Three-site transition-metal clusters: going from localized electrons to molecular orbitals

TL;DR

This study investigates how transition-metal trimers in specific compounds transition from localized electrons to molecular orbitals as the metal changes from 3d to 5d, supported by ab initio calculations.

Contribution

It provides a detailed analysis of electronic and magnetic properties across a series of compounds, revealing the gradual shift from localized electrons to molecular orbitals.

Findings

Transition from localized electrons to molecular orbitals from Mn to Ir.

Ab initio calculations match experimental magnetic and electronic data.

Metal-metal distance criterion for MO formation can sometimes be invalid.

Abstract

A recently synthesised series of isostructural compounds Ba$_4$NbTM$_3$O$_{12}$ (TM = Mn, Rh and Ir) with transition-metal trimers in a face-sharing geometry makes it possible to examine a tendency to the molecular orbitals (MO) formation going from $3d$ to $5d$ transition metal ions. Our $ab$ $initio$ calculations of electronic and magnetic properties describe the experimental findings and demonstrate gradual transition from the picture of localized electrons for Mn to the MO picture for Rh and especially for Ir. We also show that the often used criterion, according to which the metal-metal distance in a compound shorter than in a respective metal always gives MO, may break down in some cases.