Reaction of Fully Indium-Exchanged Zeolite A with Hydrogen Sulfide

4578

J. Phys. Chem. B 2002, 106, 4578-4587

Reaction of Fully Indium-Exchanged Zeolite A with Hydrogen Sulfide. Crystal Structures of Indium-Exchanged Zeolite A Containing In2S, InSH, Sorbed H2S, and (In5)7+ Nam Ho Heo,* Chang Woo Chun, Jong Sam Park, Woo Taik Lim, Man Park, Song-Lin Li, and Ling-Ping Zhou Department of Industrial Chemistry, Kyungpook National UniVersity, Taegu 702-701, Korea

Karl Seff* Department of Chemistry, UniVersity of Hawaii at Manoa, Honolulu, Hawaii 96822-2275 ReceiVed: May 14, 2001; In Final Form: December 10, 2001

Four single crystals of fully dehydrated, fully indium-exchanged zeolite A (Inca. 10-Si12Al12O48 or Inca. 10-A, colorless) were exposed to 0.5 atm of H2S for 3 h at 298, 373, 423, and 573 K for crystals 1 to 4, respectively. After evacuation at temperature followed by cooling to 294(2) K, the crystals were red, brown, yellow, and yellow, respectively. Their structures were determined by single-crystal X-ray diffraction techniques in the cubic space group Pm3hm at 294(2) K (a ) 12.083(3), 12.076(2), 12.094(2), and 12.094(2) Å; R1 ) 0.069, 0.063, 0.065, and 0.060; R2 ) 0.062, 0.058, 0.064, and 0.060 for crystals 1 to 4, respectively). The structures differ in the degree of sorption and/or reaction with H2S. Crystal 1 (In9.5H0.5-A(InSH)0.5(H2S)2.5) may be viewed as being an equimolar mixture of two kinds of unit cells with compositions In9-A(H2S)3 and In10HA(InSH)(H2S)2. Unit cell 1 contains three H2S molecules stabilized as [(In)2(H2S)3]2+ in the large cavity and a tetrahedral (In5)n+ cluster in the sodalite unit. Unit cell 2 contains unreacted (In3)2+ and an [(In)2(InSH)(H2S)2]2+ cluster with one InSH and two sorbed H2S molecules, all in its large cavity. Crystal 2 (In8.4H1.2A(In2S)0.6(H2S)2) may similarly be viewed as being 40% In9-A(H2S)2 and 60% In8H2-A(In2S)(H2S)2. In9A(H2S)2 has two sorbed H2S molecules in a [(In)2(H2S)2]2+ cluster, whereas In8H2-A(In2S)(H2S)2 has a [(In)2(In2S)(H2S)2]2+ cluster with one In2S and two sorbed H2S molecules in the large cavity. At higher reaction temperatures (423 and 573 K), the product crystals had less InHS and sorbed H2S. All crystals contain tetrahedral (In5)n+ where n is likely to be 7. The number of sorbed H2S molecules decreases monotonically with increasing reaction temperature. In2S and InSH molecules were observed only in the large cavities, where more monopositive indium cations were initially available.

1. Introduction Zeolites may be good supports or carriers for particles up to a nanometer in diameter. Some of these, such as the semiconductors, are photoactive species.1 Zeolites can stabilize these small clusters under ambient conditions and require them to be both uniform and spatially oriented. The wide range of zeolite frameworks available allow the introduction or growth of subnanometer particles with various sizes and orientation patterns.1 Elemental sulfur and various sulfur compounds have been introduced into nanoporous materials, including zeolites, by material scientists. (“Nanoporous” indicates that the channels and cavities are of the order of 10-9 m in diameter; unfortunately IUPAC has approved the word “microporous” for this.) Various sulfide nanoclusters in zeolite cavities have shown unusual optical properties.1-11 These are due to the quantum size effects of the nanoclusters and to the regular three-dimensional arrangements which the zeolite structure requires. ZnS and CdS clusters prepared in zeolite Y show an unusual blue shift in their absorption spectra, as compared to the bulk materials.2 The absorption spectra of CdS and PbS clusters synthesized in the cavities of zeolites Y and M (mordenite), respectively, are greatly shifted to the high-energy side and have weaker oscillatory strength compared to the bulk.2,3 Similarly, Laponite

(porous Vycor glass),4 zeolite X, and sodalite have been used to host small particles of CdS;5 the optical properties of these materials are studied as a function of Cd2+ concentration and are discussed in terms of particle size. InP synthesized in mordenite also showed such a quantum size effect with a larger energy gap between valence and conduction bands.6 Various compounds of indium are semiconductors,12-14 but to date these have not been introduced into zeolites in high concentration to give three-dimensionally arrayed quantum dots. Toward this end, chemically reactive cations or clusters of In have recently been introduced into zeolites as precursors for preparing such nanoclusters,15 although the chemistry that would lead to the conversion of these atoms to nanoclusters of binary compounds has not been explored yet. In this work, single crystals of fully dehydrated fully indiumexchanged zeolite A15 (which contain In in various oxidation states and degrees of aggregation) were allowed to react with hydrogen sulfide at various temperatures, and the resulting structures were determined crystallographically. This was done to explore the chemistry of In0, In+, In2+, and In3+ in zeolite A and to study the reaction or sorption properties of hydrogen sulfide with the indium zeolites. It was hoped that indium would react with hydrogen sulfide to generate subnanosized and regularly arrayed indium sulfide (or hydrogen indium sulfide) clusters with novel optical properties.

10.1021/jp011839j CCC: $22.00 © 2002 American Chemical Society Published on Web 04/17/2002

Crystal Structures of Indium-Exchanged Zeolite A

J. Phys. Chem. B, Vol. 106, No. 18, 2002 4579

TABLE 1: Experimental Conditions and Crystallographic Data unit cell formula dehydration of Tl-A (temperature and duration) reaction with indium metal washing with deionized water redehydration of In-A exposure to H2S, 0.5 atm unit cell parameter, Å no. of reflections obsd., m no. of variables, s no. of nonframework variables, s final error indices: R1a, R2b goodness of fitc a

crystal 1

crystal 2

crystal 3

crystal 4

In9.5H0.5-A(InSH)0.5(H2S)2.5 623 K, 2 days

In8.4H1.2-A(In2S)0.6(H2S)2 623 K, 2 days

In9.8H0.4-A(InSH)0.4(H2S) 623 K, 2 days

In10.2-A(H2S)0.8 623 K, 2 days

623 K, 7 days 298 K, 1 day 623 K, 2 days 298 K, 3 hrs 12.083(3) 240 50 30 0.069, 0.062 1.60




R1 ) ∑(Fo - |Fc|)/∑ Fo. b R2 ) (∑(w(Fo -|Fc|)2/ ∑wFo2)1/2. c Goodness of fit ) (∑w(Fo - |Fc|)2/(m - s))1/2.

2. Experimental Section 2.1. Sample Preparation. Crystals of zeolite A (Na12Si12Al12O48, Na-A) were prepared and provided by Kokotailo and Charnell.16 These crystals were from the same batch as all previous zeolite A single crystals reported from N. H. Heo’s laboratory. Colorless single crystals, cubes about 80 µm on an edge, of fully Tl+-exchanged zeolite A (Tl12Si12Al12O48, TlA),15,17,18 were prepared by dynamic ion-exchange (flow method) of Na-A with an aqueous solution of 0.1 M thallium acetate (pH ) 6.4, Aldrich, 99.99%) for 3 days at 294 K. Several Tl-A crystals, each in its own fine Pyrex capillary, were completely dehydrated (623 K and 1 × 10-6 Torr for 2 days)15,17,18 and were brought into contact with In0 (Aldrich, 99.999%) at 623 K for 5 days. This was achieved as described before11 by condensing In0 around the crystal whose temperature was somewhat lower than that of the metal in coaxially connected heating ovens. Although the vapor pressure of In(l) is reported to be very low at 623 K (ca. 2.92 × 10-10 N/m2 ) 2.19 × 10-12 Torr),19 droplets of In were seen to form very close to the zeolite crystals. Except for this reversed temperature gradient during the reaction period, other experimental procedures for the reaction were similar in detail to those previously described for solvent-free ion exchange.11,15,20-22 The color of the resulting crystals, still under vacuum in their capillaries, was pale yellow. Upon exposure to air, they became black. Four of these black crystals, after washing with deionized water (still black after washing), were again dehydrated as before. The crystals, now In11-A, were again colorless to pale yellow and transparent. (Previous EXMPA and XPS studies have demonstrated that this procedure results in the complete replacement of Tl by In in zeolite A15,23,24 and zeolite X23,24) After exposure to 0.5 atm of hydrogen sulfide (Fisher, 99.5%; zeolitically dried in situ) for 3 h at 298, 373, 423, and 573 K for crystals 1 to 4, respectively, and evacuation at reaction temperature followed by cooling to 294(2) K, each one of these crystals, still under vacuum, was then sealed in its capillary with a small flame. Still protected from the atmosphere in their capillaries, crystals 1 to 4 were seen under the microscope to be pale red, brown, dark yellow, and yellow, respectively. 2.2. Crystallographic Work. The cubic space group Pm3hm (no systematic absences) was used throughout this work for reasons discussed previously.25,26 A CAD4/Turbo diffractometer equipped with a rotating anode generator and a graphite monochromator was used for preliminary experiments and for the subsequent collection of diffraction intensities, all at 294(2) K. Molybdenum radiation was used for all experiments (KR1, λ ) 0.709 30 Å; KR2, λ ) 0.713 59 Å). The unit cell constants (a ) 12.083(3), 12.076(2), 12.094(2), and 12.094(2) Å for

crystals 1 to 4, respectively) were each determined by leastsquares refinement of 15 intense reflections for which 20° < 2θ < 30°. For intensity measurements, each reflection was scanned by the θ-2θ method at a constant scan speed of 0.5°/ min in 2θ. Background intensity was counted at each end of a scan range for a time equal to half the scan time. The intensities of three reflections in diverse regions of reciprocal space were recorded every 3 h to monitor crystal and instrumental stability. Only small random fluctuations of these check reflections were observed during the course of data collection. The intensities of all lattice points for which h ) k ) l and 2θ < 70° were recorded. Intensities were calculated as Iraw ) ATN(C - RB)/NPI, where C ) scan count, R ) ratio of scan time to total background counting time (1.0), B ) total background count, NPI ) ratio of fastest possible scan rate to scan rate for each measurement, and ATN ) attenuation factor, respectively. The observed structure factor amplitude of each reflection (Fo) was then obtained as the square root of Iraw after correction for Lorentz-polarization (Lp); the contribution of the monochromator crystal was calculated assuming it to be half-perfect and half-mosaic in character. Standard deviations (σ(Fo)) of observed structure factors were assigned to individual reflections by the formula (σ2(I) + (pFo2))1/2/2Fo, where σ(I) is the standard deviation, based on counting statistics, of Iraw. The value p ) 0.04 was found to be appropriate for the instrumentation used. Absorption corrections were judged to be unimportant for these crystals, because semiempirical ψ-scans for all crystals (µ ) 3.71, 3.57, 3.71, and 3.70 mm-1 for crystals 1 to 4, respectively)27 showed only negligible fluctuations for several reflections. Of the unique reflections examined, only those for which the net count I exceeded 3σ(I) were used in structure solution and refinement. This amounted 240, 169, 227, and 257 for crystals 1 to 4, respectively. Other experimental data are summarized in Table 1. 3. Structure Determination 3.1. In9.5H0.5-A‚(InSH)0.5(H2S)2.5 (Crystal 1). Full-matrix least-squares refinement28 began with the atomic parameters of the framework atoms [(Si,Al), O(1), O(2), and O(3)] and In(1) (see Table 2a) in In11-A.15 Refinement with isotropic thermal parameters converged to the error indices (defined in footnotes to Table 1) R1 ) 0.43 and R2 ) 0.49 with an occupancy of 2.9 at In(1). The progress of structure determination as subsequent peaks were found on difference Fourier functions and identified as indium ions or atoms is given in Table 3a. Finally, refinements with three additional peaks from a Fourier difference function refined isotropically as sulfur atoms at S(1) (0.276, 0.5, 0.5), S(2) (0.359, 0.452, 0.5), and S(3)

4580 J. Phys. Chem. B, Vol. 106, No. 18, 2002

Heo et al.

TABLE 2: Positional, Thermal, and Occupancy Parametersa Wyckoff position

x

y

z

U11 or Uiso

U22

U33

U12

(Si,Al) O(1) O(2) O(3) In(1) In(2) In(3) In(4) In(5) In(6) In(7) In(8) In(9) In(10) S(1) S(2) S(3)

24(k) 12(h) 12(i) 24(m) 8(g) 8(g) 8(g) 12(h) 24(l) 1(a) 12(j) 8(g) 24(m) 8(g) 6(f) 24(l) 24(m)

0 0 0 1133(5) 2546(3) 1318(3) 1023(17) 0 746(38) 0 3111(48) 2198(18) 353(21) 3848(51) 2756(132) 3587(84) 2345(98)

1825(3) 2036(12) 3011(7) 1133(5) 2546(3) 1318(3) 1023(17) 4272(18) 4016(39) 0 3111(48) 2198(18) 4479(15) 3848(51) 5000d 4515(71) 3794(61)

(a) In9.5H0.5-A(InSH)0.5(H2S)2.5, crystal 1 3678(3) 131(14) 137(15) 80(14) 0 5000d 941(120) 550(101) 143(70) 0 3011(7) 400(80) 252(45) 252(45) 0 3246(8) 412(36) 412(36) 411(57) 157(50) 2546(3) 298(10) 1318(3) 41(10) 1023(17) 342(89) 5000d 570(76) 5000d 760(127) 0 76(25) 5000d 1140(25) 2198(18) 63(76) 4479(15) 304(76) 3848(51) 1393(380) 5000d 633(380) 5000d 4(231) 3794(61) 3166(633)

(Si,Al) O(1) O(2) O(3) In(1) In(2) In(3) In(4) In(6) In(8) In(10) S(1) S(2)

24(k) 12(h) 12(i) 24(m) 8(g) 8(g) 8(g) 48(n) 1(a) 8(g) 8(g) 6(f) 48(n)

0 0 0 1129(6) 2565(3) 1332(4) 1079(10) 251(12) 0 2242(12) 3760(19) 2474(80) 2508(102)

1825(4) 2022(13) 3015(8) 1129(6) 2565(3) 1332(4) 1079(10) 4379(9) 0 2242(12) 3760(19) 5000d 3450(98)

(b) In8.4H1.2-A(In2S)0.6(H2S)2, crystal 2 3672(4) 165(18) 102(18) 57(17) 0 5000d 654(115) 538(115) 20(70) 0 3015(8) 278(84) 166(49) 166(49) 0 3247(8) 464(43) 464(43) 218(60) 213(65) 2565(3) 228(13) 1332(4) 63(13) 1079(10) 342(51) 4756(14) 608(63) 0 13(25) 2242(12) 291(63) 3760(19) 1588(152) 5000d 1381(317) 4234(90) 1343(659)

U13

U23

0 0 0 -133(38)

-1(17) 0 -19(68) -133(38)

0 0 0 -43(48)

21(20) 0 60(74) -43(48)

occupancyb fixed varied 24c 12 12 24 3.0 2.0 0.5 1.0 0.5 0.5 0.5 0.5 1.0 0.5 0.5 0.5 2.0

3.19(3) 2.03(2) 0.46(3) 0.94(4) 0.78(7) 0.51(1) 0.41(5) 0.35(2) 0.85(4) 0.30(4) 0.43(10) 0.57(12) 2.68(36)

24c 12 12 24 2.8 1.6 0.6 2.4 0.4 0.6 1.2 1.0 1.6

2.82(3) 1.64(3) 0.96(3) 2.66(4) 0.42(1) 0.74(3) 1.04(5) 1.31(13) 1.90(33)

a Positional and thermal parameters are given × 104. 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 and (Al) ) 12. d Exactly 0.5 by symmetry.

TABLE 3: Steps of Structure Determination as Indium Positions Are Found step/ In(i)

1

2

occupancies per unit cell 3 4 5 6 7 8

9

error indicesb 10 R1 R2

(a) In9.5H0.5-A(InSH)0.5(H2S)2.5, crystal 1 1 2 3 4 5 6a 7a 8a

2.9 2.7 3.3 3.5 3.2 3.2 3.2 3.2

1 2 3 4 5 6 7a

3.2 3.6 3.6 3.5 3.0 3.0 2.9

1.7 2.6 2.2 2.2 2.2 2.2 2.1 0.4

2.1 2.0 1.8 1.8 1.1

0.2 0.3 0.5 0.6

0.6 0.6 0.6 0.4 0.6 0.3 0.6 0.4 0.4 0.5 0.4 0.4

0.43 0.24 0.20 0.11 0.11 0.10 0.4 0.084 0.8 0.4 0.078

0.49 0.30 0.28 0.12 0.11 0.11 0.092 0.068

(b) In8.4H1.2-A(In2S)0.6(H2S)2, crystal 2 2.0 1.9 2.5 2.4 1.6 1.0 2.6 1.6 0.9 2.5 1.6 0.8 2.4

0.5 0.4 0.5 0.4 0.4

0.6 0.7 0.7

0.33 0.23 0.18 0.13 0.10 1.3 0.078 1.5 0.072

0.41 0.30 0.25 0.15 0.13 0.078 0.067

a Framework atoms were allowed to refine anisotropically. b Defined in footnotes to Table 1.

(0.235, 0.379, 0.379) converged to R1 ) 0.067 and R2 ) 0.059 with refined occupancies given in Table 2a. The occupancies at the sulfur positions were fixed at values close to those from crystallographic refinement, but modified (a little) where necessary to give charge balance and plausible coordination numbers and geometries. (Sulfur atoms should be in the 2-oxidation state so, unlike indium ions, they should not

approach oxygens of the zeolite framework closely. This and their very different X-ray scattering factors allow S positions to be distinguished from In.) The final cycles of the refinement were carried out with occupancies fixed at the values given in Table 2a. This model converged to the final error indices R1 ) 0.069 and R2 ) 0.062. In the last cycle of least-squares refinement, all shifts were less than 1% of their corresponding esds. Final structural parameters are presented in Table 2a and selected interatomic distances and angles are given in Table 4. 3.2. In8.4H1.2-A(In2S)0.6(H2S)2 (Crystal 2). Full-matrix leastsquares refinement28 of crystal 2 began with the same initial parameters used for crystal 1. Refinement with isotropic thermal parameters converged with the error indices R1 ) 0.33 and R2 ) 0.41 with an occupancy of 3.2 at In(1). As with crystal 1, the steps in the determination of the indium positions are described in Table 3b. Finally, refinements with two additional peaks from a Fourier difference function, refined isotropically as sulfur atoms at S(1) (0.247, 0.5, 0.5) and S(2) (0.251, 0.345, 0.423) converged to R1 ) 0.058 and R2 ) 0.052 with resulting occupancies given in Table 2b. The final cycles of the refinement were carried out with occupancies fixed at the values given in Table 2b. This model converged to the final error indices R1 ) 0.063 and R2 ) 0.058. Final structural parameters are presented in Table 2b and selected interatomic distances and angles are given in Table 4. 3.3. Crystals 3 and 4. The structures of crystals 3 and 4 were similarly determined.29 The final structure of crystal 3 was



TABLE 4: Selected Interatomic Distances (Å) and Angles (deg)a

TABLE 5: Deviations of Atoms (Å) from the (111) Plane at O(3)a

(a) In9.5H0.5-A(InSH)0.5(H2S)2.5, crystal 1 (Si,Al)-O(1) (Si,Al)-O(2) (Si,Al)-O(3)

1.617(5) 1.644(10) 1.687(9)

In(1)-O(3) In(1)-O(2) In(2)-O(3) In(2)-O(2) In(3)-O(3) In(3)-O(2) In(4)-O(2) In(4)-O(1) In(5)-O(2) In(5)-O(1) In(8)-O(3) In(8)-O(2) In(9)-O(2) In(9)-O(1) In(6)-O(3) S(3)-O(3) S(3)-O(2)

2.575(8) 3.187(4) 2.352(11) 3.302(7) 2.687(12) 3.608(21) 2.838(23) 2.68(5) 2.85(4) 2.54(8) 2.235(16) 3.004(21) 2.554(20) 3.053(34) 4.375(10) 3.51(14) 3.01(17)

In(2)-In(6) In(3)-In(6) In(4)-S(3) In(5)-S(3) In(9)-S(3) In(10)-S(3) In(10)-S(1) S(1)-S(3) S(2)-S(3) In(1)-In(7)

2.759(3) 2.152(18) 3.17(16) 3.57(15) 3.40(17) 3.48(13) 2.39(12) 3.85(17) 3.92(17) 3.087(15)

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

110.3(8) 112.6(5) 106.3(3) 108.4(5)

(Si,Al)-O(1)-(Si,Al) (Si,Al)-O(2)-(Si,Al) (Si,Al)-O(3)-(Si,Al) O(3)-In(1)-O(3) O(2)-In(1)-O(2) O(3)-In(2)-O(3) O(2)-In(2)-O(2) O(3)-In(3)-O(3) O(2)-In(3)-O(2) O(1)-In(4)-O(2) O(1)-In(5)-O(2) O(3)-In(8)-O(3) O(2)-In(8)-O(2) O(1)-In(9)-O(2)

161.8(14) 148.8(6) 135.2(7) 89.1(3) 107.6(2) 100.4(3) 102.4(8) 84.5(7) 90.9(7) 57.9(8) 59.2(14) 107.9(3) 117.8(5) 56.2(2)

In(2)-In(6)-In(2) In(1)-In(7)-In(1) In(4)-S(3)-S(2) In(4)-S(3)-S(1) In(5)-S(3)-S(2) In(9)-S(3)-In(10) In(10)-S(1)-S(3) S(1)-In(10)-S(3) S(3)-S(2)-S(3)

109.5(2)b 145.8(18) 119(1) 128(4) 106(2) 107.0(16) 124(7) 144(4) 117(4)

(b) In8.4H1.2-A(In2S)0.6(H2S)2, crystal 2 (Si,Al)-O(1) (Si,Al)-O(2) (Si,Al)-O(3)

1.618(7) 1.636(13) 1.685(11)

In(1)-O(3) In(1)-O(2) In(2)-O(3) In(2)-O(2) In(3)-O(3) In(3)-O(2) In(4)-O(2) In(4)-O(1) In(6)-O(2) In(8)-O(3) In(8)-O(2)

2.567(10) 3.182(6) 2.351(15) 3.294(9) 2.647(6) 3.563(13) 2.705(20) 2.906(31) 4.374(14) 2.230(20) 2.999(10)

In(2)-In(6) In(3)-In(6) In(4)-S(1) In(4)-S(2) In(10)-S(2) In(10)-S(1) S(1)-S(2)

2.754(5) 2.213(15) 3.364(13) 3.5(3) 3.7(3) 2.61(8) 4.2(3)

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

111.8(9) 111.6(7) 106.3(4) 109.0(7)

(Si,Al)-O(1)-(Si,Al) (Si,Al)-O(2)-(Si,Al) (Si,Al)-O(3)-(Si,Al) O(3)-In(1)-O(3) O(2)-In(1)-O(2) O(3)-In(2)-O(3) O(2)-In(2)-O(2) O(3)-In(3)-O(3) O(2)-In(3)-O(2) O(1)-In(4)-O(2) O(3)-In(8)-O(3) O(2)-In(8)-O(2)

164.7(18) 148.9(7) 135.5(9) 89.2(5) 107.5(2) 100.1(4) 102.4(1) 85.9(3) 92.2(2) 57.3(4) 107.9(13) 117.7(6)

In(2)-In(6)-In(2) In(4)-S(1)-S(2) In(4)-S(2)-S(1) In(4)-S(2)-In(10) In(10)-S(1)-In(10) S(1)-In(10)-S(2)

109.5(3)b 138(4) 129(6) 98(6) 103(5) 135(4)

a The numbers in parentheses are the estimated standard deviations in the units of the least significant digit given for the corresponding parameters. b The tetrahedral angle by symmetry.

insignificantly different from that of crystal 1 except that crystal 3 had only one sorbed H2S molecule rather than three per unit cell. Crystal 4 had fewer than one sorbed H2S per unit cell deep in large cavity; otherwise its composition and structure was about the same as the In-A sorbant. Their chemical formulas and crystallographic data are summarized in Table 1. Their structural parameters are included in the supporting material. 3.4. Scattering Factors. All atomic scattering factors were taken from the International Tables for X-ray Crystallogra-

charge In(1) In(2) In(3) In(6) In(8) In(10)

+1 +1.75 +1 0 +3 +1

In9.5H0.5-A(InSH)0.5(H2S)2.5 In8.4H1.2-A(In2S)0.6(H2S)2 (crystal 1) (crystal 2) 1.50 -1.09b -1.70b -3.85b,c 0.75 4.21

1.53 -1.05b -1.58b -3.84b,c 0.85 4.03

a The more positive the Inn+ ion, the more closely it approaches the plane of the O(3) oxygens. b A negative deviation indicates that the ion lies on the same side of the plane as the origin, i.e., inside the sodalite unit. c Located at the origin, at the center of the sodalite unit.

phy.30,31 Atomic scattering factors for In3+, In2+, In+, In0, S0, and (Si,Al)1.75+ were used. Because the cubic space group Pm3hm does not distinguish between Al and Si positions, the scattering factor of (Si,Al)1.75+, the mean of the Si0, Si4+, Al0 and Al3+ scattering functions, was used. Scattering factors for In2+ and In+ were calculated from those of In3+ and In0: In2+ ) (2In3+ + In0)/3 and In+ ) (In3+ + 2In0)/3. All scattering factors were modified to account for anomalous dispersion.32,33 3.5. Assignment of Oxidation State to In. The oxidation state at each indium position is identified on the basis of its approach distances to framework atoms and sulfur atoms (see section 4.4) with the general expectation that indium ions furthest from framework oxygens should have the smallest cationic charges, as was done in In11-A and In8.75-A(S2).11,15 The requirement of electrical neutrality was also used to select the fixed occupancies in Table 2. 4. Results and Discussion 4.1. Assignment of Oxidation States to Indium Cations. Each of the indium ions at In(1) (3.0 in crystal 1 and 2.8 in crystal 2) is 2.575(8) and 2.567(10) Å, respectively, from three six-ring oxygens at O(3) (see Table 4). These indium ions extend 1.50 and 1.53 Å into the large cavity from the (111) planes at O(3) in these two crystals, respectively (see Table 5). Considering the ionic radii of the framework oxygens to be 1.32 Å,34,35 the radii of these indium ions must be ca. 2.58 (2.57 for crystal 2) - 1.32 ) 1.26 (1.25 for crystal 2) Å, essentially identical to that seen for In+ in In11-A, 1.25 Å.15 This is somewhat shorter than the In+ radii seen in various indium halides, which range from 1.32 to 1.51 Å.36,37 However, similarly shortened radii have been found for Tl+ ions in zeolites: ca. 1.30 vs. ca. 1.47 Å in various thallium halides, respectively,17,18 probably due to the low coordination number of these ions in the dehydrated zeolite. An even smaller radius, 1.17 Å, was suggested for In+ by a theoretical calculation using the numerical HF method.38 Accordingly, the oxidation state of the indium ions at In(1) appears to be 1+. Similarly, 2.5 and 2.4 In+ ions per unit cell in crystals 1 and 2, respectively, are found at three different positions (In(4), In(5), and In(9)) in crystal 1 and one position (In(4)) in crystal 2, all near eight-ring planes. Their approach distances to nearest eightring oxygens are within the range discussed above for In+ ions at In(1): In(4)-O(1) ) 2.68(5), In(5)-O(1) ) 2.54(8), and In(9)-O(2) ) 2.55(2) Å in crystal 1 and In(4)-O(2) ) 2.71(2) Å in crystal 2 (see Table 4). Some of these approach distances are somewhat longer, probably due to differences in their environments, including approaches to sorbed sulfur compounds (see sections 4.3 and 4.4). Also, monopositive cations commonly approach eight-ring oxygens at longer distances than six-ring oxygens in zeolite A.17,18,20,21,34

4582 J. Phys. Chem. B, Vol. 106, No. 18, 2002 For the same reasons, the indium ion at In(3) is also judged to be In+. Its approach distances to the nearest six-ring oxygens, three O(3)s, are 2.69(1) and 2.65(1) Å in crystals 1 and 2, respectively. The radii of these indium ions must be ca. 2.69 (2.65 for crystal 2) - 1.32 ) 1.37 (1.33 for crystal 2) Å, which are also somewhat longer than those of the corresponding In+ ions at In(1). Again, such a difference is commonly seen for many cations located in the sodalite unit.17,18,20,21 Each of the 2.0 and 1.6 indium ions per unit cell at In(2) in crystals 1 and 2 is 2.35(1) and 2.35(2) Å, respectively, from three six-ring oxygens at O(3) (see Table 4). The radii of these indium ions are both ca. 2.35-1.32 ) 1.03 Å, sharply less than those of the In+ ions, indicating a higher oxidation state, probably In2+. This value, 1.03 Å, is somewhat longer than the average value, 0.95 Å, of the ionic radii of Cd2+ (0.97 Å) and Sn2+ (0.93 Å),35,39 the adjacent 2+ cations in the periodic table. This is probably because of the reduced cationic character at In(2) due to association with the In0 atoms at the center of the sodalite unit (see section 4.2). These In2+ ions may have been produced by the well-known disproportionation of In+ ions, i.e. 2In+ f In2+ + In0, upon exposure of the crystal to the atmosphere just after reaction with In0.40 In2+ ions had been seen before only in fully indium exchanged zeolite A,15 its sulfur sorption complex,11 and in some indium trihalide dimers41 such as [In2Cl6]2-. In2+ ions have an odd number of electrons and are unstable unless they participate in clusters such as those at In(2). See the last paragraph of section 4.2. Each of 0.5 and 0.6 indium per unit cell at In(8) in crystals 1 and 2, respectively, is found to be sharply closer than all others to framework oxygens. The radius of these indiums is ca. 2.24 (2.23 for crystal 2) - 1.32 ) 0.92 (0.91 for crystal 2) Å. This is somewhat longer than those found for In3+, which range from 0.77 to 0.87 in various indium oxides and indium sulfide,42,43 but shorter than that found for In2+. In3+, like In2+, may also have formed by the disproportionation of In+. The failure of In(6) to approach the negatively charged framework oxygens indicates that atoms, not cations, are located there. 4.2. Indium Atoms and Clusters. The location of indium atoms at In(6), at the very center of the sodalite units in both crystals, is unambiguous because no other chemically possible atom or ion, such as Si, Al, O, or S, could account for the high electron density found at this special position. As atoms, they may preferentially approach cations, to which they could delocalize electron density, rather than framework oxygens. Indeed, they are reasonably close to the indium cations at In(2) and In(3) in the sodalite units. These In0 atoms at In(6) might have been retained during the reaction between In0 and Tl-A, or might have been produced by disproportionation during later exposure to the atmosphere or to hydrogen sulfide, or both. The possible In(6) to In(3) approach distance (ca. 2.15 and 2.21 Å in crystals 1 and 2, respectively) is unreasonably short when compared to 2.92 Å, the sum of the atomic radius of In0 (1.67 Å) and the ionic radius of In+ (ca. 1.25 Å); it can readily be avoided by not putting both In(6) and In(3) in the same sodalite units. However, the In(6)-In(2) distance (2.759(3) and 2.754(5) Å for crystals 1 and 2, respectively) is reasonable, comparable to 2.70 Å, the sum of the atomic radius of In0 and the ionic radius of In2+ (1.03 Å). The association of In0 at In(6) with In(2) supports the rather longer approach distances of In2+ at In(2) to the six-ring oxygens, due to the reduced cationic character of In2+. These reasonable distances between In0 and In2+ indicate that clusters such as (In2)2+, (In3)4+ (linear or bent), (In4)6+, or (In5)8+ (four In2+ ions tetrahedrally arranged in the

Heo et al. sodalite unit with an In0 at their center) exist. The final paragraph of this section argues that the latter are (In5)7+ clusters. With the occupancies of 0.5 and 0.4 at In(6) for crystals 1 and 2, respectively, the presence of a mixture of the clusters (In2)2+, (In3)4+, or (In4)6+ would require the sodalite units to have nonequivalent In2+ ions in the vicinity of In(2), as well as nonequivalent In0 atoms near the present In(6) position. However, differentiation of these two kinds of In2+ and In0 at In(2) and In(6), respectively, was impossible crystallographically and is not suggested by the small thermal parameters at both In(2) and In(6) (see Table 2). The (In5)8+ cluster was found in fully indium-exchanged zeolite A,15 and the ratios of their occupancies (In(2)/In(6)), 2.0/0.5 ) 4.0 and 1.6/0.4 ) 4.0 in crystals 1 and 2, respectively, have always been observed to be 4.0 in various structures in this system.11,15,44 These considerations strongly suggest that only the highly symmetric (In5)8+ cluster (see final paragraph of this section), with four In2+ ions at In(2) placed tetrahedrally about an In atom at In(6), is present in about half of the sodalite units (unit cell 1), whereas the other half (unit cell 2) contain only an In+ ion at In(3). By the same arguments, indium atoms must occupy the In(7) position in crystal 1, deep in the large cavity. These atoms must associate with In+ ions at In(1) or those near the eight-ring planes. Of the possible inter-indium distances, only In(7)-In(1) ) 3.09(2) Å is acceptable, as seen in In11-A and In8.75-A(S2) system.11,15 Considering the sum of the ionic and atomic radii, 2.92 Å ) 1.25 (rIn+) + 1.67 (rIn0) Å, and the inter-indium distances of 2.759(3) Å for In2+-In0, the most plausible cluster is (In3)2+, In(1)-In(7)-In(1), with In+-In0 distances of 3.09(2) Å and an angle of 146(2)o (see Table 4). (In5)8+ is an odd species which may be viewed as having seven electrons around the central atom. (In5)7+ with eight electrons around the central atom seems far more likely, and is consistent with its apparent stability, having been found in all four crystals and in zeolite X.11,15,44,45 A formal charge of 1.75+ at In(2) is as acceptable as the integral formal charge of 2+ assigned in the previous section. A simpler argument is not made for the (In3)2+ cluster, which is also an odd species, because it is not widely seen; (In3)+ would have an octet of electrons about the central atom. 4.3. InSH, In2S, H2S, and their Sorption Sites. The environments of the sulfur ions or atoms allowed In2S, InSH, and sorbed H2S molecules to be identified in both crystals. The In-S bond length is ca. 2.56 Å46 in various indium sulfide compounds, including InSH and In2S. Sorbed sulfur atoms, e.g., Sn or sulfur in covalent compounds such as H2S, are expected to approach indium cations at noticeably longer distances, from 3.14 to 3.40 Å (rS0(vdw) + rIn+ ) 1.89 + 1.25 (or 1.51) Å); the range 3.26 to 3.45 Å is actually observed for such approach distances.11 The hydrogen bonding distances between H2S molecules are much longer, ca. 3.94 Å.47 In crystal 1, In9.5H0.5-A‚(InSH)0.5(H2S)2.5, a total of 3.0 sulfur atoms were found at three crystallographic positions: 0.5 at S(1), 0.5 at S(2), and 2.0 at S(3), respectively. First of all, considering the approach distances of S(3) to several large-cavity In+ ions, such as S(3)-In(4) ) 3.17(16), S(3)-In(5) ) 3.57(15), S(3)-In(9) ) 3.40(17), and S(3)-In(10) ) 3.48(13) Å, and to other sulfur atoms via hydrogen bonds, such as S(3)-S(1) ) 3.85(17) and S(3)-S(2) ) 3.92(17) Å, the sulfur atoms at S(3) appear to represent sorbed H2S molecules. Furthermore, a consideration of the occupancies at S(2) and S(3) (see Table 6) strongly suggested the presence of a weakly constituted In(4)S(3)-S(2)-S(3)-In(5) cluster, [(In)(H2S)3(In)]2+, deep in the large cavities of some unit cells. The angles in this cluster would



TABLE 6: Distribution of In and S Species in Component Unit Cells (a)In9.5H0.5-A(InSH)0.5(H2S)2.5, crystal 1 In9-A(H2S)3 unit cell 1 (50%) In and S species In(1) In(2) In(3) In(4) In(5) In(6) In(7) In(8) In(9) In(10) S(1) S(2) S(3) H ∑(S) ∑(In) (In5)7+ (In3)2+ [(In)2(H2S)2]2+ [(In)2(InSH)(H2S)2]2+ In+ In+ In+ In3+ H+ ∑(S) ∑(In)

position

no.

average

charge

no.

charge

no.

charge

+1 +7 0 +1 +1 0 0 0 +1 0 0 0 0 0 0 +11

5 0 1 1 0 0 1 1 1 1 1 0 2 1 3 11

+5 0 +1 +1 0 0 0 +3 +1 +1 -1 0 0 +1 -1 +12

3.0 2.0 0.5 1.0 0.5 0.5 0.5 0.5 1.0 0.5 0.5 0.5 2.0 0.5 3.0 10.0

+3.0 +3.5 +0.5 +1.0 +0.5 0 0 +1.5 +1.0 +0.5 -0.5 0 0 +0.5 -0.5 +11.5f

(b) As monatomic and polyatomic cations (4In(2), In(6))c +7 1 +7 (2In(1), In(7))a +2 0 0 (In(5), In(4), S(2), 2S(3))a +2 1 +2 a (In(10)-S(1), In(4), In(9), 2S(3)) +2 0 0 In(1)a +1 1 +1 In(3)c +1 0 0 In(9)a +1 1 +1 In(8)a +3 0 0 +1 0 0 3 0 9 +11

0 1 0 1 3 1 0 1 1 3 11

0 +2 0 +2 +3 +1 0 +3 +1 0 +11

0.5 0.5 0.5 0.5 2.0 0.5 0.5 0.5 0.5 3.0 10.0

+3.5 +1.0 +1.0 +1.0 +2.0 +0.5 +0.5 +1.5 +0.5 0 +11

opposite 6-ringa,b opposite 6-ringb,c opposite 6-ringb,c 8-ringa,d 8-ringa,d originc,e opposite 4-ringa opposite 6-ringa,b 8-ringa,d opposite 6-ringa,b

charge

In10H-A(InSH)(H2S)2 unit cell 2 (50%)

(a) As individual ions or atoms +1 1 +1.75 4 +1 0 +1 1 +1 1 0 1 0 0 +3 0 +1 1 +1 0 0 (or -1) 0 0 1 0 2 +1 0 3 9

(b) In8.4H1.2-A(In2S)0.6(H2S)2, crystal 2 In9-A(H2S)2 unit cell 1 (40%) In and S species In(1) In(2) In(3) In(4) In(6) In(8) In(10) S(1) S(2) H ∑(S) ∑(In) (In5)7+ [(In)2(H2S)2]2+ [(In)2(In2S)(H2S)2]2+ In+ In+ In+ In3+ H+ ∑(S) ∑(In)

position

no.

charge

average

no.

charge

no.

charge

+1 +7 0 +3 0 0 0 0 0 0 0 +11

4 0 1 2 0 1 2 1 2 2 3 10

+4 0 +1 +2 0 +3 +2 -2 0 +2 -2 +12

2.8 1.6 0.6 2.4 0.4 0.6 1.2 1.0 1.6 1.2 2.6 9.6

+2.8 +2.8 +0.6 +2.4 0 +1.8 +1.2 -1.2 0 +1.2 -1.2 +11.6f

(b) As monatomic and polyatomic cations (4In(2), In(6))c +7 1 +7 (2In(4), S(1), S(2))a +2 1 +2 (In(10)-S(1), 2In(4), 2S(2))a +2 0 0 In(1)a +1 1 +1 In(3)c +1 0 0 In(4)a +1 1 +1 a In(8) +3 0 0 +1 0 0 2 0 9 +11

0 0 1 4 1 0 1 2 3 10

0 0 +2 +4 +1 0 +3 +2 0 +10

0.4 0.4 0.6 2.8 0.6 0.4 0.6 1.2 2.6 9.6

+2.8 +0.8 +1.2 +2.8 +0.6 +0.4 +1.8 +1.2 0 +10.4

opposite 6-ringa,b opposite 6-ringb,c opposite 6-ringb,c 8-ringa,d originc,e opposite 6-ringa,b opposite 6-ringa,b

charge

In8H2-A(In2S)(H2S)2 unit cell 2 (60%)

(a) As individual ions or atoms +1 1 +1.75 4 +1 0 +1 3 0 1 +3 0 +1 0 0 (or -2) 1 0 1 +1 0 2 9

a In the large cavity. b On 3-fold axes. c In the sodalite unit. d Off the 8-ring plane. e At the origin, at the center of sodalite unit. f The failure of the charges of the indium ions to sum to 12+ per unit cell indicates either that additional H+ ions are present (these may have left the zeolite with framework oxygens as water), or that framework oxygens have partially reduced indium cations and have left the zeolite as dioxygen gas. Only a fraction of an ion or atom per unit cell would be involved; this would not be observable crystallographically.

be In(4)-S(3)-S(2) ) 119(1)°, S(3)-S(2)-S(3) ) 117(4)°, and S(2)-S(3)-In(5) ) 106(2)°. The In+ ions at In(9) and In(10) and the sulfur atoms at S(1) were excluded from this

cluster because they are more closely involved with another similar cluster, one with an InSH molecule in it (see section 4.4).


Heo et al.

Figure 1. Stereoview of a sodalite unit in In9-A(H2S)3 (unit cell 1 of crystal 1, In9.5H0.5-A(InSH)0.5(H2S)2.5) with an (In5)7+ cluster in its center. The zeolite A framework is drawn with solid bonds between tetrahedrally coordinated (Si,Al) and oxygen atoms. Thick solid lines are used to indicate the bonds among the In ions and atoms. Fine ones are used for the bonds between In ions and framework oxygens. Ellipsoids of 20% probability are shown.

The indium atom at In(10) is located deep in the large cavity, where only the S(1) and S(3) positions are in its primary coordination sphere. The In(10)-S(1) distance is 2.39(12) Å, a reasonable value for an In-S bond length as observed in various indium sulfides.46 Furthermore, their occupancies are the same, 0.5 per unit cell, indicating their simultaneous presence in onehalf of the unit cells of crystal 1. Considering this and the occupancies of 0.5 and 2.0 for In+ ions at In(9) and sulfur atoms at S(3), respectively, it seems reasonable to recognize the presence of In(4)-S(3)-S(1)-In(10)-S(3)-In(9) cluster, [(In)(H2S)(HSIn)(H2S)(In)]2+, with In(4)-S(3)-S(1) ) 128(4)°, S(3)-S(1)-In(10) ) 124(7)°, S(1)-In(10)-S(3) ) 144(4)°, and In(10)-S(3)-In(9) ) 107(2)°. In crystal 2, In8.4H1.2-A‚(In2S)0.6(H2S)2, a total of 2.6 sulfur atoms per unit cell was found at two crystallographic positions: 1.0 sulfur atom at S(1) and 1.6 at S(2), both deep in the large cavity. The S(1) position is very similar to that found in crystal 1, where it bonds to an In+ ion at In(10) as InSH. Indeed, as in crystal 1, the sulfur atoms at S(1) have similar bond distances to In+ ions at In(10), but this time to two In+ ions, indicating the presence of In2S, with a possible charged van der Waals (sorption) distance to In+ ions at In(4) (S(1)-In(4) ) 3.36(1) Å). The In(10)-S(1) distance, 2.61(8) Å, is very close to those found in various indium sulfides, ca. 2.56 Å.46 Furthermore, these In+ ions at In(10) are 3.7(3) Å from the sulfur atoms of sorbed H2S molecules at S(2), which in turn approach In+ ions at In(4) near the eight-ring planes (S(2)-In(4) ) 3.5(3) Å). This again suggests the presence of a In(4)-S(2)-In(10)S(1)-In(10)-S(2)-In(4) cluster, [(In)(H2S)(InSIn)(H2S)(In)]2+, with a local symmetry of C2 about S(1) and bond angles of In(4)-S(2)-In(10) ) 98(6)°, S(2)-In(10)-S(1) ) 135(4)°, and In(10)-S(1)-In(10) ) 103(5)°. Considering the occupancies of 2.4, 1.6, 1.2, and 1.0 at In(4), S(2), In(10), and S(1), respectively, only 60% of the unit cells could have this cluster in their large cavities. The other 40% would have a somewhat simpler cluster, In(4)-S(1)-S(2)-In(4), [(In)(H2S)2(In)]2+, without the central In2S molecule. Its bond lengths would be In(4)-S(1) ) 3.364(13) Å, In(4)-S(2) ) 3.54(26) Å, and S(1)S(2) ) 4.18(25) Å (a hydrogen bond), with bond angles of In(4)-S(1)-S(2) ) 138(4)° and S(1)-S(2)-In(4) ) 129(6)°. 4.4. Arrangement of Indium and Sulfur Species. The fractional occupancies observed for both crystals 1 and 2 can be described in terms of two kinds of “unit cells” for each. Because the In+ ions at In(3) and In(6) are too close to coexist in the same sodalite unit, one kind of unit cell in each structure must contain only In(3) and the other only In(6). The occupancies at In(2) and In(6), positions seen before in the sodalite units of zeolites A11,15 and X,45 indicate that 50% of the unit cells in

crystal 1 and 40% in crystal 2 contain (In5)7+ clusters11,15,45 in their sodalite units (unit cell 1), whereas the remainder (unit cell 2) do not (see Table 6). By completing each unit cell reasonably, avoiding contacts which are too short and distributing cationic charge most evenly, the formulas In9-A(H2S)3 (unit cell 1) and In10H-A(InSH)(H2S)2 (unit cell 2) for crystal 1 and In9-A(H2S)2 (unit cell 1) and In8H2-A(In2S)(H2S)2 (unit cell 2) for crystal 2, respectively, emerge. For each crystal, the placements of the various indium atoms and ions, and the In2S, InHS, and H2S molecules, and their clusters in the two kinds of unit cells, are shown in Table 6. In unit cell 1 (50%, In9-A(H2S)3) of crystal 1 (In9.5H0.5A(InSH)0.5(H2S)2.5), four In2+ ions at In(2) are arranged tetrahedrally opposite six-rings in the sodalite unit with one In0 atom at In(6) at their center (at the center of the sodalite unit), forming an (In5)7+ cluster. One In+ ion at In(1) lies on a 3-fold axis opposite six-rings in the large cavity. Three more In+ ions, one each at In(4), In(5), and In(9), are located near the planes of the eight-rings, completing the charge balance of the negative framework, -12 per unit cell. Furthermore, deep in the large cavity, two sulfur atoms at S(3), as sorbed H2S molecules (see section 4.4), are found off 3-fold axes but opposite six-rings. One more sulfur atom at S(2) is found near the center of the large cavity, where it bridges between the two sulfurs at S(3) via hydrogen atoms to form a [H2S]3 molecular cluster which is stabilized between two In+ ions at In(4) and In(5) of the eightrings (see section 4.3). Therefore, unit cell 1, (In+)4(In1.75+)4(In0)-A(H2S)3, contains an (In5)7+ cluster in its sodalite unit and a [(In)2(H2S)3]2+ cluster in its large cavity. Stereoviews of the sodalite unit and large cavity of unit cell 1 are shown in Figures 1 and 2, respectively. In unit cell 2 (50%, In10H-A(InSH)(H2S)2) of crystal 1, one In+ ion at In(3) is located on a 3-fold axis opposite a six-ring in the sodalite unit. In the large cavity, five In+ ions at In(1) are placed opposite six-rings. One In0 atom at In(7) is located relatively deep in the large cavity opposite a four-ring; it bridges between two adjacent In+ ions at In(1) to form a (In3)2+ cluster. (See last paragraph of section 4.2) Two more In+ ions, one each at In(4) and In(9), are again found near eight-rings. One In3+ ion at In(8) is found opposite a six-ring in the large cavity. An additional cation for this unit cell is assumed to be, at least predominantly, a H+ ion produced by the reaction between In+ and H2S, i.e., In+ + H2S f InSH + H+, because it could not be located crystallographically. Alternatively, it may have been lost as water.34 Finally, one In+ ion at In(10) is a part of the InHS molecule formed by the above reaction, and is found opposite a six-ring deep in the large cavity, together with a sulfur at S(1) (see section 4.3). Two heavy atoms in this InSH



Figure 2. Stereoview of the large cavity of In9-A(H2S)3 (unit cell 1 of crystal 1, In9.5H0.5-A(InSH)0.5(H2S)2.5), showing a [In2(H2S)3]2+ cluster, In(4)-S(2)-S(1)-S(2)-In(5): two eight-ring In+ ions at In(4) and In(5) and three sorbed H2S molecules, one at S(1) and two at S(2). See the caption to Figure 1 for other details.

Figure 3. Stereoview of a sodalite unit in In10H-A(InSH)(H2S)2) (unit cell 2 of crystal 1) with five and one In+ ions at In(1) and In(3), respectively, and one In3+ ion at In(8), all opposite six-rings. Fine broken lines are used to indicate the bonds among the In ions and S atoms. See the caption to Figure 1 for other details.

Figure 4. Stereoview of the large cavity of In10H-A(InSH)(H2S)2) (unit cell 2 of crystal 1), showing a [In2(InSH)(H2S)2]2+ cluster, In(4)-S(3)S(1)-In(10)-S(3)-In(9): two eight-ring In+ ions at In(4) and In(9) are at the ends, one InSH molecule at In(10) and S(1) is at the center, and two H2S molecules at S(3) bridge. The (In3)2+ cluster, In(1)-In(7)-In(1), is also shown. See the captions to Figures 1 and 3 for other details.

molecule, In(10) and S(1), are again within “hydrogen-bonding” distance of two sulfur atoms at S(3) (sorbed H2S molecules), forming a [(H2S)(InSH)(H2S)] cluster which is in turn stabilized by approaches to two sulfurs at S(3) and to two eight-ring In+ ions at In(4) and In(9) (see section 4.3). Stereoviews of the sodalite unit and large cavity of unit cell 2 are shown in Figures 3 and 4, respectively. In unit cell 1 (40%, In9-A(H2S)2) of crystal 2 (In8.4H1.2A(In2S)0.6(H2S)2), the (In5)7+ cluster was found in each sodalite unit with four tetrahedrally arranged In1.75+ ions at In(2) and one In0 atom at their center (In(6)), as found in unit cell 1 of crystal 1. Again one In+ ion at In(1) opposite a six-ring and three more at In(4) near the eight-rings were found in each large cavity. Finally, two sorbed H2S molecules at S(1) and S(2) are found in the large cavity within “hydrogen-bonding” distances of each other: S(2) is off a 3-fold axis and opposite a six-ring and S(1) is deep in the large cavity opposite an eight-ring. These two sorbed H2S molecules form a [(H2S)2] molecular cluster which is again stabilized by approaches to two eight-ring In+ ions at In(4). Therefore, this unit cell contains one (In5)7+ cluster

in its sodalite unit and [(In)2(H2S)2]2+ in its large cavity. A stereoview of the large cavity is shown in Figure 5; the sodaliteunit view of unit cell 1 of crystal 2 is essentially the same as that of unit cell 1 of crystal 1 (Figure 1). In unit cell 2 (60%, In8H2-A(In2S)(H2S)2) of crystal 2, one In+ ion at In(3) lies on a 3-fold axis opposite six-rings in the sodalite unit as in the unit cell 2 of crystal 1. In the large cavity, four In+ ions at In(1) are placed opposite six-rings. Two more In+ ions at In(4) are again found near eight-rings. One In3+ ion at In(8) is also found opposite a six-ring in the large cavity. The remaining cations are assumed to be H+ ions produced by the reaction between In+ (or In2+) and H2S, i.e., 2In+ (or In2+) + H2S f In2S (or InS) + 2H+. Alternatively, they may have been lost as water molecules.34 Finally, two In+ ions at In(10) and a sulfur atom at S(1) comprise the In2S molecule formed by the above reaction; it is deep in the large cavity (see section 4.3). Each of the two In+ ions in this In2S molecule is within a reasonable adsorption distances of S(2) (sorbed H2S molecules), forming a [(H2S)(InSIn)(H2S)] cluster which is in turn stabilized by approaches to two eight-ring In+ ions at In(4) (see section


Heo et al.

Figure 5. Stereoview of the large cavity of In9-A(H2S)2 (unit cell 1 of crystal 2, In8.4H1.2-A(In2S)0.6(H2S)2), showing a [In2(H2S)2]2+ cluster, In(4)-S(1)-S(2)-In(4): two eight-ring In+ ions at In(4) and two sorbed H2S molecules, each at S(1) and at S(2). See the captions to Figures 1 and 3 for other details.

Figure 6. Stereoview of the large cavity of In8H2-A(In2S)(H2S)2 (unit cell 2 of crystal 2), showing a [In2(In2S)(H2S)2]2+ cluster, In(4)-S(2)In(10)-S(1)-In(10)-S(2)-In(4): two 8-ring In+ ions at In(4) are at the ends, two sorbed H2S molecules at S(2) coordinate to them, and one In2S molecule at In(10) and S(1) is at the center. See the captions to Figures 1 and 3 for other details.

4.3). A stereoview of the large cavity of unit cell 2 is shown in Figure 6; the sodalite-unit view is very similar to that of unit cell 2 of crystal 1 (Figure 3). Interestingly, InSH or In2S molecules were found only in the large cavities of unit cell 2 where more monopositive indium cations were available for reaction. The highly charged (In5)7+ clusters may be absent from some of their surrounding sodalite units. The (In5)7+ clusters appear to be quite stable: they do not react with H2S. 4.5. Summary Descriptions of the Crystal Structures. The structures of crystals 1 and 2 are similar except for the numbers and positions of the In2S, InSH, and H2S molecules deep in large cavities, and their immediate environments. Each unit cell of crystal 1, In9.5H0.5-A‚(InSH)0.5(H2S)2.5, contains 10.0 indium atoms or ions distributed over 10 crystallographically distinct positions with 0.5 InSH and 2.5 sorbed H2S molecules, while each unit cell of crystal 2, In8.4H1.2-A‚(In2S)0.6(H2S)2, has 9.6 indium atoms or ions distributed over seven crystallographic positions with 0.6 In2S and 2.0 H2S molecules. In the rather complex structure of In9.5H0.5-A‚(InSH)0.5(H2S)2.5 (crystal 1), 6.5 In ions per unit cell are found at five nonequivalent 3-fold-axis equipoints. On the 3-fold axes of each large cavity, 3.0 In+ ions at In(1) and 0.5 In3+ ions at In(8) lie opposite six-rings within the primary coordination spheres of framework oxygens, whereas 0.5 In+ ions at In(10) are located deep in large cavity, probably as InSH molecules stabilized by sorbed H2S molecules and In+ ions (see sections 4.3 and 4.4). On the 3-fold axes of each sodalite unit, 2.0 In1.75+ ions at In(2) and 0.5 In+ ions at In(3) are found opposite six-rings, as seen in previously reported crystal structures of In11-A and In8.75A(S2).11,15 Near the eight-rings of each unit cell, a total of 2.5 more In+ ions are found at three different Wyckoff positions (1.0, 0.5, and 1.0 at In(4), In(5), and In(9), respectively), where they are extensively involved in the stabilization of newly formed and sorbed molecules deep in large cavity (see sections 4.3 and 4.4). One In0 atom per unit cell, probably associated

with indium ions, is found: one-half of an In0 lies at the center of sodalite unit (In(6)) and the other half of the In0 is opposite a four-ring relatively deep in the large cavity (In(7)). Finally, three sulfur atoms per unit cell are found at three crystallographic sites: 0.5, 0.5, and 2.0 sulfur atoms at S(1), S(2), and S(3), respectively, all deep in the large cavity. In the crystal structure of In8.4H1.2-A‚(In2S)0.6(H2S)2 (crystal 2), 6.8 In ions per unit cell are again found at five nonequivalent 3-fold-axis equipoints: 2.8 In+ ions at In(1) and 0.6 In3+ ions at In(8) lie opposite six-rings in the large cavity, 1.2 In+ ions, probably as In2S, at In(10) lie deep in the large cavity, and 1.6 In1.75+ ions at In(2) and 0.6 In+ ions at In(3) lie opposite sixrings in the sodalite unit. Near the eight-ring planes, 2.4 In+ ions per unit cell are found at In(4). Only 0.4 In0 atoms per unit cell, associated with In1.75+ ions, are found at the center of the sodalite unit (at In(6)). Finally, 2.6 sulfur atoms per unit cell are found at two crystallographically different positions: 1.0 and 1.6 sulfur atoms at S(1) and S(2), respectively, all deep in the large cavity. Finally, considering the complexity of these structures, the apparent presence of some low occupancy positions, and the relatively small excess of diffraction data, there may be inaccuracies in some of details reported here. 4.6. The Effect of Reaction/Sorption Temperature. The following three reactions might have occurred between indium ions of indium-exchanged zeolite A (In-A) and H2S to give neutral occluded products

In2++H2SfInS+2H+

(1)

In++H2SfInSH+H+

(2)

2In++H2SfIn2S+2H+

(3)

and

Crystal Structures of Indium-Exchanged Zeolite A Only the products of reactions 2 and 3 are found in some unit cells of crystals 1 (298 K) and 2 (373 K), respectively. The numbers of H+ ions produced by reactions 2 and 3 can be judged from the SH- and S2- occupancies; their charge nicely supplements those of the crystallographically locatable cations and anions to balance the anionic charge of the zeolite framework. This number of H+ ions agrees also with the crystallinity observed: more H+ ions are produced at the higher reaction temperature to give less data with I > 3σ(I) (240 and 169 such reflections for crystals 1 and 2, respectively). Reaction 1 may have occurred to a small degree in crystal 2, but it did not proceed far because the apparent stability of the (In5)7+ clusters in their sodalite units. Even at the higher reaction temperatures 423 and 523 K, (In5)7+ occupancies did not change. As the reaction/sorption temperature increased above 373 K, the extent of reaction and the amount of sorbed H2S decreased sharply. At 423 K, indium hydrogen sulfides (InSH) and H+ ions, formed by reaction 2 as in crystal 1, were found in some unit cells (see Table 1). However, fewer than one sorbed H2S molecule per unit cell was found at 573 K. In accordance with that, its crystallinity (257 3σ data) appears to have been well preserved as fewer or no H+ ions formed. 29 Acknowledgment. M. Park, S. L. Li, and L. P. Zhou gratefully acknowledge postdoctoral support from Kyungpook National University. All authors acknowledge the support of the Central Laboratory of Kyungpook National University for the diffractometer and computing facilities. Supporting Information Available: Observed and calculated structure factors for In9.5H0.5-A‚(InSH)0.5(H2S)2.5 (crystal 1) and In8.4H1.2-A‚(In2S)0.6(H2S)2 (crystal 2). Structural parameters of In9.8H0.4-A(InSH)0.4(H2S) (crystal 3) and In10.2A(H2S)0.8 (crystal 4). This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Fox, M. A.; Pettit, T. L. Langmuir 1989, 5, 1056-1061. (2) Moran, K. L.; Harrison, W. T. A.; Kamber, I.; Gier, T. E.; Bu, X. H.; Herren, D.; Behrens, P.; Eckert, H.; Stucky, G. D. Chem. Mater. 1996, 8, 1930-1943. (3) Wang, Y.; Herron, N. J. Phys. Chem. 1987, 91, 257-260. (4) Kuczynski, J.; Nakamura, T.; Thomas, J. K. J. Phys. Chem. 1985, 89, 9, 2720-2722 (5) Stramel, R. D.; Thomas, J. K. J. Chem. Soc., Faraday Trans. 1 1988, 84, 1287-1300. (6) Uchida, H.; Ogata, T.; Yoneyama, H. Chem. Phys. Lett. 1990, 173(1), 103-106. (7) Brus, L. J. Phys. Chem. 1986, 90, 2555-2560. (8) Tricot, Y.; Fendler, J. H. J. Phys. Chem. 1986, 90, 3369-3374. (9) Kowalak, S.; Strozyk, M. J. Chem. Soc., Faraday Trans. 1996, 92, 1639-1641. (10) Moran, K. L.; Harrison, W. T. A.; Kamber, I.; Gier, T. E.; Bu, X. H.; Herren, D.; Behrens, P.; Eckert, H.; Stucky, G. D. Chem. Mater. 1996,

J. Phys. Chem. B, Vol. 106, No. 18, 2002 4587 8, 1930-1943. (11) Heo, N. H.; Kim, S. H.; Choi, H. C.; Jung, S. W.; Seff, K. J. Phys. Chem. B 1998, 102, 17. (12) Su, Y. K.; Liaw, U. H. J. Appl. Phys. 1994, 76(8), 4719-4723. (13) Thilakan, P.; Kalainathan, S.; Kumar, J.; Ramasamy, P. J. Electron. Mater. 1995, 24(6), 719-724. (14) Rossetto, G.; Franzheld, R.; Camporese, A.; Favaro, M. L.; Torzo, G.; Ajo, D.; Zanella, P. J. Cryst. Growth 1995, 146(1-4), 511-514. (15) Heo, N. H.; Choi, H. C.; Jung, S. W.; Park, M.; Seff, K. J. Phys. Chem. B 1997, 101, 5531-5539. (16) Charnell, J. F. J. Cryst. Growth 1971, 8, 291-294. (17) Firor, R. L.; Seff, K. J. Am. Chem. Soc. 1977, 99, 4039-4044. (18) Riley, P. E.; Seff, K.; Shoemaker, D. P. J. Phys. Chem. 1972, 76, 2593-2597. (19) Wade, K.; Banister, A. J. ComprehensiVe Inorganic Chemistry; Bailar, J. C., Jr., Eds.; Pergamon Press: Oxford, 1973; Vol. 1, pp 9971000. (20) Heo, N. H.; Seff, K. J. Am. Chem. Soc. 1987, 109, 7986-7992. (21) Heo, N. H.; Seff, K. ACS Symposium Series No. 368: PerspectiVes in Molecular SieVe Science 1988; pp 177-193. (22) Sun, T.; Seff, K. J. Phys. Chem. 1993, 97, 5213-5214. (23) Jung, S. W. PhD Thesis, Kyungpook National University, 2001. (24) Heo, N. H.; Jung, S. W.; Park, S. W.; Noh, J. S.; Lim, W. T.; Park, M.; Seff, K. Studies in Surface Science and Catalysis 135, Proceedings of the 13th Zeolite Conference, Montpellier, France, 2001, p 289 and CD. (25) Cruz, W. V.; Leung, P. C. W.; Seff, K. J. Am. Chem. Soc. 1978, 100, 6997-7003. (26) Mellum, M. D.; Seff, K. J. Phys. Chem. 1984, 88, 3560-3563. (27) International Tables for X-ray Crystallography; Kynoch Press: Birmingham: England, 1974; Vol. IV, pp 61-66. (28) Calculations were performed with: Structure Determination System, MolEN; Enraf-Nonius: The Netherlands, 1990. (29) Chun, C. W. ME Thesis, Kyungpook National University, 1998. (30) Doyle, P. A.; Turner, P. S. Acta Crystallogr. Sect. A 1968, 24, 390397. (31) International Tables for X-ray Crystallography; Kynoch Press: Birmingham: England, 1974; Vol. IV, pp 73-87. (32) Cromer, D. T. Acta Crystallogr. 1965, 18, 17-23. (33) International Tables for X-ray Crystallography; Kynoch Press: Birmingham: England, 1974; Vol. IV, pp 149-150. (34) Heo, N. H.; Cho, K. H.; Kim, J. T.; Seff, K. J. Phys. Chem. 1994, 98, 13 328-13 333. (35) Shannon, R. D.; Prewitt, C. T. Acta Crystallogr., Sect. B 1969, 25, 925-946. (36) Brode, H. Ann. Physik 1940, 37, 344. (37) Barrett, A. H.; Mandel, M. Phys. ReV. 1955, 99, 666-666. (38) Barrow, R. F.; Glaser, D. V.; Zeeman, P. B. Proc. Phys. Soc. 1955, 68, 962-968. (39) Handbook of Chemistry and Physics, 64th ed.; Chemical Rubber Co.: Cleveland, OH, 1983; p F-187. (40) Thiel, A. Z. Anorg. Chem. 1904, 40, 280. (41) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.; John Wiley & Sons: New York, 1988; pp 209-233. (42) Roy, R.; Shafer, M. W. J. Phys. Chem. 1954, 58, 372-375. (43) Wade, K.; Banister, A. J. ComprehensiVe Inorganic Chemistry, Vol. 12; Pergamon Press: Oxford, 1973; p 1097. (44) Choi, H. C. ME Thesis, Kyungpook National University, 1995. (45) Heo, N. H.; Jung, S. W.; Park, S. W.; Park, M.; Lim, W. T.: Seff, K. J. Phys. Chem. B 2000, 104, 8372-8381. (46) Wells, A. F. “Structural Inorganic Chemistry”; 5th ed., 1984, p 1150. (47) Wells, A. F. “Structural Inorganic Chemistry”; 5th ed., 1984, p 357.

Reaction of Fully Indium-Exchanged Zeolite A with Hydrogen Sulfide

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