MAGNESIUM IODATE DECAHYDRATE MG(IO3)(2)CE NTER-DOT-10H(2)O - CRYSTAL-STRUCTURE, RAMAN-SPECTRA, THERMAL-DECOMPOSITION, LONE-PAIR RADIUS OF IODINE(V)

Mg(IO3)(2) . 10H(2)O crystallizes in the triclinic space group <P(1)ov er bar> (a = 654.25(9), b = 1109.8(2), c = 1176.7(2)pm; alpha = 105.47 0(8), beta = 104.086(8), gamma = 101.744(8)degrees; Z = 2). The struct ure has been determined by single-crystal X-ray diffraction at 273 K, and refined to a final R value of 0.0272 for 4372 observed reflections (I > 2 sigma(I)). The magnesium ions are coordinated to six different H2O molecules forming a slightly distorted octahedron with Mg-O dista nces varying between 202.2(2) and 211.6(3) pm. The hexaaquamagnesium i ons are arranged parallel to (010). The two kinds of iodate ions and t he four different ''free'' water molecules are filled between the laye rs thus formed. There are twenty independent hydrogen bonds with O ... O distances from 268.7(3) to 287.6(4) pm. On the basis of all inter m olecular I ... I distances of iodates reported in the literature, 180 pm are recommended as van-der-Waals radius resp. lone-pair radius of i odine(V). DSC and Raman spectroscopic experiments as well as high-temp erature Raman and X-ray measurements were performed and are discussed with respect to the energetic and geometric distortion of the IO3- ion s and the dehydration of the decahydrate via the tetrahydrate (308 K) to Mg(IO3)(2) (428 K).