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

Unconventional Radical and Radical-Hole Site-Based Interactions in Halogen-Bearing Dimers and Trimers: A Comparative Study

Radical (R•) and R•-hole site-based interactions are comparatively studied, for the first time, using ab initio methods. In this regard, R•-bearing molecules •XO3 (where X = Cl, Br, and I) were subjected to direct interaction with NH3 within dimeric and trimeric forms in the form of NH3···•XO3/•XO3···NH3 and NH3···•XO3···NH3 complexes, respectively. As confirmed by electrostatic potential analysis, the studied R•-bearing molecules •XO3 had the outstanding potentiality to interact as Lewis acid centers via two positive sites dubbed as R• and R•-hole sites. Such an observation proposed the potentiality of the considered •XO3 molecules to engage in unconventional R• and well-established R•-hole site-based interactions with Lewis bases. This was confirmed by negative interaction (E int) energies, ranging from -4.93 to -19.89 kcal/mol, with higher favorability for R• site-based interactions over the R•-hole site-based ones. MP2 energetic features furnished higher preferability for the R• site-based interactions than the R•-hole site-based ones in the case of chlorine- and bromine-bearing complexes, and the reverse was true for the iodine-bearing complexes. Moreover, elevated E int values were recorded for the NH3···•XO3···NH3 trimers over the NH3···•XO3 and •XO3···NH3 dimers, outlining the higher preference of the •XO3 molecules to engage in R• and R•-hole site-based interactions in the trimeric form over the dimeric one. These results might be considered a requisite linchpin for numerous forthcoming supramolecular chemistry and crystal engineering studies.

Intermolecular hydrogen bonds between 1,4-benzoquinones and HF molecule: Synergetic effects, reduction potentials and electron affinities

Some biological activities of quinones can be attributed to the H-bonding ability of acceptor oxygen atoms. According to the results obtained from the quantum mechanical calculations performed on a wide variety of complexes between the 1,4-benzoquinone (BQ) derivatives and HF molecules, the interplay between H-bonds and individual H-bond interaction energies (E_HB) can be affected by the substituents placed on the six-membered ring of BQ. The total binding energies of complexes become more negative by the electron donating substituents (EDSs) while the changes are reversed by the electron withdrawing substituents (EWSs). The mutual interplay between the X-BQ⋯(HF)_n (n=1-3) interactions has been investigated using the geometrical parameters, synergetic energies (SE) and the E_HB values. Hydrogen bonding decreases the reduction potentials (E⁰_red) and increases the electron affinities (EA) of X-BQ derivatives. Linear relationships have been observed between the E⁰_red (and EA) values and the Hammett constants of substituents.

Benchmark, DFT assessments, cooperativity, and energy decomposition analysis of the hydrogen bonds in HCN/HNC oligomeric complexes

Hydrogen cyanide (HCN) and its tautomer hydrogen isocyanide (HNC) are relevant for extraterrestrial chemistry and possible relation to the origin of biomolecules. Several processes and reactions involving these molecules depend on their intermolecular interactions that can lead to aggregates and liquids especially due to the hydrogen bonds. It is thus important to comprehend, to describe, and to quantify their hydrogen bonds, mainly their nature and the cooperativity effects. A systematic study of all linear complexes up to pentamers of HCN and HNC is presented. CCSD(T)/CBS energy calculations, with and without basis set superposition error (BSSE) corrections for energies and geometries, provided a suitable set of benchmarks. Approximated methods based on the density functional theory (DFT) such as BP86, PBE, TPSS, B3LYP, CAM-B3LYP with and without dispersion corrections and long-range corrections, were assessed to describe the interaction energies and cooperativity effects. These assessments are relevant to select DFT functionals for liquid simulations. Energy decomposition analysis was performed at the PBE/STO-TZ2P level and provided insights into the nature of the hydrogen bonds, which are dominated by the electrostatic component. In addition, several linear relationships between the various energy components and the interaction energy were obtained. The cooperativity energy was also found to be practically linear with respect to the interaction energy, which may be relevant for designing and/or correcting empirical force fields. Graphical Abstract Hydrogen bonds in HCN/HNC oligomeric complexesᅟ.

Enhancing the hydrogen bond between the bridged hydrogen atom of diborane and ammonia

The character of the bridged hydrogen atom (Hb) of B2H6 has become a hot issue in recent years. In this work, the complexes B2H6 · · · NH3, B2H2X4 · · · nNH3 (n = 1, 2) and 2HF · · · B2H2X4 · · · 2NH3 (X = Cl, Br, I) were constructed and studied based on the M06-2X calculations to investigate how to enhance the Hb · · · N hydrogen-bonded interaction. When the terminal hydrogen atoms (Ht) of B2H6 were replaced by X (X = Cl, Br, I) atoms, the Hb · · · N hydrogen bond were strengthened. According to the electrostatic potentials in B2H2X4, two HF molecules were added to the interspace of the B-H-B-H four-membered ring of the B2H2X4 · · · 2NH3 complexes, and H · · · X hydrogen bond formed, resulting in further enhancing effect of Hb · · · N hydrogen bond. As a result, the positive cooperative effect of Hb · · · N hydrogen bond and H · · · X hydrogen bond do enhance the interactions of each other. The two measures not only enhance the strength of Hb · · · N hydrogen bond, but also achieve the goal to make the Hb · · · N hydrogen bond perpendicular to B · · · B direction.

Effect of cooperativity in lithium bonding on the strength of halogen bonding and tetrel bonding: (LiCN)n···ClYF3 and (LiCN)n···YF3Cl (Y = C, Si and n = 1-5) complexes as a working model

This paper reports results of cooperativity in lithium bonding on the strength of halogen bonding and tetrel bonding in complexes pairing CF3Cl and SiF3Cl with (LiCN)n complexes, where n varies from 1 to 5. Molecular geometries and stabilization energies of title complexes are calculated at the MP2 level with 6-311++G(d,p) basis set. Cooperative effects are found in terms of structural and energetic properties when lithium, halogen, and tetrel bonds are present in these complexes simultaneously. Our results reveal that strength of halogen and tetrel bondings are enhanced due to cooperativity of Li···N interactions in lithium bonded complexes. Good linear correlations between cooperativity parameters and electronic properties of complexes were established in the present study.

Study on the cooperativity of hydrogen bonds between H2Y and HX (X = F, Cl, Br; Y = O, S, Se)

The structure characteristics, interaction energies, cooperative energies of the complexes between chalcogen hydrides ( H 2 Y ) and halogen hydrides (HX) have been studied theoretically at the MP2 level with aug-cc-pVTZ basis set in this paper. The conclusions show that there are strong interactions between H 2 Y and HX. The stability of the complex is decided by the electronegativity of the negatively charged atom. The cooperativity is observed in the two or three hydrogen bonds of each trimer structures in title system. The values of the cooperative energies and the cooperative contributions all illustrate that the cooperativity is of great importance in these complexes. The "atoms in molecules" (AIM) analyses show that the complexes in title system are mainly electrostatic interactions (closed-shell interactions) in character. For H ⋯ O bonds in H 2 O ⋯ HF ⋯ H 2 O , H 2 O ⋯ HBr ⋯ H 2 O and HF ⋯ H 2 O ⋯ HF , the 1 < |Vc|/Gc < 2 and -Gc < Hc < 0 indicate the interactions in these compounds are between closed-shell interaction and opened-shell interaction.

The structures of heterocyclic complexes ruled by hydrogen bonds and halogen interactions: interaction strength and IR modes

In this work, the existence of multiple interactions in heterocyclic complexes of C2H4O⋯nHCCl3 and C2H4S⋯nHCCl3 with n=2 and 3 was unveiled at the B3LYP/6-311++G(d,p) level of theory. The forward analyses of the vibrational spectra revealed the appearing of red-shifts in the H-C bond. In agreement with this and through the optimized geometries of these systems, an increase in the H-C bond length was also observed. Besides O⋯H and S⋯H, other hydrogen bonds formed between chlorine⋯hydrogen and mainly the halogen interactions formed by chlorine⋯chlorine were identified. Thereby, the vibration spectra of the heterocyclic complexes were reanalyzed with the purpose to locate new red-shifts, although only those characterized in H-C have been detected up to then. In addition to the correlation between the frequencies shifted to downward values followed by increases in the bond lengths, the interpretation of the red-shifts was conducted by means of the Bent rule of the hybridization theory. The interaction strength was examined in several viewpoints, and one of them was the relationship between the H-bond energies and the intermolecular electronic density computed by means of the Quantum Theory of Atoms in Molecules (QTAIM). Moreover, the prediction of the interaction strength was also made through the combination between vibration modes (red-shifts) and variation of topological parameters, such as the electronic density and Laplacian of the proton donor bond (C-H).

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

A single-electron tetrel bond was predicted and characterized in FXH₃⋯CH₃ (X = C, Si, Ge, and Sn) complexes.

Ab Initio Study of Cooperative Effects in Complexes X:HBO:Z, with X, Z=LiH, HNC, HF, HCN, HCl, ClF, and HBO: Structures, Binding Energies, and Spin-Spin Coupling Constants across Intermolecular Bonds

A systematic ab initio investigation has been carried out to determine the structures, binding energies, and spin-spin coupling constants of ternary complexes X:HBO:Z for X, Z= LiH, HNC, HF, HCN, HCl, ClF, and HBO. All complexes X:HBO:Z are linear with C∞ v symmetry, except for HCl:HBO:Z and ClF:HBO:Z which have Cs symmetry, thereby reflecting the structures of the corresponding X:HBO and HBO:Z complexes. Cooperative effects on energies are synergistic in all ternary complexes. The enhanced binding energies of complexes X:HBO:Z correlate with the binding energies of the X:HBO and HBO:Z complexes. Coupling constants 1J(B-H) and 2hJ(B-A) across B-H···sA hydrogen bonds correlate with the B-A distance, and exhibit synergistic effects due to the presence of Z. 1hJ(H-A) indicates that these bonds have little proton-shared character. Coupling constants across D-H···sO hydrogen bonds, H-Li···sO lithium bonds, and F-Cl···sO halogen bonds are also sensitive to the synergistic effects arising from the presence of X. D-H···sO hydrogen bonds in ternary complexes are traditional (normal) hydrogen bonds.

Cooperative and diminutive interplay between lithium and dihydrogen bonding in F3YLi…NCH…HMH and F3YLi…HMH…HCN triads (Y=C, Si; M=Be, Mg)

The F(3)YLi…NCH…HMH and F(3)YLi…HMH…HCN triads (Y=C, Si; M=Be, and Mg) are connected by lithium and dihydrogen bonds. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries, binding energies, infrared spectra and NMR properties of monomers, dyads, and triads are investigated at the MP2/6-311++G** computational level. Particular attention is paid to parameters, such as cooperative energies, and many-body interaction energies. Triads with the HMH molecule located at the end of the chain, show energetic cooperativity ranging between -3.66 to -7.59 kJ mol(-1). When the HMH molecule is located in the middle, the obtained cluster is diminutive with an energetic effect between 3.49 to 5.17 kJ mol(-1). The electronic properties of the complexes are analyzed using parameters derived from the atoms in molecules (AIM) methodology.

Modulating the Strength of Hydrogen Bonds through Beryllium Bonds

The mutual influence between beryllium bonds and inter- or intramolecular hydrogen bonds (HBs) has been investigated at the B3LYP/6-311++G(3df,2p) level of theory, using the complexes between imidazole dimer and malonaldehyde with BeH2 and BeF2 as suitable model systems. Imidazole and its dimer form very strong beryllium bonds with both BeH2 and BeF2, accompanied by a significant geometry distortion of the Lewis acid. More importantly, we have found a clear cooperativity between these two noncovalent interactions, since the intermolecular HB between the two imidazole molecules in the dimer-BeX2 complex becomes much stronger than in the isolated dimer, whereas the beryllium bond becomes also stronger in the dimer-BeX2 complex, with respect to that found in the imidazole-BeX2 complex. The effects of beryllium bonds are also dramatic on the strength of intramolecular HBs. Depending on to which center the BeX2 is attached, the intramolecular HB becomes much stronger or much weaker. The first situation is found when the beryllium derivative is attached to the HB donor, whereas the second occurs if it is attached to the HB acceptor. The first effect can be so strong as to produce a spontaneous proton transfer, as it is actually the case of the malonaldehyde-BeF2 complex.

The NHF Interactions in the X-Pyridazine Complexes: Substituent Effects and Energy Components

The effects of substituents on the N⋯HF interactions in the X-pyridazine (X = N(CH3)2, NHCH3, NH2, C2H5, CH3, OCH3, OH, CN, OF, NO2, F, Br, Cl, and ) complexes have been studied at the B3LYP/6-311++G(d,p) level of theory. In all complexes, the binding energies increase for the electron-donating substituents and decrease for the electron-withdrawing substituents. A negative cooperativity is observed for two hydrogen bond interactions. There are meaningful relationships between the Hammett constants and the energy data and the results of population analysis in the binary and ternary complexes. Symmetryadapted perturbation theory (SAPT) analysis was also carried out to unveil the nature of hydrogen bond in the complexes 2 and 3. The electron-donating substituents increase the magnitude of the SAPT interaction energy components and the electron-withdrawing substituents decrease those components. The highest/lowest change is observed for the component. The effect of C2H5 (or CH3) on different components is higher than OCH3 in the complex 2 while the trend is reversed in the complex 3. It is demonstrated that the electrostatic interaction plays a main role in the interaction, although induction and dispersion interactions are also important.

Theoretical study of the interplay between lithium bond and hydrogen bond in complexes involved with HLi and HCN

The lithium- and hydrogen-bonded complex of HLi-NCH-NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6-311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19% and 61% for the lithium and hydrogen bonds, respectively. A big cooperative energy (-5.50 kcal mol(-1)) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many-body interaction analysis has also been performed for HLi-(NCH)(N) (N=2-5) systems.