# Theoretical Photoelectron Spectroscopy of Metal–Metal Quintuple Bonds: Relativity-Driven Reordering of Frontier Orbitals

## TL;DR

This paper explores how relativity affects the electronic structure of metal-metal quintuple bonds, particularly in tungsten complexes.

## Contribution

The study reveals that relativistic effects significantly alter orbital energies in tungsten compared to chromium and molybdenum complexes.

## Key findings

- Scalar-relativistic calculations show lower ionization potentials for tungsten complexes.
- Relativistic effects cause larger HOMO–LUMO gaps in tungsten compared to lighter metals.
- DFT calculations indicate higher electron affinities in tungsten-based complexes.

## Abstract

A recent reinvestigation
of the gas-phase photoelectron spectra
of Group 6 metal–metal quadruple-bonded complexes with scalar-relativistic
DFT calculations showed that common exchange-correlation functionals
reproduce the lowest ionization potentials in a semiquantitative manner.
The finding encouraged us to undertake a DFT study of metal–metal
quintuple bonds in a set of bisamidinato complexes with the formula
MI2[HC(NR)2]2 (M = Cr,
Mo, W; R = H, Ph, 2,6-iPr2C6H3) and idealized D2h symmetry. Scalar-relativistic OLYP/STO-TZ2P calculations indicated
significant shifts in valence orbital energies among the three metals,
which translate to lower first ionization potentials, higher electron
affinities, and lower HOMO–LUMO gaps for the W complexes relative
to their Cr and Mo counterparts. These differences are largely attributable
to substantially larger relativistic effects in the case of tungsten
relative to those of its lighter congeners.