Zinc iodates - Infrared and Raman spectra, crystal structure of Zn(IO3)(2)center dot 2 H2O

The zinc iodates Zn(IO3)(2).2H2O and Zn(IO3)(2) as well as alpha-Co(IO3)(2) . 2H(2)O were studied by X-ray, IR- and Raman spectroscopic methods. The cr ystal structure of the dihydrate, which is isostructural with the respectiv e cobalt compound, was determined by X-ray single-crystal studies (space gr oup P (1) over bar, Z = 2, a = 490,60(4), b = 667,31(5), c = 1088,85(9) pm, alpha = 98,855(6), beta = 91,119(7), and gamma = 92,841(6)degrees, R1 = 2, 55%, 2639 unique reflections I>2 sigma(I)). Transconfigurated Zn(IO3)(4)(H2 O)(2) octahedra are threedimensionally connected via common IO3- ions paral lel to [001] and hydrogen bonds parallel to [100] and [010], respectively. Anhydrous Zn(IO3)(2) crystallizes in space group P2(1) (Z = 2) with a = 548 ,9(2), b = 512,4(1), c = 941,8(2) pm, and beta = 90,5(3)degrees. Tac struct ure of Zn(IO3)(2) is a monoclinically distorted variant of the structures o f beta-Ni(IO3)(2) (space group P6(3)) and Co(IO3)(2) (P3). The O-H...O-IO2 hydrogen bonds of the crystallographically different H2O molecules of the d ihydrates (nu(OD) (OD stretching modes of isotopically dilute samples) 2430 , 2415, 2333 and 2300 cm(-1), Zn(IO3)(2). 2H(2)O, 90 K) are examples to the matter of fact that O...O distances are only a bad measure for the strengt h of hydrogen bonds. The infrared and Raman spectra as well as a group theo retical treatment are presented and discussed with respect to mutual exclus ion principle (possible space groups), the strength of the hydrogen bonds a nd the distortion of the IO3- ions at the C-1 lattice sites.