Synthesis, Structure, and Characterization of Two New Layered Mixed-Metal Phosphates, BaTeMO₄(PO₄) (M = Nb⁵⁺ or Ta⁵⁺)

Two new isostructural mixed-metal phosphates, BaTeMO4(PO4) (M = Nb5+ or Ta5+), have been synthesized as bulk phase powders and single crystals by standard solid-state techniques using BaCO3, TeO2, Nb2O5 (or Ta2O5), and NH4H2PO4 as reagents. The materials have novel layered crystal structures consisting of [M5+O6/2]- corner-sharing octahedral chains that are connected to [Te4+O4/2]0 polyhedra and [P5+O2/1O2/2]- tetrahedra. The Ba2+ cations reside between the layers and maintain charge balance. The Te4+ cations are in asymmetric coordination environments attributable to their lone pairs. The Nb5+ distorts along the local C4 direction of its octahedron resulting in a “short−long−short−long” Nb−O−Nb bond motif. The Nb5+ cation displaces away from the oxide ligands that are bonded to Te4+ or P5+ cations, attributable to the structural rigidity of the TeO4 and PO4 polyhedra. Thus, the TeO4 and PO4 polyhedra support and reinforce the intraoctahedral distortion observed within the NbO6 octahedra. Infrared and Raman spectroscopy, thermogravimetric analysis, and ion-exchange experiments are also presented. Crystal data: BaTeNbO4(PO4), orthorhombic, space group Pbca (No. 61), with a = 6.7351(9) Å, b = 7.5540(10) Å, c = 27.455(4) Å, V = 1396.8(3) Å3, and Z = 8; BaTeTaO4(PO4), orthorhombic, space group Pbca (No. 61), with a = 6.734(2) Å, b = 7.565(3) Å, c = 27.435(9) Å, V = 1372.6(8) Å3, and Z = 8.本研究通过标准固相合成法，以碳酸钡（BaCO₃）、二氧化碲（TeO₂）、五氧化二铌（Nb₂O₅，或五氧化二钽Ta₂O₅）以及磷酸二氢铵（NH₄H₂PO₄）为反应物，成功合成了两种同构的新型混合金属磷酸盐BaTeMO₄(PO₄)（其中M为五价铌Nb⁵+或五价钽Ta⁵+），产物涵盖本体相粉末与单晶两种形态。 该类材料具有新颖的层状晶体结构：由[M⁵+O₆/₂]⁻共顶点八面体链构成，该链与[Te⁴+O₄/₂]⁰多面体以及[P⁵+O₂/₁O₂/₂]⁻四面体相连。二价钡阳离子（Ba²+）位于层间区域，起到维持电荷平衡的作用。 四价碲阳离子（Te⁴+）因存在孤对电子，呈现不对称的配位环境。五价铌阳离子（Nb⁵+）沿其八面体的局域C₄轴发生畸变，形成“短-长-短-长”型的Nb-O-Nb键结构基元。由于TeO₄与PO₄多面体具有结构刚性，五价铌阳离子会偏离与四价碲或五价磷相连的氧配体位点。因此，TeO₄与PO₄多面体可支撑并强化NbO₆八面体内部的八面体畸变。 本研究同时对样品进行了红外光谱、拉曼光谱、热重分析以及离子交换实验表征。 晶体学数据：BaTeNbO₄(PO₄)属于正交晶系，空间群为Pbca（编号61），晶胞参数a=6.7351(9) Å，b=7.5540(10) Å，c=27.455(4) Å，晶胞体积V=1396.8(3) ų，Z=8；BaTeTaO₄(PO₄)同样属于正交晶系，空间群为Pbca（编号61），晶胞参数a=6.734(2) Å，b=7.565(3) Å，c=27.435(9) Å，晶胞体积V=1372.6(8) ų，Z=8。