FTIR and EXAFS investigations of microstructures of gold solvent extraction: hydrogen bonding between modifier and Au(CN)(2)(-)

The microstructures of loaded organic phases of three quaternary amine solv ent extraction systems for gold, which were N263-xylene, N263-tributyl phos phate (TBP)-dodecane and N263-2-ethylhexanol (isooctanol)-dodecane (N263-tr ialkylmethylammonium chloride; alkyl=C-8-C-10), were studied by Fourier tra nsform infrared (FTIR) spectroscopy and extended X-ray absorption fine stru cture (EXAFS) spectroscopy. According to the EXAFS results, it was found th at the gold coordination environment was the same before and after extracti on. However, the C=N stretching vibrations of Au(CN)(2)(-) in the three sys tems differed greatly. The second derivative spectra of C=N stretching band s of Au(CN)(2)(-) were also found to be different. In order to explain the differences in the IR characteristics of C=N in the three extraction system s, three microstructure models are proposed. For the N263-xylene system, th e model is a simple ion pair. For the other two systems with a modifier (TB P and isooctanol), the models are two supramolecular structures based on hy drogen bonding between the modifier and Au(CN)(2)(-). Some related work suc h as on the hydration of acetonitrile and the fine structure of C=N in soli d KAu(CN)(2) was also performed in order to offer additional supporting evi dence for the reliability of the proposed models.