Molecular and Electronic Structures of (TiXH<sub>6</sub>)<sup>0/-</sup>, X = B, Al, Ga, Compounds

The molecular and electronic structures of the isomers of both neutral and negative (TiXH<sub>6</sub>)<sup>0/-</sup>, X = B, Al, Ga, systems have been studied. For each of the neutral systems, a <i>C</i><sub>s</sub> isomer of signature (2, 3, 1) (where (a, b, c) signifies <i>a </i>is the number of terminal Ti−H bonds, <i>b</i> is the number of hydrogen bridging bonds, and <i>c</i> is the number of terminal X−H bonds) was characterized as a stable minimum. The X = Al, Ga neutral systems also had two additional minima of signature (2, 2, 2) (<i>C</i><sub>2</sub><i><sub>v</sub></i>) and (3, 3, 0) (<i>C</i><sub>3</sub><i><sub>v</sub></i>). In the anionic cases, each system has a stable <i>C</i><i><sub>s</sub></i> structure of signature (3, 2, 1). The X = Al, Ga systems, again showing more complexity, have minima on their anionic singlet potential energy surfaces of signatures (2, 2, 2), (3, 3, 0), and (3, 0, 3). The bonding characteristics of these various minima have been analyzed in detail through examination of molecular orbitals, natural bond orbitals, and Bader topological analysis. One important structural feature of the stable isomers is that strong hydrogen bridging electron-deficient bonds are responsible for holding the molecular structure together. For the neutrals, the (2, 3, 1) and (2, 2, 2) isomers have almost the same energy and the (3, 3, 0) isomer lies more than 30 kcal/mol higher. However, for the anions, the three structures with hydrogen bridging bonds are the most stable and lie very close in energy, within 0.31 kcal/mol for X = Al and within 5.96 kcal/mol for X = Ga. Ionization energies and electron affinities have also been calculated and discussed.