Abstract
Hypervalent molecules are one of the exceptions to the octet rule. Bonding in most hypervalent molecules is well rationalized by the Rundle–Pimentel model (three-center four-electron bond), and high ionic bonding between the ligands and the central atom is essential for stabilizing hypervalent molecules. Here, we produced one of the simplest hypervalent anions, HF−, which is known to deviate from the Rundle–Pimentel model, and identified its ro-vibrational features. High-level ab inito calculations reveal that its bond dissociation energy is comparable to that of dihalides, as supported by secondary photolysis experiments with irradiation at various wavelengths. The charge distribution analysis suggested that the F atom of HF− is negative and hypervalent and the bonding is more covalent than ionic.
Highlights
Lewis and Langmuir debated the nature of hypervalent chemical bonding as early as the 1920s3, 4, the term “hypervalency” was first defined by Musher in 1969 as a molecule with a central atom of group 15–18 in any oxidation state other than the lowest oxidation state[5]
Theoretical analysis of the electron localization function (ELF) for hypervalent species bonded with electronegative ligands, such as SF6 and PCl5, indicated that the ligands can pull electron density away from the central atom, and the central atom has fewer than eight valence electrons[14, 15]
HF− was produced by electron bombardment of the Ar matrix containing a small amount of CH3F during deposition, and its ro-vibrational bands corresponding to the HF stretching mode were assigned and compared with those obtained using high-level calculations
Summary
Meng-Chen Liu[1], Hui-Fen Chen[2], Chih-Hao Chin[1], Tzu-Ping Huang[1], Yu-Jung Chen3 & Yu-Jong Wu1,4. Theoretical analysis of the electron localization function (ELF) for hypervalent species bonded with electronegative ligands, such as SF6 and PCl5, indicated that the ligands can pull electron density away from the central atom, and the central atom has fewer than eight valence electrons[14, 15] This finding supported the term “hypercoordination”[16, 17] to describe such species. A new parameter called the valence electron equivalent, γ, was introduced to describe the effective number of valence electrons on any particular atom This new definition really echoes ELF calculations[14, 15] for those hypervalent species with strong ionic bonding characters defined by Musher’s definition[5] are reclassified as hypercoordinate. Using this definition, some species previously generally accepted as obeying the octet rule, such as O3 and N2O, would be considered as hypervalent
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