Redox Potential and Crystal Chemistry of Hexanuclear Cluster Compounds.

Elena Levi,Carlo Gatti,Doron Aurbach

doi:10.3390/molecules26113069

Abstract

Most of TM6-cluster compounds (TM = transition metal) are soluble in polar solvents, in which the cluster units commonly remain intact, preserving the same atomic arrangement as in solids. Consequently, the redox potential is often used to characterize structural and electronic features of respective solids. Although a high lability and variety of ligands allow for tuning of redox potential and of the related spectroscopic properties in wide ranges, the mechanism of this tuning is still unclear. Crystal chemistry approach was applied for the first time to clarify this mechanism. It was shown that there are two factors affecting redox potential of a given metal couple: Lever’s electrochemical parameters of the ligands and the effective ionic charge of TM, which in cluster compounds differs effectively from the formal value due to the bond strains around TM atoms. Calculations of the effective ionic charge of TMs were performed in the framework of bond valence model, which relates the valence of a bond to its length by simple Pauling relationship. It was also shown that due to the bond strains the charge depends mainly on the atomic size of the inner ligands.

Highlights

One of the main questions often arising in the studies of redox potential of metal–organic complexes is whether their electrochemical behavior can be predicted through the properties of the metal and the isolated ligands [1]
In our previous works we showed that the Bond Valence Model (BVM) is very effective in the case of cluster compounds [20,21]
The effective ionic charge of the TM in a given cluster compound can be calculated as bond valence sum (BVS) of the metal–ligand bonds based on the lengths of these bonds, R TM-L, and respective empirical constants, R0 TM-L [22]

Summary

Introduction

Organic complexes is whether their electrochemical behavior can be predicted through the properties of the metal and the isolated ligands [1]. This question is pertinent for the TM6-cluster compounds (TM = transition metal) (Figure 1). It was shown that a high lability and diversity of the outer (apical or terminal) ligands in these compounds allow for tuning of redox potential and the related spectroscopic properties in wide ranges [2,3]. A mechanism of the potential tuning is still unclear To elucidate this mechanism, in this paper we will discuss possible correlation between structural and electrochemical properties of cluster compounds

Objectives

Methods

Results

Conclusion