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- (Cl₂-MB) and tetrachloroderivatives (Cl₄-MB) of the ortho Mannich base. The spectra were analyzed based on the DFT calculated frequencies and intensities and compared with those recorded in CCl₄ 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 Cl₂-MB and Cl₄-MB, respectively.     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

Time-dependent fluctuations in infrared vsCH2 frequencies in acyl chain membranes of Acholeplasma laidlawii cells

We measured FT-IR spectra of intact Acholeplasma laidlawii cells grown at 37 °C on palmitic acid (C16:0) or on binary palmitic acid-d31/oleic acid (C16:0-d31/C18:1(9)) at an initial mole ratio of 2:3, which have been previously reported to produce significant fluctuations in CH₂ symmetric stretching (ν_sCH₂) and CD₂ asymmetric stretching (ν_aCD₂) frequencies (Biochim. Biophys. Acta 1279 (1996) 49). Time courses for acyl chain ν_sCH₂ and ν_aCD₂ frequencies determined from fourth derivative spectra are presented. Fluctuations were detected with the C16:0 enriched cells at temperatures above 40 °C as well as with the cells enriched in 2:3 C16:0-d₃₁/C18:1(9). These observations at temperatures above 40 °C for the C16:0 enriched cells were not in agreement with the conclusion in the previous work by Moore et al. Our results have suggested that the 2850 cm⁻¹ ν_sCH₂ band comprises two components arising from trans and gauche conformations, and that the fluctuations in ν_sCH₂ frequency are caused by random temporal changes in the relative intensities of these two components.     

Photoinduced nitrosyl linkage isomers in complexes based on the photochromic cation [RuNO(NH3)5] with the paramagnetic anion [Cr(CN)6] and the diamagnetic anions [Co(CN)6] and [ZrF6]

Two metastable nitrosyl linkage isomers SI and SII are generated by light irradiation in the spectral range 370–500 nm in the two diamagnetic compounds [RuNO(NH₃)₅][Co(CN)₆] and [RuNO(NH₃)₅]₂[ZrF₆]₃ as well as in the paramagnetic compound [RuNO(NH₃)₅][Cr(CN)₆]. The frequencies of the ν(NO) stretching vibrations of SI and SII identify SI as the isonitrosyl Ru–O–N isomer and SII as the side-on η² isomer of NO. The population, i.e., the number of generated linkage isomers, is determined from the decrease of the area of the fundamental ν(NO) and of the higher harmonic 2 · ν(NO) of the ν(NO) stretching vibration of the ground state. Using differential scanning calorimetry (DSC) the heat release during the thermal decay of the metastable linkage isomers is determined. The activation energies, frequency factors, and the energetic position of the metastable linkage isomers are determined from the DSC and infrared spectroscopic experiments. It is found that the exchange of the counter ion significantly influences the energetic positions of the linkage isomers, while the activation energy and frequency factor are much less affected.     

Ab initio calculations of stretching vibrational transitions for the linear molecules HCN, HNC, HCCF and HC3N up to high overtones

Accurate electric dipole moment functions have been calculated for the stretching vibrational coordinates of the linear molecules HCN, HNC, HCCF and HC₃N by means of coupled cluster theory with single and double excitation operators plus a quasi-perturbative treatment of connected triples (CCSD(T)). Combining these with anharmonic stretching vibrational wave-functions absolute IR intensities for strecthing vibrational transitions up to high overtones are obtained. For HCN, excellent agreement with experiment is observed up to 7 ν₁ + η₃ at 23047 cm⁻¹. HCCF and DCCF show unusual behavior, with the ν₂ band with origin at 2239.2 cm⁻¹ being strongest in HCCF and the ν₁ band with origin at 2645.1 cm⁻¹ being the most intense in DCCF. The Fermi resonance system 2ν₃/ν₂ of DCCF is analysed in detail. The calculated IR intensities of the stretching fundamentals of HC₃N and DC₃N, which are difficult to obtain with high accuracy, are in very good agreement with the existing experimental data.     

Characterization and decomposition mechanism of an unusual nickel, thiocyanate and 4-methylpyridine polymeric complex

The synthesis, characterization, and thermal decomposition of the [Ni(SCN)₂(H⁺SCN)₂(4-mepy)₂] compound with an octahedral structure in polymeric chain were reported, in which SCN groups form bridges among Ni(II) ions. The compound decomposes in water resulting in a pH<4 solution. The FT-IR spectrum presented doublet bands at 2117; 2128 cm⁻¹, 788; 773 cm⁻¹ assigned to ν(C---N) and ν(C---S) stretching modes, respectively, and δ(SCN) deformation modes at 468; 476 cm⁻¹. The Raman spectrum of the compound presented the ν(C---N) stretching as a strong doublet at 2122; 2128 cm⁻¹, ν(C---S) at 783; 770 cm⁻¹, and δ(SCN) at 468; 477 cm⁻¹. No significant changes were observed in the 4-mepy ligand bands compared with the vibrational frequencies of the pure compound or the compound in aqueous solution 0.2 mol l⁻¹. The crystal UV–vis reflectance spectrum presented two bands centered in 626 and 424 nm tentatively assigned to the d→d type transitions, ³A_2g→³T_1g and ³A_2g→³T_1g, for a symmetry close to O_h. The TG curve showed a mass loss between 120 and 200 °C assigned to the loss of the two 4-mepy molecules; from 200 to 265 °C, the loss of the two H⁺SCN groups; and from 265 to 450 °C, the loss of the two SCN groups that formed the bridges among the nickel atoms. Based on these mass loss data, a mechanism of thermal decomposition for the compound was proposed.     

Infrared matrix isolation studies of complexes formed between dimethylsulfide, dimethyldisulfide and nitrous acid

The complexes formed by dimethylsulphide (DMS) and dimethyldisulphide (DMDS) with two isomers of nitrous acid have been observed, and characterised in argon and nitrogen matrices. The ν₁ OH stretching vibration of the perturbed trans-HONO monomer is 425 and 294 cm⁻¹ red shifted, respectively, for the DMS and DMDS complex in solid argon, and 441 and 301 cm⁻¹ in solid nitrogen. A large blue shift is also observed for the ν₃ NOH in-plane deformation mode: 101 and 80 cm⁻¹ for DMS–HONO-trans in argon and nitrogen matrices and 46 cm⁻¹ for DMDS–HONO-trans in nitrogen matrix. The results indicate formation of strong hydrogen bonds in the studied DMS–HONO and DMDS–HONO systems. The origin of the complicated shape of the ν₁ OH absorption is discussed. Similarities and differences between argon and nitrogen matrices are considered.     

The ν(OH/OD) band shape of strong hydrogen bonded dimers of phosphinic acids. Phenomenology and formation models

The infrared spectra of phosphinic acid R₂POOH dimers (R=CH₃, CH₂Cl, C₆H₅) have been studied in CCl₄ and CH₂Cl₂ solutions (T=300 K). The infrared spectra of deuterated R₂POOD dimers (R=CH₃, CH₂Cl) were also studied in the gas phase (T=400–550 K) and solid state (T=100–300 K). They are compared with previously studied spectra of the light (non-deuterated) dimers in the gas phase, in the solid state and in low-temperature argon matrices (T=12–30 K) in the 4000–400 cm⁻¹ spectral region. It is found that the strong and broad ν(OH) dimer bands have similar shapes, nearly equal values of bandwidth and low-frequency shift, and possess the Hadzi ABC structure irrespective of the type of acid, significant differences of dimerization enthalpies, influence of solvent, the type of H-bonded complexes (cyclic dimers in the gas phase, in solutions, and in inert matrices, and infinite chains in the solid state), and temperature in the range 12–600 K. Isotopic ratio of the first moments of light and deuterated acid bands has been measured. Analysis of the ν(OH/OD) band of hydrogen bonded dimers of phosphinic acids shows that the interaction between the two intermolecular bonds O–HOP in a cyclic complex plays virtually no role in the mechanism of the ν(OH/OD) band formation; the shape of ν(OH/OD) band is controlled mainly by the POOH(D)O fragment; and the band shape of strong hydrogen bonded complexes is formed by a number of vibrational transitions from the ground state to different combination levels in the region 3500–1500 cm⁻¹.     

Experimental absolute intensities of the 4ν9 and 5ν9 O–H stretching overtones of H2SO4

This work uses cavity ring-down spectroscopy to measure two high vibrational overtones (4ν₉ and 5ν₉) of the O–H stretch in sulfuric acid. The frequencies, bandwidths, and intensities are obtained for these previously unobserved transitions. The atmospheric J-values for the overtone-induced photodissociation are calculated using the experimental cross-sections. Accurate J-values are essential for understanding the formation of the springtime polar sulfate layer by overtone-induced dehydration of H₂SO₄. The results are compared to previous experimental and theoretical studies of sulfuric acid.     

Application of the spectroscopic modifications of Pippard relations to NaNO2 in the ferroelectric phase

This study examines a linear variation of the specific heat C_P with the frequency shifts 1/ν(∂ν/∂T) for the Brillouin frequencies of the L-mode [010], [001] and [100] in the ferroelectric phase of NaNO₂ according to our spectroscopically modified Pippard relation. We obtain this linear relationship for those modes studied and calculate dT_C/dP in the ferroelectric phase of NaNO₂. Our calculated values of dT_C/dP for the [001] and [100] modes are in good agreement with the values given in the literature.     

Vibration-rotation spectra of C containing acetylene: anharmonic resonances

High resolution vibration-rotation spectra of ¹³C₂H₂ were recorded in a number of regions from 2000 to 5200 cm⁻¹ at Doppler or pressure limited resolution. In these spectral ranges cold and hot bands involving the bending-stretching combination levels have been analyzed up to high J values. Anharmonic quartic resonances for the combination levels ν₁ + mν₄ + nν₅, ν₂ + mν₄ + (n + 2) ν₅ and ν₃ + (m − 1) ν₄ + (n + 1) ν₅ have been studied, and the l-type resonances within each polyad have been explicitly taken into account in the analysis of the data. The least-squares refinement provides deperturbed values for band origins and rotational constants, obtained by fitting rotation lines only up to J ≈ 20 with root mean square errors of ≈ 0.0003 cm⁻¹. The band origins allowed us to determine a number of the anharmonicity constants x_ij⁰.     

Computational study of hydrogen bonding interaction between formamide and nitrosyl hydride

The hydrogen bonding interaction of formamide–nitrosyl hydride complex has been investigated using density functional theory (DFT) and ab initio method. The natural bond orbital (NBO) analysis and atom in molecules (AIM) theory were applied to understand the nature of the interaction. Two stable geometries are found on the potential energy surface, a six-membered cyclic structure of complex A and a seven-membered cyclic structure of complex B, characterized by AIM analysis. Complex A is less stable than complex B. It is confirmed that there are contractions of CH (compared with the monomer HCONH₂), NH bonds (compared with the monomer HNO) and the corresponding stretching vibrational frequencies are blue-shifted, while there is an elongation of the NH bond and the corresponding stretching vibrational frequency is red-shifted, relative to those of the monomer HCONH₂. From NBO analysis, it is evident that the electron densities in the σ^* (CH) and σ^*(NH) of the complex A are less than those of the monomers HCONH₂ and HNO, which strengthen CH and NH bonds. Furthermore, the increases in s-characters of X also strengthen XH bonds.     

Observation and rovibrational analysis of the ν2 band of HCN–HCl

The high-resolution infrared absorption spectrum of an equilibrium mixture of HCN and HCl in a static gas long-path absorption cell is recorded in the 2500–2900 cm⁻¹ spectral region at 205 K. The spectrum shows rovibrational structure which has the typical appearance of a parallel band of a linear molecule and is assigned to the intramolecular H–Cl stretching vibration band ν₂ of the linear HCN–H³⁵Cl heterodimer. The rovibrational analysis of the band yield a band origin ν₀ of 2779.0968(12) cm⁻¹ together with a value for the upper-state rotational constant B′ of 0.067722(2) cm⁻¹. The observed red shift of 107 cm⁻¹ for the ν₂ band of HCN–H³⁵Cl relative to the H–Cl stretching vibration band of monomer H³⁵Cl is in excellent agreement with results from the MP2/6−311++G** level of theory. The value of the upper-state rotational constant shows that the intermolecular hydrogen bond shortens by 0.022 Å upon intramolecular vibrational excitation of the ν₂ mode.     

Crystal structure and infrared spectra of dicesium trans-tetraaquadichlorochromium(III) chloride

The crystal structure of dicesium trans-tetraaquadichlorochromium(III) chloride Cs₂Cr^IIICl₅·4H₂O with trans-[M^IIIX₂(H₂O)₄]⁺ complex ions (space group C2/c, Z=4, a=1915.3(4) pm, b=614.1(1) pm, c=1392.0(3) pm, and β=118.24(3)°, final R1=0.0246 for 2100 unique reflections) was redetermined by single-crystal X-ray diffraction studies. It was found to crystallize in a 2c super structure of the structure reported previously (Inorg. Chem. 20 (1981) 1566; Inorg. Chem. 36 (1997) 2248). The obtained structure data now agree with the results of infrared spectroscopic studies, which has been confirmed in this work, namely that there are two different hydrate H₂O molecules in the structure. Phase transitions, static or dynamic disorder of the hydrate H₂O molecules, and space group C2/m proposed in the literature were ruled out. The coordinates of the four hydrogen positions derived from the X-ray data have been improved via the O–H distances derived from the wave numbers of the OD stretching modes of matrix isolated HDO molecules (2426, 2323, and 2306 cm⁻¹, 263 K) by using the ν_OD versus r_O–H correlation curve reported in the literature (J. Mol. Struct. 404 (1997) 63). The ν_OD versus r_HCl correlation curve reported by Mikenda (J. Mol. Struct. 147 (1986) 1) should be improved, especially for strong hydrogen bonds. The two hydrate H₂O molecules of the title compound are strongly distorted with a weak and a relatively strong O–HCl hydrogen bond each thus intramolecular coupling of the two OH stretching vibrations to coupled ones is largely reduced and, hence, the wavenumbers of the OH and OD stretching modes of the HDO molecules mainly resemble those of the H₂O and D₂O molecules. The strength of the hydrogen bonds is in accordance with the predictions of the competitive and synergetic effects. Chloro ligands are weaker hydrogen bond acceptor groups than chloride ions.     

A study of the Raman spectra of alkanes in the Fermi-resonance region

The experimental and theoretically predicted Raman spectra for the first few alkanes in the homologous series: methane, ethane, propane and butane are presented for the region 2700–3100 cm⁻¹. The structure of the spectra is rather complex. Analysis of the results obtained shows that Fermi resonance occurs between the CH stretching vibrations in the 3000 cm⁻¹ region and the 2ν overtones of deformation vibrations in the low frequency (1450–1500 cm⁻¹) region.     

Infrared band-shape analysis and hydrogen-bonding dynamics of the HCOOH low-temperature crystal

The infrared OH-stretching band shape of crystalline formic acid (HCOOH) at low temperature is analyzed on the ground of a recent theory involving a semiclassical approximation for the evolution operator. The adiabatic potential function for the slow OO stretching mode (N coordinate) is computed from the observed spectrum for the excited state of the fast ν_OH vibration (n coordinate) and is compared with that derived from a time-independent approach. Both theories are consistent with Morse-type potentials and a large shortening of the hydrogen bond in the excited state. The dipole moment operator appears to be N independent. An additional coupling between n and an external OO bending coordinate of the hydrogen bond which manifests itself as a Franck—Condon progression of the ν_OH mode is introduced to account for the observed band manifold. The structure and the dynamics of formic acid in the ground and upper states of the ν_OH vibration are discussed and compared with those previously obtained for similar moderately strong hydrogen-bonded systems.     

The dehydroxylation of basic aluminum sulfate: An infrared emission spectroscopic study

The tridecameric aluminum polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ was prepared by forced hydrolysis of Al³⁺ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate, the tridecamer crystallized as the monoclinic basic aluminum sulfate Na_0.1[AlO₄Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)_3.55. The dehydroxylation of the basic aluminum sulfate has been studied by Fourier transform in-situ infrared emission spectroscopy over a temperature range of 200° to 750°C at 50°C intervals. The spectrum is characterized by the sulfate ν₁ (1024 cm⁻¹), ν₃ doublet (1117 and 1168 cm⁻¹) and the ν₄ doublet (568 and 611 cm⁻¹) modes. Furthermore, minor bands assigned to nitrate are observed. Upon heating from ≈350° to 400°C major changes are observed, especially in the bandwidth and band intensities. The bands in the hydroxyl stretching region due to the Al₁₃ group disappear, whereas the bands around 1050 cm⁻¹ display various changes in bandwidths, intensities and positions associated with the dehydration and dehydroxylation of the basic sulfate and the changing of the structure into an aluminum oxosulfate. The nitrate bands diminish upon heating.     

Theoretical modeling of infrared spectra of benzoic acid and its deuterated derivative

Theoretical simulation of the ν_s stretching band is presented for benzoic acid and its OD derivative at 300 K. The simulation takes into account an adiabatic coupling between the high-frequency O–H(D) stretching and the low-frequency intermolecular OO stretching modes, linear and quadratic distortions of the potential energy for the low-frequency vibrations in the excited state of the O–H(D) stretching vibration, resonance interaction between the two hydrogen bonds in the dimer, and Fermi resonance between the fundamental ν OH(D) stretching and the overtone of the δ O–H(D) bending vibrations.

Infrared, far-infarared, Raman and low-frequency Raman spectra of the polycrystalline benzoic acid and its deuterated form have been measured. The geometry and experimental frequencies are compared with the results of our B3LYP/6-311++G** and B3LYP/cc-pVTZ calculations.     

Substantial velocity dependence of rotationally inelastic collision cross sections in Li2—Xe

A Doppler-based velocity selection technique has been used to measure the relative velocity dependence of the cross sections σ_ji,Δ(ν_r) for rotationally inelastic collisions from level j_i to j_i + Δν₁ = 8,22,42) in ⁷Li^*₂ A ¹Σ⁺_u)—Xe. The σ_jν^±2(ν_r) are strongly attenuated at a smaller ν_r by “torque averaging” due to molecular rotation; in contrast, for large |Δ|, σ_jiΔ = ν_r⁻ⁿ (1 n 2). An empirical intermolecular potential which reproduces these types of behavior for 3-D classical trajectories is exhibited.