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Fluorine magnetic resonance line width as a probe for the study of gallium fluoride complexes
J. inorg,nucl.Chem..1969,Vol. 3I. pp. 3869to 3871. PergamonPress. Printedin Great Britain
NOTES
Fluorine magnetic resonance line width as a probe for the study of gallium fluoride complexes (First received 3 April 1969; in revised form 16 June 1969) THE LINE width of a resonating nucleus when bonded to another atom which has a quadrupole moment (spin > 1/2) is broad [1] because of quadrupole induced fast spin lattice relaxation of the nucleus with quadrupole moment. The relaxation time of the system will be dominated by the presence of quadrupole moment in the nucleus whose relaxation time T1 is governed by the following equation: 1 T,
3 (21+3) 1 _ (eZqQ) 2 4012(21+1~ ( l + - ~ n ~ ) ~ r
(i)
where e is the electronic charge, Q the quadrupole moment, q the electric field gradient, r the correlation time, r/the asymmetry parameter, and 1 the nuclear spin quantum number. Accordingly the line width of the laF resonance in the fluoroanions of the type MF,, -n (where M is an atom, n the valence of the anion and m the coordination number) will be broader, depending on the symmetry of the ion and magnitude of the quadrupole moment. This effect has been observed in the 19F resonance spectra of many fluoroanions [2-7]. Gallium exists in two isotopes namely 6aGa and riGa with quadrupole moment 0.178 and 0.112 (e × 10-24 cm0 respectively. Hence the 1aF line width of gallium fluoride solution should show the characteristic line width changes. This note summarizes the results of some studies on the ~OFnuclear magnetic resonance (NMR) spectra of gallium fluoride complexes (obtained by the addition of Ga 3+ ions in silver fluoride solution).
EXPERIMENTAL Reagent grade fluoride and Gallium perchlorate were placed in solution by dissolving in doubly distilled water. The NMR spectra were recorded on a Varian HR60 high resolution spectrometer, operating at 56-4 MHz. Chemical shifts and line widths were measured by the usual side band technique.
RESULTS AND DISCUSSION The 19F NMR spectrum of aqueous silver fluoride solutions showed a sharp peak around 52 ppm with reference to trifluoroacetic acid as external standard. This corresponds to a chemical shift associated with F - ion. The aqueous silver fluoride solution showed little concentration dependence of chemical shift. The range of chemical shift was 51-4 to 52.1 ppm for a 0. - 3 + molar solution. 1. T. D. Alger and H. S. Gutowsky, J. chem. Phys. 48, 4625 (1968). 2. K. J. Packer and E. L. Muetterties, Proc. chem. Soc. 147 (1964). 3. R. E. Connick and R. E. Poulson, J. Am. chem. Soc. 79, 5153 (1957); J. phys. chem. 63, 568 (1959). 4. K. Kuhlmann and D. M. Grant,J. phys. Chem. 68, 3208 (1964). 5. R. Haque and L. W. Reeves,J.phys. Chem. 70, 2753 (1966). 6. R. Haque and L. W. Reeves, Can. J. Chem. 44, 2770 (1966). 7. J. Feeney, R. Haque, L. W. Reeves and C. P. Yue, Can. J. Chem. 46, 1389 (1968). 3869
3870
Notes
However, by the addition of Ga s÷ ion a second peak around 65-73 ppm appeared, and the intensity of the first peak (F-) reduced with the increasing concentration of Ga s÷ ion. The line width and the chemical shift of the new peak was dependent on the ratio of the Ga 3+ion to fluoride ion concentration. However, the chemical shift of the F - ion peak was affected little by a change in the GaS÷/F- ion concentration. The line width and the chemical shift of the new peak at different molar ratios are given in Table 1. Table 1. ~gF chemical shift and line width of gallium fluoride peak at different molar ratios of Ga 3÷ and F - ion Molar ratio Chemical shift* [F-]/[Ga s+] (ppm) 14.3 7.15 4.76 3-52 2.42 0.95 0.47 0.15
65-3 73-3 73-0 75.0 77.8 73.4 73.5 73.0
Line width (Hz) 1450 1150 690 185 85 88 88 78
*Against trifluoroacetic acid as an external standard. The equilibrium in aqueous silver fluoride solution can be represented as: AgF ~-~ Ag ÷ + F-.
(ii)
However, by the addition of Ga 3+ ion the following additional reaction takes place in the solution. Ga s+ + n F - ~ GaF,~a-n (n varies from 1 to 6).
(iii)
The new 1OF resonance peak around 65-77 ppm can be attributed to the formation of various gallium fluoride complexes of the type GaF~ 3-". The rate of fluorine exchange between various gallium fluoride complexes is so rapid that only one average resonance peak is observable. However, the rate of fluorine exchange between the free fluoride ion (from silver fluoride) and various gallium fluoride complexes is slow and a separate peak for fluoride ion resonance and gallium fluoride complexes is always observable. The new resonance peak in the most dilute silver fluoride solutions (F-/Ga 3÷ < 1) can be associated with the GaF s÷ ion. In these solutions the chemical shift does not change much and the line width is less than 100 Hz. In more concentrated solutions of silver fluoride (F-/Ga s÷ < 1), however, chemical shift changes are observed towards low field and the broadening of the peak becomes much more prominant. These line width and chemical shift changes can be associated with the existence of complexes GaF2 +, GaFs and higher complex fluorides of gallium. The data can be compared with the work of Connick and Poulson[3] who observed similar results when aluminum ions were added to fluoride ions, and noticed increase in the line width when the (F-/AI s+) was greater than 2. The existence of quadrupole moment in 89Ga and riGa isotopes causes significant broadening of the gallium fluoride resonance peak. The quadrupole moment in the two gallium isotopes accelerates the nuclear relaxation rate so much that the gallium-fluorine couplings are not resolvable. The line width for higher floride complexes are much larger than the GaF s+ and GaF2 + complexes indicating that the higher fluoride complexes of gallium have a lower symmetry than the GaF 3+ and GaF2 + complexes.
Notes
3871
Acknowledgements-The author wishes to thank Professor L. W. Reeves for his interest during the progress of this work. R. HAQUE*
Department of Chemistry University of British Columbia Vancouver 8, British Columbia Canada
*Present address: Department of Agricultural Chemistry, Oregon State University, Corvallis, Oregon 97331.
J. inorg,nucl.Chem..1969,Vol.31, pp. 3871 to 3874. PergamonPress. Printedin Great Britain
Isolation of plutonium in chloride m e d i a - III Effects of nitrate and mono(2-ethylhexyl)phosphoric acid on extraction with di(2-ethylhexyl)phosphoric acid* (Received 2 June 1969) PREVIOUS papers in this series[l, 2] discussed methods for removing plutonium from hydrochloric acid solutions of irradiated targets in the USAEC Heavy Element Program for isolating transplutonium elements. The success of a plutonium isolation scheme involving solvent extraction with the monoacidic ester, di(2-ethylhexyl)phosphoric acid (HDEHP), has led to its routine use at the Transuranium Processing Facility (TRU) at Oak Ridge National Laboratory[3]. This note examines the influence of two contaminants, nitrate ion and mono(2-ethylhexyl)phosphoric acid, that are sometimes present in this extraction system. These contaminants increase the extraction of plutonium but impede its stripping, and the mono-ester acid also impairs intra-actinide separations. EXPERIMENTAL Reagents and experimental procedures were analogous to those described previously [2]. RESULTS AND DISCUSSION
Effect of nitrate Curves presented in Fig. 1 show the coefficients for the extraction of plutonium, curium, and californium by 1 M H D E H P in diethylbenzene (DEB) from nitric acid solution as a function of the nitric acid concentration. The order of extractability of these actinides is the same as that obtained in a hydrochloric acid system (2): Pu(IV) > Pu(VI) ~> Cf(IIl) > Cm(IIl). Each of these actinides is extracted more strongly from nitric than from hydrochloric acid media. This opposes the order of extraction that would be expected for Pu(IV) since plutonium forms a stronger complex with NO3- than with CI-; however, the extraction of thorium by 1 M H D E H P shows similar behavior [4]. *Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. 1. 2. 3. 4.
J. M. Chilton and J. J. Fardy, J. inorg, nucl. Chem. 31. I 171 (1969). J. M. Chilton and J. J. Fardy, J. inorg, nucl. Chem. To be published. D. E. Ferguson, USA EC Rep. ORNL-4145, p. 132 (1967). D. F. Peppard, G. W.Mason and S. McCarty, J. inorg, nucl. Chem. 13, 138 (1960).
NOTES
Fluorine magnetic resonance line width as a probe for the study of gallium fluoride complexes (First received 3 April 1969; in revised form 16 June 1969) THE LINE width of a resonating nucleus when bonded to another atom which has a quadrupole moment (spin > 1/2) is broad [1] because of quadrupole induced fast spin lattice relaxation of the nucleus with quadrupole moment. The relaxation time of the system will be dominated by the presence of quadrupole moment in the nucleus whose relaxation time T1 is governed by the following equation: 1 T,
3 (21+3) 1 _ (eZqQ) 2 4012(21+1~ ( l + - ~ n ~ ) ~ r
(i)
where e is the electronic charge, Q the quadrupole moment, q the electric field gradient, r the correlation time, r/the asymmetry parameter, and 1 the nuclear spin quantum number. Accordingly the line width of the laF resonance in the fluoroanions of the type MF,, -n (where M is an atom, n the valence of the anion and m the coordination number) will be broader, depending on the symmetry of the ion and magnitude of the quadrupole moment. This effect has been observed in the 19F resonance spectra of many fluoroanions [2-7]. Gallium exists in two isotopes namely 6aGa and riGa with quadrupole moment 0.178 and 0.112 (e × 10-24 cm0 respectively. Hence the 1aF line width of gallium fluoride solution should show the characteristic line width changes. This note summarizes the results of some studies on the ~OFnuclear magnetic resonance (NMR) spectra of gallium fluoride complexes (obtained by the addition of Ga 3+ ions in silver fluoride solution).
EXPERIMENTAL Reagent grade fluoride and Gallium perchlorate were placed in solution by dissolving in doubly distilled water. The NMR spectra were recorded on a Varian HR60 high resolution spectrometer, operating at 56-4 MHz. Chemical shifts and line widths were measured by the usual side band technique.
RESULTS AND DISCUSSION The 19F NMR spectrum of aqueous silver fluoride solutions showed a sharp peak around 52 ppm with reference to trifluoroacetic acid as external standard. This corresponds to a chemical shift associated with F - ion. The aqueous silver fluoride solution showed little concentration dependence of chemical shift. The range of chemical shift was 51-4 to 52.1 ppm for a 0. - 3 + molar solution. 1. T. D. Alger and H. S. Gutowsky, J. chem. Phys. 48, 4625 (1968). 2. K. J. Packer and E. L. Muetterties, Proc. chem. Soc. 147 (1964). 3. R. E. Connick and R. E. Poulson, J. Am. chem. Soc. 79, 5153 (1957); J. phys. chem. 63, 568 (1959). 4. K. Kuhlmann and D. M. Grant,J. phys. Chem. 68, 3208 (1964). 5. R. Haque and L. W. Reeves,J.phys. Chem. 70, 2753 (1966). 6. R. Haque and L. W. Reeves, Can. J. Chem. 44, 2770 (1966). 7. J. Feeney, R. Haque, L. W. Reeves and C. P. Yue, Can. J. Chem. 46, 1389 (1968). 3869
3870
Notes
However, by the addition of Ga s÷ ion a second peak around 65-73 ppm appeared, and the intensity of the first peak (F-) reduced with the increasing concentration of Ga s÷ ion. The line width and the chemical shift of the new peak was dependent on the ratio of the Ga 3+ion to fluoride ion concentration. However, the chemical shift of the F - ion peak was affected little by a change in the GaS÷/F- ion concentration. The line width and the chemical shift of the new peak at different molar ratios are given in Table 1. Table 1. ~gF chemical shift and line width of gallium fluoride peak at different molar ratios of Ga 3÷ and F - ion Molar ratio Chemical shift* [F-]/[Ga s+] (ppm) 14.3 7.15 4.76 3-52 2.42 0.95 0.47 0.15
65-3 73-3 73-0 75.0 77.8 73.4 73.5 73.0
Line width (Hz) 1450 1150 690 185 85 88 88 78
*Against trifluoroacetic acid as an external standard. The equilibrium in aqueous silver fluoride solution can be represented as: AgF ~-~ Ag ÷ + F-.
(ii)
However, by the addition of Ga 3+ ion the following additional reaction takes place in the solution. Ga s+ + n F - ~ GaF,~a-n (n varies from 1 to 6).
(iii)
The new 1OF resonance peak around 65-77 ppm can be attributed to the formation of various gallium fluoride complexes of the type GaF~ 3-". The rate of fluorine exchange between various gallium fluoride complexes is so rapid that only one average resonance peak is observable. However, the rate of fluorine exchange between the free fluoride ion (from silver fluoride) and various gallium fluoride complexes is slow and a separate peak for fluoride ion resonance and gallium fluoride complexes is always observable. The new resonance peak in the most dilute silver fluoride solutions (F-/Ga 3÷ < 1) can be associated with the GaF s÷ ion. In these solutions the chemical shift does not change much and the line width is less than 100 Hz. In more concentrated solutions of silver fluoride (F-/Ga s÷ < 1), however, chemical shift changes are observed towards low field and the broadening of the peak becomes much more prominant. These line width and chemical shift changes can be associated with the existence of complexes GaF2 +, GaFs and higher complex fluorides of gallium. The data can be compared with the work of Connick and Poulson[3] who observed similar results when aluminum ions were added to fluoride ions, and noticed increase in the line width when the (F-/AI s+) was greater than 2. The existence of quadrupole moment in 89Ga and riGa isotopes causes significant broadening of the gallium fluoride resonance peak. The quadrupole moment in the two gallium isotopes accelerates the nuclear relaxation rate so much that the gallium-fluorine couplings are not resolvable. The line width for higher floride complexes are much larger than the GaF s+ and GaF2 + complexes indicating that the higher fluoride complexes of gallium have a lower symmetry than the GaF 3+ and GaF2 + complexes.
Notes
3871
Acknowledgements-The author wishes to thank Professor L. W. Reeves for his interest during the progress of this work. R. HAQUE*
Department of Chemistry University of British Columbia Vancouver 8, British Columbia Canada
*Present address: Department of Agricultural Chemistry, Oregon State University, Corvallis, Oregon 97331.
J. inorg,nucl.Chem..1969,Vol.31, pp. 3871 to 3874. PergamonPress. Printedin Great Britain
Isolation of plutonium in chloride m e d i a - III Effects of nitrate and mono(2-ethylhexyl)phosphoric acid on extraction with di(2-ethylhexyl)phosphoric acid* (Received 2 June 1969) PREVIOUS papers in this series[l, 2] discussed methods for removing plutonium from hydrochloric acid solutions of irradiated targets in the USAEC Heavy Element Program for isolating transplutonium elements. The success of a plutonium isolation scheme involving solvent extraction with the monoacidic ester, di(2-ethylhexyl)phosphoric acid (HDEHP), has led to its routine use at the Transuranium Processing Facility (TRU) at Oak Ridge National Laboratory[3]. This note examines the influence of two contaminants, nitrate ion and mono(2-ethylhexyl)phosphoric acid, that are sometimes present in this extraction system. These contaminants increase the extraction of plutonium but impede its stripping, and the mono-ester acid also impairs intra-actinide separations. EXPERIMENTAL Reagents and experimental procedures were analogous to those described previously [2]. RESULTS AND DISCUSSION
Effect of nitrate Curves presented in Fig. 1 show the coefficients for the extraction of plutonium, curium, and californium by 1 M H D E H P in diethylbenzene (DEB) from nitric acid solution as a function of the nitric acid concentration. The order of extractability of these actinides is the same as that obtained in a hydrochloric acid system (2): Pu(IV) > Pu(VI) ~> Cf(IIl) > Cm(IIl). Each of these actinides is extracted more strongly from nitric than from hydrochloric acid media. This opposes the order of extraction that would be expected for Pu(IV) since plutonium forms a stronger complex with NO3- than with CI-; however, the extraction of thorium by 1 M H D E H P shows similar behavior [4]. *Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. 1. 2. 3. 4.
J. M. Chilton and J. J. Fardy, J. inorg, nucl. Chem. 31. I 171 (1969). J. M. Chilton and J. J. Fardy, J. inorg, nucl. Chem. To be published. D. E. Ferguson, USA EC Rep. ORNL-4145, p. 132 (1967). D. F. Peppard, G. W.Mason and S. McCarty, J. inorg, nucl. Chem. 13, 138 (1960).