Structural studies on metal halides and related species using matrix isolation and molecular beam techniques

Millington, Keith Reginald (1987) Structural studies on metal halides and related species using matrix isolation and molecular beam techniques. University of Southampton, Doctoral Thesis.

Abstract

Methods for establishing molecular structures of isolated small molecules are critically reviewed. In particular the advantages and limitations of matrix isolation infrared spectroscopy and laser induced fluorescence of seeded molecular beams are discussed. The infrared spectra of certain matrix isolated AMF₆ species are shown to be dependant on the matrix gas used. Either a doublet or a triplet is observed for the ν3 band of the MF^-₆ anion depending on whether host-guest interactions are weak (Ne, Ar) or strong (N₂, CO). These results are interpreted as due to the presence of a tridentate (facial) interaction between A⁺ and the MF^-₆ anion in Ne or Ar, and a bidentate (edge) interaction in N₂ or CO. Interaction between the host species and the cation is shown to be responsible. The degree of interaction is measured for several matrix gases using CsClO₄ as a probe. The infrared spectra of NbF₅, TaF₅, PF₅ and AsF₅ are shown in matrices. For NbF₅ and TaF₅ the observed spectra are complicated by the presence of several oligomers. The isolation of PF₅ and AsF₅ in several matrix gases shows a preferential interaction between AsF₅ and CO. When ThCl₄ or UCl₄ are isolated in neon matrices the spectra can be interpreted in terms of a T_d molecule with a small site effect. Calculations in the infrared spectra of isotopically substituted ThCl₄ show that in inert gases other than neon, ThCl₄ is not tetrahedral. The infrared spectra of several transition metal halides have been obtained in matrices by passing seeded halogen mixtures over hot metal foils. The interaction between metal halides and CO in matrices is studied and the formation of strongly-bound π-type complexes of the type trans-Fe(CO)_4X_2 (where X = Cl or I) has been observed for the first time. The factors determining whether σ- or π- type complexes are likely to be formed in matrices are discussed. Part of the laser-induced fluorescence spectrum of chromyl fluoride in a free jet expansion has been obtained at an instrumental resolution of better than 0.001 cm^-1. This spectrum (together with that of the dispersed fluorescence) allows the identification of the (0,0) band of the absorption spectrum. The design and development of a heated nozzle for studying the seeded expansion of metal dihalides is discussed. The laser-induced fluorescence spectrum of NiCl_2 has been obtained. (D81703)

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