Structural and spectroscopic investigations of halogeno complexes of iridium (III) and iridium (IV)
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis reports the results of some structural and spectroscopic studies performed on a number of crystalline chloro and bromoiridate (III) and (IV) complexes. The crystal and molecular structures of K₃[IrC1₆] , K₃[IrCl₆] H₂O, (NH₄)₃ [IrCl₆] H₂O, Rb₃[IrBr₆] H₂O, Cs₂[IrCl₅(H₂O) ] and [N(CH₃)₄]₃[Rh₂Br₉] have been determined using single crystal X-ray diffraction methods. Infrared and Raman, ultraviolet-visible and nuclear quadrupole resonance spectroscopic studies of these and other halogenoiridate(III) and (IV) complexes have been undertaken. In studying the preparative chemistry of Ir(III) halogeno compounds, and the interrelation of these with Ir(IV) compounds, the new complexes A₃[Ir₂X₉] (A = univalent cation, X = Cl, Br) have been isolated. Unit cell parameters and space groups have been determined for most of the complexes prepared using both single crystal and powder X-ray diffraction techniques, and isomorphism between these complexes has been studied and compared with stoichiometrically related complexes of other transition metal ions. The influence of the cations on the formation of particular structures for the complex salts has been discussed. A notable feature of the structures of halogenoiridate(III) compounds reported is the distortion of the halogenoiridate(III) anions from their ideal molecular point symmetry. This contrasts with the regular octahedral symmetry retained by the hexahalogenoiridate(IV) anions in their A₂[MX₆] salts. The cause of this distortion has been attributed to crystal packing effects. Low frequency infrared spectroscopic studies have been performed on all the complexes isolated and observed spectra have been interpreted with the aid of factor group analyses. This has proved useful in explaining the complexity of many of the observed spectra. Previously reported nuclear quadrupole resonance data on a number of hexachloroiridates(III) have been reinterpreted in the light of the structures determined in this work and a further study has been made of the structural phase transitions that some of these complexes undergo below room temperature. The reported nuclear quadrupole resonance data are consistent with the reported structures and give further evidence for the unsymmetrical crystal environment and distortion of the hexachloroiridate(III) anions in the solid state. The diffuse reflectance spectra of a number of crystalline halogenoiridate(III) and (IV) complexes are also reported and interpreted.