New inorganic frameworks containing asymmetric oxyanions
This thesis describes the hydrothermal synthesis and structural characterisation of twenty-seven new inorganic frameworks based upon the asymmetric oxyanions of selenium(IV) and tellurium(IV). Of particular interest is how the lone pair of electrons that both these species possess, are locally contained within each structure, and the effect this has on the global topology. Selenites: The BaM2(SeO3)3.nH2O (M = Co, Ni, Mn, Mg;n = 3) family of phases, and Hg2O(SeO3).0.5H2O both contain one-dimensional hexagonal channels into which the Se(IV) lone pairs are orientated, which appear to hinder the movement of the extra-framework cations and water molecules. Ion exchange experiments carried upon BaCo2(SeO3)3.3H2O with LiCl2 resulted in the new phase, Ba2CoCl2(SeO3)2. Edge-sharing between SeO3 and MO6 groups in SrM(SeO3)2 (M = Zn and Mn) results in novel ZnO4+2s bicapped tetrahedra and highly distorted MnO5+1 octahedra, respectively, whilst Sc2(SeO3)3.H2O contains novel ScO7 pentagonal bipyramids and ScO6+1 monocapped octahedra. Mn3(SeO3)3.H2O, Mn4(SeO3)4.3H2O, Ba2Mn3(SeO3)6, PbFe2(SeO3)4, LiCd2(SeO3)2(OH) and Hg2SeO3 all posses “empty” channels occupied by the Se(IV) lone pair electrons. Tellurites: BaTe3O7 and BaTe4O9 demonstrate a novel self-containment effect whereby the Te(IV) lone pairs are contained within “empty” 6- and 8-ring (6 and 8 Te nodes) tellurite tubes, respectively. In contrast, the lone pairs in the condensed phases MTe6O13 (M = Mn, Co, Ni), are contained within isolated closed cavities. In the mixed valence vanadium selenite (VIVO2)(VVO2)(TeO3).NH4 the anionic [(VIVO2)(VVO2)(TeO3)]- layers are bridged by ammonium cations and the Te(IV) lone pairs are unusually orientated into the layers, confined in small  tunnels. There are no interstitial cations bridging the neutral layers in Li(VO2)3(TeO3)2 and a series of very long Te...O and Li...O interactions appear to bind the structure.