A microporous potassium vanadyl phosphate analogue of mahnertite: hydrothermal synthesis and crystal structure

Abstract

Abstract The novel phase K2.5Cu5Cl(PO4)4(OH)0.5(VO2)•H2O was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using low-temperature (100 K) single-crystal synchrotron diffraction data and refined against F 2 to R = 0.035. The compound crystallizes in the tetragonal space group I4/mmm, with unit-cell parameters a =9.8120(8), c = 19.954(1) Å, V = 1921.1(2) Å3, and Z = 4. Both symmetrically independent Cu2+ sites show elongated square-pyramidal coordination. The V5+ ions reside in strongly distorted five-vertex VO5 polyhedra with 50% occupancy. The structure is based on a 3D anionic framework built from Cu- and V-centered five-vertex polyhedra and PO4 tetrahedra. Channels in the [100] and [010] directions accommodate large K atoms and H2O molecules. The compound is a new structural representative of the topology shown by the lavendulan group of copper arsenate and phosphate minerals. Their tetragonal or pseudotetragonal crystal structures are characterized by two types of 2D slabs alternating along one axis of their unit cells. One slab, described by the formula [Cu4 X(TO4)4]∞ (where X = Cl, O and T = As, P), is common to all phases, whereas the slab content of the other set differs among the group members. We suggest interpreting this family of compounds in terms of the modular concept and also consider the synthetic phase Ba(VO)Cu4(PO4)4 as a simplest member of this polysomatic series.