J . Phys. Chem. 1987, 91, 1267-1270
1267
A Study of the Phase Transition and Molecular Motion in Adamantanamine Hydrochloride Pierre D. Harvey, Denis F. R. Gilson,* and Ian S. Butler* Department of Chemistry, McGill University, Montreal, Quebec, Canada H3A 2K6 (Received: October 8, 1986)
The temperature-induced phase transition in solid adamantanamine hydrochloride, CloH15NH3+Cl-,has been studied by differential scanning calorimetry, infrared and Raman spectroscopy, and proton spin-lattice relaxation time measurements. The transition occurs at 124 K, with enthalpy and entropy of transition of 0.31 kJ mol-' and 2.5 J K-'mol-', respectively. The changes in the vibrational spectra, and the low transition entropy, indicate that both phases are ordered. The activation energy for molecular rotation in the high-temperature phase is 33.6 kJ mol-' and is attributed to rotation of the adamantyl moiety.
Introduction
Results and Discussion
The occurrence of order4isorder phase transitions in adamantane and its derivatives is well-known.' For simple substitution, even though the high symmetry of adamantane itself is destroyed, the disordered phases involve extensive molecular rotations in a face-centered-cubic structure. Intermolecular interactions, such as hydrogen bonding, can affect the behavior. For example, in 1-adamantanolz the phase transition occurs at 353 K, with a large entropy of transition of 40.6 J K-' mol-'. Thus, the hydrogen bonding in this compound shifts the phase transition to a higher temperature, compared with other adamantyl derivatives, but does not prevent the disordered phase from occurring. Recently, we have investigated the transition in the more strongly hydrogen-bonded 1-adamantanecarboxylic acid.3 The phase transition was observed by using differential scanning calorimetry, at 25 1 K, and the Raman and infrared spectra showed that both the high- and low-temperature phases are ordered; Le., no order-disorder transition occurs. The molecules form hydrogenbonded dimers in the solid state, and this structure persists through the transition. Proton spin-lattice relaxation time measurements were interpreted in terms of rotation of the adamantyl group alone, with activation energies of 19.3 and 31.0 kJ mol-' for the highand low-temperature phases, respectively. A further study of the influence of hydrogen bonding on the properties of the solid phases of these compounds seemed to be appropriate, and a study of the adamantanamine hydrochloride salt, and comparison with the acid derivative, is the subject of the present paper. Differential scanning calorimetry was used to determine the phase transition temperature, enthalpy, and entropy. Vibrational spectroscopy, primarily Raman scattering, was used to investigate the changes in local symmetry, and proton spinlattice relaxation measurements were used to determine the barrier to rotation of the adamantyl groups. The existence of a phase transition in this compound has not been previously reported. The far-infrared spectra of the 1-adamantyl derivatives, adamantanol, adamantanamine, and adamantanamine hydrochloride, have been studied at room temperature, and the observed torsional frequencies used to determine the barriers to substituent r ~ t a t i o n . ~
Differential scanning calorimetry revealed a sharp phase transition at 124 K, without hysteresis, and changes in the scanning rate below 10 OC min-I, or cycling several times through the transition, affected neither the temperature nor the enthalpy of transition. N o other thermal transition was observed between 100 and 400 K. The enthalpy and entropy of transition were 0.31 kJ mol-' and 2.51 J K-' mol-', respectively. These values are much lower than those reported to date for any adamantane derivative. The only comparable transition appears to be the lower temperature transition, at 279 K, in 1-bromoadamantane (AH= 0.88 kJ mol-', A S = 3.16 J K-' mol-')? which is attributed to a nearly second-order transition from a monoclinic to an orthorhombic crystal structure.6 The corresponding values for adamantanecarboxylic acidZare 2.25 kJ mol-' and 8.97 J K-' mol-' for the transition at 251 K. The Guthrie-McCullough relationship' equates the number of distinguishable sites, N 1 and Nz, in the two different phases according to eq 1:
Experimental Section 1-Adamantanamhe hydrochloride (Aldrich Chemical Co.) was purified by slow sublimation Torr, 100 "C). Differential scanning calorimetric, Raman and infrared spectroscopic, and spin-lattice relaxation time measurements were performed as described previ~usly.~ (1) Parsonage, N. G.; Staveley, L. A. K. Disorder in Crystals; Clarendon: Oxford, 1978. (2) Amoureux, J. P.; Bee, M.; Gors, C.; Warin, V.; Baert, F. Cryst. Struct. Commun. 1979, 8, 449. ( 3 ) Harvey, P. D.; Gilson, D. F. R.; Butler, I. S. J . Phys. Chem. 1986, 90, 126 ._-.
(4) Craven, S. M. Spectrochim. Acta, Part A 1973, 29A, 679.
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A S = R In ( N z / N 1 )
(1)
This equation does not hold for order-disorder transitions in some cage hydrocarbons, and an alternative interpretation, involving an excess entropy contribution, has been proposed.8 However, according to Newns and Staveley: the large majority of transitions in ionic compounds do follow the Guthrie-McCullough equation, and when this is applied to adamantanamine hydrochloride, a ratio of N z j N 1 = 1.35 is obtained. This suggests that the phase transition involves a 4 to 3 ratio of distinguishable postions. In 1-methyladamantane, which has the same molecular symmetry as the adamantanamine ion but is not involved in hydrogen bonding, two phase transitions O C C Uat~ ,169.5 ~ and 21 1.5 K, with transition entropies of 11.27 and 6.95 J K-' mol-', respectively. In this case, the high-temperature phase is disordered to, probably, the face-centered-cubic structure. Figure 1 shows the room-temperature Raman and infrared spectra of adamantanamine hydrochloride for the spectral region 1650-750 cm-', and Figure 2 compares the Raman spectra, at room temperature and 50 K, for the region 1400-250 cm-I. The frequencies and assignments are listed in Table I. If the isolated adamantanamine cation, CloH15NH3+,is assumed to have C3, symmetry, there should be 45 fundamental vibrational frequencies:
rYib = 18al(IR,R) + 9az(inact) + 27e(IR,R) ( 5 ) Clark, T.; Knox, T. Mc. 0.;Mackle, H.; McKervey, M. A. J . Chem. SOC.,Faraday Trans. 1 1977, 73, 1224. (6) Virlet, J.; Quiroga, L.; Boucher, B.; Amoureux, J. P.; Castelain, M. Mol. Phys. 1983, 48, 1289. (7) Guthrie, J. B.; McCullough, J. P. J. Phys. Chem. Solids 1961, 18, 28. (8) Clark, T.; Mackle, H.; McKervey, M. A,; Rooney, J. J. J . Chem. Soc., Faraday Trans. 1 1974, 70, 1279. (9) Newns, D. M.; Staveley, L. A. K. Chem. Rev. 1968, 68, 267.
0 1987 American Chemical Society
1268 The Journal of Physical Chemistry, Vol. 91, No. 5, 1987
Harvey et al.
Figure 1. Vibrational spectra of solid adamantanaminehydrochloride at room temperature. Upper: Raman spectrum, laser excitation 488 nm, 21 mW at the samples. Slit width 200 Mm; 8 scans. Lower: FT-IR spectrum. 800 scans, resolution 1 em-'.
The spectra show good correspondence between the infrared and Raman vibrational frequencies. However, the room-temperature spectra show more than the predicted number of bands, due to site group splitting of degenerate modes and, possibly, factor group splitting as well. In comparison with the spectra of the high-temperature phases of other substituted adamantane derivatives,lO." the room-temperature spectra show quite narrow vibrational bands. This observation suggests that the high-temperatures phase is ordered. In the spectral region 1650-1500-~m-~, there are six different bands: 1502 (IR,R), 1514 (IR) and 1509 (R), 1594 (IR) and 1596 (R), 1605 (IR), 1627 (IR,R), and 1641 (R) cm-'. These bands are assigned to the N H 3 bending modes (al + e) and indicate that there are at least two molecules per unit cell. In the Raman spectra of the low-temperature phase, the vibrations split, usually into two or three components (Table I). The weak and broad band at 143 cm-' (161 cm-' in the infrared spectrum), which is assigned to the N-H-CI stretching mode, splits into four components, indicating that the local symmetry of the -NH3 group is changed in the low-temperature phase. The 970-cm-' band is a mixture of several modes12 and is well-known to split in the low-temperature phases.l0t1*The splittings, in general, are more extensive than those observed for the carboxylic acid d e r i ~ a t i v e . ~ In view of these spectral changes, the phase transition is probably first order even though the enthalpy and entropy changes are small. The N-H stretching frequencies in the Raman spectrum are weak (10) Harvey, P. D.; Butler, I. S.; Gilson, D. F. R. In Proceedings ofthe International Conference on Fourier Transform and Computerized Infrared Spectroscopy; Grasselli, J., Cameron, D., Eds.; SPIE Publications: Washington, D.C., 1985; Vol. 553, pp 398-399. ( 1 1 ) Burns, G.; Dacol, F. H.; Welber, B. Solid State Commun. 1979, 32, 151.
(12) Bailey, R. T. Spectrochim. Acta, Part A 1971, 2 7 4 1447.
1400
1350
500
600
700
1300
1250
1200
1150
400
1100
1050
300
1000
950
900
-W Figure 2. Raman spectra of solid adamantanamine hydrochloride. Conditions are the same as Figure 1, except at 50 K the laser power was 310 mW at the sample and the slit width was 150 p m .
I
e
I
4
3
T -'( l
6
K";
~ ~ - a
Figure 3. Proton spin-lattice relaxation times vs. reciprocal temperature.
and broad and do not provide any additional information. The dependence of the proton spin-lattice relaxation times on reciprocal temperature is shown in Figure 3. The relaxation times became too long to measure on our spectrometer at temperatures below 200 K, and it was not possible to observe either the phase transition or the relaxation times of the low-temperature phase.
The Journal of Physical Chemistry, Vol. 91, No. 5, 1987
Phase Transition in Adamantanamine Hydrochloride
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TABLE I: List of Observed Frequencies for Adamantanamine Hydrochloride
Raman at 50 K ca. 3040 vvw
at RT
3087 w 3023 s 2980 s, br 2961 s
3010 vvw 2984 vvw 2956 vw, br 2947.5 vw 2935 m 2930 s 2924.5 vs 2918 s 2907.5 w 2890.5 w 2878 vw 2866 vw 2858 w, br
2955 vw, br ca. 2945 w, sh 2938 vs
2891 w 2876 ?
2885 s 2875 s
2855.5 w
2857 vs 2840 s 2815 s
1641 w 1627 vw
1327 w
1146.5 vw 1128 vw 1 1 19.5vw 1114vw ca. 1097 vw 1089 m
assignments combination
I
1028.5 w w
FT-IR at RT, f l cm-I 1072 w
NH stretch 1019 ww "985m 980 vs 976.5 vs
assignments CC stretch + CH, twist
982 w 919 s 914 s
\
CH stretch
2 weak features ca. 970 959.5 vw, br ca. 930 926.5 w 915 vw
959 w 928 w 926.4 913 w
ca. 880
881 vw
1325 w 1313.5 m 1292 w 1286 w ca. 1247 1207.1 s
1626 w 1605 m 1514 m 1502 m 1477 w 1453 m 1439 w 1426 w 1377 w 1366 m 1350 w 1349 w 1325 w 1322 w
+ CC stretch
CC stretch
960 w 929 w
I
914 w 894 vw
::: 1)
CN stretch
884 vw
ca. 2730 w w
1596 vw 1509 vw 3 very weak features 1502 w at 1500-1515 1478 vvw 1478 w 1453 vvw 1458 w 1453 w ca. 1443 w 1445 m 1440 w 1440 m 1429 vvw 1429 w, br, sh 1376 vw weak features at 1 350-1 400 1365 vw 1352 vvw, br 1350 w
1323.5 vvw 1316.5 w 1291 vvw 1285 vw ca. 1247 vvw 1208.5 ws
Raman at 50 K at RT ca. 1085 m
bend 2925.5 vs 2923 vs ca. 2920 m, sh 2915 vs
ca. 2822 vvw, br 2728 vvw 1646.5w
FT-IR at RT, f 1 cm-'
\
776.5s
/
759 ww 720.5vs 713.5 ww
i
776 vw
CC stretch
719 vw 718.5 706 w 698 vw 664 vw, br 646 w 646 w 544 w 543 w
CH bend
I
1313 m 1288 w, sh 1285 w
545.5 m 540.5m 487 ww 477 vw CH2 wag + CH bend 459 m 457 vs CH bend 454 s 424.5 m CH bend + CH2 wag 420.5 m 404 mw 402.5 w 390 s CC stretch + CH, wag 387.5 m 314 ww 288.5 w 281 w
775.2 s 763 w
CC stretch
I
+ CH bend
1197 w, sh
1210 vw, sh CH2 twist 1201 vw 1198 vw, sh C H 2 twist
1125 w 1123 w 1 1 16.8 1107 w 1090 m, sh 1085 m
1116 w 1112w J lo90 m' sh 1086 w
CH, wag
+ CH bend
1
1 CH bend
The relaxation is assumed to occur by a dipole-dipole mechanism such that eq 2 applies 1/Tl = ( 2 / 3 ) C ~ [ 1 / ( 1 + W2T2)+ 4/(1 -k 402T2)] (2) where C i s a constant related to the change in the second moment of the resonance line, w is the resonance frequency (33 MHz), and r = T~ exp(E/RT) is the correlation time for molecular rotation. The fit to the experimental data, using eq 2, gave C = 9.69 X lo9 rad2 s - ~ , ro = 4.94 X s, and an activation energy of 33.6 kJ mol-'. In comparing the different values of the constant C that have been reported for similar studies of rotation in adamantyl compounds, it appears that the magnitude of this constant is in the range expected for rotation of the adamantyl group alone about its threefold axis. For intramolecular interactions only, the calculated values of the TI minima for adamantyl fixed -NH3 rotating and adamantyl rotating -NH3 fixed are 50 and 29 ms, respectively. Comparing these values with the experimental value of 24 ms favors the latter case. Thus, the hydrochloride salt
457 m
NH3 torsion
457 w
422 w 400 w
422
390 w 283 w, br
395 w, br 291 w. br
CCC bend
other shoulders 150.5 m 146 mw, br 132.5 w 114 w 83.5 w, br 77.5 w 68 m 59 mw
143 w
143 w 161
1
N-H-CI stretch
64 m
lattice modes 58 m
resembles the carboxylic acid in that the substituent group is fixed and the motion observed by the TI studies is the adamantyl rotation. The earlier work of Craven: using the torsional frequency measured in the far-infrared spectrum, gave a value of 54.4 kJ mol-' for the barrier to rotation of the -NH3 group. This high barrier consists of both intra- and intermolecular contributions and suggests that the amine group is involved in a hydrogenbonded network in the solid phase and confirms that the adamantyl group rotation is responsible for the spin-lattice relaxation process. A calculation of the intramolecular barrier in the isolated ion, using the molecular mechanics program of Allinger,13gave a value of 8.2 kJ mol-'. Thus, the intermolecular contribution to the barrier for the adamantyl group rotation is about 25 kJ mol-' (33.6 - 8.2 kJ mol-'). This value can be compared with that obtained for adamantane carboxylic acid, where the internal barrier should be small, and the measured barriers thus represent the intermolecular packing. In the acid derivative, these barriers are 19.3 (13) Allinger,N.J. Am. Chem. SOC.1977,99,8127
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J. Phys. Chem. 1987, 91, 1270-1273
and 3 1.O kJ mol-' in the high- and low-temperature phases, respectively. The lower barrier in the high-temperature phase, compared with the amine salt, reflects a looser packing, which is in agreement with a larger entropy change for the acid.
Acknowledgment. This research was supported by grants from
the Natural Sciences and Engineering Research Council of Canada and FCAR (Quebec). P.D.H. acknowledges the award of scholarships from NSERC and the McConnell Foundation (McGill University). Registry No. Adamantanamine hydrochloride, 665-66-7.
Muons and Muonium Atoms in Solid and Liquid Methanet Y. C. Jean,* R. Ganti, and J. Stadlbauert Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri 641 10 (Received: October 29, 1985; In Final Form: October 15, 1986)
Muon and muonium spin rotation experiments have been performed in pure liquid and solid methane between 25 and 138 K. Muonium atoms have been observed for the first time in liquid and solid methane. The muonium formation probabilities are found to be 15-20% in both solid and liquid phases. The depolarization rates of muonium atoms increase slightly as a function of temperature and are interpreted as a thermal Mu reaction with methane molecules in liquids and as a spin-lattice interaction in solids. Diamagnetic muon fractions (P,) are found to be strongly temperature dependent; PD increases from 20% at 25 K to 57% at 65 K and stays constant at value 58% above 65 K in both solid and liquid phases. This variation is interpreted as a result of depolarization by muon spin-lattice interactions in methane lattices. An activation energy (52 meV) for spin-lattice relaxation for muons in solid methane was obtained. The diamagnetic fractions of CH,Mu and MuH in condensed phase methane were thus calculated to be 38% and 20%, respectively.
Introduction The positive muon and muonium (Mu), which is a bound atom of a positive muon and an electron, play a special role in condensed matter science today.' Since the mass of a muon is only one-ninth that of a proton, the hyperfine interaction between muons and electrons is distinctly different from that between electrons and protons. The muon is thus an excellent probe2 to study the local magnetic properties of condensed matter, particularly those properties related to protons. Mu is a light isotope of the H atom having a mass only oneninth that of H. Its atomic size and electronic energy levels are nearly identical with those of H atoms. Due to the large mass ratio between Mu and H atoms, Mu is an important probe for studying the kinetic isotope effect (KIE) involving H reaction^.^,^ With the special hyperfine interactions between Mu and surrounding electrons of molecules, Mu is also known to be a unique probe in structural research5 for H atoms. Since 1977, Mu has been successfully observed in many molecular systems, such as water: alcohols,' and hydrocarbonss The utilization of Mu as a nuclear probe in chemical kinetics and structural chemistry depends strongly on the amount of observable Mu formation in the pure solvent. As a practical matter in Mu experiments, the observable Mu signals increase as the square of the amount of Mu formation. Previous investigations of Mu formation and reaction kinetics3 in liquids have been performed principally near room temperature, while the KIE becomes pronounced at low temperatures. Significant KIE which can be observed by using Mu probes a t low temperature includes a large zero point energy at the transition state, a large quantum tunneling, and the solvent effect. Therefore it would be useful to have easily purified low temperature liquid solvents on which Mu is known to form. Methane with a fairly large liquid temperature region, should be a very important solvent for chemical kinetics studies of H atoms using Mu probes. Methane is a classical molecule for structural research. It possesses the strongest C-H bond (439 kl/m01)~among saturated hydrocarbons and a unique symmetrical structure. Theoretical and experimental investigations on the structure of solid and liquid 'The experiments were ptrformed at TRIUMF, Vancouver, B.C. *Current address: Hood College, Frederick, MD.
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methane have been made extensively in the past decades.I0 For these reasons, the search for Mu atoms in solid and liquid methane has been one of the very interesting projects in the recent years. Experimental complications such as the trace impurity problem and the difficulty in manipulating a sizable volume of liquid at low temperatures have until now delayed successful Mu experiments in methane. In this paper, we report the first successful muon spin rotation (pSR) observation of muons and muonium in liquid and solid methane over a wide range of temperatures.
Experiments Sample Preparations. As reported in our previous papers,* observations of Mu atoms in hydrocarbons require a special care in removing trace impurities such as oxygen and unsaturated molecules because these molecules react with Mu at a diffusion-controlled rate. We have made a special effort to overcome these impurity problems in methane. The research grade methane was purchased from Matheson Gas Co. (Secaucus, NJ) at 99.99% purity with reported total oxygen and unsaturated impurity C20 (1) For example, see Brewer, J. H.; Crowe, K. M.; Gygax, F. N.; Schenck, A. Muon Physics, Vol. 111, Hughes, V. M., Wu, C. S., Ed.; Academic: New York, 1975. (2) For example, see Schenck, A. Muon Spin Rotation Spectroscopy; Adam Hilger Ltd.: Bristol, 1985. (3) Walker, D. C. J . Phys. Chem. 1981,85, 3960. Walker, D. C. Muon and Muonium Chemistry; Cambridge: London, 1983. (4) Jean, Y. C. Mater. Sei. Forum 1984, 2, 177. (5) Roduner, E.; Fisher, H. Chem. Phys. 1981, 54, 261. (6) Percival, P. W.; Roduner, E.; Fisher, H.; Camani, M.; Gygax, F. N.; Schenck, A. Chem. Phys. Lett. 1977, 47, 11. Jean, Y. C.; Brewer, J. H.; Fleming, D. G.; Garner, D. M.; Mikula, R. J.; Vaz, L. C.; Walker, D. C. Chem. Phys. Lett. 1978, 57, 293. Nagamine, K.; Nishiyama, K.; Imzato, J.; Nakayama, H.; Yashida, M.; Sakai, Y.; Sato, H.; Tominaga, T. Chem. Phys. Lett. 1982, 87, 166. (7) Percival, P. W.; Roduner, E.; Fisher, H. Positronium and Muonium Chemistry; American Chemical Society: Washington, DC, 1979; Adv. Chem. Ser. No. 175, p 335. (8) Ito, Y . ;Ng, B. W.; Jean, Y. C.; Walker, D. C. Can. J . Chem. 1980, 58, 2395. Ng, B. W.; Stadlbauer, J. M.; Jean, Y . C.; Walker, D. C. 1983, 61, 671. (9) CRC Handbook of Chemistry and Physics, Weast, R. C., Astle, M. J., Beyer, W. H., Ed.; CRC: Boca Raton, FI, 1984; p f-182, 65th ed. (10) For example, see Bloom, M.; Morrison, J. A. Surface and Defect Properties of Solids, Vol. 2; The Chemical Society Burlington House: London, 1973; p 140.
0 1987 American Chemical Society
