Hibble Simon J., Cooper Steven P., Hannon Alex C., Patat Saban, McCarroll William H.
Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AD, U.K., ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, U.K., Department of Chemistry, Faculty of Arts and Science, University of Erciyes, Tr-38039 Kayseri, Turkey, and Chemistry Department, Rider College, 2083 Lawrenceville Road, Lawrenceville, New Jersey 08648.
Inorg Chem. 1998 Dec 28;37(26):6839-6846. doi: 10.1021/ic980313j.
The structure of the disordered lanthanum molybdate, LaMo(2)O(5), has been solved and refined using powder neutron diffraction data collected at 300 K. The average structure is described in P6(3)/mmc, a = 8.373(1) Å, c = 19.1510(1) Å, Z = 12. The compound contains two types of Mo-Mo bonded units: isolated octahedral Mo(6)O(18) clusters, and infinite molybdenum oxide sheets, formed from condensed triangular Mo(3)O(13) clusters joined together to give a total of four Mo-Mo bonds for each molybdenum. The Mo(6)O(18) clusters have 16 electrons available for metal-metal bonding and the Mo-Mo distances within the unit are 2.643(4) Å x 6 and 2.695(5) Å x 6. In the infinite sheets the molybdenum-molybdenum distances are 2.612(9) Å within one equilateral triangular cluster and 2.621(8) Å within another. Each of the molybdenum atoms in the two different Mo(3) clusters has two molybdenum neighbors from the other cluster at a distance of 2.882(6) Å. Disorder in this layered structure occurs because of interchange of layers of Mo sheets with layers of lanthanum ions. The Bragg scattering is accounted for by including layers occupied with a 50% probability by each of these structural elements and their associated oxygen atoms. A model showing how ordered subunits are stacked together to produce the average structure is presented. Extended X-ray absorption fine structure spectroscopy (EXAFS) at the Mo K-edge was used to give information on the local structure around molybdenum and to confirm that the final structural model gives a good description of Mo-O and Mo-Mo bonding.
利用在300 K下收集的粉末中子衍射数据，解析并精修了无序钼酸镧（LaMo₂O₅）的结构。其平均结构描述为P6₃/mmc空间群，a = 8.373(1) Å，c = 19.1510(1) Å，Z = 12。该化合物包含两种类型的Mo-Mo键合单元：孤立的八面体Mo₆O₁₈簇，以及由缩合的三角形Mo₃O₁₃簇连接而成的无限氧化钼片层，每个钼原子总共形成四个Mo-Mo键。Mo₆O₁₈簇有16个电子可用于金属-金属键合，单元内的Mo-Mo距离为2.643(4) Å×6和2.695(5) Å×6。在无限片层中，一个等边三角形簇内的钼-钼距离为2.612(9) Å，另一个为2.621(8) Å。两个不同的Mo₃簇中的每个钼原子都有来自另一个簇的两个钼邻居，距离为2.882(6) Å。这种层状结构中的无序是由于Mo片层与镧离子层的互换引起的。通过包含由这些结构元素及其相关氧原子以50%概率占据的层来解释布拉格散射。提出了一个展示有序亚基如何堆叠在一起以产生平均结构的模型。利用Mo K边的扩展X射线吸收精细结构光谱（EXAFS）来获取钼周围局部结构的信息，并确认最终的结构模型能很好地描述Mo-O和Mo-Mo键合。
