- Email: [email protected]
Tantalum-181 solution NMR spectroscopy
JOURNAL
OF MAGNETIC
RESONANCE
68, 157- 160 ( 1986)
Tantalum-181
Solution NMR
Spectroscopy
DIETER REHDERAND W O L F BASLER Fachbereich Chemie der Universitiit, Martin-Luther-King-Platz 6, D-2 Hamburg 13. Federal Republic of Germany Received December 12, 1985 The “‘Ta NMR spectra of solutions of [Et.,N][TaL6] (L = Cl-, CO) and KJTaF,] have been obtained. The shift range encompasses3450 ppm, limited by [TaClJ at the lowfield and [Ta(CO)& at the high-field side. The shielding sensitivity of the ‘s’Ta nucleus is about 1.6 times that of “Nb and 0.6 times that of ‘83W. Half widths are 4.3 (L = Cl-), 6.7 (L = CO) and 29 kHz ([TaFJ). o 1986 Academic press, ~nc.
“‘Ta (nuclear spin = z) belongs to the nuclei having a large quadrupole moment ((2 = 3 X 10mz8m2), and this fact is usually considered to seriously hamper NMR studies due to effective line broadening by quadrupole relaxation. There have been a few solid state studies including K[Ta03] (I, 2), M ’[TaY,] (M’ = Cu, T l; Y = S, Se, Te) (3), tantalum metal (4), and TaY2 (Y = S, Se) (5). O n ly one single investigation in solution has been reported, viz., a 1 7 % Ta solution in a l/ 1 m ixture of concentrated HF and HN03, where the predominant specieshad been assumed to be [TaFJ (6) (vide infra). An unsuccessful effort to detect the “‘Ta resonance in HF solutions of TaF5 had been noted by Hatton et al. (7). For nuclei in a cubic environment, the field gradient vanishes and quadrupole relaxation becomes ineffective. Sharp signals should arise and this has been verified for many quadrupolar nuclei belonging to the small to m e d ium quadrupole category (5’V, 55Mn, 59Co,93Nb, 95Mo) in a local Td or O h symmetry. However, even small deviations from the idealized local symmetry, m e d iated, e.g., by instantaneous distortions caused by m o lecular collisions, counter-ion and solvation effects may give rise to comparatively broad lines for nuclei belonging to the large quadrupole category. W e have shown recently that, for the octahedral cation [Re(CO)$ (8) and the tetrahedral anions [ReOJ (8, 9) and [ReSJ (9), the resonance of the two rhenium isotopes “‘Re and ‘*‘Re, which have quadrupole moments comparable (2.8 and 2.6 X 1 0 m 2 ’m2, respectively) to that of 18’Ta, are still reasonably sharp (width at half height, W l,2, in organic solvents and with large counter-ions are between 1.5 and 4 kHz). W e report here on a similar observation for the two octahedral complexes [Et4N][Ta(CO),] and [EtdN][TaC16], prepared according to published procedures for the analogous niobium compound (I&12), and the noncubic, commercially available (Alfa) Kz[TaFT]. Further encouragement for the investigation of these systems came from the large receptivity r(“‘Ta) = 2.5 (relative to r(‘H) = 1) at constant radiofrequency vo, which compares to the considerably less favorable r = 0.036 at constant field Bo. 157
0022-2364186 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form reserved
158
REHDER AND BASLER
ppm -7 I
FIG. I. 8 MHz ‘*‘Ta NMR spectra (first derivative) ofanionic Ta complexes. Central magnetic field 1.5735 T, sweep width 25 mT; rf,, = 0.1 mT. Modulation amplitudes are 0.5 mT for [Ta(CO)J and [TaClJ (4 scans), and 1 mT for [TaF,]‘- (380 scans). Scan time 2 min, time constant 0.3 s.
The measurements were carried out on a Varian DP 60 wideline instrument at vg = 8 MHz (exact) and a central magnetic field of ca. 1.57 T. Spectra are shown in Figs. 1 and 2, and data are listed in Table 1. The resonances of the two octahedrally coordinated Ta complexes dissolved in organic solvents ( WIj2 = 4.3 and 6.7 kHz)
FIG. 2. 8 MHZ ‘*ITa resonances for [TaLJ, L = CO and Cl-. Sweep range 8 mT, modulation amplitude 0.16 mT (L = CO) and 0.1 mT (L = Cl-); 64 scans.
TANTALUM
SOLUTION
159
NMR SPECTRA
TABLE I “‘Ta NMR Data Compound
Medium (Concentration) CH$ZN/(CH&CO (0.6 M)
K21TaFd
[EtNI[Ta(CC%l
b(18’Ta) (mm) I/ 1
0
4.3
48% HF (saturated)
-2295(35)
28.7’
THF/CH,CN 5/l (0.6 M)
-3450( 15)
6.7
’ Relative to [TaClJ; estimated error in parentheses. ’ Width at half height. Estimated error ca. 10%. ’ Calculated according to WI0 = fi* IV,, where W, (peak-to-peak width of the first derivative) = 3.25 mT (16.6 kHz).
were detected without difficulty. Kz[TaF,] in 48% HF gives rise to a rather broad line ( WrlZ = 29 kHz). An identical signal is observed for a solution of Na[TaOs] in 48% HF. The reported peak-to-peak width for a solution of Ta metal in HF/HN03 at room temperature is 7 m T (6), which amounts to Wrj2 = 62 kHz. The species present in this solution therefore is unlikely to be [TaF&, but rather a m ixture of [TaF,]@-“(n = 6-8) in mutual exchange of F- (13). The separation of the signals for [Ta(CO),J and [TaClJ, A&18’Ta), amounts to 3450 ppm with the carbonyl tantalate, as expected (Id), at higher field. This shift difference compares to a A6 of 2130 ppm for the 93Nb resonances (II, 1.5)and 5687 ppm for the lg3W resonances (16, 17) for the corresponding hexacarbonyls and hexachlorides of the neighboring elements niobium and tungsten. The shift intervals for analogous complexes of different nuclei can be interpreted in terms of differing intrinsic NMR sensitivities s of the respective nuclei (15). This leads to the sensitivity ratios s(‘8’Ta/93Nb) = 1.62 and s(‘81Ta/‘83W) = 0.61. Similar ratios are obtained for the pairs MF6/M(C0)6[s(‘8’Ta/93Nb) = 2.1; s(‘8’Ta/‘83W) = 0.61, ifthe 6(18’Ta) observed for [TaFTI*- (-2295 ppm relative to [TaCl&) is reduced to that for [TaFJ (-2065 ppm) according to the linear relationship between 6(M) and the electronegativity of the ligand set coordinated to M established, e.g., for M = 5’V (18). REFERENCES 1. L. H. BENNEI-I AND J. T. BUDNIK, Bull. Am. Phys. Sot. (Ser. 2) 4, 417 (1959). J. J. VAN DER KLINK AND F. BORSA, Phys. Rev. B 30, 52 (1984). K. D. BECKERAND U. BERLAGE, J. Magn. Reson. 54,272 (1983). J. I. BUDNIK AND L. H. BENNETT, J. Phys. Chem. Solids 16,37 (1960). H. NISHIHARA, G. A. S~HOLZ, M. NAITO, R. F. FRINDT, AND S. TANAKA, J Magn. Magn. Mat. 3134, 7 17 (1983); M. NAITO, H. NISHIHARA AND S. TANAKA, J. Chem. Phys. C 16, L387 (1983). 6. L. C. ERICH, A. C. GOSSARD, AND R. L. HARTLESS, J. Chem. Phys. 59,39 11 (1973). 7. J. V. HATTON, Y. SAITO, AND W. G. SCHNEIDER, Can. J. Chem. 43,47 (1965). 8. A. KECECI AND D. REHDER, 2. Natqibrsch. B Xi,20 (1981). 9. A. MOLLER, E. KRICKEMEYER, H. B&GE, M. PENK, AND D. REHDER, Chimia 40,50 (1986). 2. 3. 4. 5.
160
REHDER
AND
BASLER
10. F. CALDERAZZO, U. ENGLERT, G. PAMPALONI, G. PELLIZI, AND R. ZAMBONI, Znorg. Chem. 22,1865 (1983). II. K. BACHMANN AND D. REHDER, .I. Organomet. Chem. 276, 177 (1984). 12. D. M. ADAMS, J. CHAT, D. M. DAVIDSON, AND J. GERRAT, J. Chem. SOL, 2189 (1963). 13. 0. L. KELLER AND A. CHETHAM-STRODE, Znorg. Chem. 5,376 (1966); cf. also Gmelin, “Handbook of inorganic Chemistry,” Ta Bl, p. 89. 14. D. REHDER, Magn. Reson. Rev. 9, 125 (1984). IS. R. K. HARRIS AND B. E. MANN (Eds.), “NMR and the Periodic Table,” p. 2 11, Academic Press, New York, 1978. 16. W. MCFARLANE, A. M. NOBLE, AND J. M. WINFIELD, J. Chem. Sot. A, 948 (1971). 17. G. T. ANDREWS, I. J. COLQUHOUN, W. MCFARLANE, AND S. 0. GRIM, J. Chem. Sot. Dalton Trans., 2353 (1982). 18. W. PRIEBSCHAND D. REHDER, Znorg. Chem. 24,263 (1985).
OF MAGNETIC
RESONANCE
68, 157- 160 ( 1986)
Tantalum-181
Solution NMR
Spectroscopy
DIETER REHDERAND W O L F BASLER Fachbereich Chemie der Universitiit, Martin-Luther-King-Platz 6, D-2 Hamburg 13. Federal Republic of Germany Received December 12, 1985 The “‘Ta NMR spectra of solutions of [Et.,N][TaL6] (L = Cl-, CO) and KJTaF,] have been obtained. The shift range encompasses3450 ppm, limited by [TaClJ at the lowfield and [Ta(CO)& at the high-field side. The shielding sensitivity of the ‘s’Ta nucleus is about 1.6 times that of “Nb and 0.6 times that of ‘83W. Half widths are 4.3 (L = Cl-), 6.7 (L = CO) and 29 kHz ([TaFJ). o 1986 Academic press, ~nc.
“‘Ta (nuclear spin = z) belongs to the nuclei having a large quadrupole moment ((2 = 3 X 10mz8m2), and this fact is usually considered to seriously hamper NMR studies due to effective line broadening by quadrupole relaxation. There have been a few solid state studies including K[Ta03] (I, 2), M ’[TaY,] (M’ = Cu, T l; Y = S, Se, Te) (3), tantalum metal (4), and TaY2 (Y = S, Se) (5). O n ly one single investigation in solution has been reported, viz., a 1 7 % Ta solution in a l/ 1 m ixture of concentrated HF and HN03, where the predominant specieshad been assumed to be [TaFJ (6) (vide infra). An unsuccessful effort to detect the “‘Ta resonance in HF solutions of TaF5 had been noted by Hatton et al. (7). For nuclei in a cubic environment, the field gradient vanishes and quadrupole relaxation becomes ineffective. Sharp signals should arise and this has been verified for many quadrupolar nuclei belonging to the small to m e d ium quadrupole category (5’V, 55Mn, 59Co,93Nb, 95Mo) in a local Td or O h symmetry. However, even small deviations from the idealized local symmetry, m e d iated, e.g., by instantaneous distortions caused by m o lecular collisions, counter-ion and solvation effects may give rise to comparatively broad lines for nuclei belonging to the large quadrupole category. W e have shown recently that, for the octahedral cation [Re(CO)$ (8) and the tetrahedral anions [ReOJ (8, 9) and [ReSJ (9), the resonance of the two rhenium isotopes “‘Re and ‘*‘Re, which have quadrupole moments comparable (2.8 and 2.6 X 1 0 m 2 ’m2, respectively) to that of 18’Ta, are still reasonably sharp (width at half height, W l,2, in organic solvents and with large counter-ions are between 1.5 and 4 kHz). W e report here on a similar observation for the two octahedral complexes [Et4N][Ta(CO),] and [EtdN][TaC16], prepared according to published procedures for the analogous niobium compound (I&12), and the noncubic, commercially available (Alfa) Kz[TaFT]. Further encouragement for the investigation of these systems came from the large receptivity r(“‘Ta) = 2.5 (relative to r(‘H) = 1) at constant radiofrequency vo, which compares to the considerably less favorable r = 0.036 at constant field Bo. 157
0022-2364186 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form reserved
158
REHDER AND BASLER
ppm -7 I
FIG. I. 8 MHz ‘*‘Ta NMR spectra (first derivative) ofanionic Ta complexes. Central magnetic field 1.5735 T, sweep width 25 mT; rf,, = 0.1 mT. Modulation amplitudes are 0.5 mT for [Ta(CO)J and [TaClJ (4 scans), and 1 mT for [TaF,]‘- (380 scans). Scan time 2 min, time constant 0.3 s.
The measurements were carried out on a Varian DP 60 wideline instrument at vg = 8 MHz (exact) and a central magnetic field of ca. 1.57 T. Spectra are shown in Figs. 1 and 2, and data are listed in Table 1. The resonances of the two octahedrally coordinated Ta complexes dissolved in organic solvents ( WIj2 = 4.3 and 6.7 kHz)
FIG. 2. 8 MHZ ‘*ITa resonances for [TaLJ, L = CO and Cl-. Sweep range 8 mT, modulation amplitude 0.16 mT (L = CO) and 0.1 mT (L = Cl-); 64 scans.
TANTALUM
SOLUTION
159
NMR SPECTRA
TABLE I “‘Ta NMR Data Compound
Medium (Concentration) CH$ZN/(CH&CO (0.6 M)
K21TaFd
[EtNI[Ta(CC%l
b(18’Ta) (mm) I/ 1
0
4.3
48% HF (saturated)
-2295(35)
28.7’
THF/CH,CN 5/l (0.6 M)
-3450( 15)
6.7
’ Relative to [TaClJ; estimated error in parentheses. ’ Width at half height. Estimated error ca. 10%. ’ Calculated according to WI0 = fi* IV,, where W, (peak-to-peak width of the first derivative) = 3.25 mT (16.6 kHz).
were detected without difficulty. Kz[TaF,] in 48% HF gives rise to a rather broad line ( WrlZ = 29 kHz). An identical signal is observed for a solution of Na[TaOs] in 48% HF. The reported peak-to-peak width for a solution of Ta metal in HF/HN03 at room temperature is 7 m T (6), which amounts to Wrj2 = 62 kHz. The species present in this solution therefore is unlikely to be [TaF&, but rather a m ixture of [TaF,]@-“(n = 6-8) in mutual exchange of F- (13). The separation of the signals for [Ta(CO),J and [TaClJ, A&18’Ta), amounts to 3450 ppm with the carbonyl tantalate, as expected (Id), at higher field. This shift difference compares to a A6 of 2130 ppm for the 93Nb resonances (II, 1.5)and 5687 ppm for the lg3W resonances (16, 17) for the corresponding hexacarbonyls and hexachlorides of the neighboring elements niobium and tungsten. The shift intervals for analogous complexes of different nuclei can be interpreted in terms of differing intrinsic NMR sensitivities s of the respective nuclei (15). This leads to the sensitivity ratios s(‘8’Ta/93Nb) = 1.62 and s(‘81Ta/‘83W) = 0.61. Similar ratios are obtained for the pairs MF6/M(C0)6[s(‘8’Ta/93Nb) = 2.1; s(‘8’Ta/‘83W) = 0.61, ifthe 6(18’Ta) observed for [TaFTI*- (-2295 ppm relative to [TaCl&) is reduced to that for [TaFJ (-2065 ppm) according to the linear relationship between 6(M) and the electronegativity of the ligand set coordinated to M established, e.g., for M = 5’V (18). REFERENCES 1. L. H. BENNEI-I AND J. T. BUDNIK, Bull. Am. Phys. Sot. (Ser. 2) 4, 417 (1959). J. J. VAN DER KLINK AND F. BORSA, Phys. Rev. B 30, 52 (1984). K. D. BECKERAND U. BERLAGE, J. Magn. Reson. 54,272 (1983). J. I. BUDNIK AND L. H. BENNETT, J. Phys. Chem. Solids 16,37 (1960). H. NISHIHARA, G. A. S~HOLZ, M. NAITO, R. F. FRINDT, AND S. TANAKA, J Magn. Magn. Mat. 3134, 7 17 (1983); M. NAITO, H. NISHIHARA AND S. TANAKA, J. Chem. Phys. C 16, L387 (1983). 6. L. C. ERICH, A. C. GOSSARD, AND R. L. HARTLESS, J. Chem. Phys. 59,39 11 (1973). 7. J. V. HATTON, Y. SAITO, AND W. G. SCHNEIDER, Can. J. Chem. 43,47 (1965). 8. A. KECECI AND D. REHDER, 2. Natqibrsch. B Xi,20 (1981). 9. A. MOLLER, E. KRICKEMEYER, H. B&GE, M. PENK, AND D. REHDER, Chimia 40,50 (1986). 2. 3. 4. 5.
160
REHDER
AND
BASLER
10. F. CALDERAZZO, U. ENGLERT, G. PAMPALONI, G. PELLIZI, AND R. ZAMBONI, Znorg. Chem. 22,1865 (1983). II. K. BACHMANN AND D. REHDER, .I. Organomet. Chem. 276, 177 (1984). 12. D. M. ADAMS, J. CHAT, D. M. DAVIDSON, AND J. GERRAT, J. Chem. SOL, 2189 (1963). 13. 0. L. KELLER AND A. CHETHAM-STRODE, Znorg. Chem. 5,376 (1966); cf. also Gmelin, “Handbook of inorganic Chemistry,” Ta Bl, p. 89. 14. D. REHDER, Magn. Reson. Rev. 9, 125 (1984). IS. R. K. HARRIS AND B. E. MANN (Eds.), “NMR and the Periodic Table,” p. 2 11, Academic Press, New York, 1978. 16. W. MCFARLANE, A. M. NOBLE, AND J. M. WINFIELD, J. Chem. Sot. A, 948 (1971). 17. G. T. ANDREWS, I. J. COLQUHOUN, W. MCFARLANE, AND S. 0. GRIM, J. Chem. Sot. Dalton Trans., 2353 (1982). 18. W. PRIEBSCHAND D. REHDER, Znorg. Chem. 24,263 (1985).