Matrix Isolation FTIR Studies Research Articles

Matrix-isolation FT-IR and DFT theoretical studies of the intramolecular hydrogen bonding in Mannich bases

FT-IR Ar-matrix isolated spectra were studied for dichloro- (Cl 2-MB) and tetrachloroderivatives (Cl 4-MB) of the ortho Mannich base. The spectra were analyzed based on the DFT calculated frequencies and intensities and compared with those recorded in CCl 4 solution in the region of the ν(OH) and ν(OD) vibrations. The matrix-isolated spectra are characterized by narrower ν(OH) and ν(OD) bands with much better resolved fine structure than in solution. The fine structure originates from the anharmonic coupling with the low frequency modes as well as from Fermi resonance. The ν(OD) band shapes can be reproduced exclusively by assuming the Fermi resonance with overtones and summation of the frequencies of modes into which the bridge atoms are involved. The frequency isotopic ratio (ISR) is for both compounds 1.33 while the half-width ratios are equal to 1.82 and 1.94, for Cl 2-MB and Cl 4-MB, respectively.

Matrix isolation FTIR and DFT studies of methyl isocyanide-boron trifluoride complex

The FTIR spectra of CH 3NC and BF 3 as well as their isotopomers co-deposited in low temperature Ar matrices were recorded. We observed several new infrared bands absent in the spectra of each component. These bands were assigned to the 1:1 EDA complex of CH 3NC and BF 3 based on the DFT calculations at the B3LYP/6-311++G** level. The vibrational assignments and frequencies of the observed bands are the NC stretching at 2319.9 cm −1, the BF 3 degenerate stretching at 1203.8 cm −1, the BF 3 symmetric stretching at 840.4 cm −1 and the BF 3 symmetric deformation at 638.0 cm −1 for the CH 3NC− 11BF 3 isotopomer. Although the BF 3 symmetric stretching is infrared inactive for free BF 3 of D 3 h symmetry, complexation with methyl isocyanide would have induced a structural change in the BF 3 moiety and the activation of this mode. Apart from some numerical discrepancies, the observed frequency shifts on complexation were in good agreement with the results of DFT calculation. Therefore, the structure of CH 3NC-BF 3 in solid Ar would be similar to the optimized C 3 v geometry, which corresponds to the gas phase structure.

Insights into the thermal fragmentation of intramolecularly coordinated gallanes. A matrix-isolation FTIR study.

High-vacuum thermolyses (400-1000 degrees C) of the intramolecularly coordinated gallanes [Me(2)N(CH(2))(3)](2)GaX [X = Cl (1), Br (2)] and (Me(2)NCH(2)CD(2)CH(2))(2)GaBr (2D(4)) have been investigated with matrix-isolation FTIR techniques. Around 850 degrees C, the fragmentation of these compounds was completed, and their typical IR absorptions could no longer be detected in argon matrices. Products have been identified with IR spectroscopy with the help of ab initio and DFT calculations and known literature data. In the case of precursors 1 and 2, respectively, we identified GaH(3), XGaH(2), X(2)GaH, GaH, GaX, HX, HCN, CH(4), H(2)C=CH(2), H(2)C=CHCH(3), H(2)C=NMe, [H(2)CCHCH(2)]., and H(2)C=CHCH(2)NMe(2). In the case of the precursor 2D(4), we found GaH(3), GaH(2)D, BrGaH(2), BrGaDH, GaH, GaD, GaBr, HBr, HCN, CH(4), H(2)C=CD(2), H(2)C=CDCH(3), H(2)C=NMe, [H(2)CCDCH(2)]., and H(2)C=CDCH(2)NMe(2). Among the monomeric hydrides, BrGaH(2) and BrGaDH were isolated for the first time. These compounds have been characterized by their six normal modes, and the experimental frequencies have been compared to the results of MP2(fc)/6-311+G(2d,p) and B3LYP/6-311+G(2d,p) calculations. These results have been interpreted by assuming that the intramolecularly coordinated precursors 1, 2, and 2D(4) eliminate their ligands through Ga-C homolysis and beta-hydrogen elimination.

Matrix isolation FTIR and theoretical study of α-pyrone photochemistry

A combined matrix isolation FTIR and molecular orbital study on the photochemistry of alpha-pyrone (AP) was undertaken. The most efficient of the observed photoprocesses was the Norrish type I, ring opening reaction leading to conjugated ketene. Upon irradiation of matrix isolated AP with UV (λ > 285 nm) light, rapid formation of Z isomers of the aldehyde–ketene was observed. After a few minutes of irradiation the IR bands assigned to these photoproducts stopped growing. Further irradiation generated, by excited state internal rotations around the central CC bond in the Z forms, new aldehyde–ketene isomers, which were assigned to the E forms of the conjugated ketene. These forms were identified in the present work for the first time. Upon subsequent UV (λ > 337 nm) irradiation, the Z aldehyde–ketene isomers reverted back to the closed-ring, initial form of AP, while the E forms did not react further. The ring opening reaction occurring upon UV (λ > 285 nm) irradiation was accompanied by very slow valence isomerization of AP to the Dewar form (2-oxa-3-oxobicyclo[2.2.0]hex-5-ene; OOBH). Observation of cyclobutadiene, produced by shorter wavelength UV irradiation (λ > 235 nm) of OOBH, was also achieved in the present study. The structure of the cage confined complex of cyclobutadiene with CO2 was theoretically investigated. The possibility of formation of 4-formyl-2-cyclobutene-1-one, by photochemical ring closure of aldehyde–ketene isomers with the central CC bond and the ketene group in s–cis position with respect to each other is also discussed.

Matrix-isolation FTIR study of azidoacetone and azidoacetonitrile

Azidoacetonitrile (N3CH2CN) and azidoacetone (N3CH2COCH3) are studied by matrix-isolation FTIR spectroscopy in solid neon, argon, and nitrogen. The IR spectra calculated using the density-fuctional theoretical method are discussed in comparison with the experimental data. Significant broadening of the recorded azide bands indicate an awkward fit of these compounds into the solid environment. The strongest absorption is observed for both compounds in the regions of asymmetric and symmetric stretches of the N3 azide group. Strong band splittings in the N3 asymmetric stretch region can be most likely explained by very strong Fermi resonances with the CN stretch and combinations and overtones of the numerous lower-frequency vibrational modes.

Reactions of Titanium Dioxides with Acetylene Molecules. A Matrix Isolation FTIR and Density Functional Study

Reactions of titanium dioxide with acetylene molecules have been studied using matrix isolation infrared absorption spectroscopy. The titanium dioxide molecules were prepared by the reactions of laser-ablated titanium atoms with dioxygen. In solid argon, titanium dioxide molecule reacted with acetylene to form the TiO 2 -C 2 H 2 complex spontaneously on annealing. The complex underwent photochemical rearrangement to the OTi(OH)CCH and H 2 Ti(CO) 2 isomers upon UV-visible photolysis. The product absorptions were identified by isotopic substitutions and density functional calculations of isotopic frequencies.

Combined Matrix-Isolation FT-IR and Theoretical Study of the Intrinsic Tautomeric, Vibrational, and H-Bonding Properties of N4-Methoxycytosine

The tautomeric, vibrational, and H-bonding characteristics of N4-methoxycytosine (N4MC) are investigated by a combined experimental, matrix-isolation Fourier transform infrared spectroscopic and computational study. For the theoretical part of the study, the methods RHF, MP2, and DFT(B3LYP) are used with the 6-31++G** basis set. N4MC occurs in a low-temperature Ar matrix exclusively in the oxo-imino form. Two isomers of this tautomer exist. Using IR intensities of characteristic bands, an approximate value of 2.3 × 10-2 is obtained for the isomerization constant KI (anti/syn). Theoretically, two closed H-bonded complexes with water are found for both isomers, i.e., N1−H...O−H...OC2 and N3−H...O−H...OC2, as well as one less stable open complex, N7...H−O and O8...H−O, for the syn and anti isomer, respectively. In the experimental FT-IR spectra, both closed H-bonded complexes are clearly identified based on characteristic H-bonding absorptions predicted by the calculations. Trace amounts of the open complexe...

Photodecomposition of formohydroxamic acid. Matrix isolation FTIR and DFT studies

Primary dissociation pathways of formohydroxamic acid have been investigated in argon and xenon matrices. The irradiation of the HCONHOH/Ar(Xe) matrices with full output of an Xe arc lamp leads to the formation of hydrogen bonded HNCO–H2O and NH2OH–CO complexes. Two structures were identified for the isocyanic acid–water complex, in the first one HNCO is hydrogen bonded to an oxygen atom of the water molecule and in the second, water serves as a proton donor toward the nitrogen atom of HNCO. For the hydroxylamine–carbon monoxide complex the spectra prove the existence of the structure with the OH group attached to the carbon atom and also suggest the existence of the structure with the NH2 group interacting with the carbon atom. The identification of the products is confirmed by 15N isotopic substitution and by DFT calculations (at the B3LYP level of the theory with 6-311++G(2d,2p) basis set) of the structure and vibrational frequencies of the identified complexes.

Vibrational spectrum and molecular structure of triphenylamine monomer: A combined matrix-isolation FTIR and theoretical study

Theoretical optimization of triphenylamine geometry, carried out at DFT(B3LYP) level using 6-31G** and aug-cc-pVDZ basis sets, predicted a propeller-like structure of the compound with D3 overall symmetry. In this structure, the central NCCC atoms are coplanar and the phenyl rings are symmetrically twisted from this plane by 41.5° (6-31G**) or 41.6° (aug-cc-pVDZ). The experimental FTIR spectrum of triphenylamine monomers isolated in an argon matrix was measured and interpreted by comparison with theoretical spectra calculated at the DFT(B3LYP) level with 6-31G** or aug-cc-pVDZ basis sets. The good agreement between the experimental and theoretical spectra allowed a positive assignment of the observed infrared absorption bands. Conformational flexibility of triphenylamine was investigated by carrying out a series of theoretical scans of the potential energy hypersurface of the system. Special attention was granted to the minimal energy pathway between the left-hand rotating and right-hand rotating symmetry identical structures of the compound. A route conserving a C2 symmetry axis was identified as implying an energy barrier of 20 kJ mol−1 only, whereas the calculated barrier for the concerted twist of all the phenyl rings (the route with conservation of the C3 symmetry axis) was as high as 54 kJ mol−1.

Matrix-isolation FT-IR studies and theoretical calculations of the vibrational properties of 4-methyl-2′-hydroxy-4′-ethyloxyazobenzene

Abstract The vibrational spectrum of 4-methyl-2 ′ -hydroxy-4 ′ -ethyloxyazobenzene (MHEAB) has been studied in low-temperature argon matrices and in CCl 4 solutions. Calculations at the DFT (B3-LYP) level of theory with the 6-31++G** basis set, as well as additional IR experiments of deuterated samples and of derivatives without the OH group, have been used to analyze the IR MHEAB spectrum. In the calculations we used the conventional harmonic approach, as well as an approach based on an one-dimensional anharmonic model. It has been shown that introduction of the OH group into the compound and formation of the OH⋯N intra-molecular hydrogen bond cause an increase of the intensity of the stretching NN mode, but do not affect the frequencies of the azo-bridge vibrations.

Matrix isolation FTIR and molecular orbital study of E and Z acetaldoxime monomersElectronic supplementary information (ESI) available: Internal coordinates for the Z and E isomers, calculated barriers for the rotation of methyl groups and the relative energies of the relevant stationary points for acetaldoxime. See http://www.rsc.org/suppdata/cp/b2/b203240f/

The molecular structures and vibrational spectra of the monomers of the Z and E acetaldoxime isomers were investigated by ab initio MP2/6-311++G** and DFT (B3LYP)/6-311++G** calculations. Experimentally, acetaldoxime was studied using FTIR spectroscopy combined with the technique of isolation in low temperature argon matrixes. Significant dependence of the ratio of E and Z isomers in the matrix on the method of sample preparation was observed. Matrixes with high predominance of the Z form were deposited, as well as such with dominating E form or with both forms in nearly the same amount. That allowed separation of the infrared spectra of both isomers. An assignment of the vibrational spectra of the two isomeric forms was based on comparison with the spectra theoretically calculated at the DFT and MP2 levels. The vibrational data were correlated with some important structural parameters, in particular the different methyl torsional barriers present in the two isomers.

Matrix-Isolation FT-IR Study and Theoretical Calculations of the Hydrogen-Bond Interaction of Hypoxanthine with H2O

The H-bonding interaction between the oxopurine base hypoxanthine and water is investigated using matrix-isolation FT-IR spectroscopy combined with theoretical density functional theory and ab initio methods. For vibrational frequency predictions, only the DFT/B3-LYP method is used, while for the prediction of relative energies and H-bond interaction energies of the complexes, four different theoretical methods are compared, i.e., RHF//RHF, MP2//RHF, DFT//DFT, and MP2//DFT. The oxo-N1HN7H, the oxo-N1HN9H, and the hydroxy-N9H (rotamer with the hydroxy-H atom pointed toward the N1 atom) are found to be the three most stable tautomeric forms of the free base. Different, stable complexes between these three tautomers and water have been predicted theoretically. The experimental FT-IR spectra agree well with this prediction, and most of the characteristic spectral data for the four most stable closed complexes, N7H···OH···OC6 and N1H···OH···OC6 of the O17 tautomer and N1H···OH···OC6 and N9H···OH···N3 of the O1...

Reactions of Atomic Silicon and Germanium with Ammonia: A Matrix-Isolation FTIR and Theoretical Study

The reactions of Si atoms with NH3 molecules have been studied using matrix-isolation FTIR spectroscopy and density functional theoretical calculations. Silicon atoms reacted with NH3 to form the SiNH3 complex spontaneously in solid argon upon annealing. Mercury arc photolysis with a 290-nm long-wavelength pass filter destroyed the SiNH3 absorptions and produced HSiNH2 absorptions. Full-arc irradiation (250−580 nm) destroyed the HSiNH2 absorptions and produced SiNH absorptions. The potential energy surface along the reaction path leading to the observed products has also been calculated. Similar experiments with Ge gave spectra for the analogous product molecules.

Reactions of titanium oxides with water molecules. A matrix isolation FTIR and density functional study

Reactions of titanium dioxides with water molecules have been studied by matrix isolation infrared and density functional theoretical calculations. In solid argon, titanium dioxide molecules reacted with water to form OTi(OH) 2 molecules spontaneously on annealing. The potential energy surface along the TiO 2+H 2O→OTi(OH) 2 reaction path was calculated. Although titanium dioxide–water complex was predicted to be stable, this complex was not observed due to low energy barrier and high exothermicity for the hydrolysis reaction. Evidence is also presented for the formation of OTi–OH 2 complex.

Reactions of Fe with H2O and FeO with H2. A Combined Matrix Isolation FTIR and Theoretical Study

The study of the reactions of transition metal atoms with water is continued in this work. Here we report the study of the reactions of Fe with H2O and FeO with H2. In agreement with previous thermal atom experiments, laser-ablated Fe atoms reacted with H2O to form the FeOH2 and HFeOH molecules as characterized by matrix isolation FTIR spectroscopy. On photolysis, the Fe atoms could further insert into the OH bonds in H2O molecules with a stepwise pattern to form multi metal−oxo core species including HFeOFeH, HFeOFeOH, and possibly HFeOFeOFeH, which were identified by isotopic substitutions and density functional calculations. Reactions of FeO with H2 also lead to HFeOH as the primary product. In addition, a potential energy surface for the Fe + H2O ⇔ FeO + H2 reaction was constructed to elucidate the reaction mechanisms.

Reactions of Mn with H2O and MnO with H2. Matrix-Isolation FTIR and Quantum Chemical Studies

The reactions of Mn atoms with water and MnO with H2 have been studied using matrix-isolation FTIR and DFT theoretical calculations. In solid argon, Mn atom reacted with H2O molecule to form the MnOH2 complex spontaneously. Photolysis destroyed the MnOH2 complex and produced the inserted HMnOH molecule. In addition, HMnOMnH, Mn(OH)2, HMnOMnOH, and posssibly HMnOMnOMnH molecules were also produced on photolysis. Reaction of MnO with H2 gave the (H2)MnO complex without activation energy. Photolysis of the (H2)MnO produced the inserted HMnOH molecule as well. The aforementioned species were identified via isotopic substitutions as well as density functional theoretical frequency calculations. Potential energy surface for the Mn + H2O ⇔ MnO + H2 reaction was also given. Our calculation results showed that all these reaction intermediates and products are high spin molecules. The MnOH2, HMnOH and (H2)MnO molecules have ground states with S = 5/2, the HMnOMnH, and HMnOMnOH molecules have ground states with S = 10/2, and the HMnOMnOMnH molecule has ground state with S = 15/2.

Formation and characterization of the AsCO and AsCO − molecules. A matrix isolation FTIR and theoretical study

Infrared spectra of arsenic carbonyls trapped in an argon matrix by co-condensation of laser-ablated arsenic atoms and electrons with carbon monoxide are reported. Based on isotopic substitution experiments and theoretical calculations, an IR band at 1919.3 cm −1 has been assigned to the C–O stretching vibration of the neutral AsCO, and a 1756.4 cm −1 band to the C–O stretching mode of the AsCO − anion. The ground states of AsCO and AsCO − were predicted to be 2Π and 1Σ + , respectively. The formation mechanism and the nature of bonding are discussed.

Matrix-isolation FT-IR study and theoretical calculations of the vibrational, tautomeric and H-bonding properties of hypoxanthine

The neutral compound hypoxanthine is investigated using the technique of matrix-isolation FT-IR spectroscopy combined with density functional theory (DFT) and ab initio methods. Two theoretical methods (RHF and DFT/B3-LYP) are compared for vibrational frequency prediction, and four methods (RHF//RHF, MP2//RHF, DFT//DFT and MP2//DFT) for prediction of the relative energies of the tautomers and the interaction energies of the complexes. All the possible tautomeric forms have been considered theoretically, and the results indicate that two oxo forms (O17 and O19) and one hydroxy form (H9-r1) are the three most stable forms. The experimental FT-IR spectra are consistent with this prediction, and nearly all the characteristic spectral features of these forms have been identified in the spectrum. A theoretical study of the H-bonded complexes of these three tautomers with water is also performed. Several structures have been found for each form and the results demonstrate that the closed complexes with two H-bonds are the most stable systems due to the H-bond cooperative effect.

Reactions of group V metal atoms with water molecules. Matrix isolation FTIR and quantum chemical studies.

Laser-ablated group V metal atoms (V, Nb, Ta) were co-deposited with water molecules in excess argon. The V atoms reacted with water to form the inserted HVOH molecule spontaneously. The Nb atoms reacted with water to form the NbOH2 complex and the inserted HNbOH molecule. Broad-band photolysis produced the H2VO and H2NbO molecules as well as the VO and NbO monoxides. For Ta + H2O reactions, neither TaOH2 nor HTaOH was observed, while the H2TaO molecule was produced on annealing, and the H2 elimination process was not observed on photolysis. The aforementioned species were identified via isotopic substitutions as well as density functional calculations. Qualitative analysis of the possible reaction paths leading to the observed products is proposed. The results have been compared with our earlier works concerning the Sc and group IV metal atoms with water reactions in order to observe existent trends for the early transition metal atoms.

Reactions of Group IV Metal Atoms with Water Molecules. Matrix Isolation FTIR and Theoretical Studies

Laser-ablated group IV metal atoms have been co-deposited at 11 K with water molecules in excess argon. The metal atoms reacted with water to form the insertion product HMOH and H2M(OH)2 (M = Ti, Zr, Hf) molecules spontaneously. Photolysis of the HTiOH species produced the H2TiO molecule as well as the TiO monoxide. In the cases of Zr and Hf, however, the H2ZrO and H2HfO molecules were produced on annealing, and the H2 elimination process was not observed on photolysis. In addition, the HMO species were also observed and identified. The aforementioned species were identified via isotopic substitutions as well as theoretical frequency calculations. Qualitative analysis of the possible reaction paths leading to the observed products is proposed.