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The direct synthesis and characterization of the pillared layer indium phosphate Na4[In8(HPO4)14(H2O)6]·12(H2O)
Pergamon
Materials Research Bulletin 35 (2000) 1007–1015
The direct synthesis and characterization of the pillared layer indium phosphate Na4[In8(HPO4)14(H2O)6]䡠12(H2O) Martin P. Attfielda,*, Anthony K. Cheethama, Srinivasan Natarajanb a
Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur Campus, Jakkur P. O., Bangalore 560 064, India
b
(Communicated by C.N.R. Rao) Received 21 December 1999; accepted 30 December 1999
Abstract Na4[In8(HPO4)14(H2O)6]䡠12(H2O) (trigonal, Pc1, a ⫽ 13.8500(2), c ⫽ 18.4930(3) Å, V ⫽ 3072.12(4) Å3, and Z ⫽ 2), was prepared directly in its sodium form by hydrothermal methods at 398 K, and its structure solved by single crystal methods. The three-dimensional framework structure consists of a network of InO6 and InO5(OH2) octahedra, and PO3(OH) tetrahedra forming layers, which are held in position by InO6 octahedra acting as pillars forming 12-membered ring channels. The extra-framework sodium cations are located at the sides of the 12-rings within this framework structure and are coordinated by framework oxygen atoms and extra-framework water molecules. The structure was solved using room-temperature single-crystal X-ray diffraction data from 1732 observed reflections (I ⬎ 3.0(I), R ⫽ 0.025, and Rw ⫽ 0.030). © 2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Inorganic compounds; B. Crystal growth; C. X-ray diffraction
1. Introduction The synthesis of open-framework metal phosphates has become an area of intense research effort since the first three-dimensional aluminum phosphates (AlPOs) were
* Corresponding author. Present address: Department of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK. Tel.: ⫹44-171-409-2992; fax: ⫹44-171-629-3569. E-mail address: [email protected] (M.P. Attfield). 0025-5408/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 0 ) 0 0 3 0 2 - 0
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discovered in 1982 [1,2]. The number of metals incorporated into the frameworks of these materials is constantly increasing and now includes metals such as Be [3], Ga [4], In [5], Sn [6], Zn [7], and the transition metals Ni [8], Fe [9], Co [10], and Mo [11]. Structures are known that contain one-dimensional polymeric chains, two-dimensional layers, and three-dimensional open-frameworks, some of which are novel while others are analogous to those of known aluminosilicate zeolite structures [12]. Some of the structures of these materials are intermediate between those of layered clays and the truly three-dimensional network structure of a zeolite. In most cases, the layered materials are intercalated by other inorganic polymeric forms such as the Keggin ion, which renders stability as well as a porous architecture to the structure. However, recently a new pillared layer material, [In8(HPO4)14(H2O)6](H2O)5(H3O)(C3N2H5)3 [5], has been synthesized whose nonporous layers are pillared by InO6 octahedral moieties to form an analogue to the pillared clay materials found for aluminosilicates. Such frameworks appear to combine the attractive features of the large spatial area of clays with the greater thermal stability of a zeolite. The majority of the new phases have been synthesized in the presence of an organic template molecule, which can lead to limitations for their applications and commercial utility. In many cases, the removal of the organic template molecule is only achieved by calcining the material, with subsequent collapse of the framework and loss of any exploitable properties. The cost of the organic template molecule in the synthesis and the subsequent calcination may reduce the commercial viability of the material. Thus, it is of extreme importance to find synthetic routes to these materials that involve templating species that are relatively inexpensive and easily replaced, such as alkali metal cations. Such routes have been devised for many of the aluminosilicate zeolite family, such as faujasite and ZSM-5, this being one of the main reasons for the enormous commercial utility of these materials. Similar routes have been found for the synthesis of open framework metal phosphates of Ga [13] and In [14]. In this work, we present the synthesis and characterization of Na4[In8(HPO4)14(H2O)6]䡠12(H2O), a pillared layer indium phosphate formed without the use of an organic template molecule and in a directly usable form.
2. Experimental 2.1. Synthesis and initial characterization The synthesis of Na4[In8(HPO4)14(H2O)6]䡠12(H2O) initially involved the preparation of a sodium phosphite intermediate material. The latter was formed by addition of 3.45 g of solid NaOH (Fischer) and 3.54 g of solid H3PO3 (Aldrich) to 20 ml of ethanol (Fischer). The mixture was stirred overnight. The white precipitate formed was removed from its mother liquor by suction filtration, washed in ethanol, and dried in air. A minimal quantity of deionized water was added to this precipitate to form a material whose X-ray powder diffraction pattern indicated that the predominant phase was Na2HPO3䡠5H2O (PDF 19-1267). 1.57 g of this white precipitate was added to 15 ml of deionized H2O, followed by 2.60 g of In(NO3)3䡠3H2O (Kodak) and 1.23 g of H3PO3 (Aldrich). The mixture was stirred, sealed in
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Table 1 Crystal and structure refinement data for Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) Formula Mw Crystal system Space group F(000) A C V Z Dc Crystal shape and dimensions (Mo K␣, ⫽ 0.71073 Å) 2max Limiting indices No. of reflections No. of independent reflections No. of observed reflections (I ⬎ 3.0(I)) Rint No. of refined parameters Largest difference hole and peak (eÅ⫺3) R(F), Rw(F)
Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) 2657.97 Trigonal P3c1 2520 13.8500(2) Å 18.4930(3) Å 3072.12(4) Å3 2 2.87 g cm⫺3 Hexagonal prism, 0.14 ⫻ 0.14 ⫻ 0.05 mm 34.4 cm⫺1 56.56° ⫺15 ⱕ h ⱕ 0, 0 ⱕ k ⱕ 18, 0 ⱕ l ⱕ 24 18731 2538 1732 0.040 209 ⫺0.962/0.528 0.025, 0.030
a 23 ml Teflon-lined steel autoclave, and heated at 10°C min⫺1 from room temperature to 125°C, where it was held for 50 h before being cooled to room temperature. The crystalline product was separated by suction filtration, washed in deionized water, and dried in air. The product was obtained as colorless crystals with a hexagonal prismatic habit. The crystals are stable to exposure to atmospheric conditions. Elemental analysis (ICPES) indicated a Na:In:P ratio of 3.5:8.2:13.8 (5% error in values). Thermogravimetric analysis (TGA) studies were carried out using a DuPont system (model 2000) in flowing oxygen from room temperature to 600°C. 2.2. Single crystal structure determination A suitable single crystal was carefully selected under a polarizing microscope and glued to a thin glass fiber with cyanoacrylate (superglue) adhesive. Crystal structure determination by X-ray diffraction was performed on a Siemens Smart-CCD diffractometer equipped with a normal focus, 2.4 kW sealed tube X-ray source (Mo K␣ radiation, ⫽ 0.71073 Å) operating at 50 kV and 40 mA. A full-sphere of intensity data was collected at room temperature in 2082 frames with scans (width of 0.30° and exposure time of 10 s per frame). The final unit-cell constants were determined from 4352 reflections and optimized by least-squares refinement. Pertinent details of the structure determination are presented in Table 1. On the basis of the systematic absence conditions in the reduced data and the subsequent successful solution and refinement of the structure, the space group was determined to be Pc1 (No. 165). The structure was solved by direct methods (SHELXS-
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Table 2 Final atomic coordinates, equivalent temperature factors, and fractional occupancies for Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) Atom
x
y
z
Ueq (Å2)
Occupancy
In(1) In(2) In(3) P(1) P(2) P(3) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) Na(1) Na(2) Na(3) O(1w) O(2w) O(3w) O(4w) O(5w) H(8) H(9) H(10) H(11) H(12)
0.0000 0.0000 ⫺0.43966(3) ⫺0.1924(1) ⫺0.4940(1) ⫺0.6667 ⫺0.1457(3) ⫺0.1187(3) ⫺0.3093(3) ⫺0.4351(4) ⫺0.4321(4) ⫺0.5529(4) ⫺0.5579(4) ⫺0.1988(7) ⫺0.4931(6) ⫺0.6667 ⫺0.3103(4) 0.265(3) 0.454(2) 0.237(1) 0.606(2) 0.362(1) 0.270(2) 0.558(6) 0.333(2) ⫺0.2454(7) ⫺0.5316(6) ⫺0.57610(1) ⫺0.260(7) ⫺0.284(7)
0.0000 0.0000 ⫺0.29356(3) ⫺0.1589(1) ⫺0.1239(1) ⫺0.3333 ⫺0.0648(3) ⫺0.1381(3) ⫺0.1849(4) ⫺0.1463(4) ⫺0.4338(4) ⫺0.3839(3) ⫺0.3252(4) ⫺0.2637(6) ⫺0.1910(6) ⫺0.3333 ⫺0.2549(4) 0.265(3) 0.514(2) 0.272(1) 0.606(2) 0.423(1) 0.425(2) 0.624(5) 0.461(3) ⫺0.3436(6) ⫺0.2046(6) ⫺0.26500(1) ⫺0.194(7) ⫺0.301(7)
⫺0.2500 0.0000 ⫺0.03991(2) ⫺0.12930(8) 0.05871(8) ⫺0.1420(1) ⫺0.1846(2) ⫺0.0633(2) ⫺0.1097(3) ⫺0.0028(3) ⫺0.0778(2) 0.0436(2) ⫺0.1206(3) ⫺0.1683(4) 0.1263(4) ⫺0.2268(6) 0.0455(3) ⫺0.2500 ⫺0.200(2) ⫺0.285(2) ⫺0.2500 ⫺0.1656(9) ⫺0.2369(9) ⫺0.244(2) ⫺0.301(1) ⫺0.1295(4) 0.1861(4) ⫺0.2479(6) 0.046(4) 0.044(4)
0.0152 0.0158 0.0190 0.0181 0.0184 0.0190 0.0219 0.0238 0.0275 0.0314 0.0303 0.0270 0.0364 0.0756 0.0785 0.0689 0.0282 0.1219 0.1219 0.0627 0.0860 0.0856 0.1276 0.1139 0.1591 0.0500 0.0500 0.0500 0.0500 0.0500
1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 0.33(3) 0.23(1) 0.29(1) 0.47(5) 0.50(1) 0.55(1) 0.27(2) 0.45(1) 1.0000 1.0000 0.3333 1.0000 1.0000
86) [15] which gave the indium, phosphorous and some of the framework oxygen atom positions; all remaining non-hydrogen atoms and two hydrogen atoms were located from subsequent difference Fourier syntheses. The remaining hydrogen atoms attached to the three terminal P–OH groups were geometrically placed, refined individually, and finally refined in riding mode. None of the hydrogen atoms attached to the non-framework oxygen atoms could be located and were not geometrically placed. The occupancy of the extra-framework oxygen atoms were restrained to preclude the possibility of simultaneous occupation of atomic sites too close together to be physically reasonable. None of the remaining peaks in the final difference Fourier synthesis could be refined as other atoms. Refinement of 209 variables was by full-matrix least-squares analysis (CRYSTALS) [16], with anisotropic thermal parameters for all non-hydrogen atoms. Complex neutral atom scattering factors were obtained from ref. 17. Final fractional atomic coordinates, equivalent isotropic temperature factors, and selected bond distances and angles are given in Tables 2, 3, and 4, respectively.
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Table 3 Selected bond distances for Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) Moiety
Distance, Å
Moiety
Distance, Å
In(1)–O(1) 6⫻ In(3)–O(3) In(3)–O(5) In(3)–O(7) P(1)–O(1) P(1)–O(3) P(2)–O(4) P(2)–O(6) P(3)–O(7) 3⫻ Na(1)–O(1) 2⫻ Na(1)–O(3w) 2⫻ Na(2)–O(5) Na(2)–O(1w) Na(2)–O(4w) Na(2)–O(5w) Na(3)–O(1) Na(3)–O(8) Na(3)–O(2w) Na(3)–O(3w)
2.127(4) 2.115(4) 2.116(4) 2.094(5) 1.523(4) 1.516(4) 1.519(5) 1.507(4) 1.506(4) 2.55(3) 2.19(3) 2.64(3) 2.06(4) 2.36(6) 2.55(4) 2.72(3) 2.49(2) 2.40(3) 2.64(3)
In(2)–O(2) 6⫻ In(3)–O(4) In(3)–O(6) In(3)–O(11) P(1)–O(2) P(1)–O(8) P(2)–O(5) P(2)–O(9) P(3)–O(10) Na(1)–O(2w) 2⫻ Na(1)–O(5w) 2⫻ Na(2)–O(7) Na(2)–O(3w) Na(2)–O(5w)
2.142(4) 2.123(4) 2.109(4) 2.244(5) 1.524(4) 1.583(7) 1.508(4) 1.561(7) 1.57(1) 2.46(3) 2.56(5) 2.74(3) 2.31(4) 2.37(4)
Na(3)–O(1) Na(3)–O(2w) Na(3)–O(3w) Na(3)–O(5w)
2.36(1) 2.94(3) 2.13(2) 2.29(4)
3. Results and discussion The framework of the title compound, [In8(HPO4)14(H2O)6]4⫺ is shown in Fig. 1 and is the same as that described by Chippindale et al. [5]. The framework consists of layers of PO3(OH) tetrahedra, and In(2)O6 and In(3)O5(OH2) octahedra linked together in an alternating fashion to produce nonporous layers that contain 4- and 6-membered rings. Bond valence calculations [18] and the longer than average bond lengths indicate the presence of one terminal P–OH group in each of the three P-based tetrahedra (P–OHav, 1.571 Å; P–Oav, 1.513 Å) and of the In—OH2 group in the In(3) based octahedra (In(3)–OH2, 2.244(5) Å; In(3)–Oav, 2.111 Å). The layers are stacked in an ABAB sequence with In(1)O6 octahedra linking the layers together to form a structure with a two-dimensional array of channels. Entrance to the channel system is restricted by the 12-membered rings formed between adjacent pillaring In(1)O6 octahedra, as shown in Fig. 1. The channels contain the extra-framework sodium cations and water molecules. Eight extra-framework species were located, of which three were assigned as Na⫹ cations and the remainder as the oxygen atoms of water molecules. The assignation of the three Na⫹ cations was made on the basis that these extra-framework species had the most and closest contacts with the framework oxygen atoms, and the total occupancy of these sites was 4.11(2), which is in good agreement with that required to balance the framework charge (4 –), and the value found from elemental analysis (3.5(2)). The total occupancy of the five extra-framework oxygen sites was too high to be chemically reasonable when bonding distances were considered and, thus, the sum of their total occupancy was restrained. Similar problems are found in other hydrated zeolite structures, where the high thermal and static disorder of the extra-framework species makes it hard to accurately determine their correct occupancy [19].
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Table 4 Selected bond angles for Na4[In8(HPO4)14(H2O)6]䡠12(H2O) Moiety
Angle (°)
Moiety
O(1)–In(1)–O(1) 6⫻ O(1)–In(1)–O(1) 3⫻ O(2)–In(2)–O(2) 3⫻ O(2)–In(2)–O(2) 6⫻ O(3)–In(3)–O(4) O(4)–In(3)–O(5) O(4)–In(3)–O(6) O(3)–In(3)–O(7) O(5)–In(3)–O(7) O(3)–In(3)–O(11) O(5)–In(3)–O(11) O(7)–In(3)–O(11) O(1)–P(1)–O(2) O(2)–P(1)–O(3) O(2)–P(1)–O(8) O(4)–P(2)–O(5) O(5)–P(2)–O(6) O(5)–P(2)–O(9) O(7)–P(3)–O(7) 3⫻
90.9(1) 174.0(2) 180 87.0(1) 84.8(2) 176.1(2) 89.4(2) 90.8(2) 87.9(2) 87.9(2) 93.0(2) 178.5(2) 114.8(2) 112.8(3) 105.2(3) 110.6(3) 112.6(3) 108.5(4) 113.4(2)
O(1)–In(1)–O(1) 3⫻ O(1)–In(1)–O(1) 3⫻ O(2)–In(2)–O(2) 6⫻
Angle(°) 85.0(2) 93.5(2) 93.0(1)
O(3)–In(3)–O(5) O(3)–In(3)–O(6) O(5)–In(3)–O(6) O(4)–In(3)–O(7) O(6)–In(3)–O(7) O(4)–In(3)–O(11) O(6)–In(3)–O(11)
92.0(2) 170.4(2) 93.5(2) 94.4(2) 97.2(2) 84.6(2) 83.9(2)
O(1)–P(1)–O(3) O(1)–P(1)–O(8) O(3)–P(1)–O(8) O(4)–P(2)–O(6) O(4)–P(2)–O(9) O(6)–P(2)–O(9) O(7)–P(3)–O(10) 3⫻
108.1(2) 106.4(3) 109.1(4) 112.5(3) 108.3(4) 104.1(3) 105.2(2)
The locations of the three Na⫹ cations within one channel are shown in Fig. 1, and the individual coordination environment of each type of Na⫹ cation is shown in Fig. 2. All the Na⫹ cations are found in the plane of the 12-ring window. Na(1) is coordinated by two framework O(1) atoms (2 ⫻ Na(1)–O(1) 2.55(3) Å) of the In(1)O6 pillaring octahedra and by three extra-framework oxygen species at distances in the range 2.19(3) to 2.56(5) Å. Na(3) is situated very closely to Na(1) (0.78(3) Å), but its occupancies are low enough to assume that two adjacent sites are never occupied simultaneously. The Na(3) cations are coordinated by two O(1) atoms of the In(1)O6 octahedra at 2.36(1) and 2.72(3) Å, respectively, and another framework oxygen atom, O(8), at 2.49(2) Å. Again, Na(3) is coordinated by the same three extra-framework oxygen species as Na(1) with distances in the range 2.13(2) to 2.94(3) Å. The final Na⫹ cation type, Na(2), is bound to two framework oxygen atoms of the In(3)O5(OH2) octahedra, O(5) and O(7) at distances of 2.64(3) and 2.74(3) Å, respectively. This cation is bound to three extra-framework oxygen species with bonding distances in the range 2.06(4) to 2.55(4) Å. The exact nature of the coordination of the Na⫹ cations by the extra-framework oxygen atoms is difficult to determine, because of all the extra-framework atoms being in close proximity to one another, thus providing many different possible coordination environments. The range of Na–Oframework and Na–Onon-framework bond distances are 2.36(1) to 2.74(3) Å and 2.06(4) to 2.94(3) Å, respectively. Similar ranges are found in other hydrated Na-zeolites, for example, in hydrated Na zeolite-X, Na–Oframework and Na–Onon-framework bond distances lie in the ranges 2.29(3) to 2.623(7) Å and 2.1(2) to 2.51(7) Å, respectively [20]. TGA measurements show an 8.6% weight loss from 20 to 250°C, followed by a 4.4% weight loss between 250 and 550°C. A complete loss of crystallinity is seen after the first weight loss. The first weight loss may correspond to the removal of the 12 extra-framework water molecules per formula unit
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Fig. 1. View down the [100] direction showing the non-porous layers of In octahedra and P tetrahedra linked by In(1)O6 octahedra, to form a structure with a two-dimensional array of channels accessed through 12-membered rings (all hydrogen and extra-framework oxygen atoms are omitted for clarity). The extra-framework sodium cations within one channel are also shown. The atoms, in the order of decreasing size, are Na, In, P, and O.
(calculated weight loss 8.06%), with a further loss of the 6 water molecules attached to the In(3) cations at higher temperatures (calculated weight loss 4.03%). Similar behavior is seen for framework water molecules bound to In3⫹ cations in InPO4(H2O)2 䡠 0.1Et3N [21], which contains [InO4(H2O)2] octahedra. The extra-framework water and some of the framework water in the latter material is lost between 130 and 300°C, with loss of the remaining framework water between 300 and 610°C. However, this structure maintains its crystallinity to much higher temperatures than the title compound.
4. Conclusions The compound Na4[In8(HPO4)14(H2O)6]䡠12(H2O) has been synthesized directly without the use of an organic templating molecule, and the locations of the hydrated Na⫹ cations
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Fig. 2. The coordination environment of the sodium cations by the framework and extra-framework oxygen atoms is shown for (a) Na(1), (b) Na(2), and (c) Na(3). All the possible extra-framework oxygen sites are shown for each sodium cation. However, for any particular sodium cation in the structure, it is not possible to determine which of the extra-framework oxygen sites will be occupied. The atoms, in the order of decreasing size, are Na, In, P, and O.
within the channel system have been determined using single crystal X-ray diffraction. The hydrated Na⫹ cations are presumed to act as the templating agent for the framework, as is found for minerals and some laboratory synthesized aluminosilicates. The low thermal stability of the [In8(HPO4)14(H2O)6]4⫺ framework precludes many uses of this material; however, preliminary results on its ion-exchange properties show that ion exchange in KCl solution causes a lowering of symmetry of the structure. Further work is currently in progress.
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Acknowledgments This work was funded by the MRSEC program of the National Science Foundation under the award DMR 9632716.
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Materials Research Bulletin 35 (2000) 1007–1015
The direct synthesis and characterization of the pillared layer indium phosphate Na4[In8(HPO4)14(H2O)6]䡠12(H2O) Martin P. Attfielda,*, Anthony K. Cheethama, Srinivasan Natarajanb a
Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur Campus, Jakkur P. O., Bangalore 560 064, India
b
(Communicated by C.N.R. Rao) Received 21 December 1999; accepted 30 December 1999
Abstract Na4[In8(HPO4)14(H2O)6]䡠12(H2O) (trigonal, Pc1, a ⫽ 13.8500(2), c ⫽ 18.4930(3) Å, V ⫽ 3072.12(4) Å3, and Z ⫽ 2), was prepared directly in its sodium form by hydrothermal methods at 398 K, and its structure solved by single crystal methods. The three-dimensional framework structure consists of a network of InO6 and InO5(OH2) octahedra, and PO3(OH) tetrahedra forming layers, which are held in position by InO6 octahedra acting as pillars forming 12-membered ring channels. The extra-framework sodium cations are located at the sides of the 12-rings within this framework structure and are coordinated by framework oxygen atoms and extra-framework water molecules. The structure was solved using room-temperature single-crystal X-ray diffraction data from 1732 observed reflections (I ⬎ 3.0(I), R ⫽ 0.025, and Rw ⫽ 0.030). © 2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Inorganic compounds; B. Crystal growth; C. X-ray diffraction
1. Introduction The synthesis of open-framework metal phosphates has become an area of intense research effort since the first three-dimensional aluminum phosphates (AlPOs) were
* Corresponding author. Present address: Department of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK. Tel.: ⫹44-171-409-2992; fax: ⫹44-171-629-3569. E-mail address: [email protected] (M.P. Attfield). 0025-5408/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 0 ) 0 0 3 0 2 - 0
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discovered in 1982 [1,2]. The number of metals incorporated into the frameworks of these materials is constantly increasing and now includes metals such as Be [3], Ga [4], In [5], Sn [6], Zn [7], and the transition metals Ni [8], Fe [9], Co [10], and Mo [11]. Structures are known that contain one-dimensional polymeric chains, two-dimensional layers, and three-dimensional open-frameworks, some of which are novel while others are analogous to those of known aluminosilicate zeolite structures [12]. Some of the structures of these materials are intermediate between those of layered clays and the truly three-dimensional network structure of a zeolite. In most cases, the layered materials are intercalated by other inorganic polymeric forms such as the Keggin ion, which renders stability as well as a porous architecture to the structure. However, recently a new pillared layer material, [In8(HPO4)14(H2O)6](H2O)5(H3O)(C3N2H5)3 [5], has been synthesized whose nonporous layers are pillared by InO6 octahedral moieties to form an analogue to the pillared clay materials found for aluminosilicates. Such frameworks appear to combine the attractive features of the large spatial area of clays with the greater thermal stability of a zeolite. The majority of the new phases have been synthesized in the presence of an organic template molecule, which can lead to limitations for their applications and commercial utility. In many cases, the removal of the organic template molecule is only achieved by calcining the material, with subsequent collapse of the framework and loss of any exploitable properties. The cost of the organic template molecule in the synthesis and the subsequent calcination may reduce the commercial viability of the material. Thus, it is of extreme importance to find synthetic routes to these materials that involve templating species that are relatively inexpensive and easily replaced, such as alkali metal cations. Such routes have been devised for many of the aluminosilicate zeolite family, such as faujasite and ZSM-5, this being one of the main reasons for the enormous commercial utility of these materials. Similar routes have been found for the synthesis of open framework metal phosphates of Ga [13] and In [14]. In this work, we present the synthesis and characterization of Na4[In8(HPO4)14(H2O)6]䡠12(H2O), a pillared layer indium phosphate formed without the use of an organic template molecule and in a directly usable form.
2. Experimental 2.1. Synthesis and initial characterization The synthesis of Na4[In8(HPO4)14(H2O)6]䡠12(H2O) initially involved the preparation of a sodium phosphite intermediate material. The latter was formed by addition of 3.45 g of solid NaOH (Fischer) and 3.54 g of solid H3PO3 (Aldrich) to 20 ml of ethanol (Fischer). The mixture was stirred overnight. The white precipitate formed was removed from its mother liquor by suction filtration, washed in ethanol, and dried in air. A minimal quantity of deionized water was added to this precipitate to form a material whose X-ray powder diffraction pattern indicated that the predominant phase was Na2HPO3䡠5H2O (PDF 19-1267). 1.57 g of this white precipitate was added to 15 ml of deionized H2O, followed by 2.60 g of In(NO3)3䡠3H2O (Kodak) and 1.23 g of H3PO3 (Aldrich). The mixture was stirred, sealed in
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Table 1 Crystal and structure refinement data for Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) Formula Mw Crystal system Space group F(000) A C V Z Dc Crystal shape and dimensions (Mo K␣, ⫽ 0.71073 Å) 2max Limiting indices No. of reflections No. of independent reflections No. of observed reflections (I ⬎ 3.0(I)) Rint No. of refined parameters Largest difference hole and peak (eÅ⫺3) R(F), Rw(F)
Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) 2657.97 Trigonal P3c1 2520 13.8500(2) Å 18.4930(3) Å 3072.12(4) Å3 2 2.87 g cm⫺3 Hexagonal prism, 0.14 ⫻ 0.14 ⫻ 0.05 mm 34.4 cm⫺1 56.56° ⫺15 ⱕ h ⱕ 0, 0 ⱕ k ⱕ 18, 0 ⱕ l ⱕ 24 18731 2538 1732 0.040 209 ⫺0.962/0.528 0.025, 0.030
a 23 ml Teflon-lined steel autoclave, and heated at 10°C min⫺1 from room temperature to 125°C, where it was held for 50 h before being cooled to room temperature. The crystalline product was separated by suction filtration, washed in deionized water, and dried in air. The product was obtained as colorless crystals with a hexagonal prismatic habit. The crystals are stable to exposure to atmospheric conditions. Elemental analysis (ICPES) indicated a Na:In:P ratio of 3.5:8.2:13.8 (5% error in values). Thermogravimetric analysis (TGA) studies were carried out using a DuPont system (model 2000) in flowing oxygen from room temperature to 600°C. 2.2. Single crystal structure determination A suitable single crystal was carefully selected under a polarizing microscope and glued to a thin glass fiber with cyanoacrylate (superglue) adhesive. Crystal structure determination by X-ray diffraction was performed on a Siemens Smart-CCD diffractometer equipped with a normal focus, 2.4 kW sealed tube X-ray source (Mo K␣ radiation, ⫽ 0.71073 Å) operating at 50 kV and 40 mA. A full-sphere of intensity data was collected at room temperature in 2082 frames with scans (width of 0.30° and exposure time of 10 s per frame). The final unit-cell constants were determined from 4352 reflections and optimized by least-squares refinement. Pertinent details of the structure determination are presented in Table 1. On the basis of the systematic absence conditions in the reduced data and the subsequent successful solution and refinement of the structure, the space group was determined to be Pc1 (No. 165). The structure was solved by direct methods (SHELXS-
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Table 2 Final atomic coordinates, equivalent temperature factors, and fractional occupancies for Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) Atom
x
y
z
Ueq (Å2)
Occupancy
In(1) In(2) In(3) P(1) P(2) P(3) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) Na(1) Na(2) Na(3) O(1w) O(2w) O(3w) O(4w) O(5w) H(8) H(9) H(10) H(11) H(12)
0.0000 0.0000 ⫺0.43966(3) ⫺0.1924(1) ⫺0.4940(1) ⫺0.6667 ⫺0.1457(3) ⫺0.1187(3) ⫺0.3093(3) ⫺0.4351(4) ⫺0.4321(4) ⫺0.5529(4) ⫺0.5579(4) ⫺0.1988(7) ⫺0.4931(6) ⫺0.6667 ⫺0.3103(4) 0.265(3) 0.454(2) 0.237(1) 0.606(2) 0.362(1) 0.270(2) 0.558(6) 0.333(2) ⫺0.2454(7) ⫺0.5316(6) ⫺0.57610(1) ⫺0.260(7) ⫺0.284(7)
0.0000 0.0000 ⫺0.29356(3) ⫺0.1589(1) ⫺0.1239(1) ⫺0.3333 ⫺0.0648(3) ⫺0.1381(3) ⫺0.1849(4) ⫺0.1463(4) ⫺0.4338(4) ⫺0.3839(3) ⫺0.3252(4) ⫺0.2637(6) ⫺0.1910(6) ⫺0.3333 ⫺0.2549(4) 0.265(3) 0.514(2) 0.272(1) 0.606(2) 0.423(1) 0.425(2) 0.624(5) 0.461(3) ⫺0.3436(6) ⫺0.2046(6) ⫺0.26500(1) ⫺0.194(7) ⫺0.301(7)
⫺0.2500 0.0000 ⫺0.03991(2) ⫺0.12930(8) 0.05871(8) ⫺0.1420(1) ⫺0.1846(2) ⫺0.0633(2) ⫺0.1097(3) ⫺0.0028(3) ⫺0.0778(2) 0.0436(2) ⫺0.1206(3) ⫺0.1683(4) 0.1263(4) ⫺0.2268(6) 0.0455(3) ⫺0.2500 ⫺0.200(2) ⫺0.285(2) ⫺0.2500 ⫺0.1656(9) ⫺0.2369(9) ⫺0.244(2) ⫺0.301(1) ⫺0.1295(4) 0.1861(4) ⫺0.2479(6) 0.046(4) 0.044(4)
0.0152 0.0158 0.0190 0.0181 0.0184 0.0190 0.0219 0.0238 0.0275 0.0314 0.0303 0.0270 0.0364 0.0756 0.0785 0.0689 0.0282 0.1219 0.1219 0.0627 0.0860 0.0856 0.1276 0.1139 0.1591 0.0500 0.0500 0.0500 0.0500 0.0500
1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 0.33(3) 0.23(1) 0.29(1) 0.47(5) 0.50(1) 0.55(1) 0.27(2) 0.45(1) 1.0000 1.0000 0.3333 1.0000 1.0000
86) [15] which gave the indium, phosphorous and some of the framework oxygen atom positions; all remaining non-hydrogen atoms and two hydrogen atoms were located from subsequent difference Fourier syntheses. The remaining hydrogen atoms attached to the three terminal P–OH groups were geometrically placed, refined individually, and finally refined in riding mode. None of the hydrogen atoms attached to the non-framework oxygen atoms could be located and were not geometrically placed. The occupancy of the extra-framework oxygen atoms were restrained to preclude the possibility of simultaneous occupation of atomic sites too close together to be physically reasonable. None of the remaining peaks in the final difference Fourier synthesis could be refined as other atoms. Refinement of 209 variables was by full-matrix least-squares analysis (CRYSTALS) [16], with anisotropic thermal parameters for all non-hydrogen atoms. Complex neutral atom scattering factors were obtained from ref. 17. Final fractional atomic coordinates, equivalent isotropic temperature factors, and selected bond distances and angles are given in Tables 2, 3, and 4, respectively.
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Table 3 Selected bond distances for Na4[In8(HPO4)14(H2O)6] 䡠 12(H2O) Moiety
Distance, Å
Moiety
Distance, Å
In(1)–O(1) 6⫻ In(3)–O(3) In(3)–O(5) In(3)–O(7) P(1)–O(1) P(1)–O(3) P(2)–O(4) P(2)–O(6) P(3)–O(7) 3⫻ Na(1)–O(1) 2⫻ Na(1)–O(3w) 2⫻ Na(2)–O(5) Na(2)–O(1w) Na(2)–O(4w) Na(2)–O(5w) Na(3)–O(1) Na(3)–O(8) Na(3)–O(2w) Na(3)–O(3w)
2.127(4) 2.115(4) 2.116(4) 2.094(5) 1.523(4) 1.516(4) 1.519(5) 1.507(4) 1.506(4) 2.55(3) 2.19(3) 2.64(3) 2.06(4) 2.36(6) 2.55(4) 2.72(3) 2.49(2) 2.40(3) 2.64(3)
In(2)–O(2) 6⫻ In(3)–O(4) In(3)–O(6) In(3)–O(11) P(1)–O(2) P(1)–O(8) P(2)–O(5) P(2)–O(9) P(3)–O(10) Na(1)–O(2w) 2⫻ Na(1)–O(5w) 2⫻ Na(2)–O(7) Na(2)–O(3w) Na(2)–O(5w)
2.142(4) 2.123(4) 2.109(4) 2.244(5) 1.524(4) 1.583(7) 1.508(4) 1.561(7) 1.57(1) 2.46(3) 2.56(5) 2.74(3) 2.31(4) 2.37(4)
Na(3)–O(1) Na(3)–O(2w) Na(3)–O(3w) Na(3)–O(5w)
2.36(1) 2.94(3) 2.13(2) 2.29(4)
3. Results and discussion The framework of the title compound, [In8(HPO4)14(H2O)6]4⫺ is shown in Fig. 1 and is the same as that described by Chippindale et al. [5]. The framework consists of layers of PO3(OH) tetrahedra, and In(2)O6 and In(3)O5(OH2) octahedra linked together in an alternating fashion to produce nonporous layers that contain 4- and 6-membered rings. Bond valence calculations [18] and the longer than average bond lengths indicate the presence of one terminal P–OH group in each of the three P-based tetrahedra (P–OHav, 1.571 Å; P–Oav, 1.513 Å) and of the In—OH2 group in the In(3) based octahedra (In(3)–OH2, 2.244(5) Å; In(3)–Oav, 2.111 Å). The layers are stacked in an ABAB sequence with In(1)O6 octahedra linking the layers together to form a structure with a two-dimensional array of channels. Entrance to the channel system is restricted by the 12-membered rings formed between adjacent pillaring In(1)O6 octahedra, as shown in Fig. 1. The channels contain the extra-framework sodium cations and water molecules. Eight extra-framework species were located, of which three were assigned as Na⫹ cations and the remainder as the oxygen atoms of water molecules. The assignation of the three Na⫹ cations was made on the basis that these extra-framework species had the most and closest contacts with the framework oxygen atoms, and the total occupancy of these sites was 4.11(2), which is in good agreement with that required to balance the framework charge (4 –), and the value found from elemental analysis (3.5(2)). The total occupancy of the five extra-framework oxygen sites was too high to be chemically reasonable when bonding distances were considered and, thus, the sum of their total occupancy was restrained. Similar problems are found in other hydrated zeolite structures, where the high thermal and static disorder of the extra-framework species makes it hard to accurately determine their correct occupancy [19].
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Table 4 Selected bond angles for Na4[In8(HPO4)14(H2O)6]䡠12(H2O) Moiety
Angle (°)
Moiety
O(1)–In(1)–O(1) 6⫻ O(1)–In(1)–O(1) 3⫻ O(2)–In(2)–O(2) 3⫻ O(2)–In(2)–O(2) 6⫻ O(3)–In(3)–O(4) O(4)–In(3)–O(5) O(4)–In(3)–O(6) O(3)–In(3)–O(7) O(5)–In(3)–O(7) O(3)–In(3)–O(11) O(5)–In(3)–O(11) O(7)–In(3)–O(11) O(1)–P(1)–O(2) O(2)–P(1)–O(3) O(2)–P(1)–O(8) O(4)–P(2)–O(5) O(5)–P(2)–O(6) O(5)–P(2)–O(9) O(7)–P(3)–O(7) 3⫻
90.9(1) 174.0(2) 180 87.0(1) 84.8(2) 176.1(2) 89.4(2) 90.8(2) 87.9(2) 87.9(2) 93.0(2) 178.5(2) 114.8(2) 112.8(3) 105.2(3) 110.6(3) 112.6(3) 108.5(4) 113.4(2)
O(1)–In(1)–O(1) 3⫻ O(1)–In(1)–O(1) 3⫻ O(2)–In(2)–O(2) 6⫻
Angle(°) 85.0(2) 93.5(2) 93.0(1)
O(3)–In(3)–O(5) O(3)–In(3)–O(6) O(5)–In(3)–O(6) O(4)–In(3)–O(7) O(6)–In(3)–O(7) O(4)–In(3)–O(11) O(6)–In(3)–O(11)
92.0(2) 170.4(2) 93.5(2) 94.4(2) 97.2(2) 84.6(2) 83.9(2)
O(1)–P(1)–O(3) O(1)–P(1)–O(8) O(3)–P(1)–O(8) O(4)–P(2)–O(6) O(4)–P(2)–O(9) O(6)–P(2)–O(9) O(7)–P(3)–O(10) 3⫻
108.1(2) 106.4(3) 109.1(4) 112.5(3) 108.3(4) 104.1(3) 105.2(2)
The locations of the three Na⫹ cations within one channel are shown in Fig. 1, and the individual coordination environment of each type of Na⫹ cation is shown in Fig. 2. All the Na⫹ cations are found in the plane of the 12-ring window. Na(1) is coordinated by two framework O(1) atoms (2 ⫻ Na(1)–O(1) 2.55(3) Å) of the In(1)O6 pillaring octahedra and by three extra-framework oxygen species at distances in the range 2.19(3) to 2.56(5) Å. Na(3) is situated very closely to Na(1) (0.78(3) Å), but its occupancies are low enough to assume that two adjacent sites are never occupied simultaneously. The Na(3) cations are coordinated by two O(1) atoms of the In(1)O6 octahedra at 2.36(1) and 2.72(3) Å, respectively, and another framework oxygen atom, O(8), at 2.49(2) Å. Again, Na(3) is coordinated by the same three extra-framework oxygen species as Na(1) with distances in the range 2.13(2) to 2.94(3) Å. The final Na⫹ cation type, Na(2), is bound to two framework oxygen atoms of the In(3)O5(OH2) octahedra, O(5) and O(7) at distances of 2.64(3) and 2.74(3) Å, respectively. This cation is bound to three extra-framework oxygen species with bonding distances in the range 2.06(4) to 2.55(4) Å. The exact nature of the coordination of the Na⫹ cations by the extra-framework oxygen atoms is difficult to determine, because of all the extra-framework atoms being in close proximity to one another, thus providing many different possible coordination environments. The range of Na–Oframework and Na–Onon-framework bond distances are 2.36(1) to 2.74(3) Å and 2.06(4) to 2.94(3) Å, respectively. Similar ranges are found in other hydrated Na-zeolites, for example, in hydrated Na zeolite-X, Na–Oframework and Na–Onon-framework bond distances lie in the ranges 2.29(3) to 2.623(7) Å and 2.1(2) to 2.51(7) Å, respectively [20]. TGA measurements show an 8.6% weight loss from 20 to 250°C, followed by a 4.4% weight loss between 250 and 550°C. A complete loss of crystallinity is seen after the first weight loss. The first weight loss may correspond to the removal of the 12 extra-framework water molecules per formula unit
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Fig. 1. View down the [100] direction showing the non-porous layers of In octahedra and P tetrahedra linked by In(1)O6 octahedra, to form a structure with a two-dimensional array of channels accessed through 12-membered rings (all hydrogen and extra-framework oxygen atoms are omitted for clarity). The extra-framework sodium cations within one channel are also shown. The atoms, in the order of decreasing size, are Na, In, P, and O.
(calculated weight loss 8.06%), with a further loss of the 6 water molecules attached to the In(3) cations at higher temperatures (calculated weight loss 4.03%). Similar behavior is seen for framework water molecules bound to In3⫹ cations in InPO4(H2O)2 䡠 0.1Et3N [21], which contains [InO4(H2O)2] octahedra. The extra-framework water and some of the framework water in the latter material is lost between 130 and 300°C, with loss of the remaining framework water between 300 and 610°C. However, this structure maintains its crystallinity to much higher temperatures than the title compound.
4. Conclusions The compound Na4[In8(HPO4)14(H2O)6]䡠12(H2O) has been synthesized directly without the use of an organic templating molecule, and the locations of the hydrated Na⫹ cations
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Fig. 2. The coordination environment of the sodium cations by the framework and extra-framework oxygen atoms is shown for (a) Na(1), (b) Na(2), and (c) Na(3). All the possible extra-framework oxygen sites are shown for each sodium cation. However, for any particular sodium cation in the structure, it is not possible to determine which of the extra-framework oxygen sites will be occupied. The atoms, in the order of decreasing size, are Na, In, P, and O.
within the channel system have been determined using single crystal X-ray diffraction. The hydrated Na⫹ cations are presumed to act as the templating agent for the framework, as is found for minerals and some laboratory synthesized aluminosilicates. The low thermal stability of the [In8(HPO4)14(H2O)6]4⫺ framework precludes many uses of this material; however, preliminary results on its ion-exchange properties show that ion exchange in KCl solution causes a lowering of symmetry of the structure. Further work is currently in progress.
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Acknowledgments This work was funded by the MRSEC program of the National Science Foundation under the award DMR 9632716.
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