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

Ae Ran Lim,Sung Soo Park,Jin-Hae Chang

doi:10.1063/1.5003981

Abstract

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.

Highlights

Stable complex compounds ABX3 and A2BX4 (A, B, and X are alkaline ion, metal ion, and halide, respectively) are well known; if the coordination number exceeds 4, the stable group is BX6
Tetrahedral Co compounds exhibit several characteristics at low temperatures that make them ideal candidates for studying magnetic properties; the situation is very similar for the tetrahedral cobalt salts Cs3CoCl5 and Cs3CoBr5.17–20 The compound Cs3CoBr5 is isomorphous with Cs3CoCl5 and contains the approximately tetrahedral anion CoX42
The results showed that the two inequivalent Cs(1) and Cs(2) sites can be clearly distinguished using 133Cs static nuclear magnetic resonance (NMR) and 133Cs magic angle spinning (MAS) NMR spectra

Summary

Introduction

Stable complex compounds ABX3 and A2BX4 (A, B, and X are alkaline ion, metal ion, and halide, respectively) are well known; if the coordination number exceeds 4, the stable group is BX6. There are compounds of the type AnBX5 that can appear to contain a BX5 group.[1] The perovskite crystals ABX3 and A2BX4-type halide substances have hexagonal and orthorhombic structures, respectively Characteristics of these two types of perovskite crystals have been investigated, especially their ferroelectricity and incommensurate phase transitions.[2,3,4,5,6,7,8,9,10,11] In addition, Cs3CoX5 (X=Cl, Br) crystals with the BX5 type have received significant attention because of the high degree of symmetry in the tetragonal structure of this crystal, which makes Cs3CoX5 the most convenient type of crystal to study the electric and magnetic structures of the [CoX4]2 cluster.[12,13,14,15,16,17,18,19,20,21,22,23,24] The tetrahedral coordination of most transition metal complex ions (BX4)[2] (B=Co2+, Fe2+, Cu2+; and X=Cl, Br) in crystals is approximately distorted from a regular tetrahedral coordination.[15,16] Tetrahedral Co compounds exhibit several characteristics at low temperatures that make them ideal candidates for studying magnetic properties; the situation is very similar for the tetrahedral cobalt salts Cs3CoCl5 and Cs3CoBr5.17–20 The compound Cs3CoBr5 is isomorphous with Cs3CoCl5 and contains the approximately tetrahedral anion CoX42-.21–25.

Methods

Results

Conclusion