Molecular structures of M(Bu^t)₃ (M = Al, Ga, In) using gas-phase electron diffraction and ab initio calculations: experimental and computational evidence for charge-transfer processes leading to photodissociation

The gas-phase structures of Al(Bu^t)₃ and Ga(Bu^t)₃ have been investigated by electron diffraction and are shown to consist of monomeric units with very slightly pyramidal geometries. Salient structural parameters (r_h1) include r(Al-C) = 2.008(2) Å and r(Ga-C) = 2.032(2) Å. For both compounds the ligand orientations and geometries are controlled by interligand interactions. The structures of M(Bu^t)₃ (M = Al, Ga, In) have been calculated ab initio and those for the aluminium and gallium derivatives are in good agreement with the electron-diffraction structures. Comparison of the ab initio calculated structure of In(Bu^t)₃ with those of Al(Bu^t)₃ and Ga(Bu^t)₃ suggests that the significantly different photochemistry exhibited by the former does not result from structural factors. In fact the compounds undergo a charge-transfer process in the UV region, with the wavelength required calculated to be slightly longer for the indium compound than for the other two.