In order to probe the electronic structures of aluminium/gallium silyimides [1a] -, [1b] -, [1c] -and [3] -quantum chemical calculations were carried out using Density Functional Theory at the r2scan-3c level using the complete anionic component in each case (see ESI for details). The calculated geometries for crystallographically characterized imide anions, [1a] -and [1b] -, are in good agreement with those determined experimentally, in particular the key bond lengths and angle relating to the Al-N-X unit (Table ).