The structural and thermodynamic characteristics of 36 MX₃YH₃ complexes (M = Al, Ga, In; X = F, Cl, Br, I; Y = N, P, As) and of their components were calculated by ab initio methods [self-consistent field (SCF) and density functional (B3LYP)] in combination with the method of effective core potentials. Taking into account the polarization functions is important for adequate description of the thermodynamic characteristics of the complexes and components. The calculated characteristics of MX₃ and YH₃ fragments are well consistent with experimental observations. The trends in variation of the dissociation enthalpy ΔH of the complexes in these series, F > Cl > Br > I, Al > Ga < In, N ≫ P ≥ As, are explained by significant electrostatic interaction in the systems with F, N and Al and by its weakening in the systems with Ga, P and As. Charge transfer at formation of donor-acceptor bond affects all atoms, but the main tendency is increase in the negative charge at the halide atoms. However, the known correlation of the complex formation enthalpy and the extent of charge transfer is not valid in this class of systems. Interaction of nonbonded X and H atoms leads to advantage of eclipsed structure of the complexes for the systems whith high effective charges on X and H atoms (the complexes MF₃NH₃).