Abstract
B3LYP/6-31G*-B3LYP/3-21G,* and B3LYP/LANL2DZ**-based density functional theory (DFT) methods were used to investigate the ground-state structural and configurational properties of ethene (1), silaethene (2), germaethene (3), and stannaethene (4). All three methods showed that the ground-state structure of compounds 1–4 is planar. The results confirmed that the π bond energies (rotational barriers) are decreased from compound 1 to 4. The double-bond rotation energy profiles show the existence of plane symmetrical intermediates, due to the pyramidalization at the silicon, germanium, and tin center in compounds 2–4 , respectively. Based on the B3LYP/6-31G*, B3LYP/3-21G* and B3LYP/LANL2DZ** optimized ground state geometries, the Natural Bond Orbital (NBO) analysis of donor-acceptor (bond-antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from σ M−H bonding orbitals to π * C = M antibonding orbitals increase from compounds 1 to 4. Also, the donor-acceptor interactions, as obtained from NBO analysis, could fairly explain the decrease of occupancies of σ M − H bonding orbital and the increase of occupancies of π * C = M antibonding orbitals from compounds 1 to 4. Also, the NBO results showed that by increase of π C = M → σ * M − H resonance energy in compounds 1–4, the π C = M bonding orbital occupancies decrease, while the σ * M − H antibonding orbital occupancies increase. The results confirmed that by increase of σ M − H → π * C = M and also π C = M → σ * M − H resonance energies, the π bond energies (rotational barriers) decrease from compounds 1 to 4. It has to be noted that the energy gap between π C = M bonding and π * C = M antibonding orbitals decreased from compounds 1 to 4.
Published Version
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