Charge-Shift Bonding in Xenon Hydrides: An NBO/NRT Investigation on HXeY···HX (Y = Cl, Br, I; X = OH, Cl, Br, I, CCH, CN) via H-Xe Blue-Shift Phenomena

Abstract

Noble-gas bonding represents curiosity. Some xenon hydrides, such as HXeY (Y = Cl, Br, I) and their hydrogen-bonded complexes HXeY•••HX (Y = Cl, Br, I; X = OH, Cl, Br, I, CN, CCH), have been identified in matrixes by observing H-Xe frequencies or its monomer-to-complex blue shifts. However, the H-Xe bonding in HXeY is not yet completely understood. Previous theoretical studies provide two answers. The first one holds that it is a classical covalent bond, based on a single ionic structure H-Xe + Y −. The second one holds that it is resonance bonding between H-Xe + Y − and H − Xe +-Y. This study investigates the H-Xe bonding, via unusual blue-shifted phenomena, combined with some NBO/NRT calculations for chosen hydrogen-bonded complexes HXeY•••HX (Y = Cl, Br, I; X = OH, Cl, Br, I, CN, CCH). This study provides new insights into the H-Xe bonding in HXeY. The H-Xe bond in HXeY is not a classical covalent bond. It is a charge-shift (CS) bond, a new class of electron-pair bonds, which is proposed by Shaik and Hiberty et al. The unusual blue shift in studied hydrogen-bonded complexes is its H-Xe CS bonding character in IR spectroscopy. It is expected that these studies on the H-Xe bonding and its IR spectroscopic property might assist the chemical community in accepting this new-class electron-pair bond concept.

Complexes of HXeY with HX (Y, X = F, Cl, Br, I): Symmetry-Adapted Perturbation Theory Study and Anharmonic Vibrational Analysis

“…This method allowed the synthesis, for example, of the first ever compound of argon: the HArF molecule [ 11 , 12 ]. From quantum-mechanical simulations, it is known that the atoms in the positive (H–Ng) part are covalently bonded [ 4 , 7 , 9 , 13 , 14 , 15 , 16 ], although this can be described as a charge-shift bond [ 15 ]. The bonding between the (H–Ng) moiety and the negative Y moiety is predominantly of ionic nature.…”

“…Indeed, xenon forms a large number of compounds and complexes compared to other noble-gas elements, including the HXeY family of compounds: among these, the HXeOH molecule has been studied extensively [ 10 , 14 , 17 , 18 , 19 , 31 ]. The different properties of other complexes have also received considerable attention, both experimentally and computationally: the reported studies include HXeCl/Br/I⋯H O [ 32 , 33 ], HXeCl/Br⋯HCl/Br [ 20 , 34 ], HXeI⋯HBr/I [ 35 ], HXeI⋯HCl and HXeI⋯HCCH [ 36 ], (HXeF) and (HXeF) [ 37 ], HXeF⋯HF [ 13 , 34 , 38 ], HXeBr/Cl⋯HCl/Br and HXeCCH⋯CO [ 14 ], HXeBr⋯CO [ 39 ], HXeSH⋯H O/H S [ 40 ], and HXeOH⋯H S. Recently, Zhang et al [ 15 ] investigated a large set of systems, i.e., HXeY⋯HX (Y = Cl/Br/I and X = OH/Cl/Br/I/CCH/CN), and established the charge-shift nature of the H-Xe bonding in the noble-gas molecule.…”

Equivalent and Complement of the ω-Bonding Model and Charge-Shift Bonding Model: A Natural Bond Orbital/Natural Resonance Theory/Atoms in Molecules Investigation via Cu/Ag/Au Bonding in BMX (B = H2O, H2S, NH3, and PH3; M = Cu, Ag, and Au; and X = F, Cl, Br, and I)

“…However, we anticipate that CS bonding should also be important in understanding Cu/Ag/Au bonding based on some studies by Shaik et al. − The CS bond belongs to a new class of chemical bonds, emerging from the valent bond (VB) theory, and it is supported by the atoms in molecules (AIM) theory. − Since 1992, this model has been successfully applied to understand the bonding in diatomic halogen molecules (e.g., F 2 ), hypermolecules (e.g., Cl 3 – and XeF 2 ), , transition metal species (e.g., Au 2 and MX), , etc. Our recent study on xenon hydrides using NBO/NRT analyses demonstrated that the H–Xe bonds in all studied molecules exhibit a CS bonding character . In comparison to the CS bonding model, ω-bonding is also one quantum chemically derived model.…”

“…In recent decades, two new resonance bonding models, charge-shift (CS) bonding and ω-bonding, which involve the delocalization of σ-electrons have been proposed. These two models have been proven valuable in understanding bonding and rationalizing stability of some novel molecules, such as the three-center (3c), four-electron (4e) hypervalent molecule HXeF. , Coincidentally, Legon et al prepared many 3c/4e transition metal complexes BMX (where B is a small Lewis base, M is a coinage metal atom, and X is a halogen atom) in matrix and characterized them using rotational spectroscopy. − Their studies provide opportunities to probe the relation between the ω-bonding model and CS bonding model by examining the Cu/Ag/Au bonding in BMX complexes.…”

“…Our recent study on xenon hydrides using NBO/NRT analyses demonstrated that the H−Xe bonds in all studied molecules exhibit a CS bonding character. 4 In comparison to the CS bonding model, ω-bonding is also one quantum chemically derived model. Weinhold et al 2 were the first to propose the ω-bonding model and rationalize the bonding in some 3c/4e hypervalent molecules (e.g., F 3 − ) by considering the strong resonance of two natural Lewis structures.…”