Theoretical Predictions of C3v Symmetric Three-H-Bridged Noble Gas Compounds NgBeH3BeR, NgBeH3BR+, and NgBH3BR2+

Theoretical prediction of donor-acceptor type novel complexes with strong noble gas-boron covalent bond

The experimental identification of NgBeO molecules, followed by the recent theoretical exploration of super-strong NgBO+ (Ng = He-Rn) ions motivated us to investigate the stability of iso-electronic NgBNH+ (Ng = He-Rn) ions using various ab initio-based quantum chemical methods. The hydrogen-like chemical behavior of gold in small clusters and molecules also inspired us to study the nature of the bonding interactions in NgBNAu+ ions compared to that in NgBNH+ ions. The calculated Ng-B bond lengths in the predicted ions have been found to be much lower than the corresponding covalent limits, indicating a covalent Ng-B interaction in both the NgBNH+ and NgBNAu+ ions. In addition, the Ng-B bond dissociation energies are found to be in the range of 136.7-422.8 kJ mol-1 for NgBNH+ and 77.4-319.1 kJ mol-1 for NgBNAu+, implying the stable nature of the predicted ions. Interestingly, the Ng-B bond length (except for Ne) is the lowest reported to date together with the highest He-B and Ne-B binding energies considering all the neutral and cationic complexes containing Ng-B bonding motifs. Moreover, the natural bonding orbital (NBO) and electron density-based atoms-in-molecule (AIM) analysis reveal the covalent nature of the Ng-B bond in the predicted ions. Furthermore, the energy decomposition analysis together with the natural bond orbital in the chemical valence (EDA-NOCV) studies indicate that the orbital interaction energy is the main contributor to the total attraction energy in the Ng-B bonds. All the calculated results indicate the hydrogen-like chemical behavior of gold in the predicted NgBNM+ ions, showing further evidence of the concept of "gold-hydrogen analogy". Also, for comparison, the corresponding Cu and Ag analogs are investigated. All the computed results together with the experimental identification of the NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl), ArOH+, and NgBeO (Ng = Ar-Xe) systems clearly indicate that it may be possible to prepare and characterize the predicted NgBNM+ ions experimentally using suitable technique(s).

BH4 Ng+ (Ar-Rn): Viable Compounds with a B-Ng Covalent Bond

In this work, we explore, using high-level calculations, the ability of BH₄ ⁺ to interact with noble gases. The He system is energetically unstable, while the Ne system could only be observed at cryogenic temperatures. In the case of the Ar, Kr and Xe systems, all are energetically stable, even at room temperature. The different chemical bond descriptors reveal a covalent character between B and the noble gas from Ar to Rn. However, this interaction gradually weakens the multicentric bond between the boron atom and the H₂ fragment. Thus, although BH₄ Rn⁺ exhibits a strong covalent bond, it tends to dissociate at room temperature into BH₂ Rn⁺ +H₂ .

Superstrong Chemical Bonding of Noble Gases with Oxidoboron (BO+) and Sulfidoboron (BS+)

Inspired by the overwhelming exploration of noble gas-boron (Ng-B) bond containing chemical compounds, the stability of the Ng bound BY⁺ and AlY⁺ (Y = O and S) has been investigated by using various ab initio based quantum chemical methods. Ng atoms are found to form exceptionally strong bonds with BO⁺ species in the predicted NgBO⁺ (Ng = He-Rn) complexes with remarkably high Ng-B dissociation energies ranging from 138.0 to 462.2 kJ mol^-1 for the He-Rn series. It is the highest ever Ng-B binding energy in conjunction with the smallest Ng-B bond length for any of the cationic species involving a Ng-B bond as reported until today. More importantly, the calculated Ng-B bond lengths have been found to be much lower than the respective covalent limits in both NgBO⁺ and NgBS⁺ ions. The electronegativity difference between O and S atoms has been reflected nicely in the Ng-B and Ng-Al binding energies, which are found to be 91.9-346.5, 9.6-169.2, and 6.8-142.1 kJ mol^-1 in NgBS⁺, NgAlO⁺, and NgAlS⁺, respectively. The strong covalent bonding between Ng and B/Al atoms in the predicted chemical systems has also been supported by the natural bonding orbital (NBO) and electron density based atoms-in-molecule (AIM) analysis. In addition, the energy decomposition analysis (EDA) in combination with the natural bond orbital for chemical valence (NOCV) indicates that the orbital interaction term is the prime contributor to the total attraction energy in the Ng-B and Ng-Al bonds. Furthermore, Ng-B and Ng-Al bonding can be assessed using the donor-acceptor model where the σ-electron donation that takes place from Ng (HOMO) → XY⁺ (LUMO) (X = B and Al; Y = O and S) is the major contributor to the orbital interaction energy. All the computational results along with the very recent experimental observation of ArOH⁺ and NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl) clearly indicate that it might be possible to synthesize and characterize these superstrong complexes, NgXY⁺ (Ng = He-Rn; X = B and Al; Y = O and S), under suitable experimental technique(s).

RgnBe3B3+: theoretical investigation of Be3B3+ and its rare gas capability

A series of Be₃B₃⁺ and its rare gas (Rg) containing complexes Rg_nBe₃B₃⁺ (Rg = He-Rn, n = 1-6) have been predicted theoretically using the B3LYP, MP2, and CCSD(T) methods to explore structures, stability, charge distributions, and nature of bonding. Both Be₃B₃⁺ and RgBe₃B₃⁺ are the global minima on the potential energy surfaces. In the Rg_nBe₃B₃⁺ complexes, the dissociation energy drops with the increase in number of Rg. Natural bond orbital (NBO) and topological analysis of the electron density (AIM) show that the Rg-Be bonds for Kr-Rn have some covalent character. The Rg-Be bond is stabilized dominantly by the Rg → Be₃B₃⁺ σ-donation from the valence p orbital of Rg to the vacant valence LUMO orbital of Rg_n-1Be₃B₃⁺. Besides, other two π-donations also play important roles in stabilizing the Rg-Be bonds.

Neutral nano-polygons with ultrashort Be–Be distances

DFT calculations revealed that neutral polygons (E-Be₂H₃)_n are the viable targets for realizing ultrashort metal–metal distances between main group metals.

Quantum chemical prediction of a superelectrophilic dianion and its binding with noble gas atoms

A counterintuitive superelectrophilic dianion with a positive charge as well as lowest occupied molecular orbital (LUMO) localized on free-Be1 in Dianion1 embedded in the negatively charged framework, forms stable [NgBeB₁₁(CN)₁₁]²⁻ compounds.

Compounds with Rare Gas-Selenium/Tellurium Bonds: A Theoretical Investigation on FRgLF n and FRgLF n-1+ (Rg = Kr-Rn, L = Se and Te, n = 1, 3, and 5)

A new type of interesting insertion compounds FRgLF _n (Rg = Kr-Rn, L = Se and Te, n = 1, 3 and 5) and ionic FRgLF _n-1⁺ obtained through the insertion of a rare gas atom into the selenium fluorides and tellurium fluorides have been explored theoretically using MP2, CCSD(T), and PBE0 calculations. These predicted species were examined to present the optimized geometries, vibrational modes, molecular properties, thermodynamic and kinetic stabilities and bond nature. The optimized structures are without imaginary frequencies and metastable. In neutral FRgLF _n, F-Rg bonds should be of ionic character with large dissociation energy ranging from 150-200 kcal mol^-1 that could be best described by F^-(RgLF _n)⁺. Rg-L bonds have some covalent character with lower interaction energies within the range 25-40 kcal mol^-1. In FRgL⁺ and FRgLF₂⁺, the bonding nature of the F-Rg and Rg-L bonds are somewhat similar to that of the neutral compounds. In FRgLF₄⁺, the F-Rg bond could be of partial covalent type but the Rg-L bond could be considered as an ionic bond.

Noble gas supported boron-pentagonal clusters B5Ngn3+: exploring the structures and bonding

A novel type of trivalent BNg five-membered cational species B₅Ng_n³⁺(Ng = He~Rn, n = 1~5) has been found and investigated theoretically using the B3LYP and MP2 methods with the def2-QZVPPD and def2-TZVPPD basis sets. The geometry, harmonic vibrational frequencies, bond energies, charge distribution, bond nature, aromaticity, and energy decomposition analysis of these structures were reported. The calculated B-Ng bond energy is quite large (the averaged bond energy is in the range of 209.2~585.76 kJ mol^-1) for heavy rare gases and increases with the Ng atomic number. The analyses of the molecular wavefunction show that in the BNg compounds of heavy Ng atoms Ar~Rn, the B-Ng bonds are of typical covalent character. Nuclear independent chemical shifts display that both B₅³⁺ and B₅Ng_n³⁺(n=1~5) have obvious aromaticity. Energy decomposition analysis shows that these BNg compounds are mainly stabilized by the σ-donation from the Ng valence p orbital to the B₅³⁺ LUMO. These findings offer valuable clues toward the design and synthesis of new stable Ng-containing compounds.

Monocyclic aromatic compounds BnRgn(n-2)+ of boron and rare gases

The monocyclic compounds (BRg)₃⁺(D_3h), (BRg)₄²⁺(D_4h), (BRg)₅³⁺(D_5h) and (BRg)₆⁴⁺(D_6h) formed between boron and rare gases Rg (He-Rn) are theoretically predicted to be stable structures and have π-aromaticity with a delocalized nc-2e π-system. For heavier rare gases Ar-Rn, the B-Rg bond energy is quite high and ranges from 15 to 96 kcal mol^-1, increasing with the ring size and the atomic number of rare gases; the B-Rg bond length is close to the sum of covalent radii of B and Rg atoms; NBO and AIM analyses show that the B-Rg bonds for Ar-Rn have a typical covalent character. The B-Rg bond is stabilized mainly by σ-donation from the valence p orbital of Rg to the vacant valence orbital of the boron ring. We searched for a large number of isomers for the systems of Ar and found that the titled monocyclic compounds (BAr)₃⁺(D_3h), (BAr)₄²⁺(D_4h) and (BAr)₅³⁺(D_5h) should be global energy minima. For (BAr)₆⁴⁺ the global energy minimum is an octahedral caged structure, but the titled monocyclic compound is the secondary stable local energy minimum. The energy and thermodynamic stability of the ring B_nRg_n^(n-2)+ cations indicate that these rare gas compounds may be viable species in experiments.