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The Journal of Physical Chemistry, Vol. 82, No. 15, 1978
highly dependent on the electronegativity of the phosphorus ligand. This parameter could be used to identify the radical. Acknowledgment. The gift of two chemicals as well as fruitful discussions with Dr. D. Houalla, Dr. M, Sanchez, and Dr. R. Wolf (CNRS, ERA 82, structure des mol6cules phosphorEes) are greatly acknowledged.
References and Notes (1) E. G. Janzen, A m . Chem. Res., 4, 31 (1971). (2) C. Lagercrantz, J. Phys. Chem., 75, 3466 (1971). (3) P. Tordo, M. Boyer, F. Vila, and L. Pujol, Phosphorus Sulfur, 3, 43 (1977). (4) P. Tordo, M. Boyer, V. Cerri, and F. Vila, Phosphorus Sulfur, 3, 373 (1977).
A. Loewenstein, M. Brenman, and R. Schwarzmann
(5) E. G. Janzen and J. I. Ping Liu, d . Magn. Reson., 9 , 510 (1973). (6) A. V. Il'Yasov, Ya. A. Levin, and A. Sh. Mukhtarov, Teor. Eksp. Khim., 5, 612 (1975); A. V. II'Yasov, Ya. A. Levin, A. Sh. Mukhtarov, and M. S. Skorobogatova, Izv. Akad. Nauk. SSSR, Ser. Khim., 7, 1654 (1975); Ya. A. Levin, A. V. II'Yasov, I. D. Morozova, A. Sh. Mukhtarov, and M. S. Skorobogatova, ibid., 2, 314 (1975); A. Sh. Mukhtarov, A. V. II'Yasov, Ya. A. Levin, and M. S. Skorobogatova, bid., 12, 2816 (1976). (7) G. Brunton, B. C. Gilbert, and R. J. Mawby, J. Chem. SOC.,Perkin Trans. 2 , 650 (1976). (6)The B values are estimated assuming that a,, = 25.2 cos2 OH, and a 120' value for the PB-C-HB angle. (9) A. G. Davies, R. W. Dennis, D. Griller, K. U. Ingold, and B. P. Roberts, Mol. Phys., 25, 989 (1973). (10) J. F. Brazier, D. Houalla, M. Loenig, and R. Wolf, Top. Phosphorus Chem., 8, 99 (1976). (11) J-R. Llinas, E. J. Vincent, and G. Peiffer, Bull. SOC. Chem. Fr,, 11, 3208 (1973); L. Ernst, Org. M g n . Reson., 9, 35 (1977); R. M. Lequan, M.-J. Panet, and M.-P. Simonin, ibid., 7, 392 (1975).
Nuclear Magnetic Resonance Studies of Cations and Water in Lyotropic Systems A. Loewenstein," M. Brenman, and R. Schwarzmann Chemlstry Department, Technion-Israel
Institute of Technology, Haifa, Israel (Received February 2 1, 1978)
NMR measurements of deuterium, sodium, and nitrogen in three lyotropic lamellar systems are reported. Quadrupolar splittings were observed in ND4+,N(CD&+, and Na+ ions which indicate that the ions are apparently oriented. This effect may be caused either by distortion or through an extramolecular electric field gradient. Deuterium resonances of D20 show quadrupolar splittings which are due to partial orientation of the water molecules. Qualitative analysis of the results indicates that a distortion model is more appropriate in the interpretation of the results.
Introduction Molecules dissolved in liquid crystalline solvents, both thermotropic and lyotropic, have been studied extensively by the nuclear magnetic resonance (NMR) technique.lV2 The solutes may be divided coarsely in two classes: (a) nonsymmetric molecules and (b) species possessing high (e.g., spherical or tetrahedral) symmetry. Molecules belonging to the former class are partially oriented by the solvent and consequently their NMR spectra exhibit dipolar and quadrupolar interactions. Splittings which result from these interactions may serve to determine the geometric structure and various other properties of the solutes. In isotropic solvents these interactions are usually averaged to zero and not observed. Solutes belonging to the latter class are not expected to orient in the anisotropic media but nevertheless dipolar and quadrupolar splitting have invariably been observed in their NMR spectra. Measurements in both l y o t r ~ p i c ~ -and ' ~ thermotropic1'-'* solvents have shown this effect. So far no satisfactory complete interpretation to this phenomenum has been presented. Still two semiquantitative approaches to the solution of the problem have been suggested: (1)Molecules or ions may be subjected to dynamic distortions which would cause effective partial ~rientation.~ One difficulty in this approach is that the use of an ordering parameter becomes inappropriate (unless a fixed distortion is a ~ s u m e d l ~ - 'since ~ ) the angle between an axis in the distorted molecule and an external axis (solvent molecule or external magnetic field) is not defined. Furthermore, different distortions may produce species with differing symmetries and be a function of the type of solvent, concentration of the solute, temperature, etc., as has also 0022-365417812082-1744$0 1.OOlO
been assumed for nonsymmetric species.lg (2) In lyotropic systems containing water, which consist predominantly of charged molecules, the ions may be subjected to extramolecular electric fields or electric field gradients (efg) which would result in nonvanishing dipolar or quadrupolar interactions.20 These effects are essentially equivalent to those observed in NMR of the solid phase. One difficulty, among others, in estimating the magnitude of the quadrupole interactions in such cases is the uncertainty in evaluating the Sternheimer factors.21 In this paper we present NMR measurements of D, Na, and N in ions (ND4+,N(CDJ4+, Na+) of some lyotropic systems. The structure of the ordered phases in the systems used in this work is uncertain. However, preliminary X-ray diagrams of very similar systems show small angle reflections which suggest lamellar order with finite extent.18 We therefore assume that the structure is lamellar but in any case this assumption has a minor effect on most of the arguments presented henceforth. We have chosen nuclei with spins greater than 112, where quadrupolar interactions are predominant, since the interpretation of the spectra in these cases is simpler than for spectra resulting from dipolar interactions. The latter are small and often superimposed on spin-spin (J)couplings of similar magnitude. Dipolar interactions may also have different signs when the symmetry of the distortion change^.^^^ In addition, the quadrupolar splittings of D20 and some proton resonances in NH4+in these systems are reported. In previous reports of similar measurementse-10J8the resonances of various nuclei have been measured in different systems. This situation is very unsatisfactory since 0 1978 American Chemical Society
NMR of
Cations and Water in Lyotropic Systems
the interpretation of data in these systems must be based on the comparison of measurements of different nuclei in the same system. It is well known that lyotropic systems are very sensitive to several factors such as the chemical purity of the components, the techniques of mixing, thermal treatments, etc. These factors may have pronounced effects on the nature of the final products. For example, in the course of our investigations we have unsuccessfully attempted to reproduce results for lyotropic systems described e l ~ e w h e r e ,although ~,~ great care was taken to follow precisely the prescribed procedures. We have therefore concluded that reliable interpretations could be achieved only if all measurements would be performed on the same system. We feel confident that our results provide reliable data for comparison with those derived from t,he calculations based on different theoretical models. Experimental Section Samples. Sodium decyl sulfate, decanol, DzO, ammonium sulfate, and tetramethyl-d12-ammonium chloride, were commercial materials and used without purification. Ammonium decyl sulfate was prepared from sodium decyl sulfate, using the procedure given in ref 23. Three mixtures were prepared with the following composition (in weight percent): (1)sodium decyl sulfate, 27.5; ammonium decyl sulfate, 11;decanol, 5.5; D 2 0 (acidified to pD -1.5), 56.5 (SADS); (2) sodium decyl sulfate, 40.2; decanol, 4.3; ammonium sulfate, 3.0; DzO (acidified), 52.3 (ASDS); (3) sodium decyl sulfate, 36.4; decanol, 6.2; tetramethyld12-ammonium chloride, 5.6; D20, 52.2 (TASDS). The addition of acid suppresses the deuterium exchange in the ND4+ ion and permits the observation of the deuterium resonance in this ion. On the other hand, the acid catalyzes the decomposition of the ester% (sodium decyl sulfate) and consequently reduces the lifetime of the samples. Hydrolysis is easily observed through the appearance of two phases (alcohol and water). Still, we believe that hydrolysis is not a major factor in the irreproducibility of results from different laboratories or that it induces large uncertainties in the compositions of our samples. The reason is that hydrolysis would change the sodium decyl sulfate (SDS)-water ratio which in turn strongly affects all quadrupolar splittings (cf. Figure 5). We have not observed significant changes in repeated measurements throughout the duration of the experiments. It seems that as long as the acid concentration remains below a certain level hydrolysis is slow and that only beyond that limit autocatalysis (by H+) becomes very effective. Attempts to replace the ammonium sulfate, in ASDS, by ammonium chloride in various concentrations proved unsuccessful. This contrasts the data in ref 6. The criterion for a good sample was the observation of a fairly narrow doublet for the deuterium resonance of DzO in the samples. Other samples produced either a broad doublets, with tails, typical for polycrystalline samples, or a narrow single line characteristic for isotropic or decomposed samples. NMR Measurements. Deuterium and sodium resonances were taken on a Bruker HFX-10 spectrometer operating in the continuous wave mode at 13.82 and 22.63 MHz for D and Na, respectively. Nitrogen resonances at 5.5 MHz were taken in the FT mode on a combination of BKR-322s Bruker pulsed NMR spectrometer and a Bruker WP-60 spectrometer (computer part). Between 500 and 2000 accumulations were usually necessary. Proton spectra were taken at 60 MHz on a Bruker WP-60 spectrometer. Spinning of the samples reduced the splittings and broadened the lines, contrary to measurements reported in ref 9 for samples that are almost identical with our SADS system. Samples were contained
The Journal of Physical Chemistry, Vol. 82, No. 15, 1978
A SADS 0 ASDS 0 TASDS
60
+
I a"
1745
0
i
Oa
401
0
0 O
A
0
301
A 1
0
1
1
I
IO
20
30
,
40
Temperature PC)
Deuterium splittings of the ND4+ and N(CD,),+ in lyotropic systems as a function of the temperature. The composition of the system is given in the text. Figure 1.
c?
SADS 0 ASDS A
,500~0 TASDS
i
I
I
AA
5001
A I
IO
,
20 Temperalure
'
0 A
30
I
40
R3 .
Figure 2. Nitrogen splittings of ND4' and N(CD,),+ in lyotropic systems as a function of the temperature. The composition of the systems is given in the text.
in 10-mm 0.d. tubes except for proton measurements (5-mm 0.d. tubes). The precisions of the measurements are as follows: DzO, h 6 Hz; ND4+&3 Hz, MI4+,f10 Hz, Na+, h50 Hz. Results and Discussion Measurements of the deuterium, nitrogen, and sodium resonances as a function of the temperature are shown in Figures 1-4. While Figures 1-3 relate to the symmetric species in the system, Figure 4 gives the ordering parameter of the DzO molecules. All quadrupolar splittings decrease with increasing temperature which is typical behavior in such systems. The TASDS system seems to be the least sensitive, in most measurements, to temperature changes. The changes of the splittings (except N) as a function of the water contents in one system (ASDS) are given in Figure 5. There seems to be a linear proportionality between the ratio of sodium decyl sulfate to water concentrations and the splittings. This might be expected since an increase in the sodium decyl sulfate concentration decreases the thickness of the water layers between the ordered lamella and enhances the order of the system. Proton spectra of the NH protons in SADA give a triplet with a splitting of 50 f 1 Hz over the entire temperature
1746
The Journal of Physical Chemistry, Vol. 82, No. 15, 1078
A. Loewenstein, M. Brenman, and R. Schwarzmann
TABLE I: Temperature Dependence of Quadrupolar Splittings (Hz/"C) ND,' Figure 2 40 36 19.3
NDC
system SADS ASDS TASDS
corr 1.8 1.4
Figure 1
1.8 1.4 1.1
1.1
corr 7 6.4 3.4
Na' Figure 3 corr 28 2.4 87 7.2 56 4.0
D2O Figure 4 corr 2.4 2.4 8.8 8.8 1.8 1.8
A SADS 0 ASDS 0 TASDS A 8
t
8
0
0
0 O O
0
.
0
ASDS
2
20
IO
Temperature
b 0.5
4c
30
Figure 3. Sodium splittings (between adjacent lines in the observed triplet) in lyotropic systems as a function of the temperature. The composition of the systems is given in the text.
0 ASDS
TASDS
3 4
A
I2 P(2P - 1) O
A A
A
IO
o 0
400-
t
O
A
A
300 2001,
Figure 5. The splittings of deuterium in ND,' (O), D20 (A),and sodium (H) in the ASDS system (see text) as a function of the ratio of sodium decyl sulfate to D20 at 22 OC. Note the changes in the vertical scale for the different measurements.
13 e 2 & ' ( d ) 1
0
500-
0.9
quadrupole moments (e&). For a given nucleus, i, the quadrupolar splitting between adjacent resonances is given by
A SADS
--2
0.8
0.7
[SDS/D,O]
(OC)
600
0.6
,
,
,
20
30
40
1
Temperature PC) Figure 4. Deuterium splittings of D20 in lyotropic systems as a function of the temperature. The composition of the systems is given in the text.
range. This is slightly larger than the value of 45.75 Hz obtained previously on a very similar systemqgAs mentioned earlier we were unable to spin the sample and consequently could not observe the proton-proton dipolar splitting (D"). Since the observed splitting equals to IJ + 2D"I and J = 52 f 1 Hz (measured in the same system in the isotropic phase), the value of D" is small and susceptible to large errors. We therefore believe that under these circumstances D" is not a very useful quantity in this system. Furthermore, in the distortion model,7 the sign of D" (and DHH) depends upon the type of the distortion, which adds to the ambiguity of the interpretation. Comparison of data for different nuclei requires a correction taking into account their different spins (I)and
I
For N, D, and Na, I = 1, 1, and 3/2 and e& = 1.55 X 0.273 X and 10 X e cm2, r e ~ p e c t i v e l y .The ~~ quantity ( 9 ' ) is the average efg at the site of the nucleus. Therefore, for equal efg's, the ratios of Na/D, N/D, and Na/N splittings should be 12.2, 5.7, and 2.15, respectively. These factors must be applied in the comparison of data for different nuclei. Another problem in the evaluation of data for N and D in ND4+might arise from the possibility of a contribution to the splittings from its dissociation to ND3 + D'. An estimate based on assumed Kb 2 X pD -2, and the maximum splitting of N and D in ND3 of 4 X lo6 and 2 X lo5 Hz, respectively, results in a neglible contribution from this effect. Let us start our evaluation of the data by examining the temperature dependence of the quadrupolar splittings. Table I gives the approximate slopes (assuming linearity) of the data shown in Figures 1-4. The slopes are given as they appear in the figures together with the corrected values with respect to D splittings. With two exceptions (N resonances in SADS and D resonances in ASDS) the corrected slopes are similar, within a factor of 2, for each system. This points to a possible connection between the ordering of D 2 0 and the efg operating in the symmetric species. It seems likely that the assymetric arrangement of water molecules around a given ion may either directly induce the efg at the site of the nuclei or actually promote the distortion of the ions. Our data should now be examined with reference to the distortion and extramolecular efg models which were discussed briefly earlier.
-
NMR of Cations and Water in Lyotropic Systems
The Journal of Physical Chemistry, Vol. 82, No. 15, 1978
Distortion Model. The model used by Buckingham et al.7 predicts that the ratio between the quadrupolar splittings of N and D in the ND4+ion should be given by AvQN (e2qQ)NX 54.02 -- = 1.01 X ' l O 2 AvQD (e2qQ)Dx 13.5 The e2qQ's are the quadrupole coupling constants of the bonds and their assumed values are (e2qQ)D= 175 X lo3 Hz26and (e2qQ)N= 4.58 X lo6 Hz. The calculation of the latter quantity is based on the tensor projection of the e2qQ for ND3 (4.084 X lo6 Hz) along the N-D bond. This procedure assumes that the conversion from ND3 to ND4+ produces a negligible perturbation on the immediate electronic environment of the nitrogen atom and consequently on the bond's efg. The average experimental ratio of the splittings is 15 f 5 for the SADS and ASDS system and 45 f 5 for the TASDS system. These discrepancies may be a consequence of the simplicity of the model or its inadequacy in application to this problem. We suggest that the weak point in the model is the estimation of the values of the quadrupole coupling constants and in particular that of nitrogen. Values given in the literature for (e2qQ)Din ND3 or NHzD (mostly in the gas phase) vary from about 50 to 280 kHz and in ND4+ (solid phase) they are about 170 kHz but depend strongly on temperature, deuterium bond strength, and type of the crystal.27 Still a choice of 175 kHz for e2qQ seems quite reasonable. The estimation of (e2qQ)Nby the procedure used by Buckingham et al.7 is more doubtful especially since it gives a value for the (e2qQ)Nin ND4+which is higher than that of ND3. This difficulty has also been pointed out by Buckingham et al. We suggest that a preferable choice for (e2qQ)Nwould be the actual nitrogen quadrupole coupling constant measured in an environment close to tetrahedral, Le., in compounds where the nitrogen carries a positive charge and is bonded to four groups (methyls, hydrogens, acid residues, etc.). Such measurements2s give a value of (e2qQ)Nbetween 0.8 and 1.2 MHz. Choosing an approximate average value for (e2qQ)Nof 1 X lo6 Hz would give A v Q N / ~ v Q D 0.2 x lo2
-
which fits rather well with our experimental results. Extramolecular efg Model. An estimation of the quadrupolar splitting resulting from an extramolecular efg would involve several assumptions: (1)The functional form of the efg produced by the charged lammella. For a point charge e, at a distance r, the function is ( er-3) but this should be modified for a charge distribution. (2) The averaging procedure (denoted as ( ) ) should take into account the distribution of the ions between the charged layer and their partial immobilization. The value of ( r-3) would be different for each deuteron in the ND4+ if its rotation is not completely free. (3) The Sternheimer factor would affect the splitting of the nitrogen. A recent attemptz1to calculate this factor gives a value of -13 while experimental values are -4 for and -6.5 for N(CH3)4+.30 These values are susceptibile to relatively large errors. We have attempted to calculate the ratio of the nitrogen and deuterium splittings on the basis of a simple geometrical model (I). The deuterons are located on a sphere
point charge
I
1747
2.01 0 A N a~
==,
0
1.5-
B
Z N W U
0
1.0 -
i
b : @
2
4
6 2
8
IO
(4,
Flgure 6. Calculated ratio for the efg at the nitrogen and deuterium nuclei in ND,' as a function of its distance from a point change.
of radius R (= 1.03 A in ND4+). The ratio of the efg's a t the sites of the nitrogen and deuterium nuclei is
-(qZzN) - (qzzD)
((R + G 3 ( 3 cos2 4 - 1))(p-3(3 cos2 4 - 1))
2(R
+ Z)-3
(p-3(3 cos2 4 -1))
If the deuterons move freely on the surface of the sphere the ratio is unity. We have calculated this ratio for three discrete configurations of the ND4+tetrahedron and the results are shown in Figure 6. It turns out that only for 2 < 1the ratio of (qZzN) / ( qzzD)has a small positive value. In comparison, the experimental ratio is about 15 though one migh supply a Sternheimer factor correction which would reduce it. A t any rate it seems rather unlikely that the average separation of the ion from the charged layer is so small. This simple calculation indicates that the extra molecular efg model does not account adequately for the experimental results. An inspection of our results for the N and D measurements in systems containing ND4' and N(CD3)4+ions also suggests that the extramolecular efg does not play an important role in producing the quadrupolar splittings. In Figures 1 and 2 we note that replacing the ND4' ion by N(CD3)4' barely affects the deuterium splittings while the nitrogen increase by a factor of 3-4. One would expect the nitrogen splittings to be reduced in comparison to the deuterium splitting when the size of the ion is increased because of the increase in the ratio (RD-3/RN-3). Quadrupolar splittings of sodium, due to an external point charge or dipole, have been calculated by Wennerstrom et aL20 These calculations can hardly be applied to real systems because of uncertainties in the averaging procedures and intermolecular distances. We are therefore unable to determine whether sodium splittings are due to electronic distortions in its outer orbitals or to an efg induced by extramolecular sources (water molecules or charged lamella). Finally we wish to point out that molecular distortions of solute radicals dissolved in liquid crystalline solvents have been observed through their ESR spectra.31 Also, in methanes and silanes dissolved in nematic liquid crystals, which are obviously distorted (electric field effects must be excluded), both the deuterium splittings and their temperature dependence are quite ~ i m i l a r ' ~to- ~those ~
1748
The Journal of Physical Chemishy, Vol, 82, No. 15, 1978
reported here for ND4+and N(CD3)4+. These arguments support our conclusion that the distortions of ions apparently exist in lyotropic systems and that they are responsible for the observed splittings in their NMR spectra. Note Added in Proof. A recent paper by D. M. Chen and J. D. Glickson (J. Mag. Reson., 28, 9 (1977)) investigates the problem of distortions of ammonium ions in other lyotropic phases. Results of 14N,D, and H NMR spectra are analyzed exclusively in terms of the distortion modeL7 In comparing the results given in this paper with ours we note that they observe much smaller quadrupole splittings of deuterium (particularly for ND4+). Consequently they deduced a value for (e2qQINof about 3 MHz, quite bigger than the value suggested by us.
Acknowledgment. Part of this research has been sponsored by a research grant from the United StatesIsrael Binational Science Foundation. References and Notes (1) J. W. Emsley and J. C. Lindon, "NMR Spectroscopy Using Liquid Crystal Solvents", Pergamon Press, New York, N.Y., 1975. (2) C. L. Khetrapal, A. C. Kunwar, A. S. Tracey, and P. Diehl, "Nuclear Magnetic Resonance Studies in Lyotropic Liquid Crystals" in "NMR, Basic Principles and Progress", P. Diehl, E. Fluck, and R. Kosfeld, Ed., Vol. 9, Springer-Verlag, West Berlin, 1975. (3) K. Radley and L. W. Reeves, Can J . Chem., 53, 2998 (1975). (4) K. Radley, L. Reeves, and A. S. Tracey, J. fhys. Chem., 80, 174 (1976). (5) F. Fujiwara, L. W. Reeves, and A. S. Tracey, J. Am. Chem. SOC., 96, 5250 (1974). (6) L. W. Reeves and A. S.Tracey, J. Am. Chem. Soc., 96,365 (1974). (7) D. Bailey, A. D. Buckingham, F. Fujiwara, and L. W. Reeves, J . Mag. Reson., 18, 344 (1975). (8) H. Gustavsson, G. Lindblom, B. Lindman, N-0. Persson, and H. Wennerstrom in "Liquid Crystals and Oriented Fluids", Vol. 2, J. F.
S. Furuyama and T.
(9) (10)
(11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25)
(26) (27) (28) (29) (30)
(31)
Morimoto
Johnson and R. S. Porter, Ed., Plenum Press, New York, N.Y., 1973, p 161. K. Radley and A. Saupe, Mol. Phys., 32, 1167 (1976). B. Lindman and S. Forsen, "CI, Br, I NMR, Physico-Chemical and Biological Applications", Vol. 12 of "NMR, Basic Principles and Progress", P. Diehl, E. Fluck, and R. Kosteld, Ed., Springer-Verlag, West Berlin, 1976. L. C. Snyder and S. Meiboom, J. Chem. fhys., 44, 4057 (1966). R. Ader and A. Loewenstein, Mol. Phys., 24, 455 (1972). R. Ader and A. Loewenstein, Mol. fhys., 30, 199 (1975). A. Loewenstein, Chem. fhys. Lett., 38, 543 (1976). I. Y. Wei and C. S. Johnson Jr., J . Mag. Reson., 23, 259 (1976). A. Amanzi, P. L. Barili, P. Chidichimo, and C. A. Veracini, Chem. fhys. Lett., 44, 110 (1976). A. Frey and R. R. Ernst, Chem. Phys. Lett., 49, 75 (1977). J. Charvolln, A. Loewenstein, and J. Virlet, J. Mag. Reson., 26, 529 (1977). J. Bulthuis and C. A. de Lange, J . Mag. Reson., 14, 13 (1974). H. Wennerstrom, G. Lindblom, and B. Lindman, Chem. Scr., 6, 97 (1974). S. Engstrom, H. Wennerstrom, B. Jonsson, and C. Karlstrom, Mol. Phys., 34, 813 (1977). N-0 Persson and B. Lindman, Mol. Cryst. Liq. Cryst., 38, 327 (1977). L. W. Reeves, J. Sanches de Cara, M. Suzukl, and A. S. Tracey, Mol. fhys., 25, 1481 (1973). J. L. Kurz, J. Phys. Chem., 86, 2239 (1962). The quadrupole moments, for N in particular, are susceptibleto large errors. Data on eQNcan be found in J. M. Lehn and J. P. Kintzinger, "Nitrogen NMR", M. Witanowski and G. A. Webb, Ed., Plenum Press, New York, N.Y., 1973, p 84 and 8; H. Kopfermann, "Nuclear Moments", Academic Press, New York, N.Y., 1956; W. D. White and R. S. Drago, J . Chem. Phys., 52, 4717 (1970), and Erratum to this paper. W. J. Caspary, F. Millet, M. Reichbach, and B. P. Dailey, J . Chem. fhys., 51, 623 (1969). Cf. P. Pvkko, Ann. Univ. Turku., Ser. A, 103 (19671: H. H. Mantsch, H. Saitoand I. C. P. Smith, frog. NMR Spect;osc.,'ll, 212 (1977). D. T. Edmonds, M. J. Hunt, and A. L. MacKay, J. Mag. Reson., 9, 66 (1973); M. J. Hunt, ibid., 15, 113 (1974). W. C. Bailey and H. S. Story, J. Chem. fhys., 60, 1952 (1970). J. P. Kintzinger and J. M. Lehn, Helv. Chim. Acta, 58, 905 (1975). Cf. G. F. Pedulli, C. Zannoni, and A. Alberti, Mol. Phys., 10,372(1973).
Sorption of Nitric Oxide, Carbon Monoxide, and Nitrogen by Sodium Mordenite Shoro Furuyama* and Tetsuo Morlmoto Department of Chemistry, Faculty of Science, Okayama University, Tsushima, Okayama 700, Japan (Received January 12, 1978; Revised Manuscript Received May 23, 1978) Publication costs assisted by Okayama University
The sorption of NO, CO, and Nzby sodium mordenite was measured in the temperature range -80-75 "C. The strength of the sorption affinity was found to vary in the order of N2 < NO < CO. The slopes of the isotherms (log (sorption amount) vs. log (equilibrium pressure)) were almost unity at lower coverage for all three gases. At higher coverage, the slope for NO became steep, possibly due to dimerization, while the slopes for CO and Nz decreased gradually as usual. The saturation sorption amount, V,, was 25.0 mL (STP)/g for CO and Nz, which gave a value of 0.4 nm for the effective diameter of the sorbed molecules. The isosteric heat of sorption, qst, changed with temperature and coverage. At 0 = 0.02, the values of qst for CO, Nz, and NO were 8.8,8.0, and 7.1 kcal/mol at -30 "C, and 8.1, 6.6, and 6.6 kcal/mol at 30 "C, respectively. It is concluded that the magnitude of qat is principally determined by dispersion forces and that the contributions of the quadrupole and dipole moments are less significant. The temperature dependence of the thermal entropy of sorbed molecules suggests that the sorbed molecule rotates freely above 40 "C, but librates below -25 "C. However, the degree of the rotational hindrance is independent of the magnitude of the dipole moment. At higher coverage, the sorption isotherms of CO and Nzcan be expressed in a virial form. The second virial coefficient obtained decreases m/molecule in the temperature gradually with increases in temperature and falls in the range 1-2 X region 0-45 "C.
Introduction Mordenite has a bundle of elliptical (0.7 and 0.58 nm for the maximum and minimum free diameters, respectively) straight cylindrical channels running parallel to the c axis.l On account of this unique structure, mordenite can sorb permanent gases even a t room temperature.2
According to studies by Takaishi et al., the translational mode of the sorbed molecule well be described in terms of a model for a one-dimensional g a ~ . ~The - ~rotational state of the sorbed molecule is apparently affected by the magnitude of its molecular quadrupole moment. The rotation of sorbed nitrogen is seriously hindered below 0
0022-3654/78/2082-1746$01.00/00 1978 American Chemical Society
