Author's Accepted Manuscript
Comment on the reference compound for chemical shift and Knight shift determination of 209Bi nuclei Bogdan Nowak
www.elsevier.com/locate/ssnmr
PII: DOI: Reference:
S0926-2040(14)00079-4 http://dx.doi.org/10.1016/j.ssnmr.2014.12.001 YSNMR666
To appear in:
Solid State Nuclear Magnetic Resonance
Received date: 10 September 2014 Revised date: 27 November 2014 Accepted date: 2 December 2014 Cite this article as: Bogdan Nowak, Comment on the reference compound for chemical shift and Knight shift determination of 209Bi nuclei, Solid State Nuclear Magnetic Resonance, http://dx.doi.org/10.1016/j.ssnmr.2014.12.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Comment on the reference compound for chemical shift and Knight shift determination of
209
Bi nuclei.
Bogdan Nowak W. Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław, Poland e-mail: [email protected] Abstract Several groups exploring the 209Bi NMR in solids, including usual insulators, metallic and magnetic materials and recently diamagnetic topological materials, use different standards (usually old and invalid) for chemical shift (Knight shift) determination, ignoring IUPAC recommendations. As a consequence the published shift values exhibit considerable differences ( up to 17 500 ppm)
Keywords : chemical shifts( Knight shifts) referencing 209
Bi NMR
solid state topologically nontrivial materials
1
According to IUPAC unified δ scale the 209Bi resonance shifts, 209δiso, should be determined with reference to Ξ 209Bi = 0.16069288 connected with
209
Bi signal in Bi(NO3)3 [1,2]. Here Ξ
is defined as the ratio of the isotope-specific frequency to that of 1H in tetramethylsilane (TMS) in the same magnetic field. Usually, in solid state the shifts 209δiso measured with respect to 209Bi signal in Bi(NO3)3 are positive in nonmagnetic bismuth containing materials [3], including metallic YBi [4]. Using the same standard, in liquid bismuth a value of 209δiso = +1.4 % has been measured. [5]. However, a large and negative shift 209δiso = − 1.25 % has already been observed at 4.2 K in diamagnetic bismuth metal [5] and discussed in [6]. This simply indicates that 209δiso exhibit a large splitting of their values and well defined reference is needed. In some journals having rather general chemical or physical character, a referencing of NMR shift in solids is not controlled. It means that recommendations of IUPAC are not respected by authors and referees, as well. This procedure is especially dangerous in the case of heavy nuclei like 209Bi . Here the differences in the determined chemical shifts (Knight shifts) are so large as few thousands of ppm, depending on used reference standards. Some time the shifts are reported, but reference standards are wrong (usually old) or undefined. Some time the reference materials are not reported at all. The positive sign and large values of 209δiso are reported for metallic La3Pt3Bi4 and small-gap semiconductor Ce3Pt3Bi4 [7] but very large negative values of 209δiso are reported for strongly magnetic YbBiPt [8] and U3Ni3Bi4 [9], isostructural with La3Pt3Bi4 and Ce3Pt3Bi4 . However, no details are given in papers [7-9] how the shift were measured. Unfortunately, in some papers the values or even the sign of measured shifts are interpreted without a reflection that δiso depends strongly on the standard chosen. And so, the sample dependent positive 209
Bi isotropic shifts ranging from 0.34 to 0.67 % were recently observed in topologically
nontrivial, diamagnetic materials Bi2Se3 [10,11]. Their positive sign, magnitude and the dependence on carrier concentration were explained in terms of dominating Fermi contact (positive) hyperfine interaction which gives rise to Knight shift [11]. However, the data are derived from frequency swept spectra using old value of magnetogyric ratio 209(γ/2π) = 0.6842 MHz/kG [12], instead of recommended by IUPAC 209Bi magnetogyric ratio γ = 4.3750×107 rad s-1 T-1 [1] equivalent to 209(γ/2π) = 0.6963 MHz/kG . Results can easily be recalculated using the formula (γnew/2π)(1 + δnew) = (γold/2π)(1 + δold)
2
(1)
where dimensionless values of δ should be used. Consequences are such that, for example, old value 209δiso = + 0.65% cited for Bi2Se3 in Ref.10 changes now into 209δiso = − 1.10 %.
Quite recently, using a Bruker Avance DSX 300 spectrometer operating at a field of 7.05 T and using the recommended by IUPAC the Ξ 209Bi = 0.16069288 as the standard, we have measured the shifts 209δiso in half-Heusler compounds YPdBi and YPtBi and have obtained at room temperature 209δiso = + 0.113 % for topologically trivial YPdBi and 209δiso = − 0.178 % for topologically nontrivial YPtBi. [13]. In our laboratory we have also prepared single crystalline samples of topologically nontrivial LuPdBi and LuPtBi and have obtained at room temperature 209δiso = − 0.435 % and 209δiso = − 0.61 % , respectively. Interestingly, our 209Bi frequency shift in LuPtBi and corrected shift in Bi2Se3 look reasonably similar, both being negative, exhibiting a band inversion and being candidates for topologically nontrivial materials. An profound analysis of the data needs some other experiments and will be given elsewhere.
In conclusion we state that as relative shifts are usually measured in NMR, it is useful to employ the same, actually recommended reference standard so that data can be compared, although the absolute accuracy may be lower. In my opinion the authors, who use the reference materials evidently different from that commonly employed and recommended, should explain in their paper why they do it. May be their arguments are reasonable and should be presented .
Acknowledgement. This work was supported by the National Science Centre (Poland) under research grant 2011/01/B/ST3/04466. I express my sincere thanks to O. Pavlosiuk for providing the samples of LuPdBi and LuPtBi, and its characterization by x-ray diffraction, energy dispersive x-ray scattering (EDXS) and magnetic susceptibility.
3
References .
[1] R. K. Harris , E. D. Becker, S. M. Cabral de Menezes, R. Goodfellow, and P. Granger, Solid State Nucl. Magn. Reson. 22 (2002) 458-483; reprinted from Pure Appl. Chem. 73 (2001) 1795 [2] R. K. Harris, E. D. Becker, S. M. Cabral de Menezes, P. Granger, R.E. Hoffman, and K.W. Zilm, Solid State Nucl. Magn. Reson. 33 (2008) 41-56; reprinted from Pure Appl. Chem. 80 (2008) 59 [3] H. Hamaed, M.W. Laschuk, V.V. Terskikh, and R.W. Schurko, J. Am. Chem. Soc. 131 (2009) 8271-8279 [4] G.C. Carter, L.H. Bennett, D.J. Kahan, Prog. Mater. Sci., 20 (1977) ”Metallic shifts in NMR” Part II, p.846 [5] B.F. Williams and R.R. Hewitt, Phys. Rev. 146 (1966) 286-290 [6] R.E. Watson, L.H. Bennett, G.C. Carter, and I.D. Weisman , Phys. Rev. B 3 (1971) 222225 [7] A.P. Reyes, R.H. Heffner, P.C. Canfield, J.D. Thompson, and Z. Fisk, Phys. Rev. B 49 (1994) 16321-16330 [8] A.P. Reyes, L.P. Le, R.H. Heffner, E.T. Arens, Z. Fisk, P.C. Canfield, Physica B 206 & 207 (1995) 332-335 [9] S.-H. Baek, N.J. Curro, T. Klimczuk, H. Sakai, H. Lee, E.D. Bauer, F. Ronning, and J.D. Thompson, Phys. Rev. B 79, (2009) 195120 [10] Ben-Li Young, Zong-Yo Lai, Zhijun Xu, Alina Yang, G.D. Gu, Z.-H. Pan, T. Valla, G.L. Shu, R. Sankar, and F.C. Chou, Phys. Rev. B 86 (2012) 075137-1-5 [11] D.N. Nisson, A.P. Diouguardi, P. Klavins, C.H. Lin, K. Shirer, A.C. Shockley, J. Crocker, and N.J. Curro, Phys. Rev. B 87 (2013) 195202-1-7 [12] G.C. Carter, L.H. Bennett, D.J. Kahan, Prog. Mater. Sci., 20 (1977), ”Metallic shifts in NMR” Part I, Tables 2a and 2b, Chapter 9 [13] B. Nowak and D. Kaczorowski, J. Phys. Chem. C 118, (2014) 18021-18026
4
Reference 2
Reference 1
δ1
δ2
Graphical Abstract
5
Comment on the reference compound for chemical shift and Knight shift determination of 209Bi nuclei Bogdan Nowak
www.elsevier.com/locate/ssnmr
PII: DOI: Reference:
S0926-2040(14)00079-4 http://dx.doi.org/10.1016/j.ssnmr.2014.12.001 YSNMR666
To appear in:
Solid State Nuclear Magnetic Resonance
Received date: 10 September 2014 Revised date: 27 November 2014 Accepted date: 2 December 2014 Cite this article as: Bogdan Nowak, Comment on the reference compound for chemical shift and Knight shift determination of 209Bi nuclei, Solid State Nuclear Magnetic Resonance, http://dx.doi.org/10.1016/j.ssnmr.2014.12.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Comment on the reference compound for chemical shift and Knight shift determination of
209
Bi nuclei.
Bogdan Nowak W. Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław, Poland e-mail: [email protected] Abstract Several groups exploring the 209Bi NMR in solids, including usual insulators, metallic and magnetic materials and recently diamagnetic topological materials, use different standards (usually old and invalid) for chemical shift (Knight shift) determination, ignoring IUPAC recommendations. As a consequence the published shift values exhibit considerable differences ( up to 17 500 ppm)
Keywords : chemical shifts( Knight shifts) referencing 209
Bi NMR
solid state topologically nontrivial materials
1
According to IUPAC unified δ scale the 209Bi resonance shifts, 209δiso, should be determined with reference to Ξ 209Bi = 0.16069288 connected with
209
Bi signal in Bi(NO3)3 [1,2]. Here Ξ
is defined as the ratio of the isotope-specific frequency to that of 1H in tetramethylsilane (TMS) in the same magnetic field. Usually, in solid state the shifts 209δiso measured with respect to 209Bi signal in Bi(NO3)3 are positive in nonmagnetic bismuth containing materials [3], including metallic YBi [4]. Using the same standard, in liquid bismuth a value of 209δiso = +1.4 % has been measured. [5]. However, a large and negative shift 209δiso = − 1.25 % has already been observed at 4.2 K in diamagnetic bismuth metal [5] and discussed in [6]. This simply indicates that 209δiso exhibit a large splitting of their values and well defined reference is needed. In some journals having rather general chemical or physical character, a referencing of NMR shift in solids is not controlled. It means that recommendations of IUPAC are not respected by authors and referees, as well. This procedure is especially dangerous in the case of heavy nuclei like 209Bi . Here the differences in the determined chemical shifts (Knight shifts) are so large as few thousands of ppm, depending on used reference standards. Some time the shifts are reported, but reference standards are wrong (usually old) or undefined. Some time the reference materials are not reported at all. The positive sign and large values of 209δiso are reported for metallic La3Pt3Bi4 and small-gap semiconductor Ce3Pt3Bi4 [7] but very large negative values of 209δiso are reported for strongly magnetic YbBiPt [8] and U3Ni3Bi4 [9], isostructural with La3Pt3Bi4 and Ce3Pt3Bi4 . However, no details are given in papers [7-9] how the shift were measured. Unfortunately, in some papers the values or even the sign of measured shifts are interpreted without a reflection that δiso depends strongly on the standard chosen. And so, the sample dependent positive 209
Bi isotropic shifts ranging from 0.34 to 0.67 % were recently observed in topologically
nontrivial, diamagnetic materials Bi2Se3 [10,11]. Their positive sign, magnitude and the dependence on carrier concentration were explained in terms of dominating Fermi contact (positive) hyperfine interaction which gives rise to Knight shift [11]. However, the data are derived from frequency swept spectra using old value of magnetogyric ratio 209(γ/2π) = 0.6842 MHz/kG [12], instead of recommended by IUPAC 209Bi magnetogyric ratio γ = 4.3750×107 rad s-1 T-1 [1] equivalent to 209(γ/2π) = 0.6963 MHz/kG . Results can easily be recalculated using the formula (γnew/2π)(1 + δnew) = (γold/2π)(1 + δold)
2
(1)
where dimensionless values of δ should be used. Consequences are such that, for example, old value 209δiso = + 0.65% cited for Bi2Se3 in Ref.10 changes now into 209δiso = − 1.10 %.
Quite recently, using a Bruker Avance DSX 300 spectrometer operating at a field of 7.05 T and using the recommended by IUPAC the Ξ 209Bi = 0.16069288 as the standard, we have measured the shifts 209δiso in half-Heusler compounds YPdBi and YPtBi and have obtained at room temperature 209δiso = + 0.113 % for topologically trivial YPdBi and 209δiso = − 0.178 % for topologically nontrivial YPtBi. [13]. In our laboratory we have also prepared single crystalline samples of topologically nontrivial LuPdBi and LuPtBi and have obtained at room temperature 209δiso = − 0.435 % and 209δiso = − 0.61 % , respectively. Interestingly, our 209Bi frequency shift in LuPtBi and corrected shift in Bi2Se3 look reasonably similar, both being negative, exhibiting a band inversion and being candidates for topologically nontrivial materials. An profound analysis of the data needs some other experiments and will be given elsewhere.
In conclusion we state that as relative shifts are usually measured in NMR, it is useful to employ the same, actually recommended reference standard so that data can be compared, although the absolute accuracy may be lower. In my opinion the authors, who use the reference materials evidently different from that commonly employed and recommended, should explain in their paper why they do it. May be their arguments are reasonable and should be presented .
Acknowledgement. This work was supported by the National Science Centre (Poland) under research grant 2011/01/B/ST3/04466. I express my sincere thanks to O. Pavlosiuk for providing the samples of LuPdBi and LuPtBi, and its characterization by x-ray diffraction, energy dispersive x-ray scattering (EDXS) and magnetic susceptibility.
3
References .
[1] R. K. Harris , E. D. Becker, S. M. Cabral de Menezes, R. Goodfellow, and P. Granger, Solid State Nucl. Magn. Reson. 22 (2002) 458-483; reprinted from Pure Appl. Chem. 73 (2001) 1795 [2] R. K. Harris, E. D. Becker, S. M. Cabral de Menezes, P. Granger, R.E. Hoffman, and K.W. Zilm, Solid State Nucl. Magn. Reson. 33 (2008) 41-56; reprinted from Pure Appl. Chem. 80 (2008) 59 [3] H. Hamaed, M.W. Laschuk, V.V. Terskikh, and R.W. Schurko, J. Am. Chem. Soc. 131 (2009) 8271-8279 [4] G.C. Carter, L.H. Bennett, D.J. Kahan, Prog. Mater. Sci., 20 (1977) ”Metallic shifts in NMR” Part II, p.846 [5] B.F. Williams and R.R. Hewitt, Phys. Rev. 146 (1966) 286-290 [6] R.E. Watson, L.H. Bennett, G.C. Carter, and I.D. Weisman , Phys. Rev. B 3 (1971) 222225 [7] A.P. Reyes, R.H. Heffner, P.C. Canfield, J.D. Thompson, and Z. Fisk, Phys. Rev. B 49 (1994) 16321-16330 [8] A.P. Reyes, L.P. Le, R.H. Heffner, E.T. Arens, Z. Fisk, P.C. Canfield, Physica B 206 & 207 (1995) 332-335 [9] S.-H. Baek, N.J. Curro, T. Klimczuk, H. Sakai, H. Lee, E.D. Bauer, F. Ronning, and J.D. Thompson, Phys. Rev. B 79, (2009) 195120 [10] Ben-Li Young, Zong-Yo Lai, Zhijun Xu, Alina Yang, G.D. Gu, Z.-H. Pan, T. Valla, G.L. Shu, R. Sankar, and F.C. Chou, Phys. Rev. B 86 (2012) 075137-1-5 [11] D.N. Nisson, A.P. Diouguardi, P. Klavins, C.H. Lin, K. Shirer, A.C. Shockley, J. Crocker, and N.J. Curro, Phys. Rev. B 87 (2013) 195202-1-7 [12] G.C. Carter, L.H. Bennett, D.J. Kahan, Prog. Mater. Sci., 20 (1977), ”Metallic shifts in NMR” Part I, Tables 2a and 2b, Chapter 9 [13] B. Nowak and D. Kaczorowski, J. Phys. Chem. C 118, (2014) 18021-18026
4
Reference 2
Reference 1
δ1
δ2
Graphical Abstract
5
