The pressure-stabilized polymorph of indium triiodide

A layered rhombohedral polymorph of indium(iii) triiodide is synthesized at high pressure and temperature. The unit cell symmetry and approximate dimensions are determined by single crystal X-ray diffraction. Its R3 crystal structure, with a = 7.214 angstrom, and c = 20.47 angstrom, is refined by the Rietveld method on powder X-ray diffraction data. The crystal structure is based on InI6 octahedra sharing edges to form honeycomb lattice layers, though with considerable stacking defects. Different from ambient pressure InI3, which has a monoclinic molecular structure and a light-yellow color, high pressure InI3 is layered and has an orange color. The band gaps of both the monoclinic and rhombohedral variants of InI3 are estimated from diffuse reflectance measurements. A layered rhombohedral polymorph of indium(iii) triiodide is synthesized at high pressure and temperature. It has an orange color, which is different from ambient pressure InI3, which has a monoclinic molecular structure and a light-yellow color.