INS,IR, RAMAN, 1H NMR and DFT investigations on dynamical properties of l-asparagine

Results of inelastic neutron scattering (INS), infra-red (IR), Raman and ¹H NMR spectroscopy used for investigations on the l-asparagine dynamics are reported. The crystallographic structure and experimental vibrational spectra are compared with those calculated by the DFT methods applied to the solid state. Very good conformity of the experimental and theoretical structures has been found. The NH₃⁺ torsional vibration mode is observed in the INS spectra at 494 cm⁻¹, while the bands assigned to the vibrations of the strong NH⋯O hydrogen bonds are observed at 2849, 2650, and 2480 cm⁻¹ in the IR spectrum. A ¹H NMR investigation has been carried out at 26.75 MHz in the temperature range 150–300 K. For l-asparagine the activation energy needed for the NH₃⁺ group reorientation is equal 5.6 kcal/mol.     

Vibrational spectroscopy and DFT calculations of 1,3-dibromo-2,4,6-trimethylbenzene: Anharmonicity,coupling and methyl group tunneling

The Raman, IR and INS spectra of 1,3-dibromo-2,4,6-trimethylbenzene (DBMH) were recorded in the 80–3200 cm⁻¹ range. The molecular conformation and vibrational spectra of DBMH were computed at the MPW1PW91/LANL2DZ level. Except for the methyl 2 environment, the agreement between the DFT calculations and the neutron diffraction structure is almost perfect (deviations < 0.01 Å for bond lengths, <0.2° for angles). The frequencies of the internal modes of vibration were calculated with the harmonic and anharmonic approximations; the later method yields results that are in remarkable agreement with the spectroscopic data, resulting in a confident assignment of the vibrational bands. Thus, no scaling is necessary. The coupling, in phase or anti-phase, of the motions of symmetrical CBr and CMe bonds is highlighted. Our DFT calculations suggest that the torsion of methyl groups 4 and 6 is hindered in deep wells, whereas methyl group 2 is a quasi-free rotor. The failure of the calculations to determine the frequencies of the methyl torsional modes is explained as follows: DFT does not consider the methyl spins and assumes localization of the protons, whereas the methyl groups must be treated as quantum rotors.     

X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine (DMP) chloranilic acid (CLA) complex

The DMP · CLA and DMP · CLA-d₂ crystals below 100 K are monoclinic, space group P2₁/c with four molecules in the unit cells. Infinite chains of hydrogen bonded counterparts are formed with O?N distances equal to 2.767(2) and 2.639(2) for non-deuterated DMP · CLA. Deuteration leads to the Ubbelohlde effect particularly well manifested in the second short O–H?N bridge (elongation by ca. 0.02 Å). In the IR spectra a Had?i’s trio of the broad absorption is observed characteristic of strong hydrogen bonds. In the INS spectra the vibrational density of states and methyl rotational tunnel splittings were determined. The temperature dependence of tunneling bands enabled to make mode assignments and to determine the methyl rotational potentials. Comparison of the results to the pure electron donor DMP was made and the difference found can be almost completely assigned to the steric changes of the environment. A weak isotope effect with deuteration of the OH?N bridges of the DMP · CLA complex is assigned to a charge transfer of δe/e = 0.006.     

Vibrational frequencies of (H2O) n and (D2O) n clusters for n = 2 and 8: possible relevance to inelastic neutron scattering of ice

Hartree-Fock plus MP2 corrections are reported for the vibrational frequencies in (H₂O)₂ and (D₂O)₂ and in the cubic octamers (H₂O)₈ and (D₂O)₈. The motivation was the inelastic incoherent neutron scattering of ice as studied experimentally by Li et al. (J.-C. Li, D. Londono, D.K. Ross, J.L. Finney, S.M. Bennington and A.D. Taylor (1992). J. Phys. Cond. Matter, 4, 2109). Some contact is made between our results and these experiments, and also with earlier infrared and Raman studies of Bertie and coworkers.     

Vibrational spectroscopy of a crystallographically unsettled uranyl carbonate: Structural impact and model

Room-temperature vibrational and photoluminescence (PL) spectra of a natural, rare hydrated calcium copper uranyl carbonate mineral, voglite (Ca₂Cu(UO₂)(CO₃)₄·6H₂O) are recorded and discussed in details. Vibrational spectroscopy gives information about the structure of voglite, which is still missing due to its unknown crystallographic features. By comparison with other uranyl carbonates and sulfates, a strong Raman line occurring at 834 cm⁻¹ is assigned to the ν₁(UO₂)²⁺ symmetric stretching vibration rather than to the ν₂(CO₃)²⁻ out-of-plane bending vibration. The ν₃(UO₂)²⁺ antisymmetric stretching vibration is tentatively identified at 897 cm⁻¹ from infrared (IR) spectroscopy. Several well resolved bands found at 1074,1092, 1381, 1566 cm⁻¹ in the Raman and 1046, 1114, 1145, 1376, 1426, 1510, 1561 cm⁻¹ in the IR are ascribed to symmetric and antisymmetric stretching motions of the carbonate units. The presence of all these intense vibrational bands points to different CO bond lengths. The infrared water band is well structured, suggesting a few different OH moieties in the crystal. Original micro-PL spectra show a manifold of vibronic features whose energy spacing is close to the frequency of the symmetric OUO stretching vibration and confirms the uranium origin of the most intense Raman band. The study suggests that voglite structure has no inversion centers, a low symmetry, and contains molecular units similar to those of the parent phases, andersonite or liebigite, like uranyl tricarbonate clusters (UTC). The existence of these UTCs in voglite is confirmed by density functional theory calculations. A new assignment of all vibrational modes is proposed.     

Synthesis and vibrational study of platinum(II) and palladium(II) complexes of glyoxilic acid oxime

New platinum(II) and palladium(II) complexes of glyoxilic acid oxime (gao) have been prepared and characterised by infrared (4000–150 cm⁻¹) and Raman (4000–200 cm⁻¹) spectra. The gao acts as bidentate ligand bonding through the oxime nitrogen and carboxyl oxygen atoms to form neutral bis-chelate square-planar complexes. The lowest energy conformer of the gao ligand (ectt) was selected among 16 theoretically possible conformers on the basis of ab initio calculations at HF/3-21G*, HF/6-31G* and HF/6-311** levels of the theory from which structural parameters and conformational stabilities have been obtained. A complete vibrational assignment of the gao was performed for the lowest energy ectt conformer on the basis of ab initio optimised parameters and normal coordinate analysis calculations (PED). NCA calculations of the complexes studied were also performed.     

The crystal structure and vibrational spectra of two molecules emitting dual fluorescence: 4-(1H-Pyrrol-1-yl)benzonitrile (PBN) and 5-cyano-2-(1pyrrolyl)-pyridine (CPP)

Crystal structures and vibrational spectra are reported for the two title molecules which exhibit dual fluorescence due to the existence of a low lying charge transfer excited state. The data show that in the ground state PBN is twisted whereas CPP is planar, and the crystal structures are quite different. The experimental spectra are in very good agreement with quantum mechanical calculations, which also predict considerable differences between the vibrational spectra of CPP in the ground state and in the charge transfer excited state.     

Vibrational spectroscopy study of essential oils from Plectranthus amboinicus Lour. Spreng and Vanillosmopsis arborea Baker

Essential oils are aroma compounds extracted from plants with pharmacology and mecial uses, being also utilized as perfumes, cosmetics and for flavoring foods. In this work, Fourier Transform-Raman and Attenuated Total Reflection-infrared spectra of essential oils from Plectranthus amboinicus Lour. Spreng (Labiateae) and Vanillosmopsis arborea Baker (Asteraceae) were investigated at room temperature. The analysis of the vibrational spectra of the major constituents performed on the basis of density functional theory (DFT) calculations allowed us to assign the normal modes of these essential oils. Our analyses show that vibrational spectra of these essential oils in the spectral region of lower wavenumber (<1500 cm⁻¹) present bands with characteristic profile of their main chemical constituents. Additionally, this study also shows that compounds which participated in an essential oil composition in relatively low percentage can have a significant influence on the Raman and infrared spectra of these essential oils, in particular in the high wavenumber spectral region.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.     

DFT and Raman spectroscopy of porphyrin derivatives: Tetraphenylporphine (TPP)

Raman spectrum of the meso tetraphenylporphine (TPP) deposited onto smooth copper surface as thin film were recorded in the region 200–1700 cm⁻¹. To investigate the effect of meso-phenyl substitution rings on the vibrational spectrum of free base porphyrin, we calculated Raman and infrared (IR) spectra of the meso-tetraphenylporphine (TPP), meso tetramethylporphine (TMP), copper (II)porphine (CuPr) and free base porphine (FBP) at the B3LYP/6-311+G(d,p) level of the density functional theory (DFT). The observed Raman spectrum of the TPP is assigned based on the calculated its Raman spectrum in connection with the calculated spectra of the TMP, CuPr and FBP by taking into account of their corresponding vibrational motions of the Raman modes of frequencies. Results of the calculations clearly indicated that the meso tetraphenyl substitution rings are totally responsible for the observed Raman bands at ∼1593, 1234 and 1002 cm⁻¹. The calculated and observed Raman spectra also suggested that the observed Raman band with a medium intense at 962 cm⁻¹ might result from the surface plasmon effect. Furthermore, the observed Raman bands with medium intense at ∼334 and ∼201 cm⁻¹ are as results of the dimerization or aggregation of the TPP or would be that related to intramolecular interaction. We also calculated IR spectra of these molecules at same level of the theory. To investigate the solvent effect on the vibrational spectrum of porphine, the Raman and IR spectra of the TPP and FBP are calculated in solution phase where water used as solvent. The results of these calculation indicated that there is no any significant effect on the vibrational spectrum of the TPP.     

Impact of molecular structure of smectogenic chiral esters (3FmX1X2r) on vibrational dynamics as seen by IR and Raman spectroscopy

Smectogenic chiral esters with three-ring rigid core were examined by infrared and Raman spectroscopy. These compounds differ in the type of chiral centre, length of non-chiral chain and substitution of phenyl ring by fluorine atoms. The influence of molecular structure on the type of handedness of helical structure, as well as the shift and split of absorption bands on IR and Raman spectra were determined. The change of the length of non-chiral terminal chain has the most significant influence on the type of helical twist sense. All considered structural elements of tested compounds have the biggest influence on the value of wavelength of vibrational bands related to the carbonyl group located in the rigid core.     

Computationally-assisted approach to the vibrational spectra of molecular crystals: study of hydrogen-bonding and pseudo-polymorphism.

A new computationally-assisted methodology (PiMM), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suitable molecular pairs, using the B3LYP/6-31G* approach.The proposed methodology provides an answer to the current demand for a reliable assignment of the vibrational spectra of these methyl-xanthines, and clarifies several misleading assignments. The most relevant intermolecular interactions in each system and their effect on the vibrational spectra are considered and discussed. Based on these results, significant insights are obtained for the structure of caffeine in the anhydrous form (stable at room temperature), for which no X-ray structure has been reported. A possible structure based on C((8))--H...N((9)) and C((1,3))--H...O intermolecular interactions is suggested.     

An experimental and theoretical study of molecular structure and vibrational spectra of 2-chloronicotinic acid by density functional theory and ab initio Hartree–Fock calculations

In this work, the Fourier transform Raman and Fourier transform infrared spectra of 2-chloronicotinic acid (2-CNA) are recorded in the solid phase. The molecular geometry, vibrational frequencies, infrared intensities and Raman scattering activities of 2-CNA in ground state have been calculated by using ab initio Hartree–Fock (HF) and density functional (B3LYP and B3PW91) methods with 6-31G(d) and 6-311G(d) basis sets level. On the basis of the comparison between calculated and experimental results and the comparison with related molecule, assignments of fundamental vibrational modes are examined. The optimized geometric parameters (bond lengths and bond angles) obtained by using HF show the best agreement with the experimental values of 2-CNA. Comparison of the observed fundamental vibrational frequencies of 2-CNA and calculated results by density functional (B3LYP and B3PW91) and Hartree–Fock methods indicates that B3LYP is superior to the scaled Hartree–Fock and B3PW91 approach for molecular vibrational problems.     

Synthesis and vibrational spectroscopic characterisation of nickel containing aurichalcite

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise a synthetic nickel substituted aurichalcite a zinc/nickel hydroxy carbonate, (Zn²⁺, Cu²⁺, Ni²⁺)₅(CO₃)₂(OH)₆. XRD patterns show high orientation and indicate the presence of some minor impurities. The diffraction patterns for the Ni-aurichalcite are well correlated with the standard reference patterns. EDAX analyses indicate variations in chemical composition of Zn/Ni ratios of ∼20:1. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band for the Ni-aurichalcite at 1070 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for Ni-aurichalcite at 1372, 1480 and 1543 cm⁻¹. Multiple Raman bands are observed in the regions from 800 to 850 cm⁻¹ and 720 to 750 cm⁻¹, and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. This research proves that nickel containing aurichalcites can be synthesised in the laboratory thus mimicing the natural nickel containing aurichalcites.     

Inelastic neutron scattering and vibrational spectra of 2-(N-methyl-α-iminoethyl)-phenol and 2-(N-methyliminoethyl)-phenol: Experimental and theoretical approach

The infrared, Raman, and inelastic neutron scattering (INS) spectra of two ortho-hydroxy aryl Schiff’s bases, 2-(N-methyliminoethyl)-phenol and 2-(N-methyl-α-iminoethyl)-phenol, were recorded. Ab initio molecular orbital calculations employing the DFT (B3LYP) method with the 6-31G** basis set for both compounds were done. Assignments of vibrational modes within the 3500–50 cm⁻¹ spectral region were carried out. On the basis of the DFT calculations, four rotomers of 2-(N-methyl-α-iminoethyl)-phenol were analysed.     

A spectroscopic and ab initio study on Bi(III) complex formation with 3-mercaptopropanesulfonic acid

This article deals with complex formation of Bi(III) with 3-mercaptopropanesulfonic acid (H₂MPS) in aqueous perchloric acid solutions, with synthesis and characterization of a solid 3-mercaptopropanesulfonate complex of bismuth(III). The stoichiometry and structures of Bi-MPS species in aqueous solution and of a solid complex have been studied by UV–Vis, ¹H-NMR, ICP-AES, Raman, and EXAFS spectroscopic methods; the structures have also been simulated with DFT/PBE0 calculations. The Bi(III) L_III-edge EXAFS oscillation for a solid compound with the empirical formula [Bi(HMPS)₂(ClO₄)]⁰ was simulated with two Bi–S interatomic distances at 2.50 ± 0.01 Å, two Bi–O distances at 2.56 ± 0.02 Å and two Bi–O distances at 2.75 ± 0.02 Å. Implementation of the same approach for aqueous solutions on the assumption of S₃BiO₃ coordination at the H₂MPS?:?Bi(III) mole ratio ≥ 3.0 revealed three Bi–S bonds at 2.53 ± 0.02 Å and three Bi–O bonds at 2.68 ± 0.02 Å, respectively. Optimized geometries, electronic structures of Bi(HMPS)₃ and [Bi(HMPS)₂ClO₄]⁰, vibrational properties of [Bi(HMPS)₂ClO₄]⁰, and electronic absorption spectrum of Bi(HMPS)₃ species obtained by DFT and TD–DFT modeling are consistent with empirical parameters. In the UV–Vis spectrum of Bi(HMPS)₃ the LMCT and MLCT S^2? ? Bi³⁺ band appears at 268 nm.     

Structure and vibrational spectra of the bis(betaine)-selenic acid molecular crystal

The crystal structure of bis(betaine)-selenic acid has been determined by X-ray diffraction as orthorhombic, space group Pbca, with a = 11.591(2), b = 22.930(5), c = 12.045(2) Å and Z = 8. The crystal comprises hydrogen selenate ions, HSeO⁻₄, and two distinct betaine molecules, which are held together into a complex by short hydrogen bonds. One of the betaine molecules is present as the zwitterion form (CH₃)₃N⁺---CH₂---COO⁻ and the second occurs as the protonated form (CH₃)₃N⁺---CH₂---COOH. Powder FTIR and Raman spectra were measured. An assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the hydrogen selenate ion and the betaine molecules is proposed.     

Frequency-domain Fourier-transform terahertz spectroscopy of the single-molecule magnet (NEt4)[Mn2(5-Brsalen)2(MeOH)2Cr(CN)6

We have investigated the novel single-molecule magnet (NEt(4))[Mn(2)(5-Brsalen)(2)(MeOH)(2)Cr(CN)(6)] (1; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylidene)iminato anion) using spectroscopic as well as magnetization and susceptibility measurements. Frequency-domain Fourier-transform terahertz electron paramagnetic resonance (FDFT THz-EPR) based on the generation of THz radiation from a synchrotron in combination with inelastic neutron scattering (INS) allows for the discrimination between intermultiplet and intramultiplet transitions. Together with ac/dc magnetic susceptibility measurements the obtained set of data provides a complete characterization of the lowest energetic magnetic excitations. We find that the new compound 1 exhibits much weaker intermolecular interactions than found in the closely related compound: K[Mn(2)(5-Brsalen)(2)(H(2)O)(2)Cr(CN)(6)] (2). Furthermore, two phonon lines in the vicinity of the magnetic excitations are detected.