Donor-acceptor (DA) complexes MX3.LL.M'X-3 (M, M' = Al, Ga; X = Cl, Br; LL = 4,4'-bipyridyl) have been theoretically investigated at the B3LYP/pVDZ level of theory. Addition of the first molecule of MX3 to 4,4'-bipyridyl has a similar exothermicity compared to complexes with the monodentate donor pyridine. Addition of the second molecule of MX3 is significantly (by about 15 kJ mol(-1)) less exothermic. Nevertheless all 2:1 complexes (including heteroacceptor) are predicted to be stable in the vapor phase up to 660, 760, 830 and 920 K for GaBr3, GaCl3, AlBr3, and AlCl3, respectively. Four homoacceptor MX3.4,4'bpy.MX3 complexes have been synthesized for the first time, and their existence in the vapor phase has been proven by mass spectrometry. The theoretically predicted order of the complex stability AlCl3 > AlBr3 > GaCl3 > GaBr3 correlates well with the experimental observations of M(2)X(5)bpy(+) ion abundances in the mass spectra. The results obtained show for the first time that the synthesis of the gas-phase stable heteroacceptor complexes is feasible, which opens the prospect for their future use as single-source precursors to the stoichiometry-controlled synthesis of 13-15 alloys.