Syntheses, crystal and electronic structures of two new lead indium phosphates: Pb2In4P6O23 and Pb2InP3O11

Two compounds Pb2In4P6O23 and Pb2InP3O11 in the new family of lead indium phosphates were synthesized by high temperature solution growth (HTSG) method and structurally characterized by X-ray single crystal diffraction, powder diffraction and electron microscopy. Two title compounds display different types of 3D architectures with interesting tunnel structure are built up of the InO6 octahedra and PO4 tetrahedra, sharing the corners or edges, and the Pb2+ cations are sitting in the tunnel. The structure of Pb2In4P6O23 features a novel 3D open framework which can be considered as built from the layer of {In-4(P2O7)(PO4)(2)}(2-) parallel to the ac plane interconnected by bridging the single PO4. The structure of Pb2InP3O11 can be described by the assemblage of [InP2O11] units with monophosphate groups. The stereochemical activity of the Pb-II lone pair has also been discussed. The electronic band structure calculations for the two compounds have also been performed with the density functional theory method. The study of calculations and optical diffuse reflectance absorption spectrum measurement show both compounds are indirect band-gap insulators. (C) 2009 Elsevier Masson SAS. All rights reserved.