Abstract: The crystal structure of the compound RbIO_3·2HIO_3 has been redetermined by heavy-atom method and refined by full matrix least-squares method. The crystal belongs to triclinic system with cell dimensions; a=0.8332 nm, b=0.8232 nm, c=0.8264 nm; α=60.66°, β=85.80°, γ=66.10°. Z= 2, D_m = 4.61 g cm~(-3). The structure is non-centrosymmetric; nevertheless, it has a high degree of centrosymmetry, as a measurement of it, < |△r|>w=0.009 nm. The reliable factor is R=0.076.
Three O atoms are bound to each I atom with mean distance of about 0.18 nm forming a distorted IO_3~- triangular cone; in addition other three neighbour O atoms are bound to it with distances of 0.25—0.33 nm. These six O atoms and their centering I atom form a distorted IO_6 octahedron. Nine O atoms are bound to each Rb atom with distances of 0.286—0.351 nm forming a RbO_9 polyhedron.