Structures of XH₄ ⁺ and XH₆ ⁺ (X = B, Al and Ga) Cations

Abstract

Structures and energies of XH₄ ⁺ and XH₆ ⁺ (X = B, Al and Ga) have been calculated at the density functional theory (DFT) B3LYP/6-311++G(3df,2pd) level. Calculations indicate that although the structure with a three center two electron (3c-2e) bond is the global minimum for BH₄ ⁺, the global minima of AlH₄ ⁺ and GaH₄ ⁺ are not those with one 3c-2e bond, but those with two 3c-2e bonds. For calibration, both structures of AlH₄ ⁺ were also calculated at the ab initio CCSD(T)/cc-pVTZ level and results in agreement with the DFT results were found. Similar calculations also indicate that although the C_2v symmetrical structure with two 3c-2e bonds is the global minimum for BH₆ ⁺, the global minima of AlH₆ ⁺ and GaH₆ ⁺ are not the C_2v symmetrical structures with two 3c-2e bonds but the C₂ symmetrical structures with three 3c-2e bonds.