CO Bond Dissociation Energies Research Articles

Measuring the strongest chemical bond with spectroscopic accuracy: CO bond-dissociation energy via predissociation of superexcited states

Measuring the strongest chemical bond with spectroscopic accuracy: CO bond-dissociation energy via predissociation of superexcited states

Guided Ion Beam Studies of the Thorium Monocarbonyl Cation Bond Dissociation Energy and Theoretical Unveiling of Different Isomers of [Th,O,C]+ and Their Rearrangement Mechanism.

Threshold collision-induced dissociation (TCID) of the thorium monocarbonyl cation, ThCO+, with xenon is performed using a guided ion beam tandem mass spectrometer. The only product observed is Th+ resulting from loss of the CO ligand. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of Th+-CO at 0 K as 0.94 ± 0.06 eV. Calculated BDEs at the CCSD(T) level of theory with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation are in good agreement with the experimental result. The Feller-Peterson-Dixon composite coupled-cluster methodology was also applied on both ThCO+ and ThCO, with contributions up to CCSDT(Q) and a four-component treatment of spin-orbit coupling effects. The final 0 K Th+-CO BDE of 0.94 ± 0.04 eV is in excellent agreement with the current experimental result. The ionization energy of ThCO, as well as the atomization energies and heats of formation for both ThCO and ThCO+, is reported at this same level of theory. Complete potential energy profiles of both quartet and doublet spin are also constructed to elucidate the mechanism for the formation and interconversion of different isomers of [Th,O,C]+. Chemical bonding patterns in low-lying states of ThCO+ and potential energy curves for ThCO+ dissociation are also investigated.

Tuning Ion-Pair Interaction in Cuprous-Based Protic Ionic Liquids for Significantly Improved CO Capture

Because of the high bond dissociation energy of CO, achieving efficient absorption of CO in liquid solvents is still a significant challenge in gas separation. Herein, it is unprecedently found tha...

Evaluation of the exothermicity of the chemi-ionization reaction Nd + O → NdO+ + e- and neodymium oxide, carbide, dioxide, and carbonyl cation bond energies.

The exothermicity of the chemi-ionization reaction, Nd + O → NdO+ + e-, has been indirectly determined by measuring the thermochemistry for reactions of the lanthanide metal neodymium cation (Nd+) with O2, CO2, and CO and reactions of NdO+ with CO, O2, and Xe. Guided ion beam tandem mass spectrometry was used to measure the kinetic energy dependent product ion cross sections for these reactions. NdO+ is formed through a barrierless exothermic process when the atomic metal cation reacts with O2 and CO2. All other reactions are observed to be endothermic. Analyses of the kinetic energy dependences of these cross sections yield 0 K bond dissociation energies (BDEs) for several species. The 0 K BDE for Nd+-O is determined to be 7.28 ± 0.10 eV from the average of four independent thresholds. This value is combined with the well-established Nd ionization energy to indicate an exothermicity of the title reaction of 1.76 ± 0.10 eV, which is lower and more precise than literature values. In addition, the Nd+-C, ONd+-O, and Nd+-CO BDEs are determined to be 2.61 ± 0.30, 2.12 ± 0.30, and 0.30 ± 0.21 eV. Additionally, theoretical BDEs of Nd+-O, Nd+-C, ONd+-O, and Nd+-CO are calculated at several levels for comparison with the experimental values. B3LYP calculations seriously underestimate the Nd+-O BDE, whereas MP2 and coupled-cluster with single, double-and perturbative triple excitations values are in reasonable agreement. Good agreement is generally obtained for Nd+-C, ONd+-O, and Nd+-CO BDEs as well.

Activation of CO2 by Gadolinium Cation (Gd+): Energetics and Mechanism from Experiment and Theory

The exothermic and barrierless activation of CO2 by the lanthanide gadolinium cation (Gd+) to form GdO+ and CO is investigated in detail using guided ion beam tandem mass spectrometry (GIBMS) and theory. Kinetic energy dependent product ion cross sections from collision-induced dissociation (CID) experiments of GdCO2 + are measured to determine the energetics of OGd+(CO) and Gd+(OCO) intermediates. Modeling these cross sections yields bond dissociation energies (BDEs) for OGd+–CO and Gd+–OCO of 0.57 ± 0.05 and 0.38 ± 0.05 eV, respectively. The OGd+–CO BDE is similar to that previously measured for Gd+–CO, which can be attributed to the comparable electrostatic interaction with CO in both complexes. The Gd+(OCO) adduct is identified from calculations to correspond to an electronically excited state. The thermochemistry here and the recently measured GdO+ BDE allows for the potential energy surface (PES) of the Gd+ reaction with CO2 to be deduced from experiment in some detail. Theoretical calculations are performed for comparison with the experimental thermochemistry and for insight into the electronic states of the GdCO2 + intermediates, transition states, and the reaction mechanism. Although the reaction between ground state Gd+ (10D) and CO2 (1Σg +) reactants to form ground state GdO+ (8Σ−) and CO (1Σ+) products is formally spin-forbidden, calculations indicate that there are octet and dectet surfaces having a small energy gap in the entrance channel, such that they can readily mix. Thereby, the reaction can efficiently proceed along the lowest energy octet surface to yield ground state products, consistent with the experimental observations of an efficient, barrierless process. At high collision energies, the measured GdO+ cross section from the Gd+ reaction with CO2 exhibits a distinct feature, attributed to formation of electronically excited GdO+ products along a single dectet PES in a diabatic and spin-allowed process. Modeling this high-energy feature gives an excitation energy of 3.25 ± 0.16 eV relative to the GdO+ (8Σ−) ground state, in good agreement with calculated excitation energies for GdO+ (10Π, 10Σ−) electronic states. The reactivity of Gd+ with CO2 is compared with the group 3 transition metal cations and other lanthanide cations and periodic trends are discussed.

Penta- and tetracarbonyls of Ru, Os, and Hs: Electronic structure, bonding, and volatility

Calculations of the electronic structures and properties of M(CO)5 and M(CO)4, where M = Ru, Os, and Hs, have been performed using a variety of relativistic methods such as density functional theory and Dirac-Coulomb correlated ones implemented in program packages such as ADF, DIRAC, and ReSpect. The obtained results show that trends in spectroscopic properties of the M(CO)5 species in group 8 follow the same pattern as that of other compounds of group 4 through group 8 elements. The calculated first M–CO bond dissociation energy (FBDE) of Hs(CO)5 turned out to be significantly weaker than that of Os(CO)5. This was obtained both at the scalar relativistic and spin-orbit levels of theory. The reason for that is the relativistic destabilization and the expansion of the 6d AOs, responsible for weaker σ-forth and π-back donations in the Hs compound. Thus, the FBDEs of M(CO)5 have a Λ-shape behavior in the row Ru–Os–Hs. The non-relativistic FBDEs steadily increase in this row. Using the results of the molecular calculations and a molecule-slab dispersion interaction model, the volatility of the group-8 carbonyls was estimated as adsorption enthalpies, ΔHads, on surfaces of quartz and Teflon used in gas-phase chromatography experiments. It was found that Hs(CO)5 should be almost as volatile as the homologs; however, its interaction strength with these surfaces should be somewhat larger than that of both Ru(CO)5 and Os(CO)5, while the M(CO)4 (M = Ru, Os, and Hs) molecules should be non-volatile. It will, therefore, be difficult to distinguish between group-8 M(CO)5 species by measurements of their volatility as ΔHads on inert surfaces with error bars of ∼4 kJ/mol.

Decomposition studies of group 6 hexacarbonyl complexes. Part 1: Production and decomposition of Mo(CO)6 and W(CO)6

Abstract Chemical studies of superheavy elements require fast and efficient techniques, due to short half-lives and low production rates of the investigated nuclides. Here, we advocate for using a tubular flow reactor for assessing the thermal stability of the Sg carbonyl complex – Sg(CO)6. The experimental setup was tested with Mo and W carbonyl complexes, as their properties are established and supported by theoretical predictions. The suggested approach proved to be effective in discriminating between the thermal stabilities of Mo(CO)6 and W(CO)6. Therefore, an experimental verification of the predicted Sg–CO bond dissociation energy seems to be feasible by applying this technique. By investigating the effect of 104,105Mo beta-decay on the formation of 104,105Tc carbonyl complex, we estimated the lower reaction time limit for the metal carbonyl synthesis in the gas phase to be more than 100 ms. We examined further the influence of the wall material of the recoil chamber, the carrier gas composition, the gas flow rate, and the pressure on the production yield of 104Mo(CO)6, so that the future stability tests with Sg(CO)6 can be optimized accordingly.

DFT Study of the Products, Potential Energy Surface, and Substituent Effects for Methyl Radical Addition to [Rh(PMe3)2(CO)X] (X = Halogen or CN)

Methyl radical addition to [trans-Rh(PMe3)2(CO)Cl] (1) has been studied using density functional theory utilizing ECPs on the heavy elements. At the B3LYP level, Δ H 298 ∘ for the transformation from separate reactants to the five-coordinate 17-e Rh−alkyl product (2) is −8.6 kcal/mol. On the other hand, Δ H 298 ∘ for formation of the four-coordinate 15-e Rh−acyl radical (3) resulting from methyl addition to the carbonyl of 1 is −11.5 kcal/mol. The latter result implies that coordination of CO in 1 reduces the exothermicity of its reaction with CH3 by 5.2 kcal/mol. A 3D potential energy surface of the given reaction reveals that the lowest energy path from separate reactants to 2 does not have any electronic barrier. Similarly, there is no distinct transition state for direct methyl attack on the carbonyl of 1. Instead, the lowest energy trajectory connecting the separate reactants to the acyl product passes through a CO insertion transition state (TS2,3) corresponding to methyl migration between the rhodium and carbon atoms of the Rh−CO bond, with Δ H 298 ∘ of TS2,3 being only 3.1 kcal/mol above the separate reactants. To explore the extent to which the methyl affinity of the coordinated carbonyl in the given system may change when the substituents on the metal are varied, additional calculations have been carried out on the F, Br, I, and CN analogues of 1. Attempts have been made to account for the calculated methyl affinity trends using the ionization and Rh−CO bond dissociation energies of the square-planar reactants.

Photodissociation of CO2− in water clusters via Renner-Teller and conical interactions

The photochemistry of mass selected CO(2) (-)(H2O)(m), m=2-40 cluster anions is investigated using 266 nm photofragment spectroscopy and theoretical calculations. Similar to the previous 355 nm experiment [Habteyes et al., Chem. Phys. Lett. 424, 268 (2006)], the fragmentation at 266 nm yields two types of anionic products: O(-)(H2O)(m-k) (core-dissociation products) and CO(2) (-)(H2O)(m-k) (solvent-evaporation products). Despite the same product types, different electronic transitions and dissociation mechanisms are implicated at 355 and 266 nm. The 355 nm dissociation is initiated by excitation to the first excited electronic state of the CO(2) (-) cluster core, the 1 (2)B(1)(2A") state, and proceeds via a glancing Renner-Teller intersection with the ground electronic state at a linear geometry. The 266 nm dissociation involves the second excited electronic state of CO(2) (-), the 2 (2)A(1)(2A') state, which exhibits a conical intersection with the 3 (2)B(2)(A') state at a bent geometry. The asymptotic O(-) based products are believed to be formed via this 3 (2)B(2)(A') state. By analyzing the fragmentation results, the bond dissociation energy of CO(2) (-) to O(-)+CO in hydrated clusters (m> or =20) is estimated as 2.49 eV, compared to 3.46 eV for bare CO(2) (-). The enthalpy of evaporation of one water molecule from asymptotically large CO(2) (-)(H(2)O)(m) clusters is determined to be 0.466+/-0.001 eV (45.0+/-0.1 kJ/mol). This result compares very favorably with the heat of evaporation of bulk water, 0.456 eV (43.98 kJ/mol).

Velocity map ion imaging of H atoms from the dissociation of HCO ( [formula omitted]) using Doppler-free multi-photon ionization

Velocity map ion imaging using Doppler-free 2+1 multi-photon ionization at λ = 243.1 nm has been applied to monitor the nascent H atoms from the predissociation of HCO ( A ∼ 2 A ″ ) in the (0, 0, 10 1) vibrational state. Employing two balanced, counterpropagating circularly (σ + and σ −) polarized probe beams, complete velocity map images were accumulated with every laser shot without having to scan the probe wavelength over the strongly Doppler-broadened line profile. The H–CO bond dissociation energy, CO internal energy distribution, and anisotropy parameter are presented and compared with literature data.

Density functional investigation on copper carbonyl complexes

The structure and bonding of copper carbonyl complexes, [Cu(CO) n] 0/+/−, have been investigated at density functional levels of theory. It was found that the bond parameters and CO bond dissociation energy are very sensitive to the size of the employed basis set. The best agreement between theory and the available experimental data has been achieved at the B3LYP level with the cc-pVTZ/TZV2P basis set.

On the binding of carbonyl to a single palladium atom

All-electron CCSD(T), QCISD(T) and MP4(SDQ) calculations including relativistic effects via the use of the IORAmm Hamiltonian have been performed for PdCO. The optimized molecular geometry is in nice agreement with the recently obtained experimental data. The Pd–CO bond dissociation energy is estimated to be 38.8 kcal/mol. The vibrational spectrum of PdCO is calculated and a reassessment of the experimental datum for the frequency of bending mode is suggested.

Optimized structures and energetics of mixed-metal binuclear carbonyl ions MCr(CO)n+ (M=Ti–Fe, n=4–6) by density functional method

Optimized structures and energetics of coordinatively unsaturated mixed-metal binuclear carbonyl ions MCr(CO)n+ (M=Ti, V, Cr, Mn and Fe; n=4–6), previously obtained by the laser ablation-molecular beam (LAMB) experiment, have been studied by the density functional method with the gradient correction at the Becke–Perdew level. The positive charge lowers the metal d orbitals in energy, weakens their interaction with the carbonyl 2π∗ orbitals, and strengthens that with the carbonyl 5σ orbitals in comparison with the neutral carbonyls. The predominance of the σ-donation over the π∗-back donation increases from M=Ti to Fe in this order and with the increase of n for each M. These are reflected in the M–C and the C–O bond lengths. M-dependent variation in the M–Cr bond distance, significant in diatomic ions MCr+, is largely lost in MCr(CO)5+ and MCr(CO)6+. Anticorrelation is found between the C–O bond lengths on the M side and those on the Cr side. The relative stability inferred from the relative abundance of the ions in the LAMB experiments is qualitatively explained by comparing the M+–Cr binding energy with the successive CO bond dissociation energies of MCr(CO)6+.

Trends in Molecular Geometries and Bond Strengths of the Homoleptic d10 Metal Carbonyl Cations [M(CO)n]x+ (Mx+=Cu+, Ag+, Au+, Zn2+, Cd2+, Hg2+;n=1-6): A Theoretical Study

Surprising trendsin the M–CO bond dissociation energies (see illustration; n = number of carbonyl ligands) are revealed by quantum chemical calculations for the title molecules. Analysis of the bonding interactions reveals an interplay of coulombic and covalent interactions between the metal cations and CO. Theoretical predictions are made for strongly bound carbonyl complexes which have not yet been synthesized.

Density functional study of the Fe–CO bond dissociation energies of Fe(CO)5

Fe(CO) n (n=1–5) complexes have been studied using density functional theory (DFT) methods. Several functionals have been used in the geometry optimizations, harmonic frequencies computation and calculation of the iron–carbonyl bond dissociation energies. Coupled-cluster single double (triple) bond dissociation energies have also been computed for the smaller systems. The obtained results show that DFT methods yield reasonable geometries and vibrational frequencies. Regarding the bond dissociation energies, it is shown that the validity of the results depends on whether there is a change in the atomic state of the metal during the dissociation. When the atomic state is the same for both complexes, the bond dissociation energy computed using gradient corrected functionals is within the range of the experimental values, while when the atomic state changes, DFT methods overestimate the bond dissociation energy due to a poor description of the atomic multiplets.

The First Carbonyl Bond Dissociation Energies of M(CO)5and M(CO)4(C2H2) (M = Fe, Ru, and Os): The Role of the Acetylene Ligand from a Density Functional Perspective

Recent kinetics experiments have shown that the rate of carbonyl substitution in complexes of the type M(CO)4(C2R2), where M = Fe, Ru, and Os, is accelerated by factors of 102−1013 over their respective pentacarbonyl complexes. These substitution reactions have been shown to be dissociative in nature and show a marked metal dependence of the rate. The origin of the increased reactivity of these alkyne complexes was studied with nonlocal density functional theory (BLYP functional), using both effective core potential (ECP) and all-electron basis sets, in conjunction with Frenking's charge decomposition analysis (CDA) scheme and Bader's atoms in molecules (AIM) analysis. We found that the BLYP/ECP method predicted geometries very close to experiment for both the parent carbonyl and alkyne complexes (in this study C2H2 was used). The calculated CO bond dissociation energies (BDEs) were also found to agree well with experiment and mirrored the metal dependence trends observed experimentally for both M(CO)5 an...

Density Functional Theory Calculations on 19-Electron Organometallic Complexes: The Mn(CO)5Cl- Anion. The Difference between Unpaired Electron Density and Spin Density Due to Spin Polarization

The anisotropic hyperfine coupling (hfc) constants for the 19-electron Mn(CO)5Cl- complex, 1, and for the 17-electron Mn(CO)4Cl- complex, 2, were calculated using density functional theory (DFT). The calculated hfc values for 1 are in good agreement with the experimental ones reported in two EPR studies, which were not able to distinguish between 1 and 2. The Mn−CO(axial) bond dissociation energy in 1 was calculated to be 19 kcal/mol, which shows that 1 is stable to loss of axial CO. These data indicate that the species observed in the EPR experiments was the 19-electron complex, 1. The unpaired electron population of the manganese dz2 orbital indicated by the SOMO of the DFT wave function (ca. 0.2−0.3) is significantly less than that obtained from the two EPR analyses (0.49, 0.63), which neglected spin polarization. The calculations show that spin polarization in 1 causes the spin density (as measured by EPR) to differ significantly from the unpaired electron density (SOMO). It is concluded that neglect ...

Alkali ion carbonyls: sequential bond energies of Li +(CO) x ( x = 1−3), Na +(CO) x ( x = 1, 2) and K +(CO)

The sequential bond dissociation energies for Li +(CO) x ( x = 1−3), Na +(CO) x ( x = 1,2), and K +(CO) are determined by examining the collision-induced dissociation reactions with argon in a guided ion beam mass spectrometer. Analysis of the kinetic energy dependent cross sections yield values for the (CO) x−1 M +CO bond dissociation energies (BDEs) of 0.57 ± 0.13, 0.37 ± 0.04 and 0.36 ± 0.04 eV for M  Li ( x = 1–3, respectively), 0.33 ± 0.08 and 0.25 ± 0.03 eV for M  Na ( x = 1 and 2, respectively), and 0.19 ± 0.05 eV for K +CO. In addition, the M +Ar BDEs are determined by examining the ligand exchange reaction of M +(CO) with Ar and are found to be 0.34 ± 0.14, 0.16 ± 0.09 and 0.14 ± 0.07 eV for M  Li, Na and K, respectively. The trends in BDEs can be explained readily in terms of electrostatic bonding interactions. A comparison of the alkali metal ion—CO BDEs with those of transition metal ion carbonyls reveals the contributions of s-dσ hybridization and d-π ∗ back-donation in the chemical bonding of the latter systems.

Photodissociation of triplet and singlet states of the CCO radical

The triplet and singlet states of the ketenylidene (CCO) radical are investigated using fast radical beam photofragment translational spectroscopy, in which CCO is generated by laser photodetachment of CCO− and subsequently photodissociated, and anion photoelectron spectroscopy. In the photodissociation experiment, two bands in which the upper state of CCO predissociates are studied. Photodissociation from excitation of the à 3Π–X̃ 3Σ− band in CCO is observed from 16 666–23 529 cm−1; resonances are observed and assigned to excited vibrational levels involving all three vibrational modes. We also report the first observation of the c̃ 1Π–ã 1Δ band in CCO. Here, the ã 1Δ state of CCO is generated by laser photodetachment at higher photon energy than was used to generate the X̃ 3Σ state. The c̃ 1Π state is approximately located by photoelectron spectroscopy of CCO−, and the photodissociation experiment shows that the origin of the c̃ 1Π–ã 1Δ band occurs around 17 170 cm−1. Kinetic-energy release spectra from both bands yield accurate values for the C–CO bond dissociation energy and heat of formation of CCO: D0(C–CO)=2.24±0.02 eV (51.7±0.5 kcal/mol) and ΔHf,2980(CCO)=4.04±0.02 eV (91.1±0.5 kcal/mol). Although the translational-energy distributions resulting from excitation to the à 3Π and c̃ 1Π states are clearly nonstatistical, consideration of the potential-energy surfaces indicates that dissociation from both states occurs via radiationless transitions to the X̃ 3Σ− state.

Structure and Bonding of the Isoelectronic Hexacarbonyls [Hf(CO)6]2-, [Ta(CO)6]-, W(CO)6, [Re(CO)6]+, [Os(CO)6]2+, and [Ir(CO)6]3+: A Theoretical Study1

Equilibrium geometries, vibrational frequencies, and metal−CO bond dissociation energies of the title compounds have been calculated using quantum-chemical methods at the DFT (B3LYP and BP86) and CCSD(T)//MP2 levels of theory, utilizing relativistic effective core potentials for the metals. The nature of the metal−CO interactions has been analyzed using the CDA method. The theoretically predicted geometries and vibrational spectra at B3LYP, BP86, and MP2 are in good agreement with experimental data. The calculated C−O bond lengths show a regular decrease and the C−O stretching frequencies increase from [Hf(CO)6]2- to [Ir(CO)6]3+. The calculated first dissociation energies (FDE) of one CO show the trend [Ir(CO)6]3+ > [Os(CO)6]2+ > [Hf(CO)6]2- > [Re(CO)6]+ > W(CO)6 ≈ [Ta(CO)6]-, which does not correlate with the C−O bond length. A remarkable result of the calculations is that the highest FDE is predicted for [Ir(CO)6]3+, which has very little IR→CO π-back-donation. The high FDEs of [Ir(CO)6]3+ and [Os(CO)6]...