Ultrasonic absorption data for pure dimethyl, diethyl, dipropyl, dibutyl, and propylene carbonates in the frequency range 3-300 MHz and in the temperature range 25-55 °C are reported. An ultrasonic relaxation process of the Debye type with a relaxation frequency fR = 8.5-10 MHz at 25 °C, which is largely independent of the length of the alkyl chain in the alkoxy group, has been found for the noncyclic carbonates. No such process has been observed for the cyclic propylene carbonate and for dimethoxymethane which lacks the carbonyl group. The observed relaxation process is interpreted as being due to a cis-trans isomerization of the alkoxy groups.By using theories for thermal relaxation processes both the activation parameters AH* and AS* for the reverse step of the equilibrium and the thermodynamic parameters AH°and K for the equilibrium have been determined.Complex dielectric permittivities in the microwave frequency range 0.6-67 GHz for the above noncyclic carbonates at 25 °C are also reported. The data can be described over almost all the frequency range studied by a single Debye relaxation process. The high end of the frequency range shows some positive deviations of the loss in accord with literature data. The dielectric relaxation process is interpreted as due to a segmental motion of the molecule under the influence of the electric field. The different nature of the relaxation mechanisms for the ultrasonic and dielectric processes is attributed to the different type of perturbing function inherent in the two methods.
Complex permittivities in the frequency range of 0.3-67 GHz are reported for the systems 0.1 M LiN03,0.05 M sodium picrate, 0.1 M Bu4NN03 in THF at 25 °C and for the systems 0.1 M LiC104, and 0.1 M LiSCN in diethyl carbonate (DEC) at 25 °C. The permittivities of the electrolyte solutions can be described within experimental error by the sum of two Debye relaxation processes. The high frequency process is comparable to the one observed for the pure solvents while the low frequency process is due to the presence of the electrolytes.Apparent dipole radii aT for the electrolytes in the THF solutions are calculated from the Debye relation using the macroscopic viscosity of the solvent. Charge to charge separation distances µ are calculated from the Bottcher relation which relates the change in dielectric strength (e0 -e^), for a dipolar relaxation process, with the apparent dipole moment. These two parameters oT and o" determined for the present systems and two previous systems (LiC104 and NaC104 in THF) are linearly related to each other (correlation coefficient r2 = 0.89). The oT's also correlate linearly (r2 = 0.91) with the sums of the crystallographic radii. These relations reinforce our previous conclusions that the solute relaxation process in THF is mainly due to the rotation of ion-pair dipoles. For DEC solutions the appearance of a single relaxation process for the solute (instead of a distribution of relaxation times as the presence of two molecular species would suggest) is discussed in terms of the structure of the quadrupoles. Recent Raman and IR spectra in the literature suggest a centrosymmetric structure for (LiSCN)2 in ethers. This structure if present for the carbonate solutions would predict the absence of a quadrupole dielectric relaxation process in accord with our results in dimethyl carbonate (DMC) and DEC.
Dielectric Relaxation in Dimethyl Carbonate orbitals for the bis Ir(III) complexes are likely single ring delocalized orbitals, hence a similar situation for the other (tris, bisesquis) Ir(III) complexes would not be surprising.
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