Intermolecular Interactions in Weak Donor–Acceptor Complexes from Symmetry‐Adapted Perturbation and Coupled‐Cluster Theory: Tetracyanoethylene–Benzene and Tetracyanoethylene–p‐Xylene

The interactions in the complexes of tetracyanothylene (TCNE) with benzene and p‐xylene, often classified as weak electron donor–acceptor (EDA) complexes, are investigated by a range of quantum chemical methods including intermolecular perturbation theory at the DFT‐SAPT (symmetry‐adapted perturbation theory combined with density functional theory) level and explicitly correlated coupled‐cluster theory at the CCSD(T)‐F12 level. The DFT‐SAPT interaction energies for TCNE–benzene and TCNE–p‐xylene are estimated to be ?35.7 and ?44.9 kJ mol^?1, respectively, at the complete basis set limit. The best estimates for the CCSD(T) interaction energy are ?37.5 and ?46.0 kJ mol^?1, respectively. It is shown that the second‐order dispersion term provides the most important attractive contribution to the interaction energy, followed by the first‐order electrostatic term. The sum of second‐ and higher‐order induction and exchange–induction energies is found to provide nearly 40 % of the total interaction energy. After addition of vibrational, rigid‐rotor, and translational contributions, the computed internal energy changes on complex formation approach results from gas‐phase spectrophotometry at elevated temperatures within experimental uncertainties, while the corresponding entropy changes differ substantially.     

Force field development for organic molecules: Modifying dihedral and 1–n pair interaction parameters

We comprehensively illustrate a general process of fitting all‐atom molecular mechanics force field (FF) parameters based on quantum mechanical calculations and experimental thermodynamic data. For common organic molecules with free dihedral rotations, this FF format is comprised of the usual bond stretching, angle bending, proper and improper dihedral rotation, and 1–4 scaling pair interactions. An extra format of 1–n scaling pair interaction is introduced when a specific intramolecular rotation is strongly hindered. We detail how the preferred order of fitting all intramolecular FF parameters can be determined by systematically generating characteristic configurations. The intermolecular Van der Waals parameters are initially taken from the literature data but adjusted to obtain a better agreement between the molecular dynamics (MD) simulation results and the experimental observations if necessary. By randomly choosing the molecular configurations from MD simulation and comparing their energies computed from FF parameters and quantum mechanics, the FF parameters can be verified self‐consistently. Using an example of a platform chemical 3‐hydroxypropionic acid, we detail the comparison between the new fitting parameters and the existing FF parameters. In particular, the introduced systematic approach has been applied to obtain the dihedral angle potential and 1–n scaling pair interaction parameters for 48 organic molecules with different functionality. We suggest that this procedure might be used to obtain better dihedral and 1–n interaction potentials when they are not available in the current widely used FF. © 2014 Wiley Periodicals, Inc.     

Ab initioMODPOT/VRDDO/MERGE calculations on energetic compounds. III. Nitroexplosives: Polyaminopolynitrobenzenes (including DATB,TATB, and tetryl)

Quantum chemical ab initio MODPOT /VRDDO calculations have been carried out on the following aminonitrobenzenes for which crystal structures had been determined experimentally: 4-nitroaniline; N,N-dimethyl-p-nitroaniline; 2,4,6-trinitroaniline; 1,3-diamino-2,4,6-trinitrobenzene (DATB—Form I); 1,3,5-triamino-2,4,6-trinitrobenzene (TATB); 2,3,4,6-tetranitroaniline; N-methyl-N,2,4,6-tetranitroaniline (Tetryl); and N-(β,β,β-trifluoroethyl)-N,2,4,6-tetranitroaniline. These quantum chemical calculations were performed on the molecules in their conformations as found in their crystal structures. The calculations were carried out with our own ab initio programs which also incorporate as options several desirable features for calculations on large molecules: ab initio effective core model potentials (MODPOT) which enable calculations of valence electrons only explicitly, yet accurately, and a charge conserving integral prescreening evaluation (which we named VRDDO-variable retention of diatomic differential overlap) especially effective for spatially extended molecules. Aminonitrobenzenes are especially interesting since there are inherent intramolecular ring distortions and deviations from planarity and intramolecular hydrogen bonds as well as intermolecular hydrogen bonds causing further deviations from planarity. The theoretical indices resulting from the quantum chemical calculations are relevant to a number of properties and behavioral characteristics of these molecules, both intramolecular and intermolecular. The charges on the atoms [from the gross atomic populations (GAP 's)] are needed for calculation of the atomic multipole–atomic multipole electrostatic contributions (a dominant factor) to the intermolecular interaction energies. These electrostatic interaction energies are part of the input necessary for calculations on the crystal packing and densities of these molecules. These GAP 's are also of value in interpreting the experimental photoelectron and ESCA spectra of these molecules. The total overlap populations (TOP 's) between atoms are related to the inherent bond strengths and can serve as a quantitative replacement for the old empirical bond length-bond order-bond energy relationship still used by explosives chemists to identify the “target bonds” (the weakest bonds). The TOP 's are of considerable value in predicting and tracing initiation and subsequent steps of explosive phenomena. The molecular orbital energies of the lowest unoccupied orbitals are of interest since nitroexplosives have been implicated in testicular toxicity and the initial metabolic activation appears to proceed through a one-electron reduction of the nitroexplosive.     

Triel–hydride triel bond between ZX3 (Z = B and Al; X = H and Me) and THMe3 (T = Si,Ge and Sn)

Complexes between THMe₃ (T = Si, Ge and Sn) and ZX₃ (Z = B and Al; X = H and Me) have been characterized using MP2/aug‐cc‐pVTZ calculations. These complexes are chiefly stabilized by a triel–hydride triel bond with the T–H bond pointing to the π‐hole on the triel atom. The triel–hydride interaction is mainly attributed to the charge transfer from the T–H bond orbital to the empty p orbital of the triel atom. These complexes are very stable with a large interaction energy (>10 kcal mol^?1) excluding THMe₃···BMe₃ (T = Si and Ge), indicating that the sp²‐hydridized triel atom has a strong affinity for the T–H bond. The formation of THMe₃···BH₃ results in proton transfer, characterized by conversion of orbital interaction and large charge transfer (ca 0.5e). The large deformation is primarily responsible for the abnormally greater interaction energy in THMe₃···BH₃ (>30 kcal mol^?1) than in the AlH₃ analogue. Methyl substitution on the triel atom weakens the triel–hydride interaction and causes a larger interaction energy in THMe₃···AlMe₃ with respect to its BMe₃ counterpart. Most of these interactions possess characteristics of covalent bonds. Polarization makes a contribution to the stability of most complexes nearly equivalent to the electrostatic term.     

On the importance of intramolecular hydrogen bond cooperativity in d‐glucose – an NMR and QTAIM approach

The idea that hydrogen bond cooperativity is responsible for the structure and reactivity of carbohydrates is examined. Density functional theory and gauge‐including atomic orbital calculations on the known conformers of the α and β anomers of d ‐glucopyranose in the gas phase are used to compute proton NMR chemical shifts and interatomic distances, which are taken as criteria for probing intramolecular interactions. Atom–atom interaction energies are calculated by the interacting quantum atoms approach in the framework of the quantum theory of atoms in molecules. Association of OH1 in the counterclockwise conformers with a strong acceptor, pyridine, is accompanied by cooperative participation from OH2, but there is no significant change in the bonding of the two following 1,2‐diol motifs. The OH6 ^... O5 (G?g+/cc/t and G+g?/cc/t conformers) or OH6 ^... O4 (Tg+/cc/t conformer) distance is reduced, and the OH6 proton is slightly deshielded. In the latter case, this shortening and the associated increase in the OH6–O4 interaction energy may be interpreted as a small cooperative effect, but intermolecular interaction energies are practically the same for all three conformers. In most of the pyridine complexes, one ortho proton interacts with the endocyclic oxygen O5. Analogous results are obtained when the clockwise conformer, G?g+/cl/g?, detected for the α anomer, and a hypothetical conformer, Tt/cl/g?, are complexed with pyridine through OH6. Generally, the cooperative effect does not go beyond the first two OH groups of a chain. Copyright © 2017 John Wiley & Sons, Ltd.     

脯氨酸硫酯自然化学连接反应中的轨道相互作用

采用密度泛函理论(DFT)方法(M06//B3LYP)对脯氨酸硫酯在自然化学连接(NCL)反应中低反应活性的现象进行了详细的理论研究.通过对脯氨酸和丙氨酸硫酯NCL反应的具体反应路径(Path-Pro和Path-Ala)分别进行计算发现,两个分子的反应路径均先后经历外源硫醇-硫酯交换、硫酯-硫酯交换、分子内S→N酰基化重排三个主要步骤.两者的决速步骤均为第一步骤.其中Path-Pro的总能垒较高,即脯氨酸硫酯的反应活性较低,这与实验结果一致.对两路径的决速步骤进一步考察,发现脯氨酸中αN上的羰基对反应中心羰基的n→π*相互作用使得脯氨酸硫酯的LUMO轨道能量升高,相应羰基C与S(芳基硫醇)原子之间的相互作用较小,从而使得反应能垒升高.     

Improving description of hydrogen bonds at the semiempirical level: water–water interactions as test case

Hydrogen bonding is not well described by available semiempirical theories. This is an important restriction because hydrogen bonds represent a key feature in many chemical and biochemical processes, besides being responsible for the singular properties of water. In this study, we describe a possible solution to this problem. The basic idea is to replace the nonphysical gaussian correction functions (GCF) appearing in the core–core repulsion terms of most MNDO‐based semiempirical methods by a simple function exhibiting the correct physical behavior in the whole range of intermolecular separation distances. The parameterized interaction function (PIF) is the sum of atom‐pair contributions, each one having five adjustable parameters. In this work, the approach is used to study water–water interactions. The parameters are optimized to reproduce a reference ab initio intermolecular energy surface for the water–water dimer obtained at the MP2/aug‐cc‐pVQZ level. OO, OH, and HH parameters are reported for the PM3 method. The results of PM3‐PIF calculations remarkably improve qualitatively and quantitatively those obtained at the standard PM3 level, both for water–dimer properties and for water clusters up to the hexamer. For example, the root‐mean‐square deviation of the PM3‐PIF interaction energies, with respect to ab initio values obtained using 700 points of the water dimer surface, is only 0.47 kcal/mol. This value is much smaller than that obtained using the standard PM3 method (4.2 kcal/mol). The PM3‐PIF water dimer energy minimum (−5.0 kcal/mol) is also much closer to ab initio data (−5.0±0.01 kcal/mol) than PM3 (−3.50 kcal/mol). The method is therefore promising for the development of new semiempirical approaches as well as for application of combined quantum mechanics and molecular mechanics techniques to investigate chemical processes in water. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 572–581, 2000     

Experimental and Theoretical Study of Helium Broadening and Shift of HCO+ Rotational Lines

An experimental and theoretical study of pressure broadening and pressure shift of HCO⁺ rotational lines perturbed by collisions with He is presented. Results are reported from measurements at 88 K for the lines j=4←3, 5←4 and 6←5 with frequencies ranging from 0.35 to 0.54 THz. Using a new CCSD(T)/aug‐cc‐pVQZ potential energy surface for the He–HCO⁺ interaction, the collisional line shape parameters are studied from fully quantum and semiclassical calculations. Results from the quantum treatment are in satisfactory agreement with experiments whereas the semiclassical approach can lead to appreciable differences. A study of the dependence of line width Γ and shift s as a function of the translational energy shows the presence of quantum oscillations. Calculations on a previous Hartree–Fock‐based potential energy surface lead to quite similar results for the collisional line shape parameters. Using a simplified version of the potential morphing method it is found that the line width Γ is particularly sensitive to the long‐range part of the potential energy surface. This also explains the success of the first line‐broadening calculations which date back to the 1950s.     

Properties of halogen atoms for representing intermolecular electrostatic interactions related to halogen bonding and their substituent effects

The electrostatic properties of halogen atoms are studied theoretically in relation to their ability of halogen bonding, which is an attractive intermolecular interaction of a covalently bonded halogen atom with a negatively charged atom of a neighboring molecule. The electric quadrupole (of electronic origin) with a positive zz component Θ_zz of a covalently bonded halogen atom, where the z axis is taken along the covalent bond involving the halogen atom, is mainly responsible for the attractive electrostatic interaction with a negatively charged atom. This positive Θ_zz is an intrinsic property of halogen atoms with the p_x²p_y²p_z configuration of the valence electronic shell, as shown by ab initio molecular orbital calculations for isolated halogen atoms with this electronic configuration, and increases in the order of F < Cl < Br < I, in parallel with the known general sequence of the strength of halogen bonding. For halogen‐containing aromatic compounds, the substituent effects on the electrostatic properties are also studied. It is shown that the magnitude of Θ_zz and the electric field originating from it are rather insensitive to the substituent effect, whereas the electric field originating from atomic partial charges has a large substituent effect. The latter electric field tends to partially cancel the former. The extent of this partial cancellation is reduced in the order of Cl < Br < I and is also reducible by proper substitution on or within the six‐membered ring of halobenzene. Perspectives on the development of potential function parameters applicable to halogen‐bonding systems are also briefly discussed. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

硝酰胺二聚体静电能和交换能的理论计算

根据对称性匹配微扰理论, 并运用多个微扰和非微扰方法, 计算了硝酰胺二聚体在不同分子间距(R)时静电能和交换能. 这些具有轨道弛豫的静电能不仅含有第4级单、双、四和三重激发态项, 而且含有CCSD的第5级和更高级的能量项. 同时发现: 第4级的三重激发态能量项比第5级和更高级的能量项之和还重要. 求得的含有分子内电子相关效应的交换能达到了CCSD水平. 用于计算交换能关联校正项的单对交换近似在硝酰胺二聚体的范德华最小距离0.42 nm附近区域才较合理. 在R为0.32～1.42 nm范围, 静电能与R的关系有两种: 一是在小于等于0.47 nm时, (R^－7.64; 二是大于0.47 nm时, (R^－3.97. 交换能具有明显的短程作用特点, 其与R间的关系为指数衰减: 21.061exp(－R/0.318). 最后发现: 在硝酰胺二聚体中, 分子内的电子相关效应对和的影响很显著.     

Quantum chemical study of the nature of the interaction between the proton and phosphoryl compounds in the H+ ...OPX3 complex

Based on CNDO/2 (spd basis) quantum chemical calculations of the proton affinity, we propose a model describing the nature of the interaction between the proton and the molecule of phosphoryl compounds in the monocation X₃POH⁺. We have established that in the series of phosphoryl compounds, the change in the proton affinity is subject to two effects: the shift in electron density from the base to the proton, and the ionic interaction between the proton complexing agent and the phosphorus atom and substituents; and in the latter case we observe electrostatic repulsion for the substituents R, OR, NR₂ and attraction for F.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2579–2583, November, 1992.     

Magnetic ordering and metal‐atom site preference in tetragonal CrMnAs: Electronic correlation effects

The electronic and magnetic structures of tetragonal, Cu₂Sb‐type CrMnAs were examined using density functional theory. To obtain reasonable agreement with reported atomic and low‐temperature magnetic ordering in this compound, the intra‐atomic electron–electron correlation in term of Hubbard U on Mn atoms are necessary. Using GGA + U, calculations identify four low‐energy antiferromagnetically ordered structures, all of which adopt a magnetic unit cell that contains the same direct Cr Cr and Cr Mn magnetic interaction, as well as the same indirect Mn⋅⋅⋅Mn magnetic interaction across the Cr planes. One of these low‐energy configurations corresponds to the reported case. Effective exchange parameters for metal–metal contacts obtained from SPRKKR calculations indicate both direct and indirect exchange couplings play important roles in tetragonal CrMnAs. © 2018 Wiley Periodicals, Inc.     

Correlation energy,correlated electron density,and exchange‐correlation potential in some spherically confined atoms

We report correlation energies, electron densities, and exchange‐correlation potentials obtained from configuration interaction and density functional calculations on spherically confined He, Be, Be²⁺, and Ne atoms. The variation of the correlation energy with the confinement radius R_c is relatively small for the He, Be²⁺, and Ne systems. Curiously, the Lee–Yang–Parr (LYP) functional works well for weak confinements but fails completely for small R_c. However, in the neutral beryllium atom the CI correlation energy increases markedly with decreasing R_c. This effect is less pronounced at the density‐functional theory level. The LYP functional performs very well for the unconfined Be atom, but fails badly for small R_c. The standard exchange‐correlation potentials exhibit significant deviation from the “exact” potential obtained by inversion of Kohn–Sham equation. The LYP correlation potential behaves erratically at strong confinements. © 2016 Wiley Periodicals, Inc.     

2,6-Di(1H-tetrazol-1-yl)pyridine and its cupric chloride complex

2,6-Di(1H-tetrazol-1-yl)pyridine (DTP) was prepared by a four-stage procedure, including step-by-step heterocyclization of both amino groups of 2,6-diaminopyridine with triethyl orthoformate and sodium azide. According to quantum-chemical calculations and single crystal X-ray diffraction data, DTP crystallizes in the form of the thermodynamically most stable conformer and has an almost flat molecular geometry. DTP was found to react with CuCl₂ ⋅ 2H₂O in ethanol to give the [Cu(DTP)Cl₂(H₂O)]_n complex, which is a 1D coordination polymer, formed at the expense of bridging DTP ligand via the tetrazole ring nitrogen atoms N⁴. Possible coordination cites in DTP molecule are discussed using the data of quantum chemical calculations. The pyridine ring nitrogen atom of DTP does not participate in the formation of either coordination or intermolecular hydrogen bonds. This is explained by the results of quantum chemical calculations showing that this atom is less basic than N3 and N4 atoms of DTP molecule.     

Influence of metal ion on chelate–aryl stacking interactions

CCSD(T)/CBS and DFT methods are employed to study the stacking interactions of acetylacetonate‐type (acac‐type) chelates of nickel, palladium, and platinum with benzene. The strongest chelate–aryl stacking interactions are formed by nickel and palladium chelate, with interaction energies of −5.75 kcal mol⁻¹ and −5.73 kcal mol⁻¹, while the interaction of platinum chelate is weaker, with interaction energy of −5.36 kcal mol⁻¹. These interaction energies are significantly stronger than stacking of two benzenes, −2.73 kcal mol⁻¹. The strongest nickel and palladium chelate–aryl interactions are with benzene center above the metal area, while the strongest platinum chelate–aryl interaction is with the benzene center above the C2 atom of the acac‐type chelate ring. These preferences arise from very different electrostatic potentials above the metal ions, ranging from very positive above nickel to slightly negative above platinum. While the differences in electrostatic potentials above metal atoms cause different geometries with the most stable interaction among the three metals, the dispersion (correlation energy) component is the largest contribution to the total interaction energy for all three metals.     

The Role of Molecular Electrostatic Potentials in the Formation of a Halogen Bond in Furan⋅⋅⋅XY and Thiophene⋅⋅⋅XY Complexes

The halogen bonding of furan???XY and thiophene???XY (X=Cl, Br; Y=F, Cl, Br), involving σ‐ and π‐type interactions, was studied by using MP2 calculations and quantum theory of “atoms in molecules” (QTAIM) studies. The negative electrostatic potentials of furan and thiophene, as well as the most positive electrostatic potential (V_S,max) on the surface of the interacting X atom determined the geometries of the complexes. Linear relationships were found between interaction energy and V_S,max of the X atom, indicating that electrostatic interactions play an important role in these halogen‐bonding interactions. The halogen‐bonding interactions in furan???XY and thiophene???XY are weak, “closed‐shell” noncovalent interactions. The linear relationship of topological properties, energy properties, and the integration of interatomic surfaces versus V_S,max of atom X demonstrate the importance of the positive σ hole, as reflected by the computed V_S,max of atom X, in determining the topological properties of the halogen bonds.     

Influence of insertion of a noble gas atom on halogen bonding in H2O···XCCNgF and H3N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes

The H₂O···XCCNgF and H₃N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes have been studied with quantum chemical calculations at the MP2/aug-cc-pVTZ level. The results show that the inserted noble gas atom has an enhancing effect on the strength of halogen bond, and this enhancement is weakened with the increase of noble gas atomic number. The methyl and Li substituents in the electron donor strengthen the halogen bond. The interaction energy increases from ?3.75 kcal/mol in H₃N–BrCCF complex to ?9.66 kcal/mol in H₂LiN–BrCCArF complex. These complexes have been analyzed with atoms in molecules, natural bond orbital, molecular electrostatic potentials, and energy decomposition calculations.     

Superelectrophilicity of 1,2‐Azaborine: Formation of Xenon and Carbon Monoxide Adducts

The BN analogue of ortho‐benzyne, 1,2‐azaborine, is shown to bind carbon monoxide and a xenon atom under matrix isolation conditions, demonstrating its strongly Lewis acidic superelectrophilic nature. The Lewis acid–base complexes involving CO and Xe can be cleaved photochemically and reformed by mildly annealing the matrices. The interaction energy of 1,2‐azaborine with Xe is 3 kcal mol^?1 according to quantum chemical computations, and is similar to that of the superelectrophilic carbene difluorovinylidene.