THE CRYSTAL-STRUCTURE OF I2O4 AND ITS RELATIONS TO OTHER IODINE-OXYGEN-CONTAINING COMPOUNDS

Although the existence of iodine dioxide (I2O4) has been known since 1844, its crystal structure has remained unsolved up to the present. The main reason for this is that I2O4 is obtained as a fine powder through controlled hydrolysis of (IO)(2)SO4 and that no suitable solvent for recrystallization of I2O4 has been found. The crystal structure of I2O4 has been determined from combined powder X-ray (synchrotron radiation, HASYLAB, DESY, Hamburg) and neutron (ILL, Grenoble) diffraction data. I2O4 crystallizes monoclinically [a = 848.3(1), b = 669.6(1), c = 833.3(1) pm, beta = 124.69(1)degrees; space group P(2)1/c; all atoms in position 4e]. The I2O4 structure is to a reasonable approximation a one-dimensional solid, comprising infinite ...-I-O-IO2-O-... chains (in the listed order, tri- and penta-valent iodine), which are bonded together by much weaker interchain interactions. The atomic arrangement in I2O4 is discussed mainly in relation to the structures of (IO)(2)SO4 from which the dioxide is synthesized, and I2O5, into which it decomposes. Its relation to other iodine-oxygen-containing compounds is also considered.