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Clathrate and inclusion compounds. Part 11 [1]. A pre-resonance Raman study of the ?-quinol/SO2 clathrate
Abstract
A pre-resonance Raman study of the yellow ß-quinol/SO2 clathrate has been carried out using 609.8, 586.8, 514.5, 488.0 and 457.9 run excitation. Pre-resonance enhancement is observed for the guest vl (Al) band at 1147 cm-1 and the host band at 1257 cm-1. These observations are consistent with a charge transfer interaction arising from the LUMO of S02 (S 3pz) and the HOMO of quinol, which consists mainly of the ring p electrons.
This paper gives an overall review of the literature since 1980 on the use of valproate in bipolar affective disorders. Randomised comparative studies definitely demonstrate that valproate proves superior in comparison with placebo and equivalent in comparison with lithium in the treatment of acute manic episodes. A series of open studies indicates a reduction in frequency and intensity of manic and depressive episodes with the long-term administration of valproate suggesting efficaciousness in the prophylaxis of bipolar affective disorders. Details on dosage, side effects and potential interactions with this group of patients are presented. Valproate constitutes a further valuable and well tolerated alternative to lithium, antipsychotic agents and carbamazepine not only in acute therapy of manic episodes but also in prophylactic treatment of patients with bipolar psychosis.
The orientational ordering in a system of dipolar molecules located on a trigonal lattice is studied in the eight-sublattices approximation. Our concrete example is SO2 molecules enclosed in beta-hydroquinone clathrate. It is assumed that the molecules interact with each other via effective dipole-dipole interactions, and that the crystal field acting on those molecules is of the form WA=C cos[ nu( phi- deltaA ) ], where phi is a rotational angle and A is a sublattice number. If nu is an odd integer, we assume that deltaA may be different for different A. The mean electric field which depends on the depolarization field is obtained. Various cases of C, nu, deltaA are investigated. Results are as follows: the possible dipole arrangement is antiferroelectric in all cases; the phase transition for nu=2, 4, 5, 6 is of second order; if nu= 1, no disordered phase occurs; if nu= 3, the phase transition is weakly of first order except for special cases; the C dependence of the transition temperature is weak unless nu= 2; deltaA chiefly determines the equilibrium direction. A comparison with experiment suggests that the low-temperature phase of SO2-beta-hydroquinone has nu= 2 or 3, and that interactions between enclosed SO2 molecules other than dipole-dipole interactions may be also effective.
Infrared, Raman and solid state 13C-NMR spectra have been recorded for a range of clathrates of Dianin''s compound containing straight chain aliphatic carboxylic acids (formic - octanoic) as guests. The IR, Raman and NMR spectra can be satisfactorily interpreted in terms of dimer (formic and acetic) and monomer (propionic - octanoic) occupation of the cavities. The clathrates containing straight chain alcohol guests (methanol - octanol) have also been prepared to aid in the interpretation of the NMR data.
The infrared spectra of 16 para-substituted phenols have been recorded between 1600 and 300 cm−1. Assignments have been made for the frequencies of the p-X-C6H4-OH molecule where × is considered as a point-mass group. These assignments were made taking into account both the Raman spectra reported in the literature and Raman spectra obtained experimentally. Disregarding the four carbon-hydrogen stretching frequencies and the oxygen-hydrogen stretching frequency, 25 of the remaining 28 frequencies of the p-X-C6H4-OH group have been assigned. Nine of the assigned frequencies were found to be either substituent sensitive or characteristic of para-substituted phenols.
Infrared (4000–200 cm–1) and Raman (3700–50 cm–1) spectra are reported for α- and β- quinol, and for β-quinol clathrates containing the following guest molecules: N2, O2, HCl, HBr, CO2, SO2, H2S, C2H2, HCO2H, CH3OH, CH3CN, and CD3CN. Comparison of the room-temperature and the low-temperature (77 K) Raman spectra of the HCl and HBr clathrates indicates a rotational motion of these guest molecules in the host lattice. The results are less conclusive for the N2 and O2 guest molecules due to the smaller values of their rotational constants. The guest-molecule vibrational frequencies are, in general, closer to the vapour-phase values than to the liquid-or solid-phase values. This is particularly true for the methanol and formic acid guest molecules, the spectra suggesting that these molecules are present as the monomeric species in the host cavities.
The solid state 13C NMR spectra of a series of aliphatic carboxylic acids as guests in various host lattices are reported. The information is compared with that obtainable from infrared spectroscopy and X-ray crystallography.
Raman spectra of the SO2 clathrate of hydroquinone excited with several radiations revealed a pre-resonance enhancement of some hydroquinone bands. Based on this result and on the electronic absorption spectrum of the clathrate, it is suggested that a charge transfer complex is formed between sulfur dioxide and hydroquinone.
An x-ray structural study of the clathrate compound formed by fl-hydroquinone with sulfur dioxide, with the composition 3C6H4(OH)~ �9 0.884 SO2, has been carried out (diffractometer, kMoK~, 649 reflections, anisotropic full-matrix refinement with weightings w = (a + IFmeasl + bF2meas) -1, SO 2 molecule in the refinement regarded as a rigid body, R = 0.046). The compound is a type lI clathrate of fl-hydroquinone, formed in the space group R3. The O-O direction of the SO~ molecules in the cavities of the framework is not parallel to the c axis, and a weak interaction is observed between the SO~ molecule, through one of its O atoms, and the [OH]6 ring of the hydroquinone framework (O4...H22.43 /~), and between the sulfur atom and one of the C atoms of the hydroquinone molecule (S-C G 3.50 ~)~
The polymorphism of sodium and potassium sulphates has been studied using differential scanning calorimetry (d.s.c.) and vibrational spectroscopy. For Na2[SO4] the d.s.c. study has yielded enthalpy changes for the various phase transitions. The polymorphs have distinct Raman spectra whereas the i.r. spectra do not show such distinct differences. The phase-transition temperature of K2[SO4] is outside the range of the d.s.c. instrument, but the vibrational spectra indicate that K2[SO4], unlike Na2[SO4], does not exist in a metastable phase on cooling below the transition temperature.
The i.r., far i.r. and Raman spectra of the triclinic and monoclinic forms of the hydroquinone-p-benzoquinone 1:1 complex (quinhydrone) have been recorded and compared to the solution and vapour phase vibrational spectra of the components. The largest shifts have been observed on the characteristic vibrations of the hydroxyl and carbonyl groups which can be attributed to the OH · OC hydrogen bonds. The frequency changes of the ring stretching modes are negligible indicating that the charge transfer interaction is very weak. Correlation splitting has been observed only in the spectra of the monoclinic form, in accord with the result of factor group analysis. The disputed assignments of the bands in the 1700-1600 cm−1 range of the Raman spectrum of p-benzoquinone could be clarified by taking into account their shifts in the spectra of quinhydrone.