# Electronic Manifestations of Scandide Contraction: Theoretical Photoelectron Spectroscopy of Monovalent Group 13 Compounds

## TL;DR

This paper uses theoretical calculations to explore electronic trends in monovalent Group 13 compounds, linking them to scandide contraction.

## Contribution

The study provides a theoretical framework connecting electronic properties of Group 13 compounds to scandide contraction effects.

## Key findings

- Gallium-based lone pairs have higher ionization potentials than aluminum-based ones.
- Indium's ionization potentials are intermediate between aluminum and gallium.
- Aryl complexes show muted scandide contraction effects due to different orbital contributions.

## Abstract

A wide-ranging density functional theory (DFT) survey
of monovalent
Group 13 complexes (trielylenes) has afforded detailed insights into
periodic trends in these compounds. Five classes of neutral complexes
were examined, based on β-diketiminate, bis­(imino)­carbazolate
(pincer), hydrotrispyrazolylborate, cyclopentadienide, and monocoordinate
aryl ligands. Also examined was a set of N,N′-diaryl-1,4-diazabutadiene dianion-coordinated
triel­(I) anions. In general, the ionization potential of the Ga-based
lone pairs was found to be nearly 1 eV or more higher than that of
Al-based lone pairs in similar species; the corresponding IPs for
In were found to hover around the values calculated for Ga. This general
trend may be thought of as an electronic manifestation of scandide
contraction, which results in stabilization of the 4s and 4p subshells
due to poor screening by the filled 3d subshell. Only for the aryl
series was this effect found to be quite muted, apparently because
these complexes do not harbor a genuine metal-based lone pair. Instead,
the highest occupied molecular orbital (HOMO) consists of a metal–carbon
σ-antibonding orbital, spread over multiple atoms. The calculations
also underscore the major role of the supporting ligand in modulating
the electronic properties of trielylenes and help explain why certain
species such as Al­(I) bis­(imino)­carbazolates might not be stable enough
to permit isolation.