Synthesis, Structure And Properties Of Novel Transition Metal Polyborates

Borates have a great of diverse of structure and outstanding physical chemistryproperties. With the coordination of oxygen, boron can form two kinds of basic unit:plane triangle BO₃and tetrahedron BO₄,which can share vertice, edge and face toconstruct different shapes and dimensional polyanionic borates, such as isolatedrings,chains, planes and three-dimensional structures. So we may search functionalmaterials which show excellent optics and magnetism behavior in the ocean oftransitional borates. In my paper, some transitional borates have been obtained bymolten boric acid method, boric acid–oxalic acid secondary synthesis method andboric acid–oxalic acid communion method. Their structures were determined by singlecrystal X-ray diffraction. The magnetism and optics of related compounds were alsostudied. An initial attempt with first principle calculations of those borates also havebeen studied.（1）Transition metal polyborates MB₁₂O₁₄（OH）₁₀（M=Mn,Fe,Zn） have beensynthesised in the boric acid–oxalic acid secondary synthesis method. Single crystalX-ray diffraction shows that these compounds crystallize in the monoclinic crystalsystem with space group P21/C, and are isostructural with MgB₁₂O₁₄OH)₁₀。Theirframework are constructed by two dimensional layers consisting of two Building BlockUnits:[B₃O₈] and [B₃O₇], and two neighboring layers are interconnected by hydrogenbonds from [B₃O₇] groups. For ZnB₁₂O₁₄OH)₁₀compound, UV-vis diffuse reflectancespectrum measurement shows a band gap of4.6eV. Electronic band structurecalculations indicate it is an insulator with the calculated band gap close to the observedone. For MnB₁₂O₁₄OH)₁₀, the magnetic susceptibility datas indicate the presence oflong-range antiferromagnetic ordering. For FeB₁₂O₁₄OH)₁₀,the magnetic susceptibilitydatas may suggest the ferromagnetic ordering which is induced by an antiferromagneticinteraction.（2） CdB₁₀O₁₉H₆was obtained by molten boric acid method. Single crystaldiffraction shows that the compound crystallize in the monoclinic crystal system withspace group P21/n, Z=4,a=7.7277,b=18.95,c=9.8616,β=91.454°. Its frameworkis constructed by two dimensional layers consisting of two Building Block Units:[B₇O₁₁（OH）₂]^3-and [B₈O₁₅（OH）₂]^8-, and two neighboring layers are interconnected byhydrogen bonds. the FBB（fundamental building block）[B₇O₁₁（OH）₂]^3-was composed of three BO₄, three BO₃, and one BO（OH）2,which was respresented by3T+4Δ. For[B8O15（OH）2]8-was composed of three BO₄, three BO₃, two BO₂OH which wasrespresented by3T+5Δ.（3）An unknown iron borate and two unknown （Mn.Co） borates were obtained byboric acid–oxalic acid secondary synthesis method and boric acid–oxalic acidcommunion method. Fe-unknown borate is isostructural with Co-unknown borate.because of the serious orientation of the growth of single crystal, we still can not resolvethe structure of the above compounds. However, for those unknown compounds, furtherresearch is underway.