- Email: [email protected]
Synthesis and single crystal structure of an AFX-type magnesium aluminophosphate
Microporous and Mesoporous Materials 50 (2001) 145±149
www.elsevier.com/locate/micromeso
Synthesis and single crystal structure of an AFX-type magnesium aluminophosphate Pingyun Feng a,*, Xianhui Bu b, Chung-Sung Yang a b
a Department of Chemistry, University of California, Riverside, CA 92521, USA Department of Chemistry, University of California, Santa Barbara, CA 93106, USA
Received 15 July 2001; accepted 12 September 2001
Abstract SAPO-56 (framework type: AFX) has a framework topology slightly dierent from that of zeolite chabazite (framework type: CHA). While metal substituted aluminophosphate chabazite analogues can be prepared under a variety of experimental conditions with dozens of dierent amines, the synthesis of SAPO-56 type materials has been more dicult, particularly in non-SAPO compositions. Prior to this work, the growth of large crystals of the AFX-type materials suitable for single crystal diraction has not been possible in any composition. Here we report the synthesis and single crystal structure of a magnesium aluminophosphate denoted as MAPO-AFX. This represents the ®rst time that the AFX-type topology is made in a metal aluminophosphate composition. The synthesis was accomplished with a novel polyether diamine as the structure-directing agent. Crystal data for MAPO-AFX, RH2 0:10 NH4 0:45 Mg0:65 Al1:35 PO4 2 H2 O where R OCH2 CH2 O CH2 3 NH2 2 , space group P-31c (#163), Z 12, MoKa radia c 20:204(1) A, V 3352:7(3) A 3 , re®nement on F 2 , R F 7:94% for 131 tion, 2hmax 50°, a 13:8425(6) A, parameters and 1218 unique re¯ections with I > 2:0r(I). Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Magnesium aluminophosphate; Aluminophosphate; Open framework structures; Zeolite; Metal substituted aluminophosphate; Molecular sieve; Single crystal structure
1. Introduction The discovery of a family of aluminophosphate based molecular sieves in early 1980s was a major breakthrough in the study of porous materials and has stimulated a tremendous amount of research activity focused on synthesis, structure, and characterization of three-dimensional framework materials other than traditional aluminosilicates [1±6]. One class of materials that can have industrial applications are silicon or metal substituted alu*
Corresponding author.
minophosphates called SAPOs or MeAlPOs [7,8]. For example, SAPO-34 with the chabazite topology has been widely studied for the catalytic conversion of methanol to ole®ns [9]. MeAlPOs have been investigated not only for their acidic properties, but also for their catalytic properties in redox reactions [10]. In order to meet the need of a variety of applications, it is clearly desirable to have a zeolite-type material in various dierent compositions. Here we report synthesis and single crystal structure of a magnesium aluminophosphate with the AFX framework type. The AFX-type framework topology was ®rst found in polycrystalline
1387-1811/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 1 8 1 1 ( 0 1 ) 0 0 4 4 1 - 3
146
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149
SAPO-56 samples [11]. The availability of large single crystals in the MeAlPO composition could give more comprehensive and accurate structural information, which may have signi®cant chemical implication (e.g. determination of uniformity of cation substitutions among framework Al3 sites) as well.
2. Experimental procedure 2.1. Synthesis Slurry A was prepared by adding aluminum isopropoxide (1.46 g, 98%, Aldrich) and H3 PO4 (1.48 g, 85 wt.% in water) into ethylene glycol (7.79 g). The mixture was stirred for 1 week. Solution B was prepared by mixing 1.23 g magnesium hydrogenphosphate trihydrate (99%, Aldrich) with H2 O (7.41 g) and H3 PO4 (0.86 g, 85 wt.% in water) and was stirred for 1 h. To the mixture of A and B, 2.22 g of 4,7,10-trioxa-1,13-tridecanediamine (TCI America, Fig. 1) was slowly added with stirring. The ®nal pH of the mixture was 7.09. The mixture was stirred for 3 h at room temperature, transferred into a 23 ml autoclave, and heated in an oven at 170° for seven days. The product was ®ltered, washed with distilled H2 O and ethanol, and further puri®ed with the ultrasonic technique. The product consisted of crystals with two dierent morphologies. The majority of crystals were thick hexagonal plates and these were identi®ed to be crystals of UCSB-10Mg by single crystal X-ray diraction [12]. Crystals of MAPO-AFX were smaller and adopted the shape of hexagonal bipyramid (Fig. 2). Two phases could be separated manually under an optical microscope. Results of the elemental analysis on pure crystals of MAPOAFX (in wt.%) are 4.18 (calc. 4.13), 2.37 (calc. 2.22), and 3.10 (calc. 3.13) for C, H, and N, respectively.
Fig. 1. The structural diagram for 4,7,10-trioxa-1,13-tridecanediamine.
Fig. 2. A SEM picture of a crystal of MAPO-AFX showing the hexagonal bipyramidal morphology.
2.2. Microscopy Scanning electron microscopy (SEM) images were obtained from Philips XL30-FEG with a 5 kV scanning voltage. Samples were deposited onto conducting carbon ®lm and coated with Au/Pd by ion sputtering at room temperature. Energy dispersive spectra (EDS) showed distinct peaks from both Al and Mg, supporting the substitution of Mg2 into the host framework. 2.3. Single crystal diraction A crystal was glued to a thin glass ®ber with epoxy resin and mounted on a Bruker Smart 1000 CCD diractometer equipped with a normal focus, 2.4 kW sealed tube X-ray source (MoKa radiation, operating at 45 kV and 40 mA. A k 0:71073 A) hemisphere of intensity data were collected with x scans (width of 0.30° and exposure time of 10 s per frame). The structure was solved by direct methods followed by successive dierence Fourier methods. All calculations were performed using SHELXTL running on Silicon Graphics Indy 5000. Final full-matrix re®nements were against F 2 and included anisotropic thermal parameters for all framework atoms. Crystallographic results are
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149 Table 1 A summary of crystal data and re®nement results Formulaa
Table 3 and angles (°) Selected bond lengths (A)
RH2 0:10 NH4 0:45 Mg0:65 Al1:35 PO4 2 H2 O Clear hexagonal bipyramid 0:24 0:13 0:13 13.8425(6) 20.204(1) 3352.7(3) 12 P-31c 50 16659 1984 1218 131 7.94 26.1 1.23
Habit Size (mm3 ) a (A) c (A) 3 ) V (A
Z Space group 2hmax (°) Total data Unique data Unique data, I > 2r I Parameters R(F )b Rw (F 2 )c GOF
a R is 4,7,10-trioxa-1,13-tridecanediamine, O[CH2 CH2 O(CH2 )3 NH2 ]2 (or C10 H24 N2 O3 ). P P b R F jjFo j jFc jj= jFo j with Fo > 4:0r F . P P c 2 2 2 2 Rw F w Fo Fc = w Fo2 2 1=2 with Fo > 4:0 r F .
Table 2 Atomic coordinates (104 ) and equivalent isotropic displace2 103 ). Ueq is de®ned as one-third of the ment parameters (A trace of the orthogonalized Uij tensor Al(1) Al(2) P(1) P(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8)
147
x
y
z
Ueq
8937(2) 9947(1) 8945(1) 9957(1) 9261(4) 7747(3) 10878(3) 9712(4) 9083(4) 8842(3) 9963(4) 9865(4)
3315(1) 2258(2) 3335(1) 2262(1) 3270(3) 2445(4) 1980(4) 3167(4) 4466(3) 1247(3) 2640(4) 3064(4)
8248(1) 5737(1) 6687(1) 4184(1) 7392(2) 6551(2) 4097(2) 6233(2) 6550(2) 4014(2) 4889(2) 8719(2)
51(1) 51(1) 45(1) 46(1) 66(1) 68(1) 82(1) 79(2) 72(1) 64(1) 68(1) 85(2)
summarized in Table 1 while atomic coordinates and selected bond distances are listed in Tables 2 and 3, respectively. 3. Results and discussion The AFX type topology was ®rst discovered in a silicon-substituted aluminophosphate called SAPO-46 [11]. An aluminosilicate form called SSZ-16 was discovered later by use of diquater-
Al(1)±O(5) Al(1)±O(2) Al(2)±O(3) Al(2)±O(6) P(1)±O(1) P(1)±O(4) P(2)±O(7) P(2)±O(6) P(1)±O(1)±Al(1) P(2)±O(3)±Al(2) P(1)±O(5)±Al(1) P(2)±O(7)±Al(2)
1.760(4) 1.782(5) 1.759(4) 1.779(4) 1.505(4) 1.507(4) 1.517(4) 1.518(4) 145.5(3) 148.5(3) 153.0(3) 143.2(3)
Al(1)±O(8) Al(1)±O(1) Al(2)±O(4) Al(2)±O(7) P(1)±O(5) P(1)±O(2) P(2)±O(3) P(2)±O(8) P(1)±O(2)±Al(1) P(1)±O(4)±Al(2) P(2)±O(6)±Al(2) P(2)±O(8)±Al(1)
1.767(4) 1.796(4) 1.761(4) 1.790(4) 1.505(4) 1.517(4) 1.519(4) 1.518(4) 144.1(3) 148.5(3) 148.8(3) 148.7(3)
nary ammonium compounds [13]. In both cases, the crystal structure was modeled from the powder sample. In this work, we were able to grow large single crystals (Fig. 2) of the magnesium aluminophosphate analogue and determined the crystal structure from single crystal diraction data. One noticeable dierence between MAPO-AFX and SAPO-56 is in their unit cell parameters. Be is signi®cantly cause Mg2 (ionic radius: 0.57 A) 4 [14], the unit larger than Si (ionic radius: 0.26 A) and cell parameters of MAPO-AFX (a 13:843 A c 20:204 A) are also larger than those of SAPO and c 19:949 A). In addition, 56 (a 13:762 A SAPO-56 was prepared using N ,N ,N 0 ,N 0 -tetramethyl-1,6-hexanediamine while MAPO-AFX was synthesized from a distinctly dierent polyether diamine called 4,7,10-trioxa-1,13-tridecanediamine (Fig. 1). MAPO-AFX is among about a dozen of zeolite structure types that are based on the stacking of hexagonal rings. Two simplest structures in this family are cancrinite built from the AB sequence and sodalite built from the ABC sequence. Among the most complicated structures is AlPO4 -52 (the structure type: AFT) that has a sequence of AABBCCAACCBB. MAPO-AFX reported here has an intermediate level of complexity in its stacking sequence known as AABBCCBB [8]. The asymmetric unit of MAPO-AFX consists of four tetrahedral atom sites (Fig. 3). The level of the magnesium substitution is relatively high and leads to an obvious lengthening of the metal± for oxygen bond from a typical value of 1.74 A for the the pure Al3 sites to an average of 1.78 A
148
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149
Fig. 3. The ORTEP view of coordination environments for tetrahedral atoms in MAPO-AFX. Atoms having ``A'' in their labels are symmetry-generated.
mixed Mg2 /Al3 sites in MAPO-AFX. It is noteworthy that in MAPO-AFX, the average metal±oxygen distances for two unique metal atom sites are identical within the experimental errors. This suggests that magnesium cations are more or less uniformed distributed among framework Al3 sites even though there are two crystallographically unique metal sites. Similar to structures such as chabazite and AlPO4 -52, MAPO-AFX also consists of double six-ring units. In MAPO-AFX, there are two different types of cages. One is called the gmelinite cage originally discovered in the mineral gmelinite
while the other type of cage is called the AFT cage originally found in AlPO-52 (Fig. 4). The gmelinite cage consists of 24 tetrahedral atoms located on four hexagonal sheets whereas the AFT cage consists of 48 tetrahedral atoms distributed on eight hexagonal sheets. The framework of MAPOAFX consists of three-dimensional eight-ring channels (Fig. 5). Compared to a similar diamine with the backbone chain consisting of only carbon atoms, 1,13-tridecanediamine, 4,7,10-trioxa-1,13-tridecanediamine is more hydrophilic because of the presence of three oxygen atoms in the 13-atom chain (excluding two NH2 head groups). This is advantageous because of the increase in the solubility of the structure-directing agent. In addition, this could also allow 4,7,10-trioxa-1,13-tridecanediamine to adopt con®gurations within the MAPOAFX framework that might not be possible if 1, 13-tridecanediamine were used. This ability in the ®ne-tuning of the hydrophobicity/hydrophilicity of long-chain amine molecules is expected to be useful in the rational synthesis of other zeolite-type materials. While the framework atoms have been precisely located, the structure-directing agent is severely
Fig. 4. Two dierent cages in MAPO-AFX: (a) the gmelinite cage capped by two double six-ring units; (b) the AFT cage capped by two double six-ring units.
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149
149
Fig. 5. Projections of the three-dimensional framework down (a) the a axis (b) the c axis in MAPO-AFX. Large cross-hatched circles represent Al(Mg) sites whereas small open circles represent P sites.
disordered and the overall molecular position is not determined. This is in part because the molecular symmetry of 4,7,10-trioxa-1,13-tridecanediamine is too low compared to the host framework. There are some residual peaks located away from framework oxygen atom about 3 A sites. These are likely nitrogen (or oxygen) atoms that form N±H O (or O±H O) type hydrogen bonding with framework oxygen atoms. Acknowledgements This work is supported in part by UC Riverside and UC Energy Institute. References [1] S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan, E.M. Flanigen, J. Am. Chem. Soc. 104 (1982) 1146±1147. [2] S.T. Wilson, E.M. Flanigen, ACS Symp. Ser. (Zeolite Synth.) 398 (1989) 329±345.
[3] T.E. Gier, G.D. Stucky, Nature 349 (1991) 508±510. [4] J.B. Parish, D.R. Corbin, T.E. Gier, R.L. Harlow, L. Abrams, R.B. von Dreele, Zeolites 12 (1992) 360± 368. [5] P. Feng, X. Bu, G.D. Stucky, Nature 388 (1997) 735± 741. [6] X. Bu, P. Feng, T.E. Gier, D. Zhao, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 13389±13397. [7] R. Szostak, Handbook of Molecular Sieves, Van Nostrand-Reinhold, New York, 1992. [8] W.M. Meier, D.H. Olson, Ch. Baerlocher, Atlas of Zeolite Structure Types, Elsevier, Amsterdam, 1996. [9] Z. Zhu, M. Hartmann, L. Kevan, Chem. Mater. 12 (2000) 2781±2787. [10] R. Wendelbo, D. Akporiaye, A. Andersen, I.M. Dahl, H.B. Mostad, Appl. Catal. A 142 (1996) L197±L207. [11] S.T. Wilson, N.K. McGuire, C.S. Blackwell, C.A. Bateman, R.M. Kirchner, Stud. Surf. Sci. Catal. (Zeolite Science 1994: Recent Progress and Discussions) 98 (1995) 9±10. [12] X. Bu, P. Feng, G.D. Stucky, Science 278 (1997) 2080±2085. [13] R.F. Lobo, S.I. Zones, R.C. Medrud, Chem. Mater. 8 (1996) 2409±2411. [14] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751±767.
www.elsevier.com/locate/micromeso
Synthesis and single crystal structure of an AFX-type magnesium aluminophosphate Pingyun Feng a,*, Xianhui Bu b, Chung-Sung Yang a b
a Department of Chemistry, University of California, Riverside, CA 92521, USA Department of Chemistry, University of California, Santa Barbara, CA 93106, USA
Received 15 July 2001; accepted 12 September 2001
Abstract SAPO-56 (framework type: AFX) has a framework topology slightly dierent from that of zeolite chabazite (framework type: CHA). While metal substituted aluminophosphate chabazite analogues can be prepared under a variety of experimental conditions with dozens of dierent amines, the synthesis of SAPO-56 type materials has been more dicult, particularly in non-SAPO compositions. Prior to this work, the growth of large crystals of the AFX-type materials suitable for single crystal diraction has not been possible in any composition. Here we report the synthesis and single crystal structure of a magnesium aluminophosphate denoted as MAPO-AFX. This represents the ®rst time that the AFX-type topology is made in a metal aluminophosphate composition. The synthesis was accomplished with a novel polyether diamine as the structure-directing agent. Crystal data for MAPO-AFX, RH2 0:10 NH4 0:45 Mg0:65 Al1:35 PO4 2 H2 O where R OCH2 CH2 O CH2 3 NH2 2 , space group P-31c (#163), Z 12, MoKa radia c 20:204(1) A, V 3352:7(3) A 3 , re®nement on F 2 , R F 7:94% for 131 tion, 2hmax 50°, a 13:8425(6) A, parameters and 1218 unique re¯ections with I > 2:0r(I). Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Magnesium aluminophosphate; Aluminophosphate; Open framework structures; Zeolite; Metal substituted aluminophosphate; Molecular sieve; Single crystal structure
1. Introduction The discovery of a family of aluminophosphate based molecular sieves in early 1980s was a major breakthrough in the study of porous materials and has stimulated a tremendous amount of research activity focused on synthesis, structure, and characterization of three-dimensional framework materials other than traditional aluminosilicates [1±6]. One class of materials that can have industrial applications are silicon or metal substituted alu*
Corresponding author.
minophosphates called SAPOs or MeAlPOs [7,8]. For example, SAPO-34 with the chabazite topology has been widely studied for the catalytic conversion of methanol to ole®ns [9]. MeAlPOs have been investigated not only for their acidic properties, but also for their catalytic properties in redox reactions [10]. In order to meet the need of a variety of applications, it is clearly desirable to have a zeolite-type material in various dierent compositions. Here we report synthesis and single crystal structure of a magnesium aluminophosphate with the AFX framework type. The AFX-type framework topology was ®rst found in polycrystalline
1387-1811/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 1 8 1 1 ( 0 1 ) 0 0 4 4 1 - 3
146
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149
SAPO-56 samples [11]. The availability of large single crystals in the MeAlPO composition could give more comprehensive and accurate structural information, which may have signi®cant chemical implication (e.g. determination of uniformity of cation substitutions among framework Al3 sites) as well.
2. Experimental procedure 2.1. Synthesis Slurry A was prepared by adding aluminum isopropoxide (1.46 g, 98%, Aldrich) and H3 PO4 (1.48 g, 85 wt.% in water) into ethylene glycol (7.79 g). The mixture was stirred for 1 week. Solution B was prepared by mixing 1.23 g magnesium hydrogenphosphate trihydrate (99%, Aldrich) with H2 O (7.41 g) and H3 PO4 (0.86 g, 85 wt.% in water) and was stirred for 1 h. To the mixture of A and B, 2.22 g of 4,7,10-trioxa-1,13-tridecanediamine (TCI America, Fig. 1) was slowly added with stirring. The ®nal pH of the mixture was 7.09. The mixture was stirred for 3 h at room temperature, transferred into a 23 ml autoclave, and heated in an oven at 170° for seven days. The product was ®ltered, washed with distilled H2 O and ethanol, and further puri®ed with the ultrasonic technique. The product consisted of crystals with two dierent morphologies. The majority of crystals were thick hexagonal plates and these were identi®ed to be crystals of UCSB-10Mg by single crystal X-ray diraction [12]. Crystals of MAPO-AFX were smaller and adopted the shape of hexagonal bipyramid (Fig. 2). Two phases could be separated manually under an optical microscope. Results of the elemental analysis on pure crystals of MAPOAFX (in wt.%) are 4.18 (calc. 4.13), 2.37 (calc. 2.22), and 3.10 (calc. 3.13) for C, H, and N, respectively.
Fig. 1. The structural diagram for 4,7,10-trioxa-1,13-tridecanediamine.
Fig. 2. A SEM picture of a crystal of MAPO-AFX showing the hexagonal bipyramidal morphology.
2.2. Microscopy Scanning electron microscopy (SEM) images were obtained from Philips XL30-FEG with a 5 kV scanning voltage. Samples were deposited onto conducting carbon ®lm and coated with Au/Pd by ion sputtering at room temperature. Energy dispersive spectra (EDS) showed distinct peaks from both Al and Mg, supporting the substitution of Mg2 into the host framework. 2.3. Single crystal diraction A crystal was glued to a thin glass ®ber with epoxy resin and mounted on a Bruker Smart 1000 CCD diractometer equipped with a normal focus, 2.4 kW sealed tube X-ray source (MoKa radiation, operating at 45 kV and 40 mA. A k 0:71073 A) hemisphere of intensity data were collected with x scans (width of 0.30° and exposure time of 10 s per frame). The structure was solved by direct methods followed by successive dierence Fourier methods. All calculations were performed using SHELXTL running on Silicon Graphics Indy 5000. Final full-matrix re®nements were against F 2 and included anisotropic thermal parameters for all framework atoms. Crystallographic results are
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149 Table 1 A summary of crystal data and re®nement results Formulaa
Table 3 and angles (°) Selected bond lengths (A)
RH2 0:10 NH4 0:45 Mg0:65 Al1:35 PO4 2 H2 O Clear hexagonal bipyramid 0:24 0:13 0:13 13.8425(6) 20.204(1) 3352.7(3) 12 P-31c 50 16659 1984 1218 131 7.94 26.1 1.23
Habit Size (mm3 ) a (A) c (A) 3 ) V (A
Z Space group 2hmax (°) Total data Unique data Unique data, I > 2r I Parameters R(F )b Rw (F 2 )c GOF
a R is 4,7,10-trioxa-1,13-tridecanediamine, O[CH2 CH2 O(CH2 )3 NH2 ]2 (or C10 H24 N2 O3 ). P P b R F jjFo j jFc jj= jFo j with Fo > 4:0r F . P P c 2 2 2 2 Rw F w Fo Fc = w Fo2 2 1=2 with Fo > 4:0 r F .
Table 2 Atomic coordinates (104 ) and equivalent isotropic displace2 103 ). Ueq is de®ned as one-third of the ment parameters (A trace of the orthogonalized Uij tensor Al(1) Al(2) P(1) P(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8)
147
x
y
z
Ueq
8937(2) 9947(1) 8945(1) 9957(1) 9261(4) 7747(3) 10878(3) 9712(4) 9083(4) 8842(3) 9963(4) 9865(4)
3315(1) 2258(2) 3335(1) 2262(1) 3270(3) 2445(4) 1980(4) 3167(4) 4466(3) 1247(3) 2640(4) 3064(4)
8248(1) 5737(1) 6687(1) 4184(1) 7392(2) 6551(2) 4097(2) 6233(2) 6550(2) 4014(2) 4889(2) 8719(2)
51(1) 51(1) 45(1) 46(1) 66(1) 68(1) 82(1) 79(2) 72(1) 64(1) 68(1) 85(2)
summarized in Table 1 while atomic coordinates and selected bond distances are listed in Tables 2 and 3, respectively. 3. Results and discussion The AFX type topology was ®rst discovered in a silicon-substituted aluminophosphate called SAPO-46 [11]. An aluminosilicate form called SSZ-16 was discovered later by use of diquater-
Al(1)±O(5) Al(1)±O(2) Al(2)±O(3) Al(2)±O(6) P(1)±O(1) P(1)±O(4) P(2)±O(7) P(2)±O(6) P(1)±O(1)±Al(1) P(2)±O(3)±Al(2) P(1)±O(5)±Al(1) P(2)±O(7)±Al(2)
1.760(4) 1.782(5) 1.759(4) 1.779(4) 1.505(4) 1.507(4) 1.517(4) 1.518(4) 145.5(3) 148.5(3) 153.0(3) 143.2(3)
Al(1)±O(8) Al(1)±O(1) Al(2)±O(4) Al(2)±O(7) P(1)±O(5) P(1)±O(2) P(2)±O(3) P(2)±O(8) P(1)±O(2)±Al(1) P(1)±O(4)±Al(2) P(2)±O(6)±Al(2) P(2)±O(8)±Al(1)
1.767(4) 1.796(4) 1.761(4) 1.790(4) 1.505(4) 1.517(4) 1.519(4) 1.518(4) 144.1(3) 148.5(3) 148.8(3) 148.7(3)
nary ammonium compounds [13]. In both cases, the crystal structure was modeled from the powder sample. In this work, we were able to grow large single crystals (Fig. 2) of the magnesium aluminophosphate analogue and determined the crystal structure from single crystal diraction data. One noticeable dierence between MAPO-AFX and SAPO-56 is in their unit cell parameters. Be is signi®cantly cause Mg2 (ionic radius: 0.57 A) 4 [14], the unit larger than Si (ionic radius: 0.26 A) and cell parameters of MAPO-AFX (a 13:843 A c 20:204 A) are also larger than those of SAPO and c 19:949 A). In addition, 56 (a 13:762 A SAPO-56 was prepared using N ,N ,N 0 ,N 0 -tetramethyl-1,6-hexanediamine while MAPO-AFX was synthesized from a distinctly dierent polyether diamine called 4,7,10-trioxa-1,13-tridecanediamine (Fig. 1). MAPO-AFX is among about a dozen of zeolite structure types that are based on the stacking of hexagonal rings. Two simplest structures in this family are cancrinite built from the AB sequence and sodalite built from the ABC sequence. Among the most complicated structures is AlPO4 -52 (the structure type: AFT) that has a sequence of AABBCCAACCBB. MAPO-AFX reported here has an intermediate level of complexity in its stacking sequence known as AABBCCBB [8]. The asymmetric unit of MAPO-AFX consists of four tetrahedral atom sites (Fig. 3). The level of the magnesium substitution is relatively high and leads to an obvious lengthening of the metal± for oxygen bond from a typical value of 1.74 A for the the pure Al3 sites to an average of 1.78 A
148
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149
Fig. 3. The ORTEP view of coordination environments for tetrahedral atoms in MAPO-AFX. Atoms having ``A'' in their labels are symmetry-generated.
mixed Mg2 /Al3 sites in MAPO-AFX. It is noteworthy that in MAPO-AFX, the average metal±oxygen distances for two unique metal atom sites are identical within the experimental errors. This suggests that magnesium cations are more or less uniformed distributed among framework Al3 sites even though there are two crystallographically unique metal sites. Similar to structures such as chabazite and AlPO4 -52, MAPO-AFX also consists of double six-ring units. In MAPO-AFX, there are two different types of cages. One is called the gmelinite cage originally discovered in the mineral gmelinite
while the other type of cage is called the AFT cage originally found in AlPO-52 (Fig. 4). The gmelinite cage consists of 24 tetrahedral atoms located on four hexagonal sheets whereas the AFT cage consists of 48 tetrahedral atoms distributed on eight hexagonal sheets. The framework of MAPOAFX consists of three-dimensional eight-ring channels (Fig. 5). Compared to a similar diamine with the backbone chain consisting of only carbon atoms, 1,13-tridecanediamine, 4,7,10-trioxa-1,13-tridecanediamine is more hydrophilic because of the presence of three oxygen atoms in the 13-atom chain (excluding two NH2 head groups). This is advantageous because of the increase in the solubility of the structure-directing agent. In addition, this could also allow 4,7,10-trioxa-1,13-tridecanediamine to adopt con®gurations within the MAPOAFX framework that might not be possible if 1, 13-tridecanediamine were used. This ability in the ®ne-tuning of the hydrophobicity/hydrophilicity of long-chain amine molecules is expected to be useful in the rational synthesis of other zeolite-type materials. While the framework atoms have been precisely located, the structure-directing agent is severely
Fig. 4. Two dierent cages in MAPO-AFX: (a) the gmelinite cage capped by two double six-ring units; (b) the AFT cage capped by two double six-ring units.
P. Feng et al. / Microporous and Mesoporous Materials 50 (2001) 145±149
149
Fig. 5. Projections of the three-dimensional framework down (a) the a axis (b) the c axis in MAPO-AFX. Large cross-hatched circles represent Al(Mg) sites whereas small open circles represent P sites.
disordered and the overall molecular position is not determined. This is in part because the molecular symmetry of 4,7,10-trioxa-1,13-tridecanediamine is too low compared to the host framework. There are some residual peaks located away from framework oxygen atom about 3 A sites. These are likely nitrogen (or oxygen) atoms that form N±H O (or O±H O) type hydrogen bonding with framework oxygen atoms. Acknowledgements This work is supported in part by UC Riverside and UC Energy Institute. References [1] S.T. Wilson, B.M. Lok, C.A. Messina, T.R. Cannan, E.M. Flanigen, J. Am. Chem. Soc. 104 (1982) 1146±1147. [2] S.T. Wilson, E.M. Flanigen, ACS Symp. Ser. (Zeolite Synth.) 398 (1989) 329±345.
[3] T.E. Gier, G.D. Stucky, Nature 349 (1991) 508±510. [4] J.B. Parish, D.R. Corbin, T.E. Gier, R.L. Harlow, L. Abrams, R.B. von Dreele, Zeolites 12 (1992) 360± 368. [5] P. Feng, X. Bu, G.D. Stucky, Nature 388 (1997) 735± 741. [6] X. Bu, P. Feng, T.E. Gier, D. Zhao, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 13389±13397. [7] R. Szostak, Handbook of Molecular Sieves, Van Nostrand-Reinhold, New York, 1992. [8] W.M. Meier, D.H. Olson, Ch. Baerlocher, Atlas of Zeolite Structure Types, Elsevier, Amsterdam, 1996. [9] Z. Zhu, M. Hartmann, L. Kevan, Chem. Mater. 12 (2000) 2781±2787. [10] R. Wendelbo, D. Akporiaye, A. Andersen, I.M. Dahl, H.B. Mostad, Appl. Catal. A 142 (1996) L197±L207. [11] S.T. Wilson, N.K. McGuire, C.S. Blackwell, C.A. Bateman, R.M. Kirchner, Stud. Surf. Sci. Catal. (Zeolite Science 1994: Recent Progress and Discussions) 98 (1995) 9±10. [12] X. Bu, P. Feng, G.D. Stucky, Science 278 (1997) 2080±2085. [13] R.F. Lobo, S.I. Zones, R.C. Medrud, Chem. Mater. 8 (1996) 2409±2411. [14] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751±767.