A theoretical study of nonlinearity in heterocyclic hydrogen-bonded complexes

Ab initio calculations are performed at the MP2/6-311++G(d,p) and DFT/B3LYP/6-311++G(d,p) theoretical levels to obtain geometries, H-bond energies and harmonic infrared vibrational properties for the Cs symmetry structures of heterocyclic hydrogen-bonded complexes, CnHmY-HX. The H-bond lengths in DFT/B3LYP calculation level are in better agreement with the experimental values than the MP2 results. The geometry optimization are interpreted in terms of hydrogen bond nonlinearity represented by theta; and phi angles, once the hydrogen bond is formed among n-electrons pairs of the heteroatom in heterocyclic and the hydrogen atom in HX. The hydrogen bond energy after of the zero-point vibrational energy (ZPE) and basis set superposition error (BSSE) corrections are overestimated at DFT/B3LYP, whereas the MP2 BSSE corrections are very large than corresponding DFT/B3LYP. For example, the BSSE corrections for the C2H4S-HNC complex are 7.60 and 0.09 kJ mol(-1) in MP2 and DFT/B3LYP calculations levels, respectively. The new vibrational modes in infrared harmonic spectrum arising from complexation show several interesting features, especially the intermolecular stretching mode.     

传统氢键(X—H…Y)还是X—H…π相互作用？ ——无机苯与卤化氢相互作用本质的量子化学研究

在MP2/6-311＋＋G**水平对无机苯(B3N3H6)与卤化氢HX (X＝F, Cl, Br, I)相互作用体系进行了系统研究. 结果表明在B3N3H6-HX (X＝F, Cl, Br, I)体系的平衡几何结构中, HX的H原子倾向于指向B3N3H6环上的N原子, 且从HF到HI相互作用强度依次减弱. 与苯-卤化氢体系比较, 除与HF相互作用B3N3H6较C6H6强外, 其余体系B3N3H6均较C6H6弱(结合能数值相差4 kJ/mol左右). 对称匹配微扰理论(SAPT)能量分解结果说明静电、诱导和色散力对描述B3N3H6-卤化氢体系的相互作用都很重要, 从HF到HI静电能占总吸引作用能的百分比逐渐减少, 色散能占总吸引作用能的百分比逐渐增加, 这种变化趋势与苯-卤化氢体系比较类似, 表明B3N3H6与卤化氢的相互作用随着卤素原子序数的递增, 传统氢键作用趋势减弱, X—H…π相互作用趋势增强.     

Infrared spectra of the Cl- -C2H4 and Br- -C2H4 anion dimers

Infrared spectra of mass-selected Cl- -C2H4 and Br- -C2H4 complexes are recorded in the vicinity of the ethylene CH stretching vibrations (2700-3300 cm(-1) using vibrational predissociation spectroscopy. Spectra of both complexes exhibit 6 prominent peaks in the CH stretch region. Comparison with calculated frequencies reveal that the 4 higher frequency bands are associated with CH stretching modes of the C2H4 subunit, while the 2 weaker bands are assigned as overtone or combinations bands gaining intensity through interaction with the CH stretches. Ab initio calculations at the MP2/aug-cc-pVDZ level suggest that C2H4 preferentially forms a single linear H-bond with Cl- and Br- although a planar bifurcated configuration lies only slightly higher in energy (by 110 and 16 cm(-1), respectively). One-dimensional potential energy curves describing the in-plane intermolecular bending motion are developed which are used to determine the corresponding vibrational energies and wavefunctions. Experimental and theoretical results suggest that in their ground vibrational state the Cl- -C2H4 and Br- -C2H4 complexes are localized in the single H-bonded configuration, but that with the addition of modest amounts of internal energy, the in-plane bending wavefunction also has significant amplitude in the bifurcated structure.     

Theoretical investigation of the dihydrogen bond linking MH2 with HCCRgF (M = Zn, Cd; Rg = Ar, Kr)

An ab initio computational study of the properties of four linear dihydrogen-bonded complexes pairing MH2 (M = Zn, Cd) with HCCRgF (Rg = Ar, Kr) was undertaken at the MP2/DGDZVP level of theory. The calculated complexation energies of the linear complexes vary between 6.5 kJ/mol for M = Zn to 8.5 kJ/mol for M = Cd. Equilibrium interatomic H...H distances are roughly 2.07 A for all four complexes. The red shifts of the H-C stretching frequency of HCCRgF correlate nicely with the interaction energies.     

Theoretical study of the potential energy surfaces of the Van Der Waals H2O-X2+ (X = Cl or Br) complexes

An ab initio study of the interactions between H2O and Cl2+ and H2O and Br2+ has been performed. We present calculations using both the UMP2 level and the UCCSD(T) level of correlation with the aug-cc-pVTZ basis. The aug-cc-pVQZ basis was tested for selected geometries and was found to yield results similar to the smaller basis. For the H2O-Cl2+ cation, a C2v structure has been identified as the minimum, with De = 6500 cm-1 (78 kJ/mol). A low-lying excited state has De = 6000 cm-1 (72 kJ/mol). The adiabatic and vertical ionization energies of the complex are 10.7 and 11.0 eV, compared to the experimental adiabatic value, 11.5 eV, for free chlorine. For the H2O-Br2+ cation, the calculations are more subtle due to second-order Jahn-Teller effects and result in a Cs structure at the minimum, with De = 6300 cm-1 (75 kJ/mol), yielding an adiabatic ionization energy of 9.9 eV compared to the corresponding experimental value, 10.5 eV, for free bromine. The relatively large binding energies give rise to strong normal mode couplings such that the halogen stretching mode becomes mixed with the water bending and other intermolecular modes, resulting in very large frequency shifts. Vertical ionization energies and ion vibrational frequencies also are reported and used to discuss possible experiments to obtain more precise data for each of the complexes.     

The effect of the torsional and stretching vibrations of C2H6 on the H + C2H6 --> H2 + C2H5 reaction

We present a three-dimensional quantum scattering model to treat reactions of the type H + C2H6 --> H2 + C2H5. The model allows the torsional and the stretching degrees of freedom to be treated explicitly. Zero-point energies of the remaining modes are taken into account in electronic structure calculations. An analytical potential-energy surface was developed from a minimal number of ab initio geometry evaluations using the CCSD(T,full)/cc-pVTZ//MP2(full)/cc-pVTZ level of theory. The reaction is endothermic by 1.5 kcal mol(-1) and exhibits a vibrationally adiabatic barrier of 12.0 kcal mol(-1). The results show that the torsional mode influences reactivity when coupled with the vibrational C-H stretching mode. We also found that ethyl radical products are formed internally excited in the torsional mode.     

An MP2 study on pre-reactive complexes (CH_2)_2O … XY (X,Y = H,F,Cl,Br,I)

The structures, energies, atomic chaiges and IR spectra of complexes (CH2)2O…XY (X, Y = H, F, Cl, Br, and I) have been examined by means of ab initio molecular orbital theory at the second-order level of Moller-Plesset perturbation correction. It is found that the hydrogen bond O…H-X is non-linear. The attraction between X and the H atoms in oxirane ring causes O…H-X bond bending. The hydrogen bond slighdy weakens the bond strength of C-O, and leads the bending and stretching mode of IR to shift to the red. The calculation results show that there is no evidence of a significant extent of proton transfer to give (CH2)2OH …X- in the isolated complexes.     

Stabilities and properties of complexes pairing hydroperoxyl radical with monohalomethanes

UMP2/aug-cc-pvdz calculations are used to analyze the interaction between hydroperoxyl radical (HOO) and CH(3)X (X = F, Cl, Br). Two minima are located on the potential energy surface of each complex. The more strongly bound contains a OH...X bond, along with CH...O; only CH...O bonds occur in the less stable minimum. Binding energies of the dominant minimum lie in the range of 20-24 kJ/mol, with X = F the most strongly bound. Analysis of the perturbations of the covalent bond lengths within each subunit caused by complexation, coupled with vibrational frequencies and charge transfers, opens a window into the nature of the interactions.     

Redshift and blueshift of the Ar-H vibrational stretching frequency in complexes of FArH and acetylene

Two planar hydrogen-bonded complexes of FArH and acetylene were found to be stable using second-order M?ller-Plesset perturbation theory (MP2) with 6-311++G(2d,2p) basis sets. The more stable complex involves bonding between the F atom of FArH and a H atom of acetylene, while the other isomer is a T-shaped complex with the H atom of FArH bonded to the center of the CC bond of acetylene; the zero-point energy corrected dissociation energies are 29 and 27 kJ mol(-1), respectively. Interestingly, the Ar-H harmonic vibrational stretching frequency is blueshifted in the more stable isomer and redshifted in the less stable form. The electron density rearrangement of FArH on complexation was investigated and used to explain these unusual findings.     

Theoretical investigation of hydrogen bonds between CO and HNF2, H2NF, and HNO

Ab initio quantum mechanics methods were applied to investigate the hydrogen bonds between CO and HNF2, H2NF, and HNO. We use the Hartree-Fock, MP2, and MP4(SDQ) theories with three basis sets 6-311++G(d,p), 6-311++G(2df,2p), and AUG-cc-pVDZ, and both the standard gradient and counterpoise-corrected gradient techniques to optimize the geometries in order to explore the effects of the theories, basis sets, and different optimization methods on this type of H bond. Eight complexes are obtained, including the two types of C...H-N and O...H-N hydrogen bonds: OC...HNF2(C(s)), OC...H2NF(C(s) and C1), and OC...HNO(C(s)), and CO...HNF2(C(s)), CO...H2NF(C(s) and C1), and CO...HNO(C(s)). The vibrational analysis shows that they have no imaginary frequencies and are minima in potential energy surfaces. The N-H bonds exhibit a small decrease with a concomitant blue shift of the N-H stretch frequency on complexation, except for OC...HNF2 and OC...H2NF(C1), which are red-shifting at high levels of theory and with large basis sets. The O...H-N hydrogen bonds are very weak, with 0 K dissociation energies of only 0.2-2.5 kJ/mol, but the C...H-N hydrogen bonds are stronger with dissociation energies of 2.7-7.0 kJ/mol at the MP2/AUG-cc-pVDZ level. It is notable that the IR intensity of the N-H stretch vibration decreases on complexation for the proton donor HNO but increases for HNF2 and H2NF. A calculation investigation of the dipole moment derivative leads to the conclusion that a negative permanent dipole moment derivative of the proton donor is not a necessary condition for the formation of the blue-shifting hydrogen bond. Natural bond orbital analysis shows that for the C...H-N hydrogen bonds a large electron density is transferred from CO to the donors, but for the O...H-N hydrogen bonds a small electron density transfer exists from the proton donor to the acceptor CO, which is unusual except for CO...H2NF(C(s)). From the fact that the bent hydrogen bonds in OC(CO)...H2NF(C(s)) are quite different from those in the others, we conclude that a greatly bent H-bond configuration shall inhibit both hyperconjugation and rehybridization.     

The mechanism of H-bond rupture: the vibrational pre-dissociation of C2H2-HCl and C2H2-DCl

Pair correlated fragment rovibrational distributions are presented following vibrational predissociation of the C2H2-DCl van der Waals dimer initiated by excitation of the asymmetric (asym) C-H stretch. The only observed fragmentation pathways are DCl (v= 0; j= 6-9)+ C2H2(nu2= 1; j= 1-5). These and previously reported data on the related C2H2-HCl species are analysed using the angular momentum (AM) method. Calculations accurately reproduce fragment rovibrational distributions following dissociation of the C2H2-HCl dimer initiated either by excitation of the asym C-H stretch or via the HCl stretch, and those from C2H2-DCl initiated via asym C-H stretch excitation. The calculations demonstrate that the dimer is bent at the moment of dissociation. Several geometries are found that lead to H-bond breakage via a clearly identified set of fragment quantum states. The results suggest a hierarchy in the disposal of excess energy and angular momentum between fragment vibration, rotation and recoil. Deposition of the largest portion of energy into a C2H2 vibrational state sets an upper limit on HCl rotation, which then determines the energy and AM remaining for C2H2 rotation and fragment recoil. Acceptor C2H2 vibrational modes follow a previously noted propensity, implying that the dissociating impulse must be able to induce appropriate nuclear motions both in the acceptor vibration and in rotation of the C2H2 fragment.     

A computational study of the dihydrogen bonded complexes HBeH ... HArF and HBeH ... HKrF

We report an ab initio computational study of the properties of two linear dihydrogen-bonded complexes of HBeH with the recently discovered rare gas compounds HArF and HKrF at the MP2(full)/6-311++G(2d,2p) level of theory. The HBeH ... HArF and HBeH ... HKrF complexes were found to have zero-point energy corrected binding energies of 27 and 12 kJ mol(-1), respectively. Large red shifts of the H-Rg vibrational stretching frequency in both complexes were also predicted. The electron density rearrangement of the rare gas compounds on complexation was also examined. We also consider the relative stabilities of D-containing isotopomers of the complexes by comparison of their computed zero-point vibrational energies.     

Theory of late-transition-metal alkyl and heteroatom bonding: analysis of Pt, Ru, Ir, and Rh complexes

Density functional and correlated ab initio methods were used to calculate, compare, and analyze bonding interactions in late-transition-metal alkyl and heteroatom complexes (M-X). The complexes studied include: (DMPE)Pt(CH(3))(X) (DMPE = 1,2-bis(dimethylphosphino)ethane), Cp*Ru(PMe(3))(2)(X) (Cp* = pentamethylcyclopentadienyl), (DMPE)(2)Ru(H)(X), (Tp)(CO)Ru(Py)(X) (Tp = trispyrazolylborate), (PMe(3))(2)Rh(C(2)H(4))(X), and cis-(acac)(2)Ir(Py)(X) (acac = acetylacetonate). Seventeen X ligands were analyzed that include alkyl (CR(3)), amido (NR(2)), alkoxo (OR), and fluoride. Energy decomposition analysis of these M-X bonds revealed that orbital charge transfer stabilization provides a straightforward model for trends in bonding along the alkyl to heteroatom ligand series (X = CH(3), NH(2), OH, F). Pauli repulsion (exchange repulsion), which includes contributions from closed-shell d(π)-p(π) repulsion, generally decreases along the alkyl to heteroatom ligand series but depends on the exact M-X complexes. It was also revealed that stabilizing electrostatic interactions generally decrease along this ligand series. Correlation between M-X and H-X bond dissociation energies is good with R(2) values between 0.7 and 0.9. This correlation exists because for both M-X and H-X bonds the orbital stabilization energies are a function of the orbital electronegativity of the X group. The greater than 1 slope when correlating M-X and H-X bond dissociation energies was traced back to differences in Pauli repulsion and electrostatic stabilization.     

Theoretical study of the interaction between HNZ (Z = O, S) and H(2)XNH(2) (X = B, Al). Conventional and dihydrogen bonds

Theoretical calculations at the MP2/6-311++G(2d,2p) level are used to analyze the interaction between HNZ (Z = O, S) and H(2)XNH(2) (X = B, Al). In the most stable conformation, the complexes are cyclic, the molecules being held together by conventional NHZ hydrogen bonds and by XHHN dihydrogen bonds. Binding energies including ZPE- and BSSE-corrections lie in the range 6.2-6.9 kJ mol(-1) and there is little sensitivity to the nature of the X and Z atoms. In the XHHN dihydrogen bonds, the NH stretching vibrations are blue-shifted in the HNO complexes and red-shifted in the H(2)AlNH(2)-HNS complex. In the conventional NHZ hydrogen bonds, the NH stretching vibrations are red-shifted. The topological parameters at the bond critical point are in the usual range for hydrogen or dihydrogen bonds. A natural bond orbital analysis including the calculation of the atomic charges, hybridization, occupation of the antibonding orbitals and hyperconjugation energies shows that the shifts of the NH stretching vibrations in the conventional and dihydrogen bonds are mainly determined by the changes in occupation of the sigma*(NH) antibonding orbitals. The mechanism of intramolecular coupling is discussed and appears to be different for the HNO and HNS complexes. The analysis of all the theoretical data reveals that the NHZ bonds are stronger in the H(2)BNH(2) than in the H(2)AlNH(2) systems and that the XHHN dihydrogen bonds are stronger in the H(2)AlNH(2) than in the H(2)BNH(2) complexes.     

Charge penetration and the origin of large O-H vibrational red-shifts in hydrated-electron clusters, (H2O)n-

The origin of O-H vibrational red-shifts observed experimentally in (H2O)n(-) clusters is analyzed using electronic structure calculations, including natural bond orbital analysis. The red-shifts are shown to arise from significant charge transfer and strong donor-acceptor stabilization between the unpaired electron and O-H sigma* orbitals on a nearby water molecule in a double hydrogen-bond-acceptor ("AA") configuration. The extent of e(-) --> sigma* charge transfer is comparable to the n --> sigma* charge transfer in the most strongly hydrogen-bonded X(-)(H2O) complexes (e.g., X = F, O, OH), even though the latter systems exhibit much larger vibrational red-shifts. In X(-)(H2O), the proton affinity of X(-) induces a low-energy XH...(-)OH diabatic state that becomes accessible in v = 1 of the shared-proton stretch, leading to substantial anharmonicity in this mode. In contrast, the H + (-)OH(H2O)(n-1) diabat of (H2O)n(-) is not energetically accessible; thus, the O-H stretching modes of the AA water are reasonably harmonic, and their red-shifts are less dramatic. Only a small amount of charge penetrates beyond the AA water molecule, even upon vibrational excitation of these AA modes. Implications for modeling of the aqueous electron are discussed.     

Electron and positron scattering from 1,1-C2H2F2

1,1-difluoroethylene (1,1-C2H2F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (nu2 and nu9) stretching and the combined C-F (nu3) stretching and CH2 (nu11) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B2, B1, and A1 symmetries, respectively. The pi* resonance peak at 1.8 eV in C2H4 is observed shifted to 2.3 eV in 1,1-C2H2F2 and to 2.5 eV in C2F4; a phenomenon attributed to the decreasing C=C bond length from C2H4 to C2F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV.     

Energetics of halogen bonding of group 10 metal fluoride complexes

A study is presented of the thermodynamics of the halogen-bonding interaction of C(6)F(5)I with a series of structurally similar group 10 metal fluoride complexes trans-[Ni(F)(2-C(5)NF(4))(PCy(3))(2)] (2), trans-[Pd(F)(4-C(5)NF(4))(PCy(3))(2)] (3), trans-[Pt(F){2-C(5)NF(2)H(CF(3))}(PR(3))(2)] (4a, R = Cy; 4bR = iPr) and trans-[Ni(F){2-C(5)NF(2)H(CF(3))}(PCy(3))(2)] (5a) in toluene solution. (19)F NMR titration experiments are used to determine binding constants, enthalpies and entropies of these interactions (2.4 ≤ K(300) ≤ 5.2; -25 ≤ ΔH(o) ≤ -16 kJ mol(-1); -73 ≤ ΔS(o) ≤ -49 J K(-1) mol(-1)). The data for -ΔH(o) for the halogen bonding follow a trend Ni < Pd < Pt. The fluoropyridyl ligand is shown to have a negligible influence on the thermodynamic data, but the influence of the phosphine ligand is significant. We also show that the value of the spin-spin coupling constant J(PtF) increases substantially with adduct formation. X-ray crystallographic data for Ni complexes 5a and 5c are compared to previously published data for a platinum analogue. We show by experiment and computation that the difference between Pt-X and Ni-X (X = F, C, P) bond lengths is greatest for X = F, consistent with F(2pπ)-Pt(5dπ) repulsive interactions. DFT calculations on the metal fluoride complexes show the very negative electrostatic potential around the fluoride. Calculations of the enthalpy of adduct formation show energies of -18.8 and -22.8 kJ mol(-1) for Ni and Pt complexes of types 5 and 4, respectively, in excellent agreement with experiment.     

Halogen-hydride interaction between Z-X (Z = CN, NC; X = F, Cl, Br) and H-Mg-Y (Y = H, F, Cl, Br, CH3)

Halogen-hydride interactions between Z-X (Z = CN, NC and X = F, Cl, Br) as halogen donor and H-Mg-Y (Y = H, F, Cl, Br, CH(3)) as electron donor have been investigated through the use of Becke three-parameter hybrid exchange with Lee-Yang-Parr correlation (B3LYP), second-order M?ller-Plesset perturbation theory (MP2), and coupled-cluster single and double excitation (with triple excitations) [CCSD(T)] approaches. Geometry changes during the halogen-hydride interaction are accompanied by a mutual polarization of both partners with some charge transfer occurring from the electron donor subunit. Interaction energies computed at MP2 level vary from -1.23 to -2.99 kJ/mol for Z-F···H-Mg-Y complexes, indicating that the fluorine interactions are relatively very weak but not negligible. Instead, for chlorine- and bromine-containing complexes the interaction energies span from -5.78 to a maximum of -26.42 kJ/mol, which intimate that the interactions are comparable to conventional hydrogen bonding. Moreover, the calculated interaction energy was found to increase in magnitude with increasing positive electrostatic potential on the extension of Z-X bond. Analysis of geometric, vibrational frequency shift and the interaction energies indicates that, depending on the halogen, CN-X···H interactions are about 1.3-2.0 times stronger than NC-X···H interactions in which the halogen bonds to carbon. We also identified a clear dependence of the halogen-hydride bond strength on the electron-donating or -withdrawing effect of the substituent in the H-Mg-Y subunits. Furthermore, the electronic and structural properties of the resulting complexes have been unveiled by means of the atoms in molecules (AIM) and natural bond orbital (NBO) analyses. Finally, several correlative relationships between interaction energies and various properties such as binding distance, frequency shift, molecular electrostatic potential, and intermolecular density at bond critical point have been checked for all studied systems.     

Infrared spectra of chlorinated ethylene cations: C2Cl4+, C2HCl3+, 1,1-C2H2Cl2+, and trans-C2H2Cl2+ in solid argon

Infrared spectra of chlorinated ethylene cations: C2Cl4+, C2HCl3+, 1,1-C2H2Cl2+, and trans-C2H2Cl2+ isolated in solid argon are presented. These cations were produced by co-deposition of chlorinated ethylene/Ar mixtures with high-frequency-discharged Ar at 4 K. Photosensitive absorptions are assigned to different vibrational modes of the cations on the basis of observed chlorine isotopic shifts and quantum chemical frequency calculations. With the removal of one electron from the HOMO of chlorinated ethylene neutrals that is C=C bonding and C-Cl antibonding in character, the observed C-Cl stretching vibrational frequencies of the cations are blue-shifted relative to those of the chlorinated ethylene neutrals. The results also show that the cations can be regarded as "isolated" with the vibrational frequencies only slightly shifted when compared to the available gas-phase values.