Spectroscopic studies on the higher binary fluorides of chromium: CrF4, CrF5, and CrF6, both in the solid state and isolated in inert gas matrices

Abstract

Pure samples of CrF₄, CrF₅, and CrF₆, together with the related salts CsCrF₆, and Cs₂CrF₆, have been prepared, and a number of spectroscopic measurements made. In particular, the solid state i.r. and u.v.–visible spectra of CrF₄ and CrF₅ indicate fluorine-bridged polymeric structures, whilst CsCrF₆ and Cs₂CrF₆ contain essentially discrete CrF₆ units. Matrix isolation studies on CrF₄ and CrF₆ lead to the identification of molecular CrF₄(T_d) and CrF₆(O_h) which are characterised by intense i.r. bands at 784.3 and 763.2 cm^–1 respectively (argon matrices); the vaporisation of CrF₅ is shown to yield CrF₄+ CrF₆ by disproportionation. The u.v.–visible spectrum of CrF₆ contains prominent charge-transfer bands at ca. 38 450 and ca. 26 700 cm^–1.