Matrix isolation FTIR spectroscopic and theoretical study of dimethyl sulfite

The preferred conformations of dimethyl sulfite and their vibrational spectra were studied by matrix-isolation Fourier transform infrared spectroscopy and theoretical methods (density functional theory (DFT) and Moller-Plesset (MP2), with basis sets of different sizes, including the quadruple-zeta, aug-cc-pVQZ basis). Five minima were found at these levels of theory. At the MP2/6-31++G(d,p) and DFT/B3LYP/aug-cc-pVQPZ levels, the GG conformer (where the O-S-O-C dihedral angles are 73.2 and 70.8 degrees ) resulted in the conformational ground state. At the highest level of theory used, the GT conformer (O-S-O-C = +68.5 and -173.2 degrees ) is 0.83 kJ mol(-1) higher in energy than the GG form, while conformer GG' (O-S-O-C = +85.7 and -85.7 degrees ) has a relative energy of 1.18 kJ mol(-1). The remaining two conformers (G'T and TT) are high-energy forms and not experimentally relevant. In consonance with the theoretical predictions, conformer GG was found to be the most stable conformer in the gaseous phase as well as in the low-temperature matrices. Annealing of the argon matrices first promotes the GG'-->GT isomerization, which is followed by conversion of GT into the most stable conformer. There is no evidence of occurrence of GG'-->GG direct conversion in the low-temperature matrices. On the other hand, during deposition of the xenon matrices conformer GG' totally converts to conformer GT. Two observations demonstrated this fact: no evidence of bands corresponding to GG' were observed in xenon matrices and the GG/GT intensity ratio became similar to the GG/(GT + GG') intensity ratio observed in argon matrices. All these results could be explained by taking into account the relative values of the theoretically predicted energy barriers for the different isomerization processes: GG'-->GT, 1.90 kJ mol(-1); GT-->GG, 9.64 kJ mol(-1); and GG'-->GG, 19.46 kJ mol(-1).     

Matrix isolation FTIR spectroscopic and theoretical study of 3,3-dichloro-1,1,1-trifluoropropane (HCFC-243)

The molecular structure and infrared spectrum of the atmospheric pollutant 3,3-dichloro-1,1,1-trifluoropropane (HCFC-243) were characterized experimentally and theoretically. The theoretical calculations show the existence of two conformers, with the gauche (G) and trans (T) orientation around the HCCC dihedral angle. Conformer G was calculated to be more stable than form T by more than 10 kJ mol (-1). In consonance with the large predicted relative energy of conformer T, only the G form was identified spectroscopically in cryogenic argon (10 K) and xenon (20 K) matrices prepared from room-temperature equilibrium vapor of the compound. The observed infrared spectra of the matrix-isolated HCFC-243 were interpreted with the aid of high-level density functional theory calculations and normal coordinate analysis. For experimental identification of the weakest IR absorption bands, the spectrum of HCFC-243 in the neat solid state at 145 K was obtained. This spectrum also confirmed the sole presence of the G conformer in the sample. Natural bond orbital and atomic charge analyses were carried out for the two conformers to shed light on the most important intramolecular interactions in the two conformers, in particular those responsible for their relative stability.     

Matrix isolation FTIR spectroscopical study of ethene secondary ozonide

A new method is used for the separation of ethene secondary ozonide (SOZ) from the other products of ethene ozonization reaction. The reaction was performed in the neat films of the reactants at 77 K. Ethene SOZ was separated from other products of the reaction by vacuum distillation at 190–210 K and analyzed by means of the matrix isolation IR absorption spectroscopy. Spectroscopic data from photolysis of the matrix isolated ozonide was used as an argument for assignment of the infrared spectral bands either to ethene SOZ or to other products of the reaction. The spectra of ethene SOZ isolated in the Ar matrix were analyzed by combining experimental results with the theoretical calculations performed at the MP2 6-311+G (3df, 3pd) level. A new assignment of some experimental fundamental bands is proposed taking in to account the Fermi resonance between CH stretch and the five membered ring vibrations. For the first time more than 30 weak infrared absorption bands were observed and assigned to various combination vibrations and overtones. By using new spectral information concerning the overtones and the combination bands it is concluded that the dissociation of unstable ethene SOZ involving breaking of any of the four CO bonds of the five membered ring of ethene SOZ has low probability. Dissociation of the ring starts from breaking of the OO bond.      

Matrix isolation infrared spectroscopic and theoretical study of the hydrolysis of boron dioxide in solid argon

The reaction of boron dioxide with water molecule has been studied using matrix isolation infrared spectroscopy. The boron dioxide molecules produced by codeposition of laser-evaporated boron atoms with dioxygen react spontaneously with water molecules to form OB(OH)2, which is characterized to have a doublet ground-state with two OH groups in the cis-trans form. Isotopic substitution results indicate that the hydrolysis process proceeds via a concerted two hydrogen atom transfer mechanism. The cis-trans-OB(OH)2 molecule is photosensitive; it decomposes to the OH x OB(OH) complex upon broadband UV-visible irradiation. The OH x OB(OH) complex is determined to have a (2)A' ground-state with a bent C(s) symmetry, in which the terminal oxygen atom of the OB(OH) fragment is hydrogen bonded with the hydroxyl radical. The OH x OB(OH) complex recombines to the cis-trans-OB(OH)2 molecule upon sample annealing.     

Vibrational spectra and structure of 1-phenyltetrazole and 5-chloro-1-phenyltetrazole: A combined study by low temperature matrix isolation and solid state FTIR spectroscopy and DFT calculations

Infrared spectra of 1-phenyltetrazole (C₇N₄H₆) and 5-chloro-1-phenyltetrazole (C₇N₄H₅Cl) isolated in argon matrixes (T=8 K) and in the solid state (at room temperature) were studied. DFT(B3LYP)/6-31G* calculations predict the minimum energy conformation of 1-phenyltetrazole as being non-planar, with the two rings (phenyl and tetrazole) twisted by 29°. For 5-chloro-1-phenyltetrazole, the optimized dihedral angle between the two rings is larger (48°). The theoretically calculated IR spectra of both compounds fit well the spectra observed experimentally. This allowed a reliable assignment of observed IR absorption bands.     

FTIR spectroscopic study of low temperature NO adsorption and NO + O2 coadsorption on H-ZSM-5

Adsorption of NO and coadsorption of NO and O2 on H-ZSM-5 have been studied at low and room temperature by means of FTIR spectroscopy. For better interpretation of the spectra, experiments involving isotopic labeled molecules have been performed. Low temperature adsorption of NO on H-ZSM-5 results initially in formation of NO which is H-bonded to the zeolite acidic hydroxyls. A second NO molecule is inserted into the OH-NO species at higher coverages, thus forming OH(NO)2 complexes. Different kinds of NO dimers are also formed. Negligible amounts of oxygenated compounds have been detected. In the presence of oxygen, the (di)nitrosyl species are oxidized very fast even at 100 K to N2O3, NO+, NO2, and N2O4. Different kinds of adsorbed N2O3 species have been evidenced. With increasing temperature, NO+ migrates and occupies cationic positions. The latter species interacts with NO at low temperature to give an [ONNO]+ complex. This reaction is used to prove that the different bands in the 2206-2180 cm(-1) region are also due to NO+ species.     

A vibrational spectroscopic study of salicylaldoxime in the solid state

The infrared and Raman spectra of solid salicylaldoxime have been measured both for normal and deuterated substance; the polarized infrared spectra of oriented samples have been also obtained. Assignments have been proposed on the basis of i.r. dichroism, Raman data and isotopic effects. The possible occurrence of Fermi resonance effects in some regions of the i.r. spectra has been also investigated.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated rhodium-dioxygen complexes

Reactions of rhodium atoms with dioxygen molecules in solid argon have been investigated using matrix isolation infrared absorption spectroscopy. The rhodium-dioxygen complexes, Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO), are produced spontaneously on annealing. The Rh(eta2-O2) complex rearranges to the inserted RhO2 molecule under visible light irradiation. Experiments doped with xenon in argon show that the rhodium-dioxygen complexes are coordinated by one or two noble gas atoms in solid noble gas matrixes. Hence, the Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO) molecules trapped in solid noble gas matrixes should be regarded as the Rh(eta2-O2)(Ng)2, Rh(eta2-O2)2(Ng)2, and Rh(eta2-O2)2(eta1-OO)(Ng) (Ng = Ar or Xe) complexes. The product absorptions are identified on the basis of isotopic substitution and density functional theory calculations.     

Matrix isolation spectroscopic and theoretical study of carbon dioxide activation by titanium oxide molecules

The reactions of titanium monoxide and dioxide molecules with carbon dioxide were investigated by matrix isolation infrared spectroscopy. It was found that the titanium monoxide molecule is able to activate carbon dioxide to form the titanium dioxide-carbon monoxide complex upon visible light excitation via a weakly bound TiO(η(1)-OCO) intermediate in solid neon. In contrast, the titanium dioxide molecule reacted with carbon dioxide to form the titanium monoxide-carbonate complex spontaneously on annealing. Theoretical calculations predicted that both activation processes are thermodynamically exothermic and kinetically facile.     

UV-visible spectroscopic study of solid state 12-molybdophosphoricacid catalyst

Summary UV-visible spectroscopic studies of solid H₃PMo₁₂O₄₀were carried out to elucidate the effect of crystalline water molecules, and in turn, to provide a guideline for utilizing UV-visible spectra of solids to probe reduction potentials of HPA catalysts. UV-visible spectra of reduced/reoxidized H₃PMo₁₂O₄₀were also measured to check the possibility of utilizing UV-visible spectroscopy as a probe of reduction/oxidation states of H₃PMo₁₂O₄₀catalyst. Absorption edges of solid H₃PMo₁₂O₄₀ shifted to longer wavelength with heating to decrease the number of crystalline water molecules. It was also revealed that UV-visible spectra of the H₃PMo₁₂O₄₀catalyst varied in a systematic way depending on the reduction/oxidation states of the H₃PMo₁₂O₄₀catalyst.</o:p>     

Matrix isolation and spectroscopic characterization of perfluorinated ortho- and meta-benzyne

The matrix isolation and spectroscopic characterization of two C6F4 isomers, the perfluorinated o-benzyne 4 and the m-benzyne 5, is reported. UV photolysis of tetrafluorophthalic anhydride 6 in solid argon at 10 K results in the formation of CO, CO2, and 1,2-didehydro-3,4,5,6-tetrafluorobenzene (4) in a clean reaction. On subsequent 350 nm irradiation 4 is carbonylated to give the cyclopropenone 7. 1,3-Didehydro-2,4,5,6-tetrafluorobenzene (5) was synthesized by UV irradiation of 1,3-diiodo-2,4,5,6-tetrafluorobenzene (8) via 2,3,4,6-tetrafluoro-5-iodophenylradical 9. Photolysis of 8 in solid neon at 3 K produces good yields of both radical 9 and benzyne 5, while in argon at 10 K no reaction is observed. Thus, the photochemistry in neon at extremely low temperature markedly differs from the photochemistry in argon. The formation of 5 from 8 via 9 is reversible, and annealing the neon matrix at 8 K leads back to the starting material 8. The benzynes 4 and 5 and the radical 9 were characterized by comparison of their matrix IR spectra with density functional theory (DFT) calculations.     

Matrix isolation, spectroscopic characterization, and photoisomerization of m-xylylene

A new efficient synthesis of m-xylylene 1 is reported. The diradical 1 was trapped in argon matrices at 10 K and characterized by IR, UV-vis, and EPR spectroscopy. The syntheses reported before only allowed generation of 1 in organic glasses, and the spectroscopic identification was limited to fluorescence and EPR spectroscopy. Diradical 1 proved to be highly photolabile, and irradiation results in the formation of three isomeric hydrocarbons 7, 9, and 11 which could be identified by comparison of their IR spectra with the results of DFT calculations.     

Matrix isolation spectroscopic and theoretical study of dihydrogen activation by group V metal dioxide molecules

The reactions of group V metal dioxide molecules with dihydrogen have been studied by matrix isolation infrared spectroscopy. The ground state VO(2) molecule is able to cleave dihydrogen heterolytically and spontaneously in forming the HVO(OH) molecule in solid argon. In contrast, the reaction of VO(2) with dideuterium to form DVO(OD) proceeds only under UV-visible excitation via a weakly bound VO(2)(η(2)-D(2)) complex. Theoretical calculations predict that the dihydrogen cleavage process is thermodynamically exothermic with a small barrier. The niobium and tantalum dioxide molecules react with dihydrogen to give primarily the side-on bonded metal dioxide bis-dihydrogen complexes, NbO(2)(η(2)-H(2))(2) and TaO(2)(η(2)-H(2))(2), which are further transferred to the HNbO(OH) and HTaO(OH) molecules via photoisomerization in combination with H(2) elimination under UV-visible light excitation.     

FTIR spectroscopic study of titanium-containing mesoporous silicate materials

The surface acidity of different mesoporous titanium-silicates, such as well-organized hexagonally packed Ti-MMM, Ti-MMM-2, Ti-SBA-15, and amorphous TiO(2)-SiO(2) mixed oxides (aerogels and xerogels), was studied by means of FTIR spectroscopy of CO adsorbed at 80 K and CD(3)CN adsorbed at 293 K. The surface hydroxyl groups of mesoporous titanium-silicates with 2-7 wt % Ti revealed a Br?nsted acidity slightly higher to that of pure silicate. TiO(2)-SiO(2) xerogels revealed the highest Br?nsted acidity among the titanium-silicates studied. CO adsorption revealed two additional sites on the surface in comparison to pure silicate, characterized by nu(CO) from 2185 (high pressure) to 2178 (low pressure) cm(-1) and from 2174 (high pressure) to 2170 (low pressure) cm(-1). These bands are due to CO adsorbed on isolated titanium cations in the silica surrounding or having one Ti(4+) cation in their second coordination sphere and due to CO interactions with Ti-OH groups, respectively. CD(3)CN adsorption similarly revealed the existence of two additional sites, which were not detected for pure silicate: at 2289 cm(-1) due to CD(3)CN interaction with titanol groups and from 2306 (low pressure) to 2300 (high pressure) cm(-1) due to acetonitrile interaction with isolated framework titanium cations with probably one Ti(4+) cation in their second coordination shell. The spectroscopic results are compared with computational data obtained on cluster models of titanium-silicate with different titanium content. According to the IR data, the Ti accessibility on the surfaces for mesoporous titanium-silicates with similar Ti loading (2 wt %) was found to fall in the order TiO(2)-SiO(2) aerogel approximately TiO(2)-SiO(2) xerogel > Ti-MMM approximately Ti-MMM-2 > Ti-SBA-15. This order (except TiO(2)-SiO(2) xerogel) correlates with the catalytic activity found previously for titanium-silicates in 2,3,6-trimethylphenol oxidation with H(2)O(2).     

Matrix isolation infrared spectroscopic and theoretical study of the reactions of tantalum oxide molecules with methanol

The reactions of tantalum monoxide (TaO) and dioxide (TaO(2)) molecules with methanol in solid neon were investigated by infrared absorption spectroscopy. The ground-state TaO molecule reacted with CH(3)OH in forming the CH(3)OTa(O)H molecule via the hydroxylic hydrogen atom transfer from methanol to the metal center spontaneously on annealing. The observation of the spontaneous reaction is consistent with theoretical predictions that the OH bond activation process is both thermodynamically exothermic and kinetically facile. In contrast, the TaO(2) molecule reacted with CH(3)OH to give primarily the TaO(2)(CH(3)OH) complex, which further rearranged to the CH(3)OTa(O)OH isomer via the hydroxylic hydrogen atom transfer from methanol to one of oxygen atom of metal dioxide upon visible light excitation.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated dipalladium–dioxygen complexes

The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η²–O₂) and Pd(η²–O₂)₂, dinuclear palladium–dioxygen complexes: Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η²–O₂), Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η²–O₂)(Ng)₂, Pd₂(η²–O₂)(Ng)₂ and Pd₂(η²–O₂)₂(Ng)₂ (NgAr or Xe) complexes isolated in solid argon.     

Thermal and spectroscopic study of the lanthanide 2-aminoterephthalate compounds in the solid state

Lanthanides 2-aminoterephthalate compounds were synthetized and characterized on the basis of TG–DTA data in order to study their thermal behavior, as well as to establish hydration grade and stoichiometry, while TG/FTIR system identified the gaseous products evolved during the thermal decomposition of these compounds in each step of the TG curve, in which water and carbon dioxide were the main products with a small amount of carbon monoxide and ammonia. Through the FT-IR spectroscopic data of the compounds in the solid state, information concerning the coordination mode of the carboxylate groups to the metal was provided, and by analysis of fluorescence, with excitation at 405 nm, the respective electronic transitions supported by the data reported in the literature were identified. In addition, the excitation was made for the ligand salt and acid with the aim of understanding the contribution of the ligand in the emission of the compounds. In summary, the ligand influenced on the fluorescence of lanthanide ions, being more intense for the compounds of La, Ce, Pr, and Nd, making this material interesting for optical and photonic applications.     

Matrix isolation spectroscopic and theoretical study of water adsorption and hydrolysis on molecular tantalum and niobium oxides

The reactions of molecular tantalum and niobium monoxides and dioxides with water were investigated by matrix isolation infrared spectroscopy. In solid neon, the metal monoxide and dioxide molecules reacted with water to form the MO(H(2)O) and MO(2)(H(2)O) (M = Ta, Nb) complexes spontaneously on annealing. The MO(H(2)O) complexes photochemically rearranged to the more stable HMO(OH) isomers via one hydrogen atom transfer from water to the metal center under visible light excitation. In contrast, the MO(2)(H(2)O) complexes isomerized to the more stable MO(OH)(2) molecules via a hydrogen atom transfer from water to one of the oxygen atoms of metal dioxide upon visible light irradiation. The aforementioned species were identified by isotopic-substituted experiments as well as density functional calculations.     

Matrix isolation infrared spectroscopic and theoretical study of nickel, palladium, and platinum nitrous oxide complexes

Binary nickel, palladium, and platinum nitrous oxide complexes Ni(NNO)x, Pd(NNO)x (x = 1, 2), and PtNNO have been produced by the reactions of laser-evaporated metal atoms with nitrous oxide in solid argon. The complexes were identified on the basis of isotopically substituted infrared absorptions as well as theoretical frequency calculations. These complexes were characterized to have structures with the terminal N atom of N(2)O bound to the metal atoms. The MNNO complexes are photosensitive and rearrange to OMNN or MO + N(2) upon ultraviolet-visible irradiation.     

Hydrogen bonding of adenine with benzoic acids in the solid state. An FTIR study

Complex formation by hydrogen bonding, in the solid-state, between adenine and benzoic acid derivatives, was studied by IR spectroscopy.