The Journal of Physical Chemistry, Vol. 82, No. 4, 1978 497
Communications to the Editor (4) A. R. Davis and B. G. Oliver, J . Phys. Chem., 77, 1315 (1973). (5) G. K. Ward and F. J. Millero, Geochim. Cosmochim. Acta, 39, 1595-1604 (1975). (6) W. A. Adams, C. M. Preston, and H. A. M. Chew, Electrochemical Societv. Princeton. N.J.. Extended Abstracts 77-1. 779-780 (19771. (7) J. T. Bulmer, D. E. Irish, and L. Odberg, Can. J . Ched., 53, 3806-3811 (1975). Energy Conversion Division Defence Research Establishment, Ottawa Department of National Defence Ottawa, Canada K1A 024 Inland Water Directorate Environment Canada Ottawa, Canada K I A OE7 Atomic Energy Control Board P. 0. Box 1046 Ottawa, Canada K 7P 5S9
W.A. Adams"
from the tables published by Jaff@J for a Cu-N distance of 2.035 A. We took the more realistic sp3 hybridization on N. The values of the overlap integrals were as follows:
So = 2( 3d,
2-y2
IuN)
= 0.240490
where u = p2pN + (1 - p2)1/22sNwith hybridization
p =
&/2
for sp3
S2 = &%3d,. 12h,z)= 0.051619 A. R. Davis
SI = 2(3d,y12pN,x)= 4 23, = 0.0730
The value of the integral (2sla/ax12px), featured in the expressions of the g values and hyperfine splitting constants, was taken from Misetich and Watson8 to be 0.331. Three d-d transitions are possible, but only one band is observed.1,2 Therefore, we calculated the MO coefficients Received November 4, 1977 with the following two hypotheses: (i) the 2B1g 2Eg transition frequency was taken as the experimental band maximum. The 2B1g 2Bzgtransition frequency was derived from gli under the assumption that XII = X, with X as the spin-orbit coupling constant. (ii) The three Analysis of the Electron Paramagnetic Resonance transitions possible have equal frequency which is the Spectra of Bis(ethylenediamine)copper(11) on the experimental band maximum. The calculations were performed on a Nova 8 computer Surfaces of Zeolites X and Y and of a Camp Berteau with an interation procedure until two consecutive values Montmorillonite of the squares of the MO coefficients of 3d,z,z ( a 2 )3dxy , Publication costs assisted by the Catholic University of Leuven (p12),and 3d,, (p2)differed by less than 0.02. The results are given in Table I together with the coefficients previously obtained with the KN theory.'J The calculations Sir: Recently, we reported the reflectance spectra and produced also x,the isotropic contribution to the hyperfine EPR parameters of [Cu(en),12+(en = ethylenediamine), ion exchanged on zeolites and a Camp Berteau montinteraction, due to core polarization. There is a general morillonite.lr2 These data were analyzed in the framework trend emerging from Table I in that all the coefficients are of the Kivelson-Neiman (KN) theory for planar Cu(I1) systematically higher than those calculated from the KN complexe~.~ This theory assumes sp2hybridization of the theory. Secondly, there is no significant difference between nitrogen atoms and neglects the overlap integrals between the a2's and the p12's among complexes on different surthe 3d and N orbitals, which make up the in-plane and faces and in solution. Thus, the substrate does not inout-of-plane x orbitals of the complex. The absolute values fluence significantly the in-plane molecular orbitals. Their high values indicate low covalent characters. p2, the square of such MO coefficients do not have that much physical significance but coefficients for one complex, in this case of the coefficient of 3d,, in the out-of-plane x orbital [Cu(en),12+, on different substrates were said to be depends on the choice of the 'B1, 2Bzgtransition frecomparable. To improve the absolute values of the MO quency. For both choices however, p2 is less than p12, coefficients we recalculated our experimental data with the indicating a higher covalent character of the out-of-plane more general theory of Moreno and B a r r i ~ s o . ~The ,~ x orbital with respect to the in-plane x orbital. Furmolecular orbitals and overlap integrals were defined in thermore, p2 is significantly less for [Cu(en),12+on a surface the KN paper and the papers of Moreno and B a r r i ~ s o . ~ - ~ than for [Cu(en),12+in aqueous solution. This is especially We estimated the overlap integrals between the 3d orbitals evident on a montmorillonite surface. In the latter case of Cu(I1) and the 2s and 2p orbitals of the four N atoms [Cu(en),l2' is in direct interaction with the surface, both R. M. Chatterjee
-
-
-
TABLE I: d-d Transitions, g Values, Hyperfine Splitting Constants, and MO Coefficients for [Cu(en),12+on Zeolites and a Camp Berteau Montmorillonite *B1g +ZB2g cm-' Cu(en),Y hydrated
18200 18200 18200
12486 12486 18200
Agll 0.1917 0.1917 0.1917
Cu(en),Y dehydrated
17300 17300 17300
12009 12009 17300
0.1917 0.1917 0.1917
Cu(en),X hydrated
18200 18200 18200
13359 13359 18200
Cu(en),CB hydrated
20200 20200 20200 18200 18200 18200
Ag, 0.0327 0.0327 0.0327
All, cm-' A,, cm-I
01,
PI2
P2
X
Remarks
0.0194 0.0194 0.0194
0.0028 0.0028 0.0028
0.79 0.84 0.84
0.54-0.76 0.93 0.92
0.56 0.64 0.76
0.37 07 0.3615
KN Present calculation
0.0327 0.0327 0.0327
0.0194 0.0194 0.0194
0.0028 0.0028 0.0028
0.79 0.84 0.85
0.52-0.63 0.89 0.89
0.54 0.61 0.74
0.3716 0.3647
KN Pres en t calculation
0.1737 0.1737 0.1737
0.0317 0.0317 0.0317
0.0202 0.0202 0.0202
0.0038 0.0038 0.0038
0.79 0.81 0.82
0.52-0.69 0.90 0.90
0.54 0.66 0.77
0.3880 0.3822
KN Present calculation
12524 12524 20200
0.1787 0.1787 0.1787
0.0277 0.0277 0.0277
0.0204 0.0204 0.0204
0.0019 0.0019 0.0019
0.79 0.87 0.88
0.54-0.76 0.90 0.90
0.52 0.54 0.71
0.3490 0.3424
KN Present calculation
15088 15088 18200
0.1877 0.1877 0.1877
0.0387 0.0387 0.0387
0.0201 0.0201 0.0201
0.0029 0.0024 0.0029
0.81 0.85 0.85
0.61-0.73 0.90 0.89
0.63 0.74 0.82
0.3764 0.3723
KN Present calculation
0022-3654/78/2082-0497$01 .OO/O
0 1978 American Chemical Society
498
The Journal of Physical Chemistry, Val. 82, No. 4, 1978
in the +z and -z directions. In zeolites the most probable situation is that the complex adheres to the surface with one side only. The value of this coefficient, therefore, reflects the interaction of [Cu(en),l2' with the surfaces. The general trend emerging from the data of Table I is that these negatively charged surfaces increase the covalent character of the out-of-plane 7~ orbital, Le., the orbital directed toward the surface. The effect is small, indicating a very weak interaction of the surface orbitals with the Cu(I1) orbitals, probably due to long distances.
Communications to the Editor
30
Acknowledgment. R.A.S. is indebted to the N.F.W.O. (Belgium) for a grant as "Bevoegdverklaard Navorser". This work was sponsored by the Belgian Government (Staatssekretariaat van het Wetenschapsbeleid). References and Notes (1) P. Peigneur, J. H. Lunsford, W. De Wilde, and R. A. Schoonheydt, J . Phys. Chem., 81, 1179 (1977). (2) F Velghe, R. A. Schoonheydt, J. B. Uytterhoeven, P. Peigneur, and J. H. Lunsford, J. Phys. Chem., 81, 1187 (1977). (3) D. Kivelson and R. Neiman, J. Chem. Phys., 35, 149 (1961). (4) M. Moreno and M. T. Barriuso, An. Fis., 71, 205 (1975). (5) M. Moreno and M. T. Barriuso, SolUState Commun., 17, 1035 (1975). (6) H. H. Jaff6, J . Chem. Phys., 21, 258 (1953). (7) H. H. Jaff6 and G. 0. Doak, J. Chem. Phys., 21, 196 (1953). (8) A. A. Misetich and R. E. Watson, Phys. Rev., 143, 335 (1966). Katholieke Universiteit Leuven Centrum, voor Oppervlaktescheikunde en Colloidale Scheikunde De Croylaan 42, 6-3030Leuven (tieverlee), Belgium
Robert A. Schoonheydt
Received October 5. 1977
1
0
moles of salt
Figure 1. Plots of the change in temperature observed in the calorimeter vs. the moles of dianion salt in the glass bulbs. The slopes of the lines are 12.54 and 8.64 deg/mol for Li,COT and Na,COT, respectively. A similar plot for potassium metal has a slope of 12.25 deg/mol.' Both plots represent reactions of the solid material and liquid water.
Chart I H 2 C O T ~ ,t 2Li0Haq LizCOT,,ud t 2H, Ofiq COTfi, t H, H, COTE, 2Liosoud t 2HzOfiq 2LiOH,, t H,, -+
-+
Heats of Solvation of the Alkali Metal Salts of Cyclooctatetraene Anion Radical and Dianion in Tetrahydrofuran Publication costs assisted by the Petroleum Research Fund
Sir: In the gas phase doubly charged negative ions from hydrocarbon substrates are unknown, and only one uncontested report of a gas phase organic dianion has appeared.l The very low thermodynamic stability of organic dianions in the gas phase is due to the very strong electron-electron repulsion energy, which amounts to about 90 kcal/mol in the cyclooctatetraene (COT) dianionS2 Solvation, including ion association, can readily overcome this repulsion term and actually result in an exothermic disproportionation of COT-. in tetrahydrofuran (THF).3 Indeed, ion association and the other factors that go into the solvation of anions appear to be the controlling factors upon the thermodynamic stability and chemistry of organic anions and dianions in s o l ~ t i o n . Despite ~ this, an experimental determination of actual solvation energies of anion radicals or dianions has not been reported. Here we wish to show that the heat of solvation of the COT anion radical is more than an order of magnitude greater than the electron affinity of the neutral molecule and that just the variation in the heat of solvation of the dianion with counterion can be almost as great as the electron-electron repulsion energy. Evacuated glass bulbs containing the Li salt of the COT dianion (LizCOT,ofid)5 were crushed under 100 mL of water in a calorimeter using the conditions described previously.6 0022-3654/78/2082-0498$0 1.OO/O
2
-+
COTfi, t 2Lios,kd LizCOTso~d
-+
A H " , kcal/mol- -t37.3 i 1.7
- 25.6 - 106.2 -94.5
f
-
2
The heat of reaction (LiZCOTBolid + 2H201iq 2LiOH,, + c y c l o ~ c t a t r i e n ewas ~ ~ ~found ) ~ to be -37.3 f 1.8 kcal/mol (Figure 1).8 This enthalpy can be combined with the heat of hydrogenationg of COT and the heat of reaction of lithium with waterlo to yield the heat of reaction of Liowith COT to form LizCOT as shown in Chart I. The heat of hydrogenation of COT used in this calculation was actually measured in acetic acid, but the heat of solution of hydrocarbons in polar and nonpolar solvents is very small, and the difference in the heats of solution of HzCOT and COT is necessarily very small. Thus -25.6 kcal/mol is a very good estimation of the heat of hydrogenation of liquid COT. NMR analysis of the reaction products of the dry salt and DzO showed that no THF is incorporated into the crystal structure of Li2COT. The same result was obtained for the disodium and dipotassium saltsa6 In THF the dilithium salt of the COT dianion exists as a neutral ion aggregate (both lithium ions associated with the dianion) most probably with the lithium cations located above and below the T cloud of the dianion in a sandwich arrangement," thus AG"(so1n) = -RT In [ COT2-,2Li+THF].Utilizing the technique previously described for the sodium and potassium salts, the heat of solution of LizCOT from the crystal lattice was determined. Three determinations of the solubility of Li&OT in T H F were made at two different temperatures. At --19 "C the 0 1978 American Chemical Society
