Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
J Am Chem Soc. 2010 Mar 3;132(8):2802-10. doi: 10.1021/ja910103d.
The low-temperature reduction of YBaCo(2)O(5) and LaBaCo(2)O(5) with NaH to form YBaCo(2)O(4.5) and YBaCo(2)O(4.25), respectively, demonstrates that the structures of anion-deficient materials formed by such topotactic reductions can be directed by the ordering and identity of the A-site cations. YBaCo(2)O(4.5) adopts a structure consisting of a corner-shared network of square-based pyramidal CoO(5) and distorted tetrahedral CoO(4) units. The structure of LaBaCoO(4.25) is more complex, consisting of an array of square-based pyramidal CoO(5), distorted tetrahedral CoO(4), and square planar CoO(4) units. Magnetic susceptibility and variable-temperature neutron diffraction data reveal that YBaCo(2)O(4.5) adopts a G-type antiferromagnetically ordered structure below T(N) approximately 280 K. LaBaCo(2)O(4.25) also adopts antiferromagnetic order (T(N) approximately 325 K) with ordered moments consistent with the presence of square-planar, low-spin, s = 0, Co(I) centers. A detailed analysis reveals that the different anion vacancy ordered structures adopted by the two REBaCo(2)O(5-x) phases are directed by the relative sizes and ordering of the La(3+) and Y(3+) cations. This suggests that ordered arrangements of A-cations can be used to direct the anion vacancy order in topotactically reduced phases, allowing the preparation of novel metal-oxygen networks containing unusual transition metal coordination environments.
YBaCo(2)O(5)和 LaBaCo(2)O(5)与 NaH 在低温下反应，分别形成 YBaCo(2)O(4.5)和 YBaCo(2)O(4.25)，这表明通过这种拓扑还原形成的阴离子缺陷材料的结构可以通过 A 位阳离子的有序性和同一性来指导。YBaCo(2)O(4.5)采用由共角连接的正方形基三角锥形 CoO(5)和扭曲四面体 CoO(4)单元组成的结构。LaBaCoO(4.25)的结构更为复杂，由一系列正方形基三角锥形 CoO(5)、扭曲四面体 CoO(4)和正方形平面 CoO(4)单元组成。磁化率和变温中子衍射数据表明，YBaCo(2)O(4.5)在 T(N)约 280 K 以下采用 G 型反铁磁有序结构。LaBaCo(2)O(4.25)也采用反铁磁序(T(N)约 325 K)，有序磁矩与正方形平面、低自旋、s = 0、Co(I)中心的存在一致。详细分析表明，两种 REBaCo(2)O(5-x)相采用的不同阴离子空位有序结构是由 La(3+)和 Y(3+)阳离子的相对大小和有序性决定的。这表明 A 位阳离子的有序排列可以用于指导拓扑还原相中阴离子空位的有序，从而可以制备含有不寻常过渡金属配位环境的新型金属-氧网络。
