In situ site-selective transition metal K-edge XAS: a powerful probe of the transformation of mixed-valence compounds

Abstract

We present herein the first in situ site-selective XAS experiment performed on a proof-of-principle transformation of a mixed-valence compound: the calcination of the K 0.1 Co II 4 [Co III (CN) 6 ] 2.7 ·20H 2 O Prussian Blue analogue (containing Co 2+ and Co 3+ ions in two different O h sites) into Co 3 O 4 (containing Co 2+ ions in a T d site and Co 3+ in an O h site). By recording the Co K-edge X-ray absorption spectra using a spectrometer aligned at the Co Kβ 1,3 emission line, the evolution of each species was singly monitored from 20°C up to the oxide formation. The experimental spectrum of the Co 2+ (T d) and Co 3+ (O h) species in Co 3 O 4 is reported for the first time. Our results demonstrate the possibilities offered by site-selective XAS for the investigation of chemical transformations and the study of materials under working conditions whenever the chemical element of interest is present in several states and/or sites.