Rodriguez Efrain E, Poineau Frédéric, Llobet Anna, Czerwinski Ken, Seshadri Ram, Cheetham Anthony K
Manuel Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Inorg Chem. 2008 Jul 21;47(14):6281-8. doi: 10.1021/ic8003273. Epub 2008 Jun 24.
Two new oxides have been unambiguously identified as Bi2Tc2O7-delta with delta = 0.14(1) and Bi3TcO8 through X-ray absorption near-edge structure spectroscopy and neutron powder diffraction. The compound Bi2Tc2O7-delta has a cubic pyrochlore-type structure with a = 10.4746(1) A, space group Fd3m (origin choice 2), and Z = 8. The compound Bi3TcO8 is also cubic, a = 11.5749(1) A, space group P2(1)3, Z = 8, and has a fluorite-related crystal structure. In Bi2Tc2O7-delta the Tc(IV) cations are octahedrally coordinated, whereas in Bi3TcO8 the Tc(VII) cations are tetrahedrally coordinated. A third new phase, probably Bi3Tc3O11, could not be obtained pure, but preliminary X-ray powder diffraction data affords a primitive cubic lattice with a = 9.3433(1) A. On the basis of structural similarities between Bi2Tc2O7-delta and closely related oxides, Bi2Tc2O7-delta is expected to be a metallic oxide with Pauli paramagnetism. Electronic structure calculations of both Bi2Tc2O7-delta and Bi3TcO8 further support metallic conductivity in the former and insulating behavior in the latter. The inert pair effect of the Bi cations on the crystal structures of Bi2Tc2O7-delta and Bi3TcO8 is also described. In addition, calculations of the valence electron localization function for Bi2Tc2O7-delta and Bi3TcO8 provide further visualization of the Bi 6s(2) lone pair electrons in the real space of the crystal structures.
通过X射线吸收近边结构光谱和中子粉末衍射，已明确鉴定出两种新氧化物，分别为δ = 0.14(1)的Bi2Tc2O7-δ和Bi3TcO8。化合物Bi2Tc2O7-δ具有立方焦绿石型结构，a = 10.4746(1) Å，空间群Fd3m（原点选择2），Z = 8。化合物Bi3TcO8也是立方结构，a = 11.5749(1) Å，空间群P2(1)3，Z = 8，具有萤石相关的晶体结构。在Bi2Tc2O7-δ中，Tc(IV)阳离子呈八面体配位，而在Bi3TcO8中，Tc(VII)阳离子呈四面体配位。第三个新相，可能是Bi3Tc3O11，无法得到纯品，但初步的X射线粉末衍射数据给出了一个原始立方晶格，a = 9.3433(1) Å。基于Bi2Tc2O7-δ与密切相关氧化物之间的结构相似性，预计Bi2Tc2O7-δ是一种具有泡利顺磁性的金属氧化物。对Bi2Tc2O7-δ和Bi3TcO8的电子结构计算进一步支持了前者的金属导电性和后者的绝缘行为。还描述了Bi阳离子对Bi2Tc2O7-δ和Bi3TcO8晶体结构的惰性对效应。此外，对Bi2Tc2O7-δ和Bi3TcO8的价电子定位函数的计算提供了Bi 6s(2)孤对电子在晶体结构实空间中的进一步可视化。
