J . Phys. Chem. 1992, 96, 392-397
392
the buildup of long-chain hydrocarbons during the conversion of methanol. This might well be due to the narrower (IO-membered) channels in ZSM-5, as opposed to 12-membered offretite channels, which might prevent the formation of branched polymer chains.
Acknowledgment. We are grateful to Shell Research, Amsterdam, for support. Registry No. MeOH, 67-56-1,
Orientational Disorder of the Hydrogen Dihydroxide Anion, O2H3-, in Sodium Hydroxosodalite Dihydrate, Na6[A16Si602,](OH)202H20:SingleCrystal X-ray and Powder Neutron Diffraction and MAS NMR and FT I R Spectroscopy Michael Wiebcke,* Giinter Engelhardt, Jurgen Felsche, Paul Bernd Kempa, Peter Sieger, Faculty of Chemistry, University of Konstanz, 0-7750 Konstanz, Germany
Jiirg Schefer, Solid State Physics, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
and Peter Fischer Laboratory for Neutron Scattering, ETH Zitrich, CH-5232 Villigen PSI, Switzerland (Received: March 15, 1991; In Final Form: July 25, 1991)
The crystal structure of sodium hydroxosodalite dih drate, Nas[A16Sis024](OH)2.2H20, is cubic at 173 K with space group Pa3n (2= 1) and the cell constants a = 8.875 (2) (X-ray), a = 8.87 (5) A (neutron, nondeuterated form), and a = 8.86 (5) A (neutron, deuterated form). The 1:l aluminosilicateframework is a strictly alternating arrangement of comer-sharing A104 and SO, tetrahedra. Each [4668]polyhedral cage is occupied by four Na cations, located close to oxygen atoms of six-membered rings of the framework, and, near the center, by a Cfold or 12-foldorientationallydisordered hydrogen dihydroxide of point symmetry 2 (C2) with a very strong central hydrogen bond O--H.-O with 0--0 distances at 2.36 anion, O2H3-, (4) A (nondeuteratedpowder sample) and 2.28 (4) A (deuterated powder sample). The hydrogen atom in the central hydrogen bond is probably (dynamically) disordered between two positions near the 2-fold axis, Le. the anion is probably of the type [HO-(H,H)-OH]-. No hydrogen bonding exists between the terminal OH groups of the anion and framework oxygen atoms. The structure model is in line with the 'H MAS NMR spectrum with chemical shifts at 16.3 ppm (central hydrogen atom) and -0.1 ppm (terminal hydrogen atoms) and the mid IR spectra of the nondeuterated and deuterated forms. The is suggested for hydroxosodalite dihydrate. Reversible structural-phasetransitions structural formula [Na4(02H3)]2[A&S&024] were verified by DSC measurements which showed two heat effects at 150 f 1 K and 154 f 1 K for nondeuterated, but only one heat effect at 150 f 1 K for deuterated samples. Structure chemical considerations suggest that a recently published orthorhombic crystal structure for the low-temperature phase may be incorrect.
dl
Introduction Sodalites M8[T12024]Xzare host-guest compounds with three-dimensional 4-connected host structures built up of corner-sharing TO4tetrahedra with T = Si4+,Ge4+,A13+,Ga3+,etc.' These frameworks are unique in that only one kind of polyhedral cavity, the [4668]truncated octahedron (one of the five spacefilling Federov solids), is formed in which a large variety of different cationic ( M = Li+, Na', K+,etc.) and anionic (X = OH-, C1-, NOz-, Clod-, etc.) guest species may be enclathrated. Depending on composition, sodalites possess photochromic, cathodochromic, and ion-conducting properties, show redox or decomposition reactions inside the cages ("intracage chemistry"), and have very recently attracted considerable attention as matrices for metal and semiconductor clusters and extended superclusters in the quantum size regime ("nanocompites").z Because the truncated octahedron (also known as sodalite cage or &cage) is a polyhedral building unit of the industrially important zeolites A (LTA topology) and X and Y (FAU), sodalites have also been regarded as model substances for studying pure ,&cage pr~perties.~-~ This (1) Depmeier, W. Acta Crystallogr., Sect. B 1984, B40, 185. Hassan, I.; Grundv. H. D. Acta Crvstallow.. Sect. B 1984. 840. 6. (2) Ozin, G.A.; Ku&rman,-A.; Stein, A. Angew. Chem. 1989, 101, 373. (3) Smith, J. V. Chem. Reu. 1988, 88, 149.
is especially true for the aluminosilicate hydrosodalites Na6+x[Al6Si6OZ4] (OH),.nH20, which may be divided into two endmember series, the nonbasic hydrosodalites with x = 0, n I8, and the basic hydrosodalites (hydroxosodalites) with x = 2 and n 5 4.4*5 The H20 content of hydroxosodalite hydrates Na8[Al$ig0,](OH)2-nH20 has still been in debate until very recently, when it was shown experimentally by Engelhardt et a1.6 that with the commonly used synthesis methods only Nas[A16Si6024](OH)2.2H20is formed as the primary product; all formerly reported compositions with x = 2 and n > 2 do not exist but are mixtures Of Nag [A16Si6024](OH)z'2H20 and Na6[A1&024]-8H20, due to partial exchange of NaOH against H 2 0during washing procedures. Structure and dynamics of the guest species in hydroxosodalite hydrates Na8[A16Si60z4] (OH)2.nH20 have been studied by 'H and z3NaNMR spectroscopy,' mid and far IR spectroscopy,8 as well as single-crystal X-raygJo and single-crystal neutron difFelsche, J.; Luger, S . Ber. Bunrenges. Phys. Chem. 1986, 90, 731. Felsche, J.; Luger, S. Thermochim. Acta 1987, 118, 35. Engelhardt. G.; Felsche, J.; Sieger, P. J. Am. Chem. Soc., in press. Galitskii, V. Yu.;Grechushnikov, B. N.; Ilyukhin, V. V.; Belov, N. V. Sou. Phys. Dokl. 1974, 19, 11 1. Detinich, V. A,; Kriger, Yu. G.;Galitskii, (4) (5) (6) (7)
V. Yu. Sou. Phys. Crystallogr. 1988, 33, 917. (8) Godber, J.; Ozin, G.A. J . Phys. Chem. 1988, 92, 4980.
0022-365419212096-392%03.00/0 0 1992 American Chemical Society
Orientational Disorder of the Hydrogen Dihydroxide Anion fraction." However, the structure models deduced are contradicting, which is in some cases caused by the hitherto unknown nonideal chemical compositions of the samples investigated. In what follows we present a detailed model of structure, bonding, and orientation of the guest species (1 OH-, 1 H 2 0 , 4 Na' per @-cage)in hydroxosodalitedihydrate, which we have obtained from single-crystal X-ray and powder neutron diffraction on nondeuterated and deuterated samples in combination with %i and 'H MAS NMR and mid IR spectroscopy. The experiments were carried out on the cubic high-temperature forms which are stable at temperatures above 154 K. The knowledge of the crystal structure is important for a deeper understanding of (i) chemical compositions of mixed sodalite phases, (ii) crystallization mechanisms of sodalites and zeolites, and (iii) dynamics and thermal (dehydration) behavior.
Experimental Section Preparation. Crystals up to 1 mm in size of Na8[A16Si6024](OH)2-2H20 were synthesized by hydrothermal reaction of 0.2 g of kaolinite (sintered at 1723 K for 2 h) with 2 mL of carbonate-free 16 M aqueous NaOH solution at 623 K and 110 MPa for 7 days in sealed Ag ampoules of 8-mm diameter and about 100-mm length packed in high-pressure steel autoclaves. Polycrystalline powders (grain size about 1 pm) of hydroxosodalite dihydrate and the deuterated analogue were obtained from a mixture of 2.4 g of S i 0 2 and 2.04 g of y-A1203and 40 mL of carbonate-free 16 M aqueous NaOH (NaOD) solution in 50-mL Teflon-coated steel autoclaves heated at 473 K under autogeneous pressure for 14 days. All products were washed with small amounts of H 2 0 (D20) to remove excess NaOH (NaOD) from the surface of the crystals and dried at 353 K for 12 h. Depending on the size of the crystals, the washing procedures may result in extraction of some intracage NaOH (NaOD) and the formation of Na6[Al6Si6OZ4].8H20.6 However, small admixtures of nonbasic hydrosodalite (15%) did not affect our structure determinations on a larger scale. Chemical compositions and phase purities were checked by thermogravimetric analyses and X-ray diffraction photographs obtained by the Guinier technique using Cu Kal radiation. Differential scanning calorimetric (DSC) measurements were done on a Perkin-Elmer DSC7 apparatus using open A1 pans as sample holders and heating rates of 10 K/min. Single-Crystal X-ray Diffraction Measurements. A rhombic dodecahedral crystal with an approximate diameter of 0.3 mm showed sharp reflections on precession photographs. It was mounted on an automated Enraf-Nonius CAD4 diffractometer equipped with a low-tem rature device. Monochromatic Mo Ka radiation (A = 0.71073 ) was used for the measurements carried out at about 173 K. Refinement of the 8 values of 25 reflections with 39.6 < 28 < 41.4' gave the cubic cell constant a = 8.875 (2) 8,. A total of 3795 intensities were recorded by a variable w / 2 8 scan technique up to (sin 8/X) = 1.078 8,-'in the octant 0 5 h,k,l I: 19. Averaging ( R , = 0.039) resulted in 692 unique reflections of which 399 with I > 2u1were included in the structure refinement. All observed reflections were consistent with space groups P43n and Pmln, the latter one could be excluded from the known framework str~cture.~ No absorption corrections were applied due to the small absorption coefficient (p(Mo Ka) = 0.71 mm-') and the small size of the crystal. For structure refinement the Enraf-Nonius SDP program systemI2was used with complex atomic scattering factors for neutral atoms and the Na+ cation taken from ref 13. Powder Neutron Diffraction Measurements. Data collection on powders of nondeuterated and deuterated hydroxosodalite
R
(9) Hassan, I.; Grundy, H.D. Acta Crystallogr., Sect. C 1983, C39, 3 . (IO) Bondareva, 0. S.; Malinovskii, Yu. A. Sou. Phys. Crystallogr. 1983,
The Journal of Physical Chemistry, VO~. 96, No. 1, 1992 393 dihydrate was carried out on the double-axis multicounter diffractometer (DMC) installed at the 10-MW reactor SAPHIR in the PSI, CH-Villigen.14 A closed-cycle He refrigerator was used to cool the sample of Na8[A16Si6024](OH)2.2H20 to T = 173 K, and the sample of Nas[Al6Si6024](OD)2.2D20to T = 183 K. Intensities were measured in the range 5.0 I28 I134.9O. The refined unit cell constants were a = 8.87 ( 5 ) 8, for Nag[AlsSi6024](OH)2'2H20,and 0 = 8.86 (5) 8, for Na8[Al,&024](OD)2.2D20. The values given for the esd's of the unit cell constants contain an estimate of the uncertainty in the wavelength X = 1.703 (1) 8, selected for data collection. The data were analyzed by the Rietveld profile refinement methodksusing the computer program of Young et aLk6 The background was treated by interpolation between points of no contribution from reflections. Neutron scattering lengths (in fm) were as follows: AI, 3.449; Si, 4.149; 0, 5.803; Na, 3.630; H, -3.739; D, 6.671. Spectroscopic Studies. High-resolution 29Siand 'H NMR spectra were obtained on a Bruker MSL-400 and MSL-500 spectrometer, respectively, using magic-angle sample spinning. Single-pulse excitation was applied, for the 29Sinucleus in combination with high-power proton decoupling. Measurement conditions were as follows: 29Siresonance frequency, 79.49 MHz; pulse repetition, 5 s; pulse width, 2 ps; spinning speed, 4 kHz; 'H resonance frequency, 500.13 MHz; pulse repetition, 120 s; pulse width, 2 ps; spinning speed, 9.4 kHz. Chemical shifts of both nuclei are referenced to TMS. Mid IR spectra were recorded on a Mattson-Polaris FTIR spectrometer using KBr pellets of the samples.
Structure Refinement Least-squares refinement with the X-ray data in space group P43n was started with the coordinates of the framework atoms Al, Si, and O(l), and the nonframework Na cation taken from a recent singlemystal X-ray structure analysis carried out at room temperat~re.~ The atoms O(2) and H(2), belonging to the disordered OH-and H 2 0 molecules, were localized in subsequent difference Fourier syntheses of the electron density. After refinement, the position of the missing atom H ( l ) could not be determined in LWmaps; particularly, no significant electron density was observed on site 2a (O,O,O)in the center of the sodalite cage. Rietveld profile refinement with the neutron data of the nondeuterated and deuterated samples were started with the atomic coordinates taken from the single-crystal X-ray analysis. In subsequent difference Fourier syntheses of the nuclear density a broad minimum (maximum) was found on site 2a in the case of nondeuterated (deuterated) sample. Refinements with atoms H( 1) and D(l) on site 2a yielded very large isotropic displacement parameters for these atoms, and considerations about bonding and geometry of the guest species OH- and H 2 0led to the conclusion that H(l) and D(l) could not be situated in the center of the cage. Possible off-center positions on sites 12f (x,O,O) and 24i ( X J J ) were then calculated for H(l) and D(1). From refinement and structurechemical arguments all but one or two structure models (see Discussion) could be rejected. Refinement of the occupancy factors of atoms Na and O(2) yielded no significant deviations from values expected for the chemical composition Na8[A16Si60 2 4 1 (OH)2'2H20. In the final X-ray least-squares refinement one scale factor, the coordinates of all non-hydrogen atoms, isotropic displacement parameters for atom 0(2), and anisotropicdisplacement parameters for all other non-hydrogen atoms were varied (21 parameters); hydrogen atoms were not included. The function minimized was Zw(AF)* with w = 4 p / [ a k 2 (0.04p)2]; R = 0.017, R, = 0.022, S = 0.645; maximum A/u = 0.00, maximum and minimum difference-electron densities in final AF map were +0.48 e 8,-' on position xxx with x = -0.1 1 (originating from atom H(2) and -0.43 e A-3, respectively. In the final Rietveld refinements all
+
28, 273. ( 1 1 ) Emiraliev, A.; Yamzin, I. 1. Sou. Phys. Crystallogr. 1978, 23, 27. (12) Structure Determination Package; Enraf-Nonius: Delft, The Netherlands, 1989. ( 13) International Tables for X-ray Crystallography; Kynoch: Birmingham, U.K., 1974; Vol. IV, p 72.
(14) Schefer, J.; Fischer, P.; Heer, H.; Isacson, A,; Koch, M.; Thut, R. Nucl. Instrum. Methods Phys. Res., Sect. A 1990, A288, 477. (15) Rietveld, H. M. J. J. Appl. Crystallogr. 1969, 2, 65. (16) Young, R. A.; Wiles, D. B. J. Appl. Crystallogr. 1982, 15, 430.
394 The Journal of Physical Chemistry, Vol. 96, No. I, 1992
Wiebcke et al.
TABLE I: Fractional Atomic Coordinates and Equivalent Displacement Parameters for Cubic Nondeuterated (H Form) and Deuterated (D Form) H y d r o x d l i t e Dihydrate atom site OCC" X Y z U-b (a) X-ray Refinement ( H Form) 0.00583 (5) AI 6d 6 1/4 0 1/2 0 0.00616 (4) Si 6c 6 114 112 0.14982 (6) 24i 24 0.13939 (6) 0.43810 (7) 0.00974 (9) O(1) 8 0.17517 (6) X X 0.01892 (4) Na 8e 00) 24i 4 0.0580 (8) -0.0581 (8) 0.1194 (7) 0.0301 (1)
AI Si O(1) Na O(2) H(1) H(2)
6d 6c 24i 8e 24i 12f 8e
6 6 24 8 4 2 4
(b) Neutron Refinement (H Form) 0 1/4 114 1/2 0.1391 (2) 0.1502 (2) X 0.1753 (4) 0.056 (4) -0.064 (4) 0 0.048 (18) X -0.136 (1)
AI Si O(1) Na 00) D(1) D(2)
6d 6c 24i 8e 24i 12f 8e
6 6 24 8 4 2 4
(c) Neutron Refinement (D Form) 0 114 112 114 0.1499 (2) 0.1391 (2) 0.1759 (3) X 0.059 (4) -0.061 (4) 0.061 (3) 0 -0.1339 (6) X
0.0056 (8)
112
rr,,
0 0.4384 (2)
0.0091 (4) 0.022 (1) 0.028 (4) 0.10 (6) 0.060 (4)
X
0.119 (2) 0 X
1/2 0
0.0067 (6) UAI 0.0106 (4) 0.018 (1) 0.038 (4) 0.08 (1) 0.054 (1)
0.4382 (1) X
0.1 14 (2) 0 X
"Occupancy factors are given as atoms (ions) per unit cell. bUwis defined as ('/s)CQ,a*,a*~(a;nj). TABLE 11: Selected Interatomic Distances (A) and Angles (deg) in Cubic Nondeuterated (H Form) and Deuterated (D Form) Hydroxosadafite Dihydrate X-ray neutron neutron atoms (H form) (H form) (D form) (a) Framework 1.740 (2) AI-O( 1) 1.7413 (6) 1.745 (2) 108.6 (1) 108.52 (3) 108.5 (1) O(I)-AkO(I), 4X 111.3 (1) 111.3 (1) O(l)-AkO(I), 2X 111.39 (6) 1.614 (2) 1.615 (2) Si-O(1) 1.6191 (7) 107.6 (1) 107.54 (3) 107.5 (1) O(1)-Si-O(l), 4X 113.3 (1) 113.5 (1) O(I)-Si-0(1), 2X 113.40 (6) 138.0 ( I ) 137.96 (6) 138.1 (1) A1-0( 1)-Si
Na-O(l) Na-O(l) Na-0(2) Na-0(2) Na-0(2) Na...H(l) Na. sH(2)
O(2). ..O(2) O(2). ..0(2) 0(2)-H(1) 0(2)-H(l) 0(2)-H(1)-0(2) 0(2)-H(1)-0(2) 0(2)-H(2) H( 1)-0(2)-H(2) H( 1W G 9 - W ) 0(2)...0(1) H(2). ..O( 1)
(b) Sodium Coordination 2.365 (1) 2.368 (4) 3.089 (4) 3.088 (4) 2.37 (1) 2.33 (4) 2.37 (1) 2.42 (4) 2.999 (8) 2.99 (4) 2.47 (16) 2.80 (1)
2.358 (3) 3.083 (3) 2.40 (4) 2.38 (4) 2.95 (4) 2.43 (3) 2.795 (6)
0 2 H 3Anion" 2.36 (2) 2.39 (5) 2.36 (2) 2.33 (5) 1.20 (16) 1.18 (16) 173 (15) 166 (15) 0.97 (4) 119 (15) 122 (15) 3.38 (1) 3.32 (4) 2.832 (9)
2.29 (5) 2.27 ( 5 ) 1.15 (4) 1.14 (4) 178 (4) 180 (4) 0.94 (4) 118 (4) 119 (4) 3.31 (4) 2.850 (6)
0
"Two reasonable geometric interpretations are possible.
20
40
80
60
XK)
120
140
28
0 -
1
-5.
h
0.4 0
*
20
40
80
60
100
t20
1 I
65.
140
ze
Figure 1. Observed (solid lines) and calculated (dots) powder neutron diffraction profile intensities for cubic nondeuterated (a) and deuterated (b) hydroxosodalite dihydrate. Difference plots and marks for allowed Bragg positions are added at the top of each profile.
atoms were included with isotropic displacement parameters. Due to the limited resolution of the instrument, we could not introduce anisotropic displacement parameters. Convergence with A / u I 0.02 was reached a t RF = 0.058, R, = 0.1 16, and R,, = 0.093 and calculated intensity profiles; see the recent discussion of R values in Rietxeld analysis." The profile plots are shown in Figure (Rexp= 0.061) in the case of Nag[A16Si6024](OH)2.2H20 (22 1. Final atomic parameters for the three structure refinements parameters varied), and at RF= 0.047, R = 0.095, and R,, = 0.095(Rex,= 0.042) in the case Of Nag[A%Si6024](OD)2.2D,O are listed in Table I; selected interatomic distances and angles are summarized in Table 11. (24 parameters varied). Background-subtracted conventional Rietveld R = Z(AYi,,e,)/~(U,o,,,,), R,, = [ Z W ~ ( A \ Y ~ , , ~ , ) ~ / Z W ~ (Y&t)2]l/2\nd Rex,= [(N- P ) / Z W ~ ( Y ; ~ , ,with ~,)~ wi] = ~/~ are given as measurements of the agreement between observed (17) Hill, R. J.; Fischer, R. X.J. Appl. Crystallogr. 1990, 23, 462.
Orientational Disorder of the Hydrogen Dihydroxide Anion
Figure 2. [4668]polyhedral cage in hydroxosodalite dihydrate with the guest species Na+ and OzHC in one orientation. Framework atoms and Na cations are represented by displacement ellipsoids, while the atoms of the anion are represented by spheres.
Figure 3. Truncated tetrahedron of the O(2) atomic positions of the disordered 0,H3anion and the larger Naptetrahedron with one possible orientation of the anion being illustrated. The center of the sodalite cage is marked by a dot.
Discussion Host Structure. The three-dimensional framework is a strictly alternating arrangement of corner-sharing A104 and Si04 tetrahedra. One [4668]polyhedral cage is illustrated in Figure 2; the general features of the cubic sodalite framework have been discussed in the 1iterature.I Related atomic and geometric parameters in the three structure refinements of 173 and 183 K data agree very well among each other, and, when allowing for the temperature differences, are in close agreement with the results of a recent X-ray structure analysis carried out at room temperature by Hassan and G r ~ n d y .The ~ high degree of order in the aluminosilicate framework is confirmed by the 29Si MAS NMR spectrum measured at room temperature, which shows one sharp resonance line with a chemical shift at -84.3 ppm. Guest Species. Enclathrated in each sodalite cage of point symmetry 23 (T) are four Na cations and, formally, one OH- as well as one H 2 0molecule. The cations are located on the 3-fold axes of the structure (site 8e) close to O(1) atoms of six-membered rings of the framework and form a regular tetrahedron. Within this Na, tetrahedron, the O(2) atoms of the OH- and HzO molecules are disordered over one crystallographic site (24i) forming a smaller truncated tetrahedron (see Figure 3). This is in agreement with the structure analysis of Hassan and Grundy? in which hydrogen atoms have not been determined. However, a deeper understanding of bonding and orientation states of the guest species can be obtained from the neutron data refinements in combination with structure chemical considerations as follows. All O(2)-0(2) distances in the nondeuterated and deuterated crystals are shorter than 2.4 A, which means that a very strong
The Journal of Physical Chemistry, V O ~96, . NO. 1, 1992 395 hydrogen bond O.-H.-O must join the OH- and H 2 0 molecule. The unique characteristics of such very strong hydrogen bonds-short donor-acceptor distances, covalent bonding, high bonding energy18*'9-suggest the formulation of a hydrogen dihydroxide anion, 02H2.18 A) in each truncated tetrahedron which from geometrical argumentsL9have to be considered in a first approximation as possible hydrogen bonds. The corresponding central hydrogen atom H ( l ) cannot be situated in the center of the cage (site 2a)-where it was apparently localized in the neutron but not in the X-ray refinement-because this would result in unreasonable small 0(2)-H( 1)-0(2) angles of about 137' (strong hydrogen bonds tend to be more linear than weak ones). Two of the four 0(2)-0(2) separations can be ruled out because they lead to an inhomogeneous, and therefore unrealistic, coordination of the Na cations by oxygen atoms (one Na being 5-fold, two Na being 4-fold, and one Na being 3-fold coordinated by O(2) and/or O(1) atoms), and result in too short Na-eH(1) contacts (2.83 A definitely exclude the existence of even weak hydrogen bonds between the guest species and framework oxygen atoms. The orientational disorder of the O2H3 anion may be regarded as 6-fold or 12-fold. The crystallographic studies with the geometric interpretation of time- and space-averaged data cannot decide between these cases because the two reasonable, independent 0(2)-0(2) distances are equal within the limits of experimental errors, and atom H(1) takes the same 12f site. Therefore, the statistical occupancy factors of atoms O(2) and H(1) are 1/6 or 2/12, respectively, and of atom H(2) 3/6 or 6/12, i.e. the atomic position H(2) given in Table I is the superposition of three or six close H(2) locations of different orientations of the OzH3anion. The O(2)--0(2) distances of the O2H3 and OzD3 anions belong to the shortest donor-acceptor distances of O--H.-O hydrogen bonds reported so far. The 0(2).-0(2) separation at 2.28 (4) A (average of two values) in the deuterated crystals is shorter than the corresponding separation at 2.36 (4) A (average of two values) in the nondeuterated crystals, which may indicate a geometric (18) Emsley, J. Chem. SOC.Reu. 1980, 9, 91. Emsley, J.; Jones, D. J.; Lucas, J. Reu. Inorg. Chem. 1981, 3, 105. (19) Joswig, W.; Fuess, H.; Ferraris, G. Acta Crystallogr., Sect. E 1982,
838, 2798.
(20) Olovsson, I.; JBnsson, P.-G. The Hydrogen Bond; Schuster, P., Zundel, G., Sandorfy, C., Eds.; North-Holland: Amsterdam, The Netherlands, 1976; Vol. 11, p 393.
396 The Journal of Physical Chemistry, Vo1. 96, No. I, 1992
Wiebcke et al. I
-01 2.0
1
. a
16
I/ 0.8
0.4
L
II
4000
I
3
,
3600
I
3200
,
I
2800
,
I
I
2400
I
,
1
,
I
,
I
.
I
2000
1800
1200
800
400
2ooo
1800
1200
800
400
wave“& 1
25.0
.
8
.
20.0
1
)
15.0
xl.0
5.0
0.0 PPm
-5.0
-xl.O
45.0
-20.0 .25.0
Figure 4. IH MAS NMR spectrum of cubic hydroxosodalite dihydrate at 193 K. Spinning sidebands are marked by an asterisk.
isotope effect2’ with stronger O--D...O than O-.H-.O bonds. However, due to the high degree of disorder of the guest species, the interatomic distances listed in Table I1 are not of high accuracy and do not necessarily represent actual bond lengths. In view of the difficulties inherent with the interpretation of Fourier maps of diffraction data of highly disordered crystals, independent proofs of the correctness of the structure models deduced were desirable. Those proofs are provided by additional spectroscopic studies. ‘HN M R a d IR Spectra. The ‘H MAS NMR spectrum measured at 193 K (see Figure 4) shows three sharp lines at -0.1, 5.0, and 16.3 ppm accompanied by weak spinning side bands. Due to their chemical shifts and integral intensity ratio of 2:1, the lines at -0.1 and 16.3 ppm have to be assigned to the terminal H(2) and central H( 1) atoms of the 02H3anion, respectively. The line at 5.0 ppm probably originates from impurities of H 2 0 in nonbasic hydrosodalite (Na6[A@i6024].8H20)6~22 or adsorbed at residual NaOH on the surface of the crystals. The strong downfield shift of the line of the central hydrogen atom is typical for protons involved in very strong hydrogen bonds,23and the shift value of 16.3 ppm is in excellent agreement with results of quantumchemical calculations of an isolated O2H3 anion.24 For the hydrogen atoms of an isolated H 2 0 molecule, a chemical shift of 0.2 ppm has been obtained by the quantum-chemical calcul a t i o n ~which , ~ ~ may be compared with the measured chemical shift of -0.1 ppm of the terminal H(2) atoms of the 0 2 H 3anion enclathrated in hydroxosodalite dihydrate. IR spectra of nondeuterated and deuterated samples are shown in Figure 5. The sharp O H and OD stretching modes at 3640 and 2685 cm-‘ with a frequency ratio of uH/vD= 1.35 originate from the terminal OH groups in the 0 2 H 3anion, which are not involved in hydrogen bonds. No H 2 0 bending modes at about 1650 cm-’ appear in the spectra. Due to strong bonding the stretching mode of the central OH bond is expected to be shifted strongly to lower wavenumber and may be considerably broadened.18 The weak and broad band centered at about 1500 cm-’, which appears only in the spectrum of the nondeuterated sample, probably originates from O H stretching modes in the central O-H.-O system. Similar characteristics have been observed in the IR spectrum of which shows no H 2 0 bending modes but a broad band centered at about 1750cm-’ (isotope ratio (21) Ichikawa, M. Acta Crystallogr., Secr. B 1978, 8 3 4 , 2074. (22) Buhl, J. Ch.; Engelhardt, G.;Felsche, J.; Luger, S.; Foerster, H. Ber. Bunsenges. Phys. Chem. 1988, 92, 176. (23) McMichael Rohlfing, C.; Allen, L. C.; Ditchfield, R. J . Chem. Phys. 1983, 79,4958. Jeffrey, G.A,; Yeon, Y. Acta Crystallogr., Sect. B 1986,842, 410. (24) McMichael Rohlfing, C.; Allen, L. C.; Ditchfield, R. Chem. Phys. Lett. 1982, 86, 380. (25) Lutz, H. D.; Henning, J.; Jacobs, H.; Harbrecht, B. Ber. Bunsenges. Phys. Chem. 1988, 92, 1557. (26) Harmon, K. M.; Avci, G . F.; Duffy, D.; Janos, M. S . J . Mol. Strucr. 1990, 216, 63.
4000
3600
3200
2800
2400
wavenmber
Figure 5. IR spectra of cubic nondeuterated (a) and deuterated (b) hydroxosodalite dihydrate. Deuteration was not complete as can be seen from the small band at 3640 cm-I (OH stretch) in the spectrum of the
deuterated sample.
uH/uD= 1.35) assigned to OH stretching modes in strong hydrogen bonds.26 Polymorphic C S O H - H ~ may O ~ ~contain discrete 0 2 H 3 anions in layers formed by OH- and H 2 0molecules, but accurate crystalstructures including hydrogen atom positions have not been reported so far. Low-Temperature Pbase. Structural phase transitions were verified for Nag [A16Si6024](OH)2.2H20 and Na8[A&S&OZ4] (0D)2-2D20by means of DSC measurements and variable-temperature X-ray powder diffraction. In the DSC runs, the nondeuterated samples showed two (reversible) endothermic heat effects at 150 f 1 K and 154 f 1 K on heating from 133 K, whereas the deuterated samples showed only one (reversible) endothermicheat effect at 150 f 1 K under the same conditions. Structural phase transitions have been reported previously for the sodalites “Nag[A16Si6024] (OH)2.6H20”7927 and Na8[A16Si6024](OH)2.2H205”o to Occur at about 152 K. Recently an X-ray structure analysis has been carried out on a microtwinned crystal of hydroxosodalite dihydrate at 113 K by Bondareva and Malinovskii.Io These authors report the structure of the low-temperature phase to be orthorhombic with the cell constants a = 8.925 (6), b = 8.906 (6), and c = 8.870 (6) A, and the space group P222. The structure model deduced is-apart from the distortion of the cubic P43n symmetry of the hightemperature form, the unlocalized hydrogen atoms and unidentified anionic guest species-essentially identical with our model described above. That means, principally, that the same kind and degree of disorder of the O2H3 anion would be present in the low-temperature and high-temperature forms. This is very unlikely, however, when considering the structural phase transitions as ordering processes of the 0 2 H 3 anion or the [Na4(02H,)]3+-guestcomplex accompanied by displacive relaxations in the aluminosilicate framework. In addition, bond-distance calculations using the data of Bondareva and Malinovskii showed that in one of the two independent distorted sodalite cages of point symmetry 222 (D2),which is not compatible with an ordered OzH3 (27) Ivanov, N. R.; Galitskii, V. Yu. Sou. Phys. Crystallogr. 1974,18, 762.
Orientational Disorder of the Hydrogen Dihydroxide Anion anion of any possible conformation, only unreasonable O--O distances occur, too short for O.-H-.O hydrogen bonds. These are strong indications that the reported crystal structure of the low-temperature phase may be incorrect, which prompted us to start further work on the structural phase transitions of hydroxd a l i t e dihydrate. Richardson et a1.28have very recently studied the high-temperature structure of dimorphic silica sodalite with enclathrated ethylene glycol molecules, [Sil20,,] [C2H4(OH)z]2, and have pointed to some similarities between the crystallographic data of the low-temperature forms of silica sodalite (probably monoclinic) and hydroxosodalite dihydrate (orthorhombicIo).
Structural Considerations Hydroxosudabte Hydrates. Experimental evidence has been presented by Engelhardt et a1.6 that in common synthesis procedures only Na8[M6Si60z4] (OH),-2H20 is obtained as primary hydroxosodalite phase. All compositions Na8[A16Si6024](OH)2-nH20with n > 2 reported so far are mixtures of Na8[A16Si6024](OH)2*2H20 and Na6[A16Si6024].8H20, due to exchange of NaOH against H 2 0 during washing procedures. This suggests that the O2H3 anion or the [Na4(OZH3)l3+ complex are good templates29for sodalite crystallization, and that the dihydrate is the member with the highest possible H 2 0 content among the hydroxosodalites, which may be supported by the structure model presented above. One or two additional H 2 0 molecules can apparently not be placed into the sodalite cage with overall reasonable bonding to the O2H3 anion, Na cations, and 0(1) framework atoms, and a simultaneous expansion of the aluminosilicate framework not exceeding the fully expanded state with a cubic cell constant of about 9.3 A.‘ The structure models presented previously for the sodalites “Na8[A16Si6024] (OH),. 4H20”425~22 and “Na8 [Al&,024](OH)2.6HzO”7J0have been deduced assuming a wrong chemical composition. The unusual high thermal stability of hydroxosodalite dihydrate with the release of H 2 0 from the cages between 823 and 873 K and the formation of water-free Na8[A16Si6024] (OH): should be related to the high bonding energy of about 100 kJ/mo130 of the strong central hydrogen bond of the 0 2 H 3anion. In the structure of the subsequent sodalite phase Na8[A16Si6024](OH), a highly dynamically disordered OH- anion centers each sodalite cage.3’ The crystal structure of the cubic hydroxosodalite Na8[A16Ge6024](OH)2 with germanium substituting for silicon in the framework has been determined from single-crystal X-ray3, and single-crystal neutron diffraction data.)3 The space group is P43n and the unit cell constant a = 9.038 (3) A (neutron data). The (28) Richardson, J. W., Jr.; Pluth, J. J.; Smith, J. V.; Dytrych, W. J.; Bibby, D. M. J . Phys. Chem. 1988, 92, 243. (29) Flanigen, E. M. Ado. Chem. Ser. 1973, 121, 119. (30) Gao. J.; Garner, D. S.; Jorgensen, W. L. J . Am. Chem. SOC.1986, 108, 4784. (31) Luger, S.; Felsche, J.; Fischer, P. Acta Crystallogr., Secr. C 1987, C43, 1 . Buehrer, W.; Felsche, J.; Luger, S . J . Chem. Phys. 1987,87, 2316. (32) Belokoneva, E. L.; Dem’yanets, L. N.; Uvarova, T. G.; Belov, N. V. Sou. Phys. Crystallogr. 1982, 27, 597. (33) Kanepit, V. N . ; Nozik, Yu. Z.; Fizkin, L. Ye. Geochem. Inr. 1984, 21, 134.
The Journal of Physical Chemistry, Vol. 96, No. 1, 1992 391 authors conclude from DTA measurements and from difference Fourier syntheses that some additional, unlocalized H 2 0molecules may be present in the sodalite cages. These observations along with the atomic coordinates obtained in the neutron diffraction study and simple considerations about the Na coordinations provide strong evidence that this germanium compound is actually Na8[A16Ge6024] (OH)z.2H20. Merely by doubling of the m u pancy factors of the nonframework oxygen atom (OoH) on site 24i (x = 0.073, y = -0.073, z = 0.1 12) and of the hydrogen atom (HOH)on site 8e (x,x,x; x = -0.145), and by inserting an additional hydrogen atom on site 12f, a structure model closely related to OUT model Of cubic Na8[A1&,024](OH)2*2H@ is obtained. For the thus modified structure of the germanium compound an O-.Odistance of 2.41 A is calculated for the strong central hydrogen bond O-.H-.O of the orientationally disordered 0 2 H 3anion. Hydrogen Dibydroxide Anion. Ab initio calculations of the isolated 0 2 H 3anion revealed that the potential energy surface is sufficiently flat that the conformation in crystalline states will be completely determined by crystal forces.30 Experimentally, this anion has only in the last decade been observed by X-ray crystallography in different environments with the shortest reported donoracceptor distance in the central O.-H-.O hydrogen bond at 2.29 (2) A.34 For the natrocalcite-type compound Cu2K(H@,)(SO4),, an accurate singlecrystal neutron diffraction study has shown that, in this case, the 0 2 H 3anion has a short protondisordered central hydrogen bond.35
Conclusions The crystal structure of the cubic high-temperature form of sodium hydroxosodalite dihydrate described above supports recent experimental findings for the aluminosilicate hydrosodalites, which have important implications for sodalite and zeolite chemistry. It is the first report of an hydrogen dihydroxide anion, 02H3-, with a very strong central hydrogen bond encapsulated in a microporous tectosilicate. The model presented for the possible orientation states of the anion in the high-temperature form is essential for elucidating the structures of the low-temperature forms, the static/dynamic behavior of the guest species, and the mechanisms of the structural phase transitions. Acknowledgment. We thank the PSI, Villigen, for providing measurement time at the reactor SAPHIR, and the BMFT, Bonn-Bad Godesberg, for financial support. R e t r y NO. Nas[A16Si6024](OH)2.2H20,137540-09-1; Na8[A16Si602,](0D)2*2D20, 136952-83-5.
Supplementary Material Available: Table of anisotropic displacement parameters (1 page); observed and calculated structure factors (8 pages). Ordering information is given on any current masthead page. ~
(34) Abu-Dari, K.; Freyberg, D. P.; Raymond, K. Inorg. Chem. 1979,18, 2427. Ardon, M.; Bino, A. Srrucr. Bonding Springer: Berlin, 1987; 65, 1 . Giester. G. Z. Kristallow. 1989. 187. 239. (35)’Chevrier, G.; GAter, G.;’Jarosch, D.; Zemann, J. Acta Crystallogr., Sect. C 1990, C46, 175.
