MOLECULAR-STRUCTURE AND DYNAMICS OF LICLO4 POLYETHYLENE OXIDE-400 (DIMETHYL ETHER AND DIGLYCOL SYSTEMS) AT 25-DEGREES-C

Infrared spectra of the <(nu)over bar>(4) mode of the ClO4- ion, for t he systems LiClO4-polyethylene oxide dimethyl ether of average molar m ass 400 (PEG-400) and LiClO4-polyethylene oxide glycol of average mola r mass 400 (PEG-400), at 25 degrees C, have been determined and quanti tatively described by the sum of two Gaussian-Lorentzian product funct ions centred at similar to 623 and similar to 635 cm(-1), respectively . Bands are assigned to spectroscopically free ClO4- (at similar to 62 3 cm(-1)) and to bound ClO4- (at similar to 635 cm(-1)). From the rela tive amplitudes of the two bands, it is concluded that the majority of the ClO4- exists out of contact with Li+, probably as solvent-separat ed ion pairs. This conclusion is based on a large ion-pair formation c onstant K-p = 4.5(2) X 10(3) for LiClO4 in PEO-400, as reported in the literature and reanalyzed in this work. Electrical conductance data f or LiClO4 in PEG-400 are also reported and analyzed with current theor ies furnishing values of K-p for this system. Existence of dimer aggre gates (Li+SxClO4-)(2), with S symbolizing an oxygen moiety of a polyet her chain, is inferred from ultrasonic relaxation spectra of LiClO4-PE O systems. The presence of some (LiClO4)(2) dimeric contact species is also inferred. The ultrasonic absorption spectra show two relaxation processes followed, at high frequency, by a solvent relaxation process . Matrix analysis has been applied to the two-step dimerization proces s 2LiClO(4) reversible arrow LiClO4...LiClO4 reversible arrow (LiClO4) (2) (which is used to interpret the electrolyte ultrasonic relaxation processes). The analysis yields all the rate and equilibrium constants for the above steps. In addition, from the amplitude of the ultrasoni c spectra, the isoentropic volume changes of the two normal modes, ass ociated with the above equilibria, are calculated. The larger shear vi scosity of the PEG solvent precludes the measurement of the solute ult rasonic relaxation in this medium. The molecular dynamics of the above systems have also been explored through microwave and far-infrared di electric spectra measured in the frequency range from 0.4 GHz to 15 TH z (i.e. 500 cm(-1)). The spectra are quantitatively described by the s um of a Cole-Cole distribution, operative mainly in the UHF-microwave region, and of three Powles-Rocard component bands (recently discussed in the literature) that are operative mainly at IR frequencies. In th e microwave region, the Cole-Cole distribution describes the ethereal chain segmentational rotation, influenced by Li+ cations that increase the intertangling of the ethereal chains. In the far-IR region the hi ghest frequency Powles-Rocard band at similar to 300 cm(-1) has been a ssigned, in accordance with the literature, to torsion of ethereal cha ins. The other two bands are probably due to librations, namely to hin dered molecular rotations limited to small angles. Molar refractivitie s for LiClO4 in PEO-400 and in PEG-400 have been determined in a conce ntration range comparable to that used in the above work.