J. Phys. Chem. 1981, 85, 2987-2992
Relaxation Spectrometry of NaCIO, In Dimethoxyethane and Methyl Cellosolve-Dimethoxyethane Solutions H. Farber and S. Petrucci” Department of Chemistry and Department of Electrical Engineering, Polytechnic Institute of New York, Brook&n and Farmingdale Campuses. New York (Received: March 26, 1981; In Final Form: June 22, 1981)
Complex dielectric permittivities of NaC104in 1,2-dimethoxyethane(DME) at various concentrations, at t = 25 OC, and in the frequency range 0.2-85 GHz are reported. The dielectric relaxation envelopes are interpreted by the sum of three Debye relaxation processes, one due to the solvent and two due to the solute. Alternate approaches, treating the solute relaxation as due to a continuous Cole-Davidson distribution, are presented. The relative merit of the two approaches and the ultimate criterion of choice are discussed. Additional dielectric data are reported for the mixture Methyl Cellosolve (2-methoxyethanol,symbolized here by MC) of concentration 2 M in DME and for NaC104in this solvent mixture at 25 “C. Supporting ultrasonic relaxation spectra provide information on equilibria between ion pairs and quadrupoles. Electrical conductance data analyzed up to C M by the complete Fuoss-Kraus theory reveal that the electrolyte is mainly associated to ion pairs with a small number of triple ions present. A molecular interpretation of the dielectric relaxation increments for NaC104 in DME is attempted.
Introduction Previous work for LiC104 in 1,2-dimethoxyethane (DME) reported a dielectric relaxation process for the solute which was interpreted, within experimental error, by a single Debye relaxation function. The solubility limited the investigation to concentrations of the order of 0.2 M. NaC104is considerably more soluble in this solvent. Chelation of Na+ by DME has been proposed in the literature.2 Extension of the concentration to values higher than 0.1-0.2 M could reveal the appearance of a new solute species. If dielectric relaxation reflects the presence of polar species in solution as proposed by us earlier,3 it seems conceivable that the dielectric spectrum should become more complex by increasing the concentration. This would give supporting evidence to the premise and qualify dielectric spectrometry as an additional method to study the relaxation dynamics of complexes in solution. It was with these ideas in mind that we started the present project. During the development of the work, we decided to investigate the effect of the addition of Methyl Cellosolve (2-methoxyethanol)to the NaC104-DME solutions. One may consider for Methyl Cellosolve (MC) that one of the methoxy groups of DME has been substituted by a -OH group. A mixture of MC + DME and a solution of NaC104 in this mixture were investigated as reported below. Experimental Section The equipment and the procedure for the dielectric ultrasonic and conductivity measurements have been described bef0re.l The microwave equipment for the frequency range 80-90 GHz has also been r e p ~ r t e d . As ~ for the material, NaC104 (Smith, Cleveland, OH) was dried under vacuum torr) at -70 OC for 1week; DME has been purified as described before; MC (Eastman Kodak) was distilled under vacuum twice as suggested in the literature.6 Infrared spectra of the purified DME reveal ~
complete absence of -OH (lack of OH stretching band in the 3200-3600-cm-’ range), alcohols being the most common impurities for these ethers. Results and Calculations Dielectric Data. NaC104 in DME. Figure 1 reports representative plots of the real and imaginary coefficients E’ and E” - E”, of the complex permittivity plotted vs. the frequency f (GHz) for 0.2 M NaC104at 25 OC in DME. E’’~ is the conductance contribution to the experimental loss = (1.8 X l0l2)x/f, with x the coefficient e’’, where specific conductivity of the solution. The solid lines are the sum of three Debye relaxation processes. The upper relaxation process is common with the one present for the pure solvent DME.4 The two lower ones are due to the presence of the solute NaC104. For the lowest concentration of NaC104, 0.1 M, it is possible to interpret the data by only two Debye relaxation processes, one for the solute and one for the solvent. This is shown in Figure 2 in the form of the deviations from the experimental values deal&and - (E”,,,,~ - E”~) where e‘lX is the conductance contribution to the loss coefficient. Although at c = 0.1 M the two treatments give comparable results, preference is given to the interpretation by two relaxations of the solute, only in view of the results at higher concentrations. In other words, it seems evident that the contribution of the second solute relaxation a t c I0.1 M is irrelevant. The parameters for the fitted functions
~~
(1) Onishi, S.; Farber, H.; Petrucci, S. J.Phys. Chem. 1980,84, 2922. (2) Jeanes, A.; Adams, R. J. Am. Chem. SOC.1937,59, 2608. Garst, J. “Solute-Solvent Interactions”; Goethe, J. F., Ritchie, C. D., Eds.; Marcel Dekker: New York 1969; p 544. (3) Saar, D.; Brauner,J.;Farber, H.; Petrucci,S. J.Phys. Chem., 1980, 84, 341. (4) Farber, H.; Petrucci, S. J. Phys. Chem. 1981, 85, 1396. (5) Accascina, F.;D’Angelo, P.; Schiavo, S. Sci. Tec. 1960, 4, 32. 0022-3654/81/2085-2987$01.25/0
namely, q,,eml, tmZ,cm3,f ~fb, ~and, f, are reported in Table I, together with the specific conductances. In the same table the parameters for c = 0.1 M (in accordance with the interpretations of two Debye processes) are also reported. The fit of eq I to the experimental data was achieved by minimizing the quantities xld,.&d - e’/ + Cle”dcd- (E” 0 1981 American Chemical Society
2988
The Journal of Physlcal Chemlstty, Vol. 85,No. 20, 1981
Farber and Petrucci
TABLE I: Dielectric Relaxation Parameters for NaC10, in DME and in DME-MC Mixtures at 25 "C CNaClO, 9
M
E-
€0
0.40 0.20 O.loa 0
13.2
0.10
11.1
8.0 7.5 1.2
11.0 9.2,
f ~ , GHz , f ~ , GHz , f ~ , ,GHz
E- 3
2
Solvent: DME 3.0 2.7 2.15 2.75
1.5 1.5 1.5
8 8 8
35 35 35 35
Solvent: 2 M MC in DME 6.9 2.7 1.5 7.0 2.7
10 10
40 40
6.5 6.7 6.9 1.05
8.6 8.7
0 a
E-
1
In terms of t w o relaxations, the parameters were e o = 9.25,
x,
n-' cm-'
19 x 10-4 6.1 x 1.9 x 10-
8., x
= 7.05, E , , = 2 . 7 5 , fRl = 1.8 GHz, and fR, = 35 GHz. r n
11 -
9-
E'
3.0
COLE.COLE PLOT: NiCfD40.2M IN DME: 1 ~ 2 5 ' C - - DEBYE FUNCTION -COLE~DAVIDSON FUNCTION: a.0.75
75-
3It 0.1
I
I
l
l
0.2
0.5
1
2
5
I
I
,
IO
20
50
100
,
,
I
1
f(GHz)
2.5
(a)
,
3.01
I
I
I
NsCP04 0.20M IN DME;
I
