Expanding Family of Litharge-Derived Sulfate Minerals and Synthetic Compounds: Preparation and Crystal Structures of [Bi2CuO3]SO4 and [Ln2O2]SO4 (Ln = Dy and Ho)

Abstract

During the last decades, layered structures have attracted particular and increasing interest due to the multitude of outstanding properties exhibited by their representatives. Particularly common among their archetypes, with a significant number of mineral and synthetic species structural derivatives, is that of litharge. In the current paper, we report the structural studies of two later rare-earth oxysulfates, [Ln2O2]SO4 (Ln = Dy, Ho), which belong indeed to the grandreefite family, and a novel compound [Bi2CuO3]SO4, which belongs to a new structure type and demonstrates the second example of Cu2+ incorporation into litharge-type slabs. Crystals of [Bi2CuO3]SO4 were obtained under high-pressure/high-temperature (HP/HT) conditions, whereas polycrystalline samples of [Ln2O2]SO4 (Ln = Dy, Ho) compounds were prepared via an exchange solid-state reaction. The crystal structure of [Bi2CuO3]SO4 is based on alternation of continuous [Bi2CuO3]2+ layers of edge-sharing OBi2Cu2 and OBi3Cu tetrahedra and sheets of sulfate groups. Cu2+ cations are in cis position in O5Bi2Cu2 and O6Bi2Cu2 oxocentered tetrahedra in litharge slab. The crystal structure of [Ln2O2]SO4 (Ln = Dy, Ho) is completely analogous to those of grandreefite and oxysulfates of La, Sm, Eu, and Bi.