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.     

Properties of cationic pnicogen-bonded complexes F4-nHnP+:N-base with H–P···N linear and n = 1–4

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the pnicogen-bonded complexes F_4-nH_nP⁺:N-base, for n = 1–4, each with a linear or nearly linear H_ax–P···N alignment. The sp³-hybridised nitrogen bases include NH₃, NClH₂, NFH₂, NCl₂H, NCl₃, NFCl₂, NF₂H, NF₂Cl, and NF_3, and the sp bases are NCNH₂, NCCH₃, NP, NCOH, NCCl, NCH, NCF, NCCN, and N₂. Binding energies increase as the P–N distance decreases, with an exponential curve showing this relationship when complexes with sp³ and sp hybridised bases are treated separately. However, the correlations are not as good as they are for the complexes F_4-nH_nP⁺:N-base for n = 0–3 with F–P···N linear. Different patterns are observed for the change in the binding energies of complexes with a particular base as the number of F atoms in the acid changes. Thus, the particular acid–base pair is a factor in determining the binding energies of these complexes.

Three different charge-transfer interactions stabilise these complexes, namely N_lp→σ*P–H_ax, N_lp→σ*P–F_eq, and N_lp→σ*P–H_eq. Unlike the corresponding complexes with F–P···N linear, N_lp→σ*P–H_ax is not always the dominant charge-transfer interaction, since N_lp→σ*P–F_eq is greater in some complexes. N_lp→σ*P–H_eq makes the smallest contribution to the total charge-transfer energy. The total charge-transfer energies of all complexes increase exponentially as the P–N distance decreases in a manner very similar to that observed for the series of complexes with F–P···N linear.

Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) spin–spin coupling constants ^1pJ(P–N) across the pnicogen bond vary with the P–N distance, but different patterns are observed which depend on the nature of the acid, and for some acids, on the hybridisation of the nitrogen base. ^1pJ(P–N) values for complexes of F₃HP⁺ initially increase as the P–N distance decreases, reach a maximum, and then decrease with decreasing P–N distance as the P···N bond acquires increased covalent character. ^1pJ(P–N) for complexes with H–P···N linear and those with F–P···N linear exhibit similar distance dependencies depending on the number of F atoms in equatorial positions and the hybridisation of the base. Complexation may increase, decrease, or leave the P–H_ax distance unchanged, but ¹J(P–H_ax) always decreases relative to the corresponding isolated ion. Decreasing ¹J(P–H_ax) can be related to decreasing intermolecular P–N distance.     

Some measures for making a traditional halogen bond be chlorine-shared or ion-pair one in FCl•NH3 complex

ABSTRACT

The Cl···N halogen bond (XB) in FCl·NH₃ is tuned from a traditional one to a chlorine-shared or an ion-pair one with three methods. The first method is to put this complex into different clusters of (FCl·NH₃)(H₂O)₆. The second method is to add solvents with different dielectric constants around this complex. The third method is to impose a proper external electric field on this complex. The traditional XB has the negative quantity [r₁(F–Cl) ? r₂(Cl–N)], while the chlorine-shared and ion-pair XBs exhibit the positive r₁ ? r₂, both having the ion-pair character of smaller and larger than 85%, respectively.     

Cooperative effects between tetrel bond and other σ–hole bond interactions: a comparative investigation

Covalently bonded atoms of Groups IV–VII tend to have anisotropic charge distributions, the electronic densities being less on the extensions of the bonds (σ–holes) than in the intervening regions. These σ–holes often give rise to positive electrostatic potentials through which the atom can interact attractively and highly directionally with negative sites. In this work, cooperative effects between tetrel bond and halogen/chalcogen/pnicogen bond interactions are studied in multi-component YH₃M···NCX···NH₃ complexes, where Y = F, CN; M = C, Si and X = Cl, SH and PH₂. These effects are analysed in detail in terms of the structural, energetic, charge-transfer and electron density properties of the complexes. The nature of the σ–hole bonds is unveiled by quantum theory of atoms in molecules and natural bond orbital theory. A favourable cooperativity is found with values that range between ?0.34 and ?1.15 kcal/mol. Many-body decomposition of interaction energies indicate that two-body energy term is the most important source of the attraction, which its contribution accounts for 87%–96% of the total interaction energy.     

An ab initio study on competition between pnicogen and chalcogen bond interactions in binary XHS:PH2X complexes (X = F,Cl, CCH,COH, CH3, OH,OCH3 and NH2)

Chalcogen and pnicogen bond interactions are studied in the binary XHS:PH₂X complexes (X = F, Cl, CCH, COH, CH₃, OH, OCH₃ and NH₂) using quantum chemical calculations. These interactions can be explained in terms of electrostatic effects, considering the chalcogen or pnicogen as a Lewis acid due to the presence of an σ-hole. Almost a perfect linear relationship is found between the interaction energies and the magnitudes of the product of most positive and negative electrostatic potentials. This reveals that both the negative and positive regions of the interacting atoms can be used to predict the strength of the eventual interaction. The nature of chalcogen and pnicogen bond interactions is unveiled by means of the atoms in molecules and electron localisation function analyses.     

Regium bonds formed by MX (M═Cu,Ag, Au; X═F,Cl, Br) with phosphine-oxide/phosphinous acid: comparisons between oxygen-shared and phosphine-shared complexes

ABSTRACT

Regium bonds interaction between phosphine oxide (H₃PO), the trans phosphinuous acid (T-PH₂OH), the cis phosphinuous acid (C-PH₂OH) and MX (M═Cu, Ag, Au; X═F, Cl, Br) complexes were investigated by means of ab initio MP2/aug-cc-pVTZ method. For phosphinuous acid and MX complexes, two types of regium bonded interaction (trans and cis complexes) are observed and the two types of structures are very easily transformed from one type to another due to a low energy barrier. The molecular interaction energies are in the order of Au?>?Cu?>?Ag, F?>?Cl?>?Br and increase with the decrease of intermolecular distance R_int. Two resonance-type structures of P:M-X (ωI) ? P–M:X (ωII), O:M-X (ωI) ? O–M:X (ωII) are recognised by the natural resonance theory (NRT) and the natural bond orbitals (NBOs) analysis. The competition between ωI ? ωII resonance structures mainly arises from hyperconjugation interactions, in all phosphor-shared complexes, P–M:X resonance accounts for a larger proportion which leads to the covalent characters. All of complexes have been described in terms of their electron density properties.     

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.     

Comparison between standard and counterpoise-corrected optimization using some hydrogen and halogen bonded systems

The effect of the counterpoise correction on the geometries, stabilization energies, and vibrational harmonic frequencies of some hydrogen- and halogen-bonded systems (B?=?CH₃CN,?HCN,?NH₃,?N₂,?CO,?H₂O,?H₂S,?PH₃;?HX?=?HF,?HCl,?HBr,?HCN,?HCF₃; XY?=?Br₂,?BrCl,?BrF,?Cl₂,?ClF,?F₂) has been analysed at the MP2 level of theory using the popular 6-311++G(d,p) basis set. The optimized B?···?H and B?···?X bond lengths increase with counterpoise (CP) correction. In some cases standard values and in other cases CP-corrected values are close to experimental data. The absolute values of complexation energies of CP-corrected structures are higher than standard by inclusion of BSSE correction. The effect of CP correction on intermolecular bond lengths and complexation energies of B?···?XY series are usually higher than B?···?HX. Also, this effect is higher for H₂S and PH₃ groups. The CP correction changes the vibrational harmonic frequencies by 0–100%. The changes are frequently lower than 20% for frequencies higher than 300?cm^?1.     

Effect of protonation on individual hydrogen bonds in the 8-oxoguanine-cytosine base pair: NMR,NBO and AIM analyses

Protonation increases the total binding energy of the 8-oxoguanine-cytosine (8OG:C) base pair by 60–70% at the B3LYP/6-311++G(d,?p) level of theory. It changes the individual H-bond energies, estimated from electron charge densities at bond critical points, by 1.16 to ?16.41?kcal?mol^?1. The individual H-bond energies and the two bond X–Y spin–spin coupling constants (^2hJ_X–Y) increase with protonation where 8OG behaves as an H-bond donor; the reverse is true for the H-bonds in which the 8OG unit acts as an H-bond acceptor. Similar to ^2hJ_X–Y, the value of ^1hJ_O–H (a one-bond H?···?Y spin–spin coupling constant) is distance dependent and in linear correlation with the O?···?H distance, but the ^1hJ_N–H values are independent of the N–H distance and the PSO term is the predominant portion in it. The ¹J_X–H spin–spin coupling constant is dominated by the negative FC term for all hydrogen bonds, although the PSO term is the best to investigate the behaviour of ¹J_X–H across the X–H?·?Y H-bond.     

Comparison for σ-hole and π-hole tetrel-bonded complexes involving cyanoacetaldehyde

Ab initio calculations have been performed for the complexes of cyanoacetaldehyde (CA) with TH₃F (T = C, Si, Ge and Sn) and F₂TO (T = C and Si). The σ-hole and π-hole tetrel-bonded complexes are formed for TH₃F and F₂TO, respectively. In general, three minima complexes (N, O–A and O–B) are obtained for each tetrel donor. Most complexes are stabilised by a primary tetrel bond and a secondary hydrogen bonding. TH₃F–N/F₂CO–N has greater stability than TH₃F–O/F₂CO–O, but a reverse result is found in the complexes of F₂SiO although they have comparative interaction energies. Charge transfer from the lone pair on the N/O atom of CA into the T–F σ^* antibonding orbital leads to the stabilisation of the TH₃F complexes. Accordingly, the T–F bond is extended and its stretch vibration displays a redshift. A breakdown of the individual forces involved attributes the stability of the complex mainly to electrostatic energy, with relatively large dispersion term in the CH₃F complexes and relatively large polarisation energy in the F₂SiO 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 mutual relationship between H-bonding and π-stacking interactions: the estimation of individual binding energies in the phenylalanine:G ··· C ternary complex

The mutual relationship between stacked interaction and the individual hydrogen bonds in the phenylalanine:guanine?···?cytosine (Ph:G-C) and phenylalanine:cytosine?···?guanine (Ph:C-G) complexes have been studied at the MPWB1K/6-311++G** and M05-2X/cc-pVDZ levels of theory. The interplay of π-stacking and H-bonding results in the weakening of both interactions. The effect of π-stacking on the geometries and individual hydrogen bond (HB) energies of guanine–cytosine (G-C) base pair have been investigated using electron densities calculated by the atoms in molecules (AIM) method at the hydrogen bond critical points (BCP). The results of AIM analysis are in good agreement with the calculated individual hydrogen bond energies. The π-stacking interactions strengths the HB1 and weakens HB2 and HB3 in the Ph:G-C complexes, while the opposite is true in the Ph:C-G complex. With the increase in the distance between phenylalanine ring and the groups involved in H-bond interactions the change in the H-bond energy increases and the changes in the individual H-bond and π-stacking energies decrease in the ternary complexes.     

Competition between σ-hole pnicogen bond and π-hole tetrel bond in complexes of CF2=CFZH2 (Z = P,As, and Sb)

ABSTRACT

A computational study of the complexes formed by F₂C=CFZH₂ (Z?=?P, As, and Sb) and F₂C=CFPF₂ with two Lewis bases (NH₃ and NMe₃) has been carried out. In general, two minima complexes are found, one with a σ-hole pnicogen bond and the other one with a π-hole tetrel bond in most complexes but two σ-hole pnicogen bonded complexes are obtained for F₂C=CFZH₂ and NH₃. They have similar stability though F₂C=CFSbH₂ engages in a much stronger σ-hole pnicogen bond with NMe₃. The –PF₂ substitution makes the π-hole on the terminal carbon form a tetrel bond with NH₃. A heavier –ZH₂ group engages in a stronger σ-hole pnicogen bond but results in a weaker π-hole tetrel bond. Other than electrostatic interaction, the stability of both complexes is attributed to the charge transfer from the N lone pair into the C–Z/H–Z anti-bonding orbital in the pnicogen bond and the C=C anti-bonding orbital in the tetrel bond.

The σ-hole pnicogen bonded and π-hole tetrel bonded complexes between F₂C=CFZH₂ (Z = P, As, and Sb) and two Lewis bases (NH₃ and NMe₃) have been compared. The results indicate that both interactions can compete, dependent on the nature of the N base.     

On difference of properties between organic fluorine hydrogen bond C–H···F–C and conventional hydrogen bond

The existence of C–H···F–C hydrogen bonds in the complexes of trifluoromethane and cyclic molecule (oxirane, cyclobutanone, dioxane, and pyridine) has been experimentally proven by Caminati and co-workers. This study presents a theoretical investigation on these C–H···F–C hydrogen bonds at B97D/6-311++G^** and MP2/6-311++G^** levels, in terms of C–H vibrational frequency shifts, atoms in molecules characteristics, and the bonding feature of C–H···F–C hydrogen bonds. It is found that in three important aspects, there are significant differences in properties between C–H···F–C and conventional hydrogen bonds. The C–H···F–C hydrogen bonds show a blueshift in the C–H vibrational frequencies, instead of the X–H normal redshift in X–H···Y conventional hydrogen bonds. The natural bond orbital (NBO) analyses show that σ and p types of lone pair orbitals of the F atom to an antibonding σ^*_H–C orbital form a dual C–H···F–C hydrogen bond. Such a dual hydrogen bonding leads to the proton acceptor directionality of the C–H···F–C hydrogen bond softer. Our studies also show that the Laplacian of the electron density (▽²ρ_BCP) is not always a good criterion for hydrogen bonds. Therefore, we should not recommend the use of the Laplacian of the electron density as a criterion for C–H···F–C hydrogen bonds.     

The 1,2-hydrogen shift reaction for monohalogenophosphanes PH2X and HPX (X = F,Cl)

The aim of the present study was to perform a quantum chemical investigation in the 1,2-hydrogen shift reaction for the PH₂X and HPX molecules (X = F,Cl). Several phosphorus–halogen-bearing molecules were studied, including PH₂F, PH₂Cl, HPF, HPCl, HPFH, HPClH, PFH and PClH. The energies of stationary and saddle points on the ground electronic potential energy surface were investigated with post-Hartree–Fock methods [CCSD(T), MP2, QCISD] and different DFT functionals. The PH₂F 1,2-hydrogen shift energy barrier was 75 kcal mol^?1 at the CCSD(T) level and only a small increase in this value was observed for the HPF isomerisation. In contrast, the HPCl 1,2-hydrogen shift barrier is higher than the PH₂Cl one, which presented a barrier height of 69 kcal mol^?1 among CCSD(T) and composite methods. The rate constants of these unimolecular rearrangements varied from 10^?44 to 10^?38 s^?1, and these isomerisation channels exhibited large half-lives. In addition, the heat of formation of each monohalogenophosphane was also calculated. The Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analysis were also employed to characterise the differences between the phosphorous–halogen bonds.     

Analysis of the interactions in FCCF:(H2O) and FCCF:(H2O)2 complexes through the study of their indirect spin–spin coupling constants

A theoretical study of FCCF:(H₂O)_n complexes, with n?=?1 and 2, has been carried out by means of ab initio computational methods. Three kinds of interactions are observed in the complexes: H···π and H···F hydrogen bonds and O···FC tetrel bonds. The indirect spin–spin coupling constants have been calculated at the CCSD/aug-cc-pVTZ-J computational level. Special attention has been paid to the dependence of the different intramolecular coupling constants in FCCF on the distance between the coupled nuclei and the presence or absence of water molecules. The exceptional sensitivity shown by these coupling constants to the presence of water molecules is quite notorious and can provide information on the bonding structure of the molecule.     

Vibrational spectroscopic and force field studies of copper(II) chloride and bromide compounds,and crystal structure of KCuBr3

Vibrational spectroscopic and force field studies have been performed of 15 related copper(II) chloride and copper(II) bromide compounds, including hydrated salts crystallizing in ternary aqueous systems with alkali and ammonium halides. For halocuprates with distorted octahedral coordination characteristic stretching Raman wavenumbers, corresponding to symmetric stretching Cu^II X modes in the equatorial plane, were found in the ranges 247–288 cm⁻¹ for X = Cl, and 173–189 cm⁻¹ for X = Br, while the low‐wavenumber stretching modes for the weaker axial Cu X interactions varied considerably. The tetrahedral coordination for Cs₂CuCl₄ and Cs₂CuBr₄ leads to somewhat lower Cu X symmetric stretching wavenumbers, 295 and 173 cm⁻¹, respectively. The assignments of the copper–ligand stretching vibrations were performed with the aid of normal coordinate calculations. Correlations between force constants, averaged Cu X stretching wavenumbers and bond distances have been evaluated considering the following aspects: (1) Jahn–Teller tetragonal distortion (axial elongation) of the octahedral copper(II) coordination environment, (2) differences between terminal and bridging halide ligands (3) effects of coordinated water and the influence of outer‐sphere cations. Force constant ratios for terminal and bridging metal–halide bonds reveal characteristic differences between planar and tetrahedrally coordinated M₂X₆ species. In the hydrated copper(II) halide complexes, the halide ligands are more strongly bound than coordinated water molecules. The crystal structure of KCuBr₃ (K₂Cu₂Br₆), which was determined to provide structural information for the force field analyses, contains stacks of planar dimeric [Cu₂Br₆]²⁻ complexes held together by weak axial Cu Br interactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Long distance structural consequences of H‐bonding: the case of complexes of para‐substituted phenol derivatives

H‐bonded complexes of p‐X‐PhOH/p‐X‐PhO^? with fluoride and hydrofluoric acid (X = OH, H, NO₂) were subject of optimization (by means of B3LYP/6‐311+G**) for gradually changed O···F distance from d_O···F = 4.0 Å down to (i) the distance of the proton transfer from the hydroxyl group to fluoride leading to O^?···HF interaction and (ii) fully optimized system (O^?···HF type). In this way, we simulate gradual changes of H‐bond strength estimating simultaneously the energy of interaction, E_int, energy of deformation, E_def, and the binding energy, E_tot. The obtained geometrical parameters allow us to show that H‐bond formation causes substantial changes in geometry, even at so distant parts of the system as the ring and bond length in para‐substituents (OH and NO₂). All these changes are monotonically dependent on interaction and deformation energies. Copyright © 2009 John Wiley & Sons, Ltd.