Syntheses, Crystal Structures And Electronic Structures Of Novel Alkalin-Metal-Containing Borates

In this paper, four novel borates have been prepared by high temperature solution reaction, includingα-LiZnBO3, Li0.48Na0.52ZnBO3, K2NaZnB5O10, Na2KSrB5O10. Single-crystal X-ray intensity datas were collected on an automated Rigaku AFC7R four-circle diffractometer using monochromatized Mo Kαradiation. The crystal structures were solved by the SHELX-97 software, and properties of these compounds were also investigated by IR,UV-vis diffuse reflectance spectra, solid-state fluorescence spectrum and band structure calculations.α-LiZnBO3 crystallizes in the monoclinic C2/c group with a = 8.746(2) ?, b = 5.091(1) ?, c = 6.129(1) ?,β= 118.75(3)°, Z = 4 . The crystal structure is composed of tetrahedral ZnO4 and triangular BO3 groups that are arranged into a three-dimensional (3D) network by sharing O vertices. In this structure, two inversion-center related ZnO4 tetrahedra share an edge to form a Zn2O6 dimer. Each Zn2O6 dimer is linked to six others through sharing O vertices to form a 3D Zn-O framework. Boron atoms are incorporated into the triangular hollows of oxygen atoms within this network to strengthen the structure. The structure affords open six-edge channels that are occupied by Li+ cations. Band structure calculations indicate that the compound is a direct semiconductor.Li0.48Na0.52ZnBO3 crystallizes in the triclinic P-1 group with a = 5.054(1) ?, b = 6.113(1) ?, c = 8.045(2) ?,α= 75.73(2)°,β= 89.87(3)°,γ= 89.86(3)°, Z = 4. Li0.48Na0.52ZnBO3 represents a new structure type which is unknown for the borates,it is also characterized by a 3D framework, but built up from corner-sharing ZnO4 tetratahedra, ZnO5 trigonal bipyramids and BO3 triangles. Two inversion-center related [ZnO5]8- trigonal bipyramids are linked together by sharing one edge to form a [Zn2O8]12- dimer. The [Zn2O8]12- dimers are double bridged by tetrahedral Zn2+ centers through sharing two O vertices of each [ZnO4]6- tetrahedron to generate a 1D infinite 1∞[ZnO3]4- chain extending along the [010] direction. These 1∞[ZnO3]4- chains are arranged in a parallel way and further bridged by B atoms of BO3 groups, resulting in the final 3D 3∞[ZnBO3]1- framework. The structure affords open channels that are occupied by alkali metal cations. Band structure calculations indicate that the compound is a direct semiconductor.K2NaZnB5O10 crystallizes in the monoclinic C2/c group with a = 7.9244(16) ?, b = 12.805(3) ?, c = 18.962(4) ?,β= 99.39(3)°, Z = 8. The basic structural unit in K2NaZnB5O10 is a [B5O10]5- group that consists of one BO4 tetrahedron and four BO3 triangles condensed to a double ring via the common tetrahedron. Each [B5O10]5- group is linked to four different ZnO4 tetrahedra and likewise each ZnO4 tetrahedron connected to four neighboring [B5O10]5- groups throuhg sharing all of terminal O atoms to form a two-dimensional (2D) infinite∞2 [ZnB5O10]3- layer extending in the (100) plane. The layers are stacked along the b-axis, with the interlayer void spaces filled by K+ and intralayer open channels occupied by Na+ cations to balance charge. Band structure calculations indicate that the compound is an indirect semiconductor.Na2KSrB5O10 crystallizes in the triclinic P-1 group with a = 7.3900(15) ?, b = 7.6490(15) ?, c = 9.773(2) ?,α= 79.31(2)°,β= 70.85(2)°,γ= 62.09(1)°, Z = 2. The basic structural unit in Na2KSrB5O10 is a [B5O10]5- group that consists of one BO4 tetrahedron and four BO3 triangles condensed to a double ring via the common tetrahedron. The [B5O10]5- groups are arranged around crystallographic centers of symmetry to form [B10O20]10- columns. These columns are held together by K+, Na+ and Sr2+ cations via electrostatic interactions. Band structure calculations indicate that the compound is an indirect semiconductor.Li0.48Na0.52ZnBO3, K2NaZnB5O10, Na2KSrB5O10 are the first novel borate discovered, and the correct structural datas ofα-LiZnBO3 are presented. These four compounds crystallize in centrosymmetric space groups, so they aren,t NLO materials.