Nonplanarity at Tri-coordinated Aluminum and Gallium: Cyclic Structures for X3Hnm (X = B, Al, Ga)

Academic Article


  • Structures and energies of X3H32-, X 3H4-, X3H5, and X 3H6+ (X = B, Al and Ga) were investigated theoretically at B3LYP/6-311G(d) level. The global minimum structures of B are not found to be global minima for Al and Ga. The hydrides of the heavier elements Al and Ga have shown a total of seven, six and eight minima for X 3H32-, X3H4-, and X3H5, respectively. However, X3H 6+ has three and four minima for Al and Ga, respectively. The nonplanar arrangements of hydrogens with respect to X3 ring is found to be very common for Al and Ga species. Similarly, species with Ione pairs on heavy atoms dominate the potential energy surfaces of Al and Ga three-ring systems. The first example of a structure with tri-coordinate pyramidal arrangement at Al and Ga is found in X3H4- (2g), contrary to the conventional wisdom of 63H 3+, B3H3, etc. The influence of π-delocalization in stabilizing the structures decreases from X 3H32- to X3H6+ for heavier elements Al and Ga. In general, minimum energy structures of X3H4-, X3H 5, and X3H6+ may be arrived at by protonating the minimum energy structures sequentially starting from X 3H32-. The resonance stabilization energy (RSE) for the global minimum structures (or nearest structures to global minimum which contains π-delocalization) is computed using isodesmic equations.
  • Authors

    Digital Object Identifier (doi)

    Author List

  • Srinivas GN; Anoop A; Jemmis ED; Hamilton TP; Lammertsma K; Leszczynski J; Schaefer HF
  • Start Page

  • 16397
  • End Page

  • 16407
  • Volume

  • 125
  • Issue

  • 52