Synthesis, Structures And Properties Of Galloborates Under Surfactants-Thermal Condition

Borates are of current interest because of various applications in nonlinear-optical (NLO) materials, luminescence materials, catalysis and ion exchange. Boron atoms can be three- and four-coordinated with O atoms to form diverse polyborate clusters from [B3O3(OH)4]- to [B18O36]18- via corner-or edge-sharing oxygen atoms. Ga3+ has a similar outer electronic configuration to B3+, which may adopt different coordination geometries, such as GaO4 tetrahedron, GaO5 trigonal bipyramid and GaO6 octahedron. The introduction of GaOn groups can also give rise to numerous novel galloborates constructed by B-O clusters and Ga-O clusters. Previous studies mainly use the boric-acid flux method, high temperature solid-state method and hydro/solvothermal method to synthesize new galloborate materials. Therefore, new strategies for growing crystalline galloborate materials are of great importance.In this paper, a novel galloborate, BaGa(B4O8)(OH)·(H2O) (1) has been synthesized under hydrothermal condition. Three new galloborates, namely, Na4Ga3B4O12·OH (2), Na7Ga2B13O24(OH)4 (3) and Na3GaB4O9 (4), have been obtained through surfactant-thermal method. Their structures were determined by single-crystal X-ray diffraction and characterized by powder X-ray diffraction, thermogravimetric analysis, FTIR, UV-vis-NIR diffuse reflectance spectra and photoluminescence analyses.Compound 1 displays porous layers composed of GaB4O11(OH) clusters. Each GaB4O11(OH) cluster links to four nearest neighbors giving rise to an galloborate sheet. The two adjacent layers are further linked by Ga-O bonds to give porous layers, while Ba2+ cations and water molecules are located in the interlayer space. The framework of 1 can be reduced into a rare 5-connected net with a Schlafli symbol of (4862). Compound 1 emits blue luminescence with strong emissions around 437 nm when excited at 370 nm. The decay lifetime is 2.95 ns.Compound 2 crystallizes in acentric space group F43c . Its structure is characteristic of Ga6B4O24 octahedral cages. Each Ga6B4O24 cage links to six nearest neighbors generating 3D framework with 3D tunnels where filled by Na+ ions and hydroxys. The framework of 2 can be reduced into a NaCl type topology with a Schlafli symbol of (4966). Compound 2 emits intense blue light with strong emissions around 544 nm when excited at 277 nm. The decay lifetime is 22.65 ns. It also exhibits week SHG reponse about 0.1 times that of KDP.Compound 3 contains two kinds of boron clusters:{B3} and {B7}. Each {B3} links to three GaO4 generating a galloborate double chain, and each {B7} links to four nearest neighbors giving a borate sheet. The chains and sheets connecte to each other alternately forming a novel 3D network. Na+ ions are located in the space. Compound 3 emits intense blue luminescence with strong emissions around 500 nm when excited at 274 nm. The decay lifetime is 28.44 ns.In the structure of 4, each GaO4 links with four B4O8 clusters and vice versa, resulting in a 2D sheet. Na+ ions are located in the interlayer space. Compound 4 emits blue light with emissions around 450 nm when excited at 360 nm. The decay lifetime is 6.66 ns.The work of this paper enriches the contents of synthetic and structural chemistry in borates, and opens up a new path to prepare functional borates materials, which are of significance to the exploitation of the borates materials.