Raman and FTIR spectra of [Cu(H2O)6](BrO3)2 and [Al(H2O)6](BrO3)3 x 3H2O

Raman and FTIR spectra of [Cu(H2O)6](BrO3)2 and [Al(H2O)6](BrO3)3 x 3H2O are recorded and analyzed. The observed bands are assigned on the basis of BrO3- and H2O vibrations. Additional bands obtained in the region of v3 and v1 modes in [Cu(H2O)6](BrO3)2 are due to the lifting of degeneracy of v3 modes, since the BrO3- ion occupies a site of lower symmetry. The appearance v1 mode of BrO3- anion at a lower wavenumber (771 cm(-1)) is attributed to the attachment of hydrogen to the BrO3- anion. The presence of three inequivalent bromate groups in the [Al(H2O)6](BrO3)3 x 3H2O structure is confirmed. The lifting of degeneracy of v4 mode indicates that the symmetry of BrO3- anion is lowered in the above crystal from C3v to C1. The appearance of additional bands in the stretching and bonding mode regions of water indicates the presence of hydrogen bonds of different strengths in both the crystals. Temperature dependent Raman spectra of single crystal [Cu(H2O)6](BrO3)2 are recorded in the range 77-523 K for various temperatures. A small structural rearrangement takes place in BrO3- ion in the crystal at 391 K. Hydrogen bounds in the crystal are rearranging themselves leading to the loss of one water molecule at 485 K. This is preceded by the reorientation of BrO3- ions causing a phase transition at 447 K. Changes in intensities and wavenumbers of the bands and the narrowing down of the bands at 77 K are attributed to the settling down of protons into ordered positions in the crystal.     

Infrared and polarized Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O

FTIR and single crystal Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O have been recorded at 300 and 90 K and analysed. The shifting of nu1 mode to higher wavenumber and its appearance in Bg species contributing to the alpha(xz) and alpha(yz) polarizability tensor components indicate the distortion of SO4 tetrahedra. The presence of nu1 and nu2 modes in the IR spectrum and the lifting of degeneracies of nu2, nu3, and nu4 modes are attributed to the lowering of the symmetry of the SO4(2-) ion. Coincidence of the IR and Raman bands for different modes suggest that DMA+ ion is orientationally disordered. One of the H atoms of the NH2 group of the DMA+ ion forms moderate hydrogen bonds with the SO4(2-) anion. Al(H2O)6(3+) ion is also distorted in the crystal. The shifting of the stretching modes to lower wavenumbers and the bending mode to higher wavenumber suggest that H2O molecules form strong hydrogen bonds with SO4(2-) anion. The intensity enhancement and the narrowing of nu1SO4, deltaC2N and Al(H2O)6(3+) modes at 90 K confirm the settling down of the protons in the hydrogen bonds formed with H2O molecules and NH2 groups. This may be one of the reasons for the phase transition observed in the crystal.     

The infrared and Raman spectra of trans- and cis-tetrachloro-tetramethylbicyclopropylidene

The title compounds trans- and cis-2,2,2',2'-tetrachloro-3,3,3',3'-tetramethyl-bicyclopopylidene were synthesized, and their infrared and Raman spectra were recorded. Non-coincidence between the IR and Raman bands of the trans compound suggested C(2h) symmetry and a planar ring system. In the cis compound most of the IR and Raman bands coincided and a C(2v) symmetry seems likely. The exocyclic CC double bond gave rise to a medium/weak Raman band at 1,847 cm(-1) in the trans compound. In the cis derivative IR and Raman bands both at 1,825 cm(-1) were observed. From similarities with related molecules, the ring breathing, the antisymmetric ring stretch, the CCl(2) out-of-phase and in-phase stretch and the out-of-plane ring bending modes have been tentatively assigned for the trans and cis compounds.     

Effects of hydrogen bonding on the ring stretching modes of pyridine

The effects of hydrogen bonding on the ring stretching modes (both ring breathing and triangle) of pyridine are experimentally investigated using noisy light based coherent Raman scattering spectroscopy. Three systems, pyridine/formamide, pyridine/water, and pyridine/acetic acid, provide varying degrees of strength for the diluent-pyridine hydrogen bond complex. Formamide forms a relatively weaker hydrogen bond, while acetic acid essentially fully transfers a proton to pyridine. Both dilution studies and temperature studies are performed on the three systems. Together, these provide a broad context in which a very simple model for the electronic behavior of pyridine is formulated. This model is based on a molecular orbital picture and electrostatic arguments, and it well explains the observed experimental results. Additionally, a new mechanism for the line broadening of the ring breathing mode for the pyridine-water hydrogen bonded complex is proposed.     

Raman spectra of 3-methyl-4-nitropyridine-N-oxide single crystal

A Raman study of 3-methyl-4-nitropyridine-N-oxide single crystal (3M4NPO) has been performed at 78 K in the range 10–3500 cm⁻¹. The symmetry analysis of the vibrational modes of 3M4NPO is given. The assignments are presented for internal and external modes. The results of the Raman spectra exhibit the spectroscopic proofs of hydrogen bonds in the crystal.     

Vibrational studies of biomolecules. I. 2-Thiouracil

IR, far-IR and Raman spectra of 2-thiouracil are reported and interpreted. All the thirty normal modes could be assigned. The Raman spectrum and the vibrational assignments for all the thirty modes are reported for the first time. The ring breathing and Kekule stretching modes for 2-thiouracil are observed to have lower magnitudes when compared to those for uracil which could be due to the mass effect of the sulphur atom in place of the oxygen atom.     

Vibrational spectra and infrared dichroism of tetraphenyl-silane,Ph4Si. II.

Vibrational spectra of Ph₄Si have been studied from 600 to 20 cm^?1 in solution, in the melt and in the crystalline state. The assignments proposed for the substituent sensitive benzene ring vibrations, for the skeletal bending modes and ring librations have been supported by polarized IR and Raman measurements. The crystal spectra are interpreted on the basis of the S₄ site symmetry of the molecules in the crystal. Two skeletal bending and four ring librational modes are supposed to appear below 120 cm^?1, in the range of the lattice vibrations.     

Vibrational analysis of Ag3(PO2NH)3, Na3(PO2NH)3 x H2O, Na3(PO2NH)3 x 4H2O,

FT IR and FT Raman spectra of Ag3(PO2NH), (Compound 1), Na3(PO2NH)3 x H2O (Compound II), Na3(PO2NH)3 x 4H2O (Compound III), [C(NH2)3]3(PO2NH)3 x H2O (Compound IV) and (NH4)4(PO2NH)4 x 4H2O (Compound V) are recorded and analyzed on the basis of the anions, cations and water molecules present in each of them. The PO2NH- anion ring in compound I is distorted due to the influence of Ag+ cation. Wide variation in the hydrogen bond lengths in compound III is indicated by the splitting of the v2 and v3 modes of vibration of water molecules. The NH4 ion in compound V occupies lower site symmetry and exhibits hindered rotation in the lattice. The correlations between the symmetric and asymmetric stretching vibrations of P-N-P bridge and the P-N-P bond angle have also been discussed.     

Infrared and laser Raman studies of bis(L-threoninium) sulphate monohydrate

The infrared and Raman spectra of bis(L-threoninium) sulphate monohydrate crystal have been recorded and analysed at room temperature. The proposed assignment of normal modes is based on group theoretical analysis. There is extensive intermolecular hydrogen bonding in the crystal and this is responsible for the changes in the position and intensity of several bands. The anion fundamentals continue to be degenerated which indicates that its symmetry is unaffected in the molecule.     

Structures of N—（2,3,4,6—Tetra—O—acetyl—β—D—glycosyl） thiocarbamic Benzoyl Hydrazine

The crystal structure of N-(2,3,4,6-tetra-O-acetyl-β-D-gly-cosyl)-thiocarbamic benzoyl hydrazine(C22H27N3O9S) was determined by X-ray diffracton method.The hexopyranosyl ring adopts a chair conformation.All the ring substituents are in the equatorial positions.The acetoxyl-methyl group is in synclinal conformation.The S atom is in synperiplanar conformation while the benzoyl hydrazine moiety is anti-periplanar.The thiocarbamic moiety is almost companar with the benzoyl hydrazine group.There are two intramolecular hydrogen bonds and one intermolecular hydrogen bond for each molecule in the crystal structure.The molecules form a network structure through intermolecular hydrogen bonds.     

Ion-pair interaction in pyridinium carboxylate solutions

Ion-pair interactions between pyridinium cations and various carboxylate anions are explored using noisy light based coherent anti-Stokes Raman scattering (I(2)CARS). Binary mixtures of pyridine and various carboxylic acids (including halo-acetic acids, straight-chain carboxylic acids, and pivalic acid) are prepared. A Br?nsted type acid-base reaction occurs in these mixtures to create pyridinium and carboxylate ions. Both pyridine, itself, and pyridinium have strong I(2)CARS signals originating from their ring breathing modes. The vibrational frequency of the ring breathing mode for pyridine is blue-shifted by hydrogen bonding, and that same mode for pyridinium is red-shifted by ion-pair interaction. Frequency shift data for the ring breathing mode of pyridine and pyridinium are presented. These data are discussed in terms of a simplistic model for the electronic behavior of these compounds.     

(5Z)‐4‐Amino‐2‐(4‐hydroxyphenyl)‐1H‐imidazol‐5(2H)‐one oxime 3‐oxide

The title molecule, C₉H₁₀N₄O₃, consists of benzene and imidazole rings which are almost perpendicular to each other. A hydroxyimino group is directly linked to the imidazole ring with a double C=N bond, which is the first example in this type of compound. The double bond may be a good location for the initiation of various reactions with a wide range of potential applications. In the crystal structure, there are π–π interactions between molecules related by a centre of symmetry, with the imidazole and benzene rings almost completely overlapped. The molecules are hydrogen bonded in each direction and form a three‐dimensional hydrogen‐bond network.     

The squaric acid aggregate in mordenite investigated by Raman spectroscopy

A more detailed investigation of the squaric acid aggregate within mordenite was undertaken with the use of Raman spectroscopy. The previous reported investigation was limited to the carbonyl stretching region in the IR. In the present work the entire region from 500 to 2000 cm(-1) was investigated, revealing rather substantial vibrational shifts of the oxocarbon ring modes in the aggregate. Comparison of such shifts with those observed for the squaric acid (H2Sq)/4,4'-bipyridine (Bipy) charge transfer (CT) complex reveals that the interaction is much stronger in the aggregate, a clear effect of the restrict geometry. On the other hand, the shifts observed for the CO stretching modes are rather modest. The comparison of the ring modes present in the Raman spectra of squaric acid, potassium hydrogen squarate, potassium squarate, H2Sq/Bipy and squaric acid aggregate in mordenite strongly suggests that in the latter hydrogen bonded species are present.     

Raman spectra of single H2O molecules isolated in cavities of crystals

The vibrational (Raman) spectra of H₂O molecules isolated in cavities of beryl, cordierite, bikitaite, natrolite, scolecite, lawsonite, and hemimorphite have been measured in the temperature range of 4–295 K. The influence of van der Waals and hydrogen bonds on the values of frequency, intensity, and half-width of stretching and bending modes of H₂O is considered. The spectra of translational vibrations of H₂O molecules in crystal cavities are discussed. For the firsts time, the ratio between the frequencies of translation and stretching vibrations of H₂O and the dependence of frequencies of bending vibrations on the angle H-O-H in H₂O molecule are presented.     

Infrared and laser Raman spectral studies of bis(dl-aspartic acid) sulfate

The infrared and Raman spectra of bis(dl-aspartic acid) sulfate in the crystalline state are recorded at room temperature and the vibrational assignments of the observed wavenumbers are made. The presence of two carbonyl (CO) groups has been identified in the title complex and the two carbonyl groups are in different environment. The extensive intermolecular hydrogen bonding in the crystal has been identified by the shifting of bands due to the stretching and bending modes of the various functional groups. The sulfate group forms the anion. Its fundamentals continue to be degenerate except for the asymmetric bending mode and it suggests that the T(d) symmetry of SO(4)(2-) group has not been affected in the crystal.     

Ab-initio molecular geometry and normal coordinate analysis of pyrrolidine molecule.

The molecular geometry of pyrrolidine was quantum mechanically calculated using the split valence 6-31G** basis set. Electron correlation energy has been computed employing MP2 method. The molecule showed an envelope form puckered structure with inter-plane angle of 36.4 degrees and has a total energy of -132976.80 kcal mol(-1) of which a -464.86 kcal mol(-1) electron correlation energy. The twist form of the molecule showed a twist angle of 10.2 degrees from planarity and has a total energy of -132976.05 kcal mol(-1) involving -464.097 kcal mol(-1) electron correlation energy. The normal coordinates of the molecule were theoretically analyzed on the basis of the Cs point symmetry of the envelope form. Using initial set of force constants obtained from the ab-initio calculations the fundamental vibrational frequencies were computed. The IR and laser Raman spectra of Pyrrolidine molecules were measured. All the observed vibrational bands including combination bands and overtones were assigned to normal modes with the aid of the potential energy distribution values obtained from normal coordinate calculations. The molecular force field was obtained by refining the initial set of force constants using the least square fit method. The molecular force field was determined by refining the initial set of force constants using the least square fit method instead of using the less accurate scaling factor methods. The determined molecular force field has produced simulated frequencies best match to the observed values. The low frequency molecular out-of-plane deformation modes were observed in both infrared and Raman spectra at 298 and 163 cm(-1). The barrier of ring twisting estimated from the observed ring out-of-plane vibrational mode at 163 cm(-1) was found 3.1 kcal mol(-1).     

Laser Raman and infrared spectral studies of dl-phenylalaninium nitrate

The vibrational band assignments of dl-phenylalaninium nitrate in the crystalline state are made by recording the infrared and Raman spectra at room temperature. The presence of carbonyl (C=O) group has been identified. The prominent marker bands of the aromatic amino acid phenylalanine have been observed and the various modes of vibration have been assigned. The extensive intermolecular hydrogen bonding in the crystal has been identified by the shifting of bands due to the stretching and bending modes of the various functional groups. The nitrate group forms the anion. The stretching and bending wave numbers of the NO(3)(-) anion are different from those observed for free ion state and the degenerating mode of vibrations is also lifted. These reveal that the crystalline field has influenced the symmetry of the nitrate ion.     

Molecular structure, spectroscopic studies and first-order molecular hyperpolarizabilities of p-amino acetanilide

The infrared absorption, Raman spectra and SERS spectra of p-amino acetanilide have been analyzed with the aid of density functional theory calculations at B3LYP/6-311G(d,p) level. The electric dipole moment (mu) and the first hyperpolarizability (beta) values of the investigated molecule have been computed using ab initio quantum mechanical calculations. The calculation results also show that the synthesized molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. Computed geometries reveal that the PAA molecule is planar, while secondary amide group is twisted with respect to the phenyl ring is found, upon hydrogen bonding. The hyperconjugation of the C=O group with adjacent C-C bond and donor-acceptor interaction associated with the secondary amide have been investigated using computed geometry. The carbonyl stretching band position is found to be influenced by the tendency of phenyl ring to withdraw nitrogen lone pair, intermolecular hydrogen bonding, conjugation and hyperconjugation. The existence of intramolecular C=O...H hydrogen bonded have been investigated by means of the natural bonding orbital (NBO) analysis. The influence of the decrease of N-H and C=O bond orders and increase of C-N bond orders due to donor-acceptor interaction has been identified in the vibrational spectra. The SERS spectral analysis reveals that the large enhancement of in-plane bending, out of plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a 'atleast vertical' configuration, with the ring perpendicular to the silver surface.     

Dimer and superstructure of the active form of a vitamin D3; 1 alpha,24(R)dihydroxy-vitamin D3 monohydrate, C27O3H44.H2O

The crystals of 1alpha24(R)dihydroxy-vitamin D3 monohydrate, C27O3H44.H2O are orthorhombic in the space group P2(1)2(1)2(1) with cell dimensions a=25.719, b=42.572, c=9.851A and Z=16. The asymmetric unit consists of two subunits with b/8, and each subunit contains a dimer in which two molecules are hydrogen-bonded through water molecules into non-crystallographical symmetry of C2. The two-fold axes are the straight lines, x=1/2, z=0.256 and x=1/2, z=0.623. The two dimers are the same in the rigid ring part, but differ in the conformation of the flexible chains. The dimers further make C2 symmetry between the rigid ring parts to form a superstructure, and the two-fold axis of the straight line, y=1/8, z=0.435 goes through a point that is a little apart from the hypercenter (1/2, 1/8, 1/2). The structure was solved by integrated Patterson and direct methods and refined on Fo2 under restraints. The final R1 is 0.228 on Fo for 1623 reflections with Fo>3sigma, resolutions 1.0-3.0 A, 313 restraints, 490 parameters and average Ueq=0.120. Not all the atoms of the chains appeared nor the hydrogen atoms. The missing atoms of the dimer were modeled from another pair molecule by C2 symmetry and hydrogen atoms were added. The structure of the dimer was optimized by ab initio molecular orbital of HF/6-31G.