(Na,Li) 3 (Cl,OH)[Cu 3 OAl(PO 4 ) 3 ]: a first salt-inclusion aluminophosphate oxocuprate with a new type of crystal structure.

The synthesis and characterization of a first salt-inclusion aluminophosphate oxocuprate, (Na,Li) 3 (Cl,OH)[Cu 3 OAl(PO 4 ) 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, AlO 6 octahedra and PO 4 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 PO 4 tetrahedra are shown to be topologically identical with the layers also built from Cu-centered polyhedra and AsO 4 /VO 4 tetrahedra forming the crystal structure of a fumarolic mineral aleutite, (M 0.5 Cl)[Cu 5 O 2 (AsO 4 )(VO 4 )] [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.