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Ultrasonic relaxation investigations of thorium nitrate in water
Journal
of the Less-Common
Metals,
ULTRASONIC RELAXATION NITRATE IN WATER*
HERBERT
126(1986)
323-327
323
INVESTIGATIONS
OF THORIUM
B. SILBER
Chemistry Department, San Jose State University, San Jose, CA 9519Zt and University of Texas at San Antonio, San Antonio, TX 78285fU.S.A.) (Received March 18,1986)
Summary Ultrasonic absorption measurements have been carried out on Th(NO,), solutions in water as a function of thorium(IV) and NO,- concentrations and pH. Only a single relaxation occurs in each Th(NO,), solution, attributed to complexation between Th(IV) and NO, -. The effect of complexation is discussed in terms of literature models involving hydrolysis equilibria and osmotic pressure measurements.
1. Introduction The behavior of metal ion nitrates towards ultrasonic waves has provided not only information about the kinetics of metal ion complexation, but also has led to an understanding of the differences between inner and outer sphere complexes [l]. In water, the lanthanide nitrates form both inner and outer sphere complexes, consistent with other spectroscopic measurements [2,3]. The two types of complexes are detected by the presence of two relaxations, one at high frequencies attributed to outer sphere complexes, and one at low frequencies owing to inner sphere complexes. Lanthanide chlorides are postulated to be outer sphere because of the absence of any chemical relaxations in water [4]. A comparison of the results on lanthanum(III), yttrium(II1) and scandium(II1) chlorides reveals that La3+ and Y3 ’ behave like lanthanides, whereas Sc3 ’ acts like a d-type transition metal with inner sphere chlorides detected [5]. Similarly, studies on zinc nitrates in water reveal the absence of inner sphere complexes, a feature different for this transition element from that of the f elements. Y(NO,), has been observed to have ultrasonic absorption attributed to inner sphere complexation [S]. In order to determine if Th(NO,), is
*Paper presented at the 17th Rare Earth Hamilton, Ontario, Canada, June 9 ~~12, 1986. t Correspondence address.
Research
Conference,
McMaster
63 Elsevier Sequoia/Printed
University,
in The Netherlands
324
chemically similar to the lanthanides or the d-type transition element Zn2+, we have initiated this ultrasonic investigation on Th(NO,), in water.
2. Experimental
details
The ultrasonic relaxation equipment and techniques utilized in these experiments have been described [5,7]. The Th(N0,),.4H20 (Fisher, ACS certified) was used without further purification. Studies were made as a function of pH, Th(NO,), concentration and NaNO, concentration in order to explore the chemistry, and the data are shown in Table 1. The ultrasonic absorption data are presented in terms of ct/f2,the absorption divided by the frequency squared [5,7]. An alternative procedure is to calculate the absorption in terms of the excess absorption p which is the difference between olJf’ and the solvent absorption multiplied by the experimental frequency and the solution sound velocity. When p is plotted as a function of the frequency f a maximum is observed at the frequency equal to the relaxation frequency f, [5,6], as shown in Fig. 1 for Er(NO,),. The 0.20 M Th(NO,), data do not have a maximum within the experimental frequency range, as is also shown in Fig. 1.
0 --5
___ 53
101
Frequency,
-. 149
‘-
197
245
MHz
Fig. 1. The excess absorption (104np) for 0.22 M Er(NO,), x, erbium(II1); 0. thorium(IV).
[S] and 0.20 M Th(NO,),
in water at 25 “C:
3. Results and discussion At all concentrations studied, complexation between thorium(IV) and nitrate is detected. Within experimental error only a single relaxation is
325
TABLE 1 The ultrasonic Frequency
absorption
for thorium nitrate solutions at 25 “C
10” z/f (np cm-
12)
Off@
5.15 7.03 9.16 10.45 11.29 12.19 13.26 15.23 20.19 28.17 30.48 36.22 44.24 50.91 70.85 90.88 111.20 131.91 151.93 172.83 191.91 213.18 234.11
0.2 M pH = 0.2
0.2 M pH = 1.9
0.2 M pH = 2.8
0.2M +l.BM nitrate
1686.36 1103.82 652.25 409.64 448.48 376.96 334.55 274.22 164.62 98.31 89.80 68.52 52.64 47.26 36.34 31.74 28.82 27.16 26.64 25.56 20.34 20.74 24.13
1458.27 886.15 540.17 464.01 411.41 334.12 318.19 244.84 142.72 82.76 80.00 66.46 51.21 44.64 35.57 31.16 28.69 27.99 26.99 25.78 24.87 25.56 26.55
1394.44 887.52 548.95 405.72 371.59 331.81 276.88 220.84 147.37 89.45 81.36 64.17 51.51 43.52 34.17 30.57 30.87 27.33 26.30 27.09 27.05 25.17 24.67
2263.91 1486.59 951.01 694.99 672.30 552.27 466.27 397.61 236.56 138.37 130.32 93.80 70.25 64.25 44.95 37.03 33.28 30.08 28.95 25.46 23.44 23.36 23.14
0.4M
2643.59 1507.69 1208.22 1097.15 923.60 794.67 637.80 390.83 219.02 186.56 145.44 109.62 89.21 60.27 47.77 39.49 35.59 33.77 31.70
0.6M
7099.31 4263.86 3044.06 2275.59 1862.80 1475.31 1300.73 719.47 386.92 335.63 250.05 179.64 145.29 92.02 68.61 54.75 47.93 41.05 37.99
present. Because f, occurs at a lower frequency than the low limit of the ultrasonic frequency measurements, the calculated f, is not reliable and a calculation of the kinetic rate constants from the data is ruled out. This is different from the analogous lanthanide systems where f, for the low frequency relaxation is usually within the experimental frequency range, (Fig. 1). However, even in cases where f, is below the frequency limit, the computer program used to calculate f, and the relaxation amplitude can calculate a best fit result with uncertainties. Moreover, our experience [5,7] has shown that absorption amplitudes can still be obtained, and useful information can be obtained from trends as a function of concentration. The relaxation frequency f, and the relaxation amplitude A, both increase with increases in either thorium(IV) or excess nitrate concentrations. Using freshly prepared solutions and raising the pH to about 2.8, where hydrolysed thorium species are present, slightly lowers the relaxation amplitude and has little effect upon f,, No measurements were made on aged solutions, which would have reached hydrolytic equilibrium. Making the solutions strongly acidic (pH = 0.2) increases the amplitude. Hence
326
we believe the complexation is between unhydrolyzed thorium(IV) and NO,-. Increasing thorium(IV) appears to have a greater effect than excess nitrate on the amplitude. If the reaction is simple outer sphere ion pair formation, f, would be proportional to the sum of free thorium(IV) plus NO,- concentrations and a similar increase would also occur for inner sphere complexes. The calculated f, for 0.60MTh(NO,), and 0.20 Th(NO,), with 1.8M NaNO, are within experimental error of each other, consistent with their sums being approximately the same, assuming a small complexation constant. However, the excess absorption is approximately three times greater for the 0.60 M Th(NO,), solution compared with that of the 0.20 MTh(NO,), with excess NaNO,, suggesting that the driving force of the reaction is the volume change associated with thorium(IV) complexation. Analysis of Fig. 1 shows that the amplitude is significantly higher for thorium(IV) than for erbium(III), a typical lanthanide in our ultrasonic experiments. Zinc(I1) has no excess absorption with nitrate in water, which means that the sound absorption for 0.40 M Zn(NO,), solutions is the same as that of pure water. We believe this high amplitude for thorium(IV) is the result of the higher charge on thorium(IV) compared with that of the lanthanides, consistent with the idea that thorium(IV) is a harder acid than the lanthanide(II1) ions. What is the effect of complexation between thorium(IV) and nitrate? This can be shown by analyzing two recent sets of data. The hydrolysis reactions of thorium(IV) have been studied for more than 30 years [g-14]. A summary of the results [14] demonstrates the existence of 11 models to explain which species are present with thorium(IV) concentrations varying between 1 x 1O-4 and 0.5M using NaCl, NaClO,, LiNO,, KNO, or Mg(NO,), as the “inert” electrolyte. Most papers do not include nitrate complexation in the calculations of the polymeric and hydrolyzed thorium(IV) species and hence our results would predict both deviations in the stoichiometry of Th,(OH), and formation constants when nitrate is present compared with studies in Cl- or ClO,-, where anion complexation with the electrolyte is less important. Some of these discrepancies may disappear if the models include the possibility of nitrate complexation. Another series of experiments using Th(NO,), in which different investigators use a range of Th(NO,), concentrations from dilute solutions through 0.25M is the determination of activities by vapor pressure osmometry or isopiestic measurements [15-173. The results are calculated in terms of Th(NO,), being a 4:l electrolyte, a feature which occurs in dilute solutions, but not at higher concentrations where Th(IV)-NO,complexes exist. Lemire et al. conclude that differences in the results are caused by the Th(NO,), solutions rather than the osmometry measurements, suggesting that hydrolysis may be the difference even at low pH [17]. Our results imply that some of the differences are due to Th(IV)-NO,complexes being present, but excluded in the calculations; hence, our results suggest recalculations of the activity data. This may also yield accurate values of the Th(IV)-NO, _ complex formation constants. Future ultrasonic studies for thorium(IV) systems should include both the chlorides and the perchlorates to determine if complexation with these ligands
occurs in water. This would provide further comparisons between thorium(IV) and the lanthanides where inner sphere nitrates, but not chlorides or perchlorates, which form in water, compared with zinc(I1) and scandium(II1) where the chlorides are inner sphere in water.
Acknowledgments We would like to acknowledge the financial support of the NIH Minority Biomedical Support Program (MBRS) through Grant RR-08192-06 (SJSU) and The Robert A. Welch Foundation of Houston, TX for Grant AX-659 (UTSA).
References
2 3 4 5 6 8 9 10 11 12 13 14 15 16 17
H. Diebler and M. Eigen, 2. Phys. Chem., N.F., 20 (1959) 299. M. Eigen and R. G. Wilkins in Mechanisms of Inorganic Reactions, American Chemical Society, Washington, D.C., 1965. R. Garnsey and D. W. Ebdon, J. Am. Chem. Sot., 91(1969) 50. H. B. Silber, N. Scheinin, G. Atkinson and J. J. Grecsek, J. Chem. Sot., Faraday Trans. Z, 68 (1972) 1200. J. Reidler and H. B. Silber, J. Chem. Sot., Chem. Commun., (1973) 354. H. B. Silber and T. Mioduski, Znorg. Chem., 23 (1984) 1577. H.-C. Wang and P. J. Hemmes, J. Phys. Chem., 78(1974) 261. H. B. Silber, L. U. Kromer and F. Gaizer, Znorg. Chem., 20(1981) 3323. J. Reidler and H. B. Silber, J. Znorg. Nucl. Chem., 36(1974) 175. S. Hietanen, Acta Chem. Stand., 8 (1954) 1626. S. Hietanen and L. G. Sillen, Acta Chem. &and., 18 (1964) 1018; 22 (1968) 265. K. A. Kraus and R. W. Holmberg, J. Phys. Chem., 58 (1954) 325. C. F. Baes, N. J. Meyer and C. E. Roberts, Znorg. Chem., 4 (1965) 518. P. R. Danesi, M. Magini, S. Margherita and G. D’Alessandro, Energ. Nucl. (Milan), 15 (1968) 335. N. A. Milic, Acta Chem. &and., 25(1971) 2487. P. L. Brown, J. Ellis and R. N. Sylva, J. Chem. Sot., Dalton, (1983) 31. R. A. Robinson and B. J. Levien, J. Trans. Proc. R. Sot. N.Z., 76(1946) 295. A. Apelblat, D. Azoulay and A. Saher, J. Chem. Sot., Faraday Trans. I, 69(1973) 1618. R. J. Lemire, N. H. Sagert and D. W. P. Lau, J. Chem. Eng. Data, 29 (1983) 329.
of the Less-Common
Metals,
ULTRASONIC RELAXATION NITRATE IN WATER*
HERBERT
126(1986)
323-327
323
INVESTIGATIONS
OF THORIUM
B. SILBER
Chemistry Department, San Jose State University, San Jose, CA 9519Zt and University of Texas at San Antonio, San Antonio, TX 78285fU.S.A.) (Received March 18,1986)
Summary Ultrasonic absorption measurements have been carried out on Th(NO,), solutions in water as a function of thorium(IV) and NO,- concentrations and pH. Only a single relaxation occurs in each Th(NO,), solution, attributed to complexation between Th(IV) and NO, -. The effect of complexation is discussed in terms of literature models involving hydrolysis equilibria and osmotic pressure measurements.
1. Introduction The behavior of metal ion nitrates towards ultrasonic waves has provided not only information about the kinetics of metal ion complexation, but also has led to an understanding of the differences between inner and outer sphere complexes [l]. In water, the lanthanide nitrates form both inner and outer sphere complexes, consistent with other spectroscopic measurements [2,3]. The two types of complexes are detected by the presence of two relaxations, one at high frequencies attributed to outer sphere complexes, and one at low frequencies owing to inner sphere complexes. Lanthanide chlorides are postulated to be outer sphere because of the absence of any chemical relaxations in water [4]. A comparison of the results on lanthanum(III), yttrium(II1) and scandium(II1) chlorides reveals that La3+ and Y3 ’ behave like lanthanides, whereas Sc3 ’ acts like a d-type transition metal with inner sphere chlorides detected [5]. Similarly, studies on zinc nitrates in water reveal the absence of inner sphere complexes, a feature different for this transition element from that of the f elements. Y(NO,), has been observed to have ultrasonic absorption attributed to inner sphere complexation [S]. In order to determine if Th(NO,), is
*Paper presented at the 17th Rare Earth Hamilton, Ontario, Canada, June 9 ~~12, 1986. t Correspondence address.
Research
Conference,
McMaster
63 Elsevier Sequoia/Printed
University,
in The Netherlands
324
chemically similar to the lanthanides or the d-type transition element Zn2+, we have initiated this ultrasonic investigation on Th(NO,), in water.
2. Experimental
details
The ultrasonic relaxation equipment and techniques utilized in these experiments have been described [5,7]. The Th(N0,),.4H20 (Fisher, ACS certified) was used without further purification. Studies were made as a function of pH, Th(NO,), concentration and NaNO, concentration in order to explore the chemistry, and the data are shown in Table 1. The ultrasonic absorption data are presented in terms of ct/f2,the absorption divided by the frequency squared [5,7]. An alternative procedure is to calculate the absorption in terms of the excess absorption p which is the difference between olJf’ and the solvent absorption multiplied by the experimental frequency and the solution sound velocity. When p is plotted as a function of the frequency f a maximum is observed at the frequency equal to the relaxation frequency f, [5,6], as shown in Fig. 1 for Er(NO,),. The 0.20 M Th(NO,), data do not have a maximum within the experimental frequency range, as is also shown in Fig. 1.
0 --5
___ 53
101
Frequency,
-. 149
‘-
197
245
MHz
Fig. 1. The excess absorption (104np) for 0.22 M Er(NO,), x, erbium(II1); 0. thorium(IV).
[S] and 0.20 M Th(NO,),
in water at 25 “C:
3. Results and discussion At all concentrations studied, complexation between thorium(IV) and nitrate is detected. Within experimental error only a single relaxation is
325
TABLE 1 The ultrasonic Frequency
absorption
for thorium nitrate solutions at 25 “C
10” z/f (np cm-
12)
Off@
5.15 7.03 9.16 10.45 11.29 12.19 13.26 15.23 20.19 28.17 30.48 36.22 44.24 50.91 70.85 90.88 111.20 131.91 151.93 172.83 191.91 213.18 234.11
0.2 M pH = 0.2
0.2 M pH = 1.9
0.2 M pH = 2.8
0.2M +l.BM nitrate
1686.36 1103.82 652.25 409.64 448.48 376.96 334.55 274.22 164.62 98.31 89.80 68.52 52.64 47.26 36.34 31.74 28.82 27.16 26.64 25.56 20.34 20.74 24.13
1458.27 886.15 540.17 464.01 411.41 334.12 318.19 244.84 142.72 82.76 80.00 66.46 51.21 44.64 35.57 31.16 28.69 27.99 26.99 25.78 24.87 25.56 26.55
1394.44 887.52 548.95 405.72 371.59 331.81 276.88 220.84 147.37 89.45 81.36 64.17 51.51 43.52 34.17 30.57 30.87 27.33 26.30 27.09 27.05 25.17 24.67
2263.91 1486.59 951.01 694.99 672.30 552.27 466.27 397.61 236.56 138.37 130.32 93.80 70.25 64.25 44.95 37.03 33.28 30.08 28.95 25.46 23.44 23.36 23.14
0.4M
2643.59 1507.69 1208.22 1097.15 923.60 794.67 637.80 390.83 219.02 186.56 145.44 109.62 89.21 60.27 47.77 39.49 35.59 33.77 31.70
0.6M
7099.31 4263.86 3044.06 2275.59 1862.80 1475.31 1300.73 719.47 386.92 335.63 250.05 179.64 145.29 92.02 68.61 54.75 47.93 41.05 37.99
present. Because f, occurs at a lower frequency than the low limit of the ultrasonic frequency measurements, the calculated f, is not reliable and a calculation of the kinetic rate constants from the data is ruled out. This is different from the analogous lanthanide systems where f, for the low frequency relaxation is usually within the experimental frequency range, (Fig. 1). However, even in cases where f, is below the frequency limit, the computer program used to calculate f, and the relaxation amplitude can calculate a best fit result with uncertainties. Moreover, our experience [5,7] has shown that absorption amplitudes can still be obtained, and useful information can be obtained from trends as a function of concentration. The relaxation frequency f, and the relaxation amplitude A, both increase with increases in either thorium(IV) or excess nitrate concentrations. Using freshly prepared solutions and raising the pH to about 2.8, where hydrolysed thorium species are present, slightly lowers the relaxation amplitude and has little effect upon f,, No measurements were made on aged solutions, which would have reached hydrolytic equilibrium. Making the solutions strongly acidic (pH = 0.2) increases the amplitude. Hence
326
we believe the complexation is between unhydrolyzed thorium(IV) and NO,-. Increasing thorium(IV) appears to have a greater effect than excess nitrate on the amplitude. If the reaction is simple outer sphere ion pair formation, f, would be proportional to the sum of free thorium(IV) plus NO,- concentrations and a similar increase would also occur for inner sphere complexes. The calculated f, for 0.60MTh(NO,), and 0.20 Th(NO,), with 1.8M NaNO, are within experimental error of each other, consistent with their sums being approximately the same, assuming a small complexation constant. However, the excess absorption is approximately three times greater for the 0.60 M Th(NO,), solution compared with that of the 0.20 MTh(NO,), with excess NaNO,, suggesting that the driving force of the reaction is the volume change associated with thorium(IV) complexation. Analysis of Fig. 1 shows that the amplitude is significantly higher for thorium(IV) than for erbium(III), a typical lanthanide in our ultrasonic experiments. Zinc(I1) has no excess absorption with nitrate in water, which means that the sound absorption for 0.40 M Zn(NO,), solutions is the same as that of pure water. We believe this high amplitude for thorium(IV) is the result of the higher charge on thorium(IV) compared with that of the lanthanides, consistent with the idea that thorium(IV) is a harder acid than the lanthanide(II1) ions. What is the effect of complexation between thorium(IV) and nitrate? This can be shown by analyzing two recent sets of data. The hydrolysis reactions of thorium(IV) have been studied for more than 30 years [g-14]. A summary of the results [14] demonstrates the existence of 11 models to explain which species are present with thorium(IV) concentrations varying between 1 x 1O-4 and 0.5M using NaCl, NaClO,, LiNO,, KNO, or Mg(NO,), as the “inert” electrolyte. Most papers do not include nitrate complexation in the calculations of the polymeric and hydrolyzed thorium(IV) species and hence our results would predict both deviations in the stoichiometry of Th,(OH), and formation constants when nitrate is present compared with studies in Cl- or ClO,-, where anion complexation with the electrolyte is less important. Some of these discrepancies may disappear if the models include the possibility of nitrate complexation. Another series of experiments using Th(NO,), in which different investigators use a range of Th(NO,), concentrations from dilute solutions through 0.25M is the determination of activities by vapor pressure osmometry or isopiestic measurements [15-173. The results are calculated in terms of Th(NO,), being a 4:l electrolyte, a feature which occurs in dilute solutions, but not at higher concentrations where Th(IV)-NO,complexes exist. Lemire et al. conclude that differences in the results are caused by the Th(NO,), solutions rather than the osmometry measurements, suggesting that hydrolysis may be the difference even at low pH [17]. Our results imply that some of the differences are due to Th(IV)-NO,complexes being present, but excluded in the calculations; hence, our results suggest recalculations of the activity data. This may also yield accurate values of the Th(IV)-NO, _ complex formation constants. Future ultrasonic studies for thorium(IV) systems should include both the chlorides and the perchlorates to determine if complexation with these ligands
occurs in water. This would provide further comparisons between thorium(IV) and the lanthanides where inner sphere nitrates, but not chlorides or perchlorates, which form in water, compared with zinc(I1) and scandium(II1) where the chlorides are inner sphere in water.
Acknowledgments We would like to acknowledge the financial support of the NIH Minority Biomedical Support Program (MBRS) through Grant RR-08192-06 (SJSU) and The Robert A. Welch Foundation of Houston, TX for Grant AX-659 (UTSA).
References
2 3 4 5 6 8 9 10 11 12 13 14 15 16 17
H. Diebler and M. Eigen, 2. Phys. Chem., N.F., 20 (1959) 299. M. Eigen and R. G. Wilkins in Mechanisms of Inorganic Reactions, American Chemical Society, Washington, D.C., 1965. R. Garnsey and D. W. Ebdon, J. Am. Chem. Sot., 91(1969) 50. H. B. Silber, N. Scheinin, G. Atkinson and J. J. Grecsek, J. Chem. Sot., Faraday Trans. Z, 68 (1972) 1200. J. Reidler and H. B. Silber, J. Chem. Sot., Chem. Commun., (1973) 354. H. B. Silber and T. Mioduski, Znorg. Chem., 23 (1984) 1577. H.-C. Wang and P. J. Hemmes, J. Phys. Chem., 78(1974) 261. H. B. Silber, L. U. Kromer and F. Gaizer, Znorg. Chem., 20(1981) 3323. J. Reidler and H. B. Silber, J. Znorg. Nucl. Chem., 36(1974) 175. S. Hietanen, Acta Chem. Stand., 8 (1954) 1626. S. Hietanen and L. G. Sillen, Acta Chem. &and., 18 (1964) 1018; 22 (1968) 265. K. A. Kraus and R. W. Holmberg, J. Phys. Chem., 58 (1954) 325. C. F. Baes, N. J. Meyer and C. E. Roberts, Znorg. Chem., 4 (1965) 518. P. R. Danesi, M. Magini, S. Margherita and G. D’Alessandro, Energ. Nucl. (Milan), 15 (1968) 335. N. A. Milic, Acta Chem. &and., 25(1971) 2487. P. L. Brown, J. Ellis and R. N. Sylva, J. Chem. Sot., Dalton, (1983) 31. R. A. Robinson and B. J. Levien, J. Trans. Proc. R. Sot. N.Z., 76(1946) 295. A. Apelblat, D. Azoulay and A. Saher, J. Chem. Sot., Faraday Trans. I, 69(1973) 1618. R. J. Lemire, N. H. Sagert and D. W. P. Lau, J. Chem. Eng. Data, 29 (1983) 329.