HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF M2Te3O8(M=Mn, Co, Ni, Cu, Zn): A SERIES OF COMPOUNDS WITH THE SPIROFFITE STRUCTURE

摘要

Several compounds isotypic to the mineral spiroffite were obtained as high quality single crystals via hydrothermal reactions. These materials, which have the general formula M2Te3O8, crystallize in the monoclinic space group C2/c and contain divalent transition metal ions and tellurite building blocks. Typical synthetic conditions for the preparation of these materials are 375 C for 3-5 d in an aqueous NH4Cl solution. This structure type is based on slabs containing Te2O6 groups joined by M cations. These Te2O6 groups are made up of two edge-sharing TeO3+1 polyhedra. The metal tellurite slabs are connected to one another through tellurium(IV) atoms, which are coordinated by four O atoms in a regular TeO4 trigonal bipyramidal configuration. A detailed structural characterization via single crystal XRD was performed on four compounds (Co2Te3O8: a=12.690(1) angstroms, b=5.211(2) angstroms, c=11.632(2) angstroms, beta=98.98(1) degrees, V=759.7(3) angstroms3, R(Rw)=0.023 (0.046); Ni2Te3O8: a=12.407(1) angstroms, b=5.207(1)angstroms, c=11.509(1) angstroms, beta=98.723(9) degrees, V=735.0(2) angstroms3, R(Rw)=0.025 (0.033); Cu2Te3O8: a=11.8368(8) angstroms, b=5.266(2) angstroms, c=12.2419(8) angstroms, beta=100.316(6) degrees, V=750.7(2) angstroms3, R(Rw)=0.025 (0.032); Zn2Te3O8: a=12.681(2) angstroms, b=5.200(2) angstroms, c=11.786(2) angstroms, beta=99.60(1) degrees, V=766.3(3) angstroms3, R(Rw)=0.031 (0.041)). The Mn analog (a=12.896(5) angstroms, b=5.398(2) angstroms, c=11.907(5) angstroms, beta=98.14(4) degrees) was identified via powder diffraction patterns. The Co, Ni, and Cu compounds were observed to have an antiferromagnetic transition by dc magnetic susceptibility measurements. The band gaps were obtained by optical diffuse reflectance spectroscopy and show that these compounds are all wide band gap materials. 43 refs.