| Summary: | Critical to interpreting platinum chemical speciation using X-ray absorption spectroscopy (XAS) is the availability of reference spectra of compounds with known Pt redox and coordination. Here we compare different techniques for Pt L<sub>III</sub>-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectral regions for a large set of Pt-O-Cl-S reference compounds of known structures. The measurements were conducted in HERFD (high-energy resolution fluorescence detection, high-resolution or HR) mode, as well as in two conventional modes such as transmission (TR) and nominal-resolution total fluorescence yield (TFY or NR). Samples analyzed here included Pt<sup>0</sup> (TR), Pt<sup>II</sup>S (HR), Pt<sup>IV</sup>S<sub>2</sub> (TR), K<sub>2</sub>Pt<sup>II</sup>Cl<sub>4</sub> (HR + TR), K<sub>2</sub>Pt<sup>IV</sup>Cl<sub>6</sub> (HR + TR), Pt<sup>IV</sup>O<sub>2</sub> (HR + TR), C<sub>6</sub>H<sub>12</sub>N<sub>2</sub>O<sub>4</sub>Pt<sup>II</sup> (HR + TR), and aqueous solutions of K<sub>2</sub>Pt<sup>II</sup>Cl<sub>4</sub> and H<sub>2</sub>Pt<sup>IV</sup>Cl<sub>6</sub> (NR + TR), as well as (NH<sub>4</sub>)<sub>2</sub>Pt<sup>IV</sup>(S<sub>5</sub>)<sub>3</sub> (HR + TR). XANES spectra in HERFD mode offer a better energy resolution than in conventional modes, allowing a more accurate identification of Pt redox state and coordination geometry. EXAFS spectra in all three modes for a given compound yield identical within errors values of Pt-neighbor interatomic distances and mean square relative displacement (MSRD, σ<sup>2</sup>) parameters. In contrast, both TR and NR spectra on the one hand and HR spectra on the other hand yield distinct amplitude reduction factor (S<sub>0</sub><sup>2</sup>) values, 0.76 ± 0.04 and 0.99 ± 0.07 (1 standard error), respectively. This study contributes to the development of an open-access XAS database SSHADE.
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