Electronic structures of organometallic complexes of f elements LXXIV: First Raman spectroscopic polarization measurements on uniformly oriented sandwich complex molecules: Bis(η-pentamethylcyclopentadienyl)ruthenium

The polarized Raman spectra of oriented single crystals as well as far and mid infrared spectra of pellets of RuCp₂* (Cp* = η⁵-C₅Me₅) (1) were recorded. Assuming local C_5v symmetry for the intra-ligand vibrations, pairs of Raman and IR bands of nearly equal energy result for the symmetric and antisymmetric modes, respectively, for the irreducible representations (irreps) a₁, e₁, and partly (the IR part is symmetry forbidden, in principle, but sometimes observed) of e₂ symmetry. By this means, intra-ligand and skeletal vibrations (where no pairs of Raman and IR bands are expected) could be separated, and the Raman active modes were assigned to irreps on the basis of the observed polarizations. The still questionable type of vibration of some intra-ligand modes could be elucidated by the comparison of the vibrational spectra of 1 with the already assigned ones of NaCp*. Transferring the results of 1 to the Raman and IR spectra of OsCp₂* (2) and FeCp₂* (3), a number of previous assignments have to be revised.     

Vibrational properties of the nonlinear optical crystal β-BaTeMo2O9

We report growth of large single crystals of β-BaTeMo₂O₉, and single crystal infrared (IR) reflectance spectra as well as polarized Raman spectra for these crystals. Based on these results, the symmetry and LO–TO splitting have been established for the observed modes. We also propose assignment of the observed modes to the respective vibrations of structural units.     

Raman spectra of single crystal Li2SeO4

The room temperature polarized Raman spectra of single crystal Li₂SeO₄ are assigned using a factor group analysis. The internal optic modes of the selenate ion are responsible for Raman bands from 920 to 440 cm⁻¹, the translational optic modes of the lithium occur in the interval from 444 to 290 cm⁻¹ and the external optic modes of the selenate ion are found between 210 and 70 cm⁻¹. The symmetry-based assignments of these bands are discussed.     

Raman spectra of single crystal Na2(SeO4)0.15(SO4)0.85

The room temperature polarized Raman spectra of single crystal Na₂(SeO₄)_0.15(SO₄)_0.85 are assigned, based on a factor group analysis. The internal optic modes of the oxyanions are responsible for Raman bands from 113O to 350 cm⁻¹ and the external optic modes are found between 270 and 50cm⁻¹. The symmetry-based and anion isotope abundance-based assignments of these bands are discussed.     

Polarized vibrational,electron absorption and luminescence spectra of Nd(NO3)3(DMSO)4 single crystal

Infrared and Raman spectra of polycrystalline and single crystal Nd(NO₃)₃(DMSO)₄ have been measured. The molecular and crystal structure is analysed in terms of a monoclinic unit cell of C2/c symmetry. A comparison of i.r. spectra measured parallel and perpendicular to the b axis of the unit cell as well as Raman spectra for several tensor elements was used to describe the internal and external optical modes. The optical absorption and luminescence spectra of neodymium nitrate tetra dimethyl sulphoxide single crystal were recorded at 77 and 300 K between 4000–30 000 cm⁻¹. The electronic transitions were assigned to the crystal field splitting manifolds. The band intensity measurements performed for | and ⊥ b polarizations are related to Judd—Ofeld parameters and the anisotropy of these values is discussed.     

IR and polarized Raman spectra of strontium tartrate trihydrate

The IR and polarized Raman spectra of SrC₄H₄O₆ · 3H₂O have been recorded and analysed. The factor group analysis of the divalent tartrate ion has been carried out on the basis of C₂ symmetry. As the ion possesses lower symmetry in the crystal, splittings have been observed for the different vibrational modes. Separate bands in the bending region of water suggest the existence of three crystallographically different water molecules in the crystal, which is confirmed by deuterium substitution.     

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 spectra of cis-stilbene and 1,1-diphenylethene

Raman and IR spectra of the named compounds have been measured as liquids at room temperature and as solids at low temperature. Some bands are shown to arise from atomic displacements essentially localised on the weakly interacting phenyl groups; symmetric and anti-symmetric combinations of these “phenyl modes” are almost degenerate and become appreciably mixed in some cases leading to anomalous values for their depolarisation ratios. Other modes, largely involving the ethylenic group, are identified and provide information concerning the molecular conformation in the liquid; both molecules have C₂ molecular symmetry. The low-temperature spectra are sharp and contain information about the crystal structures.     

Cryochemistry : edited by M. Moskovits and G.A. Ozin,John Wiley & Sons,New York,London, Sydney and Toronto, 1976, pp. xi + 532, price £25.85

The IR spectra of N₂F₄ solutions in liquid argon and nitrogen have been recorded and reanalyzed in the 3300–3550 cm^?1 region. The fundamental absorption bands of NF-stretching modes of both the gauche and trans isomers and the bands of the second order transition have been observed. These new IR data on the spectra of cryosystems and published Raman data allowed us to make an unambiguous interpretation of the NF₂-stretching vibrational bands for both the N₂F₄ conformers.     

Infrared and Raman multi-phonon spectra and structure of PbWO4

Improved Raman spectra of PbWO₄ show previously reported spectra contain large polarization and/or orientation errors. New spectroscopic information, obtained from polarized IR reflection and Raman spectra, allowed us to assign the IR and the previously unreported Raman multi-phonon bands. It was also used to show that it determines uniquely the C_4h factor group of PbWO₄. The use of IR reflection vs. infrared transmission spectra in the vibrational determination of crystal structures is also discussed.     

Application of the dimer approach for the analysis of vibrational spectra of BEDT—TTF-based charge-transfer salts

The dimer approach was proposed for the normal coordinate analysis of BEDT—TTF⁺ molecular vibrations. It was shown that, within the framework of the approximation used, the appearance of additional bands in the IR as well as in Raman spectra may be explained as due to the reduction of symmetry of the dimerized system in comparison with the monomeric one. The strength of intermolecular interaction in the dimer was estimated by adjusting the calculated frequencies to the observed positions of intense “vibronic” bands recorded in the IR spectra of BEDT—TTF-based monovalent charge transfer salts. It was found that for the reproduction of “vibronic shifts” observed for some vibrations it should be assumed that the intermolecular interaction takes effect not only on the totally symmetric a_g modes, but also on the vibrations of other symmetry species.     

Vibrational studies of BH−4 and BD−4 isolated in alkali halides

Single crystals of alkali halides doped with BH^?₄ and BD^?₄ were grown from the melt. Previously unreported bands in the infrared spectra of BH^?₄ and BD^?₄ isolated in different alkali halides are interpreted in terms of summation bands of internal and external modes of vibration. This has allowed the torsional and translational modes of the impurity ion to be identified. The tetrahedral symmetry of the borohydride ion is retained when it is isolated within alkali halides with the NaCl structure. A reduction of symmetry towards C_3v was observed when BH^?₄ (or BD^?₄) was isolated within lattices with CsCl structure.Raman and far infrared spectra of alkali halide/BH^?₄ systems will be reported for the first time, and high pressure infrared studies of these systems will be described. The effects of pressure in the internal mode, external modes, Fermi resonance and NaCl to CsCl structural phase changes will be discussed.     

Raman scattering study of the β-BaB2O4 crystal under low temperature

We recorded the Raman spectra at the low temperature (84 K) and determined the directional dispersion of extraordinary phonons of β-BaB₂O₄ crystal. The vibration—intensity relations between the (B₃O₆)³⁻ ring and the β-BaB₂O₄ crystal are analysed. The G—F matrix method was used to calculate the vibrational frequencies of the (B₃O₆)³⁻ ring in the β-BaB₂O₄ crystal. The assignment of internal vibration modes and vibrational symmetry are presented.     

Single crystal Raman study of potassium oxalate monohydrate,K2C2O4. H2O,and potassium oxalate monodeuterate,K2C2O4. D2O

Raman spectra of poly crystalline and single crystal K₂C₂O₄. H₂O and K₂C₂O₄. D₂O have been recorded at room temperature. From an earlier neutron diffraction study it is known that the space group is C⁶₂h. The water molecule occupies a C₂ site and the oxalate ion a C₁ site. The assigned water vibrations show small factor group splitting between g modes (Raman active) and u modes (IR active). The internal oxalate vibrations are found to have wavenumbers in good agreement with those reported from Raman studies of other oxalates.     

Vibrational and electronic spectra of copper(II) chromate

The infrared, Raman and electronic (reflectance) spectra of CuCrO₄ were recorded. The internal vibrations of the CrO²⁻₄ ions were assigned with the aid of a factor group analysis. The ‘d-d’ transitions of the Cu^IIO₆ moieties and one of the O → Cu charge transfer bands could also be assigned. Some comparisons with other structurally related compounds are made.     

Vibrational Spectra of the Cyclic SN-Compounds S4N4, S4N4H4 and S3N3Cl3

The IR and Raman spectra of solid and dissolved S₄N₄, S₄N₄H₄, S₄N₄D₄ and S₃N₃Cl₃ have been recorded and are assigned according to D_2d, C_4v and C_3v symmetry respectively. In the solid state, many forbidden bands and splittings of degenerate vibrations are observed because of the symmetry lowering in the crystals. Due to the different size and shape of the rings and to strong coupling of the normal modes there is no clear correlation between the SN ring stretching vibrations and the strength of the SN bonds, except for the one of the E modes. However, the stretching force constant show the trend expected from changes in interatomic distances.     

Infrared and Raman spectra of lithium trihorate: Vibrational assignments and a correlation with its nonlinear optical activity

Infrared and polarized single crystal Raman spectra of lithium triborate (LBO; LiB₃O₅) are reported and analysed. All four (A₁, A₂, B₁ and B₂) symmetry species of the C_2v, point group isomorphic to the C_2v⁹(Pna2₁) space group are Raman active in distinct crystal polarization experiments. A complete set of symmetry assignments based on a factor group analysis is presented. The internal and external vibrations are separated on the basis of frequency and the observation that the magnitude of the correlation splitting for the internal modes is very small. A comparison of the internal frequencies of various borate species suggests a correlation between the B-O stretching frequency and the nonlinear optical efficiency of the material.     

Crystal structure and vibrational properies of Rb2MgWO2(PO4)2—A new framework phosphate

The new compound Rb₂MgWO₂(PO₄)₂ has been synthesized and characterized by a single-crystal X-structure determination, and IR and Raman spectroscopic studies. The crystal structure is orthorhombic, space group Pbca, with the unit cell dimensions a=9.891(2), b=12.641(2), , Z=8. Compared to the K₂M^IIWO₂(PO₄)₂ series, where M^II=Mg, Mn, Fe, Co, Ni, and Cd, the volume of the unit cell in the present compound is nearly doubled. The MgO₆ and WO₆ octahedra are arranged into polyhedral groups consisting of two edge sharing MgO₆ joined by corners with two WO₆ octahedra. These groups are interconnected through the PO₄ tetrahedra into layers in a×b plane. The Rb⁺ ions perform thermally activated displacements within the cavities formed between the polyhedral layers. The origin of various Raman and IR modes is discussed. These results indicate that a clear energy gap exists between the stretching and remaining modes. The most intense modes are shown to be due to vibrations of the W-O bonds.     

Etude vibrationnelle de la phase II des hydrogénodisulfates de triammonium, (NH4)3H(SO4)2 et (ND4)3D(SO4)2

The i.r. and Raman spectra of room temperature phase (phase II) of (NH₄)₃H(SO₄)₂ and (ND₄)₃D(SO₄)₂ as polycrystalline samples and single crystals have been investigated between 4000 and 30 cm⁻¹. An assignment of internal and external modes is given in terms of group frequencies and symmetry types. This crystal contains non-centrosymmetric dimers (SO₄HSO₄)³⁻ where sulphate ions are associated by strong asymmetric OH … O hydrogen bonds; they are characterized by two strong Raman bands at 1078 and 966 cm⁻¹, and a νOH frequency at about 1250 cm⁻¹. The acidic proton is statistically disordered around the crystallographic symmetry centre while all of the NH⁺₄ ions show an important dynamical orientational disorder.     

Electronic structures of organometallic complexes of f elements LXXVII: Complementary information of polarized Raman spectra of oriented single crystals and model calculations on the basis of density functional theory for assigning the vibrational spectra of decamethylferrocene

The far and mid infrared (FIR/MIR) spectra of powdered Fe(η⁵-C₅Me₅)₂ (FeCp1₂) as well as the polarized Raman spectra of an oriented single crystal (where the four FeCp1₂ molecules of D_5d symmetry in the unit cell are pairwise perpendicular to each other) have been recorded. The polarization selection rules were developed for this situation which allow the assignment of the observed Raman lines to irreducible representations (irreps) which agree well with the predictions of a calculation applying density functional theory. This finding suggests additional correlations to the observed (unpolarized) bands in the FIR/MIR spectra with the calculated wavenumbers (and their irreps) of IR active normal modes. Neglecting the νCH vibrations, a r.m.s. deviation of 7.0 cm^?1 for 41 assignments (IR and Raman) could be achieved. The frequencies of the calculated νCH vibrations, however, are on the average 55 cm^?1 higher than the experimental ones. Skeletal and intra-ligand vibrations could be separated and all previous assignments of the former had to be revised. Because of mixing, the graphical representations of the two skeletal modes of E_1u symmetry do not resemble the idealized ones of a typical sandwich complex but those of FeCp₂ shown in the literature. In-phase and out-of-phase intra-ligand motions of the Fe[(C₅C₅)]₂ moiety have calculated wavenumber differences between 3 and 42 cm^?1. Additionally, because of mixing with skeletal modes some of the low frequency intra-ligand vibrations display a noticeable dependence on the mass of the central atom which prevents the direct transfer of the identified βCCH₃ and γCCH₃ normal modes from MCp1₂ (M = Fe, Ru) to LnCp1₃ (Ln = La, Ce, Pr, Nd, Sm) complexes.