Raman Study Of Single Crystals Research Articles

Single crystal Raman studies of complexes of the cyclic hexamer of ethylene oxide with organic molecules

Polarized Raman spectra of single crystals of complexes of 1,4,7,10,13-16-hexaoxacyclooctadecane (EOc6) with acetonitrile (EOc6·2CH 3CN), acetonitrile-d 3 (EOc6·2CD 3CN) nitromethane (EOc6·2CH 3NO 2) and acetic anhydride (EOc6·Ac 2O) have been measured. These data are consistent with the approximate D 3 d geometry for the “EOc6” molecules indicated by X-ray diffraction for the nitromethane complex and supports a similar conformation in the other complexes studied.

Single crystal Raman studies of ethylene oxide cyclic tetramer complexes

Polarized single crystal Raman spectra of the following complexes of ethylene oxide cyclic tetramer (1,4,7,10-tetraoxacylcododecane, “EOc4”) were measured: LiBr·EOc4, LiCl· EOc4, CaCl 2·EOc4·8H 2O, and M X·2EOc4·5H 2O (M X = NACl, NaBr, KBr). A vibrational assigmnent for the EOc4 molecule, which has nearly C 4 geometry in all of the complexes, was derived from the spectra of the LiBr complex, in which it has C 4 site symmetry. The intensity distributions of the EOc4 vibrations in NaBr·2EOc4·5H 2O were compared with those predicted by the oriented gas approximation.

Single crystal Raman spectrum of the external phonons in 5-bromotetrazole

The six Raman active external phonons in 5-bromotetrazole have been assigned by observing four different Raman tensor elements, a(ca)c, a(cb)c, a(ba)c, and a(bb)c. In particular, the librational and translational phonons have been identified and approximate normal modes have been described for them. These results are compared to earlier work on L-alanine and imidazole single crystals. No disorder phenomena were observed in 5-bromotetrazole as in L-alanine. Harmonic force constant calculations confirm the structural prediction that, at K̄=0, no hydrogen-bond influences should be exerted on the external phonon frequencies. To our knowledge this work represents the first unambiguous single crystal Raman study of a hydrogen-bonded ring compound.

Solution and single-crystal Raman study of M(CO)6, where M = chromium, molybdenum, and tungsten

For the three compounds M(CO)6, where M = Cr, Mo, and W, ν10(t2g) has been observed in solution for the first time; a solvent-effect study of ν1, ν2, and ν3 is also reported. Single-crystal Raman experiments yielded symmetry species consistent with currently accepted assignments for these molecules except in the region below 120 cm–1 where many new lines were found for the molybdenum compound. In the ν(CO) region full factor-group splitting is shown by the ν3(eg) mode.

Solution and single-crystal Raman study and revised assignment for hexachlorocyclotriphosphazene

The long-sought ν4(a1′) mode of (PNCl2)3 has been located at 172 cm–1 in solution and its symmetry species confirmed by a Raman Study of an oriented single crystal. Experimental evidence from the crystal spectra also allowed distinction between e′ and e″ species. A reassignment of the spectrum is offered.

Polarized Raman Scattering in Transparent Polycrystalline Solids

The polarized Raman spectra of transparent polycrystalline solids are shown to provide results essentially identical to those obtainable from single-crystal Raman studies. Analytic expressions for the polarized scattering functions are obtained and, by way of illustration, are used to determine the symmetries and frequencies of many of the phonon modes for several transparent (Pb, La)(Zr, Ti)${\mathrm{O}}_{3}$ ceramics in the tetragonal ferroelectric phase.

Vibrational spectra of the isoelectronic species IF5, TeF5–, and SbF52–

Gas-phase Raman spectra on iodine pentafluoride, and single-crystal Raman studies on KTeF5 and K2SbF5 are reported. The liquid-phase spectrum of iodine pentafluoride is discussed in terms of an associated fluid. Assignments for these molecules suggest that the (e type) antisymmetric stretching vibration is unusually low relative to the position of the highest-frequency Raman band.

Calculated and observed vibrational spectra of a linear chain, bent chain, and sheet polymer (α-bismuth pentafluoride, selenium dioxide, and tin tetrafluoride respectively)

The observed vibrational spectra of bismuth pentafluoride, tin tetrafluoride, and selenium dioxide are assigned on the basis of single-crystal Raman studies and normal-co-ordinate analyses. In the case of the fluorides the nature of the vibrational modes is discussed in some detail. The Raman spectrum of gaseous selenium dioxide shows one strong band at 923 cm–1.

Oxide phonon spectra

An attempt is made to apply ‘group frequency’ assignments to the vibrational spectra of oxides. The following oxides are considered: TiO2(both anatase and rutile), SnO2(cassiterite), ZnO, WO3, CeO2, ThO2, B-Nb2O5,V2O5, MoO3, and MoO3′. The experimental data on V2O5(single-crystal Raman study), B-Nb2O5(single-crystal Raman study), WO3, CeO2, ThO2, and MoO3′ are new. There are also additional results for SnO2 and new i.r. data (including single-crystal studies) on MoO3.

Single-crystal Raman spectrum of bismuth pentafluoride and of antimony tetrachloride fluoride and the vibrational spectrum of vanadium, niobium, tantalum, and antimony pentafluorides

Single-crystal Raman polarisation data on α-BiF5 enable an unambiguous assignment to be made of the Raman-active modes of this polymer. The corresponding i.r. data define a Bi–F–Bi bridge stretching mode at 450 cm.–1, suggesting a force constant equal to one quarter of the terminal force-constant. Single-crystal Raman studies and normal-co-ordinate calculations (based on this bridge force-constant) are used to assign the vibrational spectrum of SbCl4F. The vibrational spectra of solid VF5, of NbF5 and TaF5 in the solid and liquid states, and of liquid SbF5 are examined to study the position of the ‘fluorine-bridging’ modes and to investigate the stereochemistry of the liquid states. An interpretation in terms of cis-fluorine-bridged polymers is satisfactory for NbF5 and SbF5. In the case of SbF5 the Raman spectrum of the melt is the same at 20 and 125°. Normal-co-ordinate calculations are used to assign the vibrational spectrum of solid NbF5.

Structure of bistrimethylamine–aluminium trichloride, bistrimethylphosphine–aluminium trichloride, and bistrimethylphosphine–indium trichloride. The single-crystal Raman spectrum of bistrimethylamine–aluminium trichloride

A single crystal X-ray study of AlCl3,2NMe3 shows the space group to be Pnma with four molecules in the unit cell (a= 9·71, b= 10·05, c= 12·95 A). The compound is isomorphous with CrCl3,2NMe3. Powder X-ray diffraction patterns of AlCl3,2PMe3 and InCl3,2PMe3 show them to be isomorphous with the corresponding trimethylamine adducts. All these compounds show trigonal-bipyramidal co-ordination of the central atom with axial trimethylamine or trimethylphosphine groups. A single-crystal Raman study of AlCl3,2NMe3 strongly suggests that a totally symmetric mode at 168 cm.–1 is principally an aluminium-ligand stretching vibration.