Hexagonal Double Perovskite Cs2AgCrCl6

The quaternary halide Cs2AgCrCl6 was prepared in the form of dark purple crystals by reaction of CsCl, AgCl, and CrCl3, at 700 degrees C. It crystallizes in the trigonal Ba2NiTeO6-type structure [space group R3m, Z = 6, a = 7.2692(4) angstrom, c = 36.443(2) angstrom] belonging to the family of perovskite polytypes containing sequences of hexagonal close-packed layers. Groups of three face-sharing octahedra, which are occupied in the sequence Ag-Cr-Ag, are connected through corner-sharing by Cr-centered octahedra. The UV/Vis/NIR diffuse reflectance spectrum shows absorptions arising from d-d transitions typical of octahedral Cr3+ complexes, as confirmed by electronic structure calculations. The compound melts at 506 degrees C. Magnetic measurements revealed simple paramagnetic behavior consistent with the presence of isolated Cr3+ ions.