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LixH12xy+z[P12OyN24y]ClzЧAn Oxonitridophosphate with a Zeolitelike Framework Structure Composed of 3-Rings.

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Angewandte
Chemie
Oxonitridophosphate Structures
LixH12xy+z[P12OyN24y]Clz—An
Oxonitridophosphate with a Zeolitelike
Framework Structure Composed of 3-Rings**
Sascha Correll, Oliver Oeckler,* Norbert Stock, and
Wolfgang Schnick*
Phosphorus oxide nitride (PON) as well as HPN2 are
isoelectronic with SiO2. The network is made up of cornerlinked P(O,N)4 tetrahedra and crystallizes with structures
similar to known polymorphs of SiO2.[1] The partial substitution of silicon by aluminum in silicates allows a considerable
variation of the framework charge. This led to a large class of
compounds, the aluminosilicates, which were the first group
of materials to be recognized for their nanoporosity.[2]
The formal exchange of silicon by phosphorus and the
total or partial substitution of oxygen by nitrogen led to
nitrido- and oxonitridophosphates, whose framework charge
can be adjusted by variation of the O/N ratio. In contrast to
oxygen, nitrogen can bridge two (N[2]) as well as three (N[3])
tetrahedral centers, thus leading to an extension of the
structural possibilities. Therefore, a larger structural variety
with respect to cage structures and pore sizes is expected in
(oxo-)nitridophosphates than in aluminosilicates.
The total exchange of the bridging oxygen atoms by
nitrogen atoms in zeolitelike structures has been demonstrated by the synthesis of Zn7P12N24Cl2. This nitridophosphate crystallizes in the sodalite structure type.[3] The partial
substitution of oxygen by nitrogen[4] recently led to the
analogous oxonitridophosphate M8xHx[P12N18O6]X2 (M =
[*] Prof. Dr. W. Schnick, S. Correll, Dr. N. Stock
Department Chemie der Ludwig-Maximilians-Universit%t
Butenandtstrasse 5–13, 81377 M-nchen (Germany)
Fax: (+ 49) 89-2180-77440
E-mail: wolfgang.schnick@uni-muenchen.de
Dr. O. Oeckler
Max-Planck-Institut f-r Festk<rperforschung
Heisenbergstrasse 1, 70569 Stuttgart (Germany)
E-mail: oliver.oeckler@gmx.de
[**] The authors thank Prof. Dr. Arndt Simon and Viola Duppel, MaxPlanck-Institut f-r Festk<rperforschung, Stuttgart, for recording
transmission electron diffraction patterns. This work was supported
by the Fonds der Chemischen Industrie and the DFG.
Angew. Chem. Int. Ed. 2003, 42, 3549 –3552
DOI: 10.1002/anie.200351372
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3549
Communications
Cu, Li; X = Cl, Br, I).[5] The structures of these compounds
were determined from X-ray powder diffraction data. However, no framework structures containing larger pores were
observed in this class of compounds. With LixH12xy+z[P12OyN24y]Clz (1) we have been able for the first time to synthesize
a zeolitelike oxonitridophosphate[6] containing large 12-ring
channels and to determine its structure from single-crystal Xray diffraction data. The framework structure is composed of
corner-linked tetrahedra, which form P3(O,N)9 3-rings as
FBUs (fundamental building units).[7] To date, no similar
topology has been experimentally observed in zeolites.[8]
Pure 1 was synthesized by heating a mixture of Li2S/HPN2/
OP(NH2)3/LiCl or Li2O/SP(NH2)3/LiCl in sealed silica
ampoules at 700 8C for 3 days. Single-phase products containing suitable single crystals (40–80 mm) for X-ray crystalstructure determination were also obtained from the Li2S/
SP(NH2)3/OP(NH2)3/NH4Cl system [Eq. (1)].
The crystal structure was elucidated from single-crystal Xray diffraction experiments.[9] The indexing of the reflections
initially led to a hexagonal unit cell with a = 1641(1) and c =
475(1) pm. However, no trigonal or hexagonal space group
could be identified unambiguously based on the reflection
conditions. Nevertheless, the best structure solution was
obtained in the space group P31c, although the data set
contained reflections that violated the reflection conditions of
the c glide plane. The subsequent structure refinement led to
unreasonable thermal parameters for the phosphorus atoms
in the direction of the trigonal axis and to split positions for
the nitrogen and oxygen atoms. The detailed analysis of the
sections of the reciprocal space calculated from imaging plate
data showed systematic absences in the hk0 plane (according
to the trigonal system) that were not in agreement with
reflection conditions possible in the trigonal or hexagonal
crystal systems. Only the assumption of a partial pseudomerohedral triple twinning of index 2 with a smaller orthorhombic
unit cell (a = 475.3(1), b = 1420.8(3), c = 820.3(2) pm) could
explain the diffraction patterns, and the structure was
successfully refined in the space group Pna21. The pseudosymmetry is also manifested in the broadening of some
reflections in the X-ray powder-diffraction pattern of a singlephase sample (Figure 1).[10] Furthermore, electron-diffraction
experiments[11] revealed varying diffraction patterns from
different areas of crystallites, which were only shifted but not
tilted during the experiment (Figure 2). These diffraction
patterns could be indexed by using the orthorhombic unit cell
and assuming the presence of a triply twinned crystallite. The
absence of an inversion center was confirmed by second
harmonic generation (SHG) measurements.[12] The oxygen
and nitrogen atoms could not be differentiated based on the
3550
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 1. Observed (crosses) and calculated (line) X-ray powder diffraction pattern as well as the difference profile of the LeBail fit of a
pure sample of 1. Allowed peak positions are marked by vertical lines.
Figure 2. Electron diffraction images at different positions of a triply
twinned crystallite of 1 (view along the zone axis [111] with respect to
the measured hexagonal cell).
X-ray crystallographic data. The approximate composition of
the single crystals was determined by energy-dispersive X-ray
(EDX) analysis[13] and confirmed by chemical elemental
analysis (see Experimental Section).
Solid 1 is composed of a network of all-side corner-sharing
P(O,N)4 tetrahedra with a topology previously not
observed.[14]
According
to
the
formula
3
[4]
[2]
[2]
(12y) [15]
[(P
O
N
)
],
all
oxygen
and
nitrogen
atoms
12
y
24y
1
bridge two phosphorus atoms. The P(O,N)4 tetrahedra form 3rings, which constitute the FBU (Figure 3 a). Each FBU is
connected along [100] through three (O,N)-P-(O,N) bridges;
the resulting zigzag chains contain 6-rings (Figure 3 b). The
chains of 3-rings are connected to a 3D PON framework in
the b,c plane. Thus 12-ring channels that contain Cl ions in
their centers are formed along [100] (Figure 3 c). The Li+ ions
occupy the inner walls of these channels and are tetrahedrally
surrounded by one Cl ion and three O or N atoms. The
partial occupancy of the Li positions, which was found by
elemental analysis as well as by structure refinement, is
compensated by substitution with hydrogen atoms. Solid-state
NMR spectroscopic investigations[16] showed that the hydrogen atoms are covalently bound to the nitrogen atoms, which
results in compensation of the charge. These imido groups
were unequivocally confirmed by IR and Raman spectroscopy.[17]
The Cl ions in the channels occupy the preferred
positions close to x = 0 and x = 1=2 only with a certain
probability. Sections of the electron-density distribution
obtained from difference Fourier synthesis perpendicular to
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 3549 –3552
Angewandte
Chemie
Figure 4. Projection of the electron-density distribution along [100] calculated by difference Fourier synthesis (top) and a section at z = 0.44,
view along [001] (bottom), after refinement of the PON framework.
The Cl ions are located in the center of the channels along [100] with
a higher probability at the positions close to x = 0 and x = 1=2 .
pounds, led to diffuse diffraction patterns in the higher-order
sections of the reciprocal space perpendicular to the pseudotrigonal axis (Figure 5). The crystal structure of these single
crystals could only be refined satisfactorily by assuming a
Figure 3. a) Assembly of the P3(O,N)9 3-rings, the FBUs, in 1. P: black;
O/N: light gray; view along [100]. b) Linkage of the FBUs along [100]
through three (O,N)-P-(O,N) bridging units. Thus, chains of 6-rings
are formed. View along [001]. c) Crystal structure of 1. Chains of 3rings are connected to a 3D PON framework in the b,c plane. Thus,
12-ring channels are formed. [P(O,N)4]: gray polyedra, O/N: light gray,
Cl : dark gray, Li+: black, view along [100].
[001] through the center of the channels show blurred
electron density along the channels with maxima at the
preferred positions mentioned above (Figure 4). This implies
the partial occupancy of the Cl ions. Full occupancy of the
preferred Cl positions would lead to neighboring Cl–Cl
contacts of 223 pm, which is clearly below the sum of the ionic
radii (334 pm). On the other hand, as the Cl ions presumably
dictate the structure, an ordered occupancy of every second
position would lead to a Cl content that is too small for the
stabilization of the network. We have not yet been able to
exchange the Cl or Li+ ions with ions of similar size, for
example, F , Br , and Mg2+, in aqueous solution. Nevertheless, Cl can be partially replaced by Br if the synthesis is
carried out in the presence of NH4Br. A free diameter of the
channels of 352 pm is observed, and the framework density is
21.7 T/(1000 D3), which is the upper limit observed in oxidic
zeolites.[8] Many of the X-ray and electron-diffraction investigations of 1, and especially those of Br-containing comAngew. Chem. Int. Ed. 2003, 42, 3549 –3552
Figure 5. (3kl) section of the reciprocal space of 1 containing small
amounts of Br , calculated from imaging-plate data. Diffuse scattering
in the shape of honeycombs is observed in all sections with h > 0.
disorder in addition to the triple twinning. Furthermore, split
positions had to be introduced for the PON tetrahedral
framework for the phosphorus and nitrogen/oxygen atoms, as
was previously necessary for the refinement of the structural
model in the incorrect space group P31c. Apparently there
are regions in the crystal where the size of the triple-twin
domains is below the coherence length of the X-rays. These
are better described by a disorder model. In most cases these
regions amount to less than 10 % of the crystal. These crystals
and crystallites thus contain both large domains, which can be
covered by a triple domain refinement, and smaller domains,
www.angewandte.org
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3551
Communications
which cannot be resolved by the coherent X-ray beam.
Therefore, the latter appear as an averaged structure by
taking into account only the Bragg intensities. The boundary
of the domains are responsible for the diffuse scattering that is
observed in the sections perpendicular to [100] and leads to a
honeycomb-like arrangement (for example, Figure 5 shows
the (3kl) section). From this we can assume the presence of a
disordered rod packing. Accordingly, the small domains act as
“microfibers” of the structure that build up the crystals/
crystallites in an irregular arrangement.
Experimental Section
Typical procedure: Li2S (15.9 mg, 0.347 mmol; Alfa Aesar, 99.9 %),
SP(NH2)3 (82.5 mg, 0.742 mmol; synthesized according to reference [18]), OP(NH2)3 (21.9 mg, 0.231 mmol; synthesized according
to reference [19]), and NH4Cl (13.0 mg, 0.243 mmol; Fluka, puriss.
p.a.) were thoroughly mixed in a glove box and transferred into a
silica ampoule (wall thickness 2 mm, inner diameter 11 mm). The
sealed, evacuated ampoule (length 100 mm), was heated to 200 8C
(1 8C min1), and the temperature was maintained for 24 h. The
ampoule was then heated to 700 8C (1 8C min1), kept at that
temperature for 48 h, and then cooled down to room temperature
(1 8C min1). Excess NH4Cl and (NH4)2S, which were formed during
the reaction, sublimed at the upper end of the ampoule. The samples
were washed with water to remove further impurities. EDX investigations[13] showed a ratio P/Cl 5:1. To ensure the purity of the
sample, chemical analyses were performed in the microanalytical
laboratory Pascher, Remagen. For the reaction mentioned above the
following composition was observed: Li8H4.5[P12O2N22]Cl2.5.
Received: March 11, 2003 [Z51372]
.
Keywords: oxonitridophosphates · phosphorus · solid-state
structures · structure elucidation · zeolite analogues
[1] a) L. Boukbir, R. Marchand, Y. Laurent, P. Bacher, G. Roult,
Ann. Chim. 1989, 14, 475 – 481; b) J.-M. LKger, J. Haines, L. S.
De Oliveira, C. Chateau, A. Le Sauze, R. Marchand, S. Hull, J.
Phys. Chem. Solids 1999, 60, 145 – 152; c) C. Chateau, J. Haines,
J.-M. LKger, A. Le Sauze, R. Marchand, Am. Mineral. 1999, 84,
207 – 210; d) J. Haines, C. Chateau, J.-M. LKger, A. Le Sauze, N.
Diot, R. Marchand, S. Hull, Acta Crystallogr. Sect. B. 1999, 55,
677 – 682.
[2] a) A. K. Cheetham, G. FKrey, T. Loiseau, Angew. Chem. 1999,
111, 3466 – 3492; Angew. Chem. Int. Ed. 1999, 38, 3268 – 3292;
b) G. FKrey, A. K. Cheetham, Science 1999, 283, 1125 – 1126;
c) M. E. Davis, Chem. Eur. J. 1997, 3, 1745 – 1750.
[3] W. Schnick, J. LMcke, Angew. Chem. 1992, 104, 208 – 209; Angew.
Chem. Int. Ed. Engl. 1992, 31, 213 – 215.
3552
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
[4] R. Marchand, W. Schnick, N. Stock, Adv. Inorg. Chem. 2000, 50,
193 – 233.
[5] N. Stock, E. Irran, W. Schnick, Chem. Eur. J. 1998, 4, 1822 – 1828.
[6] N. Stock, PhD thesis, UniversitNt Bayreuth (Germany), 1998.
[7] a) L. B. McCusker, F. Liebau, G. Engelhardt, Pure Appl. Chem.
2001, 73, 381 – 394; b) L. B. McCusker, F. Liebau, G. Engelhardt,
Microporous Mesoporous Mater. 2003, 58, 3 – 13.
[8] C. Baerlocher, W. M. Meier, D. H. Olson, Atlas of Zeolite
Framework Types, 5th ed., Elsevier, Amsterdam, 2001; http://
www.iza-structure.org/databases/
[9] X-ray single-crystal structure determination: Stoe IPDS II
diffractometer, MoKa (71.073 pm), 2qmax = 56.58; crystal (80 O
50 O 40 mm3) without any diffuse scattering, orthorhombic,
space group Pna21 (no. 33), a = 475.3(1), b = 1420.8(3), c =
820.3(2) pm, V = 554.0(2) O 106 pm3, Z = 1, least-squares refinement on F2 (G. M. Sheldrick, SHELXL 97 program for the
refinement of crystal structures, University of GPttingen,
GPttingen (Germany), 1997); R1 (I 2s(I)) = 0.051 for 5929
reflections, wR2 (all data) = 0.127 for 7595 reflections and 108
parameters; residual electron density (max./min.) = 0.637/
0.550 e D3, all O and N positions were refined as N atoms,
H atoms were not observed in the difference Fourier synthesis.
Further details on the crystal structure investigations are
available from the Fachinformationszentrum Karlsruhe, 76 344
Eggenstein-Leopoldshafen, Germany (fax: (+ 49) 7247-808-666;
e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository
number CSD-391 200.
[10] The diffraction pattern was recorded on a Stoe Stadi P powder
diffractometer (CuKa1, l = 154.05 pm).
[11] Electron-diffraction experiments were performed on a Philips
CM30 ST electron microscope (300 kV, LaB6-cathode).
[12] The authors thank Prof. Dr. Alois Seilmeier and Petra Lehmeier,
Lehrstuhl Experimentalphysik III der UniversitNt Bayreuth, for
the SHG measurements.
[13] EDX analyses were performed on a JSM 6500F (Jeol, USA)
scanning electron microscope.
[14] Although the topology of the framework was not previously
observed experimentally, their existence, in principle, had been
predicted: M. O'Keeffe, Acta Crystallogr. Sect. A 1992, 48, 670 –
673. We thank Dr. R. Bell, Royal Institution of Great Britain,
London, for this information.
[15] The extensive crystal-chemical formula according to F. Liebau
(F. Liebau, Micropor. Mesopor. Mater. 2003, 58, 15 – 72) has to be
set up as follows: g j LixClz j 1 h[P12V[4]d1;4cOy[2]N12+xz[2](NH)12xy+z[2]]1 h{3/FR: uB, 3, 1, 0; uB, 3, 1} p{1/[66122]1[100]:
12R (3.55 O 3.60), (3.52 O 3.52 O ¥); 2; 46.22} (O/Pna21/4.75,
14.21, 8.20/554).
[16] S. Correll, O. Oeckler, N. Stock, J. Senker, W. Schnick,
unpublished results.
[17] IR and Raman spectroscopic investigations were performed on a
Bruker IFS 66v/S FTIR spectrometer equipped with a FRA 106/
S Raman module.
[18] W. Schnick, Z. Naturforsch. B 1989, 44, 942 – 945.
[19] R. Klement, O. Koch, Chem. Ber. 1954, 87, 333 – 340.
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