Reinterpretation of Three Crystal Structures of Alkali Oxoiodate(V) - Description of the [I3O8](-) Anion and the Infinite 2D [I3O8-](infinity) Anion

Two Cs-2(IO3)(I3O8) polymorph phases and the Rb-2(I3O8)-(IO3)(HIO3)(2)(H2O) compound were prepared by hydrothermal syntheses and characterised by X-ray single crystal diffraction. alpha-Cs-2(IO3)-(I3O8) crystallises in the hexagonal space group P6(3) (a = 7.366(1) angstrom; c = 13.883(1) angstrom; V = 652.3(1) angstrom(3); Z' = 2) whereas beta-Cs-2(IO3)(I3O8) crystallises in monoclinic space group P2(1)/n (a = 12.733(1) angstrom; b = 7.437(1) angstrom; c = 14.359(2) angstrom; beta = 106.98(1)degrees; V = 1300.4(2) angstrom(3); Z = 4) and Rb-2(I3O8)(IO3)(HIO3)(2)(H2O) in triclinic space group P (1) over bar (a = 7.043(1) angstrom, b = 7.496(1) angstrom, c = 18.203(3) angstrom; alpha = 79.70(2)degrees; beta = 85.04(2)degrees; gamma = 70.66 (1)degrees; V = 891.8(2) angstrom(3); Z = 2). beta-Cs-2(IO3)(I3O8) and Rb-2(I3O8)(IO3)(HIO3)(2)(H2O) reveal the presence of [I3O8](-) anion. These compounds have already been characterised as beta-Cs2I4O11 and Rb2I6O15(OH)(2)center dot(H2O) for which the descriptions do not reflect the chemical structure. The previous descriptions are based on different choices for the I-O bonding character. In Rb-2(I3O8)(IO3)(HIO3)(2)(H2O), the shortest I center dot center dot center dot O interaction (2316(5) A) observed between a [IO3] anion and HIO3 is in the same range of I-O bond length (2.201(4) angstrom) in the [I3O8](-) anion. Bond valence calculations clearly show three classes of I-O interactions. Finally. DFT calculations coupled to the Electron Localisation Function analysis were performed to describe chemical schemes of these bonds, which justified our chemical description of the. structures. The non-centrosymmetric alpha-Cs-2(IO3)(I3O8) compound, revealed the presence of the infinite two-dimensional [I3O8-](infinity) which was obtained by condensation of iodate anions.