Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1185, USA.
J Am Chem Soc. 2012 Feb 8;134(5):2621-5. doi: 10.1021/ja208587e. Epub 2012 Jan 30.
Na(1.5)Ag(1.5)MoO(3)F(3) and Na(1.5)Ag(1.5)WO(3)F(3) have been synthesized by solid state reactions and structurally characterized using synchrotron X-ray and neutron powder diffraction. Unlike the vast majority of salts containing MO(3)F(3) anions (M = Mo, W) the oxyfluoride groups in Na(1.5)Ag(1.5)MoO(3)F(3) and Na(1.5)Ag(1.5)WO(3)F(3) are orientationally ordered, so that the Na(+) ions are coordinated by fluorine and the Ag(+) ions by oxygen. The resulting structure type, which has not previously been reported, is related to the LiNbO(3) structure, but the combination of Na/Ag ordering and orientational ordering of the MO(3)F(3) anions produces a supercell that doubles the c-axis and changes the space group symmetry from R3 to R3. The use of hard (Na(+)) and soft (Ag(+)) cations to direct the orientational ordering of polar oxyfluoride building units provides a new approach to the design of polar materials.
采用固态反应法合成了 Na(1.5)Ag(1.5)MoO(3)F(3) 和 Na(1.5)Ag(1.5)WO(3)F(3)，并通过同步加速器 X 射线和中子粉末衍射对其结构进行了表征。与绝大多数含有MO(3)F(3)阴离子（M = Mo，W）的盐不同，Na(1.5)Ag(1.5)MoO(3)F(3)和 Na(1.5)Ag(1.5)WO(3)F(3)中的氧氟化物基团是取向有序的，使得 Na(+)离子由氟原子配位，Ag(+)离子由氧原子配位。这种以前未曾报道过的结构类型与 LiNbO(3)结构有关，但 Na/Ag 有序和MO(3)F(3)阴离子的取向有序相结合，产生了一个超晶格，使 c 轴加倍，并将空间群对称性从 R3 变为 R3。利用硬（Na(+))和软（Ag(+))阳离子来指导极性氧氟化物结构单元的取向有序，为设计极性材料提供了一种新方法。
