A vibrational study of various KAuCl 4− xBr x solid solutions

Abstract

Infrared and Raman vibrational studies have been undertaken on various powdered KAuCl 4− x Br x (0≤ x≤4) solid solutions. Characteristic variations of the spectra clearly demonstrate the existence of distinct individual planar anions. From a comparison of the vibrational data with results of valence force field calculations, we are able to discuss the domains of existence of several anions and to characterise with confidence the following halide mixed species: • The (AuCl 3Br) − anion is characterised in Infrared by four stretching (at 354, 343, 330 and 236 cm −1) and three deformation bands (at 196, 178 and 148 cm −1) and in Raman by essentially the intense line at 236 cm −1(ν Au–Br). • The (AuCl 2Br 2) − ‘ trans’ displays intense infrared (at 357 and 254 cm −1) and Raman (at 340 and 203 cm −1) stretching bands. • The (AuClBr 3) − anion exhibits three stretching Raman modes (at 236, 212 and 203 cm −1) and one stretching (at 336 cm −1) plus three bending Infrared modes (at 178, 134 and 118 cm −1). Furthermore, from intensity variations of the Raman lines at 203 and 236 cm −1, it is evidenced that the 236 cm −1 signal is mainly due at low ‘ x’ concentration to the only (AuCl 3Br) − entity, but at higher ‘ x’ values ( x>30%) to at least two species, including perhaps the (AuCl 2Br 2) − ‘ cis’ anion.