Structural properties of two inequivalent Cs(1) and Cs(2) sites in perovskite tricaesium pentahalogencobaltate, Cs3CoX5 (X = Cl, Br)

The local structures of Cs3CoX5 (X = Cl, Br) were examined using nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR experiments. The two inequivalent Cs(1) and Cs(2) sites in two compounds were clearly distinguished based on static NMR and MAS NMR spectra. We found that the structural geometry for Cs(2) changed more abruptly than that for Cs(1) with increasing temperature. The Cs(1) ions surrounded by 10X− ions exhibited long relaxation times, whereas the Cs(2) ions surrounded by 8X− ions exhibited short relaxation times. This is consistent with the bond lengths of Cs(1)-X and Cs(2)-X. The halogen species in Cs3CoX5 enabled an examination of the effect of Cl and Br ions, which was found to influence the quadrupole parameter but not the relaxation time.