Structural and thermodynamic characteristics of compounds X2MYH2 (M = Al, Ga, In; X = F, Cl, Br. I; Y=N, P, As) formed by hydrogen halide eliminationfrom donor-acceptor complexes X3MYH3

Geometry and thermodynamic characteristics of complexes X2MYH2 (M = Al, Ga, In; X = F, Cl, Br, I; Y = N, P, As) and their components were found by the B3LYP density functional method with the LANL2DZ(d,p) basic set. The nitro gen complexes X2MNH2 have a planar structure, whereas the phosphorus and ar senic complexes are pyramidal. Upon HX elimination, the dissociation energy of the M-Y bonds considerably increases (by 150-270 kJ mol(-1)), which mak es the dissociation Of X2MYH2 into components thermodynamically unfeasible even at temperatures about 1000 degreesC. A linear correlation between the dissociation enthalpies of M-Y bonds in the X3MYH3 and X2MYH2 complexes was found for each central atom M, which makes it possible to estimate the dis sociation enthalpies of coordination-unsaturated compounds of the Group Ma elements from the dissociation enthalpies of their coordination-saturated a nalogs. The enthalpies of dimerization Of X2MYH2 fall in the range from 40 (Y = P, As) to 260 kJ mol(-1) (Y = N), which makes the process X3MNH3 = [X2 MNH2](2) + HX with the retention of the metal-nitrogen bond more favorable than the dissociation of the initial complex into the components. Thus, dim ers [X2MNH2](2) can be intermediates in chemical deposition of nitrides fro m the gas phase of donor-acceptor complexes.