Syntheresand Crystal Structures Of Novel Bismuth-containing, Lead-containing Borates

In this paper, two novel borates have been prepared by high temperature solution reaction, including BiCd₃(AlO)₃(BO₃)₄ and (Pb₃O)₂(BO₃)₂WO₄. In addition, Pb₃Bi₂(SiO₄)₃ and LiNaNb₆O₁₆ have been unexpectedly obtained during our exploratory syntheses of novel borate materials. X-ray data collections of all compounds were carried out on an automated Rigaku AFC7R four-circle diffractometer.The crystal structures were solved by direct methods and refined in SHELX-97 system and physical properties of these compounds were investigated.BiCd₃(AlO)₃(BO₃)₄ crystallizes in the hexagonal space group P6₃ with a= 10.3919(15) (?), c= 5.7215(11) (?), Z= 2. In its structure, AlO₆ octahedra share edges to form 1D 1(?) [AlO₄]5- chains that are bridged by BO₃ groups through sharing O atoms to form the 3D 3(?) [AlBO₄]^2- framework. The 3D framework affords two kinds of channels that are occupied by Bi³⁺/Cd²⁺ atoms only or by Bi³⁺/Cd²⁺ atoms together with BO₃ groups. The IR spectrum further confirmed the presence of BO3 groups. Second-harmonic-generation measurements displayed a response of about 0.5×KDP (KH₂PO₄). UV-vis diffuse reflectance spectrum showed a band gap of about 3.19 eV. Solid-state fluorescence spectrum exhibited the maximum emission peak at around 390.6 nm. Band structure calculations indicated that it is an indirect semiconductor.(Pb3O)₂(BO₃)₂WO₄ crystallizes in the orthorhombic space group Cmcm with a = 18.480(4) (?), b = 6.3567(13) (?), c = 11.672(2) (?), Z = 4. The basic structural units in (Pb₃O)₂(BO₃)₂WO₄ are BO₃ triangles, OPb₄ and WO₄ tetrahedra. Each OPb₄ octahedron is connected to two other tetrahedra through sharing corners to form one- dimensional chains . These 1(?) [Pb₃O]⁴⁺ chains are further bridged by BO₃ triangles and WO₄ tetrahedra via Pb-O bonds to form the 3D framework. The IR spectra further confirmed the presence of BO3 groups, UV-vis diffuse reflectance spectra showed a band gap of about 2.9 eV, and solid-state fluorescence spectrum indicated a broad emission band at around 337.6 nm. Band structure calculations indicated that it is a direct semiconductor.Pb₃Bi₂(SiO₄)₃ crystallizes in the hexagonal space group P6₃/m with a = 9.6909(14) (?), c = 7.1886(14) (?), Z = 2. The basic structural units in Pb₃Bi₂(SiO₄)₃ are SiO₄ tetrahedra. The SiO₄ octahedra are connected to Pb²⁺ and Bi³⁺ ions to form the 3D framework. The calculated band structure of Pb₃Bi₂(SiO₄)3 indicates that it is an indirect semiconductor, resulting in an indirect energy gap of 1.703eV. Most of the O 2p character is concentrated in the valence band maximum (VBM) and the conduction band minimum (CBM) is controlled by Bi 6p states.LiNaNb₆O₁₆ crystallizes in the orthorhombic space group Amm² with a = 3.9490(8) (?), b = 10.180(2) (?), c = 14.759(3) (?), Z = 1. The basic structural units in LiNaNb6O16 are NbO6 octahedra and NbO7 pentagonal bipyramids. NbO6 octahedra share O atoms to form 1D chains that are bridged by NbO₇ groups through sharing edges to form the 3D framework.The calculated band structure of Pb₃Bi₂(SiO₄)₃ indicates that it is an indirect semiconductor, resulting in an indirect energy gap of 1.318eV, The VBM is controlled by O 2p states and the CBM is controlled by Nb 4d states.In addition, BiCd₃(AlO)₃(BO₃)₄ and LiNaNb₆O₁₆ crystallize in noncentro- symmetric space groups, and the two compound may be nonlinear optical (NLO) materials.