups are statistically distributed. Na2Li0.75(Cs,K)0.5[Cu5(PO4)4Cl]·3.5(H2O,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 [Cu4X(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.

New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XIX. Axelite, Na14Cu7(AsO4)8F2Cl2

“…No mineral or synthetic compound closely related to axelite is found in literature and databases: it represents a novel structure type. In addition, being a H-free mineral, axelite is distantly related, in both structural and chemical aspects, to lavendulan-like hydrous arsenates and phosphates [primarily Cl-bearing species mahnertite (Na,Ca,K)Cu 3 (AsO 4 ) 2 Cl⋅5H 2 O (Pushcharovsky et al , 2004), zdenĕkite NaPbCu 5 (AsO 4 ) 4 Cl⋅5H 2 O (Zubkova et al , 2003), lavendulan NaCaCu 5 (AsO 4 ) 4 Cl⋅5H 2 O and sampleite NaCaCu 5 (PO 4 ) 4 Cl⋅5H 2 O (Giester et al , 2007)] and analogous natural and synthetic compounds (Kiriukhina et al , 2022 and references therein). It is noteworthy, however, all these hydrous minerals of supergene origin differ strongly from axelite in unit-cell dimensions, powder XRD and the majority of physical properties.…”

“…In the layered structures of lavendulan (Fig. 6b), zdenekite, sampleite (Giester et al , 2007), richelsdorfite Ca 2 Cu 5 SbCl(OH) 6 (AsO 4 ) 4 ⋅6H 2 O (Süsse and Tillmann, 1987) and synthetic Na 2 Li 0.75 (Cs,K) 0.5 [Cu 5 (PO 4 ) 4 Cl]⋅3.5(H 2 O,OH) (Kiriukhina et al , 2022), Na 5 A Cu 4 (AsO 4 ) 4 Cl 2 ( A = Rb and Cs) (Hwu et al , 2002), Na 3 Cu 5 (PO 4 ) 4 F⋅4H 2 O (Yue et al , 2018) and Sr 2 Cu 5 (PO 4 ) 4 X 2 ⋅8H 2 O ( X = Cl and, Br) (Qiu et al , 2017), the neighbouring heteropolyhedral layers are shifted relative to each other. In mahnertite the neighbouring layers are connected with each other via the fifth vertices of the Cu-centred pyramids which do not belong to the [Cu 4 O 12 Cl] clusters and their bases share all vertices with AsO 4 tetrahedra linked with the clusters forming a heteropolyhedral pseudo-framework (Fig.…”