| Title
| - Role of the Terminal Atoms in the Donor−Acceptor ComplexesMX3−D (M = Al, Ga, In; X = F, Cl, Br, I; D = YH3, YX3, X-; Y= N, P, As)
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| Abstract
| - Donor−acceptor complexes MX3−D (M = Al, Ga, In; X = F, Cl, Br, I; D = YH3, PX3, X-; Y =N, P, As) and their components have been studied using self-consistent field and hybrid Hartree−Fock/densityfunctional (B3LYP) methods with effective core potentials. The theoretical dissociation energies of the MX3−Dcomplexes decrease in the orders F > Cl > Br > I, Al > Ga < In, and N ≫ P ≥ As for all investigatedcomplexes. The calculated (B3LYP/LANL2DZP) dissociation energies for ammonia adducts are on average7 kJ mol-1 higher than those from experiment. There is no correlation between the dissociation energy andthe degree of charge transfer. Complexes of ammonia and metal fluorides have mostly ionic metal−donorbonds, while the other donor−acceptor adducts are mostly covalently bonded. In addition, a significant chargeredistribution between the terminal atoms leads to further electrostatic stabilization of ammonia adducts. Coulombinteractions destabilize MX3−PX3 complexes, and despite some experimental indications, the existence ofthese particular complexes in the gas phase is improbable. Distortion of MX3 from planarity under complexformation leads to decreasing X−M−X angles. These decreasing angles correlate well with increasing M−Xbond lengths. For all investigated MX3−X- systems a strong correlation of the MX3−X- dissociation energywith the M−X bond length increase is found. Correlations between the pyramidal angle X−M−Y and thelength of the adjacent M−Y bond have been found for each donor atom Y. All observed trends in structuraland thermodynamic properties are qualitatively explained on the basis of a simple electrostatic model.
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