Analysis of the bonding in XH3-Cu+ (X=B, Al, Ga) complexes

摘要

High-level density functional theory (DFT) calculations on XH3-Cu+ (X = B, Al, Ga) complexes show that the attachment of the metal cation to the base takes place through agostic-type interactions. These interactions that can be viewed as dative bonds from the sigma(XH) bonding orbitals of the base toward low-lying empty 4s orbitals of the metal cation, and back-donations from the lone pairs of the metal into the sigma*(XH) antibonding orbitals of the neutral, are particularly favored when the X-H bonds have a high X+delta -H-delta polarity. Accordingly, the AlH3 and GaH3 Cu+ binding energies are very similar, but much larger than that of BH3. Depopulation of the sigma(XH) bonding orbital and the concomitant population of the sigma*(XH) antibonding orbital involved in the agostic interaction result in a significant weakening of the corresponding X-H linkages, whose bond length increases and whose stretching frequency appears red-shifted. (c) 2005 Wiley Periodicals, Inc.