Sanjeewa Liurukara D, Fulle Kyle, McMillen Colin D, Kolis Joseph W
Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Clemson, South Carolina 29634-0973, USA.
Dalton Trans. 2019 Jun 14;48(22):7704-7713. doi: 10.1039/c9dt00059c. Epub 2019 May 8.
Reactions are reported of early rare earth oxides, REO (RE = La, Pr, Nd) with TaO under hydrothermal conditions (650 °C, 1.5 kbar) in concentrated aqueous hydroxide (20-30 M KOH) as a mineralizer. Under various stoichiometries several members of two new structure types were isolated, LnTaO(OH) (Ln = La, Pr) and LnTaO(OH) (Ln = Pr, Nd). The analogous niobate LaNbO(OH) was also obtained. Both structure types were characterized by single crystal X-ray diffraction and contain pentavalent tantalatum oxide octahedra and complex rare earth oxide frameworks. The LnTaO(OH) structure type contains Ln-O and Ln-O building blocks and TaO octahedra in a 3-D framework. It contains a 3-D rare earth oxide framework formed by from zig-zag chains of rare earth oxides linking sheets of rare earth oxides. The tantalates form edge-shared TaO dimers occupying gaps in the rare earth oxide frameworks. The structure of LnTaO(OH) contains two types of 2-D rare earth oxide slabs built of seven and eight coordinate rare earth metals. The tantalate units form 2-D slabs through a multiple corner-sharing scheme of TaO octahedra. The LnTaO(OH) structure type has an interesting close structural relationship to the previously reported rare earth titanate LaTiO(OH), which is discussed. The presence of hydroxide in the lattice is confirmed by IR spectroscopy and the H atom locations are assigned unambiguously using bond valence sums.
据报道，在水热条件（650℃，1.5千巴）下，以浓氢氧化钾水溶液（20 - 30M KOH）作为矿化剂，早期稀土氧化物REO（RE = La、Pr、Nd）与TaO发生反应。在不同化学计量比下，分离出了两种新结构类型的几个成员，即LnTaO(OH)（Ln = La、Pr）和LnTaO(OH)（Ln = Pr、Nd）。还得到了类似的铌酸盐LaNbO(OH)。这两种结构类型均通过单晶X射线衍射进行了表征，且都包含五价钽氧化物八面体和复杂的稀土氧化物骨架。LnTaO(OH)结构类型在三维骨架中包含Ln - O和Ln - O结构单元以及TaO八面体。它包含一个由稀土氧化物之字形链连接稀土氧化物片层形成的三维稀土氧化物骨架。钽酸盐形成占据稀土氧化物骨架间隙的边共享TaO二聚体。LnTaO(OH)的结构包含由七配位和八配位稀土金属构成的两种二维稀土氧化物板。钽酸盐单元通过TaO八面体的多重角共享方案形成二维板。LnTaO(OH)结构类型与先前报道的稀土钛酸盐LaTiO(OH)具有有趣的紧密结构关系，对此进行了讨论。通过红外光谱证实了晶格中存在氢氧化物，并使用键价和明确确定了H原子的位置。
