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.

两种新型等结构的混合金属磷酸盐，BaTeMO4(PO4)（M = Nb5+ 或 Ta5+），已通过标准的固态技术，以BaCO3、TeO2、Nb2O5（或Ta2O5）以及NH4H2PO4作为试剂，成功合成出块体相粉末和单晶。这些材料具有新颖的层状晶体结构，由[M5+O6/2]-角共享的八面体链构成，这些链与[Te4+O4/2]0多面体和[P5+O2/1O2/2]-四面体相连。Ba2+阳离子位于层间，以维持电荷平衡。Te4+阳离子处于不对称的配位环境中，这归因于其孤对电子。Nb5+沿其八面体的局部C4方向发生扭曲，形成“短-长-短-长”的Nb-O-Nb键合模式。Nb5+阳离子从与Te4+或P5+阳离子键合的氧化物配位体偏离，这归因于TeO4和PO4多面体的结构刚性。因此，TeO4和PO4多面体支撑并增强了在NbO6八面体中观察到的八面体内扭曲。此外，还介绍了红外和拉曼光谱学、热重分析和离子交换实验。晶体数据：BaTeNbO4(PO4)，正交晶系，空间群Pbca（编号61），其晶格参数为a = 6.7351(9) Å，b = 7.5540(10) Å，c = 27.455(4) Å，体积V = 1396.8(3) Å3，以及Z = 8；BaTeTaO4(PO4)，正交晶系，空间群Pbca（编号61），其晶格参数为a = 6.734(2) Å，b = 7.565(3) Å，c = 27.435(9) Å，体积V = 1372.6(8) Å3，以及Z = 8。