Synthesis, crystal structures and properties of novel group 13 selenides
Ewing, Sarah Jane
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Solvothermal (and ionothermal) synthesis has been used in this work to prepare novel group 13 selenide materials. The new phases were characterised using single crystal and powder X-ray diffraction, spectroscopic methods (infrared and UV-Vis diffuse reflectance spectroscopy) and thermal analysis (thermogravimetric and elemental analysis). Other characterisation methods used include SQUID magnetometry and the measurement of optical properties. The effect of the structure directing organic molecule on the inorganic structure was investigated in this thesis, with a variety of novel materials synthesised. A family of one-dimensional chains have been prepared. The first, composed of fused four-membered rings, was found in [NH4][InSe2] (using 3,5-lutidine) and in a number of phases prepared with bicyclic superbases. The second chain-type, composed of fused four- and five-membered rings was found in [C6H16N2][Ga2-xInxSe3(Se2)] (0 < x < 2) and [C7H14N3][In2Se3(Se2)]. These chains contain a (Se2)2- perselenide bond, which was previously unreported for solvothermally prepared group 13 selenides. The third chain type, found in [C7H13N2][InSe(Se2)] and [C9H17N2][InSe(Se2)], contains fused five-membered rings. More complex one-dimensional ribbons were also prepared with superbases. Many two-dimensional layered phases have been prepared in this work. [NH4][InSe2], which contains supertetrahedral clusters, generates a second harmonic generation response. A novel phase which incorporated a transition metal into the structure has been found for [Mn(C6H14N2)3][H2O][(C6H14N2)2MnIn3(SH)2Se4.89(Se2)0.12]2. The novel hybrid gallium selenides, [Ga6Se9(C6H14N2)4][H2O] and [C6H14N2][Ga4Se6(C6H14N2)2] were also isolated. The novel layers in [C7H10N][In3Se5], contain a new octahedral building-block. A further layered material, [C8H12N][In3Se4.85(Se2)0.15] was prepared, where disorder of selenium was observed. Using weakly basic pyridine and its related methyl-substituted isomers (lutidines and picolines), a three-dimensional framework [C5H6N][In9Se14], was prepared and its ion-exchange capabilities studied. Further framework materials prepared in this work include: [enH2][NH4][In7Se12], [C6H14N2][(C6H12N2)2NaIn5Se9] and [In14Se21(Se2)3]6-. Using an ionothermal route, the known three-dimensional framework, [In33Se56]13- was prepared. The first indium selenide prepared using an ionic liquid, in this case, 1-ethyl-3-methyl-imidazolium bromide (EMIm-Br).