1074
I. E. Maxwell and J. J. de Boer
(13) H. Diehl, H. Clark, and H. H. Willard. lnorg. Syn.. I , 186 (1939). (14) A. C. Rutenberg and H. Taube, J. Chem. Phys.. 20, 825 (1952). Prepared from CNNHd&D3N03.%H20 which was synthesized as described by F. Basolo and R . K. Murmann, lnorg. Syn., 4, 171 (1953). (15) S. M. Jorgenson, Z. Anorg. Chem., 2, 294 (1892). Prepared from CO(NH3)&03N03.%!420 which was syntheslzed as described by G. Schiessinger, lnorg. Syn., 6, 173 (1960). (16) J. 6. Work, horg. Syn., 2, 221 (1946). (17) I. L. Jenkins and C. 6. Monk, J. Chem. SOC., 68 (1951). (18) W. E. Cooley. C. Fan Llu, and J. C. Ballar, Jr., J. Am. Chem. Soc., 81, 4189 (1959). (19) F. Basolo and R. G. Pearson, "Mechanisms of Inorganic Reactions", Wiley. New York, N.Y., 1967. (20) A. Elder and S. Petruccl, horg. Chem., B, 19 (1970). (21) T. J. Swift and R. E. Connlck, J. Chem. Phys., 31, 307 (1962). (22) M. Alei, Jr., horg. Chem., 3, 44 (1964). (23) F. Klanberg. J. P. Hunt, and H. W. Dodgen, horg. Chem., 2, 139 (1963). (24) G. J. Templeman and A. L. Van Geet, J. Am. Chem. SOC.,94, 5578 ( 1972). (25) K. L. Craighead and R . G. Bryant, submined for publication. (26) M. 0.Burnett, J. Chem. SOC. A, 2480 (1970). (27) R. A. Robinson and R. H. Stokes, "Electrolyte Solutions", 2nd 4, Butterworths, London, 1959, p 243.
(28) G. H. Nancoilas, "interactions In Electrolyte Solutions", Elsevier, A m sterdam, 1968, pp 25, 74. (29) T. H. Martin and B. M. Fung, J. Phys. Chem., 77, 637 (1973). (30) S. F. Mason and B. J. Norman. J. Chem. SOC.A, 307 (1966). (31) A. Abragam, "The Principles of Nuclear Magnetism", Oxford Universtty Press. London. 196 1. Chaater 8. (32) H. G. Hertz, in "Water,a~omprehenslve Treatise", Vol. 3, Felix Franks, Ed., Plenum Press, New York, N.Y., 1973, Chapter 7. (33) H. G. Hertz, G. Keiler, and H. Versmold, Ber. Bunsenges. Phys. Chem., 73, 549 (1969). (34) B. Llndman, S. Forsen, and E. Forsllnd, J. Phys. Chem., 72, 2805 (1968). (35) B. Undman, H. Wennerstrom, and S. Forsen, J. Phys. Chem., 74, 754 (1970). (36) W. Wennerstrom, B. Llndman, and S. Forsen, J. Phys. Chem., 75, 2936 (1971). (37) H. 0.Hertz and M. Holz. J. Phys. Chem., 78, 1002 (1974). (38) H. G. Hertz, Ber. Bunsenges. Phys. Chem., 77, 531 (1973). (39) C. Deverell, Prog. Nucl. Msgn. Resonance Spectrosc., 4. 235 (1969). (40) K. A. Valiev, 2.Strukt. Chim., 3, 653(1962). (41) E. S. Goukl, "Mechanism and Structure In Organic Chemistry", Hok, RC nehart and Winston, New York, N.Y., 1959, p 580. (42) K. L. Cralghead and R. G. Bryant, submined for publication.
Crystal Structures of Hydrated and Dehydrated Divalent-Copper-Exchanged Faujasite 1.
E. Maxwell.
and J. J. de Boer
Koninkl~ke/Shell-L8boratorium,Amsterdam (Shell Research 8.V.), Holknd (Recelved October 29, 1974) Amsterdam Publicatbn costs asslsted by Konlnkll~e/SheN-Laborato~um,
The crystal structures of hydrated and dehydrated Cu2+-exchangedfaujasite have been determined by single-crystal X-ray diffraction techniques. The space group is Fd3m ( a = 24.713(5) A, hydrated; a = 24.643(5) A, dehydrated). Reflection data were collected with Cu K a (A 1.54182 A) radiation using two natural single crystals each with a maximum dimension of approximately 0.2 mm. A total of 218 and 212 unique observed reflections were obtained by counter methods, and the structures were refined by leastsquares techniques to final conventional R factors of 0.046 and 0.050, for hydrated and dehydrated forms,, respectively. In the hydrated form only the copper ions in site I' have been located with certainty. By contrast, in the dehydrated form copper ions are located at sites I, 1', II', 11, and 111. The site 111cations are very favorably sited for interaction with adsorbate molecules. In the dehydrated form, the relatively strong binding of the Cu2+ ions to the zeolite framework is shown to significantly lengthen the Si(A1)-0 bonds.
Introduction Over the past few years numerous studies have been made of transition-metal ion-exchanged zeolites. In particular, divalent copper-exchanged zeolite Y has been shown to exhibit catalytic activity in oxidation,*-* crackingPgand isomerization reactions.1° A prerequisite for characterizing the nature of the active species would be a detailed knowledge of the catalyst structure. This requires the determination not only of the siting of the copper cations in the zeolite but also of any modification of the zeolite framework resulting from the Cu2+exchange. Divalent copper-exchanged zeolite Y has been extensively studied by electron spin resonance spectroscopy."-lS These studies have shown that the Cu2+cations are distributed over different sites within the zeolite framework and that the populations of these sites are markedly dependent on the presence of adsorbed molecules, e.g., water, ammonia, and butene. However, they have not revealed the exact siting of the copper cations or any modifications of the The Journal of Physical Chemistry, Vol. 79, No. 17, 1975
framework structure. Such structural details can, in principle, be determined by X-ray diffraction analysis. Gallezot et aL19 performed powder X-ray diffraction studies of dehydrated partially Cu2+-exchanged zeolite Y, before and after adsorption of various molecules. However, powder diffraction techniques, inherently, yield less precise structural data than single-crystal techniques. In an attempt to obtain detailed structural information we have carried out single-crystal X-ray studies of Cu2+exchanged hydrated and dehydrated forms of natural faujasite.
Experimental Section Crystals of natural faujasite which have initially been exchanged with K+ were further exchanged with Cu2+ cations, by contacting them for 3 weeks with 1M solutions of copper sulfate or acetate. With both anions there was no detectable loss in crystallinity. The amount of material was insufficient to determine the SiIAl ratio or the degree of
Crystal Structures of DivaientGu-Exchanged Faujasite Cu2+ exchange by chemical analysis. However, the Si/Al ratio could be estimated from the unit cell constant of the original, hydrated K+-exchanged form. T o our knowledge ion-exchange isotherms have only been published for the Cu2+/Na+-X system.20 Nevertheless, these show that the selectivity is very much in favor of Cu2+ ions in the zeolite surface and that 100% exchange can be readily achieved. The Cu2+/Na+-Y ion-exchange system would not be expected to be markedly different, thus we would expect to have achieved close to 100% Cu2+ exchange of the faujasite crystals. Mortier and Bosmans21 carried out powder X-ray analyses of four hydrated K+-exchanged synthetic zeolites, types X and Y, with different Si/Al ratios. As shown in Figure 1, the relationship between the unit cell constants and the number of cations per unit cell is approximately linear. Using this graph and the measured cell constant for our sample of K+-exchanged natural faujasite ( a = 24.761(5) A), we find a unit cell formula of K5s(A102)56(Si02)13s. xH2O and thus a Si/Al ratio of 2.42. This is in good agreement with the Si/Al ratio for natural faujasite reported by Baur22 (Si/Al = 2.31). Data collection of the hydrated form was carried out by simply mounting a suitable single crystal on a glass fibre. For the dehydrated form a crystal was firmly wedged inside a thin-walled Lindeman glass capillary. The crystal was then heated a t 150' for 20 hr while Torr). Both the capillary was evacuated to P a (= crystals (each with maximum dimensions of approximately 0.2 x 0.1 x 0.1 mm) were aligned about [110] and then placed on a Nonius three-circle automatic diffractometer equipped with scintillation counter and pulse-height discriminator. Least-squares cell refinement based on 8, -8 (8 5 15') values measured for several reflections with Cu K a radiation ( A 1.54182 A) gave the following lattice parameters: hydrated, a = 24.713(5) A; dehydrated a = 24.643(5)
1075 CUBIC UNIT ELL
25.20
24'90
24.W
24.60
CONSTANT, a i IN
r
B)
i
HYDRATED K+- EXCHANGED NATURAL FAUJASITE
I '/
40
45
I
50
,
I ,I
55
I
€0
1
I
I
1
I
I
65 70 75 80 85 93 NUMBER OF CATIONS PER UNIT CELL
Flgure 1. Plot of cubic unit cell constant against number of cations per unit cell for hydrated K+-exchanged X and Y zeolites.
cles. Scattering factors for the ions Cu2+, 0-, Si2+,and A13+ were used throughout the refinement^.^^ In both structures, the agreement between observed and calculated structure factors was poor for the 111 reflection. This was also true for the 220 reflection of the hydrated form (vide infra). These reflections were therefore removed in the final stages of the refinements. The maximum peaks on final difference Fourier syntheses were approximately 0.1 e/Aa in both structures. Most of these were either diffuse or a t chemically unacceptable locations. There was no evidence of significant anisotropic thermal motion of framework atoms from difference syntheses. In view of this and of the rather limited amount of reflection data, anisotropic refinement was not attempted. Plots of ((F,- F , ) 2 ) , in ranges of sin O/A, at early stages in the refinement of both structures, revealed that the initial weighting scheme based on counting statistics was unsatisfactory. The estimated standard deviations were accordingly modified such that for 0 < sin O/A 5 0.2062 A - l , A. For both forms six equivalent data sets were collected, cr(F,) = 9.10, hydrated; and 5.63, dehydrated; for 0.2062 < using Ni-filtered Cu K a radiation (8 I 50'). The 8 - 28 sin 8/A I 0.2598 A-l, a ( F J = 5.46, hydrated; 4.10 dehyscan method was used with a scanning speed of O.G'/min drated; and for sin 8 l A > 0.2598 A-1, a(F,,) = 3.51 hydrated; (in 8) and a scan range of 0.7'. Backgrounds were measured and 4.10 dehydrated. for half of the scan time on each side of the reflection. ConThe final residuals were R1, 0.046 and 0.050, and R2, trol reflections monitored a t regular intervals showed no 0.042 and 0.049, for hydrated and dehydrated structures, significant variations in intensity, for both crystals, during respectively (where R1 = XllFd - IF,Il/ZIFd, R2 = [Xu(lFd data collection. Initial standard deviations in observed - (Fd)2/ZulFd2]1/2and w = u - ~ ( F , , )Final . values for the structure factors were calculated from counting statistics, error in an observation of unit weight were 0.96 (hydrated) but these were later found to be inadequate. Lorentz, poand 1.00 (dehydrated). The refined positional, occupancy, larization, and $-dependent absorption corrections ( ~ c ~ Kand~ temperature factors are given in Table I. Listings of = 5.2 mm-l) were applied, that latter by means of a semobserved and calculated structure factors (Tables I1 and iempirical method as described by Furnas.23 The $-depen111) are available elsewhere.26 dent absorption corrections were obtained by averaging the Discussion measurements from several reflections of the type hhO. The variation with 8 was found to be negligible and the 8-depenThe sitings of cations and water molecules in hydrated dent absorption correction was neglected. The data were and dehydrated divaleot-copper-exchanged faujasite, as then scaled and averaged to yield 218 and 212 unique redetermined from the X-ray analyses, are compared in flections with estimated conventional R factors of 0.03 and Table IV. Assignments have been made on the basis of the 0.04 for hydrated and dehydrated crystals, respectively. cation-H20 framework distances (see Table V). In some instances it was difficult to make a clear distinction between Structure Determination water molecules and cations (e.g., OW(2), OW(6), OW(7) Full matrix least-squares refinements were initially carhydrated form and OW dehydrated form). In these cases ried out on the basis of the framework parameters for natuthe observed electron density could be due either to copper ral f a ~ j a s i t eCopper . ~ ~ cations and water molecules were loions that are very weakly bound to the framework (and cated from a series of difference Fourier syntheses and intherefore presumably strongly bound to water) or to cluded in subsequent cycles of refinement. Parameters with strongly bound water molecules. high correlation coefficients, such as occupancy and temCopper cations are evidently rather mobile and mainly perature factors, were varied separately in alternating cybound to water molecules in the hydrated form. Only 6.S('L) The Journal of Physical Chemistry. Vol. 79, No. 17, 1975
1878
I. E. Maxwell and J. J. de Boer
TABLE I: Positional, Thermal, and Occupancy Parameters for Hydrated and Dehydrated Divalent-Copper-Exchanged Faujasite Atom
Occupancy factor
Positiona
X
(a) Hydrated 0.0362(1) 0 0.0033 (5) 0.0761(5) 0.0717(4) 0.071 (1) 0.082(1) 0.01 6(2) 1/8 0.1 73(3) 0.075(3) 0.031 (6) 0.006(6)
1.o 1.o 1.o 1.o 1 .o 0.196(7) 0.84 (4) 0.70(4) O.lO(1) 0.16(2) 0.16(2) 0.18(3) 0.12(2)
1.o 1.o 1.o 1.o 1.o 0.09 5(13) 0.355(7) 0.086(9) 0.025(5) 0.1 18(6) 0.04 8 (5) 0 -017 (3) 0.1 66(26)
Y
z
0.3037(1) -0.1062 (4) -0.1431 (3) -0.03 29(3) 0.3224(3) 0.071(1) 0.168(1) -0.266(2) 1/8 -0.197(3) -0.201 (3) 0.427 (4) 0.386 (4)
0.1247(1) 0.1062(4) 0.0033(5) 0.0761(5) 0.071 7(4) 0.071(1) 0.082(1) 0.016(2) 1/8
0.048(3) 0.109 (3) 0.031(6) 0.006(6)
B,
6‘
1.42(8) 2.9 (2) 2.7(2) 2.6(2) 2.2(2) 3.6(3) 3.5(4) 5.90) 0.1(9) 11.4(1.9) 10.1(2 -0) 10.8(2.3) 5.7(2.1)
(b) Dehydrated 0.0359(1)
0.3 038 (1) 0.125(1) 1.6 7 (8) -0.1062(5) 0.1 062(5) 3.6(2) 0.0030(6) -0.1432(4) 0.0030(6) 4.3 (2) -0.0317(4) 0.073 7 (5) 0.0737(5) 3.9(2) 0.0733(5) 0.3209 (4). 0.0733(5) 3.0(2) 0 0 0 8.2(2 .O) 0.0401(7) 0.0401 (7) 0.0401(7) 3.3(2) 0.073(5) 0.073 (5) 0.073(5) 8.9(1.6) 0.047(7) 0.203 (7) 0.047(7) O.O(l.8) 0.031(2) 0.219(2) 0.031(2) 1.1(4) 0.006(4) 0.244(4) 0.006(4) 0.6(1 .O) 0.017(3) 0.418(3) 3.2(1.7) 0.084(3) 0.01 3 (6) -0.263(6) 2.5(1.9) 0.013(6) Origin at center (3m). * Standard deviations in units of t,he least significant digits of the corresponding parameter are given in parentheses in all tables. 0
cations per unit cell could be located at site I’ inside the sodalite cage. (The site nomenclature is as follows: site I, center of hexagonal prism; site 11, six-membered ring face of sodalite cage on the supercage side; site I’ and 11’ lie on the other sides of the six-membered rings, opposite sites I and 11, respectively, inside the sodalite cage.) Moreover, these cations are only relatively weak1 bonded to the zeolite framework: Cu(1’)-0(3) = 2.58(3) (cf., rcuz+ rgz- = 2.09 A). Water molecules are located at site 11’ (OW(l)], the center of the sodalite cage [OW(3)], and inside the supercage [OW(4)-0W(7)]. In marked contrast to the hydrated form, in the dehydrated form almost all the copper ions (25.1 per unit cell (puc) vs. 28 puc for complete exchange) have been located. The cations are distributed over several different sites, although site I’, as in the hydrated form, is clearly favored with a total of 14.2 cations puc. Most of the cations at this site are strongly bound to the zeolite framework [Cu(I’A)O(3) = 2.12(1) A] and a smaller number of cations are less firmly bound [Cu(I‘B)-O(3) = 2.56(1) A] and are therefore presumably interacting with residual water (see Figure 2). A similar cation-framework coordination geometry exists a t the single six-membered ring which faces onto the supercage (site 11). Copper ions, Cu(I1’) and Cu(IIA), are strong1 bound to the zeolite framework [Cu(II’)-0(2) = 2.29(9) Cu(IIA)-0(2) = 2.22(1) A] and a smaller number of cations that are less strongly bound to the framework appear
A:
1;
The Journal of Physical Chemistry, Vd. 79, No. 17. 1975
+
Flgurr 2. Perspective view showing the coordination of Cu(l), CNI’A). and CNI’B) cations to the hexagonal prism In dehydrated divalentcopper-exchanged faujastte (see ref 30).
to be interacting with residual water in the supercage [Cu(IIB)-0(2) = 2.51(10) A, see Figure 31. More interestingly, copper cations, Cu(III), have been unequivocably located inside the supercage (sites other than site 11). The site has no crystallographic symmetry and the cation coordination to the framework oxygen atoms is most unusual (see Figure 4). These cations are located at the edges of the four-membered rings formed by the O(1) and O(4) oxygen atoms. The bonding of the copper ions to these oxygen atoms is very unsymmetrical, the
1077
Crystal Structures of Divalent-Cu-Exchanged Faujasite
TABLE IV: Comparison of Sitings of Cations and Water Molecules in Hydrated and Dehydrated Divalent-Copper-Exchanged Faujasite Hydrated Atom
Coordinates"
Inside dense cage structure
0.07 1(1)" 0. 125" 0.168(1)"
Dehydrated No. per unit cell
6.3(2) 3.2(3) 26.9(1.3)
Atom
Coordinates
Cu(I) Cu(1'A) Cu(1'B)
0"
0.0401(7)" 0.073 (5)"
11.4(2)
Cu(I1')
0.203(7)" 0.219(2)" 0.244(4)" 0.263 (6)"
0.8(2) 3.8(2) 1.5(2) 5.3(8)
Cu(IL4)
Inside o r on the periphery of supercage structure
Cu(I1B)
0.266(2)" 0.173(3) 4.197(3) 0.04 8(3)
22.4(1.3) 31(4)
1
0.075(3) 4.201(3) 0.109(3) 0.031 (6) 0.427(4) 0.03 l ( 6 ) 0.006(6) 0.386(4) 0.006(6)
Total Cu2' located Total H 2 0 located a Coordinates belong to set 32(e),x = y = z
TABLE V: Cation-Water Framework Distances
ow
1.5(2) 2.8(3)
0.017 (3) 0.4 18(3) 0.084(3)
Cu(II1)
(
No. per unit cell
12(2) 6.3
25.1
143.5
5.3
cv1n
I
(A) for Hydrated and Dehydrated Divalent-Copper-Exchanged Faujasite Atoms
Cu(I)-O(3) CU(I)-0(2) Cu(I'A)-0(3) Cu(I'A)-0(2) Cu(I'B)-0( 3) Cu(I'B)-0(2) CU(II')-0(2 Cu(II')-O(4)
Distance
Atoms
Distance
(a) Hydrated 2.58(3) OW(4)-O(1) 3.15(2) OW(4)-0(4) 2.3 1(5) OW(5)-O(1) 2.42(4) OW(5)-0(2) 3.06(4) OW(6)-0(4) 3.64(5) OW(6)-0(1) 3.08(6) OW(7)-0(4) 3.37( 6) OW (7 )-0(1
3.03(6) 3.14(7) 3.000) 3.47(7) 2.94(13) 3.38(10) 2.79(18) 3.50( 14)
(b) Dehydrated 2.68(2) Cu(IIA)-0(2) 3.53 (2) Cu(IIA)-0(4) 2.12(1) Cu(IIB)-0(2) 2.95(1) Cu(IIB)-0(4) 2.56(1) Cu(III)-O(l) 3.15(2) Cu(III)-0(4) 2.29(9) .OW-0(2) 3.05(10) OW-0(4)
2.220) 2.92(1) 2.51(10) 3.03(6) 2.16(7) 2.77(7) 2.99(9) 3.35(9)
interaction with 0(1), Cu(III)-O(l) = 2.16(7) A, being much stronger than with 0(4), Cu(III)-(4) = 2.77(7) A. The short Cu(III)-O(l) distance means that the assignment of this electron density to a copper cation is unequivocal since
Figure 3. Perspective view showing the coordination of Cu(li'), Cu(IIA), and Cu(llB) cations to the single six-membered ring in dehydrated divalent-copper-exchangedfaujasite (see ref 30).
such a close approach to framework oxygen ions is not possible for residual water molecules on unexchanged K+ ions. Noteworthy is the water molecule, OW(6), which in the hydrated form is also located in the vicinity of the Cu(1II) cation but more distant from the framework as ex ected (i.e., OW(6)-0(4), 2.94(13) A, OW(6)-O(l), 3.38(10) ). T o our knowledge there are no other published X-ray data on cations (other than site I1 type) that have been located inside the supercage and are bound to the framework. However, there has been considerable speculation as to the most probable siting of these so-called site I11 type cations. Conventionally most authorsz7 have supposed that site I11 type cations are located a t the center of the souare faces ..._ of the sodalite unit, which is in contrast to the iresent results. Further studies will be necessary to determine whether this observed site is specific to Cuz+ cations or whether it is also occupied by other divalent and monovalent cations. Olsonz4 has referred to unpublished X-ray
K
The Journal of Physical Chemisrry, Vol. 79, No. 17, 1975
1878
I. E. Maxwell and J. J. de Boer
;,it
I
LU
Figure 4. Perspective views of Cu2+ cations coordinated to the oxygen atoms at the edges of the four-membered rings in the supercages of dehydrated divalent-copper-exchanged faujasite (see ref 30).
data on dehydrated NaX, where Na+ ions were also located a t the edges of the square faces. This suggests that this site may be generally occupied irrespective of the type of cation (cf., sites I, 1', 11, and 11'). The lack of symmetry together with the low occupancy factors have clearly been responsible for the previous difficulties in locating site I11 type cations by X-ray analysis. As previously mentioned, the Cu(II1) cations are almost exclusively bonded to the bridging hexagonal prism oxygen atoms, O(1). These cations are therefore located a t a position in the supercage which is highly accessible to adsorbed molecules, namely, a t the entrances to the large cavities (see Figure 5 ) . Cations a t site 11, however, which are also accessible to adsorbed molecules, are partially shielded from adsorbent molecules by the six-membered ring oxygen atoms. Thus site I11 Cu2+ cations would appear to be the most favorably sited to interact with adsorbent molecules and are therefore likely to be the catalytically most active sites, Interestingly, this site is remarkably similar to the proposed siting or protons in hydrogen faujasite. From X-ray studies, Olson and Dempsey2R concluded on the basis of Si(A1) -0 bond distances that the most reactive protons in hydrogen faujasite were also attached to the bridging oxygens, O( l ) , of the hexagonal prism. As indicated in Table VI the Si(A1)-0 distances in the dehydrated form show a marked variation whereas those in the hydrated form remain equal (within 1 estimated standard deviation). This difference can be related to the interaction between framework oxygen atoms and the copper cations. In the hydrated form there are no strong cationframework interactions, the closest approach being that of Cu(I')-O(3) = 2.58(3) 8,. However, for the dehydrated form there are several rather strong interactions between various copper cations and oxygen atoms. In Figure 6 the Si(A1)-0 distances for the dehydrated form are plotted against the percentage of each type of oxygen atom in close contact with a copper cation (these values are less than 100%due to partial occupancy of sites by cations). Clearly, there is an approximately linear relationship between these two quantities. By extrapolation it can be seen that for 100% involvement of oxygen atoms in bonding with copper cations the Si(A1)-0 bond distance is lengthened to 1.69 A (cf., 1.63 8, for 0% divalent copper-oxygen bonding), indicating The Journal of Physics/ Chemistry, Vol. 79, No. 17, 1975
Flgure 5. Perspective view showing the siting of Cu2+ cations at the pore entrance to the supercage in dehydrated divalent-copper-exchanged faujasite (see ref 30).
TABLE VI: Framework Distances (A) and Bond Angles (degrees) for Hydrated a n d Dehydrated Divalent-Copper-Exchanged Faujsite Atoms
Hydrated
Dehydrated
1.644(6) 1.643(5) 1.647(4) 1,644(5) 1.645 138.5(1.0) 146.0(7) 141.8(6) 140.5(7) 141.7 2.702( 14) 2.714(13) 2.648( 5) 2.669(8) 2.667(6) 2.710(16) 2.685 110.6(7) 111.1(6) 107.3(6) 108.4(6) 108.4(6) 110.9(8) 109.5
1.628(7) 1.640(5 ) 1.661(5) 1.629(5) 1.640 138.3(1.2) 144.8(8) 137.9(7) 145.3(8) 141.6 2.696(16) 2.696( 17) 2.655(5) 2.649(9) 2.650(8) 2.717(18) 2.677 111.2(8) 110.1(8) 109.2(7) 106.7(7) 108.3(6) 111.3(9) 109.5
a decrease in bond order. Similar effects were reported by for dehydrated Ni2+ faujasite and dehydrated CaX and SrX zeolites.28 This decrease in Si(A1)-0 bond order in dehydrated divalent copper-exchanged faujasite might explain some of the results obtained in oxygen mobility studies of zeolite Y.29 These studies showed that the activation energy for oxygen exchange with the lattice decreased markedly on exchanging Na+ for Cu2+ cations (Nay, E e x c h = 45 kcal/ mol; Cu2+Y, E e x c h = 23 kcal/mol). Evidently, the oxygen bonding to the lattice is weakened in the presence of Cu2+ cations, as is seen from the X-ray results. Unfortunately, X-ray structural data on dehydrated NaY are not available
Crystal Structures of Divalent-Cu-Exchanged Faujasite
1879
PERCENTAGE OF EACH OXYGEN ATOM IN CLOSE CONTACT WITH A COPPER ION 100 -
and calculated structure factor amplitudes (Tables I1 and 111) will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper only or microfiche (105 X 148 mm, 24X reduction, negatives) containing all of the supplementary material for the papers in this issue may be obtained from the Journals Department, American Chemical Society, 1155 16th St., N.W., Washington, D.C. 20036. Remit check or money order for $4.00 for photocopy or $2.50 for microfiche, referring to code number JPC-751874.
-I 93-
80 8070 -
60 70[ 50 -
I
40 -
1
30-
References and Notes
I
1.62
A.63
1.64
1.65
166
lI
1.67 1.68 1.69 St iAL1-0 BONG DISTANCE,
1
Figure 6. Plot of Si(AI)-0 bond distance against the percentage of each oxygen atom in close contact with a copper ion in dehydrated
divalent-copper-exchangedfaujasite. for comparison. However, it would seem that exchangeable cations, particularly those with a high polarizing power, can have a pronounced influence on the chemical bonding within the zeolite framework itself. The present X-ray study cannot be directly compared with the powder diffraction studies of Gallezot et aLZ0since the copper-exchange levels and dehydration temperatures (150" present study, 500' Gallezot et aLZ0) are different. Nevertheless, the distributions of Cu2+ cations over sites I and I' are surprisingly similar (site I, 1.5(2) puc, 3.2; site 1', 11.4(2), 11.1(2); for the present study and that by Gallezot et a1.2O respectively). This would seem to emphasize the strong preference of Cu2+ cations for site 1'. By contrast, in dehydrated nickel(I1)-exchanged faujasite (and zeolite Y) Ni2+ cations are preferentially located inside the hexagonal prisms a t site I. This difference in site preference between two cations of such similar ionic radii ( r N i p + = 0.72, rcuz+ = 0.69 A) would appear to be related to preferred coordination geometries (octahedral coordination for site I and trigonal coordination for site 1') as determined by the different electronic properties of the cations.
Supplementary Material Available, Listings of observed
(1) I. Mochida, S. Hayata, A. Kato, and T Seiyama, J. Catal., 15, 314 (1969). (2) I. Mochida. S. Hayata, A. Kato, and T. Seiyama, J. Catab. 23, 31 (1971). (3) I. Mochida, T. Jitsumatsu, A. Kato, and T. Seiyama, Bull. Chem. SOC. Jpn., 44, 2595 (1971). (4) C. Naccache and Y. BenTaarit, J. Catal., 22, 171 (1971). (5) S. Roginskii, 0. V. Altshuler, 0. M. Vinogradova, V. A. Seleznev, and I. L. Tsitovskaya, Dokl. Akad. Nauk. SSSR,196, 872 (1970). ' (6) G. K. Boreskov, N. N. Bobrov, N. G. Maksimov, V. F. Anufrienko, K. G. lone, and N. A. Shestakova. Bok/. Akad. Nauk. SSSR, 201,887 (1971). (71 I. Mochida, S. Hayata, A. Kato, and 1.Seiyama, Bull. Chem. Soc. Jpn., 44, 2262 (1971). (8) 0. V. Altshuler, I. L. Tsitovskaya, 0. M. Vinogradova, and V. A. Seleznev, /zv. Akad. Nauk. SSSR, 2145 (1972). (9) K. Tsutsumi, S. Fuji, and H. Takahashi, J. Catab, 24, 146 (1972). (10) C. Dimltrov and H. F. Leach, J. Catal., 14, 336 (1969). (11) A. Nicula, D. Stamires, and J. Turkevich, J. Chem. Phys., 42, 3684 (1965). (12) J. T. Richardson, J. Catal., 9, 178 (1967). (13) H. B. Slot and J. L. Verbeek, J. Catal., 12, 216 (1968). (14) C. Naccache and Y. Ben Taarit, Chem. Phys. Lett., 11, 11 (1971). (15) J. Turkevich, Y. Ono, and J. Soria, J. Catal., 25, 44 (1972). (16) I. R. Leith and H. F. Leach, Proc. R. SOC.,Ser. A, 330, 247 (1972). (17) E. F. Vansant and J. H. Lunsford, J. Phys. Chem., 76, 2860 (1972). (18) C . Naccache, M. Che, and Y. Ben Taarit, Chem. Phys. Lett., 13, 109 (1972). (19) P. Gallezot, Y. Ben Taarit, and B. Imelik, J. Catal., 26, 295 (1972). (20) F. Wolf, D. Ceacareanu, and K. Pilchowski, 2. Phys. Chem. (Leipzig), 252, 50 (1973). (21) W. J. Mortler and H. J. Bosmans, J. Phys. Chem., 75, 3327 (1971). (22) W. H. Baur, Am. Mlneral, 49, 697 (1964). (23) T. C.Furnas, "Single Crystal Orienter Instruction Manual", General Electric Company, Milwaukee, Wisc., 1957. (24) D. H. Olson, J. Phys. Chem., 72, 4366 (1968). (25) "International Tables for X-ray Crystallography", Vol. Ill, Kynoch Press, Birmingham, England, 1969. (26) See paragraph at end of text regarding supplementary material. (27) J. V. Smith, Adv. Chem. Ser., No. 101, 171 (1971). (28) D. H. Olson and E. Dempsey, J. Catal., 13, 221 (1969). (29) G. V. Antoshin, Kh. M. Minachev, E. N. Sevastjanov, D. A. Kondratjev, and C. 2. Newy, Adv. Chem. Ser., No. 101, 514 (1971). (30) Because of partial occupancy of sites by Cu2+ ions and repulsive forces, simultaneous occupancy of Cu2+ ion sites shown in Figures 2-5 is not expected.
The Journal of Physical Chemistry, Vol. 79, No. 17, 1975
