Origin of microporosity of ammonium dodecatungstophosphate unveiled by single crystal structure analysis

Article abstract of DOI:10.1246/cl.2001.1272

The single crystals of ammonium dodecatungstophosphate were successfully synthesized and the structure was analyzed. The intrinsic crystal structure (cubic, Pn3m) had no cavity. It follows that the microporosity observed for the powdery sample originated

Full text of DOI:10.1246/cl.2001.1272

1
272
Chemistry Letters 2001
Origin of Microporosity of Ammonium Dodecatungstophosphate Unveiled by
Single Crystal Structure Analysis
†
Takeru Ito, Masato Hashimoto, Sayaka Uchida, and Noritaka Mizuno*
Department of Applied Chemistry, School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656
Department of Material Science and Chemistry, Faculty of Systems Engineering, Wakayama University, Sakaedani, Wakayama 640-8510
†
(Received August 6, 2001; CL-010751)
The single crystals of ammonium dodecatungstophosphate
were successfully synthesized and the structure was analyzed.
–
The intrinsic crystal structure (cubic, Pn3m) had no cavity. It
follows that the microporosity observed for the powdery sample
originated from narrow spaces surrounded by the fine nanocrys-
tallites.
Ammonium dodecatungstophosphate (denoted as ADTP
hereafter) has been well-known as an insoluble fine powder
1
,2
with microporosity and high surface area.
The high surface
3
area renders it effective as ion exchange media and heteroge-
neous acid catalysts.4 As for ADTP as well as cesium hydro-
5,6
7
gendodecatungstophosphate, the uniform microporosity like
zeolites has been realized. The microporosity is of great inter-
est on the standpoint of shape-selective catalysis.
Recently, microporous ADTP has been found to be the self-
6
organized aggregates of fine nanocrystallites. Fundamental
query about the microporosity of ADTP is whether its intrinsic
1,2,5
8–10
crystal structure has pores
or not.
Therefore, the clarifi-
cation of the crystal structure of ADTP can make the decision,
11
but has not been reported yet. It has also been reported that the
crystal structure of ammonium dodecamolybdophosphate
12
changed with the stoichiometry. In this report, we successfully
synthesized single crystals of ADTP and the crystal structure
was determined to clarify the origin of the micropores.
Single crystals of (NH ) PW O were synthesized by
4
3
12 40
hydrothermal method followed by the slow cooling as follows.
Dodecatungstophosphoric acid hexahydrate (H PW O ·6H O)
results show that the single crystals consist of stoichiometric
3
12 40
2
+
3–
was prepared by the evacuation of H PW12O40·nH O.
ammonium salts of H PW O (with an NH /PW O
ratio
3
2
3
12 40
4
12 40
H PW O ·6H O (1.5 g, 0.5 mmol) and urea (45 mg, 0.75
of 3:1) and are highly pure.
3
12 40
2
The crystal structure is demonstrated in Figure 3.15 The
mmol) were dissolved in water (25 mL). To the 3 mL of the
resulting solution were added a small amount of acetone and
seed crystals. The solution was heated in 30-mL Teflon-lined
stainless containers at 473 K for 4 h, and then cooled to 433 K
for 24 h followed by the cooling to 313 K for 3 h. Colorless
prismatic crystals of 0.03–0.15 mm in size were isolated by the
decantation (30% yield based on W). The SEM image is shown
in Figure 1. The crystal was subjected to the X-ray structure
analysis. Elemental analysis (Mikroanalytisches Labor
Pascher, Remagen, Germany) of air-dried materials (%).
Found: N, 1.39; H, 0.45; P, 0.99; W, 73.7%. Calcd for
heteropolyanion had an α-Keggin structure as shown in Figure
3a. The crystal structure of (NH ) PW O was cubic (Pn3 m),
basically the same as that of H PW O ·6H O: The ammoni-
um ion occupied the position of H O in H PW O ·6H O as
–
4
3
12 40
1
6
3
12 40
2
+
5
2
3
12 40
2
1
6
discussed on Cs PW O in the literature. Figures 3b and 3c
3
12 40
show the polyhedral and space-filling representation of the
crystal structure, respectively. No space for N or Ar adsorp-
2
tion remained in the crystal lattice of stoichiometric ADTP,
(NH ) PW O .
4
3
12 40
The powder XRD pattern and the chemical formula of
powdery ADTP were the same as those of the single crystals.
Therefore, the agreements show that the micropores of powdery
ADTP do not originate from the crystal lattice.
3
1
H N O PW : N, 1.43; H, 0.41; P, 1.06; W, 75.3%. The
P
1
2
3
40
12
NMR spectra were recorded at room temperature in a special
1
3
glass cell after dehydration under vacuum. Single pulse exci-
tations were used with MAS rate = 3 kHz.
It was reported that the defect of polyoxometalates may
1
7
Elemental analysis of the crystals almost agreed with that
lead to the microporosity. On the assumption that the micro-
3
1
3–
calculated for (NH ) PW O . The P NMR spectrum is
pores originate from defects of PW O
powdery ADTP with the surface areas of 49–65 m g
estimated to have the anion defects of 3%. The defects can be
(0.8 nm in diameter),
4
3
12 40
12 40
2
–1 6b,10
shown in Figure 2. One sharp signal was observed at –14.7
is
3
–
13,14
ppm, assignable to PW O
anion without proton.
These
1
2
40
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
1273
Heimler, J. Chromatogr., 207, 29 (1981).
4
a) H. Hayashi and J. B. Moffat, J. Catal., 83, 192 (1983).
b) Y. Izumi, M. Ogawa, W. Nohara, and K. Urabe, Chem.
Lett., 1992, 1987. c) J. S. Vaughan, C. T. O’Connor, and J.
C. Q. Fletcher, J. Catal., 147, 441 (1994). d) S. Soled, S.
Miseo, G. McVicker, W. E. Gates, A. Gutierrez, and J.
Paes, Catal. Today, 36, 441 (1997).
5
6
J. L. Bonardet, J. Fraissard, G. B. McGarvey, and J. B.
Moffat, J. Catal., 151, 147 (1995).
a) K. Inumaru, H. Nakajima, T. Ito, and M. Misono, Chem.
Lett., 1996, 559. b) T. Ito, K. Inumaru, and M. Misono, J.
Phys. Chem. B, 101, 9958 (1997).
7
a) T. Okuhara, T. Nishimura, and M. Misono, Chem. Lett.,
1
995, 155. b) Y. Yoshinaga, K. Seki, T. Nakato, and T.
Okuhara, Angew. Chem., Int. Ed. Engl., 36, 2833 (1997).
N. Mizuno and M. Misono, Chem. Lett., 1987, 967.
T. Yamada, Y. Yoshinaga, and T. Okuhara, Bull. Chem.
Soc. Jpn., 71, 2727 (1998).
8
9
1
0
1
T. Ito, K. Inumaru, and M. Misono, Chem. Mater., 13, 824
(2001).
1
H. T. Evans, Jr., in “Perspectives in Structural Chemistry,”
ed. by J. D. Dunitz and J. A. Ibers, Wiley, New York
(1971), Vol. 4, p 1.
12
Two types of single crystals with cubic structure have been
reported for ammonium dodecamolybdophosphate.
(
NH4)2.6(H O) PMo O and (NH ) K1.2PMo O ,
3 0.4 12 40 4 1.8 12 40
which are not stoichiometric ammonium salts, have similar
structures to that of ADTP (J. C. A. Boeyens, G. J.
McDougal, and J. van R. Smit, J. Solid State Chem., 18,
191 (1976)). On the other hand, the stoichiometric ammo-
nium salt, (NH ) PMo O ·21H O, has the different pack-
4
3
12 40
2
ing of heteropolyanions (Y. Xu, J. -Q. Xu, G. -Y. Yang, G.
D. Yang, Y. Xing, Y. -H. Lin, and H. -Q. Jia, Acta
-
Crystallogr., C54, 9 (1998)).
13
a) S. Uchida, K. Inumaru, J. M. Dereppe, and M. Misono,
Chem. Lett., 1998, 643. b) S. Uchida, K. Inumaru, and M.
Misono, J. Phys. Chem. B, 104, 8108 (2000).
analyzed by 31P NMR or elemental analysis and could not be
detected. Therefore, the microporosity would not originate
from such defects.
All these results lead to the conclusion that the micropores
of powdery ADTP are the narrow spaces surrounded by the fine
nanocrystallites.
14 T. Okuhara, T. Nishimura, H. Watanabe, K. Na, and M.
Misono, Stud. Surf. Sci. Catal., 90, 419 (1994).
15 Crystal data: Crystal dimensions 0.13 × 0.13 × 0.10 mm,
–
formula (NH ) PW O , cubic, Pn3m, a = 11.684(4) Å, V
4
3
3
12 40
–3
= 1595.3(7) Å , Z = 2, ρ
= 6.102 g cm , 2θ
= 60.0°,
calcd
max
530 reflections collected, 270 observed [I > 2σ(I)], µ =
–
1
4
33.01 cm , T
= 1.0000/0.6311, R = 0.060, Rw =
max/min
This work was supported in part by a Grant-in-Aid from
the Ministry of Education, Culture, Sports, Science and
Technology. T. Ito is grateful to the Research Fellowships of
the Japan Society for the Promotion of Science for Young
Scientists. Prof. Tatsuya Okubo (The University of Tokyo) is
specially acknowledged for the use of a hot air rapid drying
oven.
0.039. The intensity data were collected on a Rigaku AFC-
5R automated four-circle diffractometer with graphite-
monochromated Mo Kα radiation. Lorentz polarization
and empirical absorption correction based on psi-scans
were applied. All calculations were carried out with
teXsan program package. The W atoms were located by
the direct method and other non-H atoms were found out
by successive Fourier syntheses. Tungsten and phosphorus
atoms were refined anisotropically, and oxygen and nitro-
gen atoms isotropically.
References and Notes
1
2
3
S. J. Gregg and M. M. Tayyab, J. Chem. Soc., Faraday
Trans. 1, 74, 348 (1978).
J. B. McMonagle and J. B. Moffat, J. Colloid Interface
Sci., 101, 479 (1984).
a) J. van R. Smit, J. J. Jacobs, and W. Robb, J. Inorg. Nucl.
Chem., 12, 95 (1959). b) L. Lepri, P. G. Desideri, and D.
16 G. M. Brown, M. -R. Noe-Spirlet, W. R. Busing, and H. A.
Levy, Acta Crystallogr., B33, 1038 (1977).
17 S. Berndt, D. Herein, F. Zemlin, E. Beckmann, G.
Weinberg, J. Schütze, G. Mestl, and R. Schlögl, Ber.
Bunsen-Ges. Phys. Chem., 102, 763 (1998).