Syntheses,Crystal Structures And Properties Of New Alkaline Metal And Zinc(Cadmium)-Containing Borates

In this paper,three pentaborates have been prepared by high temperature solution reaction,including KNa₂CdB₅O₁₀,Na₃Zn_0.912Cd_0.088B₅O₁₀,and Na₃Zn_0.845Mg_0.155B₅O₁₀.Single-crystal X-ray intensity data collections of all compounds were performed on an automated Rigaku AFC7R four-circle diffractometer.The crystal structures were solved by direct methods and refined in SHELX-2013 software.The properties of these three compounds were investigated by IR,UV-vis diffuse reflectance,and solid-state fluorescence spectra,respectively.Moreover,the electronic structures of KNa₂CdB₅O₁₀have also been investigated.Single crystals of KNa₂CdB₅O₁₀ were grown by the high-temperature solution reaction,using analytical grade reagents K₂B₄O₇·4H₂O,Na₂CO₃,CdO,H₃BO₃,Bi₂O₃,and PbO.The sample was first melted at 750℃,then the high-temperature solution was cooled from 750℃ to 300℃ at a rate of 0.5～5℃/h,finally single crystals of KNa₂CdB₅O₁₀ were obtained.The single-crystal X-ray structural analysis shows that it crystallizes in a new structure type with space group Pccn,a=18.4555（13）（?）,b=8.3040（10）（?）,c=12.8772（9）（?）,V=1973.5（3）（?）³,Z=8.It contains the double ring[B₅O₁₀]^5-groups composed of one BO₄ tetrahedron and four BO₃ triangles that are bridged by tetrahedrally Cd²⁺centers via common O atoms to form 2D[CdB₅O₁₀]_n^3n-layers,with A⁺（A=K/Na,Na）cations situated between and within the layers.IR spectrum confirms the existence of BO₃ and BO₄ groups.UV-VIS diffuse reflectance spectrum shows a band gap of about 3.44 eV and solid-state fluorescence spectrum exhibits a broad emission band at around 386 nm.Band structure calculations indicate that KNa₂CdB₅O₁₀ is an indirect band-gap insulator,with the calculated energy gap（3.68 eV）close to the experimental one.Crystals of Na₃Zn_0.912Cd_0.088B₅O₁₀ and Na₃Zn_0.845Mg_0.155B₅O₁₀ have been grown by using the same method as those of KNa₂CdB₅O₁₀ at 780℃ and 770℃,respectively.Their crystal structures are determined by single crystal XRD methods with the following crystal data:Na₃Zn_0.912Cd_0.088B₅O₁₀,Pbca,a=7.9407（14）（?）,b=12.293（2）（?）,c=18.0684（19）（?）,V=1763.7（5）（?）³,Z=8;Na₃Zn_0.845Mg_0.155B₅O₁₀,Pbca,a=7.8931（12）（?）,b=12.2555（12）（?）,c=18.0874（11）（?）,V=1749.7（3）（?）³,Z=8.Both of them contain the double ring[B₅O₁₀]^5-groups composed of one BO₄ tetrahedron and four BO₃ triangles that are bridged by tetrahedrally M²⁺（M=Zn/Cd,Zn/Mg）centers via common O atoms to form 2D[CdB₅O₁₀]_n^3n-layers,with Na⁺cations situated between and within the layers.IR spectra confirm the existence of BO₃ and BO₄ groups.UV-VIS diffuse reflectance spectra show band gaps of about 2.95,and 3.10 eV and solid-state fluorescence spectra exhibit emission bands at around 537,and 528 nm in turn.