Carbon-free [Al2(η4-E4)2](E = N, P, As): A new class of inorganic sandwich-type complexes containing the Al-Al bond

A new class of carbon-free sandwich-type complexes [Al2(η4-E4)2](E = N, P, As) containing Al-Al bond have been investigated by both DFT and ab initio theory calculations. The equilibrium geometries, electronic structures, vibrational frequencies, and stabilities of these complexes are researched by B3LYP and MP2(full) methods at 6-311+G(3df) level. These sandwich complexes with D4d symmetry are all true minima on the potential energy surface. NBO analyses for the series of complexes reveal that the Al-Al bond is a σ covalent bond. The E-E distance in these complexes is slightly elongated with respect to that in the isolate E42-. These novel inorganic sandwich complexes containing Al-Al bond in this work turn out to be strongly thermodynamically favored in the gas phases and may be targeted in future experiments to expand the structural domain of main type metal element sandwich-type complexes.