Gd(IO3)3, type I, crystallizes in the monoclinic system with space groupP21/aand four formulas in the unit cell. The lattice constants, at 297thinsp;deg;K, area=13.4365(9),b=8.5226(5),c=7.1356(5) Aring; and bgr;=99.717(7) deg; for lgr;CuKagr;1=1.540598 Aring;. A total of 5012 independent reflections were measured on a CADhyphen;4 diffractometer, using Nbhyphen;filtered MoKagr; radiation. The crystal structure was solved using a combination of Patterson and Fourier series, and was refined by the method of least squares. The final agreement factorRis 0.033. The iodate ions form a threehyphen;dimensional network based on shared oxygen atoms, with the Gd3+ion located within a distorted dodecahedron of oxygen atoms. The three independent IOminus;3ions form triangular pyramids, with three short Indash;O bonds of average length 1.803 Aring; and average Ondash;Indash;O angle of 98.7deg;. Each I atom has three additional oxygen neighbors at distances in the range 2.741ndash;3.194 Aring; that complete its distorted octahedron. Gd(IO3)3, type I is the archetype for an isostructural family of of rarehyphen;earth iodates extending from Ce to Lu. By contrast, no more than five (including Pm) rarehyphen;earth ions are represented in any of the other five known types of anhydrous rarehyphen;earth iodates. Small variations from monotonic in the lattice constants of type I anhydrous iodates are found, as predicted by the rsquo;rsquo;tetradrsquo;rsquo; effect.
展开▼
