J. CHEM. SOC. FARADAY TRANS., 1994, 90(4),583-586 Transport and Compressibility Studies of Some Copper([) Perchlorates in Binary Mixtures of Benzonitrile and Acetonitrile Dip Singh Gill,* Rajinder Singh, Vazid AH, Jasbir Singh and Sharwan Kumar Rehani Department of Chemistry, Panjab University, Chandigarh-160014, India Transference numbers of CIO, and Cu+ ions in copper(i) perchlorate have been measured in the concentration range 0.024.22mol dm-3 in benzonitrile(BN)-acetonitrile(AN) mixtures at 298 K by the modified Hittorf method. The limiting transference numbers of Cu+ (t",) in various solvent systems were evaluated by the modified Longsworth method. Molar conductances, ultrasonic velocities and densities of CuCIO, * 4CH,CN and [Cu(DMPhen),]CIO, were measured at 298 K in BN-AN mixtures.The limiting molar conductances (Ao) of the electrolytes were obtained by analysis of the conductance data using the Shedlovsky equation. Limiting ionic conductances (2:) for Cu', [Cu(DMPhen),]+ and CIO, ions and hence their solvated radii (ri)were calculated. The variation in solvated radii of ions as a function of solvent composition showed no preferential solvation of any ion by AN or BN. From the ultrasonic velocity and density measurements, the isentropic compressibilities (K~) and the limiting apparent molal isentropic compressibilities (K:) for CuCIO, 4CH,CN and [Cu(DMPhen),JCIO, were evaluated. That K: values for the copper(i) salts became less negative or more posi- tive with increasing BN mole fraction indicating that both these copper(i) salts are structure makers in AN and that the structure-making tendency of the salts decreased with increasing BN mole fraction. Previously'v2 we reported transference number measurements of copper(1) perchlorate in AN and its binary mixtures.To the best of our knowledge, there have been no other trans- ference number measurements of copper(1) salts. Compress- ibility studies of copper(1) salts are also lacking. BN is another potential solvent which stabilises copper(1) salts. Copper@) perchlorate tetraacetonitrile (CuClO, 4CH3CN) is much more soluble in BN than in AN. In this paper we have measured the transference numbers, molar conductances and ultrasonic velocities of two copper(1) salts, CuC10, 4CH3CN and bis(2,9-dimethyl- 1,1O-phenanthroline)copper(r) perchlor-ate ([Cu(DMPhen),]ClO,) in BN and BN-AN mixtures.Experimental BN (Puriss, >99%GC, Fluka Chemica) and AN (99% from E.Merck, India) were further purified by the methods report- ed The density, viscosity and permittivity of the purified solvents were in good agreement with the literature values. CuClO, 4CH3CN and [Cu(DMPhen),]ClO, were pre-pared by the methods reported earlier.'*2*6 A modified Hittorf transference cell (75 cm3 capacity) with three compartments separated by well greased stopcocks was used in all transport-number measurements. The cathode and anode compartments of the cell were fitted with pure (99.9%) copper spirals which acted as electrodes. The electrodes were thoroughly cleaned with dilute nitric acid, then with distilled water and finally with dry acetone and were then dried.Weighed samples of CuClO, -4CH3CN were dissolved in the appropriate solvent or mixture to obtain solutions of the desired concentration. A direct current of 4 mA (measured accurately with a digital current meter as well as by a silver coulometer connected in series with the cell) was passed through the solution with the help of a current stabilizer (Hindustan Power Tronix Inc., New Delhi) for 4-6 h to bring about a measurable change in the Cu+ concentration. The solutions from the middle and the cathode compartments were analysed for Cu+ concentration by titration with aqueous cerium(rv) ammonium sulfate s~lution.~During analysis, the copper(1) solutions in pure AN or in the AN-rich region did not present any difficulty but in pure BN or the BN-rich region of the mixtures some difficulty arose as BN is not readily miscible with water.This difficulty was, however, overcome by adding an excess of AN to a solution of the copper(1) salts to be titrated and by shaking the solutions vigorously. The other details of measurements and the equa- tions used were as given earlier.8 The accuracy of the trans- ference number measurements was f1%. Conductances were measured at lo00 Hz with a calibrated digital conductivity meter. Details of the conductance mea- surements were reported previo~sly.~ The accuracy of con- ductance measurements was f0.2%.Ultrasonic velocities were measured at 2 MHz using an ultrasonic time intervalometer model UTI- 101 from Innova- tive Instruments, Hyderabad using a pulse-echo overlap technique. The absolute accuracy of the sound velocity mea- surements was 2 parts in lo4. Densities were measured using an Anton Paar Digital Densimeter (model 60) and a calibrated cell type 602 with a reproducibility of +O.OOOOl g cm-3. Results and Discussion Transference-number Measurements Transference numbers of ClO, and Cu' ions in copper(1) perchlorate were measured in the concentration range 0.02-0.22 mol dmP3 in BN-AN mixtures at 298 K by the modified Hittorf method. Limiting transference numbers of the Cu+ cation (t&+) were obtained by the modified" Longsworth method of extrapolation.The Longsworth function for Cu + (t;70,+)was calculated by the method reported by Kay and Dye" using the equations: t;ou+= tCu+ + (0.5 - tCu+)A,/AO (1) and A, = bC''2/(1 + ~d) (2) Where p = 82.487/q(~T)'/~,= 50.2916 C'/2/(~T)'/2K and 6 is the ion-size parameter, set equal to the Bjerrum critical dis- tance, 4 = e2/2&kT.The permittivity (E), viscosity (q) and density (p) for the BN-AN mixtures are reported in Table 1. A. values for CuClO, were obtained from conductance mea- surements. Plots of the Longsworth function (tpu+)us. con-centration (C) were linear (Fig. 1) and gave limiting Table 1 Permittivity, viscosity, density and ultrasonic velocity of BN-AN mixtures at 298 K BN(molYo) E VIP p/g c~r-~ u/m s-l 0 36.00 0.003 410 0.776 85 1280.8 11.4 33.96 0.004517 0.821 11 1300.8 25.5 32.40 0.005 388 0.865 41 1323.6 43.4 30.24 0.006 776 0.911 62 1352.0 67.2 27.80 0.008 63 1 0.954 43 1382.8 100 25.16 0.011 958 1.00034 1418.0 transference numbers of Cu+ cation (tg,+; Table 2) on extrapolation to infinite dilution by the least-squares method.The tg,+ values show a strong solvent composition depen- dence. They decrease significantly with increasing BN mole fraction in the mixture. Conductance Measurements Molar conductances of CuClO, -4CH3CN and [Cu(DMPhen),]ClO, were measured in the concentration range (1-60) x lop4 mol dm-3 at 298 K in BN-AN mix-tures. The limiting molar conductances (A,) and ion-association constants (K,) in all cases were determined by analysing the conductance data by the Shedlovsky equation' ' using a procedure reported previ~usly.'~.' The A, values for CuClO, and [Cu(DMPhen),]ClO, are report- ed in Table 2 along with some literature values for these salts.' 3-1 Using the tg,+ and A, values for CuClO, from Table 2, limiting ionic conductances (A:) for Cu' and ClO, ions have been calculated (Table 3) using the equations: Ao(C~C104)t&+ A&+ (3)= Ao(CuC104)= A:,+ + A&oz (4) Table 3 also lists the 1; values for [Cu(DMPhen),]+ in various BN-AN mixtures obtained by combining the A, values for [Cu(DMPhen),]ClO, from Table 2 with the corre- sponding A&oz values. Our A&+ and A&,, values (64.64 and 103.26 S cm2 mol-' in pure AN in Table 3) are in good agreement with the values (64.7 and 103.3 S cm2 mol-') reported by Yeager and Krat~chvil'~and Kay and co-workers.' g From the A: values of Table 3 the solvated radii (ri) for various ions have been calculated by using the eq~ation.'~ r.= -''' F2 + 0.0103~+ ry' 67rNqA9 J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 0.400 I I + 0;c 0.275 0.250 0 0.05 0.10 0.15 0.20 0.25 C/mol dm-3 Fig. 1 Longsworth function for Cu+ cation (t2u+)us. molar concen- tration of CuCIO, * 4CH3CN in BN-AN mixtures at 298 K. mol% BN: 0,O; 0, 100.11.4;A, 25.5; *, 43.4; x, 67.2; 0, Where F is the Faraday constant, N is Avogadro's number, q and E are the solvent viscosity and permittivity and ry is an adjustable parameter, taken as 0.085 nm for AN, BN and all BN-AN mixtures.The solvated radii for Cu+, [Cu(DMPhen),]+ and ClO, ions thus obtained are listed in Table 3. The ri values for Cu' and [Cu(DMPhen),] cations+ increase linearly with the BN mole fraction in the mixture. The ri value for ClO, does not show any variation with solvent composition. There is, therefore, no preferential solva- tion of Cu', [Cu(DMPhen),]+ or ClO, in AN, BN or AN-BN mixture^.^*'^^'^^^^ The increase in ri for Cu+ and [Cu(DMPhen),]' with BN mole fraction is simply due to the replacement of AN molecules by the more voluminous BN molecules in the solvation sphere of these ions with increas- ing mole fraction of BN.Ultrasonic Velocity Measurements Ultrasonic velocities (u) and densities (p) of binary mixtures of BN and AN as well as of CuC10,.4CH3CN and [Cu(DMPhen),]ClO, in these mixtures containing 0, 11.4, 25.5, 43.4, 67.2 and 100 mol% BN were measured in the con- centration range 0.01-0.15 mol kg- ' at 298 K. The ultrasonic velocities of the binary mixtures are reported in Table 1 while the ultrasonic velocities as a function of molality of the copper(r) salts are presented in Fig. 2. Fig. 2 shows that in both cases the ultrasonic velocities increase linearly with the molality of the electrolytes. Also the ultrasonic velocity Table 2 Limiting transference numbers of Cu+ cation in CuCIO, and A. and K, values for CuClO, and [Cu(DMPhen),]ClO, in BN-AN mixtures at 298 K CuClO, BN(mol%) Ao/S cm2 mol-'t:U f 0.385 167.9 (1 68.2)b (1 68.4)c (1 68.0)d (167.8)" 11.4 0.376 134.3 25.5 0.366 105.5 43.4 0.346 83.0 67.2 0.332 64.1 100 0.324 43.5 a Ref. 17; ref.13; ref. 14; ref. 15; " ref. 16. Cu(DMPhen),ClO, KJdm' mol-' Ao/S cm2 mol-' KJdm3 mol-' 17 155.6 (159.4)8 3 123.9 98.2 3 77.8 5 61.0 42.5 J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 3 Limiting conductances and solvated radii (ri)in BN-AN mixtures at 298 K cu + [Cu( DMPhen),] c10;+ BN(mol%) Ip/S cm2 mol-' rJnm iLO/S cm2 mol -' rJnm Ip/S cm' mol- ' r,/nm 0 64.64 0.49 52.34 0.57 103.26 0.36 11.4 50.50 0.49 40.10 0.57 83.80 0.34 25.5 38.61 0.51 31.31 0.60 66.89 0.34 43.4 28.72 0.54 23.52 0.63 54.28 0.34 67.2 2 1.28 0.56 18.18 0.64 42.82 0.34 100 14.09 0.60 13.09 0.64 29.41 0.34 increases significantly with increasing BN mole fraction in the ent molal isentropic compressibilities, K# for both electrolytes mixture.were calculated using the equations given previously.21 The The isentropic compressibility (K~)of each electrolyte was limiting apparent molal isentropic compressibilities (K:) were calculated using the relation extrapolated from the linear plots of K# us. m1I2 by the least- squares method using the equation Ks = W2P) (6) K, = icg + A,m'I2 (7)The isentropic compressibilities for CuClO, .4CH,CN and [Cu(DMPhen),]ClO, decrease linearly with increasing Plots of K# us.m1'2are shown in Fig. 4. and the best extrapo- molality of the salts in BN-AN mixtures (Fig. 3). The appar- lated K: and A, values are reported in Table 4. There are no 90 1410 80 1360 70 601310 50 7 1260 I L E 0 0.05 0.10 0.15 0.20 0.25 2 40--. WI 90--. x1410 80 1360 70 60 1310 50 1260 0 0.02 0.04 0.06 0.08 0.10 40 0 0.02 0.04 0.06 0.08 0.10 m/mol kg-m/mol kg-' Fig. 2 Ultrasonic velocity us. molality for (a) CuCIO, .4CH3CN Fig. 3 Isentropic compressibility us. molality for (a) and (b) [Cu(DMPhen),]ClO, in BN-AN mixtures at 298 K. CuCIO, .4CH,CN and (b) [Cu(DMPhen), JCIO, in BN-AN mix-Symbols as in Fig. 1. tures at 298 K. Symbols as in Fig. 1. Table 4 Limiting apparent molal isentropic compressibilities and the slope of eqn.(7) for CuCIO, .4CH,CN and [Cu(DMPhen),]ClO, in BN-AN mixtures at 298 K CUCIO, * 4CH,CN [Cu(DMPhen),]CIO, BN(mol%) KP~O-~an3mol-' bar-' 104~~ K$'~O-~cm' mol-' bar-' 104A, 0 -40 24 -150 230 11.4 -8 -83 -56 -88 25.5 -1 -82 -29 -187 43.4 8 -39 -4 -160 67.2 10 -5 21 -221 100 49 -8 90 -222 0 -2 0 -40 -60 0.1 0.2 0.3 0.4 0.5 d1 o 50 F\ sz" 0 -50 -1 00 -1 50 L I I I I I 0.05 0.10 0.15 0.20 0.25 0.30 0.: m /2/mo11/2kg-1 /2 Fig. 4 Apparent molal isentropic compressibility us. square root of molality for (a) CuClO, * 4CH,CN and (b) [Cu(DMPhen),]CIO, in BN-AN mixtures at 298 K. Symbols as in Fig. 1. compressibility data on copper@ salts with which our K: values from Table 4 can be compared. The maximum uncer- tainty in K: values of Table 4, on the basis of our previous comparison of other salts, is estimated to be _+3 x lop4cm3 mol-' bar.-' The results indicate that both copper(1) salts are structure makers in AN and the structure-making effects decrease with increasing mole fraction of BN in BN-AN mixtures.The authors are grateful to the CSIR, New Delhi for a research grant under the research scheme 1( 1221)/91-EMR-II J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 and for the award of Senior Research Fellowship to J.S. and a Research Associateship to V.A. The authors thank Ranbir Singh for the computer analysis of the conductance data. References 1 D. S. Gill, K. S. Arora, J. Tewari and B.Singh, J. Chem. SOC., Faraday Trans., 1988,84,1729. 2 D. S. Gill, J. Tewari, G. Singh and M. S. Bakshi, J. Chem. SOC., Faraday Trans., 1991,87,1155. 3 D. S. Gill, J. Solution Chem., 1979,8, 691. 4 D. S. Gill, T. Kaur, H. Kaur, I. M. Joshi and J. Singh, J. Chem. SOC., Faraday Trans., 1993,89, 1737. 5 J. A. Riddick, W. B. Bunger and T. K. Sakano, Organic Solvents, Physical Properties and Methods of Purijication, Wiley Inter- science, New York, 4th edn., 1986. 6 B. J. Hathaway, D. G. Holah and J. D. Postlethwaite, J. Chem. SOC.,1961, 3215. 7 J. Bassett, R. C. Denny, G. H. Jeffery and J. Mendham, Vogel's Textbook of Quantitative Inorganic Analysis, Longman, London, 4th edn., 1978. 8 J. 0. Wear, C. V. McNully and E. S. Amis, J. Inorg. Nucl.Chem., 1961,18,48. 9 D. S. Gill, A. N. Sharma and H. Schneider, J. Chem. SOC., Faraday Trans. I, 1982,78,465. 10 R. L. Kay and J. L. Dye, Proc. Natl. Acad. Sci. USA, 1963,49, 5. 11 R. M. Fuoss and F. Accascina, Electrolytic Conductance, Inter-science, New York, 1959; R. M. Fuoss and T. Shedlovsky, J. Am. Chem. SOC., 1949,71,1496. 12 D. S. Gill, and M. B. Sekhri, J. Chem. SOC., Faraday Trans. 1, 1982,78, 119. 13 D. S. Gill and M. S. Chauhan, Z. Phys. Chem. NF, 1984, 140, 139. 14 H. L. Yeager and B. Kratochvil, J. Phys. Chem., 1969,73, 1963. 15 D. S. Gill and R. Nording, 2. Phys., Chem. NF, 1983,136, 117. 16 D. S. Gill, N. Kumari and M. S. Chauhan, J. Chem. SOC., Faraday Trans. I, 1985,81,687. 17 K. Miyoshi, J. Phys. Chem., 1972,76, 3029. 18 C. H. Springer, J. F. Coetzee and R. L. Kay, J. Phys. Chem., 1969, 73,471. 19 D. S. Gill, Electrochim. Acta, 1979,24,701; 1977,22,491. 20 D. S. Gill, S. Chauhan and M. S. Chauhan, Z. Phys. Chem. NF, 1986,150, 113. 21 J. Singh, T. Kaur, V. Ali and D. S. Gill, J. Chem. SOC., Faraday Trans., 1994,90,579. Paper 3/05019J; Received 18th September, 1993