Structural Regulation,Synthesis And Properties Of Borate Fluorides With Different B-O Polymerization

This article aims to explore ultraviolet optoelectronic functional crystals.Under the guidance of the cation number effect and anion group theory,by adjusting the experimental ratio,8 new borate fluorides with various degrees of polymerization were successfully prepared using high-temperature solution method,and their structural analysis and performance characterization were carried out.One of them is a potential ultraviolet nonlinear optical crystal;4 cases are potential ultraviolet birefringent crystals;there are also 3 examples of B-O groups with high polymerization,which enrich the structural chemistry of borate fluorides.The main research includes the following two aspects:（1）Obtaining B-O groups with different degrees of polymerizationThe degree of polymerization of B-O groups may affect the properties of materials,so it is of great significance to study and obtain B-O groups with different degrees of polymerization.Based on the understanding of the theory of the cation number effect,the ratio of cation A（except boron）to the boron B,i.e.,A:B,is an important indicator that affects the degree of polymerization of B-O groups,and A:B=1 is the boundary of polymerization of B-O groups.Therefore,this article has studied the cases when A:B≥1 and A:B<1,respectively.When A:B≥1,especially when A:B>1.5,there are only[BO₃]groups in the structure,and in this system,two borate fluorides containing only isolated[BO₃]groups have been found,namely Ba₃Ca₄（BO₃）（Si O₄）F（1）and K₆Ba₅Ca₆（BO₃）₆F₁₀（2）;when it is at 1.5≥A:B≥1,[BO₃]may polymerize into[B₂O₅]groups,or there may be coexistence of[BO₃]and[B₂O₅]groups,and in this system,two examples of borate fluorides ABa Ca B₂O₅F（A=K,Rb）（3,4）with[B₂O₅]were obtained,and one case of borate fluoride Ba₃Sc₂（BO₃）₂（B₂O₅）F₂（5）with both[BO₃]and[B₂O₅]was obtained.When A:B<1,[BO₃]or[BO₄]will further polymerize into larger groups,such as[B₇O₁₄]and[B₁₂O₂₄]groups,and exploring in this system,three compounds with high polymerization B-O groups were obtained,namely Cs Ba₇Mg₂B₁₄O₂₈F₅（6）,Na₂Ba₆Ca₃B₁₂O₂₄F₈（7）and Na₃Ba₇Sc B₁₂O₂₄F₈（8）.（2）Regulation of B-O group alignment and performance characterization of materialsIn addition,the arrangement of B-O groups is also crucial for material performance.Further research has found that secondary building units[F_mA_n]have an inducing effect on the arrangement of B-O groups.When[F_mA_n]is connected into a polar chain,the polar arrangement of the groups is induced,where the microscopic polar arrangement results in noncentric structure.When[F_mA_n]is connected into a two-dimensional layer,or a coplanar double chain,the groups are induced to align in parallel.For compounds2-4,7 and 8,the B-O groups are arranged in parallel under the induction of a two-dimensional layer.For compound 5,the groups are arranged in parallel under double chain induction.When[F_mA_n]is connected into a three-dimensional framework,B-O groups are filled and arranged in the holes formed by its framework,this phenomenon can be observed in compound 8.On the basis of structural analysis,the obtained compounds were characterized for their performance and evaluated for their potential applications.Compound 1 with a frequency doubling of 0.75×KDP,with a cutoff edge less than 190 nm,is a potential ultraviolet nonlinear optical crystal.In compounds 2-5,theπconjugated[BO₃]and[B₂O₅]groups are arranged in parallel,and their birefringence is measured to be close to 0.1,and in addition,their cut-off edge is around200 nm,indicating that they are potential ultraviolet birefringent crystals.Compounds6-8 possess short cut-off edges close to 200 nm,making them potential ultraviolet optical crystals.