ARTICLE pubs.acs.org/JPCA
Phonon-Driven Proton Transfer in 3,5-Pyridine Dicarboxylic Acid Studied by 2H, 14N, and 17O Nuclear Quadrupole Resonance agar† Janez Seliger*,†,‡,§ and Veselko Z †
Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia § EN-FIST Centre of Excellence, Dunajska 156, 1000 Ljubljana, Slovenia ‡
ABSTRACT: Hydrogen bonding in crystalline 3,5-pyridine dicarboxylic acid has been studied by 2H, 14N, and 17O nuclear quadrupole resonance. The 2H and 17O data show the presence of two distinct hydrogen bonds, a “normal” OH 3 3 3 O bond and a short, strong N 3 3 3 H 3 3 3 O bond, with significantly different NQR parameters. In the latter, the temperature variation of the 14N nuclear quadrupole resonance (NQR) parameters is related to the phonon-driven proton transfer in the N 3 3 3 H 3 3 3 O hydrogen bond. The temperature dependence of the N 3 3 3 H and H 3 3 3 O distances in the N 3 3 3 H 3 3 3 O hydrogen bond is extracted from the 14N NQR data.
1. INTRODUCTION Hydrogen bonds occur in a variety of organic and inorganic materials. They influence the structure as well as their physical, chemical, and biological properties. The study of short, strong hydrogen bonds (SSHBs) in solids is of particular interest because they reveal the details of the proton transfer process. Proton transfer in crystalline solids is connected with phase transitions and interesting physical properties such as ferroelectricity, pyroelectricity, ferrodistortive phenomena, etc. Recently, proton transfer has been observed without phase change by inelastic neutron scattering in SSHBs in pyridine-3,5-dicarboxylic acid (PDA),1 urea phosphoric acid,2,3 a 1:2 cocrystal of benzene-1,2,4,5-tetracarboxylic acid and 4,40 -bipyridyl4 and a 1:1 crystal of 2-methylpyridine and pentachlorophenol.5 The process is driven by specific phonons as modeled by DFT and molecular dynamics simulations.6 This type of proton transfer is attractive for nuclear quadrupole resonance (NQR) because it permits the following up of electric charge changes on the atoms involved in hydrogen bonds without changes in their surroundings. PDA crystallizes1 in the P21/c space group with four molecules in the unit cell. Two short, strong N1H5 3 3 3 O4 hydrogen bonds and one medium, strong O1H4 3 3 3 O3 hydrogen bond link the molecules in a two-dimensional planar sheet, as shown in Figure 1. The position of the proton H5 varies with temperature. At 15 K, the N1H5 distance is 1.213 Å and the H5O4 distance is 1.311 Å. At 296 K, the N1H5 distance increases to 1.308 Å, and the H5O4 distance decreases to 1.218 Å Fontaine-Vive et al.6 have identified specific phonons that influence the potential energy surface of the proton H5 in the SSHBs, driving the proton from N1 to O4 with increasing temperature. r 2011 American Chemical Society
The nuclear quadrupole interaction is well suited for the study of the hydrogen bonds formed by nitrogen and oxygen atoms. Both 14N (c ≈ 100%) and 17O (c = 0.037%) possess nuclear electric quadrupole moments. The interaction of the nuclear quadrupole moment eQ with the local inhomogeneous electric field produces quadrupole shifts of the NMR frequency in a high magnetic field and the occurrence of nuclear quadrupole energy levels in a zero external magnetic field. Two experimental parameters, the quadrupole coupling constant e2qQ/h and the asymmetry parameter η of the electric field gradient (EFG) tensor, can be extracted either from the quadrupole-perturbed NMR spectra or from pure NQR spectra of the quadrupolar nuclei. The symmetric traceless second rank EFG tensor, Vik=∂2V/∂xi ∂xk, is composed of the second derivatives of the electrostatic potential V at the position of the nucleus with respect to the coordinates. The EFG tensor has three real principal values: VZZ = eq, VYY, and VXX (|VZZ| > |VYY| g |VXX|). The quadrupole coupling constant is the product of VZZ and eQ divided by the Planck constant, h, whereas the asymmetry parameter η is equal to (VXX VYY)/VZZ.7 An alternative description of the NQR parameters is the quadrupole coupling tensor qik which is equal to the EFG tensor Vik multiplied by eQ and divided by h. The NQR parameters are very sensitive to the electric charge distribution in the vicinity of the observed nucleus. Proton migration in a NH 3 3 3 O hydrogen bond changes the NQR parameters of 14N and 17O and, exchanging 1H for 2H; also, the Received: July 19, 2011 Revised: September 9, 2011 Published: September 12, 2011 11652
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Figure 1. Hydrogen-bonded planar sheet of PDA molecules in the ab plane.
NQR parameters of the latter. In the OH 3 3 3 O hydrogen bonds, the bonding influences the 17O NQR parameters at the donor and acceptor positions. The aim of this study is the determination of the 2H, 14N, and 17O NQR parameters in PDA and establishing a relation between them and the proton position in SSHB.
2. EXPERIMENTAL SECTION A commercial sample of PDA was used with no further purification. The hydrogen bonds were deuterated by multiple recrystallizations from D2O. 2.1. 17O NQR. A 17O nucleus has a spin I = 5/2. In a zero magnetic field, it exhibits three doubly degenerated nuclear quadrupole energy levels. Their energies, Ei, are obtained as the solutions xi of the secular equation x3 7ð3 þ η2 Þx 20ð1 η2 Þ ¼ 0 2
7
ð1Þ
multiplied by e qQ /20, Ei = e2qQxi/20. The resonance, NQR, frequencies are calculated as the differences in these energies divided by the Planck constant, h. The 17O NQR frequencies are labeled as ν5/21/2 > ν5/23/2 g ν3/21/2. They depend uniquely on e2qQ /h and η that are determined from the NQR frequencies in the following way. First, the asymmetry parameter η is determined from the ratio R = ν3/21/2/ν5/23/2, which varies monotonically from R = 0.5 at η = 0 to R = 1 at η = 1. With known η, the quadrupole coupling constant is calculated from any NQR frequency. The 17O NQR frequencies are due to the low natural abundance of the isotope 17O (0.037%), usually measured by Slusher and Hahn’s 1H17O double resonance technique using the magnetic field cycling between a high magnetic field B0 and zero magnetic field.8 2.2. 2H and 14N NQR. The 14N nucleus and the 2H nucleus have spin I = 1. In zero magnetic field, they have three nondegenerated quadrupole energy levels and, correspondingly, three NQR frequencies labeled as ν+, ν, and ν0: e2 qQ ð3 þ ηÞ 4h e2 qQ ð3 ηÞ ν ¼ 4h e2 qQ η ν0 ¼ νþ ν ¼ 2h νþ ¼
Figure 2. Double resonance spectrum of protonated PDA at room temperature as measured by Slusher and Hahn’s technique.
Table 1. 17O NQR Frequencies, Quadrupole Coupling Constants and Asymmetry Parameters, η, in Protonated PDA at T = 295 K oxygen position 17 17
O1H4 3 3 3 O3 O4 3 3 3 H5 3 3 3 N1
ν3/21/2, kHz
ν5/23/2, kHz
e2qQ/h, kHz
η
1330
2310
7880
0.350
1150
1700
5960
0.546
The quadrupole coupling constant is calculated from the sum of ν+ + ν, and then the asymmetry parameter is obtained from ν0. The 14N NQR frequencies are mainly below 5 MHz, and the 2 H NQR frequencies are on the order of 100 kHz. The detection of 2H by the solid state NMR is possible, whereas the detection of 14 N in a polycrystalline sample by NMR is much more difficult or even impossible due to very broad NMR lines and a low 14N nuclear magnetic moment. The pulse NQR technique and various double resonance techniques are used for this purpose. Slusher and Hahn’s technique, which is used to detect 17O, often does not show the 14N NQR frequencies because of the spin quenching effect.9 In the present study, we used cross-relaxation spectroscopy,1012 the level crossing technique,13,14 the solid effect technique,15 and the technique using multiple frequency sweeps and two-frequency irradiation16,17 to measure the 14N NQR frequencies. The 2H NQR frequencies were measured by the solid effect technique and by the technique based on the resonant 1 H2H interaction at νH = νQ/218 in a sample deuterated at the OH positions.
3. RESULTS AND DISCUSSION 3. 1.
17
O NQR. The 1H17O double resonance spectrum of
PDA measured at T = 295 K in a naturally abundant protonated sample by Slusher and Hahn’s technique is presented in Figure 2. The strongest line at 2.2 MHz corresponds to the highestfrequency 14N NQR transition frequency, ν+, as confirmed by later experiments. The four additional lines correspond to the 17 O NQR transitions at the frequencies ν3/21/2 and ν5/23/2. Two OH oxygen positions, O3 3 3 3 H417O1 and 17O4 H5 3 3 3 N1, are observed in the crystal, in agreement with the crystal structure. The NQR frequencies, quadrupole coupling constants, and asymmetry parameters, η, of the EFG tensor are presented 11653
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Figure 4. Correlation among the principal values of the 14N quadrupole coupling tensor in protonated PDA at various temperatures (1), quinolinic acid (2), picolinic acid (3), isonicotinic acid (4), nicotinic acid (5), nicotinamide (6), 2,6-dinicotinamide (7), picolinamide (8), and isonicotinamide (9). The solid lines represent the results of Rubenacker and Brown’s model. Figure 3. 14N NQR spectrum of protonated PDA as measured by double resonance. Determination of ν0 by scanning the proton Larmor frequency, νL, under the influence of multiple frequency sweeps of a rf magnetic field (a) and the determination of ν+ and ν by the twofrequency irradiation (b).
Table 2. 14N NQR Frequencies, Quadrupole Coupling Constant and Asymmetry Parameter η in Protonated PDA T/ K
ν+, kHz
ν, kHz
e2qQ/h, kHz
η
153
1885
1810
2463
0.061
178
1900
1822
2481
0.063
208
1965
1868
2555
0.076
228 254
2010 2092
1897 1943
2605 2690
0.086 0.111
272
2132
1975
2738
0.115
295
2193
1998
2794
0.140
308
2220
2020
2827
0.142
321
2228
2030
2839
0.140
343
2240
2040
2853
0.140
in Table 1. The NQR frequencies from the third oxygen position, 17 O3 3 3 3 H4O1, have not been observed because of the weak signal-to-noise ratio and the overlap of its double resonance lines with the stronger 17O and 14N double resonance lines. The two oxygen positions, 17O1H4 3 3 3 O3 and 17O4 H5 3 3 3 N1, have been assigned on the basis of the structural data.1 The OH 3 3 3 O bond is ∼ 0.26 nm long and strongly asymmetric. The quadrupole coupling constant, e2qQ/h = 7.88 MHz, and η = 0.35 are consistent with the known 17O NQR data for the OH position in such bonds.19 On the other hand, e2qQ/ h = 5.96 MHz and η = 0.546 are close to the values observed in short, nearly symmetric hydrogen bonds.20,21 3. 2. 14N NQR. The 14N NQR frequencies in PDA have already been measured,22 but with a lower resolution. In the present study, we applied a sensitive adjustment of the two rf powers in the two-frequency irradiation technique at various temperatures to get a higher precision of the NQR data in a protonated sample. The determination of the 14N NQR frequencies in PDA at T = 295 K by multiple frequency sweeps and two-frequency irradiation
is presented in Figure 3. The 14N NQR frequencies; quadrupole coupling constant; and the asymmetry parameter, η, for various temperatures are tabulated in Table 2. A continuous variation of e2qQ/h and η is observed in the investigated temperature region. Both the quadrupole coupling constant and the asymmetry parameter, η, increase with increasing temperature. Rubenacker and Brown23 observed the correlation of the principal values of the 14N quadrupole coupling tensor in coordinated pyridine. They adopted the TownesDailey model24 and calculated the principal values of the 14N quadrupole coupling tensor in dependence on the donor orbital occupancy. A similar correlation is also observed in hydrogen-bonded pyridine.25 A diagram showing the correlation between the two smallest principal values of the quadrupole coupling tensor, qXX and qYY, and the largest principal value, qZZ, in PDA at various temperatures; quinolinic acid;21 picolinic acid; nicotinic acid; and isonicotinic acid;22 as well as in picolinamide, nicotinamide; isonicotinamide; and 2,6-dinicotinamide26 is presented in Figure 4. The full lines are the results of the Rubenacker and Brown extended TownesDailey model, whereas the points represent the experimental data. In non-hydrogen-bonded pyridine, the 14N quadrupole coupling constant, e2qQ/h = eQVzz/h, is about 4.6 MHz (7, 8, 9). With increasing strength of the hydrogen bond, the quadrupole coupling constant decreases (6, 5, 4, and 3). In the example of protonated pyridine (2, 3) the nitrogen quadrupole coupling constant is much lower, about 1 MHz. The data for PDA are in the middle of this range, suggesting an OH 3 3 3 N hydrogen bond with the proton position close to the center of the bond. The experimental points vary parallel to the correlation lines. The decrease in the quadrupole coupling constant on decreasing temperature suggests further that the proton moves from oxygen toward nitrogen with decreasing temperature, in agreement with the neutron diffraction data. A larger deviation from the correlation lines shown in Figure 4 was observed in the cocrystal of isonicotinamide oxalic acid, in which the strong, short N 3 3 3 HO hydrogen bonds link the molecules of isonicotinamide to oxalic acid. The deviation was ascribed to the additional negative electric charge on the nitrogen atom.27 The position of the proton in the OH 3 3 3 N hydrogen bond in PDA has been determined1 by inelastic neutron scattering at 11654
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Figure 6. Temperature dependence of the deuterium quadrupole coupling constants in deuterated PDA. Figure 5. The nitrogenhydrogen distance RN 3 3 3 H and the oxygen hydrogen distance RO 3 3 3 H in the OH 3 3 3 N hydrogen bond in protonated PDA as calculated from the NQR data, assuming linear dependence of the quadrupole coupling constant on hydrogen displacement, calibrated by the distances measured by neutron diffraction.
15, 100, and 296 K. The 14N NQR data are obtained in the temperature region between 153 and 343 K. Unfortunately, we have no NQR data at 100 K; however, extrapolation of the measured temperature dependence of the 14N quadrupole coupling constant on this temperature yields the value e2qQ /h (100 K) = 2430 kHz. The hydrogen position with the nitrogen-to-hydrogen distances RN 3 3 3 H = 1.18 Å and oxygento-hydrogen distance RO 3 3 3 H = 1.36 Å thus corresponds to e2qQ /h = 2430 kHz. On the other hand, the hydrogen position at room tempera corresponds to ture with RN 3 3 3 H = 1.31 Å and RO 3 3 3 H = 1.22 Å 2 e qQ /h = 2794 kHz. Assuming a linear dependence of the quadrupole coupling constant on the hydrogen displacement, we calculated the hydrogen position from the NQR data. The results are presented in Figure 5. The data show a continuous displacement of hydrogen from the NH 3 3 3 O position at low temperatures to the N 3 3 3 HO position at high temperatures. 3.3. 2H NQR. Two distinctly different deuterium positions have been observed in deuterated PDA. At one position, the 2 H NQR frequencies ν+ and ν are in the range between 145 and 160 kHz. The two NQR frequencies cannot be determined apart from the broad double resonance line. The maximum difference, ν+ ν = ν0, can be estimated to 15 kHz. Thus, the asymmetry parameter is η e 0.15 and the quadrupole coupling constant turns out to be e2qQ/h = 204 kHz. Both the quadrupole coupling constant and the asymmetry parameter are nearly temperatureindependent. These values are characteristic of a strongly asymmetric hydrogen bond, that is, in the present case of the OH 3 3 3 O hydrogen bond.2729 The 2H NQR frequencies at the second deuterium position are at T = 183 K equal to ν+ = 72 kHz, ν = 48 kHz, and ν0 = 24 kHz. The quadrupole coupling constant and the asymmetry parameter are 80 kHz and 0.60, respectively. Such a low value of e2qQ/h and large η are characteristic of a nearly centered symmetric hydrogen bond, that is, of the OH 3 3 3 N hydrogen bond. The temperature variation of the two 2H quadrupole coupling constants is presented in Figure 6. The quadrupole coupling constant of the deuterium in the OH 3 3 3 O hydrogen bond is nearly temperature-independent. However, the quadrupole coupling constant of deuterium in the O 3 3 3 H 3 3 3 N hydrogen bond
increases gradually with increasing temperature. At 158 K, e2qQ /h = 78 kHz, whereas at T = 253 K, e2qQ/h = 85 kHz. At still higher temperatures, the double resonance measurements were no longer possible because of the excessive decrease in the proton spinlattice relaxation time in the low magnetic field (B ∼1mT). The temperature variation of the 2H quadrupole coupling constant at the OH 3 3 3 N position seems to be related to the displacement of a deuteron in the hydrogen bond.
4. CONCLUSIONS Hydrogen bonds in solid PDA have been studied by 2H, 14N, and 17O nuclear quadrupole resonance. The 2H and 17O NQR data show the presence of two distinct hydrogen bonds: an asymmetric bond (OH 3 3 3 O) and a bond with the proton close to the center (N 3 3 3 H 3 3 3 O). The deuterium quadrupole coupling in the SSHB N 3 3 3 H 3 3 3 O gradually increases with increasing temperature; this may be a consequence of the phonon-driven proton displacement. The temperature dependence of the 14N NQR frequencies has been measured with high precision. The 14N quadrupole coupling constant increases with increasing temperature. The experimental results are analyzed by Rubenacker and Brown’s model. The analysis shows that with increasing temperature, a proton displaces from the NH 3 3 3 O position to the N 3 3 3 HO position. It is further assumed that the 14N quadrupole coupling constant changes linearly with the proton displacement; the displacement is then much smaller than the hydrogen bond length. The position of the proton in the N 3 3 3 H 3 3 3 O hydrogen bond has been determined by neutron diffraction at 15, 100, and 296 K.2 Using these data, we established the relation between the N 3 3 3 H and H 3 3 3 O distances in the N 3 3 3 H 3 3 3 O hydrogen bond and the 14N quadrupole coupling constant and determined the temperature dependence of these two distances from the NQR data. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT We are greatly indebted to Prof. Dusan Hadzi who proposed this study and gave us helpful much advice and many suggestions during our work. 11655
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’ REFERENCES (1) Cowan, J. A.; Howard, J. A. K.; McIntyre, J.; Lo, S. M.-F.; Williams, I. D. Acta Crystallogr., Sect. B: Struct. Sci. 2005, 61, 724–730. (2) Wilson, C. C. Acta Crystallogr., Sect. B: Struct. Sci. 2001, 57, 435–439. (3) Wilson, C. C.; Morrison, C. A. Chem. Phys. Lett. 2002, 362, 85–89. (4) Cowan, J. A.; Howard, J. A. K.; McIntyre, G. J.; Lo, S.; Williams, I. D. Acta Crystallogr., Sect. B: Struct. Sci. 2003, 59, 794–801. (5) Steiner, T.; Wilson, C. C.; Majerz, I. Chem. Commun. (Cambridge) 2000, 14, 1231–1232. (6) Fontaine-Vive, F.; Johnson, M. R.; Kearley, G. J.; Cowan, J. A.; Howard, J. A. K.; Parker, S. F. J. Chem. Phys. 2006, 124, 234503. (7) Seliger, J. In Encyclopedia of Spectroscopy and Spectrometry; Lindon, J. C., Tranter, G. E., Holmes, J. L., Eds.; Academic Press: San Diego, 2000, pp 16721680. (8) Slusher, R. E.; Hahn, E. L. Phys. Rev. 1968, 166, 332–347. (9) Leppelmeier, G. W.; Hahn, E. L. Phys. Rev. 1966, 141, 724–731. (10) Seliger, J.; Osredkar, R.; Mali, M.; Blinc, R. J. Chem. Phys. 1976, 65, 2887–2891. (11) Seliger, J.; Blinc, R.; Arend, H.; Kind, R. Z. Phys. B 1976, 25, 189–195. (12) Stephenson, D.; Smith, J. A. S. Proc. R. Soc. A 1988, 416, 149–178. (13) Blinc, R.; Mali, M.; Osredkar, R.; Prelesnik, A.; Seliger, J.; Zupancic, I.; Ehrenberg, L. J. Chem. Phys. 1972, 57, 5087–5093. (14) Edmonds, D. T. Phys. Rep. 1977, 29, 234–290. agar, V. J. Magn. Reson. 2008, 193, 54–62. (15) Seliger, J.; Z agar, V.; Blinc, R. J. Magn. Reson. A 1994, 106, (16) Seliger, J.; Z 214–222. agar, V.; Blinc, R. Z. Naturforsch. A 1994, 49, 31–34. (17) Seliger, J.; Z agar, V. J. Magn. Reson. 2009, 199, 199–207. (18) Seliger, J.; Z (19) Seliger, J. Chem. Phys. 1998, 231, 81–86. agar, V.; Blinc, R. Chem. Phys. Lett. 1989, (20) Seliger, J.; Z 164, 405–408. (21) Poplett, I. J. F.; Sabir, M.; Smith, J. A. S. J. Chem. Soc. Faraday Trans. 2 1981, 77, 1651–1668. agar, V.; Zidansek, A.; Blinc, R. Chem. Phys. 2006, (22) Seliger, J.; Z 331, 131–136. (23) Rubenacker, G. V.; Brown, T. L. Inorg. Chem. 1980, 19, 392–398. (24) Townes, C. H.; Dailey, B. P. J. Chem. Phys. 1949, 17, 782–796. agar, V. J. Phys. Chem. A 2010, 114, 12083–12087. (25) Seliger, J.; Z agar, V. Magn. Reson. Chem. 2008, 46, 58–62. (26) Seliger, J.; Z (27) Chiba, T. J. Chem. Phys. 1964, 41, 1352–1358. (28) Blinc, R.; Hadzi, D. Nature 1966, 212, 1307–1309. (29) Butler, L. G.; Brown, T. L. J. Am. Chem. Soc. 1981, 103, 6541– 6549.
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