Chemical Bonding Perspective on Low-Lying SiC4H2 Isomers: Conceptual Quantum Chemical Views

J Phys Chem A. 2022 Dec 22;126(50):9366-9374. doi: 10.1021/acs.jpca.2c06230. Epub 2022 Dec 13.

Abstract

The nature of the chemical bonding in seven low-lying isomers of SiC4H2 is analyzed through quantum chemical concepts. Out of the seven, four isomers, 1-ethynyl-3-silacycloprop-1(2)-en-3-ylidene (1), diethynylsilylidene (2), 1-sila-1,2,3,4-pentatetraenylidene (4), and 1,3-butadiynylsilylidene (5), have already been identified in the laboratory. The other three isomers, 2-methylenesilabicyclo[1.1.0]but-1(3)-en-4-ylidene (3), 4-sila-2-methylenebicyclo[1.1.0]but-1(3)-en-4-ylidene (6), and 3-ethynyl-1-silapropadienylidene (7) remain elusive in the laboratory to date (J. Phys. Chem. A, 2020, 124, 987-1002). Deep insight into the characteristics of chemical bonding is explored with different bonding analysis tools. Quantum theory of atoms in molecules (QTAIM), interaction quantum atoms analysis, natural bond orbital analysis, adaptive natural density partitioning, electron localization function (ELF), Laplacian of electron density, energy decomposition analysis, atomic charge analysis, bond order analysis, and frontier molecular orbital analysis are employed in the present work to gain a better understanding of the chemical bonding perspective in SiC4H2 isomers. Different quantum chemical topology approaches (QTAIM, ELF, and Laplacian of electron density) are employed to complement each other. The obtained results dictate that the lone pair of the silicon atom participate in delocalization and influences the structural stability of isomers.