(Na,Li)3(Cl,OH)[Cu3OAl(PO4)3]: a first salt-inclusion aluminophosphate oxocuprate with a new type of crystal structure

Abstract

The synthesis and characterization of a first salt-inclusion aluminophosphate oxocuprate, (Na,Li)3(Cl,OH)[Cu3OAl(PO4)3], obtained as single crystals, is reported. A novel phase, with a strongly pseudo-orthorhombic structure, is described as a monoclinic crystal structure established by the study of a pseudomerohedric microtwin. It was investigated using scanning electron microscopy, microprobe analysis and low-temperature X-ray diffraction. The composite crystal structure represents an original framework assembled from Cu-centered polyhedra, AlO6 octahedra and PO4 tetrahedra with channels, which incorporate the Na/Li salt component [(Na,Li)3(Cl,OH)]2+ that ensures electroneutrality of the compound. Layers of strongly corrugated chains of Cu-centered octahedra with shared edges and linked by PO4 tetrahedra are shown to be topologically identical with the layers also built from Cu-centered polyhedra and AsO4/VO4 tetrahedra forming the crystal structure of a fumarolic mineral aleutite, (M 0.5Cl)[Cu5O2(AsO4)(VO4)] [Siidra et al. (2019). MinMag, 83, 847–853]. `Sawtooth chains' and pairs of Cu-centered octahedra inherent in the title structure may be of interest in solid-state physics, engaging studies in the field of low-dimensional and frustrated magnetism.