New mixed aluminium-chromium diarsenate

Potassium chromium aluminium diarsenate, KCr_1/4Al_3/4As₂O₇, was prepared by solid-state reaction. The structure consists of (Cr_1/4/Al_3/4)O₆ octa-hedra and As₂O₇ diarsenate groups sharing corners to build up a three-dimensional anionic framework. The potassium cations are located in wide channels running along the c-axis direction. The crystal structure is isostructural with the triclinic A^IM^IIIX₂O₇ (A^I = alkali metal; M^III = Al, Cr, Fe; X = As, P) compounds. However, the M^III octa-hedrally coordinated site is 25% partially occupied by chromium and 75% by aluminium.