Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine

Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pK_a = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm⁻¹ and a band at 811 cm⁻¹ due to the ν_s(C₃N) mode of the perturbed amine. The strongest phenol, CNP (pK_a = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH⁺---O⁻) absorption between 3000−1800 cm⁻¹, by the ν_as(C₃N⁺) and ν_s(C₃N⁺) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pK_a = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm⁻¹ and 950–400 cm⁻¹ regions due to the ν(NH⁺O⁻) and ν(OHN) modes, respectively.     

The interaction of formohydroxamic acid with nitrogen: FTIR matrix isolation and ab initio studies

Argon matrix infrared spectra of the complexes formed between formohydroxamic acid, HCONHOH (FHA) and nitrogen have been recorded. The experimental results indicate formation of two isomeric complexes in which the nitrogen atom of the N₂ molecule is attached to the NH or OH groups of FHA. Theoretical studies of the structure and spectral characteristics of the complexes were carried out on the MP2 level with the 6-311++G(2d,2p) basis set. The calculated vibrational frequencies for the complexes present in the matrices are in good agreement with the experimental data.     

Infrared matrix isolation and quantum chemical studies of the nitrous acid complexes with water

The 1:1 and 2:1 complexes between water and trans- and cis-isomers of nitrous acid have been isolated in argon matrices and studied using FTIR spectroscopy and DFT(B3LYP) calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra indicate that 1:1 complexes trapped in solid argon involve very strong hydrogen bond in which acid acts as the proton donor and water as the proton acceptor. The perturbed OH stretches are −248, −228 cm⁻¹ red shifted from their free-molecules values in complexes formed by trans- and cis-HONO isomers, respectively. The calculated spectral parameters for the two complexes are in good agreement with experimental data. The calculations also predict stability of two more 1:1 weakly bound complexes formed by each isomer. In these the water acts as the proton donor and one of the two oxygen atoms of the acid as the acceptor. The experimental spectra demonstrate also formation of 2:1 complex between water and trans-HONO isomer in an argon matrix. The performed calculations indicate that the complex involves a seven-membered ring in which OH group of HONO forms very strong hydrogen bond with the oxygen atom of one water molecule and nitrogen atom acts as a weak proton acceptor for the hydrogen atom of the second water molecule of the water dimer. The observed perturbations of the OH stretch of trans-HONO (750 cm⁻¹ red shift) is much larger than that predicted by calculations (556 cm⁻¹ red shift); this difference is attributed to strong solvation effect of argon matrix on very strong hydrogen bond.     

Aggregation of acetic and propionic acid in argon matrices--a matrix isolation and computational study

Monomeric acetic acid MA and propionic acid MP were isolated in argon matrices at 10K by using a pulse deposition technique. The dimerization of the monomers was induced by warming the matrices from 10 to 40 K. Under these conditions the diffusion of small trapped molecules is rapid and the dimerization could be monitored directly by IR spectroscopy. Both carboxylic acids form the symmetrical dimers B with two strong C=O...HO hydrogen bridges as the thermodynamically most stable dimers. With acetic acid a less stable dimer AA could be obtained if high concentrations of acetic acid in argon were used during the deposition of the matrix. On annealing this dimer rearranges to the more stable BA. In contrast, propionic acid does not form a corresponding less stable dimer under any experimental condition. These observations are rationalized on the basis of DFT and ab initio calculations.     

Infrared matrix isolation and gas phase studies of complexes between trifluoroacetic acid and diethylether and acetone

The i.r. spectra of argon matrix and gas phase complexes between trifluoroacetic acid (TFA) and diethylether (DEE) or acetone (DMK) are reported. The broad absorption due to ν_s(OH) vibration appears in the spectra of both complexes in the region 2400–3300 cm⁻¹ with characteristic structure due to Fermi resonance interaction.     

at]Infrared matrix isolation and CNDO/2 studies of complexes between trifluoroacetic acid and hydrogen halides

The i.r. spectra are reported of argon matrix isolated complexes formed between trifluoroacetic acid and hydrogen chloride and between their deuterated analogues. The pattern of bands characteristic for 1:1 complex indicates that a cyclic complex is formed in which each component acts both as a proton donor and as a proton acceptor. The bands due to 1:2 complexes are also identified in the spectra of matrices containing an excess of HCl.The results of CNDO/2 calculations with molecular geometry optimalization for CF₃COOHHF model system in different geometric arrangements are presented. In agreement with presented experimental data the cyclic heterodimer with the interaction energy equal to 103.90 kJ mol⁻¹ is of the most stable structure.     

Infrared matrix isolation study of the reaction of CrCl2O2 with (CH3)2O and (CH3)2CO

Matrix isolation has been combined with infrared spectroscopy to study the reaction chemistry of CrCl₂O₂ with (CH₃)₂O and (CH₃)₂CO. Very similar results were obtained with twin jet and room temperature merged jet deposition, indicating that the initial product forms on the surface of the matrix during deposition, not in the deposition lines prior to matrix condensation. The initial product in both systems was identified as the 1:1 complex between the two reagents, with a structure in which the oxygen atom of the base donates electron density to the Cr center. A number of perturbed vibrational modes of both subunits were observed; for the bases, these modes were vibrations involving the oxygen atom. Hg arc irradiation of the CrCl₂O₂·O(CH₃)₂ complex led to growth of a secondary product that is tentatively identified as Cl₂CrO(OCH₃)₂. The CrCl₂O₂·OC(CH₃)₂ complex was not photosensitive, and no rearrangements were observed.     

Matrix isolation and theoretical study of the photochemical reaction of CH3CN with CrO2Cl2 and OVCl3

The matrix isolation technique has been combined with theoretical calculations to identify and characterize the photoproducts in the reactions of CH₃CN with CrCl₂O₂ and OVCl₃. Twin jet co-deposition of these reagents led to the formation of a 1:1 molecular complex which was observed using UV/visible spectroscopy. Irradiation of these matrices with light of λ>300 nm led to the observation of new bands in the infrared spectra, the most intense of which was seen at 1942 cm⁻¹ for the CrCl₂O₂/CH₃CN system. The product bands are assigned to the ²η complexes of acetonitrile n-oxide with CrCl₂O and VCl₃, respectively. Identification of these species was supported by extensive isotopic labeling (²H and ¹⁵N), as well as by B3LYP/6-311++G(d,2p) density functional calculations.     

Experimental infrared spectra of matrix isolated complexes of HCl with 4-substituted pyridines. Evaluation of anharmonicity and matrix effects using data from ab initio calculations

Infrared spectra have been measured for HCl complexes with 4-cyanopyridine, 4-chloropyridine, pyridine and 4-methylpyridine isolated in argon and nitrogen matrices at about 12 K. The experimental spectra are dramatically different from computed MP2/6-31+G(d,p) harmonic spectra, a consequence of the anharmonicity of the potential energy surface in the hydrogen-bonding region. Comparisons of computed and experimental data suggest that the experimental spectra correspond to complexes with HCl distances that are much longer than the computed equilibrium distances. These longer distances, R_cor(HCl), are related to the average HCl distance in the ground vibrational state of the proton-stretching mode. The value of R_cor(HCl) determines values of three effective anharmonic force constants for the HCl stretch, the NH stretch and the coupling between them for each complex. The simulated anharmonic spectra obtained when these anharmonic force constants are used in place of the corresponding harmonic constants show spectral patterns with respect to both frequencies and intensities that are very similar to those observed in the experimental spectra obtained in Ar and N₂ matrices. 1D anharmonic potential curves related to the experimental spectra are presented. They provide insight into anharmonicity of the hydrogen-bonded proton stretch for these systems, and into the sensitivity of the potential energy surface to the environment.     

The complexes between CH3OH and CF4. Infrared matrix isolation and theoretical studies

The complex formed between methanol and tetrafluoromethane has been identified in argon and neon matrixes by help of FTIR spectroscopy. Three fundamentals (nu(OH), nu(FCF), and nu(CO)) were observed for the complex isolated in the two matrixes, and the OH stretch was red shifted in a neon matrix and blue shifted in an argon matrix with respect to the corresponding vibration of the methanol monomer. The theoretical studies of the structure and spectral characteristics of the complexes formed between CH(3)OH and CF(4) were carried out at the MP2 level of theory with the 6-311+G(2df,2pd) basis set. The calculations resulted in three stationary points from which two (I-1, I-2) corresponded to structures involving the O-H...F hydrogen bond and the third one (I-3) to the non-hydrogen-bonded structure. The topological analysis of the distribution of the charge density (AIM theory) confirmed the existence of the hydrogen bond in I-1, I-2 complexes and indicated weak interaction between the oxygen atom of CH(3)OH and three fluorine atoms of CF(4) in the I-3 complex. The comparison of the experimental and theoretical data suggests that in the matrixes only the non-hydrogen-bonded complex I-3 is trapped. The blue/red shift of the complex OH stretching vibration with respect to the corresponding vibration of CH(3)OH in argon/neon matrixes is explained by the different sensitivity of the complex and monomer vibrations to matrix material. The ab initio calculations performed for the ternary CH(3)OH-CF(4)-Ar systems indicated a negligible effect of an argon atom on the binary complex frequencies.     

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.     

Matrix isolation infrared spectroscopic investigation of the coordination chemistry and reactivity of OVF3

The matrix isolation technique has been combined with infrared spectroscopy to identify and characterize the product of the codeposition of OVF₃ with NH₃ and with a series of nitrogen and oxygen donor bases into argon matrices at 14 K. This codeposition led to the formation of the isolated 1:1 complexes between OVF₃ and these bases. Each complex was characterized spectroscopically, including strong shifts to the V–F stretching modes, and a lesser shift to the V=O stretching mode. Numerous perturbed vibrational modes of the base subunits were noted, including a strong, 230 cm⁻¹ blue shift to the symmetric bending mode of NH₃. The magnitudes of these shifts indicate that OVF₃ is a moderate strength Lewis acid. However, in contrast to analogous reactions with OVCl₃, no further thermal or photochemical transformations of the complex occurred. Theoretical calculations were also carried out in support of the experimental work.     

Infrared and ab initio studies of hydrogen bonding and proton transfer in the complexes formed by pyrazoles

The results of experimental studies and quantum mechanical calculations of vibrational spectra and structure of hydrogen bonded complexes formed by pyrazole (P) and 3,5-dimethylpyrazole (DMP) are presented. IR spectra of pyrazoles in solutions, gas phase, and solid state have been investigated in wide range of concentrations and temperatures. It has been found that in the gas phase both P and DMP reveal the equilibrium between monomers, dimers, and trimers. In solutions the equilibrium between monomers and trimers dominates, no bands, which can be attributed to dimers were detected. DMP retains the trimer structure in solid state, while in the case of pyrazole P, formation of the crystal provides another type of association. Geometrical and spectral characteristics of dimers and trimers, obtained by ab initio calculations, are presented and compared with experimental data.

IR spectra of solutions containing P and DMP with a number of acids (acetic and trifluoroacetic acids, pentachlorophenol, HBr) have been studied in parallel with ab initio calculations. It has been found that pentachlorophenol forms with pyrazoles complexes with one strong hydrogen bond O–HN, while NH pyrazole group remains unbonded. With carboxylic acids DMP forms 1:1 cyclic complexes with two hydrogen bonds. In the case of acetic acid, the complex in CH₂Cl₂ solution reveals molecular structure with OHN and C=OHN bonds, in accordance with results of the calculations. For trifluoroacetic acid, the calculations predict the molecular structure to be energetically more stable in the case of the isolated binary complex (in gas phase), while the experimental spectrum of CH₂Cl₂ solution gives an evidence of the proton transfer with formation of the cyclic ionic pair with two NH⁺O⁻ bonds. The agreement with experimental results can be improved by taking into account the influence of environment in the framework of Onsager or Tomasi models. The shape of proton potential function of the complexes and medium effect on its parameters, resulted from experimental data and calculations, are discussed. It has been found that the number of potential minima and their relative depth depend strongly on the method of calculations and the basic set. Under excess of trifluoroacetic acid, the formation of 2:1 acid–DMP complex has been detected. Spectral characteristics and results of calculations point to the cyclic structure of this complex, which includes homoconjugated bis-trifluoroacetate anion and DMPH⁺ cation. With HBr both studied pyrazoles were found to form ionic complexes including one or two pyrazole molecules per one acid molecule and correspondingly monocation or homoconjugated cation BHB⁺.     

Infrared matrix isolation studies of the N-methylpiperidin-2-one-hydrogen chloride and dimethylformamide-hydrogen chloride complexes

Infrared spectra are reported of mixtures of N-methylpiperidin-2-one with hydrogen chloride and dimethylformamide with hydrogen chloride in low-temperature matrices. The spectra obtained are characteristic of strongly hydrogen-bonded complexes in which the proton is more or less equally shared between the oxygen and chlorine atoms. The absorption due to the O … H … Cl antisymmetric stretching vibration is extremely broad and diffuse for both complexes.     

Infrared and Raman matrix isolation studies of methylamine

Infrared (4000-50 cm^?1) and Raman spectra are reported of methylamine, methylamine-d₁ and methylamine-d₂ trapped in argon and nitrogen matrices at 4–20 K. An anomalous intensity variation was found for the NH₂ wagging mode of methylamine isolated in nitrogen matrices, while in argon matrices the NH₂ wagging absorption exhibited a complex structure due to matrix site effects. A normal coordinate analysis was carried out using a new assignment of the NHD twisting frequency. Barriers to internal rotation in argon and nitrogen matrices, calculated from the observed torsional frequencies, are compared with the gas phase value.     

Synthesis, spectroscopic and thermal characterization of some transition metal complexes of folic acid

Compounds having general formula: [M(FO)(Cl)(x)(H(2)O)(y)].zH(2)O, where (M=Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), FO=folate anion, x=2 or 4, y=2 or 4 and z=0, 1, 2, 3, 5 or 15) were prepared. The obtained compounds were characterized by elemental analysis, infrared as well as electronic spectra, thermogravimetric analysis and the conductivity measurements. The results suggested that all folate complexes were formed by 2:1 molar ratio (metal:folic acid) as a bidentate through both of the two carboxylic groups. The molar conductance measurements proved that the folate complexes are electrolytes. The kinetic thermodynamic parameters such as: E*, DeltaH*, DeltaS* and DeltaG* were estimated from the DTG curves. The antibacterial evaluation of the folic acid and their complexes was also done against some Gram positive/negative bacteria as well as fungi.     

An ab initio and matrix isolation infrared study of the 1:1 C2H2–CHCl3 adduct

The details of weak C–Hπ interactions that control several inter and intramolecular structures have been studied experimentally and theoretically for the 1:1 C₂H₂–CHCl₃ adduct. The adduct was generated by depositing acetylene and chloroform in an argon matrix and a 1:1 complex of these species was identified using infrared spectroscopy. Formation of the adduct was evidenced by shifts in the vibrational frequencies compared to C₂H₂ and CHCl₃ species. The molecular structure, vibrational frequencies and stabilization energies of the complex were predicted at the MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels. Both the computational and experimental data indicate that the C₂H₂–CHCl₃ complex has a weak hydrogen bond involving a C–Hπ interaction, where the C₂H₂ acts as a proton acceptor and the CHCl₃ as the proton donor. In addition, there also appears to be a secondary interaction between one of the chlorine atoms of CHCl₃ and a hydrogen in C₂H₂. The combination of the C–Hπ interaction and the secondary ClH interaction determines the structure and the energetics of the C₂H₂–CHCl₃ complex. In addition to the vibrational assignments for the C₂H₂–CHCl₃ complex we have also observed and assigned features owing to the proton accepting C₂H₂ submolecule in the acetylene dimer.     

The structures of some trimers of carbon monoxide—An infrared matrix isolation spectroscopic and ab initio molecular orbital study

Using a number of potential models for the gas-phase structure of the trimer of carbon monoxide as a guide, ab initio molecular orbital calculations have been carried out on this aggregate in order to determine its probable structure and vibrational spectrum in cryogenic matrices. The Fourier transform infrared spectra of carbon monoxide trapped in argon and nitrogen matrices have been recorded and, on the basis of the results of the theoretical calculations, a search for possible absorptions which may be assigned to trimeric species has been undertaken.