Influence of the d orbital occupation on the nature and strength of copper cation-pi interactions: threshold collision-induced dissociation and theoretical studies

Threshold collision-induced dissociation techniques are employed to determine the bond dissociation energies of a wide variety of copper cation-pi complexes, Cu(+)(pi-ligand), where pi-ligand = benzene, flurobenzene, chlorobenzene, bromobenzene, iodobenzene, phenol, toluene, anisole, pyrrole, N-methylpyrrole, indole, naphthalene, aniline, N-methylaniline, and N,N-dimethylaniline. The primary and lowest energy dissociation pathway corresponds to the endothermic loss of the intact neutral pi-ligand for all complexes except those to N-methylpyrrole, indole, aniline, N-methylaniline, and N,N-dimethylaniline. In the latter complexes, the primary dissociation pathway corresponds to loss of the intact ligand accompanied by charge transfer, thereby producing a neutral copper atom and ionized pi-ligand. Fragmentation of the pi-ligands is also observed at elevated energies in several cases. Theoretical calculations at the B3LYP/6-311G(d,p) level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Multiple low-energy conformers are found for all of the copper cation-pi complexes. Theoretical bond dissociation energies are determined from single point energy calculations at the B3LYP/6-311+G(3df,2p) level of theory using the B3LYP/6-311G(d,p) optimized geometries. The agreement between theory and experiment is very good for most complexes. The nature and strength of the binding in these copper cation-pi complexes are studied and compared with the corresponding cation-pi complexes to Na(+). Natural bond orbital analyses are carried out to examine the influence of the d orbital occupation on copper cation-pi interactions.     

Ab initio classical trajectory calculations of 1,3-cyclobutanedione radical cation dissociation

Abstract  

The dissociation of 1,3-cyclobutanedione radical cation was studied by ab initio direct classical trajectory calculations at the BH&HLYP/6-31G(d) level of theory. A microcanonical ensemble using normal mode sampling was constructed by distributing 10 kcal/mol of excess energy above the transition state for the tautomerization of the keto-enol to the diketo form. A total of 210 trajectories were run starting from this transition state, yielding chemically activated 1,3-cyclobutanedione radical cation. The majority of the trajectories resulted in CH₂CO^+· + CH₂CO, with the activated CC bond breaking nearly twice as often as the spectator CC bond. The non-statistical behavior is observed because the rate of energy redistribution within the molecule is comparable to or slower than the dissociation rates. In addition to the expected products, dissociation to CH₂COCH₂^+· + CO and formation of a proton-transferred product HCCO^· + CH₃CO⁺ were also seen in some of the trajectories.     

SiH_4与AB型卤素互化物之间的反转氢键

采用从头算方法对SiH4与AB型卤素互化物(ClF、BrF、IF、ICl、IBr、BrCl)形成的复合物的结构特征及本质进行了探讨.在MP2/6-311++G(3d,3p)水平上优化复合物的分子结构,并进行频率验证.通过分子间距离、自然键轨道(NBO)净电荷迁移数及分子图,确认SiH4与卤素互化物形成反转氢键型复合物.在MP2/6-311++G(3d,3p)水平上进行基组重叠误差(BSSE)校正后的作用能为-5.113--9.468kJ·mol-1.用对称匹配微扰理论(SAPT)对作用能进行分解,结果显示,诱导能对总吸引能的贡献在55.0%到72.2%之间,是最主要的贡献部分,静电能和色散能对总吸引能的贡献都小于25.0%.     

A theoretical study of the C–HN hydrogen bond in the methane–ammonia complex

The C–HN hydrogen bond in the methane–ammonia complex is studied by determining its bond dissociation energy (BDE) and the n(N)→σ^*(C–H) interaction. At the MP2(Full)/6-311++G(3df,2p) level of theory with basis set superposition error (BSSE) correction, the BDE was determined to be 2.5 kJ mol⁻¹. The n(N)→σ^*(C–H) interaction at this level of theory was found to be 3.7 kJ mol⁻¹ by natural bond orbital (NBO) analysis. It was also found that the NBO values are in general higher than the BDE values with BSSE correction when they are compared at the same level of theory.     

Ab initio studies on ONH3, ONF3 and OCF 3 − , using polarization functions and configuration interaction methods

SCF geometry optimizations, using double-zeta basis sets with polarization functions, either as d-orbitals or bond functions, were performed on ONH₃, ONF₃, and OCF ₃ ^? . The bonding in these molecules is discussed with the help of orbital density plots and Mulliken population analyses. ONF₃ can be explained as donor-acceptor product of O with NF₃. For OCF ₃ ^? , diffuse functions have also been added to the basis set. The CF distance is predicted to be 1.39 Å, in qualitative agreement with the known infrared spectrum. With the best basis set, the NF distance of ONF₃ is too short by 0.08 Å at the SCF level. A geometry optimization by the configuration-interaction method gives the NF distance as well as the ON distance in excellent agreement with experimental results.     

An extended-valence MC SCF procedure: determination of the dissociation energies of C2, N2, O2, and F2

A series of MC SCF calculations have been carried out on C₂, N₂, O₂, and F₂ with the goal of obtaining compact wavefunctions which recover a significant fraction of the electron correlation effects important for bond dissociation. The active orbital space is varied in size, with the largest spaces including the molecular orbitals derived from 2s, 2p, 3s, 3p and 4p atomic orbitals. Several basis sets ranging in size from 5s3p to 5s4p2d1f are investigated to determine the flexibility in the basis set needed with various choices of the active orbital space. The best extended-valence MC SCF (EVMC) dissociation energies are 0.2–0.5 eV less than the experimental values, indicating that further enlargement of the active orbital space is necessary to achieve 0.1 eV accuracy in the computed dissociation energies. The EVMC calculations reveal that, for the calculation of the dissociation energies, inclusion of non-valence orbitals is much more important for O₂ and F₂ than for C₂ and N₂. The EVMC results are compared with the predictions of full fourth-order perturbation theory, coupled cluster theory, and with the best available CI calculations.     

Gas-phase energetics of organic free radicals using time-resolved photoacoustic calorimetry

A generalized method for the determination of thermochemical data of transient species, using time-resolved photoacoustic calorimetry (TR-PAC), is described in detail. Taking phenol as an example, the procedure for the determination of the PhO–H bond dissociation enthalpy from photoacoustic experiments, in various solvents, is presented, and its assumptions discussed. To derive gas-phase bond dissociation enthalpies from the solution values, a widely used procedure is compared with a computational chemistry (CC) microsolvation method. Results from the combined TR-PAC/CC approach show that the established “hydrogen bond only” model (to describe the difference between the solvation enthalpies of phenol and phenoxy radical) leads to an underestimation of the derived gas-phase bond dissociation enthalpy. When that differential solvation is properly accounted for, the agreement between our results and a recommended gas-phase value improves, indicating that the combined TR-PAC/CC approach is a valid tool for the study of organic free radical energetics.     

On a definition of bond energies based on localized molecular orbitals

A theoretical model is presented for defining bond energies based on localized molecular Orbitals. These bond energies are obtained by rearranging the total SCF energy including the nuclear repulsion term to a sum over orbital and orbital interaction terms and then to total orbital terms, which can be interpreted as the energies of localized orbitals in a molecule. A scaling procedure is used to obtain a direct connection with experimental bond dissociation energies. Two scale parameters are employed, the C-C and the C-H bond dissociation energy in C₂H₆ for A-B and C-H type bonds, respectively. The implications of this scaling procedure are discussed. Numerical applications to a number of organic molecules containing no conjugated bonds gives in general a very satisfactory agreement between experimental and theoretical bond energies.     

Ab Initio energetics of Si?O bond cleavage

A multilevel approach that combines high‐level ab initio quantum chemical methods applied to a molecular model of a single, strain‐free Si O Si bridge has been used to derive accurate energetics for Si O bond cleavage. The calculated Si O bond dissociation energy and the activation energy for water‐assisted Si O bond cleavage of 624 and 163 kJ mol⁻¹, respectively, are in excellent agreement with values derived recently from experimental data. In addition, the activation energy for H₂O‐assisted Si O bond cleavage is found virtually independent of the amount of water molecules in the vicinity of the reaction site. The estimated reaction energy for this process including zero‐point vibrational contribution is in the range of −5 to 19 kJ mol⁻¹. © 2017 Wiley Periodicals, Inc.     

Experimental and calculated momentum densities for the valence orbitals of carbon tetrafluoride

Carbon tetraflouoride has been investigated by binary (e,2e) spectroscopy at 1200 eV impact energy. Binding energy spectra (10–60 eV) at azimuthal angles of 0° and 8° are reported and are found to be in quantitative agreement with a previous Green's function calculated spectrum. Momentum distributions corresponding to individual orbitals are also reported and compared with theoretical momentum distributions evaluated using double-zeta quality SCF wavefunctions. Excellent agreement between experimental and theories is found for the strongly bonding 3t₂ orbital and the antibonding 4a₁ orbital but agreement is less good for the outermost non-bonding orbitals. Intense structure due to molecular density (bond) oscillation is observed experimentally in the region above 1.0 a_o^?1 in the case of the non-bonding 4t₂ orbital. It is also notable that the measured 4a₁ momentum distribution exhibits an extremely well-defined “p” character with clear separation between the s and p components. Contour maps of the position-space and momentum-space orbital densities in the F-C-F plane of the molecule are used to provide a qualitative interpretation of the features observed in the momentum distribution. In order to further extend momentum-space chemical concepts to three-dimensional systems, constant density surface plots are also used to give a more comprehensive view of the density functions of the CF₈ molecule.     

Investigation on the Mechanism for C–N Coupling of 3‐Iodopyridine and Pyrazole Catalyzed by Cu(I)

The reaction mechanism for C–N coupling of 3‐iodopyridine and pyrazole catalyzed by Cu(I) was studied by the density functional theory. All of the reactants, intermediates, transition states, and products were optimized with the B3LYP method at 6–31+G(d) basis set. The single‐point energy and zero‐point energy correction were calculated for the optimized configuration of each compound with the sane method at 6–311++G(d,p) basis set. Transition states have been confirmed by the corresponding vibration analysis and intrinsic reactions coordinate. In addition, nature bond orbital and atoms in molecules (AIM) theories have been used to analyze orbital interactions and bond natures. The results showed that the activation energy of the rate‐determining step in the absence of catalysts was 250.63 kJ·mol^?1, which were 74.01 and 131.68 kJ·mol^?1 via Cu₂O and CuI catalyzed, respectively. Results indicated that catalyst Cu₂O promotes reaction effectively. All calculations were consistent with experiments.     

Study on the Physical and Dissociation Properties of Disulfur Dichloride under Electric Fields

Disulfur dichloride is a hazardous substance, which is irritating to the eyes. It is significant to study the physical and dissociation properties under external electric fields. The bond length, energy, dipole moment, orbital energy level distribution, infrared spectra and dissociation properties of disulfur dichloride molecule under different external fields are obtained by using the density functional theory at the B3LYP/6-311++G(d, p) basis set level. In addition, ultraviolet-visible absorption spectra of the molecule in different electric fields are studied with configuration interaction-single excitation(CIS)/6-311++G(d, p) method. According to the results, it has been found that as the electric field exerted along the positive direction of the z-axis increases, the two sulfur-chlorine(S-Cl) bond lengths become longer and tend to break, while the sulfur-sulfur(S-S) bond length becomes shorter and the energy gap decreases. The infrared spectrum and ultraviolet-visible absorption spectra both exhibit red shift under electric field. Moreover, by scanning the potential energy surface of disulfur dichloride about S-Cl bond, the dissociation barrier decreases with the increase of positive electric field. When the external electric field arrives at 0.040 atomic units, the barrier disappears, meaning the dissociation of disulfur dichloride. The present results offer an important reference to further study of disulfur dichloride.     

A theoretical study of H?H σ bond activation catalyzed by VO2+ in gas phase

The mechanism of H? H σ bond activation catalyzed by VO(¹A₁/³A′) has been investigated by using density functional theory at the B3LYP/6‐311G(2d, p) level and the single‐point energy calculations were done at the CCSD/6‐311G (2d, p)//B3LYP/6‐311G(2d, p) level of theory using the geometries along the minimum energy pathway. According to our calculation results, the different reaction mechanisms were found for the singlet and triplet potential energy surfaces (PESs). Specially, the crossing points (CPs) between the different PESs have been located by means of the intrinsic reaction coordinate approach used by Yoshizawa et al, and corresponding minimum energy CPs that we obtained by the mathematical algorithm proposed by Harvey et al. has also been employed. In addition, the orbital interaction for ion‐molecule complexes ¹IM1 and ³IM1 have been examined by fragment molecular orbital analysis. Finally, the frontier molecular orbital interaction analysis about ³TS1 and ³TS2 were used to gain useful information about the H? H σ bond activation by VO. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

咔咯锰(Ⅲ)与锰(V)-氧配合物与含氮配体的轴向配位性质

采用密度泛函理论(DFT)的BP86方法对含氮配体咪唑、甲基咪唑、异丙基咪唑和吡啶与5,10,15-三(五氟苯基)咔咯锰[(TPFC)Mn^Ⅲ]和5,10,15-三(五氟苯基)咔咯锰氧[(TPFC)Mn^VO]的轴向配位性质进行理论研究.计算结果表明配体能与五重态下的(TPFC)Mn^Ⅲ形成有效的轴向配位作用,结合能绝对值次序为：咪唑>4-甲基咪唑>吡啶,与实验结果一致. 另外,结合能和轴向配位键长数据显示,这些配体不能与基态(单重态)或三重态(TPFC)Mn^VO中的Mn^V原子形成有效的轴向配位作用,自然键轨道(NBO)分析表明其Mn^V没有空的3d 轨道来接受配体的孤对电子,但配体可与三重态下的(TPFC)Mn^VO形成弱的配位作用.     

Theoretical investigations of spin-orbit coupling and intersystem crossing in reaction carbon dioxide activated by [Re(CO)2]+

In order to further explore the detailed reaction mechanism of carbon dioxide activated by [Re(CO)₂]⁺ complex, CCSD(T) methods was performed to determine related potential energy surface (PES). Crossing point is determined by using a partially optimized method. The result shows that larger spin-orbital coupling (155.37 cm⁻¹) and intersystem crossing probabilities in spin-forbidden region causes the electron to spin flip at the minimum energy crossing point and access to the lower singlet PES. Nonadiabatic rate constant k is estimated to be quite rapid, so transition state (¹TS1) is rate-controlled steps. In addition, the electronic structure of oxygen-atom transfer process is further analyzed by localized molecular orbital and Mayer bond order. The analysis finds that the form of main bonding orbital is the electron contribution from the p(O) in CO₂ to the empty d(Re) orbital.     

Solvation of copper ions by acetone. structures and sequential binding energies of Cu+(acetone)x,x = 1-4 from collision-induced dissociation and theoretical studies

Collision-induced dissociation of Cu+(acetone)(x), x = 1-4, with Xe is studied as a function of kinetic energy using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed is endothermic loss of one acetone molecule. The primary cross section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-neutral collisions, internal energy of the complexes, and dissociation lifetimes. Density functional calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes and provide molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical bond dissociation energies are determined from single point calculations at the B3LYP/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) levels, using the B3LYP/6-31G* optimized geometries. The experimental bond energies determined here are in good agreement with previous experimental measurements made in a high-pressure mass spectrometer for the sum of the first and second bond energy (i.e., Cu+(acetone)2 --> Cu+ + 2 acetone) when these results are properly anchored. The agreement between theory and experiment is reasonable in all cases, but varies both with the size of the cluster and the level of theory employed. B3LYP does an excellent job for the x = 1 and 3 clusters, but is systematically low for the x = 2 and 4 clusters such that the overall trends in sequential binding energies are not parallel. In contrast, all MP2 values are somewhat low, but the overall trends parallel the measured values for all clusters. The trends in the measured Cu+(acetone), binding energies are explained in terms of 4s-3d sigma hybridization effects and ligand-ligand repulsion in the clusters.     

Sodium Cation Affinities of Commonly Used MALDI Matrices Determined by Guided Ion Beam Tandem Mass Spectrometry

The sodium cation affinities of six commonly used MALDI matrices are determined here using guided ion beam tandem mass spectrometry techniques. The collision-induced dissociation behavior of six sodium cationized MALDI matrices, Na⁺(MALDI), with Xe is studied as a function of kinetic energy. The MALDI matrices examined here include: nicotinic acid, quinoline, 3-aminoquinoline, 4-nitroaniline, picolinic acid, and 3-hydroxypicolinic acid. In all cases, the primary dissociation pathway corresponds to endothermic loss of the intact MALDI matrix. The cross section thresholds are interpreted to yield zero and 298 K Na⁺−MALDI bond dissociation energies (BDEs), or sodium cation affinities, after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G* and MP2(full)/6-311+G(2d,2p)//B3LYP/6-31G* levels of theory are used to characterized the structures and energetics for these systems. The calculated BDEs exhibit very good agreement with the measured values for most systems. The experimental and theoretical Na⁺−MALDI BDEs determined here are compared with those previously measured by cation transfer equilibrium methods.     

Cu as a one-electron atom: Molecular structure and dissociation energy of CuOH

The molecular structure and dissociation energy of CuOH have been investigated using non-empirical pseudopotentials. Two kinds of pseudopotential have been used, either including or not the 3d¹⁰ electrons of the Cu atom in the atomic core. At the SCF level and dealing explicitly with the 11 valence electrons of Cu, only about 60% of the experimental dissociation energy is recovered, while good agreement is found at the CI level. A difference of about 20 kcal/mol is found between the dissociation energies at the SCF level using the two kinds of pseudopotential. This difference is maintained at the CI level. Introduction of core-valence polarization and correlation effects overcomes the deficiency observed when only one electron is considered on the Cu atom.     

Bond functions in molecular excited states: MRD CI calculations for the A3Σ+u,B3Πg and W3Δu states of N2

Using double-zeta plus polarization (DZP) basis sets systematically augmented with a variety of bond functions, the term dissociation energies are calculated for the A³Σ⁺_u, B³Π_g and W³Δ_u states of N₂. It is found that the best agreement with literature values is generally with a basis set composition of DZP augmented by a set of s, p and d orbitals at the bond midpoint. The excited state potential energy curves and spectroscopic constants for the B³Π_g state are calculated from this basis and compared with experimental values. Good agreement was obtained, considering the small basis set size, with the spectroscopic constants ω_e, ω_eχ_e, ω_ey_e, B_e and α_e and the dissociation energy D_e (e.g., D_e = 3.38 (3.681, exp.), 4.75 (4.897) and 4.77(4.873) eV for the A, B and W stages, respectively). Poorer agreement was obtained for the term energy T′₀ (7.92 versus 7.35 eV, exp., for the B state). The error in term energy arises largely from an error in the calculated ⁴S → ²D splitting (2.705 versus 2.383 eV, exp.), and shifting the potential curve for the B state by a constant amount leads to much improved agreement relative to the ground state. The counterpoise correction applied to the potential curve of the B state causes a drastic deterioration of the results and shows qualitatively incorrect behaviour, and is therefore not recommended for calculations of this type.     

AB initio SCF LCAO MO study of the HOH…Cl− hydrogen bond

Ab initio SCF LCAO MO calculations for the [H₂O…Cl]^? complex have been performed. The energy of the linear hydrogen bond has been found to be lower than the energy of the bifurcated one. The difference of the energies is about 3 kcal/mole. The calculated equilibrium distance between the oxygen and chlorine atoms equals 5.75 au. The interaction energy of the chlorine anion and the rigid water molecule amounts to ?19 kcal/mole. The optimization of the OH bond length in the complex (linear hydrogen bond) leads to an interaction energy of ?19.5 kcal/mole (the experimental value equals ?13.1 kcal/mole). As a result of the hydrogen bond formation the OH bond length increases by 0.08 au.