C2v Structure Research Articles

Evaluation of Zn2+ Coordination Structures in Chiral Zn2+ Complexes Based on Shape Measurement Factors: Relationships between Activity and the Coordination Structure

We previously reported on enantioselective aldol reactions of acetone and cyclic ketones with benzaldehyde derivatives catalyzed by chiral Zn2+ complexes that mimic class II aldolases. The results and mechanistic studies indicated that the catalytic activity of Zn2+ complexes is dependent not only on the coordination numbers of Zn2+ but also on its coordination structure. In this study, we report on shape measures (abbreviated as S values in this manuscript) of such Zn2+ complexes with respect to the 5‐coordination structure based on calculations with continuous shape measures (CShM) using their crystal structures. The S values of Zn2+ ions in Zn2+ complexes for trigonal bipyramidal (D3h) or square pyramidal (C4v) structures suggest that Zn2+ ions in the catalytically active Zn2+ complexes possess D3h and C4v structures, while Zn2+ ions in the unreactive Zn2+ complex has a C4v structure. Moreover, the S values of Zn2+ were calculated with respect to 6‐coordination geometry, based on the assumption that aldol reactions proceed via 6‐membered transition states, and it was implied that 6‐coordinated Zn2+ ions in aldol‐active Zn2+ complexes prefer an octahedron structure (Oh). These results for the S values of Zn2+ ions in the active Zn2+ complexes and those for complexes reported by other research groups suggest that the transition of 5‐coordinated D3h to the 6‐coordinated Oh structure is essential for achieving catalytic stereoselective aldol reactions.

Jahn-Teller effect versus spin-orbit coupling: The structure of the free molybdenum pentafluoride molecule

The complete active space self-consistent field (CASSCF) and multiconfigurational quasi-degenerate second-order perturbation (MCQDPT2) calculations have been used to study the ground and low-lying excited electronic states of MoF5. Scalar-relativistic effects and spin-orbit coupling (SOC) have been taken into account employing the third-order Douglas-Kroll-Hess (DKH) Hamiltonian and full Breit-Pauli operator, respectively. The optimization and the calculation of the Hessian matrix have been performed by non-routine procedure employing the symmetry coordinates for all considered (D3h, C2v and C4v) geometrical configurations. The trigonal bipyramidal D3h structure of molybdenum pentafluoride MoF5 possesses two-fold degenerate ground first excited electronic orbital state and undergoes Jahn-Teller distortion to the C2v configurations. Accounting of SOC quenches the JT effect. As a result the D3h structure of MoF5 is no longer the conical intersection of two adiabatic potential energy surfaces (APES) but two separated APES corresponding to ground (12E1/2) and nearest excited (12E3/2) spin-orbit states are appeared instead. The D3h trigonal bipyramidal structure in the ground spin-orbit state corresponds to the 2-nd order saddle point on APES and lies above the minima (C2v structure, 12E1/2 state) by 244 cm−1. The warping barrier (another C2v structure) in the trough of APES and the Berry pseudorotation barrier (C4v structure, ground spin-orbit state 2E3/2) are 19 and 310 cm−1, respectively. Therefore MoF5 molecule is characterized in the gas phase by a large-amplitude motion of fluorine atoms in the equatorial plane and non-rigid intramolecular rearrangement by Berry mechanism. Despite such non-rigid nuclei dynamic, the calculated harmonic frequencies of MoF5 molecule do not contradict to available experimental IR spectrum. The repeat refinement of MoF5 gas electron diffraction data has been carried out using static and pseudoconformer models based on the SO-MCQDPT2 results. Corresponding to only extreme points on APES the configurations have been included into the pseudoconformer model. The both models have been fitted to the experimental data by the same quality.

Infrared Spectroscopic and Theoretical Studies of the 3d Transition Metal Oxyfluoride Molecules

A collection of 3d transition metal (V, Mn, Fe, Co, and Ni) oxyfluorides were prepared via the reactions of laser-ablated metal atoms and OF2 in an argon matrix, and the products were identified by infrared spectroscopy together with 18OF2 substitution. OMF2 is the major product from the reactions of metal atoms and OF2. The tetravalent metal center is coordinated to two fluorine atoms and one oxygen atom. Triatomic OMF molecules were observed in the reactions of V, Mn, Fe, and Co with OF2. In addition to OMF and OMF2, OMnF3 and OFeF3 were also formed presumably via the reactions of OMnF and OFeF with F2 resulting from photodecomposition of OF2. The seldom observed OF radical was produced in all of these experiments. Electronic structure calculations at the density functional theory and molecular orbital theory including electron correlation effects (CCSD(T) and CASPT2) levels are used to aid in the assignment of the structures. For OMF (M = Sc-Mn), the structures are bent and those for M = Fe-Cu are linear. The OMF2 molecules are optimized to be C2v structures. Both OMF and OMF2 have a high spin ground state, with the exception of OCoF2 in which the ground state quartet is the lower energy structure. The M-O stretching frequency is a sensitive measure of the computational method in terms of the bond angle, the coupling of the M-O and M-F stretches, and the amount of spin on the oxygen. A bonding analysis in terms of the CAS orbitals shows that a number of the structures have a multireference character after M = Cr. Oxidation states of the metal are given based on the CASPT2 results. Heats of formation for the OMF and OMF2 are reported.

Ab initio studies on the NO(X2II) − O2(X3 Σg−) van der Waals complexes in the doublet state

ABSTRACTUCCSD(T) and CASPT2 geometry optimisations were performed on six different structures of NO–O2 complexes in doublet states, using aug-cc-pVXZ basis sets up to X = 5. MRCI calculations were carried out at optimised UCCSD(T) and CASPT2 geometries. The most stable structure has NO and O2 arranged nearly parallel in the 2A′′ state, with a counterpoise adjusted dissociation energy De of 179 cm−1 (UCCSD(T) results). For the X-shaped 2A′ isomer De = 144 cm−1. C2v structures have De values between 115 and 121 cm−1, whereas linear structures are least stable. The closest and distances are 3.1–3.4 Å. The X-shaped 2A′′ isomer is not stable. The results are discussed and compared with values for other complexes.

Exploration of large amplitude motions in the Ca+Ar2 complex

ABSTRACTWe present a theoretical study of the ground electronic state potential of the Ca+Ar2 complex and of its photoabsorption spectra, simulated at temperatures ranging between 20 and 220 K. These calculations exploit a Monte-Carlo (MC) method, based on a one-electron pseudo-potential approach. A pairwise additive potential fitted to coupled cluster ab initio points, is used to model the Ca+Ar2 complex. Our study shows that the most stable form of Ca+Ar2 is a bent C2v structure, whereas the linear isomer is located at around 90 ± 10 cm−1 above in energy. The analysis of the photoabsorption spectra establishes that a structural transition from bent Ca+Ar2 to linear ArCa+Ar occurs at T∼100 K. Trends in binding energies of both isomers, bond lengths and bond angles are also discussed. Molecular orbital overlaps provide an explanation for the order of stability between the bent and linear structures.

Two-state diabatic potential energy surfaces of ClH2 based on nonadiabatic couplings with neural networks.

A general neural network (NN)-fitting procedure based on nonadiabatic couplings is proposed to generate coupled two-state diabatic potential energy surfaces (PESs) with conical intersections. The elements of the diabatic potential energy matrix (DPEM) can be obtained directly from a combination of the NN outputs in principle. Instead, to achieve higher accuracy, the adiabatic-to-diabatic transformation (ADT) angle (mixing angle) for each geometry is first solved from the NN outputs, followed by individual NN fittings of the three terms of the DPEM, which are calculated from the ab initio adiabatic energies and solved mixing angles. The procedure is applied to construct a new set of two-state diabatic potential energy surfaces of ClH2. The ab initio data including adiabatic energies and derivative couplings are well reproduced. Furthermore, the current diabatization procedure can describe well the vicinity of conical intersections in high potential energy regions, which are located in the T-shaped (C2v) structure of Cl-H2. The diabatic quantum dynamical results on diabatic PESs show large differences as compared with the adiabatic results in high collision energy regions, suggesting the significance of nonadiabatic processes in conical intersection regions at high energies.

Triple bonds between iron and heavier group-14 elements in the AFe(CO)3- complexes (A = Ge, Sn, and Pb).

Heteronuclear transition-metal-main-group element carbonyl anion complexes of AFe(CO)3- (A = Ge, Sn, and Pb) are prepared using a laser vaporization supersonic ion source in the gas phase, which were studied by mass-selected infrared (IR) photodissociation spectroscopy. The geometric and electronic structures of the experimentally observed species are identified by a comparison of the measured and calculated IR spectra. These anion complexes have a 2A1 doublet electronic ground state and feature an A[triple bond, length as m-dash]Fe triply bonded C3v structure with all of the carbonyl ligands bonded at the iron center. Bonding analyses of AFe(CO)3- (A = C, Si, Ge, Sn, Pb, and Fl) indicate that the complexes are triply bonded between the valence np atomic orbitals of bare group-14 atoms and the hybridized 3d and 4p atomic orbitals of iron.

The Role of Hyperconjugation on the Structure and C–H Stretching Frequencies of 3,3′-Ethane-1,2-diyl- bis-1,3,5-triazabicyclo[3.2.1]octane (ETABOC): An X-Ray Structure and Vibrational Study

Structural and vibrational studies have been carried out for the most stable conformer of 3,3′-ethane-1,2-diyl-bis-1,3,5-triazabicyclo[3.2.1]octane (ETABOC) at the DFT/B3LYP/6-31G(dp) level using the Gaussian 03 software. In light of the computed vibrational parameters, the observed IR Bolhmann bands for the C2V, C2, and Ci symmetrical structures of ETABOC have been analyzed. Hyperconjugative interaction was done by Natural Bond Orbital Analysis. Interpretation of hyperconjugative interaction involving the lone pairs on the bridgehead nitrogen atoms with the neighboring C–N and C–C bonds defines the conformational preference of the title compound. The recorded X-ray diffraction bond parameters were compared with theoretical values calculated at B3LYP/6-31G(d,p) and HF/6-31G(d,p) level of theory showed that ETABOC adopts a chair conformation and possesses an inversion center.

Coupled cluster and density functional investigation of the neutral sodium-benzene and potassium-benzene complexes

By means of coupled-cluster calculations we studied the neutral complexes: Na-benzene and K-benzene. They are non-ionic presenting C6v symmetry. In contrast with the results obtained for Li-benzene, the non-ionic C2v structure was not a minimum. At the CCSD(T)/CBS level of theory, with the inclusion of relativistic and core-valence effects, the dissociation energies for sodium and potassium benzene complexes are 2.4 and 3.3 kcal/mol, respectively. We found that most density functionals overestimate the adsorption energies of alkalis onto benzene. Therefore, special caution must be taken when DFT methods are employed to investigate the interactions between these elements and carbon nanomaterials.

Structure and Bonding in CE5- (E=Al-Tl) Clusters: Planar Tetracoordinate Carbon versus Pentacoordinate Carbon.

The structure, bonding, and stability of clusters with the empirical formula CE5- (E=Al-Tl) have been analyzed by means of high-level computations. The results indicate that, whereas aluminum and gallium clusters have C2v structures with a planar tetracoordinate carbon (ptC), their heavier homologues prefer three-dimensional C4v forms with a pentacoordinate carbon center over the ptC one. The reason for such a preference is a delicate balance between the interaction energy of the fifth E atom with CE4 and the distortion energy. Moreover, bonding analysis shows that the ptC systems can be better described as CE4- , with 17-valence electrons interacting with E. The ptC core in these systems exhibits double aromatic (both σ and π) behavior, but the σ contribution is dominating.

Matrix-Isolation and Quantum-Chemical Analysis of the C3v Conformer of XeF6, XeOF4, and Their Acetonitrile Adducts.

A joint experimental-computational study of the molecular structure and vibrational spectra of the XeF6 molecule is reported. The vibrational frequencies, intensities, and in particular the isotopic frequency shifts of the vibrational spectra for 129XeF6 and 136XeF6 isotopologues recorded in the neon matrix agree very well with those obtained from relativistic coupled-cluster calculations for XeF6 in the C3v structure, thereby strongly supporting the observation of the C3v conformer of the XeF6 molecule in the neon matrix. A C3v transition state connecting the C3v and Oh local minima is located computationally. The calculated barrier of 220 cm-1 between the C3v minima and the transition state corroborates the experimental observation of the C3v conformer and the absence of the Oh conformer in solid noble gas matrices. For comparison matrix-isolation spectra have also been recorded and analyzed for the 129XeOF4 and the 136XeOF4 isotopologues. The matrix-isolation complexation shifts obtained for the XeF6·NCCH3 relative to those of free matrix isolated XeF6 and CH3CN are in good agreement with those reported for crystalline XeF6·NCCH3.

Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3- (A=As, Sb, Bi) Complexes.

Heteronuclear transition-metal-main-group-element carbonyl complexes of AsFe(CO)3- , SbFe(CO)3- , and BiFe(CO)3- were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass-selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)3- . Chemical bonding analyses on the whole series of AFe(CO)3- (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp-p) type of transition-metal-main-group-element multiple bonding. The σ-type three-orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)3- (A=As, Sb, Bi) complexes.

Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3− (A=As, Sb, Bi) Complexes

AbstractHeteronuclear transition‐metal–main‐group‐element carbonyl complexes of AsFe(CO)3−, SbFe(CO)3−, and BiFe(CO)3− were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass‐selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)3−. Chemical bonding analyses on the whole series of AFe(CO)3− (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp–p) type of transition‐metal–main‐group‐element multiple bonding. The σ‐type three‐orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)3− (A=As, Sb, Bi) complexes.

The low-lying doublet electronic excited states of ZrO2−: A symmetry adapted cluster–configuration interaction (SAC-CI) study

The low-lying doublet excited states of ZrO2− were studied using the SAC-CI method. The vertical excitation spectrum of ZrO2− was calculated and compared with that of TiO2−. Similar to that for TiO2−, ZrO2− also have a dipole-bound state. The ground electronic state (X2A1) and the excited states having bound characters (22A1, 12B1, and dipole-bound states) were optimized to C2v structures. The adiabatic electronic affinity of ZrO2 and the adiabatic excitation energies of the three bound excited states were obtained at the SAC-CI level.

The low-lying doublet electronic excited states of TiO2−: A symmetry adapted cluster–configuration interaction (SAC-CI) study

The low-lying doublet excited states of the singly charged TiO2 anion (TiO2−) were investigated by the SAC-CI method. The vertical excitation spectrum of TiO2− was calculated at the SAC-CI/aug-cc-pVTZ levels. The ground electronic state (X2A1) and the lowest two valence excited states (22A1 and 12B1) having bound characters were optimized to stable C2v structures. A dipole-bound state (2A1) was found and optimized to a C2v structure. The adiabatic energies of the 22A1, 12B1, and dipole-bound states were obtained.

SmB6- Cluster Anion: Covalency Involving f Orbitals.

While boride clusters of alkali and transition metals have been observed and extensively characterized, so far little is known about lanthanide-boron clusters. Lanthanide-boride solids are intriguing, however, and therefore it is of interest to understand the fundamental electronic properties of such systems, also on the subnano scale. We report a joint experimental photoelectron spectroscopic and theoretical study of the SmB6- anion, iso-stoichiometric to the SmB6 solid-a topological Kondo insulator. The cluster is found to feature strong static and dynamic electron correlations and relativistic components, calling for treatment with CASPT2 and up sixth-order Douglass-Kroll-Hess (DKH) relativistic correction. The cluster has a C2v structure and covalent Sm-B bonds facilitated by f atomic orbitals on Sm, which are typically thought to be contracted and inert. Additionally, the cluster retains the double antiaromaticity of the B62- cluster.

High-Level ab Initio Predictions for the Ionization Energies, Bond Dissociation Energies, and Heats of Formation of Titanium Oxides and Their Cations (TiOn/TiOn+, n = 1 and 2).

The ionization energies (IEs) of TiO and TiO2 and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (ΔH°f0) and 298 K (ΔH°f298) for TiO/TiO+ and TiO2/TiO2+ are predicted by the wave-function-based CCSDTQ/CBS approach. The CCSDTQ/CBS calculations involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation (HOC), core-valence (CV) electronic, spin-orbit (SO) coupling, and scalar relativistic (SR) effect corrections. The present calculations yield IE(TiO) = 6.815 eV and are in good agreement with the experimental IE value of 6.819 80 ± 0.000 10 eV determined in a two-color laser-pulsed field ionization-photoelectron (PFI-PE) study. The CCSDT and MRCI+Q methods give the best predictions to the harmonic frequencies: ωe (ωe+) = 1013 (1069) and 1027 (1059) cm-1 and the bond lengths re (re+) = 1.625 (1.587) and 1.621 (1.588) Å, for TiO (TiO+) compared with the experimental values. Two nearly degenerate, stable structures are found for TiO2 cation: TiO2+(C2v) structure has two equivalent TiO bonds, while the TiO2+(Cs) structure features a long and a short TiO bond. The IEs for the TiO2+(C2v)←TiO2 and TiO2+(Cs)←TiO2 ionization transitions are calculated to be 9.515 and 9.525 eV, respectively, giving the theoretical adiabatic IE value in good agreement with the experiment IE(TiO2) = 9.573 55 ± 0.000 15 eV obtained in the previous vacuum ultraviolet (VUV)-PFI-PE study of TiO2. The potential energy surface of TiO2+ along the normal vibrational coordinates of asymmetric stretching mode (ω3+) is nearly flat and exhibits a double-well potential with the well of TiO2+ (Cs) situated around the central well of TiO2+(C2v). This makes the theoretical calculation of ω3+ infeasible. For the symmetric stretching (ω1+), the current theoretical predictions overestimate the experimental value of 829.1 ± 2.0 cm-1 by more than 100 cm-1. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ/CBS approach is capable of providing reliable IE and D0 predictions for TiO/TiO+ and TiO2/TiO2+ with error limits less than or equal to 60 meV. The CCSDTQ/CBS calculations give the predictions of D0(Ti+-O) - D0(Ti-O) = 0.004 eV and D0(O-TiO) - D0(O-TiO+) = 2.699 eV, which are also consistent with the respective experimental determination of 0.008 32 ± 0.000 10 and 2.753 75 ± 0.000 18 eV.

Probing the Structures of Neutral B11 and B12 Using High-Resolution Photoelectron Imaging of B11– and B12–

We report high-resolution photoelectron imaging of B11– and B12– at 354.7 and 532.0 nm, respectively, resolving several low-frequency vibrational modes for neutral B11 and B12. The vibrational information is highly valuable to verify the structures of the neutral clusters. Several isomers are considered, and vibrational frequencies are calculated for B11 and B12 using density functional theory. Comparisons between the experimental and calculated vibrational frequencies prove that the B11 neutral and anion both possess a perfectly planar C2v structure. The B12– anion is quasi-planar with Cs symmetry, while the experiment confirms that neutral B12 possesses C3v symmetry. The high-resolution photoelectron spectra also allow the electron affinities of B11 and B12 to be measured more accurately as 3.401 ± 0.002 and 2.221 ± 0.002 eV, respectively. It is shown that high-resolution photoelectron imaging can be an effective method to determine structures of small neutral boron clusters, complementary to infrared s...

Newly assigned microwave transitions and a global analysis of the combined microwave/millimeter wave rotational spectra of 9-fluorenone and benzophenone

Microwave spectra of 9-fluorenone and benzophenone have been observed using a broadband chirped-pulse Fourier Transform Microwave (cp-FTMW) Spectrometer. An analysis of the microwave spectra allowed for the assignment of 178 b-type rotational transitions for 9-fluorenone in the 8.0–13.0GHz region, the assignment of 166 b-type transitions for benzophenone in the 8.0–14.0GHz region, and effectively quadrupled the total number of pure rotational transitions observed for these molecules. This new microwave data and the previously published millimeter wave data of Maris et al. have been analyzed together in a global fit, where the resulting rotational constants accurately reproduce the spectra over the entire 8–80GHz region for both molecules. In addition, the resulting constants have been found to be consistent with the expected planar C2v structure for 9-fluorenone and the paddle-wheel like C2 structure of benzophenone. The rotational constants of the combined global fit have allowed for a more precise determination of the inertial defects (Δ) and second moments of inertia (Pcc) for 9-fluoreneone and benzophenone. Specific focus has been paid to the second moment of benzophenone, which when used in conjunction with theory strongly suggests an ∼32.9° torsional angle out of the ab-plane for the paddle-wheel structure of the gas-phase molecule.

Competition between alkalide characteristics and nonlinear optical properties in OLi3MLi3O (M = Li, Na, and K) complexes

Alkalides possess enhanced nonlinear optical (NLO) responses due to localization of excess electrons on alkali metals. Employing MP2/6-311 + G(d) level, we design novel alkalides by placing alkali atoms (M) between two Li3O superalkalis. We notice a competition between alkalide characteristics and NLO properties in OLi3MLi3O (M = Li, Na, and K) isomers. For instance, the atomic charge on M (qM) in D2h structure is −0.58e for M = Li and its first static mean hyperpolarizablity (βo) is 1 a.u., but in C2v structure, qM = −0.12e and βo= 3.4 × 103 a.u. More interestingly, the βo value for M = K (C2v) increases to 1.9 × 104 a.u. in which qM = 0.24e. These findings may provide new insights into the design of alkalides, an unusual class of salts and consequently, lead to further researches in this direction.