Zeolite ionic crystals assembled through direct incorporation of polyoxometalate clusters within 3D metal-organic frameworks

Article abstract of DOI:10.1021/ic070274o

Polyoxometalate-based metal-organic frameworks {[Gd(dpdo) ₄(H₂O)₃](PMo₁₂O₄₀)(H ₂O)₂CH₃CN}_n (2), {[Dy(dpdo) ₄(H₂O)₃](PMo₁₂O₄₀)(H ₂O)₂CH₃CN}_n (3), {[Gd(dpdo) ₄(H₂O)₃](H₃O)(SiMo ₁₂O⁴⁰)(dpdo)_0.5(CH₃CN) _0.5 (H₂O)₃}_n (4), {[Ho(dpdo) ₄(H₂O)₃](H₃O)(SiMo ₁₂0₄₀)(dpdo)_0.5(CH₃CN) _0.5(H₂O)₃}_n (5), {[Ni(dpdo) ₂(CH₃CN) (H₂O)₂] ₂(SiMo₁₂O₄₀)(H₂O)₂} _n (6), and {[Ni(dpdo)₃]₄(PW₁₂O ₄₀)₃[H(H₂O)₂₇(CH₃CN) ₁₂]}_n (7) (where dpdo is 4,4′-bipyridine-N,N′- dioxide) were constructed via self-assembly by embedding Keggin-type polyanions within the intercrystalline voids as guests or pillars. Compounds 2 and 3 are isomorphic and exhibit three-dimensional (3D) noninterwoven 6⁴ frameworks with distorted-honeycomb cavities occupied by the polyanions. Compounds 4 and 5 are comprised of 3D noninterwoven frameworks formed by linking the adjacent folded sheets through hydrogen bonds and π-π stacking interactions relative to the free isolated dpdo ligand. Compound 6 is a pillar-layered framework with the [SiMo₁₂O₄₀]^4- anions located on the square voids of the two-dimensional bilayer sheets formed by the dpdo ligands and nickel(II) ions. Compound 7 is a 3D metal-organic framework formed by nickel(II) and 4,4′-bipyridine-N,N′-dioxide with the globular Keggin-structure [PW₁₂O₄]^3- anion as the template. A large protonated water cluster H⁺(H ₂O)₂₇ is trapped and stabilized within the well-modulated cavity.

Full text of DOI:10.1021/ic070274o

Inorg. Chem. 2007, 46, 5957−5966
Zeolite Ionic Crystals Assembled through Direct Incorporation of
Polyoxometalate Clusters within 3D Metal Organic Frameworks
−
Meilin Wei,† Cheng He,‡ Qiaozhen Sun,† Qingjin Meng,† and Chunying Duan*,†,‡
State Key Laboratory of Coordination Chemistry, Nanjing UniVersity,
Nanjing 210093, P. R. China, and State Key Laboratory of Fine Chemicals,
Dalian UniVersity of Technology, Dalian 116012, P. R. China
Received February 11, 2007
Polyoxometalate-based metal
−
organic frameworks
CN (3), [Gd(dpdo)
40)(dpdo)0.5(CH
[H(H O)27(CH CN)12
{
[Gd(dpdo)
4
(H
O)(SiMo12
(5), [Ni(dpdo)
-bipyridine-N,N′
2
O)
3
](PMo12
40)(dpdo)0.5(CH
(CH CN) (H O)
-dioxide) were constructed
O
40)(H
2
O)
2
CH
3
CN
}
n
(2),
{
}
[Dy(dpdo)
(4), [Ho-
O) (6),
4
-
(
H
2
O)
dpdo)
[Ni(dpdo)
3
](PMo12
O
40)(H
O)(SiMo12
(PW12
2
O)
2
CH
3
}
n
{
4
(H
O)
2
O)
3
](H
3
O
3
CN)0.5 (H
(SiMo12
2
O)
3
n
{
}
2 n
(
4
(H O) ](H
2
3
3
O
3
CN)0.5(H
2
}
3 n
{
2
3
2
]
2 2
O40)(H
2
and
{
]
3 4
O )
40 3
2
3
]}
n
(7) (where dpdo is 4,4
′
via self-assembly by embedding Keggin-type polyanions within the intercrystalline voids as guests or pillars.
4
Compounds 2 and 3 are isomorphic and exhibit three-dimensional (3D) noninterwoven 6 frameworks with distorted-
honeycomb cavities occupied by the polyanions. Compounds 4 and 5 are comprised of 3D noninterwoven frameworks
formed by linking the adjacent folded sheets through hydrogen bonds and π−π stacking interactions relative to the
40]4 anions located on the
-
free isolated dpdo ligand. Compound 6 is a pillar-layered framework with the [SiMo12
O
square voids of the two-dimensional bilayer sheets formed by the dpdo ligands and nickel(II) ions. Compound 7 is
a 3D metal
structure [PW12
−
organic framework formed by nickel(II) and 4,4
′
-bipyridine-N,N
′
-dioxide with the globular Keggin-
]3 anion as the template. A large protonated water cluster H (H
-
+
O
4
2
O)27 is trapped and stabilized
within the well-modulated cavity.
Introduction
recently, the attention has shifted to possible applications of
these materials, preponderantly in gas storage, catalysis, and
Porous metal-organic frameworks (MOFs) have emerged
as a promising new class of materials that often have
crystalline, well-defined cavities (or channels) and can be
used for the inclusion of various guest species. Whereas
the initial focus was on synthesis and structural aspects, more
3
,4
chemical separations. Bearing unique properties and ex-
hibiting a diverse compositional range, polyoxometalates
(POMs) represent an outstanding class of molecular building
blocks for the construction of such kinds of materials.5
Despite the remarkable progress in the construction of three-
1-4
,6
7
*
To whom correspondence should be addressed. E-mail: Duancy@
dimensional (3D) POM-based coordination polymers and
nju.edu.cn.
ionic crystals composed by POMs and large discrete cations,8
the rational design and assembly of POM-based coordination
polymers, especially POM-based open MOFs, remains an
†
Nanjing University.
Dalian University of Technology.
‡
(
1) (a) Yaghi, O. M.; Li, H.; Davis, C.; Richardson, D.; Groy, T. L. Acc.
Chem. Res. 1998, 31, 474-484. (b) Batten, S. T.; Robson, R. Angew.
Chem., Int. Ed. 1998, 37, 1460-1494. (c) Kitagawa, S.; Kondo, M.
Bull. Chem. Soc. Jpn. 1998, 71, 1739-1753. (d) Li, H.; Eddaoudi,
M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276-279. (e)
Davis, M. E. Nature 2002, 417, 813-821.
(4) (a) Wu, C. D.; Hu, A.; Zhang, L.; Lin, W. J. Am. Chem. Soc. 2005,
127, 8940. (b) Pan, L.; Olson, D. H.; Ciemnolonski, L. R.; Heddy,
R.; Li, J. Angew. Chem., Int. Ed. 2006, 45, 616. (c) Matsuda, R.;
Kitaura, R.; Kitagawa, S.; Kubota, Y.; Belosludov, R. V.; Kobayashi,
T. C.; Sakamoto, H.; Chiba, T.; Takata, M.; Kawazoe, Y.; Mita, Y.
Nature 2005, 436, 238.
(5) (a) Cronin, L. Chem. Soc. ReV. 2007, 36, 105-121. (b) Cronin, L.
The Potential of Pentagonal Building Blocks in Inorganic Chemistry
Highlights; Meyer, G. Naumann, D., Wesemann, L., Eds.; Wiley-
VCH: Weinheim, Germany, 2002; pp 113 -121. (c) Pope M. T.
Isopolyanions and Heteropolyanions. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty J. A., Eds.;
Pergamon Press: Oxford, 1987; Vol. 3, pp 1023-1058. (d) Long,
D.; Cronin, L. Chem.sEur. J. 2006, 12, 3698-3706.
(
2) (a) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.;
Eddaoudi, M.; Kim. J. Nature 2003, 423, 705-714. (b) Rosi, N. L.;
Kim, J.; Eddaoudi, M.; Chen, B.; O’Keeffe, M.; Yaghi, O. M. J. Am.
Chem. Soc. 2005, 127, 1504-1518.
(3) (a) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004,
43, 2334. (b) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon,
Y. J.; Kim, K. Nature 2000, 404, 982. (c) F e´ rey, G.; Mellot-Draznieks,
C.; Serre, C.; Millange, F.; Dutour, J.; Surble’, S.; Margiolaki, I.
Science 2005, 309, 2040. (d) C oˆ te’, A. P.; Benin, A. I.; Ockwig, N.
W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Science 2005, 310,
1166.
1
0.1021/ic070274o CCC: $37.00
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 15, 2007 5957
Published on Web 06/28/2007

Wei et al.
arduous task for coordination chemists due to the large
number of potential coordination sites and the relatively weak
coordination ability of POMs. To overcome the obstacles at
presented here, a new adopted synthetic approach to embed
POMs into the frameworks of the coordination polymers by
constructing 3D POM-based coordination polymers was
Since the charges of the Keggin heteropolyanions can be
easily adjusted without changing the basic structures, dif-
3
-
4-
ferent charged polyanions [PMo12
40
O ]
40
and [SiMo12O ]
are selected to construct POM-based 3D MOFs with different
charges. It can be expected that to maintain the neutrality of
the whole crystal different solvated protons might be formed
and stabilized within these frameworks. 4,4′-Bipydidine-
N,N′-dioxide (dpdo) was used as the suitable longer spacer
ligand, not only because of the excellent hard acid/hard base
complementarity of the lanthanide cations/first-row transi-
tion-metal ions and the N-oxide donor but also because of
the small steric size of this ligand that avoids crowding at
the metal centers and encourages high connectivity and a
9
developed. Very recently, this new synthetic strategy was
improved by carefully adjusting the stoichiometric proportion
1
0
of the highly charged POMs and the metal-organic units.
The presence of nanosized highly charged anions, like the
well-known Keggin heteropolyanions, as building blocks, not
only prevented the occurrence of lattices interpenetration but
also made the cavities partially occupied by the anions, from
10
14
which the porous MOF 1 was achieved. Since the elabora-
tion of the new synthetic pathways to access novel topologies
and, more importantly, a better understanding of their
assemblage, the correlation of building block geometrical
information to the resultant structure is of significant
scientific interest. Herein, lanthanide ions that generally adopt
coordination numbers higher than six were chosen to prepare
novel MOFs.
large volume of voids.
Experimental Section
General Procedure. All organic solvents and materials used for
synthesis were of reagent grade and used without further purifica-
tion. The metal chlorides LnCl
prepared by dissolving Ln
followed by drying and crystallization. R-H
R-H O, and R-H SiMo12 40‚14H
3
‚6H
(99.9%) in hydrochloric acid,
40‚14H O,
O were prepared
2
O (Ln ) Gd, Dy, Ho) were
2
O
3
3
PMo12
O
2
3
PW12
O40‚6H
2
4
O
2
On the other hand, solvated protons are key elements in
the dissociation and transport phenomena of aqueous chem-
istry and biological systems.11 Despite recent remarkable
1
5
according to a literature method and characterized by IR spectra
and thermogravimetric analyses (TGA). Elemental analyses (C, H,
and N) were carried out on a Perkin-Elmer 240C analyzer. IR
spectra were recorded on a Vector 22 Bruker spectrophotometer
experimental progress, structural characterization is still far
more difficult to achieve.1
2,13
Therefore, both the accurate
-
1
with KBr pellets in the 400-4000 cm regions at room temper-
ature. Laser Raman spectra of the single crystals of the title
compounds were measured with a JY HR-800 spectrometer using
calculations based on gas-phase models and the crystal-
lographic characterizations in condensed phase will be
emerging to help understand the existing experimental data.
-1
the 488 Å line as the exciting source in the 100-2000 cm region
at 123 K. TGA studies of compounds 2-7 were carried out on a
Perkin-Elmer thermal analyzer in an atmosphere of N
Synthesis of {[Gd(dpdo) (H O) ](PMo12 O)
(2). The formation of heteropolyacid gadolinium salts was ac-
complished by neutralization of the acids. R-H 40‚14H
41 mg, 0.02 mmol) and GdCl ‚6H O (8 mg, 0.02 mmol) were
dissolved in water (2 mL), and the solution was heated to saturation
at 80 °C in a water bath. Yellow crystals were formed after cooling
the saturated solution and slow evaporation at room temperature
and were characterized by their IR spectrum. A buffer layer of a
solution (10 mL) of acetonitrile/water (3:2, v/v) was carefully
layered over an 4 mL aqueous solution of 4,4′-bipyridine-N,N′-
dioxide hydrate (0.1 mmol, 22 mg). Then, an acetonitrile/water (3:
1, v/v) solution (4 mL) of resultant heteropolyacid gadolinium salts
was carefully layered over the buffer layer. Orange crystals appeared
after 4-5 weeks and were collected and dried in air after quickly
2
.
(
6) (a) Anderson, T. M.; Neiwert, W. A.; Kirk, M. L.; Piccoli, P. M. B.;
Schultz, A. J.; Koetzle, T. F.; Musaev, D. G.; Morokuma, K.; Cao,
R.; Hill, C. L. Science 2004, 306, 2074-2077. (b) Neumann, R.;
Dahan, M. Nature 1997, 388, 353-355. (c) Rhther, T.; Hultgren, V.
M.; Timko, B. P.; Bond, A. M.; Jackson, W. R.; Wedd, A. G. J. Am.
Chem. Soc. 2003, 125, 10133-10143. (d) M u¨ ller, A.; Das, S. K.;
Talismanov, S.; Roy, S.; Beckmann, E.; B o¨ gge, H.; Schmidtmann,
M.; Merca, A.; Berkle, A.; Allouche, L.; Zhou, Y.; Zhang, L. Angew.
Chem., Int. Ed. 2003, 42, 5039-5044.
4
2
3
O
40)(H
2
2 3 n
CH CN}
3
PMo12O
2
O
(
3
2
(
7) (a) Uchida, S.; Mizuno, N. Chem.sEur. J. 2003, 9, 5850. (b) Uchida,
S.; Mizuno, N. J. Am. Chem. Soc. 2004, 126, 1602. (c) Uchida, S.;
Kawamoto, R.; Akatsuka, T.; Hikichi, S.; Mizuno, N. Chem. Mater.
2005, 17, 1367. (d) Kawamoto, R.; Uchida, S.; Mizuno, N. J. Am.
Chem. Soc. 2005, 127, 10560. (e) Jiang, C.; Lesbani, A.; Kawamoto,
R.; Uchida, S.; Mizuno, N. J. Am. Chem. Soc. 2006, 127, 14240.
8) (a) An, H. A.; Wang, E. B.; Xiao, D. R.; Li, Y. G.; Su, Z. M.; Xu, L.
Angew. Chem., Int. Ed. 2006, 45, 904. (b) Kang, J.; Xu, B.; Peng, Z.;
Zhu, X.; Wei, Y.; Powell, D. R. Angew. Chem., Int. Ed. 2005, 44,
(
6902. (c) Ren, Y.-P.; Kong, X.-J.; Hu, X.-Y.; Sun, M.; Long, L.-S.;
Huang, R.-B.; Zheng, L.-S. Inorg. Chem. 2006, 45, 4016. (d) Zheng,
P. Q.; Ren, Y. P.; Long, L. S.; Huang, R. B.; Zheng, L. S. Inorg.
Chem. 2005, 44, 1190.
being washed with water. Yield: 79%, based on R-H
3 40
PMo12O ‚
1
4H O. Anal. Calcd for C42 53PMo12Gd: C, 17.62; H, 1.58;
2
45 8
H N O
N, 4.40. Found: C, 17.48; H, 1.92; N, 4.55. IR (KBr): four
(9) (a) Hagrman, D.; Hagrman, P. J.; Zubieta, J. Angew. Chem., Int. Ed.
1
999, 38, 3165. (b) Knaust, J. M.; Inman, C.; Keller, S. W. Chem.
Commun. 2004, 492. (c) Kong, X.-J.; Ren, Y.-P.; Zheng, P.-Q.; Long,
Y.-X.; Long, L.-S.; Huang, R.-B.; Zheng, L.-S. Inorg. Chem. 2006,
(13) (a) Miyazaki, M.; Fujii, A.; Ebata, T.; Mikami, N. Science 2004, 304,
1134. (b) Shin, J.-W.; Hammer, N. I.; Diken, E. G.; Johnson, M. A.;
Walters, R. S.; Jaeger, T. D.; Duncan, M. A.; Christie, R. A.; Jordan,
K. D. Science 2004, 304, 1137. (c) Headrick, J. M.; Diken, E. G.;
Walters, R. S.; Hammer, N. I.; Christie, R. A.; Cui, J.; Myshakin, E.
M.; Duncan, M. A.; Johnson, M. A.; Jordan, K. D. Science 2005, 308,
1765.
(14) (a) Ma, B. Q.; Gao, S.; Sun, H. L.; Xu, G. X. J. Chem. Soc., Dalton
Trans. 2001, 130. (b) Long, D. L.; Blake, A. J.; Champness, N. R.;
Schr o¨ der, M. Chem. Commun. 2000, 2273. (c) Long, D. L.; Hill, R.
J.; Blake, A. J.; Champness, N. R.; Hubberstey, P.; Proserpio, D. M.;
Wilson, C.; Schr o¨ der, M. Angew. Chem., Int. Ed. 2004, 43, 1851-
1854.
4
5, 10702. (d) Lu, J.; Shen, E.-H.; Li, Y.-G.; Xiao, D.-R.; Wang, E.-
B.; Xu, L. Cryst. Growth Des. 2005, 5, 65.
(
10) Wei, M. L.; He, C.; Hua, W. J.; Duan, C. Y.; Li, S. H.; Meng, Q. J.
J. Am. Chem. Soc. 2006, 128, 13318-13319.
11) (a) Stowell, M. H. B.; McPhillips, T. M.; Rees, D. C.; Soltis, S. M.;
Abresch, E.; Feher, G. Science 1997, 276, 812. (b) Luecke, H.; Richter,
H. T.; Lanyi, J. K. Science 1998, 280, 1934. (c) Rini, M.; Magnes, B.
Z.; Pinre, E.; Nibbering, E. T. J. Science 2003, 301, 349.
12) (a) Zwier, T. S. Science 2004, 304, 1119. (b) Jiang, J.-C.; Wang, Y.-
S.; Chang, H.-C.; Lin, S. H.; Lee, Y. T.; Niedner-Schatteburg, G.;
Chang, H.-C. J. Am. Chem. Soc. 2000, 122, 1398. (c) Singh, N. J.;
Park, M.; Min, S. K.; Suh, S. B.; Kim, K. S. Angew. Chem., Int. Ed.
(
(
(15) Claude, R. D.; Michel, F.; Raymonde, F.; Rene, T. Inorg. Chem. 1983,
22, 207.
2006, 45, 3795.
5958 Inorganic Chemistry, Vol. 46, No. 15, 2007

Zeolite Ionic Crystals within 3D Frameworks
1
characteristic asymmetric vibrations resulting from heteropolyanions
namely, ν(N-O) (1214 cm- ), ν(ring) (1470 cm-1), δ(C-H, in
-1
plane) (1178 cm-1), and δ (N-O) (839 cm-1).
with the Keggin structure: ν(Mo-Oc) (794 cm ), ν(Mo-Ob) (880
-
1
-1
-1
cm ), ν(Mo)Ot) (960 cm ), and ν(P-Oa) (1062 cm ); four
Synthesis of {[Ni(dpdo)
7). The formation of heteropolyacid nickel salts (greenish crystals)
was accomplished by the neutralization of the acids in the same
way as gadolinium phosphomolybdate (R-H O (90 mg,
.03 mmol) and NiCl ‚6 H O (7.5 mg, 0.03 mmol)). Compound 7
3 4 40 3 2 3 n
] (PW12O ) [H(H O)27(CH CN)12]}
characteristic vibrations resulting from dpdo molecules, namely,
(
-
1
-1
ν(N-O) (1233 cm ), ν(ring) (1472 cm ), δ(C-H, in plane) (1181
-
1
-1
cm ), and δ(N-O) (838 cm ).
Synthesis of {[Dy(dpdo) (H O)
3). Compound 3 was prepared in the same way as 2, using DyCl
O (0.02 mmol) to replace GdCl ‚6H O. Orange crystals
appeared after 4-5 weeks and were collected and dried in air after
quickly being washed with water. Yield: 71%, based on R-H
40‚14H O. Anal. Calcd for C42 53PMo12Dy: C, 17.58;
3
PW12
O
40‚6H
2
4
2
3 2 2 3 n
](PMo12O40)(H O) CH CN}
0
2
2
(
3
‚
was prepared in the same way as 2, using heteropolyacid nickel
salts to replace gadolinium phosphomolybdate. Red block crystals
appeared after 2 weeks and were collected and dried in air after
6H
2
3
2
3
-
quickly being washed with water. Yield: 83%, based on R-H
O. Anal. Calcd for C144
4.29; H, 1.56; N, 4.17. Found: C, 13.91; H, 1.63; N, 4.02. IR
KBr): four characteristic asymmetric vibrations resulting from
heteropolyanions with the Keggin structure: ν(WdO
) (978 cm-1),
) (810 cm ), and ν(P-O ) (1080
cm ); four characteristic vibrations resulting from dpdo molecules,
3
-
PMo12O
2
45 9
H N O
PW12
O
40‚6H
2
187 36 4 3
H N O171Ni P W36: C,
H, 1.58; N, 4.40. Found: C, 17.61; H, 1.65; N, 4.52. IR (KBr):
1
(
four characteristic asymmetric vibrations resulting from het-
-
1
eropolyanions with the Keggin structure: ν(ModOt) (960 cm ),
t
-
1
-1
ν(Mo-Ob) (880 cm ), ν(Mo-Oc) (795 cm ), and ν(P-Oa) (1062
-
1
-1
ν(W-O
b
) (895 cm ), ν(W-O
c
a
-1
cm ); four characteristic vibrations resulting from dpdo molecules,
-
1
-
1
-1
namely, ν(N-O) (1233 cm ), ν(ring) (1473 cm ), δ(C-H, in
namely, ν(N-O) (1225 cm ), ν(ring) (1475 cm-1), δ(C-H, in
-1
plane) (1180 cm 1), and δ(N-O) (838 cm-1), respectively.
-
plane) (1180 cm 1), and δ(N-O) (840 cm-1).
-
Synthesis of {[Gd(dpdo)
CH O) (4). Compound 4 was prepared in the same
way as 2, using R-H SiMo12 40‚14H O (40 mg, 0.02 mmol) instead
of R-H 40‚14H O. Orange single crystals appeared after 5
weeks and were collected and dried in air after quickly being
washed with water. Yield: 82%, based on R-H SiMo12 40‚14H O.
Anal. Calcd for C46 56GdMo12Si: C, 18.59; H, 1.78; N,
.48. Found: C, 18.36; H, 1.63; N, 4.26. IR (KBr): four
characteristic asymmetric vibrations resulting from heteropolyanions
4 2 3 3
(H O) ](H O)(SiMo12O40)(dpdo)0.5-
Crystallography. Intensity data for the complexes 2-7 was
collected on a Siemens SMART-CCD diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å), using the
SMART and SAINT16 programs. The structures were solved by direct
methods and refined on F2 by using full-matrix least-squares
methods with the SHELXTL program, version 5.1.17 All non-
hydrogen atoms except some disordered solvent molecules were
refined anisotropically. For compounds 2 and 3, four lattice water
molecules were refined disordered with the site occupancy factors
(sof) fixed at 0.5. For compounds 4 and 5, four lattice water
molecules were refined disordered with the sof refined using free
variables, and one acetontrile molecule was refined disordered with
the sof for the atoms in it fixed at 0.5. These disordered atoms
were refined isotropically. For compound 6, several oxygen atoms
in the polyanion were refined disordered with the sof fixed at 0.5
for all these disordered atoms; however, these atoms were refined
anisotropically. For compound 7, one water molecule was refined
disordered with the sof fixed at 0.25 for O(3W); this oxygen atom
and the O(4W) were refined isotropically. The hydrogen atoms of
the organic molecules were localized in their calculated positions
and refined using a riding model. Hydrogen atoms of the ligands
were localized in their calculated positions and refined using a riding
model. The hydrogen atoms of the coordinated water molecules
were found by difference Fourier maps and refined by fixing the
O-H bond of 0.85 Å and the isotropic temperature factors at 1.2
times that of the mother oxygen atoms attached. For compounds
(
3
CN)0.5(H
PMo12
2
3 n
}
4
O
2
3
O
2
4
O
2
52.5 9.5
H N O
4
-1
with the Keggin structure: ν(ModOt) (951 cm ), ν(Mo-Ob) (865
-
1
-1
-1
cm ), ν(Mo-Oc) (793 cm ), and ν(Si-Oa) (905 cm ); four
characteristic vibrations resulting from dpdo molecules, namely,
-
1
-1
ν(N-O) (1228 cm ), ν(ring) (1470 cm ), δ(C-H, in plane) (1181
-
1
-1
cm ), and δ(N-O) (838 cm ).
Synthesis of {[Ho(dpdo) (H O)
CH O) (5). Compound 5 was prepared in the same
way as 4, using HoCl ‚6H O (0.02 mmol) to replace GdCl ‚6H O.
4
2
3 3
](H O)(SiMo12O40)(dpdo)0.5-
(
3
CN)0.5(H
2
3 n
}
3
2
3
2
Orange-yellow single crystals appeared after 4-5 weeks and were
collected and dried in air after quickly being washed with water.
Yield: 80%, based on R-H
56HoMo12Si: C, 18.55; H, 1.78; N, 4.47. Found: C,
7.95; H, 2.16; N, 4.16. IR (KBr): four characteristic asymmetric
vibrations resulting from heteropolyanions with the Keggin struc-
4 2
SiMo12O40‚14H O. Anal. Calcd for
46 52.5 9.5
C H N O
1
-
1
-1
ture: ν(ModOt) (950 cm ), ν(Mo-Ob)(865 cm ), ν(Mo-Oc)
-1
-1
(
792 cm ), and ν(Si-Oa) (905 cm ); four characteristic vibrations
resulting from dpdo molecules, namely, ν(N-O) (1228 cm ), ν-
ring) (1471 cm ), δ(C-H, in plane) (1180 cm ), and δ(N-O)
-
1
-
1
-1
(
-
1
(838 cm ).
2
-5, hydrogen atoms of the disordered lattice solvent molecules
{
[Ni(dpdo) (CH CN)(H O) ] (SiMo12O40)(H O) } (6). The
2 3 2 2 2 2 2 n
were not treated. For compound 6, hydrogen atoms of the solvent
molecules were found by difference Fourier maps and refined by
fixing the O-H bond of 0.85 Å, the C-H bond of 0.93 Å, and the
isotropic temperature factors at 1.2 times that of the mother atoms
attached. For compound 7, only the hydrogen atoms of acetonitrile
molecules were found by difference Fourier maps and refined by
fixing the C-H bond of 0.93 Å and the isotropic temperature factors
at 1.2 times that of the mother atoms attached. The crystal
parameters, data collection, and refinement results for compounds
formation of heteropolyacid nickel salts (yellowish-green crystals)
was accomplished by the neutralization of the acids in the same
way as gadolinium phosphomolybdate (R-H
mg, 0.02 mmol) and NiCl ‚6 H O (10 mg, 0.04 mmol)). Compound
was prepared in the same way as 2, using more 4,4′-bipyridine-
4 2
SiMo12O40‚14H O (41
2
2
6
N,N′-dioxide hydrate (0.15 mmol, 33 mg). Yellow block crystals
appeared after 3 weeks and were collected and dried in air after
quickly being washed with water. Yield: 80%, based on R-H
SiMo12 40‚14H O. Anal. Calcd for C44 Mo12Si: C,
8.35; H, 1.75; N, 4.87. Found: C, 18.51; H, 1.76; N, 4.69. IR
KBr): four characteristic asymmetric vibrations resulting from
4
-
O
2
50 10 2
H N O54Ni
2
-7 are summarized in Table 1.
1
(
-1
(16) SMART and SAINT, Area Detector Control and Integration Software;
Siemens Analytical X-ray Systems, Inc.: Madison, WI, 1996.
17) G. M. Sheldrick. SHELXTL V5.1 Software Reference Manual; Bruker
heteropolyanions with the Keggin structure: ν(ModOt) (951 cm ),
ν(Mo-Ob) (861 cm ), ν(Mo-Oc) (792 cm ), and ν(Si-Oa) (905
cm ); four characteristic vibrations resulting from dpdo molecules,
-1
-1
(
-1
AXS, Inc.: Madison, WI, 1997.
Inorganic Chemistry, Vol. 46, No. 15, 2007 5959

Wei et al.
Table 1. Crystal Data and Structure Refinement for Complexes 2-7
2
3
4
5
6
7
formula
C42H45N9O53-
GdMo12P
2863.37
triclinic
P1h
11.736(4)
17.472(7)
18.857(7)
92.186(6)
97.799(6)
98.882(7)
3778 (2)
2
C42H45N9O53-
DyMo12P
2868.62
triclinic
P1h
11.699(1)
17.476(2)
18.847(2)
92.071(2)
97.642(2)
98.840(2)
3767.2(6)
2
C46H52.5N9.5O56-
GdMo12Si
2971.10
triclinic
P1h
13.222(3)
16.498(4)
18.489(5)
88.827(4)
82.058(5)
83.139(5)
3965.6(18)
2
C42H52.5N9.5O54-
HoMo12Si
2978.78
triclinic
P1h
13.210(3)
16.532(3)
18.518(4)
88.736(4)
81.983(4)
83.310(4)
3977.3(14)
2
C44H50N10O54-
Ni2Mo12Si
2879.73
triclinic
P1h
11.430(3)
12.242(3)
14.279(3)
106.196(4)
94.316(4)
98.294(3)
1884.5(7)
1
C144H187N36O171-
Ni4P3W36
12104.65
cubic
fw
cryst syst
space group
a/Å
b/Å
c/Å
Im3
23.133(1)
23.133(1)
23.133(1)
R/deg
â/deg
γ/deg
3
V/Å
12379.3(10)
2
3.247
17.08
2553
Z
3
Dc/g cm
2.517
2.918
16 416
0.0787
2.529
3.038
16 141
0.0507
2.488
2.783
17 232
0.0747
2.487
2.936
15 447
0.0540
2.537
2.544
8019
0.0360
-
1
µ/mm
data unique
R(int)
0.1031
1.020
GOF
1.029
1.057
1.008
1.032
0.998
R1 [I > 2 σ(I)]
wR2 (all data)
0.0613
0.1543
0.0555
0.1561
0.0639
0.1646
0.0574
0.1301
0.0745
0.1711
0.0743
0.2498
Results and Discussion
from fourindependent dpdo ligands, and one oxygen atom
from a symmetrically relative dpdo ligand. Of the four inde-
pendent dpdo ligands, the one containing the two oxygen
atoms O(47) and O(48) acts as a bridging ligand to link two
identical metal centers in a centrosymmetrically dimeric fash-
ion, while the other three ligands act as the terminal mono-
dentate ligands to each connect with one coordinated water
molecule from different neighbors through hydrogen bonds.
And each of the three coordinated water molecules of O(1W),
O(2W), and O(3W) connects to the symmetric dpdo ligand
resulting in three centrosymmetrically 2-fold hydrogen-
Lanthanide-Based Zeolite Ionic Crystals. The reaction
of gadolinium phosphomolybdate or dysprosium phosphomo-
lybdate with 4,4′-bipyridine-N,N′-dioxide (dpdo) in acetoni-
4 2 5
trile/water solution gave compounds {Gd(dpdo) (H O) -
3 n 4 2 5
(PMo12O40)(CH CN)} (2) or {Dy(dpdo) (H O) (PMo12O40)-
(
CH CN)} (3), respectively, which were isomorphic and
3 n
exhibited 3D noninterwoven frameworks with distorted-
honeycomb cavities occupied by the anions. In compound
+
2
, each Gd3 cation is coordinated in a distorted-square-anti-
prismatic geometry by three aqua ligands, four oxygen atoms
Figure 1. Perspective of the coordinated geometry of the Gd3+ ion in compound 2 showing the four-connected node through the centrosymmetric double-
bridging linkers. Hydrogen atoms of the ligands are omitted for clarity. Selected bond distances (Å) for compound 2: Gd(1)-O(45) 2.335(6), Gd(1)-O(47)
2
.346(6), Gd(1)-O(48A) 2.353(6), Gd(1)-O(43) 2.346(6), Gd(1)-O(41) 2.389(6), Gd(1)-O(3W) 2.413(6), Gd(1)-O(1W) 2.430(6), Gd(1)-O(2W) 2.432-
(7); O(1W)· · ·O(46B) 2.63(2), O(1W)· · ·N(9A) 2.78(2), O(2W)· · ·O(44C) 2.80(2), O(2W)· · ·O(42D) 2.78(2), O(3W)· · ·O(44C) 2.85(2), O(3W)· · ·O(48A)
3
+
2
.79(2). For Dy , the ion in compound 3 has the same coordinated geometry. Selected bond distances (Å) for compound 3: Dy(1)-O(45) 2.287(6),
Dy(1)-O(47) 2.324(6), Dy(1)-O(48A) 2.336(6), Dy(1)-O(43) 2.345(6), Dy(1)-O(41) 2.354(6), Dy(1)-O(3W) 2.399(7), Dy(1)-O(1W) 2.405(7),
Dy(1)-O(2W) 2.410(6); O(1W)· · ·O(46B) 2.65(2), O(1W)· · ·N(9A) 2.79(2), O(2W)· · ·O(44C) 2.83, O(2W)· · ·O(42D) 2.79, O(3W)· · ·O(44C) 2.84,
O(3W)· · ·O(48A) 2.76(2). Symmetry code: A, 1 - x, 1 - y, 1 - z; B, 1 - x, 1 - y, 1 - z; C, 1 - x, -y, 2 - z; D, -x, -y, 1 - z.
5960 Inorganic Chemistry, Vol. 46, No. 15, 2007

Zeolite Ionic Crystals within 3D Frameworks
1
.532(7) and 1.637(8)-2.472(10) Å, respectively, in the
(2,3-Me pz) (PMo12O40)] complex, and also compa-
3 2 3
8
c
[
Cu
rable to those lengths of 1.529(6)-1.532(3) and 1.683(3)-
3
.435(2) Å, respectively, in the {[Cu(2-Mepz)1.5] (PMo12O40)-
2
9
c
(H
2
O)3.5}
n
complex.
Replacing the [PMo12
follow the assembly with the corresponding lanthanide ions
40]3 anion by [SiMo12 40]4- to
O
-
O
3+
3+
(
(
(
Gd and Ho ) gave isomorphic compounds {Gd(dpdo)4.5
H
H
-
2
O)
O)
6
(H
](H
3
O)(SiMo12
O
O
40)(CH
40)(CH
3
CN)0.5
n
} (4) and{Ho(dpdo)4.5
-
2
6
3
O)(SiMo12
3
CN)0.5
}
n
(5), respectively. An
asymmetric unit of these two compounds consists of one
Keggin-structure anion, one lanthanide ion, four coordinated
dpdo ligands, and half a free dpdo ligand. As in compound
3
+
2
, the Gd ion in compound 4 is also coordinated by three
water molecules, four oxygen atoms from four independent
dpdo ligands, and one oxygen atom from a symmetry-related
dpdo ligand. Compound 4 consists of 1D chain polymers
along the a axis with a Gd‚‚‚Gd separation of 13.21 Å.
Hydrogen bonds between the coordination water molecule
O(1W) and the oxygen atom O(42A) from a neighboring
parallel terminal ligand are found to stabilize the chains
through cooperative interactions. One of the other two
terminal dpdo ligands containing oxygen atoms O(47) and
O(48A) contacts a coordinated water molecule O(3W) from
the centrosymmetrically related lanthanide ion to form two-
fold hydrogen bonds. These interactions complete the forma-
tion of an one-dimensional (1D) ribbon (Figure 3). Face-to-
face π-π stacking interactions within these bridging pairs
are also found to stabilize the ribbons.
Adjacent ribbons are linked together through hydrogen
bonds between the oxygen atom O(49) of the free dpdo
ligand and the coordinated water molecule O(3W) to form
a two-dimensional (2D) sheet (Figure 3). Intermolecular π-π
stacking interactions between the free and the coordinated
dpdo ligands are also found to stabilize the 2D sheet. One
lattice water molecule O(4W) also precipitates the interac-
tions, linking one coordination water molecule O(2W) and
the oxygen atom O(49) from a free ligand through hydrogen
4
Figure 2. 3D 6 net formed by the [Gd(dpdo)4(H2O)3]3+ units in compound
2
(top) and the 3D noninterwoven framework with distorted-honeycomb
bonds to stabilize the sheet. Being heavy “building blocks”,
cavities occupied by the polyanions (bottom). Hydrogen atoms and the lattice
solvent molecules are omitted for clarity.
4-
40
the [SiMo12O ]
anions position at the two sides of the
sheets above and below the voids of the tetragons and
connect adjacent sheets together, featuring a 3D framework.
Intermolecular π-π stacking interactions between the py-
ridine rings within the adjacent dpdo ligands contribute to
the stabilization of the 3D framework. These stacked
aromatic rings divide the framework into rooms, with a
centrosymmetrically related shoulder-to-shoulder dimeric
anion embedded in each room (Figure 4).
bonding linkers. Thus a Gd3+ center acts as a four-connected
node (Figure 1) to form a 3D noninterwoven 6 net with
distorted-honeycomb cavities occupied by the polyanions
4
(
Figure 2). The intermolecular π-π stacking interactions
between the pyridyl rings within each pair of the centrosym-
metrically double-bridging linker are likely to stabilize the
3-
40
formed framework. To embed the Keggin-type [PMo12O ]
anions for charge compensation, each honeycomb cavity is
heavily distorted with one direction heavily condensed. The
acetonitrile solvent molecule and disordered lattice water
molecules (O(4W), O(5W), and O(6W)) are presented in the
channels. In compound 2, the bond lengths of P-O and
Mo-O are 1.524(5)-1.535(5) and 1.662(6)-2.446(5) Å,
respectively, and in compound 3, the bond lengths of P-O
and Mo-O are 1.524(5)-1.535(5) and 1.662(6)-2.446(5)
Å, respectively. The bond lengths of P-O and Mo-O in
compounds 2 and 3 are comparable to those of 1.494(7)-
Though the basic structure of the POM-based polymer
could easily be determined based on the X-ray structure
analysis, it is not clear whether the proton sits near the
oxygen atoms of the free dpdo ligand or around the water
molecules. It was reported that, based on high-resolution
1
31
solid-state H and P NMR, there were at least three different
states for protons of H O: (i) protons present
3
PW12
O
40‚nH
2
in highly hydrated samples, (ii) protonated water which is
+
hydrogen bonded to terminal oxygen, W ) O‚‚‚H (H
2
O)
2
(n ) 6), and (iii) protons which are directly bonded to
Inorganic Chemistry, Vol. 46, No. 15, 2007 5961

Wei et al.
Figure 3. View of the 1D ribbon based on [Gd(dpdo)4(H2O)3]3+ units (top) and the 2D sheets with the uncoordinated dpdo molecules as hydrogen-bonding
bridges (bottom) in compound 4. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) for compound 4: Gd(1)-O(45) 2.365(6), Gd(1)-
O(47) 2.394(5), Gd(1)-O(44A) 2.342(6), Gd(1)-O(43) 2.349(6), Gd(1)-O(41) 2.426(5), Gd(1)-O(3W) 2.405(6), Gd(1)-O(1W) 2.398(7), Gd(1)-O(2W)
2
.393(6); O(1W)· · ·O(42A) 2.57(2), O(1W)· · ·O(44A) 2.60(2), O(2W)· · ·O(4WC) 2.73(2), O(3W)· · ·O(48B) 2.67(2), O(3W)· · ·O(49) 2.85(2),
O(4W)· · ·O(49B) 2.76(2). For compound 5: Ho(1)-O(45) 2.329(6), Ho(1)-O(47) 2.365(6), Ho(1)-O(44A) 2.296(6), Ho(1)-O(43) 2.330(6), Ho(1)-
O(41) 2.431(7), Ho(1)-O(3W) 2.365(6), Ho(1)-O(1W) 2.350(6), Ho(1)-O(2W) 2.352(6); O(1W)· · ·O(42A) 2.62(2), O(1W)· · ·O(44A) 2.58(2),
O(2W)· · ·O(4WC) 2.73(2), O(3W)· · ·O(48B) 2.66(2), O(3W)· · ·O(49) 2.85(2), O(4W)· · ·O(49B) 2.73(2). Symmetry code: A, 1 + x, y, z; B, 2 - x, 1 - y,
1
- z; C, x, 1 + y, z.
bridging oxygen, W-OH-W (n ) 0).18 More recently, it
was reported that, based on REDOR experiments, acidic
examples of the protonation of the oxygen atoms of dpdo
ligands have been reported. Furthermore, in such a crystal-
lization condition, the protonation of the surfaces of a
c d
protons are localized on both bridging (O ) and terminal (O )
4-
oxygen atoms of the Keggin unit in the anhydrous state of
Keggin-structure [SiMo O ] anion is impossible, and the
12
40
1
9
3 40
H PW12O .
O(5W) centers are sited closely to the anions with the two
shoulder-to-shoulder polyanions being too close (the shortest
atom‚‚‚atom separation of O(29)‚‚‚O(11A) is 3.4 Å); the
most possible distribution of the excess proton is to attach
to the oxygen atom O(5W), so the presence of positive
charged species could bring the anions together.
In compounds 4 and 5, there are four lattice water
molecules and the separations between them are too long to
+
+
5 2 3 7
form oligomers such as H O or H O for stabilizing the
excess proton. Whereas for dpdo ligands, since N-oxide
groups have formal partial negative and positive charges on
the oxygen and nitrogen atoms, respectively, it is difficult
to protonate the oxygen atoms. To our knowledge, no
Nickel-Based Ionic Crystals. Compound 6 was synthe-
sized by using the POM Ni
2 2
(SiMo12O40)‚H O and the dpdo
ligands. A symmetric unit consists of one coordinated cation
(
18) Kanda, Y.; Lee, K. Y.; Nakata, S.; Asaoka, S.; Misono, M. Chem.
Lett. 1988, 139-142.
2+
4-
2 2 2 3
[Ni(dpdo) (H O) (CH CN)] , half a polyanion [SiMo12O40] ,
(19) Yang, J.; Janik, M. J.; Ma, D.; Zheng, A.; Zhang, M.; Neurock, M.;
Davis, R. J.; Ye, C.; Deng, F. J. Am. Chem. Soc. 2005, 127, 18274-
and one lattice water molecule. As shown in Figure 5, each
2
+
18280.
Ni ion is six-coordinated by two water molecules at the
5962 Inorganic Chemistry, Vol. 46, No. 15, 2007

Zeolite Ionic Crystals within 3D Frameworks
Figure 4. Packing diagram of a 3D structure in compound 4 stabilized by the interlayer stacking interactions between these dpdo ligands (top). View of
the structure of the shoulder-to-shoulder polyanions and the intermediate hydronium ions (bottom). Hydrogen atoms and solvent molecules of crystallization
are omitted for clarity. Selected atom· · ·atom separations (Å): O(5W)· · ·O(28A) 3.18(2), O(5W)· · ·O(29A) 3.15(2), O(5W)· · ·O(35) 3.05(2). Symmetry code:
A, 1 - x, 1 - y, 1 - z.
axial positions, three oxygen atoms from three dpdo ligand
and one nitrogen atom from the acetonitrile molecule at the
equatorial plane, respectively. Compound 6 consists of a 1D
chainlike structure along the b axis, with the Ni‚‚‚Ni
separation distance of 12.24 Å bridged by a single dpdo
molecule. The chains are further linked together into a four-
connected 2D structure through hydrogen bonds between the
terminal oxygen atoms O(21B) in the terminal dpdo ligands
and the coordinated water molecules O(1W) of adjacent
chains. The two adjacent layers are connected through the
hydrogen bonds between the oxygen atoms O(22C) of the
terminal dpdo ligands in one layer and the coordinated water
molecules O(2W) in another layer, leading to a bilayer
fashion. Intermolecular π‚‚‚π stacking interactions between
the bridging dpdo ligands are also found to stabilize the
bilayer packing fashion. These layers are further linked
together through hydrogen bonds arising from a lattice water
molecule O(3WA) featuring a 3D cation network of 6 (Figure
5
). Each water molecule O(3WA) acts as a diaqua bridge
that connects with one coordinated water molecule O(1W)
and one oxygen atom O(24D) of the bridging dpdo ligand,
-
directly incorporating the [SiMo12
O
40]4 anions within the
pores. In other words, these positive charged 2D sheets are
-
pillared by the [SiMo12
O
40]4 anions to form a pillar-layered
framework. The methyl groups of the coordinated acetonitrile
Inorganic Chemistry, Vol. 46, No. 15, 2007 5963

Wei et al.
Figure 5. Four-connected 2D structure of 6 (top) and the 3D structure based on the connection of these bilayers through hydrogen bonds (bottom). The
4
-
[
SiMo12O40] anions acting as pillars directly incorporate within the pores to form a pillar-layered framework. Hydrogen atoms are omitted for clarity.
Selected bond distances (Å) for compound 6: Ni(1)-O(23) 2.058(6), Ni(1)-O(24A) 2.089(6), Ni(1)-O(21) 2.096(6), Ni(1)-N(5) 2.124(10), Ni(1)-
O(1W) 2.098(8), Ni(1)-O(2W) 2.068(7), O(1W)· · ·O(24A) 2.85(2), O(1W)· · ·O(3W) 2.65(2), O(2W)· · ·O(21B) 2.76(2), O(2W)· · ·O(22C) 2.65(2),
O(3W)· · ·O(24D) 2.82(2). Symmetry code: A, x, 1 + y, z; B, -x, -y, -y; C, x, y, 1 + z; D, 1 - x, -1 - y, -z.
molecules all point to the channels of the 3D framework,
resulting in hydrophobic channels without any other solvent
molecules.
that nickel(II) ions have replaced cobalt(II) ions. It is well-
3
-
known that Ni(II) and [PW12
40
O ]
give greenish and
transparent-to-yellowish colors, respectively, while the crystal
color of compound 7 is red; this may be due to the
coordination bonds between nickel ion and dpdo ligands and
there being no coordination bonds between the nickel ion
and water molecules. In addition, the bond valence sum of
the Ni ion in compound 7 gave a value of 2.16, indicating
The reaction of NiHPW12
dioxide (dpdo) in acetonitrile/water solution gave the com-
pound {[Ni(dpdo) [H(H O)27(CH CN)12]} (7).
O40 with 4,4′-bipyridine-N,N′-
] (PW12O )
3 4 40 3
2
3
n
The crystal data of compound 7 were collected at 123 K.
X-ray crystallographic study reveals that both compounds 7
and 1 (at 123 K)10 have the same noninterwoven 3D
framework with cubic cavities and guest molecules, except
20
that the valence of the Ni ion is two. Each nickel(II) ion is
bound by six identical dpdo ligands in an ideal octahedral
5964 Inorganic Chemistry, Vol. 46, No. 15, 2007

Zeolite Ionic Crystals within 3D Frameworks
+
Figure 7. Perspective of the [H (H2O)27(CH3CN)12] cluster, showing the
Figure 6. Perspective of the 3D framework {[Ni(dpdo)3]n}2n+ in compound
(H2O)26 shell formed by the O(1W) (red), O(2W) (blue), and O(3W) (green)
positions that each statistically occupies at two positions and the monowater
center O(4W) (purple) as well as the acetonitrile dangling outside with the
nitrogen atoms (pink) H bonding to the O(1W) centers. Selected atom‚‚‚atom
separations (Å): O(1W)· · ·O(2W) 2.78(4), O(1W)‚‚‚O(3W) 2.62(7),
O(1W)‚‚‚N(2) 2.78(4).
7
showing crystallographic Oh symmetry (top) and models (bottom) of a
unit cell showing the positions of the nickel(II) centers (pink), the protonated
water clusters (red), and the anions having Keggin structure (blue).
geometry, with each dpdo ligand bridging two identical
nickel(II) centers alternatively to form a 3D framework with
cubic cavities (the Ni‚‚‚Ni separation is about 11.6 Å). The
+
hydronium ion (H O ) as the “guest” (Figure 7). Eight
3
3-
trivalent Keggin [PW12
40
O ]
anions (the diameter is about
O(2W) molecules and 12 O(1W) molecules are linked
together, creating a (H O) hexahedron with each face an
10.4 Å) occupy three-quarter of these cavities as templates
2
20
preventing the interpenetration. The remaining one-fourth of
2 8
octagonal water ring (H O) . The residual ample space of
the cavities is inhabited by the protonated water clusters,
the cavity was filled by six additional disordered water
molecules that embedded in the six faces of the (H O)
+
H (H
2
O)27, which are the same as those in compound 1. As
2
20
shown in Figure 6, in a unit cell, the eight nickel (II) ions
hexahedral shell; that is, six O(3W) centers, which are
disordered in twelve positions, occupy the six faces of the
(H O) hexahedron. The O‚‚‚O separations of hydrogen-
1
1
1
occupy the special positions ([ /
4 4 4
], [ / ], [ / ]) and their
symmetric related positions, the two protonated water clusters
2
20
3
-
occupy the vertexes and I centers, and the six [PW12
40
O ]
bonding pairs O(1W)‚‚‚O(2W) and O(1W)‚‚‚O(3W) are 2.74
and 2.64 Å, respectively. Just like in compound 1, consider-
ing the most rational distribution of charges in the solid-
state structure of 7 with the cubic symmetry, it is suggested
that the excess proton should be positioned in the center and
anions are positioned at the centers of the six faces and the
middle regions of the twelve edges. Around each water
2
+
cluster, eight Ni ions occupied the vertexes of the cubic
3-
cavity and six identical trivalent [PW12
40
O ]
anions occupied
+
the centers of six neighboring cavities to form the positive-
and negative-charged fields, respectively (Figure 6). Such a
specific pseudospherical static field in the solid state not only
provides an ideal environment for stabilizing protonated
water clusters with their characteristic structures but also
makes the excess proton prefer to be positioned in the center
of the water cluster rather than on the surface of the water
cluster. Twelve acetonitrile solvent molecules act as pillars
linking the anions (through C-H‚‚‚O hydrogen bonds) and
the water cluster (through O-H‚‚‚N hydrogen bonds) to
create a special hydrophilic environment around the water
cluster in the cavity.
occur in the context of the H O (Eigen) form of a
3
1
0
hydronium ion.
After considering the easy growth of single crystals and
the high cubic symmetry of its space group, we selected
Raman spectroscopy as the suitable spectroscopic method.
The single-crystal laser Raman spectrum was measured at
1
23 K. As shown in Figure 8, the spectrum of compound 7
-1
at 123 K obviously exhibits a peak at 1188 cm resulting
from the polyanions and features at 1296 and 1620 cm ,
which are assigned to the dpdo ligands. The bands at 1520
21
-1
-1
and 1260 cm are probably attributed to the vibration of
the protonated water cluster. Considering the presence of an
+
As described previously in compound 1, based on the
isolated Eigen-type hydronium H
degenerate bending fundamentals ν
3
O
in the center core,
+
results of the X-ray diffraction study and the calculation, in
4
and ν
2
of a H
3
O ion
+
-
1
compound 7, the protonated water cluster, H (H
2
O)27 also
are suggested for the bands at 1520 and 1260 cm ,
2
comprises a 26 water shell (H O)26 as the “host” and a
(
21) Rene, T.; Michel, F.; Raymonde, F.; Claude, R. D. Inorg. Chem. 1984,
(20) Brown, D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244-247.
23, 598-605.
Inorganic Chemistry, Vol. 46, No. 15, 2007 5965

Wei et al.
compound 7 in the atmosphere of N
2
shows a weight loss
(
7.44%) in the temperature range of 25-300 °C, correspond-
ing to 27 water molecules and 12 acetonitrile molecules
calcd. 8.07%), The framework began to decompose at
00 °C, corresponding to the disrupting of the structural
skeletons of the cation metal-organic framework [Ni-
(
3
2
+
3-
(dpdo)
3
]
and the template anion [PW12O40] . The TGA
diagrams of compounds 2-7 are in the Supporting Informa-
tion. The results of TGA studies of these compounds suggest
that compounds 2 and 3 have the same MOFs, which can
be retained below 230 °C by the loss of solevent molecules,
compounds 4 and 5 have the same MOFs, which have lower
thermal stability than those of compounds 2 and 3 by the
loss of solvent molecules and coordinated water molecules,
and that the MOFs of compounds 6 and 7 could be retained
below 200 °C and 300 °C, respectively. We could see that
compound 7 has the highest thermal stability among these
compounds, indicating that such a noninterwoven 3D frame-
work with cubic cavities is a suitable host for researching
protonated water clusters.
Figure 8. Single-crystal laser Raman spectrum in the range of 600-2000
-
1
+
cm of compound 7 at 123 K. Those bands assigned to the H3O ion are
indicated by arrows.
respectively.22 The bands at low frequencies are generally
23
2
assigned to the librational and translational modes of H O.
Thermogravimetric Analyses. Thermogravimetric analy-
ses of the powder of the crystalline samples of compounds
2
3
2
2
and 3 in an N atmosphere show a weight loss (3.24 and
.22% for 2 and 3, respectively) in the temperature range of
5-155 °C, corresponding to two solvent water molecules
In summary, POM-based metal-organic frameworks
represent an outstanding class of functional materials and
are regarded as green materials. In this paper, several POM-
based MOFs were prepared via self-assembly from transition-
metal ions or lanthanide ions that generally adopt coordi-
nation numbers higher than six to elaborate new synthetic
approaches to access novel topologies and to develop a better
understanding of correlating building block geometrical
information to the resultant structure. By carefully adjusting
the charges of the Keggin anions, a 3D porous metal-organic
and one acetonitrile molecule (calcd. 2.69 and 2.68% for 2
and 3, respectively). The frameworks began to slowly
decompose at 230 °C due to the loss of three coordinated
water molecules. TGA studies of the powder of the crystal-
line samples of compounds 4 and 5 in an atmosphere of N
2
show a weight loss (4.66 and 4.64% for 4 and 5, respectively)
in the temperature range of 25-200 °C, corresponding to
four solvent water molecules, three coordinated water
molecules, and half an acetonitrile molecule (calcd. 4.93 and
4.92% for 4 and 5, respectively). The anhydrous compounds
cationic framework was assembled, in which a protonated
began to rapidly decompose at 340 °C. The TGA of the
powder of the crystalline sample of compound 6 in the
+
clathrate hydrate H (H
2
O)27 was captured and stabilized. The
successful syntheses of these POM-based materials not only
provide novel examples of MOFs that can recognize special
guests but also may open the door to the formation and
stabilization of nanosized protonated water clusters. The
further investigation of the chemical/physical properties
related to the protonated water cluster inhabited in such a
MOF is underway.
2
atmosphere of N shows a weight loss (4.11%) in the
temperature range of 150-215 °C, corresponding to two
solvent water molecules, two coordinated water molecules,
and an coordinated acetonitrile molecule (calcd. 3.93%).
The anhydrous compounds began to slowly decompose at
220 °C. TGA of the powder of the crystalline sample of
(
22) (a) Taylor, R. C.; Vidale, G. L. J. Am. Chem. Soc. 1956, 78, 5999-
002. (b) Zundel, G. Hydration and Intermolecular Interaction;
Acknowledgment. This work is supported by the Na-
tional Natural Science Foundation of China.
6
Academic Press: New York, 1969. (c) Williams, J. M.; Peterson. S.
W. In Spectroscopy in Inorganic Chemistry; Rao, C. N., Ferraro, J.
R., Eds.; Academic Press: New York, 1971; Vol. 11, p 36.
Supporting Information Available: X-ray crystallographic files
for 2-7 in CIF format and a PDF file. This material is available
free of charge via the Internet at http://pubs.acs.org.
(23) (a) Berenblut, B. J.; Dawson, P.; Wilkinson, G. R. Spectrochim. Acta,
Part A 1971, 27, 1849. (b) Bates, J. B.; Khanna, B. K. Inorg. Chem.
1970, 9, 1376. (c) Kearley, G. J.; Fitch, A. N.; Fender, B. E. F. J.
Mol. Struct. 1984, 229.
IC070274O
5966 Inorganic Chemistry, Vol. 46, No. 15, 2007