Aug 6, 1997 - Crystal structure of the zeolite mutinaite, ... synthetic zeolites with the ZSM-5 framework ... an Rint = 4.76%; of these, 3,985 with I > 3a (r) were.
ELSEVIER
Crystal structure of the zeolite the natural analog of EM-5 Giovanna Vezzalini, Simona Quartieri, and Ermanno Galli Dipartimento di Scienze della Terra, Universitci di Modena, Modena, Albert0 Istituto
Alberti and Giuseppe Cruciani di Mineralogia, Universitct di Ferrara,
iike Kvick European Synchrotron
Radiation
Facility,
mutinaite,
Italy
Fe-rrara, Italy
BP 220, Grenoble, France
We describe the crystal structure of the high-silica zeolite mutinaite, recently found at Mt. Adamson (Northern Victoria Land, Antarctica). Mutinaite is the natural counterpart of the synthetic zeolite ZSM-5. The new mineral, (Na,.,,K,,,,Mg,.,,Ca,,,,) (Al,,,,, Si,,.,,) * 60 H,O H,?, is orthorhombic, space group Pnma, with a = 20.201(2), b = 19.991(2), and c = 13.469(2) A. A single-crystal X-ray diffraction experiment was performed at the synchrotron radiation source ESRF (Grenoble). No Si-AI order in the framework has been detected. Large distances between ions in the channels and framework oxygens suggest weak interactions between the framework and extraframework species. 0 Elsevier Science Inc. 1997 Keywords:
Mutinaite;
ZSM-5;
crystal
structure;
pentasil
INTRODUCTION Mutinaite, the natural counterpart of ZSM-5,‘~’ occurs in Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarctica),” and is associated with many other 5-ring zeolites: gottardiite,4*” terranovaite,” boggsite,’ tschernichite,’ heulandite, stilbite, stellerite, epistilbite, ferrierite, and mordenite. The chemical, physical, and optical properties and the powder X-ray diffraction data of the new mineral are reported by Galli et al.” The Si/Al ratio of mutinaite (7.6, as derived by microprobe analysis) is the highest found to date in a natural zeolite, but it is by far the lowest among those of the synthetic zeolites with the ZSM-5 framework synthesized both in the presence and in the absence of any organic compound. A noticeable feature of this zeolite is its high thermal stability (up to 900°C).
EXPERIMENTAL Preliminary X-ray diffraction data collection was carried out on a Siemens four-circle diffractometer using a rotating anode generator. The very small dimensions of the crystal resulted in only 25% of observed reflections, a percentage inadequate for an acceptable crystal structure refinement. However, it was posAddress reprint requests to Prof. Vezzalini at the Universita Modena, Dipartimento di Scienze della Terra, via S. Eufemia 41100 Modena, Italy. Received 6 August 1997; accepted 20 August 1997 Zeolites 19:323-325, 0 Elsevier Science 655 Avenue of the
1997 inc. 1997 Americas,
New
York,
NY 10010
di 19,
sible to verify that mutinaite has the same topology as synthetic zeolite ZSM-52 and therefore is its natural counterpart. X-ray data collection was then performed at the high-brilliance synchrotron radiation source ESRF in Grenoble, on the beamline BL2ID1 1.s This experiment was performed on a single crystal of 0.03 X 0.03 X 0.015 mm” mounted on a Siemens diffractometer; wavelength 0.87 A, crystaldetector (CCDO camera) distance 300 mm, resolution (sinO/A) 0.76 A-‘, exposure time 15 set, scan axis w, and frame width 0.05”. The cell parameters, determined by synchrotron X-ray powder diffraction and refined by the Rietveld method, are: a = 20.201(2), b = 19.991(2), and c = 13.469(2) A. 11,548 intensities were collected in the 0 range 5.1”-71.6” and were corrected for Lorentz-polarization and air absorption. The systematic extinctions were consistent with the space group Pnma. The 5,913 unique reflections had an Rint = 4.76%; of these, 3,985 with I > 3a (r) were used in the structure refinement. Least-squares refinement (SHELX-76Q) was carried out in the space group Pnma, starting from the positional parameters of the framework atoms of synthetic zeolite ZSM-5.” Atomic scattering factors for neutral atoms were used for both framework and extraframework species. The discrepancy factors were R = 12.4 and Rw = 10.1. Atomic coordinates are reported in Table 1. Interatomic distances, angles, and structure factors can be obtained from the authors upon request.
0144-2449/97/$17.00 PII 50144.2449(97)00124-3
Crystal Table
structure 1
Atomic
Atom Tl T2 T3 T4 T5 T6 T7 T8 T9 TlO Tll T12 01 02 03 04 05 06 El ::0 011 012 013 014 015
of mutinaite:
G. Vezzalini
coordinates,occupancy
xla
0.0571(2) 0.0298(2) 0.0626(2) 0.0629(2) 0.0299(2) 0.0583(2) -0.1708(2) -0.1282(2) -0.1726(2) -0.1731(2) -0.1284(2) -0.1726(2) 0.0561(7) 0.0617(5) 0.0604(6) 0.0621(6) 0.0597(7) 0.0572(8) -0.1562(6) -0.1565(6) -0.1549(4) -0.1596(6) -0.1600(6) -0.1511(6) -0.0493(6) -0.0503(5) 0.1297(5)
a UisO for all extraframework
(%) Z/C
ylb
0.4254(l) 0.3177(l) 0.2783(l) 0.1226(l) 0.0757(l) 0.1964(l) 0.4277(l) 0.3177(l) 0.2712(l) 0.1175(l) 0.0739(l) 0.1973(l) 0.3865(3) 0.3176(4) 0.2018(4) 0.0882(5) 0.1266(4) 0.2560(4) 0.3850(4) 0.3146(4) 0.1941(4) 0.0808(4) 0.1273(4) 0.2553(4) 0.3182(6) 0.0837(4) 0.4146(5)
et al.
-0.3212(3) -0.1667(3) 0.0495(3) 0.0443(3) -0.1688(3) -0.3064(2) -0.3089(3) -0.1631(3) 0.0452(3) 0.0393(3) -0.1696(3) -0.2959(2) -0.2152(7) -0.0559(7) 0.0292(8) -0.064117) -0.2494(7) -0.2303(8) -0.2094(7) -0.0545(8) 0.028317) -0.0629(8) -0.2447(9) -0.2284(g) -0.162(l) -0.1633(9) -0.3733(8)
and temperature occ 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
factors Ueqa 18(2)
2x3 23(2) 18(2)
16(2) 21ca 18(2)
ma 19La 18(2) 19(2)
ma 436) 446) 54(6)
51(E) 46(6)
637) 40(6)
Q(6) 34(5) 50(7) 57(7) 59U) 103(10) 57(5) 46(6)
Mutinaite can be considered a medium-pore zeolite whose framework contains two intersecting channel systems: one sinusoidal, running parallel to [OOl] and the other straight, running parallel to [OlO]. In catalysis science, the flexibility of the framework of ZSM-5 plays a role in processes such as diffusion and adsorption. For this reason great attention has been devoted to the unambiguous determination of the ZSM-5 symmetry. ZSM-5 synthesized in the presence of tetrapropylammonium bromide is orthorhombic, with space group Pnma, which is also its topological symmetry. The first observations concerning changes in the crystal symmetry of ZSM-5 were reported by Wu et al.‘O When this zeolite is calcined and then cooled, the symmetry changes from the orthorhombic s.g. Pnma to the monoclinic PZi/n because of the removal of the template from the channel system. This phenomenon is reversible, and the temperature at which the monoclinic-orthorombic phase change occurs (Tt) is proportional to the Si/Al ratio. Thus, Tt is lower than 272 K if Si/Al < 55,” and it is 355 K for highly crystalline and empty silicalite. iY Lopez et al.‘” stated that the nature of framework Si substituents, and specifically their valence-no matter whether they are Al, B, or Fe”+- is among the critical variables that control the symmetry change. In other words, trivalent substituents, which generate framework charges, contribute to increasing the symmetry of ZSM-5 and to stabilizing the framework. The sorbate content also plays an important role both in the value of Tt and in the s.g. of ZSM-5. So, for
Zeolites
19:323-325.
Atom 016 017 018 019 020 021 022 023 024 025 026 Ca Xl x2 x3 x4 x5 X6 x7 X8 x9 x10 x11 x12 x13 x14 x15 Xl6
of mutinaite x/a
0.4011(5) 0.3992(5) 0.1986(6) 0.1985(6) 0.1999(6) 0.0030(3) 0.0026(4) 0.4272(7) 0.2031(8) 0.2811(6) 0.1082(5) 0.4840(8) 0.458(2) 0.070(l) 0.457(l) 0.191(2) 0.047(l) 0.060(2) 0.010(2) 0.419(2) 0.999(4) 0.486(3) 0.291(3) 0.435(2) 0.425(4) 0.157(2) 0.278(2) 0.058(2)
Y/b -0.0006(5) -0.1331(5) 0.1303(5) -0.0008(5) -0.1313(5) 0.0500(6) -0.1479(5) 0.7500 0.7500 0.7500 0.7500 0.2500 0.035(2) 0.2506 0.2500 0.2500 0.163(l) 0.056(3) 0.059(2) 0.154(2) 0.138(4) 0.076(3) 0.2500 0.183(3) 0.2500 0.2500 0.218(2) 0.220(3)
ZIG -0.3916(8) -0.4040(8) -0.3646(8) -0.3857(8) -0.4000(8) -0.2063(6) -0.2153(7) -0.334(l) -0.325(l) 0.077(l) 0.070(l) 0.923(l) 0.091(3) 0.459(2) 0.113(2) O.OlO(3) 0.648(2) 0.519(4) 0.400(3) 0.955i4; 0.424(7) 0.904(5) 0.949(6) 0.038(5) 0.818(7) 0.786(4) 0.818(4) 0.922(4)
occ
Ueq"
100 100 100 100 100 100 100 100 100 100 100
48(7) 40(6)
21(l) 33(2) 98W 53(2) 46(2) 71(3) 39(3) 33(2) 42(3) 21(2) 22(2) 20(2) 21(2) 31(3) 49(3) 34(2) 30(2)
50(6) 59(6) 52(6) 35(5) 35(6) 48(g) 61(10)
41W 31(7)
234) 72(12) 82(8) 51(10) lll(15) 176(13) 219(22) 99(13) 121(16) lOO(22) 93124) 31(20) 41(16) 166(38) 174(53) 87(26) 125(27)
sites.
DISCUSSION
324
x lo3 (A')
1997
instance, ZSM-5 in its pxylene and pdichlorobenzene forms is orthorhombic with s.g. P2,2i2i.‘*,‘” In mutinaite, the observed Pnma symmetry is consistent with the low Si/Al ratio. However, the statements above are based on data from literature that concern either HZSM-5 or phases containing organic molecules, and therefore they are not directly comparable with mutinaite where the extraframework content is completely different. In conclusion, the symmetry of the natural sample could be affected not only by the framework Al content, but also by the nature of the extraframework species. The (Si,Al) distribution is the most important crystalchemical feature of zeolitic frameworks, affecting in particular their catalytic properties. The previous studies on ZSM-5 could not give any information on this topic, as the Al content in the refined samples is too low to be detected by X-ray diffraction.“,‘“-‘” Only the refinement of Lermer et al.” was carried out on a sample with a fairly low Si/Al ratio (11.9) : but unfortunately, in this case, the large standard errors in the T-O distances prevented any reliable consideration being made about the (Si,Al) distribution. In mutinaite the Al content is by far the highest found for the ZSM-5-type frameworks, and the study of (Si,Al) ordering is in principle possible on the basis of the average T--O distances. The mean T-O distances for each tetrahedron vary within the range 1.587-1.618 A, with a mean value of 1.603 A. This narrow tetrahedral distance range, considering the standard errors in the T--O mean distance (-0.007 A), is compatible with a disor-
Crystal
Figure 1 Comparison channels of TPA-ZSM-5
of the limiting ports (left) and mutinaite
of straight (right).
lo-ring
dered (&Al) distribution. When mutinaite and TPAZSM-5” frameworks (both having Pnma symmetry) are compared, it can be observed that the mean T--O-T angle is quite similar (154.1 and 155.4, respectively), whereas single TUT angles differ by up to 13”. These structural differences mainly affect the shape of the straight lO-ring channel parallel to [OlO]; this loring in mutinaite is more elliptical than in TPA-ZSM-5, having minimum and maximum pore sizes of 4.9 A and 6.1 A, respectively. Moreover, the directions of minimum and maximum elongation in mutinaite and TPAZSM-5 are interchanged (see Figure I). The shape of the two symmetrically independent lO-rings that circumscribe the sinusoidal channel parallel to [ 1001 is nearly circular in both structures. Seventeen extraframework sites have been detected in mutinaite; they are distributed throughout the whole channel space (see Figure 2) and are characterized by low electron densities and by distances of more than 2.7 A from the framework oxygens. The partial occupancies of all ion sites and their reciprocal distances prevent us from making an unambiguous distinction between cation and water molecules. Only the site labeled Ca in Table 1 was tentatively interpreted as a cation site on the basis of its low atomic displacement factor and its regular &fold coordination polyhedron. This site is not coordinated to framework oxygens, and it corre-
et al.
Financial support was provided by Consiglio Nazionale delle Ricerche, Minister0 dell’Universita e della Ricerca Scientifica e Tecnologica, Programma Nazionale di Ricerche in Antartide, and European Synchrotron Radiation Facility (Public User Program). The staff of the Swiss-Norwegian beamline (ESRF) is thanked for the collection of X-ray powder diffraction data used for cell parameter refinement.
REFERENCES 1 2 3 4 5 6
10 11 12 13 14 15 16 17 channel axis of the mutinaite by filled circles.
G. Vezzalini
ACKNOWLEDGMENTS
8 9
View down the straight The Ca site is represented
of mutinaite:
sponds to the OX2 site reported by Lermer et al.” and to the N site of TPA-ZSM-5 structure refinement.i6 It is noteworthy that almost all the “5-ring” natural zeolites have been found at Mt. Adamson; among them, two (boggsite’ and tschernichite’) are very rare, and three (gottardiite,4,5 terranovaite,‘j and mutinaites) have been discovered in this locality. Accurate structural refinements carried out on boggsite,la gottardiite,4 and terranovaite’j (all high-silica zeolites) revealed a strong disorder in the extraframework cation and water molecule distribution, as well as very large atomic displacement parameters of the framework atoms. These peculiarities indicate that somewhat special conditions were involved in the crystallization of these zeolites, such as rapid environment cooling during crystal growth. If these conditions could be identified, a way of synthesizing these phases-which are potentially useful as molecular sieves and catalysts-might be found.
7
Figure 2 structure.
structure
18
Kokotailo, G.T., Lawton, S.L., Olson, D.H. and Meier, W.M. Nature 1978,272, 437 Olson, D.H., Kokotailo, G.T., Lawton, S.L. and Meier, W.M. J. Phys. Chem. 1981,85,2238 Galli, E., Vezzalini, G., Quartieri, S., Alberti, A. and Franzini, M. Zeolites 1997, 19, in press Alberti, A., Vezzalini, G., Galli, E. and Quattieri, S. Eur. J. Mineral. 1996, 8, 69 Galli. E.. Quartieri. S.. Vezzalini. G. and Alberti. A. Eur. J. Mint&al.’ 1996, 8, $87 Galli, E., Quartieri, S., Vezzalini, G., Alberti, A. and Franzini, M. Amer. Mineral. 1997, 82, 423 Galli, E., Quartieri, S., Vezzalini, G. and Alberti, A. Eur. J. Mineral. 1995, 7, 1029 Kvick. A. and Wulff. N. Rev. Sci. lnstr. 1992. 63. 1073 Sheldrick, G.M. SH.kLX-76: A Program for drystar Structure Determination, Cambridge University, England, 1976 Wu, E.L., Lawton, S.L., Olson, D.H., Rohrman, A.C., Jr. and Kokotailo, G.T. J. Phys. Chem. 1979, 83, 2777 Hay, D.G. and Jaeger, H. J. Chem. Sot. Chem. Commun. 1984, 1433 Hay, D.G., Jaeger, H. and West, G.W. J. Phys. Chem. 1985, 85, 1070 Lopez, A., Soulard, M. and Guth, J.L. Zeolites 1990, 10, 134 van Koningsveld, H., Tuinstra, F., van Bekkum, H. and Jansen, J.C. Acta Cryst. 1989, 845, 423 van Koningsveld, F., Jansen, J.C. and van Bekkum, H. Acta Cryst. 1996, 852, 140 van Koningsveld, H., van Bekkum, H. and Jansen, J.C. Acta Cryst. 1987, 843, 127 Lermer, H., Draeger, M., Steffen, J. and Unger, K.K. Zeolites 1985, 5, 131 Howard, D.G., Tschernich, R.W., Smith, J.V. and Klein, G.L. Amer. Mineral. 1990, 75, 1200
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