The Pentatin Cation in Zeolite Y: Thallous Ion Exchange and Crystal

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The Pentatin Cation in Zeolite Y. Thallous Ion Exchange and Crystal Structure of |Sn Cl |[Si Al O ]-FAU Containing Sn , SnCl , and SnCl 36

11

128

64

384

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12+

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3+

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5+

Joon Yeob Kim, Nam Ho Heo, and Karl Seff J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b10811 • Publication Date (Web): 09 Dec 2016 Downloaded from http://pubs.acs.org on December 14, 2016

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The Journal of Physical Chemistry

The Pentatin Cation in Zeolite Y. Thallous Ion Exchange and Crystal Structure of |Sn36Cl11|[Si128Al64O384]-FAU Containing Sn512+, Sn2Cl3+, and Sn3Cl5+

Joon Yeob Kim,† Nam Ho Heo,†,* and Karl Seff §

†

Department of Applied Chemistry,

School of Applied Chemical Engineering, College of Engineering, Kyungpook National University, Daegu 41566, Korea §

Department of Chemistry, University of Hawaii,

2545 The Mall, Honolulu, Hawaii 96822, U. S. A.

ACS Paragon Plus Environment


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(abstract) Sn512+, Sn2Cl3+, and Sn3Cl5+ have replaced all of the Tl+ ions in the zeolite Tl71-Y (|Tl71|[Si121Al71O384]-FAU) by thallous ion exchange (TIE), a vapor phase ion exchange method. SnCl2(g) was allowed to react with Tl71-Y under anhydrous conditions at 673 K for 48 h.

The

crystal structure of the product, |(Sn512+)1.70Sn2+27.4Cl-10.8|[Si127.6Al64.4O384]-FAU per unit cell, was determined by single-crystal crystallography at 294 K using synchrotron X-radiation (Fd 3 m, a = 24.758(1) Å). It was refined with all 1465 unique data to the final error indices R1 = 0.061 and R2 = 0.208.

Its composition was confirmed by scanning electron microscopy energy-dispersive

X-ray analysis.

Centered tetrahedral Sn512+ clusters center 21% of the sodalite cavities.

About

10 Sn2+ ions per unit cell near 12-rings are bridged by Cl- ions to form five Sn2Cl3+ clusters. Similarly, six Sn3Cl5+ clusters have formed; each contains one 6-ring and two 12-ring Sn2+ ions.

2


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1. INTRODUCTION 1.1. Tin Containing Zeolites. 1.1.1. Extraframework Tin. Tin-exchanged zeolites were used for the syntheses of α-amino nitrile from ketones1 and for the isomerization of glucose to fructose.2, 3 By using Sn,H-beta zeolites with 2.4 wt% tin, the reaction time is decreased and conversion percent is increased for the syntheses of α-amino nitrile (Strecker reaction).1

It has been reported that it is particles of

SnO2, inside the hydrophobic channels of the beta zeolites, that isomerize glucose to fructose by a base-catalyzed proton transfer mechanism.3 Pt,Sn-ZSM-5 is an important catalyst for the dehydrogenation of propane to propene;4 propene used in the manufacture of various products such as polypropene, acrolein, polyacrylonitrile, and acrylic acid.4

In Pt,Sn-ZSM-5 catalysts, prepared by impregnation with

aqueous SnCl4, Sn reduces the catalyst acidity5 and decreases the size of the surface Pt ensembles,4 increasing the selectivity for propene. Despite the many applications of tin-containing zeolites, little is known about the extraframework tin species involved, including their identities, location, and detailed geometry. Some structural work has, however, been reported: the structure of fully Sn-exchanged zeolite LTA was determined using single-crystal X-ray diffraction,6 and clusters of average stoichiometry Sn4S64+ were reported in faujasite by powder X-ray diffraction.7

1.1.2. Framework Tin. Zeolites with Sn4+ ions incorporated into their frameworks are also efficient catalysts for a number of important chemical reactions.2, 3


8, 9

Zeolite beta with


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incorporated tin (tin-beta) is used for the oxidation of unsaturated ketones.8

In the oxidation of

bicyclohept-3-en-1-one using m-chloroperbenzoic acid as the oxidant, tin-beta zeolites yield only two regioisomeric lactones (Baeyer-Villiger oxidation10, 11).8 Tin-beta zeolites are also efficient catalysts (Meerwein-Ponndorf-Verley reduction) for the reduction of cyclohexanone with 2butanol.9

They isomerize glucose to fructose, a key reaction in industrial processes, by a Lewis

acid mediated hydride transfer.

This is used for the production of high-fructose corn syrups2 and

the chemical intermediates such as 5-hydroxymethylfurfural and levulinic acid.12

Using tin-

beta zeolites containing 2 wt% framework tin, the conversion percent of cyclohexanone to cyclohexanol is 91.0 mol%, higher than with titanium-beta or aluminum-beta zeolites.

1.2. Vapor Phase Ion Exchange (VPIE). Beta zeolites containing extraframework tin were prepared using aqueous SnCl2·2H2O or SnCl4·5H2O; because zeolite beta has a low aluminum content, only small amounts of tin could be introduced.2, 3, 8, 9 exchange, zeolites with higher Al contents should be used.

To achieve a higher degree of Unfortunately such zeolites

decompose at the low pHs that result from the extensive hydrolysis of tin.

To overcome this

difficulty, the VPIE method would be used to prepare fully Sn-exchanged zeolite Y (FAU, Si/Al = 1.69).

It had been used successfully to exchange indium and gallium ions into zeolite Na-Y

(FAU, Si/Al = 1.69)13-16 and Sn ions into zeolite Na-A (LTA, Si/Al = 1).6

1.3. Objectives and Methodology. The objectives of this work were (1) to achieve a high degree of Sn2+-exchange into a FAU zeolite, and (2) to observe the positions and coordination environments of the Sn2+ ions.

4


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It was hoped that Sn2+ could be introduced into zeolite FAU by the thallous ion exchange (TIE) method.17

TIE has shown itself to be a method that allows the preparation of ion-exchanged

zeolites that are normally impossible to prepare by conventional ion exchange methods.6, 18-21 The reaction per unit cell would be Tl71-Y + 35.5SnCl2(g) → Sn35.5-Y + 71TlCl(g).

(1)

Because dehydrated Tl-Y is stable at 673 K22 and the vapor pressure of SnCl2(g) is reasonably high (3.8 x 102 Pa)23 at that temperature, reaction 1 could go to completion. The crystal structure of the product would be determined and compared to that of Sn,Cl-LTA.6

Sn2+ and Tl+ would be

readily distinguished crystallographically because their ionic radii and scattering powers are very different.

2. EXPERIMENTAL SECTION 2.1. Preparation of the Crystal. 2.1.1. Syntheses of Na-Y.

Large colorless single crystals of sodium zeolite Y

(|Na71(H2O)x|[Si121Al71O384]-FAU, Na71-Y, or Na-Y; Si/Al = 1.69) were prepared by Lim et al. using the synthetic method of Ferchiche et al.24-26

2.1.2. Preparation of Tl–Y. A single crystal of Na-Y, a colorless octahedron about 0.08 mm in cross-section, was loaded into a fine Pyrex capillary.

It was fully Tl+-exchanged (to give

(|Tl71|(H2O)y|Si121Al71O384)-FAU, Tl71-Y or Tl-Y) by dynamic ion exchange (the flow method) using 0.10 M aqueous (pH = 6.7) thallous acetate (TlC2H3O2, Strem, 99.999%) at 294 K for 24 h. This and similar procedures had been shown to be suitable for the preparation of fully Tl+5



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exchanged Tl-Y,18, 27, 28 Tl−X,29, 30 and Tl−A.6, 31-33

2.1.3. Treatment with SnCl2. About 20 mg of slightly off-white anhydrous SnCl2 (Aldrich, ≥ 99.995%) crystals were ground to a powder. This, in a small Pyrex test tube, was placed in the tube above the capillary containing the Tl71-Y crystal.

As the temperature increased (50 K/h)

toward 673 K, the SnCl2 all sublimed and condensed higher up on the inner surface of Pyrex tube; it was now pure white. After being allowed to cool to room temperature (-25 K/h), the reaction vessel, consisting of the dehydrated Tl71-Y crystal in its capillary and the dry SnCl2 on the wall of the tube above it, was sealed off under vacuum from the vacuum line. maintained at 673 K for 48 h for reaction.

This isolated reaction vessel was

Afterwards, only the capillary end of the reaction

vessel was heated, at 623 K for another 24 h, to distill away any excess SnCl2 and TlCl that might be in or near the crystal.

After being allowed to cool (-50 K/h) to room temperature, the

resulting black crystal was sealed off under vacuum in its capillary by torch.

Similar TIE

procedures had been used to prepare In-Y18 and Sn-A.6

2.2. X-ray Diffraction. Diffraction intensities were measured with synchrotron X-radiation via a Si(111) double crystal monochromator at the Pohang Light Source (PAL), Pohang, Korea. The ADSC Q210 program was used for data collection using the omega scan method.34

Highly

redundant data sets were harvested by collecting 72 sets of frames with a 5º scan and an exposure time of 1 s per frame. The basic data files were prepared using the program HKL3000 (PLS).35 The reflections were indexed by the automated indexing routine of the DENZO program.35 These were corrected for Lorentz and polarization effects; negligible corrections for crystal decay 6


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were also applied. The space group Fd 3 m, standard for zeolite Y, was determined by the program XPREP.36

Table 1 presents a summary of the experimental and crystallographic data.

2.3. SEM-EDX Analysis. After diffraction data collection, the crystal was removed from its capillary (exposed to the atmosphere). surface for analysis.

It was then broken into two pieces to expose an inner

It was attached to a sample holder with carbon tape for scanning electron

microscopy energy dispersive X-ray (SEM-EDX) analysis.

The composition was determined

using a Horiba X-MAX N50 EDX spectrometer within a Hitachi SU8820-SR FE (field emission) scanning electron microscope at 294 K and 9 × 10−4 Pa with a beam energy of 20 keV and current of 1 µA.

The SEM-EDX results (Figure 1 and Table 2) show that tin and chlorine are both

present in the product crystal, and that thallium is absent; thallium’s highest peaks would have been at 10.267, 12.212, and 12.269 eV.

3. STRUCTURE DETERMINATION Full-matrix least-squares refinement (SHELXL2014)37 was done on F2 using all 1465 unique reflections measured. They were initiated with the atomic parameters of the framework atoms (T (Si and Al, disordered), O1, O2, O3, and O4) in dehydrated Tl71−Y.18, 27, 28 were used initially.

Fixed weights

The initial refinements with anisotropic thermal parameters for all

framework atoms converged to the high error indices (defined in footnotes of Table 1) R1 = 0.29 and R2 = 0.73 (step 1 of Table 3).

The detailed progress of structure determination, as

subsequent peaks are found on difference Fourier functions and identified as extraframework atoms, is presented in Table 3.

The final weights were assigned using the formula w = 1/[σ2(Fo2) 7



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+ (aP)2 + bP] where P = [max(Fo2,0) + 2Fc2]/3 with a and b as refined parameters.

Their final

values are given in Table 1. At one point (step 11 of Table 3), the occupancy at Sn1 was four times that at SnU (Sn1/SnU = 6.91(10)/1.74(4) = 3.97(11)) to which it bonds.

This indicates that the Sn1 position, tetrahedral

about SnU, is fully occupied about each SnU atom; hence tetrahedral Sn5 clusters are present. Their occupancies were therefore constrained to be Sn1:SnU = 4:1. This refinement quickly converged with marginal changes in the error indices (step 12 of Table 3). Similarly (step 12 of Table 3), the Sn31/Cl1 occupancy ratio became 13.0(6)/4.6(7) = 2.8(5); avoiding unacceptable interionic distances, this indicated the presence of Cl-bridged Sn2Cl clusters.

Their occupancies were constrained to be Sn31:Cl1 = 2:1 (step 13 of Table 3).

The Sn32/Cl2 occupancy ratio became 8.6(6)/3.9(6) = 2.2(3) with reasonable interatomic distances, so Sn32:Cl2 was constrained to be 2:1 (step 14 of Table 3).

At the same time the

Sn2/Cl2 occupancy ratio became 5.69(10)/4.3(3) = 1.32(9), indicating the presence of Cl-bridged Sn3Cl clusters.

Combining the above constraints, the constraint Sn2:Sn32:Cl2 = 1:2:1 was

applied (step 15 of Table 3). The occupancies at Cl1 and Cl2 were nearly the same, suggesting a 1:1 interaction between the Sn2Cl and Sn3Cl clusters. After a careful search, this possibility was dismissed. The final structural parameters are presented in Table 4 and selected interatomic distances and angles are given in Table 5. 39

Atomic scattering factors for Sn0, Cl0, O-, and T1.82+ were used.27, 38,

The function describing T1.82+ is the weighted (for Si/Al = 1.69) mean of the Si4+, Si0, Al3+,

and Al0 functions. All scattering factors were modified to account for anomalous dispersion.38, 40 8


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Additional crystallographic details are given in Table 1.

4. BRIEF DESCRIPTION OF THE FAU FRAMEWORK AND CATION SITES The framework structure of zeolite Y, a synthetic analogue of the naturally occurring mineral faujasite (FAU), is characterized by the double 6-ring (D6R), the sodalite cavity (a cuboctahedron), and the supercage (Figure 2).

Each unit cell has 8 supercages, 8 sodalite

cavities, 16 D6Rs, 16 12-rings, and 32 single 6-rings (S6Rs).

The exchangeable cations that

balance the negative charge of the FAU framework usually occupy some or all of the sites shown with Roman numerals in Figure 2.

The maximum occupancies at the cation sites I, I′, II, II′, III,

and III′ in FAU are 16, 32, 32, 32, 48, and (in Fd 3 m) 192, respectively.

Further detailed

descriptions are available.41-43

5. DESCRIPTION OF THE STRUCTURE 5.1. Framework Geometry. The mean T−O bond length (1.652 Å, Table 5) in Sn36Cl11−Y is appropriately between the Si−O (1.61 Å) and Al−O (1.74 Å) distances found in both dehydrated Ca-LSX (FAU)44 and hydrated Na-LTA.45

It is about the same as those in K71−Y,25 1.655 Å, and

in Tl71−Y,18, 27, 28 1.663 Å.

5.2. Extraframework Ions.

Per unit cell about 36 Sn atoms occupy five different

crystallographic positions: 6.82 are at site I' (Sn1), 5.77 at site II (Sn2), 10.1 and 11.55 at two sites III' (Sn31 and Sn32), and, finally 1.70 at the very centers (SnU) of the sodalite cavities (Figure 3

9



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and Table 4). cavities.

The Sn atoms at SnU and Sn1 form centered tetrahedral Sn5 clusters in the sodalite

Cl atoms occupy two positions. Cl1 bridges between two Sn atoms (Sn31) to form

Sn2Cl, and Cl2 bridges between three Sn atoms (Sn2 and two Sn32) in the supercages to form Sn3Cl. The oxidation states of these extraframework atoms were assigned primarily from a consideration of their observed ionic radii.

The ionic radii of the Sn atoms were obtained by

subtracting the conventional ionic radius of O2− (1.32 Å)46 from their shortest Sn−O bond lengths. Their coordination numbers and environments, and their actual bond lengths in related materials, were also considered.

5.2.1. Sn2+ Ions. Each of the 5.77(10) Sn atoms at Sn2, opposite S6Rs in the supercages, is 4-coordinate, bonding to three O2 framework oxygens at 2.488(4) Å and to a Cl- ion at Cl2 at 2.83(11) Å (Figure 4). They extend 1.16 Å into supercage from the (111) plane of the O2 oxygen atoms (Figure 4).

The observed radius at Sn2, 2.488 - 1.32 = 1.17 Å, is 0.24 Å longer

than the reported radius of Sn2+, 0.93 Å.46

The bonding of Cl2 to Sn2 has apparently lengthened

the Sn2-O1 bond, as it did in fully Sn-exchanged zeolite A6 where similar Sn2+-O2- distances, 2.297 - 2.425 Å, were observed. Thus, the oxidation state of the atoms at Sn2 is taken to be 2+. Each of the 10.1(3) Sn atoms at Sn31, near 12-rings in the supercages, is 3-coordinate, bonding to one O1 and one O4 framework oxygen at 2.301(6) Å and 2.483(8) Å, respectively, and to a Cl- ion at Cl1 at 2.792(20) Å (Figure 4). The observed radius at Sn31, 2.301 - 1.32 = 0.98 Å, is close to the reported radius of Sn2+, 0.93 Å.

Thus, the atoms at Sn31 are also assigned the 2+

oxidation state. Each of the 11.55(21) Sn atoms at Sn32, also near 12-rings in the supercages, is 2-coordinate to 10


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one O1 framework oxygen at 2.483(8) Å and to a Cl- ion at Cl2 at 2.72(6) Å (Figure 4).

The

observed radius at Sn32, 2.483 - 1.32 = 1.16 Å, is again somewhat longer than the reported radius of Sn2+, 0.93 Å, as discussed in the first paragraph of this section.

As before, the Sn atoms at

Sn31 are assigned the 2+ oxidation state.

5.2.2. Cl- Ions. Each of the 5.06(15) Cl atoms at Cl1 bridges between two Sn2+ ions at Sn31 with Sn31-Cl1 = 2.792(20) Å.

Each of the 5.77(10) Cl atoms at Cl2 bridges two Sn2+ ions at

Sn32 with Sn32-Cl2 = 2.72(6) Å, and one Sn2+ ion at Sn2 with Sn2-Cl2 = 2.83(11) Å.

These

bond lengths are very close to the sum of the ionic radii of Sn2+ and Cl-, 0.93 + 1.81 = 2.74 Å,46 indicating that Cl- ions occupy the Cl1 and Cl2 positions. Similar Sn2+-Cl- bond lengths, 2.50 2.65 Å, were also seen in fully Sn-exchanged zeolite A.6

Halide ions often bridge between Sn2+

ions.47, 48

5.2.3. Sn512+ Clusters. Each of the 6.82(9) Sn atoms at Sn1, opposite D6Rs in the sodalite cavities, is 4-coordinate tetrahedral, bonding to three O3 framework oxygens at 2.377(3) Å and one SnU atom at 2.684(3) Å. (Figure 3).

It extends 0.98 Å into sodalite cavity from the (111) plane at O3

Each of the 1.70(2) Sn atoms at SnU, at the very center of the sodalite cavity, is

tetrahedrally surrounded by four Sn1 atoms, forming a centered tetrahedral Sn5 cluster. To discuss the bonding and establish the charge of the Sn5 unit, note that the outer electronic configuration of Sn is 5s25p2; the n = 4 orbitals are all fully occupied.

Thus four electrons are

available for bonding from each atom, and 20 electrons are available to place.

However, many

of these must be absent because Sn5 approaches 12 anionic oxygen atoms of the zeolite framework and is thus a cation. The centered tetrahedral structure of Sn5 indicates that four 11



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bonds are needed.

If these are single bonds, eight electrons are needed and 20 – 8 = 12 must

have been lost, leaving the Sn5 unit to be Sn512+. Sn512+ is isoelectronic and isostructural with In57+, which had been found before in the sodalite cavities of zeolites18 and elsewhere.29, 30, 32 The bonding would also be the same as that in Ga57+ 13 and in the C5 unit of neopentane; all of the above are group 14 (IV A) elements.

The four SnU-Sn1 bonds complete a tetrahedral octet of

electrons about SnU, indicating sp3 bonding. The possibility of up to four double bonds is readily rejected: it would violate the octet rule and would be inconsistent with the long SnU-Sn1 bond length (Table 5) and the resulting large atomic radius at SnU (Table 6). The formal charges at SnU and Sn1 are thus 0 and 3+, respectively.

Like each terminal carbon atom in neopentane,

each Sn1 atom is tetrahedrally surrounded by four pairs of electrons, three from O3 atoms of the zeolite framework and one from SnU.

5.2.4. Sn2Cl3+ and Sn3Cl5+ Clusters. The five Cl- ions at Cl1 and 10 Sn2+ ions at Sn31 form five Sn2Cl3+ clusters per unit cell.

As can be seen in Figure 5, each of the Cl- ions at Cl1, located

opposite a central 4-ring of the three connected 4-rings but relatively deep in the supercage, bridges between two Sn2+ ions at Sn31 (site IIIʹ). Similarly, the six Cl- ions at Cl2, the six Sn2+ ions at Sn2, and the 12 Sn2+ ions at Sn32 form six Sn3Cl5+ clusters per unit cell (Figure 6).

The geometry about Cl2 is distorted trigonal with

angles of 91º, 116º, and 116º (Table 5).

The lone pair of electrons at Sn2 may be

stereochemically active48, 49 and thus may be responsible for the unusually high “thermal motion” seen at Cl2.

Attempts to refine Cl2 off the mirror plane were unsuccessful.

As seems sensible, the Sn2+-Cl- distances (Table 5) are shortest when Sn2+ is otherwise just 112


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coordinate (Sn32), intermediate in length when Sn2+ is otherwise 2-coordinate (Sn31), and longest when Sn2+ is otherwise 3-coordinate (Sn2) to framework oxygen atoms.

6. DISCUSSION Upon reaction with SnCl2(g) the sum of the extraframework charges (Sn2+, Sn512+, and Cl-) decreased from 71.0+ to 64.5(12)+ (Table 6).

This diminished charge indicates that aluminum

had been lost from the zeolite framework, as had been reported for dehydrated zeolites treated with SiCl4(g)50 or ZrCl4(g).19

Per unit cell of initial zeolite, 6.6 Al3+ ions were lost.

The following reaction is proposed for Tl-Y + SnCl2(g), per unit cell of the initial zeolite: |Tl+71|[Si121Al71O384]-FAU + 40.6SnCl2(g) → 0.948|(Sn512+)1.70Sn2+27.4Cl-10.8|[Si127.6Al64.4O384]-FAU + 71TlCl(g) + 4.97SnAl2O4 + 1.61Sn0

(2)

Because all Tl+ ions in Tl-Y exited the zeolite as TlCl(g), the desired TIE reaction (reaction 1) appears to have gone to completion.

However, of the 35.5 Sn2+ ions that might have been

produced by reaction 1, only 22.0 were.

This is because other reactions occurred also. They

are the disproportionation of Sn2+ to Sn512+ and Sn0, the loss of Al2O3 from the zeolite framework and the production of SnO (possibly combined with Al2O3 as SnAl2O4(s)51), and the retention of excess SnCl2 within the zeolite. The stability of SnAl2O4(s) may have allowed SnCl2 to extract Al2O3 from the zeolite framework; this was otherwise unexpected for a cation whose charge is only 2+.

The Si/Al ratio of the zeolite framework increased from 1.70 to 1.98.

Both Sn2+ and Tl+ could have oxidized Sn2+ to Sn512+, and thus have been reduced to the metal. 13



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Sn2+ was selected in writing reaction 2 because its aqueous reduction potential indicates that is more easily reduced.52

Also, free energy calculations indicate strongly that the product Al

should be Al2O3 (perhaps as SnAl2O4) rather than Al2Cl6(g). The integrity of the single crystal studied, as indicated by its sharp diffraction peaks and the resulting large diffraction data set, indicates that it had, upon loss of 14% of its framework aluminum and associated oxygen atoms, restructured itself to have only 94.8% of its former Such restructuring had been seen before.19, 20, 53

number of unit cells.

The product crystal,

dehydrated Sn,Cl-Y, should therefore be smaller than the reagent crystal, dehydrated Tl-Y. The color of the product crystal could be due to finely divided tin metal on its surface.

SnO is

black, but the color of SnAl2O4 is not known, nor is the contribution that Sn512+ might make to the color of the crystal.

6.1. Sn2+ Ions.

The average Sn2+-O2- bond length found in this study, 2.405(3) Å, is greater

than the sum of the conventional ionic radii of Sn2+ and O2-, 0.93 + 1.32 = 2.25 Å, and the distance in blue-black SnO(s), 2.22(2) Å.46 compounds of Sn2+.

It is, however, much like those found in other

They ranged from 2.297(10) to 2.410(7) Å in the zeolite Sn6.1Cl1.6-A.6

is 2.398 (20) Å in zeolite Y containing Sn4S64+ clusters.7 average Sn2+-O bond is 2.52 Å.54 ·0.5[NH3(CH2)6NH3]2+

and

It

In a series of tin(II) halide sulfates, the

It ranges from 2.101(7) to 2.442(6) Å in [Sn3(PO4)2((OH)]-

from

2.092(11)

to

2.467(8)

Å

in

[Sn3(PO4)2((OH)]-

·0.5[NH3(CH2)8NH3]2+.55 The average Sn2+-O2- bond length is 2.479 Å in [ClSn{Zr2(OPri)9}]2, [ClSn{Hf2(OPri)9}]2, [(C5H5)Sn{Zr2(OPri)9}]2, and [(C5H5)Pb(µ2-OBut)2Sn(OBut)].56 tetrahydroxide dinitrate they ranged from 2.14 to 2.35 Å.57

In tritin(II)

It is clear that the Sn-O bond

14


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lengthens when anions larger (softer) than O2- coordinate to Sn2+.

6.2. Sn512+ Clusters. The centered tetrahedral Sn512+ cation had not been reported before. Its Sn-Sn distance, 2.684(3) Å, is comparable to the Sn-Sn single bond length in Sn[CH(SiMe3)2]2, 2.764(2) Å, and that in K2{Sn(C6H3-2,6-Trip2)}2 (Trip = -C6H2-2,4,6,i-Pr3),

2.7763(9) Å.

Sn512+ is isostructural with In57+ 14-16, 18, 30, 32, 58 and Ga57+ 13 which were also found in the sodalite cavities of zeolites LTA and FAU.

Sn512+ is isoelectronic with In57+.

6.3. Sn2Cl3+ and Sn3Cl5+ Clusters.

The Sn2+-Cl- bond lengths in the Sn2Cl3+ cluster, Sn31-Cl1

= 2.792(20) Å, and in the Sn3Cl5+ cluster, Sn32-Cl2 = 2.72(6) Å and Sn2-Cl2 = 2.83(11) Å, are reasonable. They are the same as the sum of the ionic radii of Sn2+ and Cl-, 2.74 Å = 0.93 + 1.81,46 respectively.

The Sn2+-Cl- bond lengths in [ClSn{Zr2(OPri)9}]2 and [ClSn{Hf2(OPri)9}]2

range from 2.579(4) to 2.598(5) Å.56

They are 2.596(3) Å and 2.779(3) Å in

[{(PhMe2Si)3CMCl}2], and 2.538(2) Å and 2.952(3) Å in [M{C(SiMe3)2(SiMe2OMe)}Cl]2.59

6.4. Comparison with Sn,Cl-LTA. The results of the TIE reactions of SnCl2(g) with the fully Tl+-exchanged zeolites A (LTA) and Y (FAU, Si/Al = 1.69) can be compared. completion in the sense that no Tl+ remained in the zeolite.

Both went to

Some Sn2+ ions disproportionated in

both zeolites; the products were Sn0 and Sn4+ in zeolite A and Sn0 and Sn512+ in zeolite Y. ions bridge between Sn2+ ions in both products.

Cl-

Both contain Sn2Cl3+ clusters; in addition,

Sn3Cl24+ is found in Sn,Cl-A, and Sn3Cl5+ is present in Sn,Cl-Y. The presence of Cl- in both zeolite crystals indicates the retention of SnCl2, 0.82 molecules per 12.1-Å unit cell in Sn,Cl-A despite bake out at 723 K for 48 h, and 5.4 in Sn,Cl-Y per 24.8-Å unit cell despite bake out at 623 K for 24 h.

Under the latter milder conditions for the final bake out, 15



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enough Cl- remained to coordinate to all Sn2+ ions.

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In contrast, Sn,Cl-A contained 2.74 Sn2+ and

0.8 Sn4+ ions per unit cell that did not bond to Cl-.

7. CONCLUSION Multiple reactions occurred when Tl71-Y (|Tl71|[Si121Al71O384]-FAU) was treated with SnCl2(g) at 623 K. The intended TIE reaction, to give Sn2+ and TlCl(g), predominated, but Sn512+, Sn0, and SnAl2O4, perhaps as SnO and Al2O3, were also produced.

Cl- ions from additional retained

SnCl2 molecules bridge between all Sn2+ ions in the structure. |(Sn512+)1.70Sn2+27.4Cl-10.8|[Si127.6Al64.4O384]-FAU.

The product zeolite is

Tetrahedral Sn512+ clusters center and fill 1.70

of the eight sodalite cavities per unit cell. Cl- ions bridge between Sn2+ ions in the supercage to form Sn2Cl3+ and Sn3Cl5+ clusters.

■ ASSOCIATED CONTENT Supporting Information. Sn36Cl11-FAU.

Observed and calculated structure factors squared with esds for

This is available free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATION Corresponding Author *(N.H.H) Telephone: +82 53 950 5589; Fax; +82 53 950 6594; E-mail: [email protected]. 16


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Note The authors declare no competing financial interest.

■ ACKNOWLEDGEMENT We gratefully acknowledge the Pohang Light Source (PLS) for the use of their synchrotron facilities including diffractometer and computers.

This work was supported by a National

Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. NRF2014R1A2A1A11054075).

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TABLE 1. Experimental Conditions and Crystallographic Data crystal cross-section (mm) 0.08 + ion exchange with Tl (T (K), t (h), V (mL)) 294, 24, 10 dehydration of Tl-Y (T (K), t (h), P (Pa)) 673, 48, 5.0 x 10-5 reaction of Tl-Y with SnCl2 (T (K), t (h), P (Pa)) 623, 72, 3.8 x 102 X-ray source PLS(2D-SMC)a wavelength (Å) 0.70000 detector ADSC Quantum-210 crystal-to-detector distance (mm) 63 crystal color black data collection temperature (T (K)) 294(1) space group, No. Fd 3 m, 227 unit cell constant, a (Å) 24.758(1) maximum 2θ for data collection (deg) 66.77 no. of reflections measured 86,939 no. of unique reflections measured, m 1465 no. of reflections with Fo > 4σ(Fo) 1153 no. of variables, s 72 data/parameter ratio, m/s 20.3 weighting parameters: a, b 0.119, 108.04 b c final error indices: R1, R2 0.061, 0.208 d goodness of fit 1.10 a Beamline 2D-SMC at the Pohang Light Source (PLS), Korea. bR1 = Σ|Fo-|Fc||/ΣFo; R1 is calculated using only those reflections for which Fo > 4σ(Fo). cR2 = [Σw(Fo2-Fc2)2/Σw(Fo2)2]1/2 is calculated using all unique reflections measured. dGoodness of fit = (Σw(Fo2-Fc2)2/(m-s))1/2.

Note to Editor: The subscript o above in Fo (multiple times) is a lower-case letter o. Throughout this ms, the subscripts o and c stand for "observed" and "calculated". They also appear in the first paragraph of section 3.

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Table 2. Crystal Composition (Atomic %) by Crystallographic (SXRDa) and SEMEDXb Analyses SXRD SEM-EDXc element Si 20.49 15.00 Al 10.34 6.65 O 61.67 63.41 Sn 5.77 8.48 Cl 1.73 6.45 a Single-crystal X-ray diffraction. b Scanning electron microscope energydispersive X-ray analysis. cConsidering the relatively large esds in the EDX analysis, due in part to the zeolite decomposition to be expected in the electron beam (and the possible decomposition of the zeolite upon exposure to the atmosphere), acceptable agreement is seen for each element.

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TABLE 3. Steps of Structure Determination as Non-Framework Atomic Positions Were Found number of ions or atoms per unit cella error indicesb step Sn1 Sn2 Sn31 Sn32 SnU Cl1 Cl2 R1 R2 c 1 0.29 0.73 2 6.5(3) 0.24 0.66 3 6.8(3) 5.4(3) 0.20 0.61 4 6.7(3) 4.24(21) 13.2(7) 0.18 0.58 5 6.67(21) 4.49(19) 7.3(6) 8.7(6) 0.163 0.517 6d 6.64(21) 4.47(18) 7.3(6) 8.7(6) 0.165 0.513 7 7.50(15) 5.30(13) 6.9(4) 10.4(4) 1.85(6) 0.091 0.375 e 8 7.06(13) 5.54(13) 7.2(4) 11.2(4) 1.73(6) 0.085 0.284 9f 6.91(10) 5.72(10) 12.3(6) 8.1(6) 1.71(5) 0.0630 0.2199 10 6.92(10) 5.82(10) 12.5(6) 8.0(6) 1.73(4) 3.6(7) 0.0616 0.2170 11 6.91(10) 5.73(10) 13.0(6) 8.4(6) 1.74(4) 4.6(7) 3.8(6) 0.0592 0.2065 6.92(9) 5.73(10) 13.0(6) 8.4(6) 1.73(2) 4.6(7) 3.8(6) 0.0593 0.2066 12g 13h 6.92(9) 5.70(10) 12.8(6) 8.6(6) 1.73(2) 6.4(3) 3.9(6) 0.0593 0.2108 i 14 6.92(9) 5.69(10) 12.9(5) 8.6(5) 1.73(2) 6.4(3) 4.3(3) 0.0593 0.2102 15j 6.89(9) 5.51(9) 11.0(3) 11.02(19) 1.72(2) 5.49(14) 5.51(9) 0.0604 0.2091 k 16 6.82(9) 5.77(10) 10.1(3) 11.55(21) 1.70(2) 5.06(15) 5.77(10) 0.0608 0.2081 a Numbers in parentheses are the estimated standard deviations (esds) in the units of the least significant figure given for the corresponding parameter. bDefined in footnotes to Table 1. cOnly framework atoms were refined (anisotropically) in the initial model of the structure. dAn extinction parameter (EXTI) was introduced and refined. eA twoparameter weighting system (see Table 1) was applied. fSn1, Sn2, Sn31, and Sn32 were refined anisotropically. g The occupancies at Sn1 and SnU were constrained to be 4:1. hThe occupancies at Sn31 and Cl1 were constrained to be 2:1. iThe occupancies at Sn32 and Cl2 were constrained to be 2:1. jThe occupancies at Sn2, Sn32, and Cl2 were constrained to be 1:2:1. kCl1 and Cl2 were refined aniotropically. 23



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TABLE 4. Positional, Thermal, and Occupancy Parametersa occupancyc atom Wyckoff x y z U11 or Uisob U22 U33 U23 U13 U12 position position varied constrained fixed T 192(i) -5363(3) 3613(2) 12539(2) 188(3) 143(3) 156(3) -33(2) -28(2) 1(2) 192 O1 96(h) -10598(9) 0d 10598(9) 300(8) 398(15) 300(8) -97(8) -30(11) -97(8) 96 O2 96(g) -187(9) -187(9) 14320(12) 326(9) 326(9) 381(15) -73(9) -73(9) 128(11) 96 O3 96(g) -7535(8) -7535(8) 3185(13) 273(8) 273(8) 408(16) 18(8) 18(8) 35(10) 96 O4 96(g) 17837(8) 17837(8) 32290(11) 275(8) 275(8) 316(13) -24(8) -24(8) 106(10) 96 d d d e SnU 8(a) 12500 12500 12500 296(10) 1.74(4) 1.70(2) Sn1 32(e) 6240(8) 6240(8) 6240(8) 475(9) 475(9) 475(9) 36(7) 36(7) 36(7) 6.91(10) 6.82(9)e Sn31 192(i) 17959(40) 21837(49) 40679(25) 843(59) 1410(90) 288(27) -323(39) -205(29) 640(58) 13.0(6) 10.1(3)f d d d Cl1 48(f) 12500 12500 43872(209) 2792(591) 2792(591) 852(322) 0 0d -41(658) 4.6(7) 5.06(15)f Sn2 32(e) 24290(13) 24290(13) 24290(13) 613(15) 613(15) 613(15) 166(13) 166(13) 166(13) 5.69(10) 5.77(10)g Sn32 192(i) 16052(43) 19980(39) 42355(50) 844(58) 1003(54) 1114(71) 357(50) -600(49) -113(42) 8.6(6) 11.55(21)g Cl2 96(g) 23639(259) 32369(325) 32369(325) 514(285) 6832(1973) 6832(1973) -4000(2062) -167(383) -167(383) 3.9(3) 5.77(10)g a Positional parameters x 105 and thermal parameters x 104 are given. Numbers in parentheses are the estimated standard deviations (esds) in the units of the least significant figure given for the corresponding parameter. T represents the tetrahedral framework atoms, Si and Al. bThe anisotropic temperature factor is exp[-2π2a2 (U11h2 + U22k2 + U33l2 + 2U23kl + 2U13hl + 2U12hk)]. cOccupancy factors are given as the number of atoms or ions per unit cell. dExactly, by symmetry. eThe occupancies at Sn1 and SnU were constrained to be 4:1. fThe occupancies at Sn31 and Cl1 were constrained to be 2:1. gThe occupancies at Sn2, Sn32, and Cl2 were constrained to be 1:2:1.

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TABLE 5. Selected Interatomic Distances (Å) and Angles (deg)a distance angles T-O1 1.6465(12) O1-T-O2 112.31(12) T-O2 1.6498(11) O1-T-O3 110.79(12) T-O3 1.6639(12) O1-T-O4 107.09(13) T-O4 1.6495(11) O2-T-O3 106.26(15) mean 1.652 O2-T-O4 108.42(14) O3-T-O4 112.02(14) Sn1-O3 2.377(3) Sn2-O2 2.488(4) T-O1-T 138.99(20) Sn31-O1 2.349(8) T-O2-T 144.54(20) Sn31-O4 2.301(6) T-O3-T 139.81(20) Sn32-O1 2.483(8) T-O4-T 139.80(18) SnU-Sn1

2.684(3)

Sn2-Cl2 Sn31-Cl1 Sn32-Cl2

2.83(11) 2.792(20) 2.72(6)

O3-Sn1-O3 O2-Sn2-O2 O1-Sn31-O4

104.28(11) 99.74(17) 69.51(18)

O2-Sn2-Cl2 O1-Sn31-Cl1 O4-Sn31-Cl1 O1-Sn32-Cl2

129.97(14) 93.0(7) 83.9(11) 93.6(20)

Sn1-SnU-Sn1

109.47b

Sn31-Cl1-Sn31 147.1(21) Sn32-Cl2-Sn32 91(3) Sn2-Cl2-Sn32 116(3) a The numbers in parentheses are the estimated standard deviations (esds) in the units of the least significant digit given for the corresponding value. T represents the tetrahedral framework atoms, Si and Al. bThe tetrahedral angle by symmetry.

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TABLE 6. Unit Cell Charge Budget atom ionsb occ.c positiona SnU Sn0 1.70(2) Sn1 Sn3+ 6.82(9) 2+ Sn31 Sn 10.1(3) Cl1 Cl 5.06(15) Sn2 Sn2+ 5.77(10) 2+ Sn32 Sn 11.55(21) Cl2 Cl 5.77(10)

M-O,d Å 2.377(3) 2.301(6) 2.488(4) 2.483(8)

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r,e Å

CNf

charge x occ.

1.62 1.06g 0.98 1.81 1.17 1.16 1.56

4 4 3 2 4 2 3

0 20.5(3)+ 20.2(6)+ 5.06(15)11.5(2)+ 23.1(4)+ 5.77(10)-

ΣSn0 = 1.70(2) ΣSn2+ = 27.4(4) ΣSn3+ = 6.82(9) ΣCl- = 10.8(2) Σcharges = 64.5(8)+ a The atomic positions are listed by clusters (as in Table 4): SnU and Sn1 comprise Sn512+, Sn31 and Cl1 comprise Sn2Cl3+, and the last three positions comprise Sn3Cl5+. bExtraframework ions. c Occupancy per unit cell. dShortest Sn-O (metal ion to framework oxygen) bond lengths. eRadii of Sn2+ and Sn3+ ions were obtained by subtracting 1.32 Å, the conventional radius of O2-,46 from the shortest Sn-O bond lengths. Radii for Cl- were obtained by subtracting the observed radii of the Sn2+ ion to which it bonds from the shortest Sn-Cl bond lengths. The radius at Sn0 was obtained by subtracting the observed radius of the Sn3+ ion to which it bonds from the Sn-Sn bond length. f Coordination numbers. gIt is expected that this radius is large because of high repulsive forces within the Sn512+ cation.

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(figure captions) Figure 1.

SEM−EDX spectrum of dehydrated Sn,Cl−Y after exposure to the atmosphere.

A Na peak is present at 1.04 keV in the EDX analysis although

it was not found crystallographically; it cannot be from the SnCl2 reagent because NaCl is not volatile at 723 K.

All other peaks are due to other

transitions for the atoms shown.

Figure 2.

Stylized drawing of the framework structure of zeolite Y. Near the center of the each line segment is an oxygen atom.

The nonequivalent oxygen atoms

are indicated by the numbers 1−4. There is no evidence in this work of any ordering of the silicon and aluminum atoms among the tetrahedra, although it is expected that Loewenstein’s rule would be obeyed.

Extraframework

cation positions are labeled with Roman numerals or the letter U.

Figure 3.

A stereoview of a sodalite cavity containing a Sn512+ cation. the sodalite cavities are occupied by Sn512+.

About 21% of

The zeolite Y framework is

drawn with open bonds; solid bonds are used to show the bonding of the extraframework ions. Al.

Figure 4.

T represents the tetrahedral framework atoms, Si and

Ellipsoids of 30% probability are shown.

A stereoview of a representative supercage showing the Sn2Cl3+ and Sn3Cl5+ cations. See the caption to Figure 3 for other details.

Figure 5.

A stereoview showing a Sn2Cl3+ cation coordinating to oxygen atoms of three 4-rings in the supercage. See the caption to Figure 3 for other details.

Figure 6.

A stereoview showing a Sn3Cl5+ cation coordinating to oxygen atoms of the zeolite framework in the supercage.

See the caption to Figure 3 for other

details. 27



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Figure 1. Kim, Heo, and Seff

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Note to editor: This stereoview is the correct width, ca. 4 1/4 inches black to black, for clearest viewing. eyes.

This width is dictated by the average distance between adult human

If it is enlarged, readers will not able to see it in stereo with standard

stereoviewers.

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stereoviewers.

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stereoviewers.

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TOC Graphic

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The Pentatin Cation in Zeolite Y: Thallous Ion Exchange and Crystal

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