Single Crystal Structure of Zeolite A (LTA) - American Chemical Society

J. Phys. Chem. C 2008, 112, 11181–11193

11181

Single Crystal Structure of Zeolite A (LTA) Containing Ag4Cl4 Nanoclusters and Reduced 1,3,5-Tripyrylium Dimers with Remarkably Short 2.43 Å Interplanar Spacings Seok Han Kim,† Thanh Nga Nguyen Thi,† Nam Ho Heo,*,† Ghyung Hwa Kim,‡ Suk Bong Hong,§ John D. Head,⊥ and Karl Seff*,⊥ Laboratory of Structural Chemistry, Department of Applied Chemistry, Kyungpook National UniVersity, Daegu 702-701, Korea, Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Korea, Department of Chemical Engineering and School of EnVironmental Science and Engineering, POSTECH, Pohang 790-784, Korea, Department of Chemistry, UniVersity of Hawaii, 2545 The Mall, Honolulu, Hawaii 96822-2275, U.S.A. ReceiVed: February 27, 2008; ReVised Manuscript ReceiVed: May 2, 2008

A single crystal of Ag12-A (zeolite LTA) was prepared by the dynamic ion-exchange of Na12-A with aqueous 0.05 M AgNO3. It was washed with CH3OH and allowed to react with a stream of 0.05 M KCl in CH3OH at 294 K. The crystal structure of the product |K2.35Ag1.1(Ag4Cl4)0.45(C3H3O3)1.1(K3Cl)3.45(K3(OH)2)0.55(H2O)g3.0|[Si12Al12O48]-LTA (a ) 12.292(1) Å) was determined by single-crystal X-ray diffraction in the cubic space group Pm3jm at 294 K. It was refined to the final error index, R1 ) 0.052, based on the 371 reflections for which Fo > 4σ(Fo). Ag4Cl4 nanoclusters were found in about 45% of the sodalite cavities. Each Ag4Cl4 cluster (interpenetrating tetrahedra; symmetry Td, Ag-Cl ) 3.105(17) Å) is held in place by the coordination of each of its four Ag+ ions to three oxygens of the zeolite framework (Ag-O ) 2.493(5) Å) and by the coordination of each of its four Cl- ions to a K+ ion through a 6-ring (Cl-K ) 2.70(3) Å). In each of the remaining 55% of the sodalite cavities, two reduced planar 1,3,5-tripyrylium cations, [(CH)3O3]22+ (C-O ) 1.52(3) Å), are found. These parallel eclipsed rings (symmetry D3d) have an interplanar distance of only 2.43 Å due to σ double bonding between the rings, the result of four electrons in 12-center bonding π* orbitals, and to polar attraction. Each ring makes three strong hydrogen bonds (CH · · · O ) 2.84(3) Å) to oxygens of the zeolite framework, and a Ag+ ion coordinates to the three oxygens of one ring (Ag-O ) 2.68(9) Å). The large cavities are filled with K+, Cl-, Ag+, OH-, and H2O; the K3Cl2+ unit predominates. The 1,3,5-tripyrylium ring, isoelectronic with benzene, had not been reported before. 1. Introduction Silver and silver halide clusters have been studied extensively because of their photosensitive properties.1–3 Because they have photostimulated luminescence properties,4–9 they may find application as photocatalysts for solar energy conversion and as media for optical information or image storage. Microsized silver clusters on silver halide grains may work as latent-image and reduction-sensitization centers; these play a dominant role in photographic processes. In addition, silver chloride supported on zeolite A evolves oxygen when irradiated with UV light in the presence of water.10,11 Photocatalysis, for example, photochemical water splitting, is one of the most important options for the photochemical conversion and storage of solar energy.10,11 Rosseti et al. showed that the particle size dependence of the excited-state electronic properties of silver halides is a consequence of electron and hole localization in small crystallites.12 Much work has been done to prepare silver halide nanoparticles with a high degree of monodispersity.13,14 Among the methods used are water-in-oil microemulsion technology and advanced liquid-phase systems using supercritical fluids.13 The formation of silver halide nanoparticles in supercritical fluids offers significant advantages over conventional liquid-phase systems, * To whom correspondence should be addressed. E-mail: [email protected]; [email protected]. † Kyungpook National University. ‡ Pohang Accelerator Laboratory, POSTECH. § Department of Chemical Engineering and School of Environmental Science and Engineering, POSTECH. ⊥ University of Hawaii.

including the rapid separation of solvent and the possibility of depositing the particles in situ in porous materials by use of the unique properties of the supercritical fluid phase.14 For the preparation of unique and nanosized clusters, various nanoporous materials, including zeolites, have been used as host materials.15,16 Zeolites are used as supports for various advanced materials in the chemical and materials industries. In recently decades, zeolites have been shown to be ideal hosts for the preparation of nanosized clusters with quantum-dot effects. Zeolites can very effectively stabilize unusual chemical species, and bulk materials can readily be dispersed within their periodic unique-sized pores and channels.15,16 To effectively utilize their electrical and chemical properties, various nanoclusters have been synthesized in these zeolites with uniformity in size and regularity in orientation.17–23 Compounds are commonly introduced into porous materials by impregnation methods using solutions of the corresponding substances or by ion-exchange followed by further treatment.24,25 In recent years, both silver and silver halide nanoparticles encapsulated within zeolite Y were shown to exhibit strong photostimulated luminescence (PSL).4 The luminescence efficiency in nanophase materials appears to be enhanced relative to bulk materials. In addition, the luminescence wavelength is tunable; it is a function of cluster size. Because light scattering is significantly reduced in nanoparticles as compared with that in micrometer-sized particles (the intensity of light scattering is inversely proportional to the size of the particles), nanophase materials may represent an efficient PSL phosphor for X-ray

10.1021/jp801717e CCC: $40.75  2008 American Chemical Society Published on Web 07/03/2008

11182 J. Phys. Chem. C, Vol. 112, No. 30, 2008

Kim et al. TABLE 1: Experimental Conditions and Crystallographic Data

Figure 1. Schematic drawing of the 1,3,5-tripyrylium cation, cycloC3H3O33+, with formal charges indicated. In sharp contrast, however, a DFT calculation (vide infra, Table 9) shows that the positive charge resides essentially entirely on the carbon and hydrogen atoms.

storage. A number of studies on PSL phenomenon with nanoparticles have recently been reported.26 Using optical absorption spectra, Kodaira et al. studied the electronic states and structures of AgI clusters prepared by the direct absorption of bulk AgI into zeolite Na-LTA.3 X-ray powder diffraction patterns showed significant and systematic changes, depending on the loading density of AgI which varied from 0.2 to 4.0 molecules per unit cell. They speculated that (AgI)n clusters, where n ) 2 to 4, formed in R cages with increasing loading density. Nanoscale silver iodide guests were introduced into zeolites Na-MFI and Na-Y(FAU) by Zhai et al. who studied their products using powder X-ray diffraction (XRD), diffusion thermal anlysis (DTA), X-ray photoelectron spectroscopy (XPS), and adsorption techniques (to check the locations of the silver iodide nanoparticles in the host-guest materials).27 They prepared these host-guest nanocomposite materials by a heat diffusion method and investigated their quantum confinement effect. The photochemical and photocatalytic properties of silver halides in zeolites have been discussed extensively because they are highly commercial photosensitive materials.1,2,6,28 Ozin et al. have studied the synthesis, structure, and spectroscopic properties of dispersed semiconductor-component (silver halide) clusters in various halosodalites, claiming that they show thermochromic, photochromic, and barochromic properties.1,6,29 Hirono et al. proposed an optical recording medium, consisting of a silver halide dispersed in a large-pore zeolite.28 They expected that the material would darken when exposed to light and that it would fade back to its original color (be erased) by heating. Ag4Br430 and Ag4I431 nanoclusters have been synthesized in the sodalite cavities of fully K+-exchanged zeolite LTA single crystals. These crystals were prepared by the dynamic ionexchange method, first with aqueous AgNO3 and then with KBr or KI solution in CH3OH at 294 K for two days. The crystal structures of these products were determined by single-crystal X-ray diffraction methods in the cubic space group Pm3jm at 294 K. These Ag4Br4 and Ag4I4 nanoclusters occupied 75% and 50% of the sodalite cavities, respectively. In this work, fully Ag+-exchanged zeolite LTA (Ag12-A) was treated with KCl in CH3OH in an attempt to synthesize nanoclusters of AgCl within the zeolite. The crystal structure of the resulting product was determined to verify that nanoclusters had formed, to learn their positions, size, and geometry, and to observe their interactions with the zeolite framework. The methods used, and some of the results, closely parallel those reported earlier for |K9(K4Br)(Ag4Br4)0.75(H2O)x|[Si12Al12O48]-LTA (K(Ag4Br4)-A)30 and |K9(K4I)(Ag4I4)0.5(H2O)x|[Si12Al12O48]-LTA (K(Ag4I4)-A).31 An unexpected consequence of this work was the synthesis of reduced dimers of 1,3,5-tripyrylium (cyclo-2,4,6-tridehydro1,3,5-trioxanium, C3H3O33+) cations (see Figure 1). These have a 6-membered aromatic ring system new to chemistry. In

crystal (a cube) edge length (mm) Ag+ ion exchange T (K), t (day), V (mL) reaction with KCl T (K), t (day), V (mL) data collection T (K) X-ray source wavelength (Å) space group, No. unit cell constant, a (Å) maximum 2θ for data collection (deg) no. of unique reflections measured, m no. of reflections (Fo > 4σ(Fo)) no. of variables, s data/parameter ratio, m/s weighting parameters: a/b final error indices R1b R2c goodness of fitd

0.08 294, 2, 9 294, 2, 9 294(1) PLS(4A MXW BL)a 0.8265 Pm3jm, 221 12.292(1) 61.93 405 371 63 6.43 0.0968/4.8143 0.0522 0.1473 1.09

a Beamline 4A MXW of The Pohang Light Source. b R1 ) Σ|Fo - |Fc||/ΣFo; R1 is calculated using only the reflections for which Fo > 4σ(Fo). c R2 ) [Σw(Fo2 - Fc2)2/Σw(Fo2)2]1/2 is calculated using all unique reflections measured. d Goodness-of-fit ) (Σw(Fo2 - Fc2)2/(m - s))1/2.

addition, these dimers have the shortest interplanar spacing ever reported for an aromatic system. 2. Experimental Section 2.1. Crystal Preparation. Large colorless single crystals of zeolite 4A (|Na12(H2O)x|[Si12Al12O48]-LTA, Na12-A · xH2O, Na12-A, or Na-A) were synthesized by Kokotailo and Charnell.32 One crystal of hydrated Ag12-A (|Ag12(H2O)x|[Si12Al12O48]-LTA, Ag12-A · xH2O, or Ag-A) was prepared by the dynamic (flow) ion-exchange of Na-A with aqueous 0.05 M AgNO3 (99.998%, Aldrich) at 294 K.33,34 The resulting Ag-A crystal was thoroughly washed with CH3OH (99.9+%, Merck) and was then placed in a flowing stream of 0.05 M KCl (99.9%, Aldrich) in CH3OH (99.9+%, Merck) at 294 K for 2 days. No attempt was made to dry the CH3OH beforehand.35,36 At the end, no attempt was made to remove the solvent from the crystal, neither by evacuation nor by heating. The crystal was then isolated in its capillary by sealing both ends with a small torch. The crystal after ion-exchange with Ag+ was pale reddish brown. After reaction with KCl, it became dark reddish brown. 2.2. Crystallography. X-ray diffraction data for the resulting crystal were collected at 294(1) K on an ADSC Quantum210 detector at Beamline 4A MXW of The Pohang Light Source. The basic data file was generated by the program HKL2000 including the indexing program DENZO with the cubic space group P23. The cubic space group Pm3jm (no systematic absences) was used in this work because reasons discussed previously37,38 were found to apply. A summary of the experimental and crystallographic data are presented in Table 1. 2.3. 13C NMR. A powder sample for 13C MAS NMR experiments was prepared by using methods as similar as feasible to those used for the single crystal. Zeolite 4A powder (|Na12(H2O)x|[Si12Al12O48]-LTA, Aldrich, 2 g) was added to 80 mL of aqueous 0.05 M AgNO3 (99+%, Aldrich). The solution was stirred at 294 K for 3 h, and the resulting powder was washed with CH3OH (99.9+%, Merck) for 1 h. This process, ion-exchange and washing, was repeated nine times. The resulting fully Ag+-exchanged zeolite A powder (Ag-A) was placed in 80 mL of 0.05 M KCl (99.5%, Junsei) in CH3OH

Single Crystal Structure of Zeolite A (LTA)

Figure 2.

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J. Phys. Chem. C, Vol. 112, No. 30, 2008 11183

C NMR spectra of (a) K(Ag4Cl4)(C3H3O3)-LTA and (b) a reference sample with molar ratio 1,3,5-trioxane/methanol/D2O ) 1:1:40.

TABLE 2: Steps of Structure Determination as Nonframework Atomic Positions Are Found step/ atom K(1) K(2) K(3) K(4) K(5) K(6) 1b 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18c 19c,d 20c,d,e,f 21c,d,e,g 22c,d,e,g

3.4(7) 3.0(3) 3.1(3) 3.1(2) 2.2(2) 2.6(2) 3.1(2) 2.1(3) 3.5(2) 3.3(2) 3.3(2) 2.6(5) 2.1(2) 2.1(3) 2.0(2) 2.2(2) 1.80 1.80 1.80 1.80

6.3(6) 4.8(8) 5.5(3) 5.0(3) 3.8(2) 2.9(2) 2.9(2) 3.0(2) 3.4(3) 1.1(3) 1.3(3) 1.4(3) 1.7(5) 3.3(3) 2.7(4) 2.9(3) 2.8(2) 3.30 3.30 3.30 3.30

1.0(3) 1.8(4) 2.2(4) 2.2(3) 1.80 1.80 1.80 1.80

0.8(1) 0.8(1) 0.7(1) 0.55 0.55 0.55 0.55

3.6(3) 6.7(7) 4.5(4) 2.7(3) 2.4(2) 3.9(4) 3.3(6) 1.3(3) 1.7(3) 1.5(4) 0.8(5) 0.7(4) 1.35 1.35 1.35 1.35

1.5(4) 2.0(4) 1.9(7) 2.4(4) 1.9(3) 1.65 1.65 1.65 1.65

occupancies per unit cell K(7) Ag(1) Ag(2) Ag(3) Cl(1) Cl(2) Cl(3) O(4)

5.5(10) 6.8(9) 2.4(7) 2.5(7) 3.2(5) 2.7(4) 3.1(8) 5.6(1) 4.3(6) 3.90 3.90 3.90 3.90

2.2(1) 1.8(2) 1.4(1) 1.5(1) 1.4(1) 1.3(1) 1.5(1) 0.9(1) 0.9(1) 0.9(1) 1.0(1) 1.4(2) 1.4(2) 1.4(1) 1.6(1) 1.80 1.80 1.80 1.80

1.1(2) 0.9(1) 0.8(1) 0.7(1) 0.8(1) 0.5(1) 0.3(1) 0.4(1) 0.4(1) 0.4(1) 0.4(1) 0.4(1) 0.5(1) 0.5(1) 0.55 0.55 0.55 1.10

0.7(1) 0.7(1) 0.5(1) 0.7(1) 0.5(1) 0.9(1) 0.8(1) 0.8(1) 0.8(1) 0.6(1) 0.8(1) 0.7(1) 0.7(1) 0.55 0.55 0.55 0.55

4.7(4) 1.8(5) 4.7(3) 4.3(3) 4.4(3) 4.1(4) 1.8(9) 2.7(7) 2.4(6) 1.9(4) 1.80 1.80 1.80 1.80

4.4(3) 5.2(4) 3.1(4) 3.0(5) 5.9(8) 6.0(7) 4.0(5) 3.0(4) 4.7(5) 3.6(6) 4.1(3) 3.45 1.65 1.65 1.65

7.2(7) 5.3(7) 5.0(6) 6.1(6) 6.4(8) 4.2(6) 3.5(5) 4.0(4) 3.30 1.80 3.30 1.80 1.65 1.80 3.30

O(5)

0.8(7) 2.2(6) 0.9(4) 3.3(15) 3.1(13) 3.9(9) 3.00 3.00 3.00 3.00

O(6) C(1)

0.7(3) 1.0(3) 1.10 1.10 1.10 1.10

4.2(7) 4.4(8) 3.8(8) 4.7(8) 4.7(6) 4.2(5) 4.1(4) 3.30 3.30 1.65 3.30

error indicesa R1 R2 0.54 0.49 0.47 0.21 0.19 0.15 0.14 0.108 0.106 0.104 0.098 0.088 0.087 0.082 0.080 0.070 0.067 0.047 0.053 0.052 0.060 0.072

0.85 0.84 0.83 0.56 0.52 0.45 0.41 0.375 0.367 0.366 0.325 0.298 0.292 0.271 0.273 0.203 0.192 0.131 0.150 0.147 0.168 0.198

a Defined in footnotes to Table 1. b Only the atoms of the zeolite framework were present in the initial structure model. They were refined isotropically. c Framework atoms were allowed to refine anisotropically. d Fixed occupancies are used for all atoms. e Refinement including Cl(3). It is separated from Cl(2) opposite 4-rings. f The final result of this work. g Trial refinements (see section 3, paragraph 3).

(99.9+%, Merck) and stirred at 294 K for 3 h. This process was repeated three times with fresh KCl/CH3OH solution. The resulting powder was dried at room temperature and examined by solid-state NMR. Finally, the 13C MAS NMR spectrum (see Figure 2) was recorded on a Bruker DSX 400 spectrometer with a reference sample of 1,3,5-trioxane (99+%, Aldrich), methanol (99.9+%, Merck), and D2O (99.9%, Aldrich) in the molar ratio 1:1:40. 1,3,5-Trioxane was used because it is a related stable model compound; 1,3,5-tripyrylium itself is not available. 2.4. DFT Calculations. Density functional theory calculations using the B3LYP functional39 and a 6-31G(d) basis set40,41 were performed with the PC-GAMESS42,43 computer program to help rationalize the proposed 1,3,5-tripyrylium structure found in the sodalite cavities (described in section 4.4). Local geometry optimizations were performed on various monomer and dimer candidate structures without the presence of the zeolite surroundings. To partly simulate the influence of the zeolite cavity, all dimer structures considered were constrained to have the point group symmetry observed crystallographically, D3d. D3d (3jm) is a subgroup of Oh (m3jm), the symmetry of the zeolite

framework at the center of the sodalite cavity when Si/Al ordering is overlooked. 3. Structure Determination Full-matrix least-squares refinement using SHELXL9744 was done on Fo2 using all measured reflections. Refinement was initiated with the atomic parameters of the framework atoms [(Si,Al), O(1), O(2), and O(3)] in fully dehydrated K12-A.45 The initial refinement used isotropic thermal parameters for all four positions and converged to the high error indices (defined in footnotes to Table 1) R1 ) 0.54 and R2 ) 0.85. The progress of structure determination, as subsequent peaks were found on difference Fourier functions and identified as nonframework atoms, is given in Table 2. The isotropic refinement of all 16 nonframework positions, with anisotropic refinement of the framework atoms, led to convergence with R1 ) 0.047 and R2 ) 0.131 (step 18 in Table 2). When the occupancies were fixed at the values given in step 19 of Table 2, refinement converged with R1 ) 0.053 and R2 )


Kim et al.

TABLE 3: Positional, Thermal, and Occupancy Parametersa Atoms

Wyckoff position

x

y

z

U11or Uiso

U22

U33

U23

U13

U12

(Si,Al) O(1) O(2) O(3) K(1) K(2) K(3) K(4) K(5) K(6) K(7) Ag(1) Ag(2) Ag(3) Cl(1) Cl(2) Cl(3) O(4) O(5) O(6) C(1)

24(k) 12(h) 12(i) 24(m) 8(g) 8(g) 8(g) 1(b) 24(l) 48(n) 24(l) 8(g) 8(g) 8(g) 8(g) 24(l) 24(m) 24(m) 24(m) 6(f) 6(e)

0 0 0 1118(2) 2374(10) 2644(4) 3094(34) 5000d 940(46) 369(25) 2053(29) 1389(4) 1691(9) 2107(10) 1105(14) 2425(31) 2693(43) 246(68) 1098(37) 2465(165) 0

1829(1) 2171(5) 2971(3) 1118(2) 2374(10) 2644(4) 3094(34) 5000d 4112(42) 4370(24) 3514(28) 1389(4) 1691(9) 2107(10) 1105(14) 2822(27) 2693(43) 986(24) 4403(26) 5000d 0

3698(1) 5000d 2971(3) 3381(4) 2374(10) 2644(4) 3094(34) 5000d 5000d 4792(33) 5000d 1389(4) 1691(9) 2107(10) 1105(14) 5000d 4636(56) 986(24) 4403(26) 5000d 1692(30)

60(8) 691(40) 387(28) 349(14) 167(18) 384(17) 3372(313) 3537(448) 1007(132) 825(131) 2075(121) 294(9) 175(19) 186(26) 707(57) 658(91) 1509(266) 1331(252) 607(99) 2805(923) 821(97)

45(8) 388(31) 232(16) 349(14)

15(8) 221(27) 232(16) 542(26)

16(4) 0 67(19) 107(14)

0 0 0 107(14)

0 0 0 95(16)

Occupancyb fixed varied 24c 12 12 24 1.80 3.30 1.80 0.55 1.35 1.65 3.90 1.80 0.55 0.55 1.80 1.65 1.80 3.30 3.00 1.10 3.30

2.2(2) 2.8(2) 2.2(2) 0.7(1) 0.7(4) 1.9(3) 4.3(6) 1.6(1) 0.5(1) 0.7(1) 1.9(4) 4.1(3) f 4.0(4) 3.9(9) 1.0(3) 4.1(4)

a Positional parameters X 104 and thermal parameters X 104 are given. Numbers in parentheses are the estimated standard deviations in the units of the least significant figure given for the corresponding parameter. The anisotropic temperature factor is exp[-2π2a-2(U11h2 + U22k2 + U33l2 + 2U12hk + 2U13hl + 2U23kl)]. b Occupancy factors are given as the number of atoms or ions per unit cell. c Occupancy for (Si) ) 12, occupancy for (Al) ) 12. d Exactly 0.5 by symmetry. f This occupancy is assigned to the Cl(2) and Cl(3) positions.

0.150. These values were chosen for a variety of reasons. First of all, the occupancy at Ag(1) was particularly reliable because Ag is a strong scatterer. It was equal to that at Cl(1), and the Ag4Cl4 cluster in a fraction of the sodalite cavities, as had been found for Ag4Br430 and Ag4I4,31 could be foreseen. Similarly, the occupancies at C and O were equal. Because they are poorer scatterers, their occupancies were reduced somewhat to the maximum number that would fit. Other occupancies were chosen to complete the environment about Ag4Cl4 and to avoid overfilling positions. The final cycles of refinement included Cl(3) (0.269, 0.269, 0.465, separated from Cl(2) opposite a 4-ring) with occupancies fixed as shown in step 20 of Table 2 and in Table 3. This was done because it was clear that this position participated in two distinctly different chemical situations (see sections 4.7.1 and 4.7.2) and was therefore an averaged position. It converged with R1 ) 0.052 and R2 ) 0.147. Because it seemed odd that the two 1,3,5-tripyrylium rings in unit cell 2 (Table 2, step 20) would associate only on one side with an Ag+ ion at Ag(2), two variants of this structure were examined. One of the structures had one 1,3,5-tripyrylium ring and one Ag+ ion at Ag(2) in unit cell 2 (Table 2, step 21); the other had two 1,3,5-tripyrylium rings and two Ag+ ions at Ag(2) (Table 2, step 22). For both, the resulting R values were sharply elevated (Table 2). This indicates that the final leastsquares result, with one Ag+ ion at Ag(2) and two 1,3,5tripyrylium rings in unit cell 2 (Table 2, step 20), is correct. All shifts in the final cycles of refinement were less than 0.1% of their corresponding estimated standard deviations. The final structural parameters are given in Table 3. Selected interatomic distances and angles are given in Table 4. Fixed weights were used initially; the final weights were assigned using the formula w ) 1/[σ2(Fo2) + (aP)2 + bP] where P ) [Max(Fo2,0) + 2Fc2]/3, with a and b as refined parameters (see Table 1). Atomic scattering factors for Ag+, Cl-, K+, O-, and (Si,Al)1.75+ were used.46,47 The function describing (Si,Al)1.75+ is the mean of the Si4+, Si0, Al3+, and Al0 functions. All scattering factors were modified to account for anomalous dispersion.48,49

4. Results and Discussion 4.1. Zeolite A Framework. The flex of (distortions to) the framework structure of a zeolite can best be seen by examining the T-O-T angles at the framework oxygens. |K2.35Ag1.1(Ag4Cl4)0.45(C3H3O3)1.1(K3Cl)3.45(K3(OH)2)0.55(H2O)g3.0|[Si12Al12O48]-LTA (K(Ag4Cl4)(C3H3O3)-A) is much more like hydrated K12-A45 than dehydrated K12-A45 (see Table 5). This is reasonable because K(Ag4Cl4)(C3H3O3)-A is fully solvated. However these solvated Ag4X4 complexes of LTA differ even more from dehydrated K12-A than does hydrated K12-A. This suggests that the zeolite framework is unusually relaxed. 4.2. K+ and Ag+ Ions. Per unit cell, 14.35 K+ and 2.9 Ag+ ions are distributed over five crystallographically distinct positions: 6.9 K+ and 0.55 Ag+ ions lie on 3-fold axes opposite 6-rings in the large cavity; 2.35 Ag+ ions lie on 3-fold axes opposite 6-rings in the sodalite cavity; 3.0 K+ ions are near 8-ring planes; 3.9 K+ ions lie opposite 4-rings in the large cavity; and 0.55 K+ ions are found at the very center of the large cavity. At K(1), K(2), and K(3), 1.8, 3.3, and 1.8 K+ ions, respectively, are found on 3-fold axes opposite 6-rings in the large cavity (see Figures 3 and 4); each of these approaches three O(3) framework oxygens at 2.509(10), 2.803(7), and 3.45(5) Å, respectively (see Table 4). The K(2)-O(3) distance, 2.803(7) Å, is somewhat longer than the sum of the conventional ionic radii of K+ and O2-, 2.65 Å ) 1.33 + 1.32 Å.50 The K(3)-O(3) approach distance, 3.45(5) Å, is longer still, while K(1)-O(3), 2.509(10) Å, is somewhat shorter. Correspondingly, the K(1), K(2), and K(3) ions extend 1.07, 1.64, and 2.60 Å, respectively, into the large cavity from the (111) planes of the O(3) oxygens (see Table 6 and Figures 3 and 4). Accordingly, they make very different O(3)-K(n)-O(3) angles: 103.2(5)°, 89.1(2)°, and 69.4(12)°, respectively. This broad range of bond lengths, displacements from 6-ring planes, and O(3)-K(n)-O(3) angles can be attributed to repulsions of K+ by cations and to attractions by anions. For example, the Ag+ ions, Ag(1), of a Ag4Cl4 cluster in the sodalite unit (see section 4.3) lie opposite the K+ ions at K(3) in the



TABLE 4: Selected Interatomic Distances (Angstroms) and Angles (Degrees)a distances (Si,Al)-O(1) 1.655(2) (Si,Al)-O(2) 1.664(2) (Si,Al)-O(3) 1.675(2) K(1)-O(3) K(2)-O(3) K(3)-O(3) Ag(1)-O(3) Ag(2)-O(3) Ag(3)-O(3) K(5)-O(1) K(6)-O(1) K(6)-O(2) K(7)-O(1)

2.509(10) 2.803(7) 3.45(5) 2.493(5) 2.304(5) 2.325(6) 2.65(5) 2.75(3) 2.86(4) 3.02(4)

angles O(1)-(Si,Al)-O(2) O(1)-(Si,Al)-O(3) O(2)-(Si,Al)-O(3) O(3)-(Si,Al)-O(3)

107.8(3) 111.0(2) 108.4(2) 110.3(3)

(Si,Al)-O(1)-(Si,Al) 150.5(4) (Si,Al)-O(2)-(Si,Al) 155.0(4) (Si,Al)-O(3)-(Si,Al) 143.3(3) O(3)-K(1)-O(3) O(3)-K(2)-O(3) O(3)-K(3)-O(3)

O(3)-Ag(1)-O(3) O(3)-Ag(2)-O(3) Ag(1)-Cl(1) 3.105(17) O(3)-Ag(3)-O(3) K(1)-Cl(1) 2.70(3) Ag(2)-O(4) 2.68(9) Ag(1)-Cl(1)-Ag(1) C(1)-O(4) 1.52(3) Cl(1)-Ag(1)-Cl(1) C(1)-O(4)-C(1) K(2)-Cl(2) 2.916(7) O(4)-C(1)-O(4) K(7)-Cl(2) 3.27(4) K(1)-Cl(3) 2.83(7) K(2)-Cl(2)-K(2) K(3)-Cl(3) 2.88(8) K(2)-Cl(2)-K(7) K(7)-Cl(3) 3.25(4) Cl(2)-K(7)-O(5) K(7)-O(5) 2.91(5) K(1)-Cl(3)-K(3) O(5)-O(2) 2.83(5) K(1)-Cl(3)-K(7) O(5)-O(1) 3.14(3) K(3)-Cl(3)-K(7) K(6)-O(6) 2.70(20) Cl(3)-K(7)-O(5) O(6)-K(4) 3.12(20) K(6)-O(6)-K(4) Ag(1) · · · K(3) 3.63(7) O(6)-K(4)-O(6) K(2) · · · K(7) 3.171(15) K(3) · · · K(7) 2.72(3) Cl(1) · · · Cl(1) 3.84(4) Cl(1) · · · O(2) 3.517(16) Cl(1) · · · O(3) 2.798(18) Cl(2) · · · O(1) 3.09(4) Cl(3) · · · O(3) 3.14(8) Cl(3) · · · O(1) 3.40(6) C(1) · · · O(3) 2.84(3) C(1) · · · O(4) 2.47(7) O(4) · · · O(3) 3.14(4) O(4) · · · O(2) 3.46(4)

103.2(5) 89.1(3) 69.4(12) 104.2(2) 117.2(3) 115.5(4) 102.1(5) 76.4(7) 150(5) 90(6) 166.3(14) 61.3(7)/128.9(10) 76.8(8) 177(4) 70.8(12) 107.7(19) 60.3(12) 162.4(15) 180.0(1)

a The numbers in parentheses are the estimated standard deviations in the units of the least significant digit given for the corresponding parameter.

TABLE 5: (Si,Al)-O-(Si,Al) Angles (Degrees)a at Framework Oxygens and Unit Cell Parameters for K+-Exchanged Zeolite A K+-exchanged zeolite A

O(1)

O(2)

O(3)

a, Å

dehydrated K12-Ab hydrated K12-Ab K(Ag4Cl4)(C3H3O3)-Ac K(Ag4Br4)-Ad K(Ag4I4)-Ae

128.5(6) 145.2(9) 150.5(4) 153(3) 148.5(9)

178.4(5) 159.3(6) 155.0(4) 152.7(23) 155.7(8)

153.7(5) 146.0(9) 143.3(3) 145.5(16) 143.7(6)

12.309(2) 12.301(2) 12.292(1) 12.186(1) 12.290(1)

a The numbers in parentheses are the estimated standard deviations in the units of the least significant digit given for the corresponding parameter. b Reference 45. c This work. d Reference 30. e Reference 31.

large cavity, so intercationic repulsions push the K(3) ions further into the large cavity and away from their three nearest O(3) oxygens (see Table 4). Simultaneously, the Cl- anions, Cl(1), of a Ag4Cl4 cluster lie opposite K+ ions at K(1) which are therefore pulled closer to their nearest O(3) oxygens. Thus,

the occupancies at K(1) and K(3) are the same as those at Ag(1) and Cl(1), all 1.80. Each ion at K(3) is much closer to a Clanion at Cl(3) in the large cavity (K(3)-Cl(3) ) 2.88(8) Å) than it is to any of its three nearest O(3) oxygens, 3.45(5) Å. The ions at Cl(3) also have simultaneous interactions with K+ ions at K(1) (Cl(3)-K(1) ) 2.83(7) Å) and K(7) (Cl(3)-K(7) ) 3.25(4) Å) (discussed further in section 4.7).) The K(2)-O(3) distance, 2.803(7) Å, is somewhat longer than the sum of the radii, 2.65 Å, because each K(2) (in the large cavity) coordinates to a Cl- ion at Cl(2) opposite a 4-ring in the large cavity (K(2)-Cl(2) ) 2.916(7) Å). The remaining 6-rings are occupied by Ag+ ions at two crystallographically distinct 3-fold-axis positions, Ag(2) at (0.1691, 0.1691, 0.1691) within the sodalite cavity 0.39 Å from the (111) plane at O3, and Ag(3) at (0.2107, 0.2107, 0.2107) in the large cavity 0.50 Å from that plane (see Figure 3 and Table 4). The Ag+ occupancies at these positions are both 0.55. These Ag+ ions are each 2.304(5) Å and 2.325(6) Å, respectively, from three O(3) framework oxygens. Both distances are substantially shorter than the sum of the conventional ionic radii of Ag+ and O2-, 1.26 + 1.32 ) 2.58 Å;50 this is commonly found for Ag+ ions in general and within zeolites.51 About the 8-rings, K+ ions occupy two positions, K(5) and K(6), with occupancies of 1.35 and 1.65 per unit cell, respectively. These positions are similar to those found in hydrated and dehydrated K-A,45 K(Ag4Br4)-A,30 and K(Ag4I4)-A.31 K(5) and K(6) each approach an 8-ring O(1) oxygen at 2.65(5) and 2.75(3) Å, respectively; both distances are near the sum of the corresponding conventional ionic radii, 2.65 Å. An additional 3.9 K+ ions per unit cell at K(7) bond to 4-ring oxygens in the large cavity. Each approaches an O(1) oxygen at 3.02(4) Å (see Figures 3 and 4). This distance is long but it can be justified as an averaged position because the ions at K(7) participate in two different clusters (see section 4.7). The K(7) position is similar to those found in K(Ag4Br4)-A30 and K(Ag4I4)-A,31 but it was not found in hydrated nor in dehydrated K-A.45 Finally, 0.55 K+ ions per unit cell were found at K(4), an extraordinary position at the center of the large cavity (see Figure 4). Each of these K+ ions is 3.12(20) Å from two O(6) oxygens, each of which bridges to a K+ ion at K(6) (K(6)-O(6) ) 2.70(20) Å). Neither of these distances differs significantly from the sum of the corresponding ionic radii, 2.65 Å.50 The high positional esds and U values indicate that K(4) and O(6), both far from the zeolite framework, are loosely held at their positions. The O(6)-K(4)-O(6) angle is linear by symmetry. For charge balance, O(6) appears to be the oxygen of a hydroxide ion (see Table 7 and paragraph 2 of section 4.7.2). Because the total charge of the guest cations and cationic molecules (see section 4.4.3) sums to 18.35+ per unit cell (see Table 7), more than the 12+ needed to balance the charge of the anionic zeolite framework, some anions must be present (see sections 4.3 and 4.7). The fractional occupancies at all of the K+ and Ag+ positions can be seen to be multiples of 0.45 and 0.55 (see Table 3), indicating that two kinds of unit cells with that relative population are present in this crystal (see Table 7). 4.3. Ag4Cl4 Nanoclusters in Sodalite Units (Unit Cell 1, UC1). In the sodalite unit, 1.8 Ag+ ions and 1.8 Cl- ions per unit cell occupy nonequivalent 3-fold-axis positions. The Ag(1) ions lie opposite 6-rings in the sodalite unit and the Cl(1) ions occupy similar positions, recessed more deeply into the sodalite


Kim et al.

Figure 3. Stereoview of the large cavity of unit cell 2 in K(Ag4Cl4)(C3H3O3)-LTA. Three K+ ions bond to each chloride ion. A nearly linear K+-OH--K+-OH--K+ sequence extends from top to bottom. The zeolite A framework is drawn with fine bonds between oxygens and tetrahedrally coordinated (Si,Al) atoms. Ellipsoids of 20% probability are shown.

Figure 4. Stereoview of the large cavity of unit cell 1 in K(Ag4Cl4)(C3H3O3)-LTA. Three K+ ions bond to each chloride ion. See the caption to Figure 3 for other details.

TABLE 6: Deviations of Atoms (Angstroms) from the (111) Plane at O(3)a K(Ag4Cl4) Dehydrated (C3H6O3)-Ab K(Ag4Br4)-Ac K(Ag4I4)-Ad K12-Ae K(1) K(2) K(3) Ag(1) X(1) f

1.07 1.64 2.60 -1.03 -1.63

0.47 1.41

0.55 1.48

-1.05 -2.20

-0.98 -2.17

0.79

a A positive deviation indicates that the ion lies in the large cavity. A negative deviation indicates that the ion lies on the same side of the plane as the origin, i.e., inside the sodalite unit. b This work. c Reference 30. d Reference 31. e Reference 45. f X ) Cl, Br, or I, respectively.

unit. A single 6-ring may not simultaneously host one of each because the Ag+ · · · Cl- distance would be impossibly short, 0.61(3) Å. The Ag(1) ions are each 2.493(5) Å from three O(3) 6-ring oxygens (see Table 4). Each extends 1.03 Å into the sodalite unit from the (111) planes at O(3) (see Figure 5 and Table 6). Considering the ionic radii of the framework oxygens to be 1.32 Å, the ionic radii of these Ag+ ions must be about 2.49 - 1.32 ) 1.17 Å.50 This is closer to the ionic radius of Ag+, 1.26 Å,50 than that of K+, 1.33 Å, indicating that it is a Ag+ ion that is at Ag(1). Also the occupancy of K+ ions at the Ag(1) position would be impossibly large. The ions at Cl(1) extend 1.63 Å into the sodalite unit from the (111) planes at O(3) (see Figures 5 and 6 and Table 6). They are 2.798(18) Å from the three nearest anionic framework oxygens. This distance is somewhat shorter than the halide to oxygen distances in K(Ag4Br4)-A30 and K(Ag4I4)-A,31 3.14(4) and 3.18(6) Å, respectively (see Table 8). This shorter distance

is consistent with the smaller ionic radius of chloride, 1.81 Å, as compared to those of bromine, 1.96 Å, and iodine, 2.20 Å.50 They approach the Ag+ ions at Ag(1) closely; the Ag(1)-Cl(1) distance, 3.105(17) Å, is just a little longer than the sum of the conventional ionic radii of Ag+ and Cl-, 3.07 Å ) 1.26 + 1.81 Å.50 It is substantially longer than the Ag-Cl distance in AgCl(s), 2.778 Å, indicating perhaps, as does the acute Cl(1)-Ag(1)-Cl(1) angle, 76.4(7)°, that the Ag(1) ions are being pulled toward the oxide ions of the zeolite framework. Because there is more than one Cl(1) ion per sodalite cavity, the possible contact distances between Cl- ions within a single cavity must be considered. They are approximately 2.716, 3.841, and 4.705 Å. Considering the radius of the Cl- ion, 1.81 Å,50 only the latter two approach distances can be considered further. Considering the possible arrangements of Cl- and Ag+ ions within the space of the sodalite unit, an interpenetrating tetrahedral (puckered cubic) arrangement of four Ag+ and four Cl- ions in 45% of the sodalite units (unit cell 1) is most likely (see Figures 5 and 6). It gives the greatest number of bonds per ion (12 bonds per 8 ions) and the most regular coordination geometries (only mildly distorted octahedral for Ag+ and tetrahedral for Cl-) and is consistent with the symmetry of the Ag(1) and Cl(1) positions (both lie on 3-fold axes). In this arrangement, each Ag+ ion bonds to three Cl- ions (in addition to three framework oxygens), and each Cl- ion bonds to three Ag+ ions (in addition to one K(1) ion). Smaller clusters, AgnClm, n and/or m < 4, would necessarily have less adequate and less symmetric coordination geometries for their Ag+ and Cl- ions and would be inconsistent with the refined occupancies which indicate that the sodalite cavities are full. Ag4Cl4, a cube with Ag+ and Cl- ions alternating at its corners, is a unit of the structure of AgCl(s).



TABLE 7: Possible Distribution of Nonframework Atoms (K, Ag, O, and Cl) in Component Unit Cells atoms K(1) K(2) K(3) K(4) K(5) K(6) K(7) Ag(1) Ag(2) Ag(3) Cl(1) Cl(2) Cl(3) O(4) O(5) O(6) C(1) ∑(cationic charges) ∑(anionic charges)

position Opposite 6-ringa,b Opposite 6-ringa,b Opposite 6-ringa,b Opposite 6-ringa,b,e 8-ringa,c 8-ringa,c Opposite 4-ringa Opposite 6-ringb,d Opposite 6-ringb,d Opposite 6-ringa,b Opposite 6-ringb,d Opposite 4-ringa Opposite 4-ringa Opposite 6-ringd 8-ringa,c 8-ringa Opposite 4-ringd

(b) as monatomic and polyatomic cations 4 Ag(1), 4 Cl(1) Ag4Cl4 [C3H3O3]22+ 6 O(4), 6 C(1) [K3ClO]2+ K(1), K(3), K(7), Cl(3), O(5) [K3ClO]2+ 2 K(2), K(7), Cl(2), O(5) [K3Cl]2+ K(1), K(3), K(7), Cl(3) [K3(OH)2]1+ K(4), 2 K(6), 2 O(6) K+ K(5) K+ K(6) K+ K(7) Ag+ Ag(2) Ag+ Ag(3) ∑

charge

unit cell 1(45%)

unit cell 2(55%)

no.

no.

charge

no.

Charge

varied no.

0 6 0 1 0 3 3 0 1 1 0 3 0 6g 3 2 6g

0 +6 0 +1 0 +3 +3 0 +1 +1 0 -3 0 +2 0 -2 0 +17 -5

1.80 3.30 1.80 0.55 1.35 1.65 3.90 1.80 0.55 0.55 1.80 1.65 1.80 3.30 3.00 1.10 3.30

+1.80 +3.30 +1.80 +0.55 +1.35 +1.65 +3.90 +1.80 +0.55 +0.55 -1.80 -1.65 -1.80 +1.10 0.00 -1.10 0.00 +18.35 -6.35

2.2(2) 2.8(2) 2.2(2) 0.7(1) 0.7(4) 1.9(3) 4.3(6) 1.6(1) 0.5(1) 0.7(1) 1.9(4) 4.1(3) f

0 1 0 3 0 1 0 1 0 1 1

0 +2 0 +6 0 +1 0 +1 0 +1 +1 +12

0.45 0.55 1.35 1.65 0.45 0.55 1.35 0.55 0.45 0.55 0.55

0.00 +1.10 +2.70 +3.30 +0.90 +0.55 +1.35 +0.55 +0.45 +0.55 +0.55 +12.0

charge

(a) as individual ions or atoms +1 4 +4 +1 0 0 +1 4 +4 +1 0 0 +1 3 +3 +1 0 0 +1 5 +5 +1 4 +4 +1 0 0 +1 0 0 -1 4 -4 -1 0 0 -1 4 -4 +0.33 0 0 0 3 0 -1 0 0 0 0 0 +20 -8 0 +2 +2 +2 +2 +1 +1 +1 +1 +1 +1

1 0 3 0 1 0 3 0 1 0 0

0 0 +6 0 +2 0 +3 0 +1 0 0 +12

total (averaged)

4.0(4) 3.9(9) 1.0(3) 4.1(4)

a In the large cavity. b On 3-fold axes. c Off the 8-ring plane. d In the sodalite unit. e At the center of the large cavity. f Cl(2) and Cl(3) are not resolved in this varied occupancy. g The C(1) and O(4) atoms are members of a cationic cluster, [(CH)3O3]22+.

Figure 5. Stereoview of the sodalite cavity of unit cell 1 in K(Ag4Cl4)(C3H3O3)-LTA containing a Ag4Cl4 cluster as shown. Each Ag+ cation coordinates octahedrally to three Cl(1) ions and three O(3) framework oxygens. Each chloride ion coordinates tetrahedrally to three Ag+ ions and one K+ ion at K(1). See the caption to Figure 3 for other details.

The resulting neutral Ag4Cl4 nanocluster would be wellstabilized by the interactions of each its four Ag+ ions with three 6-ring oxygens (Ag(1)-O(3) ) 2.493(5) Å). In addition, each Cl- ion coordinates to a K(1) cation through a 6-ring. Figure 5 is a stereoview of such a sodalite unit with a Ag4Cl4 nanocluster at its center. The Ag4Cl4 cluster has a diameter of approximately 8.3 Å, similar to those of Ag4Br4, 7.9 Å, and Ag4I4, 8.0 Å (see Table 8). It is a neutral ionic nanocluster which, like others reported earlier,1–4,30,31 may have interesting optical properties. Silver halide clusters of AgnX, X ) Cl, Br, and I,1,2,29 in sodalite (SOD) were reported by Ozin et al.; each has a halide ion at its center. The single crystal studied, a cube about 80 µm on an edge, contained more than 100 Tera (1 × 1014) Ag4Cl4 clusters.

4.4. 1,3,5-Tripyrylium Pairs in Sodalite Units (Unit Cell 2, UC2). 4.4.1. Structure and Molecular Geometry. In the remaining 55% of the sodalite units (those without Ag4Cl4 nanoclusters), two extraframework positions are found, O(4) and C(1), each with an occupancy of six atoms per unit cell (see Table 3; 3.3 atoms per average unit cell ) 6 atoms in 55% of the unit cells.). At these high occupancies, these sodalite units can be considered full (glance at Figures 7 and 8). These occupancies require that each C(1) bonds to two O(4) atoms, and that each O(4) bonds to two C(1) atoms, to form 6-membered rings. The mean deviation of the C(1) and O(4) atoms from the ring plane is approximately 0.012 Å, indicating that these rings are essentially planar (see Figures 7 and 8) and therefore aromatic. The result is two parallel eclipsed C3O3 rings


Kim et al.

Figure 6. View of the Ag4Cl4 cluster in the sodalite cavity of unit cell 1. Silver is white and chloride is green.

TABLE 8: Comparison of the Geometries of the Ag4Cl4, Ag4Br4, and Ag4I4 Nanoclusters Ag(1)-X(1), Å Ag(1)-X(1)-Ag(1), degrees X(1)-Ag(1)-X(1), degrees Ag(1)-O(3), Å X(1)-K(1), Å X(1) · · · O(2), Å X(1) · · · O(3), Å deviations of Ag(1) from O(3) plane, Å a

Ag4Cl4a

Ag4Br4b

Ag4I4c

3.105(17) 102.1(5)

2.93(3) 106.6(17)

2.973(21) 112.6(8)

76.4(7) 2.493(5) 2.70(3) 3.517(16) 2.798(18) 1.03

61(3) 2.52(3) 2.67(12) 3.80(5) 3.18(6) 1.05

60.5(16) 2.478(11) 2.72(6) 3.80(6) 3.14(4) 0.98

This work. b Reference 30. c Reference 31.

related by an inversion center at the center of the sodalite unit. The overall symmetry of this dimer is D3d. The distance and angles in the rings are given in Table 4. The C(1)-O(4) distance, 1.52(3) Å, is long, longer (perhaps, considering esds) than that in the related nonplanar and nonaromatic 1,3,5-trioxane (chair form in its crystal structure), 1.429(4) Å.52 The angles, 151(6)° and 89(6)° for C(1)-O(4)-C(1) and O(4)-C(1)-O(4), respectively, are decidedly different from each other, from trigonal (120°), and quite unlike the near tetrahedral angles in 1,3,5-trioxane, 108.0(2)° and 107.8(2)°.52 Such a distortion had been seen before in 2,6-diphenyl-4-(4nitrophenyl)pyrylium perchlorate where electron density came to the pyrylium ring from the phenyl groups.53 In this work, where the electron density comes from the anionic zeolite framework and tripyrylium is present, the effect is an order of magnitude greater. Because of strong repulsion with framework oxygen, O(4) · · · O(3) ) 3.14(4) Å, the O(4) oxygens have moved more deeply into the cavities to exaggerate the ring angles at O(4). At the same time, each carbon atom, opposite a 4-ring in the sodalite unit, hydrogen bonds (see the following paragraph) at 2.84(3) Å to the zeolite framework at O(3), pulling the C(1) atoms away from the center of the pyrylium ring and diminishing the O(4)-C(1)-O(4) angles. These extreme angles also allow the rings to avoid complete eclipsation, so that the six shortest inter-ring interatomic distances (C(1) · · · O(4) ) 2.47(7) Å) are all a little longer than the interplanar spacing, 2.43 Å. The two formally positive oxygen atoms bound to each C(1) atom draw electron density from it leaving the hydrogen atom bound to it quite acidic and unusually able to participate in

hydrogen bonding. The secondary resonance forms of pyrylium indicate that this should occur,54 and calculations show that this effect is strong for 1,3,5-tripyrylium (see Tables 9 and 10). The oxygens of one ring can further delocalize electron density to the Ag+ ion at Ag(2). The C(1)-H(1) · · · O(3) hydrogen-bonded distance, 2.84(3) Å, is remarkably short, much like an O-H · · · O hydrogen bond length, approximately 2.7-3.0 Å. 4.4.2. Elementary Description of the Bonding in the Monomer. How can a 6-membered C3O3 ring (irrespective of hydrogen atoms which were not found crystallographically) be aromatic? Consider this isoelectronic sequence: benzene, pyridine, and the pyrylium ion, cyclo-C5H5O+. In these, CH is replaced by N which is replaced by O+. Pyrylium has been prepared as a variously phenyl-substituted cation and is known as a fragment of molecules with fused ring systems. Now consider the same sequence except that the replacement is done simultaneously at the 1, 3, and 5 ring positions: (HC)3(CH)3, (HC)3N3, and (HC)3(O+)3. (HC)3N3, 1,3,5-triazine, is commonly known, but (CH)3(O+)3, cyclo-C3H3O33+, the tripositive 1,3,5tripyrylium cation (see Figure 1), has not been reported, neither as a cation nor as part of a larger molecule. A B3LYP/6-31G(d) geometry optimizaton produces a planar closed shell C3H3O33+ structure which is aromatic and isoelectronic with benzene, and which corresponds to a proper local minimum computed to have all real vibrational frequencies. Additional description is given in Table 9. (Adding two electrons gives C3H3O3+ which also has a planar local minimum; it has a triplet open shell ground electronic state.) 4.4.3. DFT Results and Justification for the Short Interplanar Spacing. The geometry calculated for cyclo-C3H3O33+ (Table 9) does not agree very well with that observed in the crystal structure (Table 4). Also, the interplanar spacing between the two rings, 2.43 Å, is far shorter than any ever reported for aromatic rings. Furthermore, aromatic ring systems are generally never eclipsed in their crystal structures. In graphite, the layers alternate with an interplanar spacing of 3.354 Å. In weak 1:1 complexes like those between hexafluorobenzene and aromatic hydrocarbons, the rings are nearly parallel but also do not eclipse, with interplanar distances of about 3.5 Å at room temperature.55 In two monophenyl substituted pyrylium compounds, such π-π stacking is seen with interplanar distances of about 3.55 Å when the overlap is better and of 3.30 Å when it is poorer.56 Aromatic molecules like benzene, hexamethylbenzene, and naphthalene are not parallel in their crystal structures, so an inter-ring distance is not defined. A classic system in which two benzene rings are pulled close together in an eclipsed orientation (almost) is [2.2]paracyclophane, C16H16 (see Figure 9a).57 Except for a small twist,58 these rings are held in this strained configuration by two dimethylene (-CH2-CH2-) bridges at their para positions. The inter-ring distances are 3.09 Å for the planes defined by the central four carbon atoms of each ring, but only 2.82 Å for the ring atoms that bond to the dimethylene bridges.58 For many years, these paracyclophanic inter-ring distances were the shortest known. Substantially shorter inter-ring distances, up to 0.31 Å less, have been calculated for the lowest-energy (HOMO-LUMO) excited states of [2.2]paracyclophane.59 Here is an elementary explanation. One electron on one ring moves from a π orbital (at E1 in Figure 10a) to a π* orbital (at E2 in Figure 10a). It can then delocalize into the equivalent empty π* orbital on the other ring to give one-electron 12-center σ bonding between the rings. This also occurs between an electron in a filled π orbital of the second ring and the vacancy



Figure 7. Stereoview of the sodalite cavity of unit cell 2 in K(Ag4Cl4)(C3H3O3)-LTA containing two 1,3,5-tripyrylium cations. See the caption to Figure 3 for other details.

Figure 8. Three views of the reduced 1,3,5-tripyrylium dimer in the sodalite cavity of unit cell 2. A Ag+ ion at Ag(3) occupies a 6-ring but does not bond to [C3H3O3]22+. Oxygen is red, carbon is gray, and hydrogen (bonded to carbon) and silver are white. The hydrogen atoms bond to carbon atoms and lie in the planes of the tripyrylium rings.

TABLE 9: Calculated Geometry and Formal Charges for the 1,3,5-Tripyrylium Cation, cyclo-C3H3O33+ geometry C(1)-O(4), Å C(1)-H, Å O(4)-C(1)-O(4), degrees C(1)-O(4)-C(1), degrees

1.326 1.122 117.9 122.1

formal charges on O, C, H, e-’s -0.16, +0.64, +0.51 +0.16, +0.46, +0.39

Mulliken Lowdin

TABLE 10: Calculated Geometry and Formal Charges for [cyclo-C3H3O3]22+, a Reduced Dimer of the 1,3,5-Tripyrylium Cationa geometry C(1)-O(4), Å C(1)-H, Å O(4)-C(1)-O(4), degrees C(1)-O(4)-C(1), degrees interplanar spacing, Å

1.334 1.08 118.2 121.3 2.578

formal charges on O, C, H, e-’s Mulliken Lowdin

-0.29, +0.30, +0.33 +0.02, +0.05, +0.27

a This calculation did not include the zeolite framework. Because the framework is relatively rigid and anionic and the reduced dimer is cationic, it is expected that its proper inclusion would affect these values appreciably, bringing them closer to those observed crystallographically. See paragraphs 2 and 3 of section 4.4.1.

in a π orbital generated by the excitation of the first ring. The net result is a 12-center two-electron σ bond between the rings. Here is a more accurate presentation, using dimer MOs, of the bonding between the [2.2]paracyclophane rings in a lowlying excited state. When two benzene molecules approach each other with their rings parallel and eclipsed, each π orbital on

Figure 9. Carbon atoms in (a) [2.2]paracyclophane, C16H16, and (b) superphane, C24H24, drawn to scale using published coordinates.58,70

the first benzene (Figure 10a) combines with the equivalent π orbital on the other benzene (Figure 10a) to form a bonding and an antibonding pair of dimer π orbitals (Figure 10b) which are delocalized over both molecules. When these two benzene molecules are in their ground states, an equal number of bonding and antibonding dimer π orbitals are occupied (all orbitals below E0 in Figure 10b would be filled; six electrons bonding and six antibonding) to give zero net bonding between the two rings. However, in a HOMO-LUMO type excited state, an electron is transferred from an occupied antibonding dimer orbital (D2 in Figure 10b) to an unoccupied bonding dimer orbital (D3 in Figure 10b) to produce two singly occupied dimer orbitals. The removal of an electron from an antibonding orbital and its placement in a bonding orbital results in a net inter-ring twoelectron π dimer bonding interaction (seven electrons bonding and five antibonding) which favors a shortening of the interring separation. At the same time, the HOMO-LUMO excitation reduces the in-ring C-C bond order causing a slight lengthening of the C-C distance in each of the C6 rings. Van der Waals repulsions typically limit inter-ring distances, but smaller inter-ring distances can be found if a bonding interaction can develop across the rings. A dimer formed of two cyclo-C3H3O33+ cations would have high electrostatic inter-ring repulsion and, like an eclipsed dimer of benzene with which it is isoelectronic, no inter-ring covalent bonding. This model offers no justification for the short inter-


Figure 10. Schematic π energy level diagrams for benzene (a) using monomer orbitals and for the eclipsed dimer (b) using dimer orbitals. Bonding and antibonding orbitals are indicated by “b” and “a”, respectively. In (a), these designations represent orbitals that are bonding and antibonding with respect to bonds of the ring. In (b), they represent orbitals that are bonding and antibonding between the two rings of the dimer. For a HOMO-LUMO excitation, an electron moves from one of the two highest occupied orbitals (D2) which are antibonding between the rings to one of the two lowest unoccupied orbitals (D3) which is bonding between the rings. From the point of view of inter-ring bonding, an antibonding electron has become a bonding electron, leading to a net single bond between the rings. If four electrons are simply added at D3 to the ground-state dimer, two inter-ring bonds form.

ring distance observed, quite the opposite. However, because of its positive charge, this dimer must have a high affinity for electrons. These would initially occupy the lowest lying π* orbitals (D3 in Figure 10b) which are bonding inter-ring. If this 6+ dimer were to gain 2, 4, or 6 electrons, 1 (2 electrons bonding at D3), 2 (4 electrons bonding at D3), or 1 (4 electrons bonding at D3, 2 antibonding at D4) 12-center inter-ring bonds, respectively, would result (see Figure 10b). These π* electrons would, of course, diminish the orders of the intraring C-O bonds, causing them to lengthen. The ring C-O bonds are indeed long; they are even longer than those calculated (see Tables 4 and 9). In addition, six 2.47(7) Å C(1) · · · O(4) contacts between the two rings provide a polar contribution to the interplanar bonding, countering the electrostatic ring repulsion in the possible 4+ and 2+ dimers. As compared with the calculated reduction in inter-ring separation due to an interplanar single bond in the first excited state of [2.2]paracyclophane, approximately 0.31 Å,59 the reduction seen here, approximately 3.35 - 2.43 ) approximately 0.9 Å, indicates the presence of more than one, perhaps two or three, inter-ring 12-center bonds. This indicates that the interring bond order is two or three, and therefore that the dimers must be dipositive or neutral, respectively. Three inter-ring bonds are, however, not possible; see the fifth sentence of the previous paragraph. We may now (almost) conclude that the dimers must be dipositive, [C3H3O3]22+. B3LYP/6-31G(d) calculations on [C3H3O3]22+ were successful. They produced a closed shell system which can be geometry optimized providing the starting structure is constrained to have the D3d symmetry seen in the crystal structure. (The sodalite cavity provides this constraint by the placement of its hydrogen-bonding donor oxygen atoms.) The results are presented in Table 10. The short interplanar spacing, 2.58 Å, is gratifying, shorter than any aromatic interplanar spacing ever reported, but still 0.15 Å longer than the 2.43 Å separation seen experimentally. The calculated C-O bond lengths, 1.33 Å, are noticeably shorter than the 1.52(3) Å distance observed experimentally. However, the [C3H3O3]22+ dimer is not a true local minimum since it is computed to have three imaginary vibrational frequencies. Additional geometry optimizations initiated with the [C3H3O3]22+ dimer stationary point geometry distorted along one of the imaginary frequency normal mode directions produce lower energy and lower symmetry structures

Kim et al. which are not consistent with the crystal structure. For instance, a lower energy structure is obtained when the two C3H3O3+ rings are rotated relative to each other around the 3-fold axis so that the C atoms on different C3H3O3+ rings are eclipsed and can form inter-ring C-C bonds. Calculations on the [(CH)3(OH)3]22+ dimer (a hydrogen atom is placed on each oxygen as well as each carbon) are able to better reproduce the observed C-O bond length, but the three additional hydrogen atoms cause the rings to lose their planarity and to move further apart. Similar geometry optimizations were performed on the [C3H3O3]2 and [C3H3O3]24+ dimers to yield triplet ground states with interplanar distances of 2.97 and 11.2 Å, respectively. In all of the above calculations, except for the requirement of D3d symmetry, the effects of the zeolite framework, such as the six short CH · · · O hydrogen bonds that help to stabilize the centric dimer and maintain D3d symmetry, have been ignored. 4.4.4. Additional Discussion of [C3H3O3]22+. One 1,3,5tripyrylium cation per sodalite unit of UC2 bonds axially to a Ag+ ion at Ag(2) with three 2.68(9) Å Ag(2)-O(4) bonds (see Table 4 and Figure 7; recall that O(4) is not O+ (see Table 10)). Considering its electrostatic discharge (esd), this distance is similar to the sum of ionic radii of Ag+ and O2-, 1.26 + 1.32 ) 2.58 Å.50 The second ring per sodalite cavity of UC2 does not bond to a Ag+ ion at Ag(2). We offer no clear explanation for the association of just one Ag+ ion, rather than zero or two, with this dimer. Perhaps there is simply an electrostatic limit to the number of cations that can associate with the dimer cation. [C3H3O3]22+ is a cationic cluster. Unusual cationic clusters are commonly found in the anionic sodalite cavities of zeolites, which provide a stabilizing environment. A brief review is available.60 For example, Na43+ was found in zeolite Y (FAU);61 S44+ was found in zeolite X (FAU),60 and In57+ was found in zeolites A (LTA)62 and X.63 The clusters Zn56+ and cyclo-Zn68+ have been proposed as products of the reaction of zeolite H-Y with Zn(g).64 Cationic Pb8O4n+ clusters were found in zeolite X,65 and Cd8O48+ 66 and Pb2S2+ 67 clusters were reported in zeolite Y. Most recently, Cd6S44+, Cd2Na2S4+, and Cd2O2+ were found in the sodalite cavities of zeolite A.68 [C3H3O3]22+ may have been present in K(Ag4Br4)-A30 and K(Ag4I4)-A.31 If so, they were not found because of the poorer quality of those data sets (those crystals). The final error indices (R1) were 0.077, 0.080, and 0.052 for K(Ag4I4)-A,31 K(Ag4Br4)-A,30 and K(Ag4Cl4)(C3H3O3)-A, respectively; the number of reflections (Fo > 4σ(Fo)) were 264, 99, and 371, respectively (see Table 1). It can be estimated to one significant figure that 500 000 atm of pressure would be required at about 295 K to reduce the spacing between the layers in graphite (3.354 Å at 1 atm) to 2.43 Å, the value seen in this work for the reduced 1,3,5tripyrylium dimer. This is an extrapolation of data taken to 130 000 atm.69 At the latter pressure, graphite begins to undergo a phase transition: carbon-carbon single bonds begin to form between its planes. 4.4.5. Other Short Distances in Cyclophanes. The shortest interplanar spacing heretofore reported for planar aromatic rings that are strictly parallel by symmetry is 2.624 Å70 in superphane ([2.2.2.2.2.2](1,2,3,4,5,6)cyclophane, C24H24, symmetry 6/mmm ) D6h);71 the two rings are reported to eclipse perfectly (see Figure 9b).70 For comparison, the interplanar spacing in graphite is both much longer, 3.354 Å, and less confrontational: the layers do not eclipse. Even shorter interatomic (not interplanar) distances have been seen in less symmetric cyclophanes whose

Single Crystal Structure of Zeolite A (LTA) rings are sharply distorted from planar, deviate to a minor or major degree from being parallel, or do not have much overlap; for these, some interatomic distances between rings have become unusually short while others have lengthened. Examples are 2.376 Å in a stable derivative of [1.1]paracyclophane72 and 2.38 Å in [2.2.1]metacyclophane;73 for both of these, the two ring carbon atoms are bonded to a single methylene group and so may be viewed as meta members of the same ring. (Even shorter distances can be seen in [2.2]metacyclophanes where the two aromatic rings are approximately perpendicular, very far from parallel and not of interest here.74–76) Other short distances between an atom of one aromatic ring and an atom of another due to their incorporation in cyclophanes are 2.50 Å in 4,15diazo[2.2]paracyclopane77 and 2.65 Å in [2.2](2,5)p-bezoquinonophane.78 Again, for comparison, the shortest inter-ring distance between two atoms in the first cyclophane to be synthesized, [2.2]paracyclophane, is 2.78 Å.58 Reviews citing many more molecules with short inter-ring intramolecular contacts are available.79,80 4.5. 13C NMR Evidence for 1,3,5-Tripyrylium in the Zeolite. The presence of 1,3,5-tripyrylium in the zeolite can be further evidenced by the 13C MAS NMR spectrum of K(Ag4Cl4)(C3H3O3)-A powder (see Figure 2) in which two 13C lines around 50 and 111 ppm are observed. While the highfield line is assigned to the methyl carbon atoms of methanol, the low-field line, asymmetric in nature, may be due to carbon atoms in the 1,3,5-tripyrylium ring. It is interesting to note here that the chemical shift (93.58 ppm) of the carbon atom in liquid 1,3,5-trioxane is much more upfield by approximately 17 ppm than that of carbon atoms in the 1,3,5-tripyrylium ring. The 13C MAS NMR data in Figure 2 also indicate the absence of another conceivable candidate, formaldehyde, due to the lack of any noticeable line in the chemical shift range 190-220 ppm.81,82 However, these data clearly show the presence of a nonnegligible amount of solvent, both methanol and water, within K(Ag4Cl4)(C3H3O3)-A. This is reasonable because no attempt was made to dry the zeolite powder before 13C MAS NMR measurement. The oxygens of some of these solvent molecules were observed crystallographically at O(5) and O(6). 4.6. Justification and Net Reaction for the Synthesis of 1,3,5-Tripyrylium in the Zeolite. The synthesis of trioxanes has been studied extensively because they are used industrially to prepare polyoxymethylene and other polymers.83–89 To prepare trioxane or 1,3,5-trimethyltrioxane, respectively, formaldehyde and acetaldehyde are trimerized with an acid catalyst, either sulfuric acid or a solid acid catalyst.83,84 H2SO4 or solid acid

3 CH2O 98 1,3,5-trioxane Various zeolites are used as acid catalysts to prepare trioxanes from aldehydes.85–87 Mordenite, zeolite β, ZSM-5, and ZSM35 all show catalytic activity for the synthesis of trioxanes.85 Mordenite catalyzes the formation of trioxane from formaldehyde with high selectivity.86 Reactions of acetaldehyde were carried out using variously ion-exchanged ZSM-5 catalysts; these exhibited high activity for the formation of transparaldehyde (2R,4R,6β-trimethyl-1,3,5-trioxane).87 A primary alcohol can be converted to an aldehyde by an oxidation reaction.88 A possible mechanism for this reaction would be attack of the oxygen of the alcohol by a strongly electrophilic group, X, to elimilate H+ and X-.88 Catalytic dehydrogenation reactions (also oxidation reactions) are also used to prepare aldehydes from alcohols. Silver is employed as the catalyst for the production of formaldehyde and acetalde-

J. Phys. Chem. C, Vol. 112, No. 30, 2008 11191 hyde.88 A silver-containing ZSM-5 zeolite catalyst was used to oxidize ethanol to acetaldehyde.89 The synthesis of the 1,3,5-tripyrylium ions within the zeolite may have involved the following steps. (1) Methanol (the solvent of this experiment) is converted to formaldehyde by catalytic dehydrogenation (oxidation). (2) Formaldehyde trimerizes within the zeolite, undergoing further oxidation, to form 1,3,5tripyrylium. 1,3,5-Trioxane, which forms easily by the trimerization of formaldehyde, may have been an intermediate that underwent further catalytic dehydrogenation. Ag+ can catalyze the formation of the pyrylium ring by insertion of a water oxygen into a heavily phenyl-substituted cyclo-pentadiene ring.90,91 Perhaps Ag+ served a similar function here. The net reaction for the formation of [C3H3O3]22+, catalyzed by Ag+ ions and the zeolite, is

6CH3OH + 2H2O f [C3H3O3]22+ + 10H2 + 2OHThis reductive condensation is likely to occur in a series of steps, not necessarily all within the sodalite cavity. Reactions involving the quantitative reduction of Ag+ are not suggested because silver atoms were not seen in the crystal structure nor, because the crystal was neither black nor lustrous silver, were they present on the surface. For the synthesis of silica sodalites, 1,3,5-trioxane has been used as a structure-directing agent.92,93 Perhaps it reacts further under synthesis conditions to give the dimers found here, which fit nicely into sodalite cavities and may well stabilize them during synthesis. In addition, the high-silica forms of EMTand FAU-type zeolites, whose substructures are sodalite cavities, are synthesized by using specific organic species such as 1,3,5trioxane and ethylene glycol92,93 which may have reacted similarly under synthesis conditions. 4.7. Structures in the Large Cavities. Because two kinds of sodalite units have been identified (UC1, 45% and UC2, 55%), this discussion will proceed as though there were two kinds of large cavities with the same percentages. The atoms and molecules in those large cavities are given in Table 7. The structures in the large cavities are, however, less well-defined and are presented only to show that reasonable arrangements are possible. Any given large cavity may contain components of both structures shown in Figures 3 and 4. 4.7.1. In the Large CaWity of UC1. In 45% of the large cavities (UC1), 16 K+ ions per unit cell are distributed over four crystallographically distinct positions (see Table 7). Four K+ ions at K(1) and four at K(3) lie on 3-fold axes opposite 6-rings. Therefore, each of the eight 6-rings per unit cell contains a K+ ion. These ions are 1.07 and 2.60 Å, respectively, from the (111) planes at O(3) (see Table 6). This large difference is due to the interactions of these ions with ions in the sodalite unit (see section 4.3). Three K+ ions at K(5) lie near 8-ring planes (K(5)-O(1) ) 2.65(5) Å), and five K+ ions at K(7) are opposite 4-rings (K(7)-O(1) ) 3.02(4) Å; see Figure 4). Balancing the charges of the zeolite A framework (12 per unit cell) and the 16 K+ ions in UC1, four Cl- ions are found at Cl(3), opposite 4-rings; each is 3.14(8) Å from two nearest framework oxygens, O(3). Each Cl- bonds to three K+ ions, at K(1), K(3), and K(7), forming a K3Cl2+ ionic cluster (Cl(3)-K(1) ) 2.83(7) Å, Cl(3)-K(3) ) 2.88(8) Å, and Cl(3)-K(7) ) 3.25(4) Å; K(1)-Cl(3)-K(7) ) 70.8(12)°, K(3)-Cl(3)-K(7) ) 107.7(19)°, and K(1)-Cl(3)-K(3) ) 177(4)°; see Figure 4). The Cl(3)-K(1) and Cl(3)-K(3) distances are somewhat shorter than the sum of the ionic radii of Cl- and K+, 1.81 + 1.33 ) 3.14 Å, and the K(7)-Cl(3) distance, 3.25(4) Å, is somewhat

11192 J. Phys. Chem. C, Vol. 112, No. 30, 2008 longer. The latter may be artifactual: the K(7) position must be the unresolved average of two positions, one participating in a cluster in UC1 and the other participating in UC2. Three oxygens at O(5) are also found in a large cavity of UC1. Each O(5) oxygen is near an 8-ring where it bonds to a K+ ion at K(7) (K(7)-O(5) ) 2.91(5) Å, a member of a K3Cl2+ cluster, and hydrogen bonds to a framework oxygen, O(2) (O(5)-O(2) ) 2.83(5) Å). Therefore, only three of the four K3Cl2+ clusters in the large cavity of UC1 can bond to an O(5) oxygen. O(5) appears to represent a water molecule. 4.7.2. In the Large CaWity of UC2. In each of the remaining 55% of the large cavities (UC2), 13 K+ ions and 2 Ag+ ions per unit cell are distributed over six crystallographically distinct positions (see Table 4). The eight 6-ring positions per large cavity are again filled, here by six K+ ions at K(2), one Ag+ ion at Ag(3), and one Ag+ ion at Ag(2) in the sodalite unit. Three K+ ions at K(6) are near 8-ring planes (K(6)-O(1) ) 2.75(3) Å) and three K+ ions at K(7) lie opposite 4-rings (K(7)-O(1) ) 3.02(4) Å; see Figure 3). Finally, a K+ ion, K(4), is found at the very center of the large cavity (see Figure 3). The sum of the cationic charges including the [C3H3O3]22+ dimer is now 17+ in UC2, so five additional anions, Cl- or OH-, are needed to achieve charge balance. They are found at Cl(2) and O(6) with occupancies of three and two, respectively. The Cl(2) position lies opposite a 4-ring 3.09(4) Å from the two nearest framework oxygens, O(1). Each bonds to three K+ ions, two at K(2) and one at K(7), to form a K3Cl2+ cluster (Cl(2)-K(2) ) 2.916(7) Å and Cl(2)-K(7) ) 3.27(4) Å; K(2)-Cl(2)-K(2) ) 166.3(14)° and K(2)-Cl(2)-K(7) ) 61.3(7)° and 128.9(10)°; see Figure 3). The K(2)-Cl(2) distance, 2.916(7) Å, is somewhat shorter than the sum of the ionic radii of Cl- and K+, 1.81 + 1.33 ) 3.14 Å,50 and the K(7)-Cl(2) distance, 3.27(4) Å, is somewhat longer. (K(7) is an averaged position, so the geometry calculated for it is somewhat inaccurate: the K+ ions at K(7) participate in two different clusters, one in UC1 and the other in UC2 (see section 4.7.1).) Additionally, the two hydroxide oxygens at O(6), two of the three K+ ions at K(6), and the K+ ion at K(4) form a nearly linear K3O23+ cluster, K(6)-O(6)-K(4)-O(6)-K(6) (see Figure 3; K(6)-O(6) ) 2.70(20) and K(4)-O(6) ) 3.12(20) Å; K(6)-O(6)-K(4) ) 162.4(15)°, and O(6)-K(4)-O(6) ) 180.0° by symmetry.). As in UC2, three oxygens, presumeably water oxygens, are present at O(5). Each bonds to a K+ ion at K(7) and hydrogen bonds to the framework oxygen O(2) as described in section 4.7.1. Therefore, each K3Cl3+ cluster bonds to an O(5) oxygen. 5. Summary Ag4Cl4 nanoclusters with Td symmetry have been synthesized in about 45% of the sodalite cavities of K-A. Each Ag4Cl4 cluster (Ag-Cl ) 3.105(17) Å) is held in place by the coordination of each of its four Ag+ ions to three oxygens of the zeolite framework and by the coordination of each of its four Cl- ions to a large-cavity K+ ion through a 6-ring. Two planar 1,3,5-tripyrylium ions occupy each of the remaining 55% of the sodalite cavities. They form a nearly eclipsed [C3H3O3]22+ dimer with D3d symmetry and a very short 2.43 Å interplanar spacing due to four-electron σ bonding involving 12-center π* orbitals and polar forces. Each ring forms three strong CH · · · O hydrogen bonds with the zeolite framework. One ring bonds to a 3-fold axis Ag+ ion. The 1,3,5-tripyrylium ring, isoelectronic with benzene, had not been heretofore reported. Acknowledgment. We gratefully acknowledge the support of The Pohang Accelerator Laboratory of POSTECH for their

Kim et al. diffractometer and computing facilities. Janice G. Smith and Gordon W. Gribble helped us to recognize and to name the tripyrylium ion, respectively. This work was supported by the Korea Science & Engineering Foundation through the Basic Research Program (R01-2006-000-10192-0) and the National Research Laboratory Program (R0A-2007-000-20050-0). Supporting Information Available: Observed and calculated structure factors for |K2.35Ag1.1(Ag4Cl4)0.45(C3H3O3)1.1(K3Cl)3.45(K3(OH)2)0.55(H2O)g3.0|[Si12Al12O48]-LTA. This material is available free of charge via the Internet at http:// pubs.acs.org. References and Notes (1) Stein, A.; Ozin, G. A.; Stucky, G. D. J. Am. Chem. Soc. 1992, 114, 8119. (2) Stein, A.; Ozin, G. A.; Stucky, G. D. J. Am. Chem. Soc. 1990, 112, 904. (3) Kodaira, T.; Ikeda, T.; Takeo, H. Eur. Phys. J. D 1999, 9, 601. (4) Chen, W.; Wang, Z.; Lin, Z.; Lin, L.; Fang, K.; Xu, Y.; Su, M.; Lin, J. J. Appl. Phys. 1998, 83, 3811. (5) Beer, R.; Calzaferri, G.; Li, J. W.; Waldeck, B. Coord. Chem. ReV. 1991, 111, 193. (6) Ozin, G. A.; Godber, J.; Stein, A. U.S. Patent 4 1990, 944, 211. (7) Ekimov, A. I.; Efros, Al. L.; Onuschenko, A. A. Solid State Commun. 1985, 56, 921. (8) Randall, J. T.; Wilkins, H. F. Proc. R. Soc. London, Ser. A 1945, 184, 366. (9) Tani, T.; Murofushi, M. J. Imag. Sci. Technol. 1994, 38, 1. (10) Calzaferri, G.; Gfeller, N.; Pfanner, K. J. Photochem. Photobiol. A: Chem. 1995, 87, 81. (11) Saladin, F.; Kamber, I.; Pfanner, K.; Calzaferri, G. J. Photochem. Photobiol. A: Chem. 1997, 109, 47. (12) Rossetti, R.; Hull, J.; Gibson, M.; Brus, L. E. J. Chem. Phys. 1985, 83, 1406. (13) Nagy, B.; Barette, D.; Fonseca, A.; Jeunieau, L.; Monoyer, Ph.; Piedigrosso, P.; Ravet-Bodart, I.; Verfaillie, J. P.; Wathelet, A. Nanopartices in Solid and Solution; Fendler, J. H., Dekany, I., Eds; Reidel: Dordecht, 1996; pp 71-129. (14) Ji, M.; Chen, X.; Wai, C. M.; Fulton, J. L. J. Am. Chem. Soc. 1999, 121, 2631. (15) Bhatia, S. Zeolite Catalysis: Principles and Applications, CRC Press, Inc.: Boca Raton, FL, 1988; pp 1-2. (16) Smith, J. V. Am. Chem. Soc. Monogr. 1976, 171, 3. (17) Srdanov, V. I.; Blake, N. P.; Markgraber, D.; Metiu, H.; Stucky, G. D. AdVanced Zeolite Science and Applications: Studies in Surface Science and Catalysis; Jansen, J. C., Ed.; Elsevier Science: New York, 1994, 85, 115. (18) Terasaki, O.; Yamazaki, K.; Thomas, J. M.; Ohsuna, T.; Watanabe, D.; Sanders, J. V.; Barry, J. C. Nature (London) 1987, 330, 58. (19) Stucky, G. D.; MacDougall, J. E. Science 1990, 247, 669. (20) Alekseev; Yu., A.; Bogomolov, V. N.; Zhukova, T. B.; Petranovskii, V. P.; Romanov, S. G.; Kholodkevich, S. V. IzV. Akad. Nauk SSSR, Ser. Fiz. 1986, 50, 418. (21) Wang, Y.; Herron, N. J. Phys. Chem. 1987, 91, 257. (22) Wang, Y.; Herron, N. J. Phys. Chem. 1988, 92, 4988. (23) Herron, N.; Wang, Y.; Eddy, M. M.; Stucky, G. D.; Cox, D. E.; Moller, K.; Bein, T. J. Am. Chem. Soc. 1989, 111, 530. (24) Breck, D. W. Zeolite Molecular SieVes; Wiley: New York, 1974. (25) Preparation of Catalyst III; Poncelet, G., Granget, P., Jacobs, P. A. Eds.; Elsevier Science: Amsterdam, 1983. (26) Chen, W.; Joly, A. G.; Roark, J. Phys. ReV. B 2002, 65, 245404. (27) Zhai, Q. Z.; Qiu, S.; Xiao, F. S.; Zhang, Z. T.; Shao, C. L.; Han, Y. Mater. Res. Bull. 2000, 35, 59. (28) Hirono, T.; Yamada, T. Japanese Patent 1986, 61, 061894. (29) Godber, J.; Ozin, G. A. J. Phys. Chem. 1988, 92, 4980. (30) Lim, W. T.; Choi, S. Y.; Kim, C. M.; Lee, I. S.; Kim, S. H.; Heo, N. H. Bull. Korean Chem. Soc. 2005, 26, 1090. (31) Heo, N. H.; Kim, H. S.; Lim, W. T.; Seff, K. J. Phys. Chem. B 2004, 108, 3168. (32) Charnell, J. F. J. Cryst. Growth 1971, 8, 291. (33) Kim, Y.; Seff, K. J. Phys. Chem. 1978, 82, 1071. (34) Kim, Y.; Seff, K. J. Am. Chem. Soc. 1978, 100, 6989. (35) Ho, K.; Lee, H. S.; Leano, B. C.; Sun, T.; Seff, K. Zeolites 1995, 15, 377. (36) Bae, D.; Seff, K. Zeolites 1996, 17, 444. (37) Cruz, W. V.; Leung, P. C. W.; Seff, K. J. Am. Chem. Soc. 1978, 100, 6997. (38) Mellum, M. D.; Seff, K. J. Phys. Chem. 1984, 88, 3560.

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Single Crystal Structure of Zeolite A (LTA) - American Chemical Society

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