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[197Au_NMR_manuscript_2024.pdf](https://mdr.nims.go.jp/filesets/101fd598-7125-4616-acec-215e1a6da50a/download)

## Creator

[Kenjiro Hashi](https://orcid.org/0000-0002-0320-4768), Kazuhiko Yamada, [Shinobu Ohki](https://orcid.org/0000-0002-7357-3833), [Yuuki Mogami](https://orcid.org/0000-0002-9807-3165), [Atsushi Goto](https://orcid.org/0000-0002-9472-4098)

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[Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/)

## Other metadata

[Solid-state 197Au NMR of gold metal](https://mdr.nims.go.jp/datasets/e235624b-8953-4427-868f-852f3888e4ef)

## Fulltext

Microsoft Word - Au_NMR_revised_marked_20240215.docxSolid-state 197Au NMR of gold metal    Kenjiro HASHI,*a Kazuhiko YAMADA,*b Shinobu OHKI,a Yuuki MOGAMI a and Atsushi GOTO a  aNational Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan.  bInterdisciplinary Science Unit, Multidisciplinary Sciences Cluster, Research and Education Faculty, Kochi University, Oko Campus, Nankoku, Kochi 783-8505, Japan        KEYWORDS. Solid-state gold-197 NMR, gold metal, Knight shift   ABSTRACT.   Solid-state 197Au static nuclear magnetic resonance (NMR) spectra of gold metal, detected at 18.79666 T and at room temperature, have been presented. Thermal annealing process plays an essential role for observation of the 197Au NMR signals. A single peak at 13.937275 MHz ± 25 Hz is observed and the Knight shift at room temperature is determined to be 0.11 %. The Knight shift at 4 K is redefined to be 0.07 %, using the modern physical constants.        INTRODUCTION Solid-state 197Au nuclear magnetic resonance (NMR) spectroscopy is expected to become a powerful tool for investigation of gold metal and associated alloys. However, there have been very few literature studies on solid-state 197Au NMR, due to unfavorable nuclear properties of 197Au (nuclear spin number (I) = 3/2, natural abundance = 100 %, NMR frequency ratio Ξ= 1.729 %1, nuclear magneton quadrupole moment (Q) = 54.7 fm2). Indirect solid-state NMR measurements have been often used for investigations of gold complexes2,3. Apparently, solid-state 197Au NMR measurement of gold metal was only reported in the 1960s. Narath4 presented the first 197Au NMR spectrum of gold metal observed at 4 K, from which the Knight shift, which refers to the relative shift in a metal compared in non-metallic environment, was obtained. To the best of our knowledge, no literature except for the result at 4 K has been published for solid-state 197Au NMR of gold metal. Moreover, the Knight shift was previously calculated with the older values of physical constants, which have subsequently been revised, so that the redefinition is needed. In this paper, solid-state 197Au NMR spectra of gold metal observed at room temperature have been presented for the first time. The Knight shift is obtained and that at 4K is redefined using the latest physical constants.   EXPERIMENTAL  Gold foil (99.95 %) with a thickness of 0.02 mm was purchased from The Nilaco Corporation (Tokyo, Japan), and used without further purification. The gold foil was cut into small pieces about 10  1 mm. Samples were placed in an alumina crucible and thermally annealed in air at 523 K, 623 K, and 773 K for 1 hour each. Approximately 150 mg of the sample was packed into a glass tube with a diameter of 4 mm, and the end was sealed by plastic end-cap. A 70-turns of copper wire (0.1mm in diameter) was wound around the sample tube, which was set to a home-made NMR probe. A superconducting magnet from an 800 MHz NMR equipment manufactured by JEOL Ltd. (Tokyo, Japan) was used, and the magnetic field strength was calculated to be 18.79666 T from a resonant frequency of deuterium in D2O, 122.8531 MHz. THAMWAY NMR Spectroscopy Measurement Systems (Shizuoka, Japan), was used for all the NMR experiments. A solid echo sequence, /2-1-/2-2-ACQ was employed to detect 197Au NMR signals at 13.935 MHz with the following parameters: /2 = 10 s, 1 = 250 s, 2 = 10 s, spectral width = 2.5 MHz, number of scans = 115,200, and recycling delay time = 0.5 s. After left-shifting of an FID signal and zero-filling, Fourier transform processing was performed.        Results and Discussion Figure 1 shows the solid-state 197Au static NMR spectra of gold metal: a sample with non-thermal annealing and ones with thermal annealing at 523, 623 and 773 K for 1 hour each, from bottom to top, respectively, detected at 18.79666 T and room temperature (300 K). A single sharp peak at 13.937275 MHz ± 25 Hz can be observed for samples with annealing at 623 K and 773 K, while no peak and very weak one for those with non-thermal annealing and annealing at 523 K, respectively. The presence or absence of a signal in Figure 1 implies that sufficient heat treatment is essential for 197Au signal detection of gold metal. In an as-is sample, i.e., no treatment of thermal annealing, the gold atom sites are not in environments of high Platonic/spherical symmetry due to strain.5,6 This makes it very difficult to observe 197Au NMR spectra, since the spectral width is broadened by large quadrupolar interactions. In annealed samples, on the other hand, as the annealing temperature increases, the distortion of the face-centered cubic (fcc) lattice structure gradually decreases, which results in smaller quadrupolar interaction, i.e., a sharp peak. Similar effect of thermal annealing process has been reported for electron microscopy of gold metal7.  The nominal nuclear gyromagnetic ratio of 197Au in gold metal at room temperature can be determined to be 0.7414761 MHz/T from the above resonant frequency, which is almost the same as that at 4 K reported by Narath4, 0.074119 kHz/Oe. It is important to point out that the difference in the nuclear gyromagnetic ratio between the room temperature and 4 K is only 0.04 %.8 NMR shifts in metals were first reported by W. D. Knight.9 The relatively large NMR shift in metals is called the Knight shift and given by,  Knight shift / %   = (μmetal  μatom) /μatom  100    [1] where metal and atom are nuclear magnetic moment of gold atom in pure metal and free gold atom, respectively. metal is given by  metal  = metal  J            [2]     where metal and J are effective gyromagnetic ratio of gold metal and a total angular momentum, respectively, given by  metal/2 = (resonance frequency of gold metal) / (applied magnetic field)  [3]  and    J = h / (2 )  I        [4]  where h is Plank's constant of 6.62607015  1034 Js10 and I is nuclear spin number. atom is 0.145746 μN11, where μN is nuclear magneton. The present value of μN is 5.05078324  10-27 J/T.11 From the present results, metal can be calculated to be 0.1459102 μN. If the present metal at room temperature and atom reported by Narath4 are used for it, the Knight shift at room temperature is calculated to be 1.68 %, which is consistent in that at 4 K in the literature4. However, the Knight shift at room temperature is determined to be 0.11 %, when the present atom is used. Moreover, if the present atom and metal reported by Narath4 are used, the Knight shift at room temperature  4K becomes 0.07 %, which leads to the fact that the nuclear gyromagnetic ratio between room temperature and 4 K is 0.04 %, Therefore, it can be concluded that the Knight shift at 4K is redefined to be 0.07 %, which is inconsistent in the literature value of 1.64 % reported in 19674. We believe that the discrepancy stems from the difference in constants used for calculations. In the literature, atom of 0.143491 μN and nuclear magneton μN of 5.05050 1024 erg/G, which are different values at the present time of μatom = 0.145746 μN and μN = 5.05078324  10-27 J/T, were employed.  CONCLUSION Sold-state 197Au static NMR spectra of gold metal with thermal annealing at 623 K and 773 K for 1 hour each have been observed at room temperature. Thermal annealing process is essential for detection of the 197Au NMR signals, and the nominal nuclear gyromagnetic ratio of 197Au in gold metal at room temperature is found to be 0.7414761 MHz/T. Using modern physical constants, the Knight shift at room temperature is determined to be 0.11 %, and that at 4 K is redefined to be 0.07 %.   ACKNOWLEDGMENT This work was supported by "Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM)" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). KY thanks for JSPS KAKENHI Grant Number 21K05129. Finally, we are grateful for anonymous reviewers for very helpful discussions and comments.   AUTHOR INFORMATION Corresponding Authors Phone: +81-29-863-5521. E-mail: HASHI.Kenjiro@nims.go.jp  Phone: +81-88-880-2009. E-mail: kyamada@kochi-u.ac.jp   REFERENCES 1. R. K. Harris and E. D. Becker, J. Magn. Reson. 2002, 156, 323. 2. L.E. Marbella, S.E. Crawford, M.J. Hartmann, and J. E. Millstone, Chem. Commun., 2016, 52, 9020-9023.; S. K. Mallissery and D. Gudat, Dalton Trans., 2010, 39, 4280-4284. 3. M. Kawakami, H. Enokiya and T. Okamoto, J. Phys. F: Met. Phys. 1985, 15, 1613 4. A. Narath, Phys. Rev. 1967, 163, 232. 5. J. W. Akitt and W. S. Macdonald, J. Magn. Reson., 1984, 58, 401. 6. J. Autschbach, S. H. Zheng, and R. W. Schurko, Conc. Magn. Reson., 2010, 36A, 84. 7. D. Porath, E. Bar-Sadeh, M. Wolovelsky, A. Grayevsky, Y. Goldstein and O. Millo, J. Vac. Sci. Technol. A 1995, 13, 1165–1170. 8. L. H. Bennett, R. E. Watson and G. C. Carter, J Res Natl Bur Stand A Phys Chem. 1970, 74A, 569. 9. W. D. Knight, Phys. Rev. 1949, 76, 1259-1260. 10. Bureau International des Poids et Mesures (2019) The International System of Units (SI). 9th edition:117-216. ISBN 978-92-822-2272-0. 11. Quantities, Units, and Symbols in Physical Chemistry: 3rd edition, the IUPAC Green Book prepared for publication by E.R. Cohen, T. Cvitas, J.G Frey, B. Holmstrom, K. Kuchitsu, R. Marquardt, I. Mills, F. Pavese, M. Quack, J. Stohner, H. Strauss, M. Takami, and A.J. Thor RSC Publishing, 2007  FIGURE CAPTION Figure 1 Solid-state 197Au static NMR spectra of gold metal: a sample with non-thermal annealing and ones with thermal annealing at 523 K, 623 K and 773 K for 1 hour each, from bottom to top, respectively, detected at 18.79666 T and room temperature (300 K).                         Figure 1