Formic Acid Complex Research Articles

Formic acid stability in different solvents by DFT calculations.

New technologies have been developed toward the use of green energies. The production of formic acid (FA) from carbon dioxide (CO[Formula: see text]) hydrogenation with H[Formula: see text] is a sustainable process for H[Formula: see text] storage. However, the FA adduct stabilization is thermodynamically dependent on the type of solvent and thermodynamic conditions. The results suggest a wide range of dielectric permittivity values between the dimethyl sulfoxide (DMSO) and water solvents to stabilize the FA in the absence of base. The thermodynamics analysis and the infrared and charge density difference results show that the formation of the FA complex with H[Formula: see text]O is temperature dependent and has a major influence on aqueous solvents compared to the FA adduct with amine, in good agreement with the experiment. In these conditions, the stability thermodynamic of the FA molecule may be favorable at non-organic solvents and dielectric permittivity values closer to water. Therefore, a mixture of aqueous solvents with possible ionic composition could be used to increase the thermodynamic stability of H[Formula: see text] storage in CO[Formula: see text] conversion processes. Using the Quantum ESPRESSO package, density functional theory (DFT) calculations were performed with periodic boundary conditions, and the electronic wave functions were expanded in plane waves. For the exchange-correlation functional, we use the vdW-DF functional with the inclusion of van der Waals (vdW) forces. Electron-ion interactions are treated by the projector augmented wave (PAW) method with pseudopotentials available in the PSlibrary repository. The wave functions and the electronic densities were expanded employing accurate cut-off energies of 6.80[Formula: see text]10[Formula: see text] and 5.44[Formula: see text]10[Formula: see text] eV, respectively. The electronic density was computed from the wave functions calculated at the [Formula: see text]-point in the first Brillouin-zone. Each structural optimization was minimized according to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, with force and energy convergence criteria of 25 meV[Formula: see text]Å[Formula: see text] and 1.36 meV, respectively. The electrostatic solvation effects were performed by the [Formula: see text] package with the Self-Consistent Continuum Solvation (SCCS) approach.

Ammonia – Formic acid complex: internal rotation analysis, calculations, and new microwave measurements

New analysis and spectra are reported for the gas-phase ammonia-formic acid complex. Calculations to determine the theoretical barrier to internal rotation were conducted and led to the new internal rotation analysis of the dimer. Using the new analysis and calculations, 12 new lines were measured and assigned and included in the present analysis. This is the first internal rotation analysis for this complex. The measurements were made in the 7–22 GHz range using two Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometers. The complex was analyzed as a hindered rotor and 20 A and 16 E state transitions were fit with the XIAM5 program. The rotational constants were determined to have the following values: A = 11970.19(9) MHz, B = 4331.479(4) MHz, and C = 3227.144(4) MHz. Rotational constants, quadrupole coupling constants, and internal rotor parameters were fit to the spectrum. Double resonance was used to verify line assignments and access higher frequencies. The barrier to internal rotation was found to be 195.18(7) cm−1. High level calculations are in good agreement with experimental values. The calculated V3 barrier values range from 168.3 to 212.8 cm−1.

Microwave spectrum and structure of a glyoxylic acid – formic acid complex☆

The microwave spectrum of a second doubly hydrogen-bonded glyoxylic acid - formic acid hydrogen-bonded complex was measured in the 6–12 GHz frequency range using two Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometers. The rotational constants were determined to have the following values: A = 4113.081(4), B = 1026.9957(5), and C = 822.9584(6) MHz. The doubly hydrogen bonded structures and rotational constants were calculated for the lowest energy dimers of glyoxylic acid - formic acid using DFT and MP2 calculations with various basis sets. M11/ def2QZVPP calculations for the third lowest energy dimer yielded rotational constants of A = 4248.7, C = 1031.4, and C = 829.9 MHz, in good agreement with experimental values.

Noncovalent Interactions between Aromatic Heterocycles and Carboxylic Acids: Rotational Spectroscopy of the Furan-Formic Acid and Thiophene-Formic Acid Complexes.

The binary molecular complexes formed between the aromatic heterocycles furan and thiophene with formic acid were investigated using pulsed-jet Fourier transform microwave spectroscopy and quantum chemical computations. For both of the complexes, rotational spectra of the lowest energy isomer were detected and assigned. Rotational spectroscopic results and density functional theory calculations support that the preferred conformation of the furan-formic acid complex is characterized by a relatively strong O-H···O and a weak C-H···O hydrogen bonds while the O-H···π and C-H···O hydrogen bonds stabilize the thiophene-formic acid complex. Natural bond orbital analysis further proves the experimental observation, suggesting that the strength of the O-H···O(furan) interaction is about two times stronger than that of O-H···π(thiophene). The symmetry adapted perturbation theory analysis reveals that electrostatic interaction is dominant in stabilizing the two complexes and that dispersion becomes significant in the thiophene-formic acid complex compared to furan-formic acid.

(Invited) Gas-Phase Directional Etching of Copper Via Surface Oxidation and Chemical Complexation

Plasma-thermal atomic layer etching (ALE) is a promising technique for enabling nanometer-level metal patterning. Utilizing the anisotropic nature of low energy ions, a modified layer is defined directionally in the plasma exposure step. The isotropic etchant molecules only react with the modified region, leaving a final feature with ideal directionality and selectivity. Applying this process to pattern Cu, a controllable nanometer per cycle etch rate was achieved, with a selective and anisotropic etch profile. To delineate the reaction mechanisms, density functional theory was used to evaluate the feasibility of formation of gas-phase Cu(II) and Cu(I) complexes with formate, water, formic acid, and combinations thereof as ligands. These complexes result from the neutralization reaction between copper oxide (CuO and Cu2O) and formic acid, with and without water. We identified and evaluated the formation free energies of formato, formic acid, aquahydroxo, and aquaformato complexes of Cu(II) and Cu(I). Under relevant experimental pressures, we find the water-free dimeric tetra(m-formato)dicopper(II) “paddlewheel” complex (Cu2(HCOO)4) to be the most favorable etching product, with its formation reaching equilibrium with CuO. The most likely precursor for the dimer is the diformatodi(formic acid)copper(II) monomer, which favorably dimerizes under the same water-lean condition at which the dimer persists. Stabilization of gas-phase Cu (oxide) derivatives thus can be achieved through complexation, enabling gas-phase etching of Cu. This work provides complementary experimental and theoretical studies that illuminate the nature of highly controlled etching with formic acid of nanoscopic CuO(s) layers covering Cu nanoarchitectures, which is relevant for the fabrication of next-generation integrated circuits.

Activation of CO2 by Alkaline-Earth Metal Hydrides: Matrix Infrared Spectra and DFT Calculations of HM(O2CH) and (MH2)(HCOOH) Complexes (M = Sr, Ba).

Reactions of MH2 (M = Sr, Ba) with CO2 were explored in pure parahydrogen at 3.5 K using matrix isolation infrared spectroscopy and quantum chemical calculations. The formate complex HM(η2-O2CH) and formic acid complex (MH2)(HCOOH) were trapped and identified by isotopic substitutions and density functional theory (DFT) frequency calculations. Natural population analysis and the CO2 reduction mechanism demonstrate that hydride ion transfer from a metal hydride to a CO2 moiety facilitates the stabilization of such complexes.

(Invited) Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

We present a cyclic process for selective and anisotropic atomic layer etching of copper: an oxygen plasma modulates the depth and directionality of the oxidized layer while formic acid vapor selectively removes the copper oxide scale from the metallic copper. Via density functional theory, with finite temperature and pressure free energy corrections, we evaluate the feasibility of formation of gas-phase Cu(II) and Cu(I) complexes with formate, water, formic acid, and combinations thereof as ligands. These complexes result from the neutralization reaction between copper oxide (CuO and Cu2O) and formic acid, with and without water. We identified and evaluated the formation free energies of formato, formic acid, aquahydroxo, and aquaformato complexes of Cu(II) and Cu(I). Under relevant experimental pressures, we find the water-free dimeric tetra(μ-formato)dicopper(II) “paddlewheel” complex (Cu2(HCOO)4) to be the most favorable etching product, with its formation reaching equilibrium conditions from CuO. The most likely precursor for the dimer is the diformatodi(formic acid)copper(II) monomer, which favorably dimerizes under the same water-lean condition at which the dimer persists. Stabilization of gas-phase Cu (oxide) derivatives thus can be achieved through complexation, enabling gas-phase etching of Cu. This work provides complementary experimental and theoretical studies that illuminate the nature of highly controlled etching with formic acid of nanoscopic CuO(s) layers covering Cu nanoarchitectures, which is relevant for the fabrication of next-generation integrated circuits.

The effect of ammonia and formic acid on the oxidation of CO via a simple Criegee intermediate.

In the present work, we have investigated the effect of catalysts (ammonia, formic acid, ammonia dimer, and ammonia water complex) on the oxidation of CO via a simple Criegee intermediate by means of kinetics and quantum chemical calculations. Our finding suggests that, in the presence of ammonia and ammonia dimer the title reaction becomes a barrierless reaction with respect to the isolated reactants (energy barrier = ∼-0.53 and ∼-0.27 kcal mol-1, respectively), whereas in the presence of formic acid and ammonia-water complex the energy barrier of the CI + CO reaction becomes ∼2.84 and ∼0.82 kcal mol-1, respectively. However, among all the catalysts, due to the very low concentration of the ammonia dimer, its contribution towards the title reaction is insignificant as compared to that of the other catalysts. In addition, the relative rate of the other catalyzed channels against the uncatalyzed reaction suggests that the rate of the catalyzed CI + CO reaction is ∼8-10 orders of magnitude lower than the uncatalyzed reaction. However, the concentration of bimolecular complexes formed in the presence of catalysts (except the ammonia dimer) is ∼1-8 orders of magnitude higher than the concentration of bimolecular complexes formed in the uncatalyzed reaction.

Direct matrix isolation IR spectroscopic evidence of halogen bonding from a comparative study of complexes of CBr4 and CCl4with acetone and formic acid

Binary complexes of acetone and formic acid with tetrahalomethanes CBr4 and CCl4 have been isolated in argon matrix. Spectral shifts in the characteristic νC=O region of acetone, as well as in the fingerprint regions, are unambiguously assigned to the formation of halogen bond involving one of the halogen atoms on CBr4/CCl4 as donor, and the carbonyl oxygen of acetone as acceptor. The higher magnitude of shifts of νC=O and the fingerprint vibrations for the CBr4 complex, as compared to the CCl4 complex, is consistent with theoretical predictions of higher value of positive electrostatic potential in the “σ-hole” region of the former, and hence its higher susceptibility to halogen bonding. The formation of halogen bonded complexes involving formic acid as acceptor and CBr4/CCl4 as donors is also being reported for the first time. In this case too, distinct shifts are obtained in the νC=O as well as νC-O regions of formic acid, which again are significantly larger in magnitude for the CBr4 complex, as compared to the CCl4 complex. Electronic structure calculations have been carried out using different theoretical methods to identify the various possible structural isomers of the halogen bonded complexes, and to obtain relevant information regarding their energies and intermolecular geometrical parameters. In addition, NBO and AIM analysis have been carried out to understand the role of local interactions at the halogen bonded interface. Such predicted data are found to be consistent with experimental observations, and re-assert the stronger nature of CBr4 as halogen bond donor, as compared to CCl4.

Sustainable conversion of carbon dioxide to formic acid with Rh-decorated phosphorous-doped fullerenes: a theoretical study

We performed density functional calculations to study conversion of carbon dioxide to formic acid through designed catalyst of Rh-decorated phosphorous-doped fullerenes. Two paths of reaction are considered for this conversion. In the first pathway, CO2 is transferred to formate intermediate using the catalyst, and then, through a sequence of oxidative addition and reductive elimination reactions, formic acid is released; density functional theory results showed that in this path the oxidative addition is an easy and quite exothermic process. It is also shown that the rate-determining step in the hydrogenation of CO2 catalyzed by Rh-decorated phosphorous-doped fullerene complexes is the release of formic acid from formate intermediate. In the other pathway after the formation of rhodium formate intermediate and then addition of H2, the formic acid complex is released directly through metathesis process; our results showed a moderate energy barrier for the metathesis process, in which the oxidation state of the Rh center does not change. This barrier is found to be much smaller than the barrier of the reductive process in the first pathway.

Remarkable shifts of Csp2 -H and O-H stretching frequencies and stability of complexes of formic acid with formaldehydes and thioformaldehydes.

Thirty-six stable complexes of formic acid with formaldehydes and thioformaldehydes were determined on the potential energy surface, in which the XCHO···HCOOH complexes are found to be more stable than the XCHS···HCOOH counterparts, with X = H, F, Cl, Br, CH3 , NH2 . All complexes are stabilized by hydrogen bonds, and their contribution to the total stabilization energy of the complexes increases in going from C-H···S to C-H···O to O-H···S and finally to O-H···O. Remarkably, a significant blueshift of Csp2 -H bond by 81-96 cm-1 in the Csp2 -H···O hydrogen bond has hardly ever been reported, and a considerable redshift of O-H stretching frequency by 206-544 cm-1 in the O-H···O/S hydrogen bonds is also predicted. The obtained results in our present work and previous literatures support that a distance contraction and a stretching frequency blueshift of C-H bond involving hydrogen bond depend mainly on its polarity and gas phase basicity of proton acceptor, besides the rearrangement of electron density due to complex formation. Markedly, we suggest the ratio of deprotonation enthalpy to proton affinity (R c ) as an indicator to prospect for classification of hydrogen bonds. The symmetry adapted perturbation theory results show a larger role of attractive electrostatic term in XO-n as compared to that in XS-n and the electrostatic interaction is overwhelming dispersion or induction counterparts in stabilizing XO-n and XS-n, with n = 1, 2, 3. © 2019 Wiley Periodicals, Inc.

Multiple Hydrogen Bond Tethers for Grazing Formic Acid in Its Complexes with Phenylacetylene.

Complexes of phenylacetylene (PhAc) and formic acid (FA) present an interesting picture, where the two submolecules are tethered, sometimes multiply, by hydrogen bonds. The multiple tentacles adopted by PhAc-FA complexes stem from the fact that both submolecules can, in the same complex, serve as proton acceptors and/or proton donors. The acetylenic and phenyl π systems of PhAc can serve as proton acceptors, while the ≡C-H or -C-H of the phenyl ring can act as a proton donor. Likewise, FA also is amphiprotic. Hence, more than 10 hydrogen-bonded structures, involving O-H···π, C-H···π, and C-H···O contacts, were indicated by our computations, some with multiple tentacles. Interestingly, despite the multiple contacts in the complexes, the barrier between some of the structures is small, and hence, FA grazes around PhAc, even while being tethered to it, with hydrogen bonds. We used matrix isolation infrared spectroscopy to experimentally study the PhAc-FA complexes, with which we located global and a few local minima, involving primarily an O-H···π interaction. Experiments were corroborated by ab initio computations, which were performed using MP2 and M06-2X methods, with 6-311++G (d,p) and aug-cc-pVDZ basis sets. Single-point energy calculations were also done at MP2/CBS and CCSD(T)/CBS levels. The nature, strength, and origin of these noncovalent interactions were studied using AIM, NBO, and LMO-EDA analysis.

A spectroscopic and ab initio study of the hydrogen peroxide-formic acid complex: hindering the internal motion of H2O2.

The microwave spectrum of the hydrogen-bonded hydrogen peroxide-formic acid complex was measured in the range from 4 to 17 GHz. Assignment of transitions and analyses of the spectrum were supported by ab initio wavefunction and density functional calculations. The detected conformer features a seven-membered hydrogen-bonded ring, in which the H-atom of one hydroxyl group of H2O2 and the O-atom of the other OH group are a hydrogen bond donor and acceptor, respectively, to the carboxyl group of formic acid. The rotational transitions show a tunnelling splitting, which is attributed to a wagging-like motion of the free H-atom of H2O2 from above to below the heavy atom plane of formic acid. Transitions between tunneling states are driven by the change in dipole moment accompanying this motion and were measured and analyzed. Ab initio analyses of the tunneling path reveal an asymmetric potential, which reflects the (transiently) chiral nature of the complex.

Rotational spectroscopic and theoretical study of the perfluorobutyric acid⋯formic acid complex

Perfluorinated carboxylic acids are a special class of compounds with considerable industrial applications. In this study, we applied chirped pulse and cavity-based Fourier transform microwave spectroscopy to investigate the structural and possible tunneling properties of the perfluorobutyric acid⋯formic acid complex, together with high level ab initio calculations. Only one clearly dominant conformer, featuring an eight-membered double hydrogen-bonded ring, was predicted for the hetero acid dimer and detected experimentally. The rotational constants calculated at the B3LYP-D3BJ/6-311++G(2d,p) level are in excellent agreement with the experimental ones, better than those from MP2 calculations. No tunneling splittings were detected in the experimental spectra. Detailed analyses of the non-covalent intermolecular interactions in the hetero acid dimer provide an explanation for the absence of double proton transfer, and also identify the presence of F⋯F attractive interactions.

The Trimethylamine-Formic Acid Complex: Microwave Characterization of a Prototype for Potential Precursors to Atmospheric Aerosol.

The reactions of amines and carboxylic acids have recently received attention for their possible role in the formation of atmospheric aerosol. Here, we report a microwave study of the trimethylamine-formic acid hydrogen-bonded complex, a simple prototype in which to study amine-carboxylic acid interactions. Spectra of three isotopologues of the system have been observed using a tandem cavity and chirped-pulse Fourier transform microwave spectrometer. The complex has a plane of symmetry, with the acidic proton of the formic acid directed toward the lone pair of the nitrogen. The zero-point-averaged hydrogen bond length is 1.702 Å, and the O-H···N angle is 177°. (14)N nuclear quadrupole hyperfine structure has been used to assess the degree of proton transfer from the formic acid to the trimethylamine. Experimental results are supplemented with density functional theory calculations. M06-2X/6-311++G(3df,3pd) calculations indicate a binding energy of 16.8 kcal/mol with counterpoise correction (17.4 kcal/mol without counterpoise correction).

IR spectroscopic and calorimetric study of water and formic acid adsorption on a vanadium-titanium catalyst

Formaldehyde is oxidized to formic acid at a high selectivity over vanadium -titanium catalysts. IR spectroscopic and calorimetric techniques were used for studying the structure and energy parameters of the surface formic acid and water complexes on the of 11 wt % V2O5/89 wt % TiO2 catalyst. A decrease in the adsorption-desorption heat of formic acid from 100 down to 50 kJ/mol was observed at an increase in the surface coverage. The adsorption heat of formic acid in the form of bidentate formates is 70 kJ/mol under the conditions of the steady-state oxidation of formaldehyde that indicates, according to the earlier DFT calculations, a weak bonding of formate to the active site (V5+) to provide desorption of the intact acid from the vanadium-titanium catalyst surface. The weakly bonded formates are involved in the formation of formic acid during the catalytic oxidation of formaldehyde and provide the high selectivity of the reaction. The close adsorption heats of water (74 kJ/mol) and of formic acid indicate their possible competitive adsorption and may account for the favorable effect of water on the selectivity of formaldehyde oxidation to formic acid.

Tunneling isomerization of small carboxylic acids and their complexes in solid matrixes: a computational insight.

We have studied hydrogen-atom tunneling in the cis-to-trans conformational change of some carboxylic acid monomers and formic acid (FA) complexes and dimers at the MP2(full) and CCSD(T) levels of theory within the Wentzel-Kramers-Brillouin approximation. The barrier for the minimum energy path, where the OH bond length and the COH bending angle are optimized, is found to be a good approximation for providing the highest barrier transparency. The matrix effect on the transmission coefficients of cis-FA monomer, trans-cis FA dimer (tc1), and cis-acetic acid monomer are modeled by the polarizable continuum model (PCM) at the MP2(full) level of theory in different environments. For the cis-FA monomer and trans-cis FA dimer (tc1), the calculated transmission coefficients agree with the experimental lifetimes observed in noble-gas solids. However, this method cannot reproduce the experimental results obtained for cis-acetic acid. Moreover, the long lifetime of cis-FA and cis-acetic acid in the N2 environment cannot be reproduced either, which is most probably due to specific interactions that are not included in the PCM. The calculation for cis-HCOOD shows a strong decrease of the barrier transparency compared to that for cis-HCOOH, which is consistent with the experiments. In general, good agreement is observed between the calculated barrier transparency (including PCM) and experimental tunneling rate. However, some exceptions are found, which shows that additional factors influence the tunneling rate.

Behavior of carboxylic acids upon complexation with beryllium compounds.

A significant acidity enhancement and changes on aromaticity were previously observed in squaric acid and its derivatives when beryllium bonds are present in those systems. In order to know if these changes on the chemical properties could be considered a general behavior of carboxylic acids upon complexation with beryllium compounds, complexes between a set of representative carboxylic acids RCOOH (formic acid, acetic acid, propanoic acid, benzoic acid, and oxalic acid) and beryllium compounds BeX2 (X = H, F, Cl) were studied by means of density functional theory calculations. Complexes that contain a dihydrogen bond or a OH···X interaction are the most stable in comparison with other possible BeX2 complexation patterns in which no other weak interactions are involved apart from the beryllium bond. Formic, acetic, propanoic, benzoic, and oxalic acid complexes with BeX2 are much stronger acids than their related free forms. The analysis of the topology of the electron density helps to clarify the reasons behind this acidity enhancement. Importantly, when the halogen atom is replaced by hydrogen in the beryllium compound, the dihydrogen bond complex spontaneously generates a new neutral complex [RCOO:BeH] in which a hydrogen molecule is lost. This seems to be a trend for carboxylic acids on complexing BeX2 compounds.

Conformers of dimers of carboxylic acids in the gas phase: A rotational study of difluoroacetic acid–formic acid

The rotational spectra of two conformers of the difluoroacetic acid–formic acid complex have been identified by pulsed jet Fourier transform microwave spectroscopy. They differ from each other depending on the trans or gauche arrangement of the terminal CHF2 group. The gauche form displays a doubling of the rotational transitions, from which the internal rotation barrier hindering the two equivalent gauche forms has been estimated to be 101.8(3)cm−1. The increase of the distance between the two monomers upon OH→OD deuteration (Ubbelohde effect) has been determined.

Microwave Structure for the Propiolic Acid–Formic Acid Complex

New microwave spectra were measured to obtain rotational constants and centrifugal distortion constants for the DCCCOOH···HOOCH and HCCCOOD···DOOCH isotopologues. Rotational transitions were measured in the frequency range of 4.9-15.4 GHz, providing accurate rotational constants, which, combined with previous rotational constants, allowed an improved structural fit for the propiolic acid-formic acid complex. The new structural fit yields reasonably accurate orientations for both the propiolic and formic acid monomers in the complex and more accurate structural parameters describing the hydrogen bonding. The structure is planar, with a positive inertial defect of Δ = 1.33 amu Å(2). The experimental structure exhibits a greater asymmetry for the two hydrogen bond lengths than was obtained from the ab initio mp2 calculations. The best-fit hydrogen bond lengths have an r(O1-H1···O4) of 1.64 Å and an r(O3-H2···O2) of 1.87 Å. The average of the two hydrogen bond lengths is r(av)(exp) = 1.76 Å, in good agreement with r(av)(theory) = 1.72 Å. The center of mass separation of the monomers is R(CM) = 3.864 Å. Other structural parameters from the least-squares fit using the experimental rotational constants are compared with theoretical values. The spectra were obtained using two different pulsed beam Fourier transform microwave spectrometers.