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

摘要: Investigation of the recently synthesized series isostructural compounds ${\mathrm{Ba}}_{4}{\mathrm{NbTM}}_{3}{\mathrm{O}}_{12}$ $(\mathrm{TM}=\mathrm{Mn}, \mathrm{Rh}, \mathrm{and} \mathrm{Ir})$ with transition-metal trimers in a face-sharing geometry makes it possible to examine tendency molecular orbitals (MO) formation going from $3d$ $5d$ transition metal ions. Our ab initio calculations electronic and magnetic properties describe experimental findings demonstrate gradual picture localized electrons for Mn MO Rh especially Ir. We also show that often used criterion, according which metal-metal distance compound shorter than respective always gives MO, may break down some cases.