Molecular structure of phthalocyaninato lanthanide LnPc(OAc) complexes derived from the FTIR and FT Raman studies

Room temperature Fourier transform IR and Raman spectra in the range 30–4000 cm⁻¹ and 80–4000 cm⁻¹ of Dy, Ho, Er and Lu phthalocyanide PcLn(OAc)-type complexes have been measured, respectively. The assignment of the bands observed has been made on the literature data. The molecular structure of the PcLnX-type derivatives has been discussed on the basis of the group theory taking into account the shape and number of the bands corresponding to the stretching and bending vibrations of the LnN₄O coordination polyhedron as well as whole PcLn(OAc) complex.     

Vibrational spectroscopy of the sorosilicate mineral hemimorphite Zn4(OH)2Si2O7 · H2O

Raman spectroscopy complimented by infrared spectroscopy has been used to study the mineral hemimorphite from different origins. The Raman spectra show consistently similar spectra with only one sample showing additional bands due to the presence of smithsonite. Raman bands observed at 3510–3565 and 3436–3455 cm⁻¹ are assigned to OH stretching vibrations. Using a Libowitzky type formula, these OH bands provide hydrogen bond distances of 0.2910, 0.2825, 0.2762 and 0.2716 pm. Water bending modes are observed in the Raman spectrum at 1633 cm⁻¹. An intense Raman band at 930 cm⁻¹ is attributed to SiO symmetric stretching vibration of the Si₂O₇ units. Raman bands observed at 451 and 400 cm⁻¹are attributed to out-of-plane bending vibrations of the Si₂O₇ units. Raman bands at 330, 280, 168 and 132 cm⁻¹ are assigned to ZnO and OZnO vibrations.     

Spectroscopy of selected copper group minerals: ktenasite,orthoserpierite and kipushite

Near-infrared (NIR) and IR spectroscopy have been applied for the characterisation of three complex Cu–Zn sulphate/phosphate minerals, namely ktenasite, orthoserpierite and kipushite. The spectral signatures of the three minerals are quite distinct in relation to their composition and structure. The effect of structural cation substitution (Zn²⁺ and Cu²⁺) on band shifts is significant both in the electronic and in the vibrational spectra of these Cu–Zn minerals. The variable Cu:Zn ratio between Zn-rich and Cu-rich compositions shows a strong effect on Cu(II) bands in the electronic spectra. The Cu(II) spectrum is most significant in kipushite (Cu-rich) with bands displayed at high wavenumbers, 11,390 and 7,545 cm⁻¹. The isomorphic substitution of Cu²⁺ for Zn²⁺ is reflected in the NIR and IR spectroscopic signatures. The multiple bands for ν₃ and ν₄ (SO₄)²⁻ stretching vibrations in ktenasite and orthoserpierite are attributed to the reduction in symmetry of the sulphate ion from T_d to C_2V. The IR spectrum of kipushite is characterised by strong (PO₄)³⁻ vibrational modes at 1,090 and 990 cm⁻¹. The range of IR absorption is higher in ktenasite than in kipushite, while it is intermediate in orthoserpierite.     

Vibrational study of rotational isomerism in dialkyldichlorosilanes Cl2SiR2 (R=Bun, Hexn)

IR and Raman spectra of Cl₂SiR₂ (R=Hexⁿ (1), Buⁿ (2)) in liquid, glassy, and polycrystalline states were investigated. In the liquid and glassy states, rotational isomerism about the Si−C and C−C bonds takes place, the compounds being mixtures of conformers. In the crystalline state, only one, the most stable conformer (all-trans in relation to the C−C bonds), persists. Compound2, in contrast to1, was found to crystallize on cooling with great difficulty. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 315–319, February, 1997.     

Phase transitions,conformational lability,and intermolecular interactions in alkoxycyanobiphenyls

Vibrational spectroscopy methods (IR absorption, Raman scattering, calculations) were used to study changes in molecular structures of alkoxycyanobiphenyls during phase transitions. The spectra were measured in the 33–3500 cm⁻¹ region at temperatures of 100–450 K. The temperature dependences of the IR bands that correspond to the noncharacteristic vibrations of molecular fragments between the phenyl rings and the alkyl radicals point to the conformational polymorphism of these molecules. An analysis of the Raman bands corresponding to the characteristic vibrations of the C−H bonds of alkyl radicals [q(CH)], the C−H and C−C bonds of phenyl rings [q(CH) and Q(CC)], and the CN bonds of the cyano groups [Q(CN)] suggests significant intermolecular interactions. The conformational lability and intermolecular interactions are associated with differences in molecular packing in the substances of this homologous series. Saratov State University. Institute of Solid State Physics, Rostov State University. Institute of Physics, Uzbekistan Academy of Sciences. Samarkand State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 5, pp. 814–822, September–October, 1995. Translated by I. Izvekova     

Infrared spectra of diphenylphthalide and polydiphenylenephthalide

The splitting of the ν(C=O) absorption band (AB) of about 12 cm⁻¹ is found in the IR spectra of diphenylphthalide (DPP) in the crystalline phase and CCl₄ solution. In the crystalline phase, this splitting is likely to be caused by the inequivalence of DPP molecules in the crystallographic cell, while in the solution, by the dimerization of DPP molecules via dipole-dipole and/or hydrogen bonds. A theoretical low-frequency shift of the ν(C=O) AB for a complex of two DPP molecules (in comparison with a single molecule) is 14 cm⁻¹ in the PBE/3ξ approximation, which is close to the experimentally observed splitting. In two quantum chemical approximations (B3LYP/6-311G(d,p) (I) and PBE/3ξ (II)) the optimal structure and vibrational spectrum of DPP are calculated. Approximation I better reproduces the intensities, whereas approximation II better reproduces the IR frequencies of the DPP spectrum. Almost all 48 ABs of the IR spectrum of DPP are assigned to theoretical normal vibrations (modes). Based on the potential energy distribution over natural coordinates and the visualization of vibrations, experimental ABs (and the corresponding modes) are assigned to the stretching and bending vibrations of certain bonds in the DPP molecule. In particular, ABs at 1107 cm⁻¹ and 970 cm⁻¹ are assigned to the ν(-OC-O-) and ν(-C-O-) stretching vibrations, respectively, of the DPP lactonic ring, which differs from the previously accepted assignment. The results of the interpretation of the DPP spectrum are used to assign a number of ABs in the IR spectrum of polydiphenylenephthalide (PDP), for which DPP is a model compound. According to the calculations in approximation II of the vibrational spectrum of a model valence-bonded dimeric molecule, the intense complex AB at 800–870 cm⁻¹ in the IR spectrum of PDP is mainly due to the out-of-plane bending vibrations of C-H bonds in the 1,4-substituted benzene rings of polymer biphenyl moieties and the bending vibrations of the lactonic ring.     

Argon-matrix-isolation Raman spectra and density functional study of 1,3-butadiene conformers

s-trans, s-cis and gauche conformers of 1,3-butadiene have been studied using density functional theory and the coupled-cluster method using double substitutions (CCD). Matrix isolation Raman and IR data for the minor conformer were obtained and are used in combination with the theoretical results to resolve earlier ambiguities in vibrational assignments. Based on high-quality Hessians, new harmonic stretching force constants are reported for the carbon backbone of s-trans-1,3-butadiene. For the minor conformer the best unscaled root mean square error of the calculated frequencies for the s-cis and gauche geometries are 17.5 cm⁻¹ and 7.4 cm⁻¹, respectively, primarily due to a better agreement of the gauche results for the vibrations at 983 cm⁻¹, 596 cm⁻¹ and 470 cm⁻¹ which depend strongly on the torsional angle. Although this points towards the gauche form rather than the s-cis form, the calculated transition dipole moment directions at the CCD/6-311G(d,p) level confirm the earlier conclusion that the minor conformer has C _{2 v} symmetry in the matrix. It is concluded that either the better agreement between the frequencies calculated for the gauche form and the observed values is coincidental, or that the molecule is indeed nonplanar in the matrix and tunnels very rapidly between the two mirror-image forms (or its lowest vibrational level lies above the barrier). Received: 1 July 1998 / Accepted: 26 October 1998 / Published online: 15 February 1999     

Intramolecular donor-acceptor interaction in stilbene and styrene π-complexes with tricarbonylchromium. Observation in the IR spectra

The IR spectra of complexes derived from conjugated arylalkenes and tricarbonylchromium, namely (stilbene)tricarbonylchromium and (styrene)tricarbonylchromium, displayed three absorption bands instead of two expected in the region of carbonyl stretching vibrations (1800–2000 cm⁻¹). Additional absorption bands also appeared in the region corresponding to metal-π-fragment stretching vibrations (250–400 cm⁻¹). These findings indicated additional interaction involving the central metal atom, carbonyl ligands, and aromatic π-system. Such interaction increases mobility of the tricarbonylchromium fragment which may become capable of readily migrating from one π-fragment to another under certain conditions.     

A Raman spectroscopic study of the mono-hydrogen phosphate mineral dorfmanite Na2(PO3OH)·2H2O and in comparison with brushite

Aspects of the molecular structure of the mineral dorfmanite Na₂(PO₃OH)·2H₂O were determined by Raman spectroscopy. The mineral originated from the Kedykverpakhk Mt., Lovozero, Kola Peninsula, Russia. Raman bands are assigned to the hydrogen phosphate units. The intense Raman band at 949 cm⁻¹ and the less intense band at 866 cm⁻¹ are assigned to the PO₃ and POH stretching vibrations. Bands at 991, 1066 and 1141 cm⁻¹ are assigned to the ν₃ antisymmetric stretching modes. Raman bands at 393, 413 and 448 cm⁻¹ and 514, 541 and 570 cm⁻¹ are attributed to the ν₂ and ν₄ bending modes of the HPO₄ units, respectively. Raman bands at 3373, 3443 and 3492 cm⁻¹ are assigned to water stretching vibrations. POH stretching vibrations are identified by bands at 2904, 3080 and 3134 cm⁻¹. Raman spectroscopy has proven very useful for the study of the structure of the mineral dorfmanite.     

Thermogravimetric analysis and hot-stage Raman spectroscopy of cubic indium hydroxide

The transition of cubic indium hydroxide to cubic indium oxide has been studied by thermogravimetric analysis complimented with hot-stage Raman spectroscopy. Thermal analysis shows the transition of In(OH)₃ to In₂O₃ occurs at 219 °C. The structure and morphology of In(OH)₃ synthesised using a soft chemical route at low temperatures was confirmed by X-ray diffraction and scanning electron microscopy. A topotactical relationship exists between the micro/nano-cubes of In(OH)₃ and In₂O₃. The Raman spectrum of In(OH)₃ is characterised by an intense sharp band at 309 cm⁻¹ attributed to ν₁ In–O symmetric stretching mode, bands at 1137 and 1155 cm⁻¹ attributed to In-OH δ deformation modes, bands at 3083, 3215, 3123 and 3262 cm⁻¹ assigned to the OH stretching vibrations. Upon thermal treatment of In(OH)₃, new Raman bands are observed at 125, 295, 488 and 615 cm⁻¹ attributed to In₂O₃. Changes in the structure of In(OH)₃ with thermal treatment is readily followed by hot-stage Raman spectroscopy.     

Raman Combinations and Stretching Overtones from Water, Heavy Water, and NaCl in Water at Shifts to ca. 7000 cm−1

Photographic Raman spectra were obtained at shifts to ca. 7000 cm^–1 for pure water and for a saturated aqueous solution of NaCl using argon ion laser excitation. Raman spectra were also obtained photoelectrically for H₂O and D₂O between ca. 2500 and ca. 7000 cm^–1 using 248-nm excimer laser excitation and boxcar detection. Overtone and combination assignments are presented for H₂O and D₂O. The first IR OH-stretching overtone from water occurs 215 cm^–1 above the first Raman OH-stretching overtone because the IR overtones are dominated by asymmetric stretching. The second OH-stretching Raman overtone from water is estimated to occur near 10,020 ± 20 cm^–1, with 9950 cm^–1 as a lower limit.     

MIR and NIR spectroscopy of sol–gel hydrotalcites with various trivalent cations

Three different hydrotalcites were synthesized from magnesium ethoxide, and aluminium, gallium and indium acetylacetonate, using the sol–gel technique. The colloid suspensions initially obtained were gelled and separated by centrifugation. XRD diffraction patterns confirmed that all solids thus obtained possessed a hydrotalcite structure. The resulting hydrotalcites were characterized by mid-infrared (MIR) and near-infrared (NIR) spectroscopies. The two types of spectra were found not to depend on the synthetic medium or trivalent metal used and were thus quite similar. The MIR spectra for the three solids included a strong band at 3500–3000 cm⁻¹ due to stretching vibrations of the different types of O–H groups in them. The signal at about 1370 cm⁻¹ observed for all solids indicates that the sole interlayer anion present was carbonate. The NIR spectra exhibited the bands for the first and second overtone of the O–H stretching vibration in addition to various combination bands.     

Investigation of selective molecular interactions using two-dimensional Fourier transform IR spectroscopy

A novel method of studying molecular interactions is introduced. It is a method based on the framework of a two-dimensional (2D) infrared (IR) correlation spectroscopy technique with a new data pretreatment strategy. In this method, an additional external perturbation stimulates the system to cause some selective changes in the state, order, and surroundings of system constituents. The overall response of the stimulated system to the applied external perturbation leads to distinctive changes in the measured spectrum, and a series of perturbation-induced dynamic spectra are collected in a systematic manner. Such a set of dynamic spectra are then transformed into a set of 2D correlation spectra by cross-correlation analysis. Temperature was chosen as an external perturbation, and the molecular interaction between 4-aminopyridine (Apy) and methacrylic acid (MAA) was investigated by 2D IR correlation spectroscopy. Synchronous cross peaks exist between the stretching vibration of the C–O group of MAA at 1,298 and 1,202 cm⁻¹ and the C=N group of Apy at 1,531 cm⁻¹, and between the carbonyl group of MAA at 1,705 cm⁻¹ and the amino group of Apy at 3,382 and 3,212 cm⁻¹. The synchronous cross peaks are from orientation of MAA and Apy vibrations generated at the same time; the synchronization of microstructure movements in the molecules indicates that there exists strong interactions between MAA and Apy. According to 2D correlation rules, static electricity and hydrogen-bonding interactions exist between Apy and MAA. Such results were further verified by ¹H-NMR spectroscopy. The successful application demonstrates that 2D IR correlation spectroscopy may be a convenient and effective method in the study of molecular interactions.     

Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532 nm and 780 nm, dispersive Raman microscopy with excitation laser of 532 nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064 nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96 cm⁻¹ belongs to deformation vibrations of interlayer cations. The band at 200 cm⁻¹ corresponds to deformation vibrations of the AlO₆ octahedron and at 710 cm⁻¹ can be assigned to deformation vibrations of the SiO₄ tetrahedron. The band at 3620 cm⁻¹ corresponds to the stretching vibration of structural OH groups in montmorillonites.     

Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb₂Sb₂O₆(O,OH). The mineral is characterised by an intense Raman band at 656 cm⁻¹ assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm⁻¹ are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328 cm⁻¹ are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm⁻¹ may be assigned to δOH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm⁻¹ are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm⁻¹ supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb₂Sb₂O₆(O,OH,H₂O).     

Dehydration-induced changes in the vibrational states of dioptase Cu6Si6O18·6H2O

This paper reports on the results of temperature studies (20–880°C) of the IR absorption spectra of dioptase crystals in the range 50–4000 cm⁻¹. During the dehydration of dioptase the state of water changes as follows: (1) initial state, (2) intermediate state with damped external vibrations of H₂O, (3) isolated water molecules with new hydrogen bonds, (4) formation of hydroxyls. The bands of the external virations of H₂O (1) vanish in state (2) because of the formation of vacancies in the six-membered water rings. The frequencies of the translation vibrations of 6H₂O in initial dioptase are close to those in liquid water: 169–170 and 277–290 cm⁻¹. A factor-group analysis of the dioptase vibrations in the space group C _3i ² is performed. All IR active vibrations 23A_u+23E_u are described. The thirty five bands observed in the IR spectra are assigned. The dehydration-induced deformations of the silicate rings are determined from the shifts of the vibrational bands of Si₆O₁₈. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 68–74, January–February, 1996. Translated by I. Izvekova     

Raman spectra and molecular dynamics of R2NPX2 (R=Me and Et; X=F, Cl, and Br)

The Raman spectra of compounds R₂NPX₂ (R=Me and Et; X=F, Cl, and Br) were studied. The time correlation functions of vibrational and rotational relaxations as well as the characteristic times of these processes were calculated. Conclusions concerning the mechanisms of formation of the contours of the Raman lines with frequencies in the 670–705 cm⁻¹ range corresponding to the totally symmetric vibrations of the P-N bond in the R₂NPX₂ molecules were drawan. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 961–967, May 1997.     

Surface-enhanced Raman scattering detection of lysophosphatidic acid

Surface-enhanced Raman scattering using silver nanoparticles was applied to detect various forms of lysophosphatidic acid (LPA) to examine its potential application as an alternative to current detection methods of LPA as biomarkers of ovarian cancer. Enhancement of the Raman modes of the molecule, especially those related to the acyl chain within the 800–1300 cm⁻¹ region, was observed. In particular, the C–C vibration mode of the gauche-bonded chain around 1100 cm⁻¹ was enhanced to allow the discrimination of two similar LPA molecules. Given the molecular selectivity of this technique, the detection of LPA using SERS may eliminate the need for partial purification of samples prior to analysis in cancer screening.     

Effect of intermolecular =C–HO interaction on the crystal structure and vibrational properties of 2,6-dimethyl-4-nitropyridine N-oxide

The crystal structure of 2,6-dimethyl-4-nitropyridine N-oxide (DMNPO) has been determined at ambient temperature. The compound crystallizes as a monoclinic structure, space group P2/n, with 12 molecules per unit cell. The unit cell contains three non-equivalent formula units. The nitro group is not coplanar with the pyridine ring. Through a system of =C–HO hydrogen bonds the molecules are arranged into a two-dimensional network of layers parallel to the axc plane.The IR and Raman spectra, measured in the 3500–100 cm⁻¹ region at ambient temperature, are correlated with X-ray structural data. The assignment of IR and Raman bands is given. The appearance of characteristic vibrational features in the spectra of this compound and the observed shifts of the =C–H and N–O IR active stretching modes, when the sample is dissolved in CCl₄, is discussed in terms of the relatively strong =C–HO hydrogen bonds present in this crystal.