Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2'-bipyridine.

Group 13 M(I) compounds often disproportionate into M(0) and M(III). Here, however, we show that the reaction of the M(I) salt of the weakly coordinating alkoxyaluminate Ga(I)(C6H5F)2Al(OR(F))4 (R(F)=C(CF3)3) with 2,2'-bipyridine (bipy) yields the paramagnetic and distorted octahedral Ga(bipy)3(•){Al(OR(F))4}2 complex salt. While the latter appears to be a Ga(II) compound, both, EPR and DFT investigations assign a ligand-centred Ga(III){(bipy)3}(•) radical dication. Surprisingly, the application of the heavier homologue (I)n(I)(C6H5F)2Al(OR(F))4 leads to aggregation and formation of the homonuclear cationic triangular and rhombic In3(bipy)6, In3(bipy)5 and In4(bipy)6 metal atom clusters. Typically, such clusters are formed under strongly reductive conditions. Analysing the unexpected redox-neutral cationic cluster formation, DFT studies suggest a stepwise formation of the clusters, possibly via their triplet state and further investigations attribute the overall driving force of the reactions to the strong In-In bonds and the high lattice enthalpies of the resultant ligand stabilized M3{Al(OR(F))4}3 and M4{Al(OR(F))4}4 salts.