NOTES
3022 Table I : Physical Properties and Spectral Band Intensities of Zeolites 7 -
% Ammonium Y exchanged t o Ma+ form
Surface area, ma g-1
92 74 65 56 51 37 18
842 860 890 900 908 924 920
Calcium hydrogen Y Absorbance Absorbance 3650-om-1 3550-om-1 band band
1.0 10.0 13.0 19.1 19.4 19.2 19.0
0.1 1.3 1.6 2.9 3.7 8.6 14.8
1
Absorbance 1444-om-I band
12.3 7.8 4.0 0.2 0.9 0.0 0.0
into the structure and continues to decrease as more divalent ions are added. The absorbance of the 3650cm-l band remains constant until 56% exchange with calcium is reached and then it declines rapidly until at 90% exchange, only traces of the band are detected. Conversely, as the cation content is increased beyond the 55% level, the absorption band due to cation-pyridine interaction appears. The results for the magnesium system are analogous. Olson and Dempsey3 have shown that the 3550-cm-' absorption band represents hydrogen atoms associated with the 0 3 atoms located inside the hexagonal prism and that the 3660-cm-' band represents hydrogen associated with the O1 atoms located in the supercages. The calcium dependence of the hydroxyl group band intensities indicates that in the initial stages of exchange, the calcium ions must replace ammonium ions in the small pore system of the structure. These ions could be located either in the hexagonal prisms or the sodalite cages since the calcium ions in the sodium Y system are known to migrate as the state of hydration changes. Infrared studies of adsorbed molecules do not allow distinction between the two locations. In the Ca-NaY system, calcium ions appear in accessible positions in the structure after 16-18 calcium ions per unit cell have been added. In the Ca-HY system, the intensity of the 3650-cm-1 band remains approximately constant until 15-17 ions per unit cell have been added; it then decreases rapidly as more calcium ions are added indicating the replacement of ammonium ions in accessible positions by calcium ions. Simultaneously, the absorption band a t 1444 cm-l (1448 cm-I for Mg) due to calcium-pyridine interaction is observed, confirming the presence of calcium ions in accessible positions. The intensity of the 3 5 5 0 - ~ m -band ~ does not reach zero near 55% exchange, but it still has a positive value which decreases on further exchange. This suggests that the occupancy of the inaccessible positions is not complete before the onset of occupancy of the accessible positions. However, the residual band intensity at 55% exchange is equivalent to about 1-2 residual hydroxyl groups while at 65% exchange, the band inThe Journal of Physical Chemistry, Vol. 74, No. 16, 1970
7 -
% Ammonium Y exchanged t o Ma+ form
79 83 52 50 45 35
Magnesium hydrogen Surface Absorbance Absorbance area, 3650-om-1 3550-om-1 m2 6-1 band band
891 863 86 1 868 884 948
2.0 16.1 19.0 19.3 19.3 18.9
0.1 2.2 3.2 3.7 4.8 8.0
7
Absorbance 1448-om-1 band
7.8 3.3 1.1 0.4 0.1 0.0
tensity is equivalent to less than one hydroxyl group out of the original sixteen. Hence it can be concluded that the distribution of calcium and magnesium in the ammonium Y zeolite system is the same as in the sodium system. Although it is not possible to be specific from the infrared results, the behavior of the 3550 cm-' band suggests that approximately the first 16 calcium and magnesium ions are located in the hexagonal prisms at least after dehydration at 450". It is possible that the calcium and magnesium ions may change locations depending on the degree of hydration, similar to that reported for the calcium-sodium Y system. Other measurements will be necessary to determine the specific locations of the inaccessible cations and whether migration occurs with changes in hydration level.
Interpretations of Nuclear Quadrupole Resonance Data in Some trans-Dichlorobis-
(ethylenediamine)cobalt(III) Saltsla
by T. B. BrillIb and Z Z. Hugus, Jr. Department of Chemistry, North Carolina State Uniuersity, Raleigh, North Carolina 87607 (Received January 19,1970)
There exists an unusually large variation in the 59C0 nuclear quadrupole resonance frequencies in transdihalobis(ethylenediamine)cobalt(III) + salts as the nature of the anions is changed. For example, in going from trans-(CoenzClz)C1 to trans-(Coen2Clz)Cl .HC1* 2Hz0, the 6 9 Cresonance ~ frequency increases by about 15%. I n going from trans-(CoenzBrz)C104 to trans(Coen2Br2)Br.HBr.2Hz0,there is a 25% increase in the resonance frequency. Understanding the possible sources of these variations is an interesting problem and one of importance to nqr spectroscopy. (1). (a) Abstracted from the thesis of T. B. B. submitted to the University of Minnesota in partial fulfillment of a Doctor of Philosophy degree, (b) NDEA Fellow at the University of Minnesota, 1966-1969.
NOTES
3023
Table I: Nqr Frequenciesasb,c and Coupling Constants in MHz and Asymmetry Parameters a t 23' Compounds
(Coen,Clp) (C1.HC1.2HzO)c1-
d7/2
Ref
6/21
+
NOac104SCN BrO3(CoenzBrz)+
15.296 (70) 12 A92 (2) 13.426 (8) 12.888 (11) 12,816 (10) 12.870 (6) 13.880 (8)
10.001 (80) [8.368] 8.877 (6) 8.512 (5) 8.467 (5) 8.395 (2) 9.057 (4)
5.973 (5) [5.367] [4.777] ,.. ,,.
...
...
0.222 0.272 0.132 0.149 0.149 0.245 0 238 I
16.058 (15)
12.656 (4)
,.. ..,
...
... ...
...
...
v(79Br)
(Br-HBr.2HzO)-
Brc104-
15.503 (65) 12.860 (2) 12.264 (5)
10.104 (70) [8.392] 8.096 (3)
...
... ...
0.244 0.235 0.149
127.34 (20)
... ...
a Resonances in brackets were reported in reference 4 but could not be found in this study. noise ratios. c Frequencies listed are good to within 3 kHz.
Table 12-4shows that in general, the resonance frequencies fall into two classes: those of the acid halide double salts and those of the simple salts. It is the purpose of this note to investigate the source of this difference. Self-consistent charge and configuration LCAO-XI0 calculations5 with all 27 atoms and 65 valence orbitals in trans-(CoenzClz)+ were carried out and indicate that the converged atom charges are: Co (+0.60), C1 (-0.50), N (-0.35)) C (-0.35), H(K) (+0.34), H(C) ($0.18). Coulomb integrals for cobalt were computed using quadratically charge-adjusted valence orbital ionization potentiah6 Analytical single-term Slatertype valence orbital exponents for all atoms except cobalt were taken from Clementi and Raimondi's tables.' Those for cobalt were based on data of Schreiner and Brown.8 The same calculation was carried out on trans-(Coen2Brz)+. The ring charges in the bromo compound mere found to be about the same but the cobalt and bromine charges were +0.58 and - 0.37, respectively. However, since the trans-(Coenz(312) + cation remains essentially the same within experimental error in all of the compounds which have been studied by X-ray c r y ~ t a l l o g r a p h y , ~the - ~ ~importance of differences in the lattice must be investigated. A good comparison may be made between the acid double salt, t~ans-(Coen2Clp)Cl.HC1.2HtO, and the simple salt, trans-(Coen2Clz)CI. The lattice electric field gradient (EFG) was computed using the electrostatic point charge modellj with the atomic coordinates being obtained from the crystal structure data,9-14 and the atomic charges from the self-consistent charges in the 340 calculation. The computer programs used have been described before. The electrostatic contributions to the EFG from atoms within the ion containing the nucleus at r = 0 were neglected since these are taken into account as part of the intramolecular EFG.
... ... ...
,..
...
71.73 60.63 62.78 60.22 59.92 60.43 65.15
2, 3 4 4 This work This work This work This work
72.80 60.36 57.38
3 4 This work
@Br)
106.38 (20)
... .,.
Parenthetical numbers are signal to
Summation was carried out to r = 60 8 to ensure convergence. The eigenvalues of the resulting tensor must be corrected by the Sternheimer antishielding factor, l7 1 - ym. A multiplicative factor of 12 for 1 - ym for 59Cowas used by Watanabe and Yamagatae4 Scott and Bernheiml* reasoned that the value could not be much larger than 8. Table I1 lists the computed lattice coupling constants for several values of 1 - ym compared to the observed coupling constants. I t must be kept in mind that the models used are approximate ones, but the lattice EFG difference computed from the point charge model is about the same as the experimental difference in the (2) H. Hartmann, M. Fleissner, and H. Sillescu, Naturwissenschaften, 50, 591 (1963). (3) H. Hartmann, M. Fleissner, and H. Sillescu, Theor. Chim. Acta, 2, 63 (1964). (4) 1. Watanabe and Y. Yamagata, J . Chem. Phys., 46, 407 (1967). (5) R . Hoffmann and W. N. Lipscomb, ibid., 36, 2179 (1962). (6) H. Basch, A. Viste, and H. B. Gray, Theor. Chim. Acta, 3, 458 (1965) (7) E. Clementi and D. L. Raimondi, J . Chem. Phys., 38, 2686 (1963). (8) A. F. Schreiner and T. L. Brown, J . Amer. Chem. A ~ O C . ,90, 3366 (1968). (9) A. Nakahara, Y. Saito, and H. Kuroya, Bull. Chem. SOC. Jap., 25, 331 (1952). (10) J. M.Williams, Inorg. Nucl. Chem. Lett., 3, 297 (1967). (11) S. Ooi, Y. Komiyama, Y. Saito, and H. Kuroya, Bull. Chem. Soc. Jap., 32, 263 (1959). (12) K. A. Becker, G. Grosse, and K. Pleith, 2. Kristallogr., 112, 375 (1959). (13) S. Ooi and H. Kuroya, BulZ. Chem. Soc. Jap., 36, 1083 (1963). (14) S. Ooi, Y. Komiyama, and H. Kuroya, {bid., 33, 354 (1959). (15) R. Bersohn, J . Chem. Phys., 29, 326 (1958). (16) T. B. Brill, 2 Z. Hugus, Jr., and A. F. Schreiner, J . Phys. Chem., 74, 469 (1970). (17) R. M. Sternheimer and H. M. Foley, Phys. Rev., 102, 731 (1956), and references therein. (18) B. A. Scott and R. A. Bernheim, J . Chem. Phys., 44, 2004 (1966). I
The Journal of Physical Chemistry, Vol. 7 4 , No. 15, 1970
NOTES
3024 Table 11: Lattice Coupling Constants for Various Values of 1 Compared to the Experimental Coupling Constants Compounds
trans- (Coen*Clz)C1.
(e28dh)expti,a ---(e2Qdh)iat, MHz 1 - ym = 8
MHz10
12
71.73
-13.1
-16.8
-20.2
60.63
-2.0
-2.5
-3.0
HCl 2HzOb
trans- (CoenzClz)C1
a The sign of the coupling constant cannot be determined in pure nqr spectroscopy. I n reference 3, the lattice EFG for trans-(CoenzClz)C1.HCl.2Hz0 was computed in esu/cm3. Our values are in substantial agreement with this in view of the fact that a different charge distribution and several more atoms were included in this study.
resonance frequencies, and it appears that the crystal lattice is the source of the variation. It must be presumed that the intramolecular coupling constant has the same sign as the lattice coupling constant. Scott and Bernheim's value of 8 for 1 - ymappears to be the right magnitude for cobalt. X-Ray data are not available for many of the other salts but several comments may be made. The most strikingly different compound is that of trans-(CoenzC l ~ ) C 1 0 ~Two . 6 g Cresonances ~ of approximately equal intensity were found. The unit cell appears to contain at least two (or an even number if more than two) formula units such that the principal components of their EFG tensor differ in magnitude. This salt does not appear to be isostructural with h.ans-(Coen2Br2)-
c104. trans-(CoenzClz)Cl and trans-(CoenzBr2)Br appear to be isostructural since both their asymmetry parameters and coupling constants are similar. Acknowledgments. We wish to thank Dr. A. F. Schreiner for the use of the SCCC-MO program. The support of the North Carolina Board of Science and Technology toward the purchase of a Wilks NQR-1A nqr spectrometer is gratefully acknowledged.
A Comparison of the Gibbs Energy and Entropy of Interfaces Water-n-Hexane and Water-Perfluorotribu tylamine
by R. G. Linford, R. J. Powell, and J. H. Hildebrand Department of Chemistry, University of California, Berkeley, California 947?20 (Received March 30,1970)
Miller and Hildebrandl showed in 1968 that losses of entropy which accompany solution of nonreacting gases in water to the same mole fraction, vary linearly with the total surface area per mole of the solute molecules, from Ne to n-CIHlo. The losses agree, moreover, in order of magnitude, with values calculated The Journal of Physical Chemhtry, Vol. 7 4 , No. 16,1970
from the decrease in entropy per cm2 that occurs when an alkane liquid flows over a surface of water. They discovered, further, that a corresponding line for the gases NF3, CF4, and SF6 lies several calories per degree lower than the line for other gases. It has seemed worthwhile, therefore, to find out whether a fluorochemical liquid is more effective than an alkane in diminishing the entropy of a surface of water. We availed ourselves of a supply of perfluorotributylamine, (C4Fg)3N,"FC43," of adequate purity kindly furnished by the Minnesota Mining and Manufacturing Co. Its density, not degassed, conformed, between 20 and 45", with the expression: p = 1.9335 - 0.00218t. Its surface energy, determined by capillary rise between 15 and 35", is given by the expression: y = 17.16 0.080(t - 15) erg/cm2. Water completely wets glass in the presence of this liquid making it possible to determine their interfacial tension from the hydrostatic pressure that can be sustained by a hemispherical drop of FC43 of maximum curvature projecting into water from a glass capillary of known radius. The FC43 was contained in a U tube, one arm of which was the capillary. The internal radius of the tip was 0.0299 em. Designating the height of FC43 in the broad arm of the U tube above the level of the drop in the capillary as Ahr, and the corresponding level of water above the top of the drop as Ah,, and using the relation between hydrostatic pressure, surface tension, and drop radius, 2y = Pr, we calculate interfacial Gibbs energy (in erg/cm2) by the equation
We obtained values of y between 15 an$ 45"; they conform closely to the expression: y = 39.85 0.086(t - 15) k 0.1 erg/cm2. Its value at 26" is 40.7 erg/cm2 and the interfacial entropy is -0.086 erg/deg cm2. We select for comparison the corresponding values for normal hexane: surface tension by Jasper and King,2 interfacial tension with water by Aveyard and Hayden. We take values for pure water from a handbook. The data are summarized in Table I and plotted in Figure 1 to give a clearer view of the effects of temperature. The most striking comparison revealed is the increase with temperature of the free energy of the interface water-(C4F9),N. The entropy of the surface of water
+
(1) K. W. Miller and J. H. Hildebrand, J . Amer. Chem. Soc., 90, 3001 (1968). (2) J. J. Jasper and E. V. King, J. Phys. Chem., 59, 1019 (1965); R. Aveyard and D. A. Hayden, Trans. Faraday Soc., 61, 2255 (1965). (3) "American Institute of Physics Handbook," -McGraw-Hill, New York, N. Y., 1957.
