Structure and vibrational spectroscopy of complexes of Al⁺ and Al₂⁺ with ethane.

This article focuses on the vibrational photodissociation spectroscopy and density functional theory (DFT) analysis of aluminum cation (Al⁺) and aluminum dimer cation (Al₂⁺) clusters complexed with ethane molecules, Alₓ⁺(C₂H₆)ₙ (x = 1, 2; n = 1–3). The study reveals that both Al⁺ and Al₂⁺ interact more strongly with ethane than with methane, with preferred side-on (T-shaped) binding motifs where ligands coordinate on the same side of the metal ion or cluster. Vibrational spectra exhibit red shifts in C–H stretching frequencies proximate to the metal ions, decreasing as the number of ethane ligands increases, and show Fermi resonances involving overtones and combination bands of methyl group deformations. Computational simulations using the ωB97X-D functional combined with a local mode Hamiltonian method effectively reproduce the complex experimental spectra and support the structural assignments. These findings contribute to understanding metal ion–hydrocarbon interactions relevant to catalysis and C–H bond activation.