Figure 7: Metal-dependent behaviour of [M^I(C₆H₅F)₂]⁺[Al(OR^F)₄]⁻ (M=Ga, In) in the presence of bipy.

Disproportionation (for M=Ga) and cluster formation (for M=In) can occur via (i) an ambiphilic singlet route (bottom) or (ii) a triplet route (top). Regarding (i), the [M^I(bipy)₂]⁺ complexes feature an occupied 4 s/5 s-orbital (HOMO) and empty 4p/5p-orbitals (LUMO+6), thus being able to react via a disproportionation or a cyclotrimerization, yielding 3²⁺ and 4³⁺, respectively. The conceivability of this reaction path directly correlates to the energy gap between the 4 s/5 s- and the 4p/5p-orbitals of the reactants (Table 2). Choosing reaction path (ii), the [M^I(bipy)₂]⁺ complexes react via their triplet state. Dependent on the metal, the latter significantly differ in terms of geometries and localization of spin densities. Hence, the [Ga(bipy)₂]⁺ complex changes its coordination mode from tetragonal pyramidal in the singlet to tetrahedral in the triplet state and both unpaired electrons are equally distributed over the bipy ligands (spin density at the gallium atom=6.0%). These findings clearly speak for the tendency of the Ga^I cations to disproportionate and also explain the complex’s inability to form a di-/oligo-gallane.⁴⁴ The [In(bipy)₂]⁺ complex on the other hand, retains its tetragonal pyramidal coordination mode and 35% of the spin density is located on the indium atom, making a stepwise cyclotrimerization feasible (cf. the dicationic [(bipy)₂In−In(bipy)₂]²⁺ cluster fragment shown). The conceivability of the reaction path directly correlates to the singlet-triplet gaps of the reactants (Table 2). The Kohn-Sham orbitals shown were selected on localization of the electron density on the metal cations and the lowest possible energy (electron and spin density cutoffs at 0.06 and 0.01 a.u., B3LYP/SV(P) level; as shown in Supplementary Fig. 10, the [(bipy)₂In−In(bipy)₂]²⁺ cluster fragment only featured a spin density at the indium atoms, if the BHLYP functional was applied).