Exploring The Synthesis Of Borates With Nonlinear Optical Properties

Borates have extensive research and practical significance due to their rich structures,diverse species and unique properties, especially their outstanding second-order nonlinearoptical properties (NLO). It has been proved that boron atom can covalently bond to threeor four oxygen atoms to form BO3triangular or BO4tetrahedral group which can furtherlinked together through common vertices in varying ratios to build different isolated B Oclusters, which can be used as the structural building units (SBUs) to further polymerizeinto infinite chains, sheets, and frameworks, simultaneously the organic amines,alkali-alkaline earth metal captions or the transition metal complexes are act as the structuredirection agents (SDAs). Thus numerous borates with novel structures can be synthesized.The synthesis methods in this article are on the foundation of the synthesis experiments inour group before, continue to explore the synthesis of aluminoborates with nonlinearoptical properties under solvothermal conditions, finally a series of aluminoborates wereachieved successfully, and two alkali metal borates，two isolated borates were get in theprogress of exploring. These new crystals are characterized by single crystal X-raydiffraction, X-ray powder diffraction, infrared spectroscopy, ultraviolet spectroscopy andthermogravimetric analyzer. We also tested the SHG efficiency of acentric structurecrystals.This paper describes nine new borates which are synthesized under solvothermalconditions, in these nine compounds,[Zn(en)(dien)][AlB5O10](1),[Zn2(en)5][Al2B10O20](2), K7[AlO0.5Zn(BO2)(B12O21)(OH)4]·H2O (3),[Zn(en)3][AlB7O12(OH)2](4), AlB5O10Zn(en)2(5) are aluminoborates which were get in the exploring of borates with NLOproperties by adjusting the reaction conditions, and the compound1,2and4have NLOproperties, three kinds of zinc complexes in these three compounds are all act as SDAs. Thezinc atom in5is coordinated with four nitrogen atoms from ethylenediamine(en) and oneoxygen atom from ABOs frameworks which means that the Zn complexes linked to theABO structures directly, thus the special aluminoborates frameworks were get. And in thecompound3，the zinc atoms further inserted into the ABOs framework, and constructed the bilayer2D sheets framework, and the two single layers were linked through the specialAl-O-Al bonds, the sheets were connected by the K-O bonds. And the compoundNa5[B11O17(OH)5](H3O)(H2O)6(6) and Na3B5O8(OH)2·H2O (7) were also achieved insolvothermal conditions in the progress of exploring by changing the boron source intoNaBH4. The compound6have1D chains with big caves which the Na+cations reside in thecaves, the compound7have2D sheets frameworks with the Na+cations reside in the cavesof the sheets, and the1D chains and2D sheets are all stretched out into3D frameworksthrough Na-O bonds. And the compound [C4H11N2O][C4H9N2][B5O6(OH)4]2(8) and[Cd(dien)2][B5O6(OH)4]2(9) are all isolated structures, they both constructed from the[B5O6(OH)4]-unit and further extend to3-D frameworks via extensive hydrogen-bondinginteractions. Interestingly, a novel in-situ organic reaction between en and CH3COO-grouphas been observed during the formation of compound1, the intermediate product and thefinal product co-template as the SDAs in the structure1which is rare to see in the reportedborates before.Based on the former study of borates, we adopt solvothermal conditions，change thecomposition of the solvents, the temperature, pH values and some other conditions to makevaries novel borates with NLO properties, or other great properties.