Tuning of carbon bonds by substituent effects: an ab initio study

ABSTRACT

An ab initio study, at the MP2/aug-cc-pVTZ level of theory, is performed to study σ-hole bond in binary XH₃C···CNY complexes, where X = CN, F, NO₂, CCH and Y = H, OH, NH₂, CH₃, C₂H₅, Li. This type of interaction is labelled as ‘carbon bond’, since a covalently bonded carbon atom acts as the Lewis acid in these systems. The geometrical and energetic parameters of the resulting complexes are analysed in details. The interaction energies of these complexes are between ?4.97 kJ/mol in (HCC)H₃C···CNH and ?23.07 kJ/mol in (O₂N)H₃C···CNLi. It is found that the electrostatic interaction plays a key role in the overall stabilisation of these carbon-bonded complexes. To deepen the understanding of the nature of the carbon-bonding, the molecular electrostatic potential, natural bond orbital, quantum theory of atoms in molecules and non-covalent interaction index analyses are also used. Our results indicate that the carbon bond is favoured over the C-H···C hydrogen bond in the all complexes considered and may suggest the possible important roles of the C···C interactions in the crystal growth and design.     

Tuning of tetrel bonds interactions by substitution and cooperative effects in XH3Si···NCH···HM (X = H,F, Cl,Br; M = Li,Na, BeH and MgH) complexes

In this work, the interplay between the tetrel bond and the dihydrogen bond is investigated in ternary XH₃Si···NCH···HM complexes, where X = H, F, Cl, Br and M = Li, Na, BeH, MgH. The nature of Si···N and H···H interactions is studied by molecular electrostatic potential (MEP), noncovalent interaction and electron localisation function analyses. All binding distances in the ternary complexes are shorter than those of isolated XH₃Si···NCH and NCH···HM systems. That is, the two types of interactions have a cooperative effect on each other. The results of the MEP analysis indicate that the enhancement of the Si···N and H···H bonds can mainly be attributed to the electrostatic interaction. The plot of the reduced density gradient versus sign (λ₂)ρ indicates that the location of the spike associated with each interaction in the ternary systems moves slightly towards the negative (λ₂)ρ values with respect to the binary systems. This confirms that both Si···N and H···H interactions in the ternary complexes are strengthened by the presence of other. Besides, cooperative effects lead to a considerable change in the ¹⁴N nuclear quadrupole coupling constant values of the ternary complexes relative to the XH₃Si···NCH complexes.     

Substituent effects in cooperativity of chalcogen bonds

In the present work, substituent effects on cooperativity of S···N chalcogen bonds are studied in XHS···NCHS···4-Z–Py (X = F, Cl; Z = H, F, OH, CH₃, NH₂, NO₂, and CN; and Py = pyridine) complexes using ab initio calculations. An increased attraction or a positive cooperativity is observed on introduction of a third molecule to the XHS···NCHS and NCHS···4-Z–Py binary systems. The shortening of each chalcogen bond distance in the ternary systems is dependent on the substituent Z and is increased in the order Z = NH₂ > OH > CH₃ > H > F > CN > NO₂. The electronic aspects of the complexes are analysed using molecular electrostatic potential, and the parameters derived from the atoms in molecules and natural bond orbital methodologies. According to interaction energy decomposition analysis, the electrostatic energies are important in the interaction energy of S···N bonds and may be regarded as being responsible for the stability of these complexes.     

The strengthening effect of a hydrogen or lithium bond on the Z···N aerogen bond (Z = Ar,Kr and Xe): a comparative study

An ab initio study is performed on O₃Z···NCM···NCX (Z = Ar, Kr and Xe; M = H and Li; X = H, F and CH₃) complexes to investigate cooperativity effects between aerogen and hydrogen or lithium bonding interactions in these systems. To understand the cooperative effects, a detailed analysis of the binding distances, interaction energies and bonding properties is performed on these complexes. The results indicate that all Z···N and H/Li···N binding distances in the ternary complexes are shorter than those of corresponding binary systems. For a given M or X, cooperative energies increase as Z = Xe > Kr > Ar. Moreover, O₃Z···NCLi···NCX complexes exhibit a larger cooperative energy than O₃Z···NCH···NCX ones. The non-covalent interaction (NCI) index analysis indicates that the formation of an H/Li···N interaction in the ternary complexes shifts the location of the spike associated with the Z···N interaction towards the negative λ₂ρ values. This indicates that NCI analysis can be regarded as a useful tool for the study of cooperative effects between two different non-covalent interactions. Also, cooperative effects in O₃Z···NCM···NCX complexes make a decrease in ¹⁴N nuclear quadrupole coupling constants of NCH or NCLi molecule.     

Interplay and competition between the lithium bonding and halogen bonding: R3C···XCN···LiCN and R3C···LiCN···XCN as a working model (R = H,CH3; X = Cl,Br)

UMP2 calculations with aug-cc-pVDZ basis set were used to analyse intermolecular interactions in R₃C···XCN···LiCN and R₃C···LiCN···XCN triads (R = H, CH₃; X = Cl, Br) which are connected via lithium bond and halogen bond. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries and binding energies of dyads, and triads are investigated at the UMP2/aug-cc-pVDZ computational level. Particular attention is paid to parameters such as cooperative energies, and many-body interaction energies. All studied complexes, with the simultaneous presence of a lithium bond and a halogen bond, show cooperativity with energy values ranging between ?1.20 and ?7.71 kJ mol^?1. A linear correlation was found between the interaction energies and magnitude of the product of most positive and negative electrostatic potentials (V_S,maxV_S,min). The electronic properties of the complexes are analysed using parameters derived from the atoms in molecules (AIM) methodology. According to energy decomposition analysis, it is revealed that the electrostatic interactions are the major source of the attraction in the title complexes.     

An ab initio study on substituent and cooperative effects in bifurcated fluorine bonds

Bifurcated fluorine bond (BFB) interactions are studied in model binary complexes pairing N-formyl formamide derivatives and FX molecules (X = F, CN, NC, CF₃ and CCH) by means of ab initio calculations. The calculated F···O binding distances in these complexes are in the range of 2.813–3.048 Å. The corresponding interaction energies lie in a narrow range, from?2.25 to ?16.49 kJ/mol. The nature of BFBs is analysed by a vast number of methods including molecular electrostatic potential, quantum theory of atoms in molecules, non-covalent interaction index and natural bond orbital methods. According to the energy decomposition analysis, the electrostatic and dispersion effects have a dominant role in the formation of these complexes. The formation of a hydrogen- and lithium-bonding interaction tends to increase the strength of BFBs in the ternary XF:NFF-H:NH₃ and XF:NFF-Li:NH₃ complexes, respectively.     

Cooperative interaction between π-hole and single-electron σ-hole interactions in O2S···NCX···CH3 and O2Se···NCX···CH3 complexes (X = F,Cl, Br and I)

Ab initio calculations are performed to analyse the cooperative effects between π-hole and single-electron σ-hole interactions in O₂S···NCX···CH₃ and O₂Se···NCX···CH₃ complexes, where X = F, Cl, Br and I. These effects are investigated in terms of geometric and energetic features of the complexes, which are computed by UMP2/aug-cc-pVTZ(-PP) method. Our results indicate that the shortening of the each π-hole bond distance in the complexes is dependent on the strength of the σ-hole interaction. The maximum and minimum energetic cooperativity values correspond to the most and least stable complexes studied in the present work. The cooperativity between both types of interaction is chiefly caused by the electrostatic effects. The topological analysis, based on the quantum theory of atoms in molecules, is used to characterise the interactions and analyse their enhancement with varying electron density at bond critical points.     

Strengthening of the halogen-bonding by an aerogen bond interaction: substitution and cooperative effects in O3Z···NCX···NCY (Z = Ar,Kr, Xe; X = Cl,Br, I; Y = H,F, OH) complexes

The geometry, interaction energy and bonding properties of ternary complexes O₃Z···NCX···NCY (Z= Ar, Kr, Xe; X = Cl, Br, I and Y = H, F, OH) are investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Two different types of intermolecular interactions are present in these complexes, namely, aerogen bond (Z···N) and halogen bond (X···N). The formation mechanism and bonding properties of these complexes are analysed with molecular electrostatic potentials, quantum theory of atoms in molecules and non-covalent interaction index. It is found that the cooperativity energies in the ternary complexes are all negative; that is, the interaction energy of the ternary complex is greater (more negative) than the sum of the interaction energies of the corresponding binary systems. Also, the cooperativity energies increase with the increase of the interaction energies. The cooperative effects in the ternary complexes make a decrease in the total spin–spin coupling constants across the aerogen bonding, J(Z–N), which can be regarded as a proof for the reinforce of Z···N interactions in the ternary complexes with respect to the binary systems.     

Chalcogen bonds tuned by an N–H···π or C–H···π interaction: investigation of substituent,cooperativity and solvent effects

In the present work, ab-initio calculations are performed to investigate cooperativity effects between chalcogen bond and H···π interactions in XHY···NCH···C₆H₆ and XHY···CNH···C₆H₆ complexes, where X = F, Cl, Br, CN, NC, and Y = S, Se. The nature of these interactions and the mechanism of cooperativity are studied by means of quantum theory of atoms in molecules, noncovalent interaction index, many-body analysis of interaction energy and electron density shift analysis. For each ternary complex, the shortening of the Y···N(C) distance is more pronounced than that of the H···π. The cooperative energies of these complexes are all negative which demonstrate a positive cooperativity between the Y···N(C) and H···π interactions. The many-body analysis of interaction energy reveals that the two-body energy term has the largest contribution to the total interaction energies of ternary complexes. A good linear correlation is established between the three-body energy and cooperative energy values in the ternary systems. The cooperative energies of XHY···CNH···C₆H₆ complexes indicate a larger sensitivity on the polarity of solvent than XHY···NCH···C₆H₆ ones.     

Prediction and characterisation of a chalcogen···π interaction with acetylene as a potential electron donor in XHS···HCCH and XHSe···HCCH (X = F,Cl, Br,CN, OH,OCH3, NH2, CH3) σ-hole complexes

It is well-known that many covalently bonded atoms of group VI have specific positive regions of electrostatic potential (σ-holes) through which they can interact with Lewis bases. This interaction is called ‘chalcogen bond’ by analogy with halogen bond and hydrogen bond. In this study, ab initio calculations are performed to predict and characterise chalcogen···π interactions in XHS···HCCH and XHSe···HCCH complexes, where X = F, Cl, Br, CN, OH, OCH₃, NH₂, CH₃. For the complexes studied here, XHS(Se) and HCCH are treated as a Lewis acid and a Lewis base, respectively. The CCSD(T)/aug-cc-pVTZ interaction energies of this type of σ-hole bonding range from ?1.18 to ?4.83 kcal/mol. The calculated interaction energies tend to increase in magnitude with increasing positive electrostatic potential on the extension of X–S(Se) bond. The stability of chalcogen···π complexes is attributed mainly to electrostatic and correlation effects. The nature of chalcogen···π interactions is unveiled by means of the atoms in molecules, natural bond orbital, and electron localisation function analyses.     

The influence of halogen-bonding cooperativity on the hydrogen and lithium bonds: an ab initio study

ABSTRACT

Ab initio calculations are carried out to study linear NCH···(NCX)_1–5 and NCLi?…?(NCX)_1–5 clusters (X?=?F, Cl, Br). The aim is to study the influence of halogen-bonding cooperativity on the strength and bonding properties of hydrogen or lithium bond. Particular attention is given to parameters such as binding distances, interaction energies and cooperative energies in these systems. According to our results, the halogen-bonding cooperativity between the NCX molecules has an enhancing effect on the strength of hydrogen and lithium bonds, with an increase of 0.33–0.93 and 0.19–0.43?kcal/mol in NCH···(NCX)_n and NCLi···(NCX)_n, respectively. The enhancing effect of halogen bond on the hydrogen and lithium bond is dependent on the nature of halogen atom, and increases as X?=?F?相似文献   

Enhancement effect of lithium bonding on the strength of pnicogen bonds: XH2P···NCLi···NCY as a working model (X = F,Cl; Y = H,F, Cl,CN)

MP2 calculations with aug-cc-pVDZ basis set were used to analyse intermolecular interactions in XH₂P···NCLi···NCY triads (X = F, Cl; Y = H, F, Cl, CN) which are connected via pnicogen bond and lithium bond. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries and interaction energies of dyads, and triads are investigated at the MP2/aug-cc-pVDZ computational level. Particular attention is paid to parameters such as cooperative energies and many-body interaction energies. All studied complexes, with the simultaneous presence of a lithium bond and a pnicogen bond, show cooperativity with energy values ranging between ?4.73 and ?8.88 kJ mol^?1. A linear correlation was found between the interaction energies and magnitude of the product of most positive and negative electrostatic potentials. According to energy decomposition analysis, it is revealed that the electrostatic interactions are the major source of the attraction in the title complexes.     

An ab initio study on the nature of σ-hole interactions in pnicogen-bonded complexes with carbene as an electron donor

ABSTRACT

A theoretical study of the complexes formed between ZH₂X (Z = P, As, Sb, Bi; X = F, Cl, Br, CN, NC, OH, NH₂) and an N-heterocyclic carbene (imidazol-2-ylidene) is carried out by means of ab initio calculations. According to molecular electrostatic potential analysis, it is inferred that the divalent C atom of the carbene can act as a Lewis base with the pnicogen atom Z of ZH₂X. The pnicogen bond distances (Z–C) are in the range of 2.050–2.911 for these complexes. While the Z?X bonds are longer than the corresponding Z?C bonds in the X = Cl and Br complexes, most of the Z?X bonds are short enough to suggest that they should be considered as covalent bonds which have lost some degree of covalency. For a given Z, the ZH₂Br forms the strongest complex, followed by ZH₂Cl and ZH₂F. On the other hand, the binding energy in the halogenated ZH₂X complexes follows the reverse ranking expected based on the values of the σ-hole of the isolated ZH₂X monomers. The nature of the pnicogen bond interaction in these complexes is analysed by quantum theory of atoms in molecules (QTAIM) and natural bond orbital methods. According to QTAIM analysis, a partially covalent character can be attributed to the pnicogen bonds studied here.     

Tuning of pnicogen and chalcogen bonds by an aerogen-bonding interaction: a comparative ab initio study

Using high-level ab initio calculations, the cooperativity effects between an aerogen-bonding and a pnicogen- or chalcogen-bonding interactions are studied in ternary Y···PH₂CN···ZO₃ and Y···SHCN···ZO₃ complexes (Y?=?NH₃, N₂ and Z?=?Ar, Kr, Xe). A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes, a favourable cooperativity is observed between Z···N and P/S···N interactions, especially in complexes involving NH₃ and XeO₃ molecules. It is found that for a given Y or Z, the amount of cooperativity effects in Y···PH₂CN···ZO₃ complexes are important than Y···SHCN···ZO₃ ones. For each ternary complex considered, the effect of a Z···N aerogen bond on a P/S···N bond is more pronounced than that of a P/S···N bond on a Z···N bond. The mechanism of the cooperativity effects in the ternary complexes is studied by electron density difference, quantum theory of atoms in molecules and natural bond orbital analyses. The solvent effects are also studied on the interaction energy and cooperativity of Z···N and P/S···N bonds in the ternary systems.     

Pnicogen bonds in complexes with CO and CS: differentiating properties

ABSTRACT

Ab initio MP2/aug’-cc-pVTZ calculations have been performed on pnicogen-bonded complexes with CO and CS as electron-pair donors to PH₂X, for X?=?F, NC, OH, CN, CCH, and H. CO:PH₂X and OC:PH₂X complexes are stabilised by traditional pnicogen bonds. CS is an electron-pair donor through its in-plane π system to four PH₂X molecules. It forms C···^?P phosphorus-shared bonds with some ion-pair character with PH₂F, PH₂(OH-Z), and PH₂(OH-E), and traditional pnicogen bonds with all PH₂X except PH₂F. C-O and C-S stretching frequencies are blue-shifted for C···P pnicogen bonds, and red-shifted for O···P and S···P bonds. EOM-CCSD spin-spin coupling constants ^1pJ(P-C) for OC:PH₂X and ^1pJ(P-O) for CO:PH₂X are characteristic of complexes stabilised by traditional pnicogen bonds. Coupling constants ^1pJ(P-C) as a function of the P-C distance for SC:PH₂X illustrate the evolution of the C···P pnicogen bond. They increase as the P-C distance decreases in complexes with traditional bonds, reach a maximum for SC:PH₂OH transition structures as the P-C distance further decreases and the bonds gain phosphorus-shared character, and then change sign and continue to decrease as the P-C distance further decreases and the phosphorus-shared pnicogen bonds gain ion-pair character. They approach the values of ¹J(P-C) for the cation (H₂PCS)⁺.     

Symmetric bifurcated halogen bonds: substituent and cooperative effects

ABSTRACT

The aim of this study is to investigate the geometries, interaction energies and bonding properties of the symmetrical bifurcated halogen bond interactions (BXBs) by means of ab initio calculations. For this purpose, the NCX (X = Cl, Br) molecule is paired with a series of N-formyl formamide (NFF) derivatives (NFF-Z, Z = H, CN, CCH, OH, CH₃ and Li), and the properties of the resulting complexes are studied by molecular electrostatic potential, quantum theory of atoms in molecules, noncovalent interaction index and natural bond orbital analyses. For a fixed NCX molecule, interaction energies increase in the order of Z = Li > CH₃ > H > OH > CCH > CN. We found a strong correlation between the interaction energies of NCX:NFF-Z complexes and molecular electrostatic potential minimum values associated with NFF-Z monomers. Moreover, cooperative effects between BXB and X???N halogen bond interactions are studied in the ternary NCX:NCX:NFF-Z systems. Our results indicate that the strength of BXB interactions in the ternary complexes is enhanced by the presence of X???N bonds. Besides, cooperativity effects tend to increase the covalency of BXBs in these systems.     

Tuning of non-covalent interactions involving a halogen atom that plays the role of Lewis acid and base simultaneously

In this work, a series of model complexes (MH₃X)(HNC)(N'C’H’), where M = C–Pb and X = Cl–At, is studied using a first-principles computational approach. Each of these complexes possesses a halogen atom (X) simultaneously acting as the Lewis base for X···H hydrogen bonding (HB) with HNC and as the Lewis acid for X···N’ halogen bonding (XB) with N'C’H’. The strengths of these non-covalent interactions are tuned by sharing the same halogen centre and by substituting M and X with consecutive elements from groups 14 and 17. Variations in the strengths are estimated mostly by means of various energetic quantities, such as the total interaction energy (E_int), two- and three-body contributions to E_int, their fundamental physical components and donor–acceptor orbital interaction energies. The coexistence of HB and XB involving the same X-centre weakens these interactions, but the magnitude of the total interaction in the complexes increases due to the three-body interaction and the appearance of additional lateral non-covalent interaction between HNC and N'C’H’. Substituting M and X with consecutive elements from groups 14 and 17 leads to several regularities in the changes of E_int. A dependence of three-body interaction on the kinds of M and X is also detected.     

Structural and energetic properties of alkylfluoride–BF3 complexes in the gas phase and condensed‐phase media: computations and matrix infrared spectroscopy

We have undertaken an experimental and computational study of the structural properties of a few alkylfluoride–BF₃ complexes (RF′–BF₃), which are proposed intermediates in a certain class of Friedel–Crafts reactions. Using density functional theory and second‐order Møller–Plesset calculations, we have obtained gas‐phase structures, frequencies, and B–F′ bond potentials for CH₃F–BF₃, (CH₃)₂CHF–BF₃, and (CH₃)₃CF–BF₃. All the complexes are weakly‐bonded in the gas phase, with B–F′ distances (X3LYP/aug‐cc‐pVTZ) of about 2.4 Å and binding energies (MP2/aug‐cc‐pVTZ) ranging from 5.4 and 6.7 kcal/mol. Accordingly, gas‐phase bond potentials are relatively shallow and flat for these complexes. However, even though the inner walls of the potentials are rather soft (the energies rise by only about 5 to 10 kcal/mol between 2.4 and 1.6 Å), we observe no global or local minima at short B–F′ distances. For the (CH₃)₂CHF–BF₃ and (CH₃)₃CF–BF₃ potentials in dielectric media, we do observe a distinct flattening along the inner wall, which results in shelf‐like region near 1.7 Å, but this feature is not a true local minimum. We have also obtained low‐temperature infrared spectra of the (CH₃)₂CHF–BF₃ complex in solid neon, and the frequencies agree quite favorably with those obtained via computations, which validates the computational assessment of the gas‐phase complexes. Copyright © 2011 John Wiley & Sons, Ltd.     

The strengthening effect of a halogen,chalcogen or pnicogen bonding on halogen–π interaction: a comparative ab initio study

The aim of this work is to study the possible cooperative effects between Z···N and X···π interactions (Z = Cl, S, P and X = Cl, Br) in some model complexes, where both these interactions coexist. The nature of the interactions in these complexes is characterised by means of molecular electrostatic potential, electron localisation function, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. According to the results, the formation of an Z···N interaction in these systems makes a significant shortening of X···π distance. The cooperative enhancement of the X···π bonding in the ternary complexes depend on the strength of the Z···N interaction, and it becomes larger in the order Z = Cl > S > P. The mechanism of the cooperativity between the Z···N and X···π interactions is studied using the parameters derived from the QTAIM and NBO analyses.     

Hydrogen bond nature in formamide (CYHNH2···XH; YO,S, Se,Te; XF,HO, NH2) complexes at their ground and low‐lying excited states

A theoretical study on the nature of hydrogen bond for formamide and its heavy complexes (CYHNH₂···XH; Y?O, S, Se, Te; X?F, HO, NH₂) was performed on the basis of density functional theory and the quantum chemistry analysis. Except for the CYHNH₂···NH₃ complexes, the substitution of O atom at formamide with less electronegative atoms (S, Se, and Te) is found to weaken the hydrogen bond (H‐bond). This substitution results in cyclic structure of hydrated and ammoniated formamide complexes by the formation of bifunctional H‐bonds (Y···H₄X; X···H₃C). Natural bond orbital analysis indicates that the H‐bond is weakened because of less charge transfer from a lone pair orbital of H‐bond acceptor to antibonding orbital of H‐bond donor. The quantum theory of atoms in molecules analysis reveals that the acyclic structure with single H‐bond stabilizes the complexes more than the cyclic structure formed by bifunctional H‐bonds. Natural energy decomposition analysis (NEDA) and block‐localized wavefunction energy decomposition (BLW‐ED) analyses show that the H‐bond stabilization energies of NEDA and BLW‐ED have good correlation with the dissociation energy of formamide complexes and charge transfer from donor to acceptor atom play an important role in H‐bonding. We have also studied the low‐lying electronic excited states (T₁, T₂, and S₁) for CYHNH₂···H₂O complexes to explore the nature of H‐bond on the basis of electronegativity and found that NEDA also establishes a good correlation with relative electronic energy (with respect to their ground state) and H‐bond strength at their excited states. Copyright © 2014 John Wiley & Sons, Ltd.