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.