Single-electron Hydrogen Bond Research Articles

On the formation of beryllium bonds where radicals act as electron donors

The complexes between BeX2 (X = F, H) with CH3, CH2CH3, CH(CH3)2 and C(CH3)3 radicals have been characterized by using the MP2 and CCSD(T) methods and AIM procedure. The formation of these complexes is found to originate from the interaction between the positively charged Be atom and the unpaired electron of the radicals, and this interaction is closed shell in essence. During complexation with radicals, all the BeX2 molecules feature redshifted X–Be–X antisymmetric stretching vibrations, according well with the lengthening of Be–X bonds. According to the computed interaction energies, methyl substitution imposes a positive effect on the complex formation. Energy decomposition analysis indicate that the stability of the topic complexes mainly comes from the attractive electrostatic and polarization terms, which is similar to the case of π-beryllium bonds. By comparisons with some related systems, it can be concluded that the bond strength increases in the order single-electron hydrogen bond < single-electron sodium bond < single-electron lithium bond < single-electron beryllium bond ≈ π-beryllium bond.

Binding energies and interaction origins between nonclassical single-electron hydrogen, sodium and lithium bonds and neutral boron-containing radicals: a theoretical investigation

Nonclassical single electron hydrogen, sodium and lithium bonds (SEHBs, SENaBs and SELiBs) between single electron acceptors X–A (A=H, Na, Li; X=CN, HCC, HO, NC, CF3) and neutral radicals BY2 (Y=H, OH, CH3) and have been systematically investigated by high level theoretical methods, such as second-order Moller-Plesset perturbation theory (MP2), spin-component-scaled Moller-Plesset theory (SCS-MP2), the coupled cluster method with perturbative triples (CCSD(T)), and the correlation consistent composite approach (ccCA). Binding energies have been corrected for zero-point vibrational effects and (when applicable) basis set superposition error. The quantum theory of atoms in molecules (AIM) and natural bond orbital (NBO) analyses were also employed to qualitatively characterize the single electron bond interactions. The stabilization energy was partitioned via the localized molecular orbital energy decomposition analysis (LMO-EDA) method, and both electrostatic and exchange interactions were seen to be major driving forces for the complex stabilization. Interestingly, the sum of the energy contributors of exchange (EEX), repulsion (EREP), polarization (EPOL), dispersion (EDIS) is close to zero and the changes in the interaction energy follow the trend of the electrostatic energy (EES). We observe several linear relationships among the optimized intermolecular parameters and the interaction energies of the various complexes.

The single-electron hydrogen, lithium, and halogen bonds with HBe, H2B, and H3C radicals as the electron donor: an ab initio study

Quantum chemical calculations have been performed for the complexes with HBe, H2B, and H3C radicals as the electron donors and with HF, LiF, and ClF as the electron acceptors. For HBe, H2B, and H3C radicals, the ability of donating electrons is dependent on the nature of the electron donor atom. In addition, it is also affected by the nature of the electron acceptor atom. A partially covalent bond is formed in HBe–Cl···F and H2B–Cl···F complexes, which exhibits a large interaction energy, short binding distance, large bond elongation, and big frequency shift. The complexes have also been analyzed with natural bond orbital and atoms in molecules.

Hydrogen and covalent bonding in H 2B [sbnd]HX and H 2B [sbnd]XH (X = CN and NC) dimers and cooperative effect in H 2B [sbnd]HX [sbnd]HX and H 2B [sbnd]XH [sbnd]XH trimers

Quantum chemical calculations have been performed to investigate the interaction of the neutral H 2B radical with hydrogen cyanide (HCN) and hydrogen iso-cyanide (HNC) at the MP2/aug-cc-pVTZ level. The results show that a weak hydrogen bond and a strong covalent interaction can be formed between the two molecules. In H 2B HCN HCN and H 2B HNC HNC trimers, there is enhancing interplay between the single-electron hydrogen bond and another type of hydrogen bond. Although the covalent interaction in H 2B NCH and H 2B CNH dimers is also enhanced due to presence of the second NCH (CNH) molecule in H 2B NCH NCH and H 2B CNH CNH trimers, there exists a negative cooperativity between the covalent interaction and the hydrogen bond. The complexes have been analyzed with natural bond orbital (NBO) and atoms in molecules (AIM) theories.

Theoretical study of the interaction mechanism of single-electron halogen bond complexes H3C⋯Br-Y (Y = H, CN, NC, CCH, C2H3)

The characteristics and structures of single-electron halogen bond complexes [H3C⋯Br-Y (Y = H, CCH, CN, NC, C2H3)] have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP/6-311++G** level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyses at the MP2/6-311++G** level. For each H3C⋯Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH3 (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond also possesses the character of a “three-electron bond”. Due to the formation of the single-electron Br bond, the C-H bonds of the CH3 radical bend away from the Br-Y moiety and the Br-Y bond elongates, giving red-shifted single-electron Br bond complexes. The effects of substituents, hybridization of the carbon atom, and solvent on the properties of the complexes have been investigated. The strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.

Influence of Substitution, Hybridization, and Solvent on the Properties of C−HO Single-Electron Hydrogen Bond in CH3−H2O Complex

The effect of substitution, hybridization, and solvent on the properties of the C...HO single-electron hydrogen bond has been investigated with quantum chemical calculations. Methyl radical, ethyl radical, and vinyl radical are used as the proton acceptors and are paired with water, methanol, HOCl, and vinyl alcohol. Halogenation (Cl) of the proton donor strengthens this type of hydrogen bond. The methyl group in the proton donor and proton acceptor plays a different role in the formation of the C...HO single-electron hydrogen bond. The former is electron-withdrawing, and the latter is electron-donating, both making a constructive contribution to the enhancement of the interaction. The contribution of the methyl group in the proton acceptor is larger than that in the proton donor. The increase of acidity of the proton is helpful to form a single-electron hydrogen bond. As the proton acceptor varies from the methyl radical to the vinyl radical, the interaction strength also increases. The solvent has an enhancing influence on the strength of the C...HO single-electron hydrogen bond. These factors affect the C...HO single-electron hydrogen bond in a similar way that they do other types of hydrogen bonds.

Cooperativity between two types of hydrogen bond in H3C–HCN–HCN and H3C–HNC–HNC complexes

Hydrogen-bonded clusters, H(3)C-HCN, HCN-HCN, H(3)C-HCN-HCN, H(3)C-HNC, HNC-HNC, and H(3)C-HNC-HNC, have been studied by using ab initio calculations. The optimized structures, harmonic vibrational frequencies, and interaction energies are calculated at the MP2 level with aug-cc-pVTZ basis set. The cooperative effects in the properties of these complexes are investigated quantitatively. A cooperativity contribution of around 10% relative to the total interaction energy was found in the H(3)C-HCN-HCN complex. In the case of H(3)C-HNC-HNC complex, the cooperativity contribution is about 15%. The cooperativity contribution in the single-electron hydrogen bond is larger than that in the hydrogen bond of HCN-HCN and HNC-HNC complexes. NMR chemical shifts, charge transfers, and topological parameters also support such conclusions.

Unusual hydrogen bonds in [AH3–H3O]+ radical cations (A=C, Si, Ge, Sn and Pb)Single-electron hydrogen bond, proton-hydride hydrogen bond and formation of [H2AOH2]+–H2 complexes

The hydrogen bond interaction in [AH3–H3O]+ radical cations for A = C, Si, Ge, Sn and Pb is studied at the CCSD(T)/6-311G++(3df,2pd)//MP2/6-31G++(d,p) level of theory. Two unusual hydrogen bond structures are found to be stable: the single-electron (SEHB) and the proton-hydride (PHHB) ones. The latter structures have been found to easily evolve to a [AH2H2O]+–H2 complex, from which H2 can be eliminated.

Unusual hydrogen bonds in [AH 3–H 3O] + [rad] radical cations (A = C, Si, Ge, Sn and Pb) : Single-electron hydrogen bond, proton-hydride hydrogen bond and formation of [H 2AOH 2] + [rad]–H 2 complexes

The hydrogen bond interaction in [AH 3–H 3O] + radical cations for A = C, Si, Ge, Sn and Pb is studied at the CCSD(T)/6-311G++(3df,2pd)//MP2/6-31G++(d,p) level of theory. Two unusual hydrogen bond structures are found to be stable: the single-electron (SEHB) and the proton-hydride (PHHB) ones. The latter structures have been found to easily evolve to a [AH 2H 2O] + –H 2 complex, from which H 2 can be eliminated.

Single-electron hydrogen bonds in the methyl radical complexes H 3C⋯HF and H 3C⋯HCCH: an ab initio study

The methyl radical (CH 3) complexes with hydrogen fluoride (HF) and ethyne (HCCH) are reported to show the existence of a single-electron hydrogen bond. Their geometrical structures are optimized at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels and C 3v stationary structures are obtained for the two complexes. The single-electron hydrogen bond energies of H 3C⋯HF and H 3C⋯HCCH are calculated at six levels of theory [SCF, MP2, MP3, MP4, CCSD, and CCSD(T)] and their harmonic vibrational frequencies are calculated at the MP2/aug-cc-pVTZ level.