Crystal structures of alkali-metal indium (III) phosphates of [M3In(PO4)2]n (M=K, image; M=Rb, image) compounds, and band structures and chemical bond properties of [Rb3In(PO4)2]2 crystal

Ternary indium (III) phosphates with three-dimensional frameworks, [M3In(PO4)2]n (M=K, image; M=Rb, image), are found and firstly reported in this paper. These compounds have been obtained by high temperature solid-state reactions and their crystal structures have been determined by single crystal X-ray diffraction analysis. The title compounds, which crystallize in monoclinic system, possess the same [In(PO4)2]n3n− anionic frameworks built up from interconnected InO6 octahedra and PO4 tetrahedra and have an interesting tunnel structure where M+ cations are located. Optical and bonding properties of [Rb3In(PO4)2]2 are investigated in terms of measured absorption and emission spectra, and calculated band structures and density of states. The crystal band structures obtained by the DFT method show that the solid compound of [Rb3In(PO4)2]2 is an insulator with direct band gap, and the P–O covalent bond characters are larger than the In–O ones in this compound.