TETRASILVERMESOPERIODATE, AG4H2I2O10 - STRUCTURE AND COLOR PHENOMENON

A single-crystal X-ray structural analysis of the material previously known as ''Ag2HIO5'' has shown it to be Ag4H2I2O10, M(r) = 847.29, mon oclinic, P2(1)/n, a = 6.243(3), b = 7.247(3), c = 10.196(4) angstrom, beta = 98.00(3)-degrees, V = 456.8(3) angstrom3, Z = 2, D(x) = 6.160 g cm-3, lambda(MoK(alpha)) = 0.71069 angstrom, mu = 151.1 cm-1, F(000) = 744, T = 90K, R = 0.0570, wR = 0.0547, S = 1.85 for 898 unique obser ved reflections and 73 parameters. The dark-red crystal is composed of centrosymmetric H2I2O10(4-) ions built up of two edge-sharing IO5(OH) units. The Ag+ ions equally surrounding the anion display the coordin ation numbers 5 and 7. The shortest Ag-Ag distance is 3.321(2) angstro m, revealing the absence of any attractive Ag-Ag interaction. The geom etrical parameters obtained for the H2I2O(10)4- ion are in close accor dance with those reported for the same anion in the colorless alkaline metal salts. The color-induction phenomenon is due to considerable co valent Ag-O interaction causing a red shift of electronic transitions in the ''cation-anion complex''. (C) 1994 Academic Press, Inc.