Single-crystal neutron study on cobalt iodate tetrahydrate, a compound with H••• |I(V)O3- hydrogen bonds?

The crystal structure of cobalt iodate tetrahydrate Co(IO3)(2).4H(2)O (space group P2(1)/c, Z = 2, a = 836.8(5) pm, b = 656.2(3) pm, c = 850.2(5) pm, and beta = 100.12degrees, final R1 = 0.0349 (I greater than or equal to 2sigma(1)) for 1031 unique reflections) was redetermined by single-crystal neutron diffraction studies. The structure is built up by layers parallel (100) connected by interionic O3I-...OIO2- bonds. Unequivocal interpretation of the four differently strong (OHOIO3-)-O-... hydrogen bonds of the two crystallographic different hydrate H2O molecules of the isostructural series M(IO3)(2).4H(2)O (M = Mg, Co, Ni) on the basis of the observed hydrogen-bond distances and assignment to the uncoupled OD stretching modes of matrix isolated HDO molecules is only possible if weak hydrogen bonds to the iodine lone-pairs of adjacent IO3- ions are additionally considered. The potential strength of (HI)-I-...(V)O-3(-) hydrogen bonds with respect to (HI)-I-... distances and H-IO3- angles is discussed. A bond-valence concept for estimating the strength of (HI)-I-...(V)O-3(-) hydrogen bonds is given.