A Contrivance for a Dynamic Porous Framework: Cooperative Guest Adsorption Based on Square Grids Connected by Amide - Amide Hydrogen Bonds

Article abstract of DOI:10.1021/ja039914m

Flexible porous coordination polymers containing amide groups as a function origin have been synthesized and categorized as Coordination Polymer with Amide Groups . Bispyridyl ligands with a spacer of amide group afford two-dimensional (2-D) motifs with a deformed square grid, resulting in three-dimensional (3-D) frameworks of [Co(NO₃) ₂(3-pna)₂]_n (1), [Co(Br) ₂(3-pna)₂]_n (2), and {[Co(NCS) ₂(4-peia)₂]· 4Me₂CO}_n (3 ? 4Me₂CO) (3-pna = N-3-pyridylnicotinamide, 4-peia = N-(2-pyridin-4-yl-ethyl)-isonicotinamide), where the 2-D motifs are bound by complementary hydrogen bond between the amide groups. In the case of the 3 ? 4Me₂CO, the amide groups form a contrivance for a dynamic porous framework because of their relevant position and orientation in the mutual nearest neighboring motifs. Consequently, 3 ? 4Me₂CO shows amorphous (nonporous)-to-crystal (porous) structural rearrangement in the Me₂CO adsorption and desorption process, where the framework of the 2-D motif is maintained. The adsorption isotherm has threshold pressure (P _th), a sort of gate pressure. The heat of Me₂CO adsorption (ΔH_ad = -25 kJ/mol) is obtained from the temperature dependence of threshold pressure (P_th), which is close to acetone vaporization enthalpy (ΔH_vap = 30.99 kJ/mol).

Full text of DOI:10.1021/ja039914m

Published on Web 03/04/2004
A Contrivance for a Dynamic Porous Framework:
Cooperative Guest Adsorption Based on Square Grids
Connected by Amide-Amide Hydrogen Bonds
Kazuhiro Uemura,† Susumu Kitagawa,*,† Koˆichi Fukui,‡ and Kazuya Saito§
Contribution from the Department of Synthetic Chemistry and Biological Chemistry,
Graduate School of Engineering, Kyoto UniVersity, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan, Regional Joint Research Project of Yamagata Prefecture,
Matsuei 2-2-1, Yamagata 990-2473, Japan, and Research Center for Molecular
Thermodynamics, Graduate School of Science, Osaka UniVersity,
Toyonaka, Osaka 560-0043, Japan
Received December 3, 2003; E-mail: kitagawa@sbchem.kyoto-u.ac.jp
Abstract: Flexible porous coordination polymers containing amide groups as a function origin have been
synthesized and categorized as “Coordination Polymer with Amide Groups”. Bispyridyl ligands with a spacer
of amide group afford two-dimensional (2-D) motifs with a deformed square grid, resulting in three-
dimensional (3-D) frameworks of [Co(NO3)2(3-pna)2]n (1), [Co(Br)2(3-pna)2]n (2), and {[Co(NCS)2(4-peia)2]‚
4Me2CO}n (3 ⊃ 4Me2CO) (3-pna ) N-3-pyridylnicotinamide, 4-peia ) N-(2-pyridin-4-yl-ethyl)-isonicotina-
mide), where the 2-D motifs are bound by complementary hydrogen bond between the amide groups. In
the case of the 3 ⊃ 4Me2CO, the amide groups form a contrivance for a dynamic porous framework because
of their relevant position and orientation in the mutual nearest neighboring motifs. Consequently, 3 ⊃ 4Me2CO
shows amorphous (nonporous)-to-crystal (porous) structural rearrangement in the Me2CO adsorption and
desorption process, where the framework of the 2-D motif is maintained. The adsorption isotherm has
threshold pressure (Pth), a sort of gate pressure. The heat of Me2CO adsorption (∆Had ) -25 kJ/mol) is
obtained from the temperature dependence of threshold pressure (Pth), which is close to acetone vaporization
enthalpy (∆Hvap ) 30.99 kJ/mol).
Introduction
recent targets for the porous coordination polymers is a robust
framework such as inorganic zeolites10,16 and large pores with
In a decade, coordination polymers have been extensively
studied and added a new dimension to materials-directed
coordination chemistry. The synthetic method is rapidly being
developed from accidental to rational stage,1-10 affording porous
frameworks, which could be relevant for storage and exchange
of specific guests, catalysis, and guest alignment.11-15 Two
high specific surface area.17 In addition to such targets, an
approach to create other properties, characteristic of porous
coordination polymers, has been explored, and the most
interesting is a dynamic micropore, which responds to a
chemical stimulus.18,19 This property could come from a sort
of “soft” framework with bistability, whose two states go back
from and forth to one of counterparts; a system could exist in
one or two states for the same values of external field
parameters. Recently, several articles19-37 have reported dynamic
† Kyoto University.
‡ Regional Joint Research Project of Yamagata Prefecture.
§ Osaka University.
(1) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460-1494.
(2) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276-
279.
(16) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe,
M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319-330.
(17) Noro, S.-i.; Kitagawa, S.; Yamashita, M.; Wada, T. Chem. Commun. 2002,
222-223.
(3) Hagrman, P. J.; Hagrman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999,
38, 2638-2684.
(4) Noro, S.-I.; Kitagawa, S.; Kondo, M.; Seki, K. Angew. Chem., Int. Ed.
2000, 39, 2082-2084.
(18) Kitagawa, S.; Kondo, M. Bull. Chem. Soc. Jpn. 1998, 71, 1739-1753.
(19) Uemura, K.; Kitagawa, S.; Kondo, M.; Fukui, K.; Kitaura, R.; Chang, H.-
C.; Mizutani, T. Chem.-Eur. J. 2002, 8, 3586-3600.
(20) Kitaura, R.; Fujimoto, K.; Noro, S.-i.; Kondo, M.; Kitagawa, S. Angew.
Chem., Int. Ed. 2002, 41, 133-135.
(5) Seki, K. Chem. Commun. 2001, 1496-1497.
(6) Desiraju, G. R. Nature 2001, 412, 397-400.
(7) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629-1658.
(8) Zaworotko, M. J. Chem. Commun. 2001, 1-9.
(9) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.;
Yaghi, O. M. Science 2002, 295, 469-472.
(21) Kitaura, R.; Seki, K.; Akiyama, G.; Kitagawa, S. Angew. Chem., Int. Ed.
2003, 42, 428-431.
(22) Halder, G. J.; Kepert, C. J.; Moubaraki, B.; Murray, K. S.; Cashion, J. D.
Science 2002, 298, 1762-1765.
(10) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.;
Kim, J. Nature 2003, 423, 705-714.
(23) Cussen, E. J.; Claridge, J. B.; Rosseinsky, M. J.; Kepert, C. J. J. Am. Chem.
Soc. 2002, 124, 9574-9581.
(11) Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112, 1546-1554.
(12) Fujita, M.; Kwon, J. Y.; Washizu, S.; Ogura, K. J. Am. Chem. Soc. 1994,
116, 1151-1152.
(24) Biradha, K.; Hongo, Y.; Fujita, M. Angew. Chem., Int. Ed. 2002, 41, 3395-
3398.
(13) Yaghi, O. M.; Li, H. J. Am. Chem. Soc. 1996, 118, 295-296.
(14) Kondo, M.; Yoshitomi, T.; Seki, K.; Matsuzaka, H.; Kitagawa, S. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1725-1727.
(25) Biradha, K.; Fujita, M. Angew. Chem., Int. Ed. 2002, 41, 3392-3395.
(26) Suh, M. P.; Ko, J. W.; Choi, H. J. J. Am. Chem. Soc. 2002, 124, 10976-
10977.
(15) Langley, P. J.; Hulliger, J. Chem. Soc. ReV. 1999, 28, 279-291.
(27) Seki, K. Phys. Chem. Chem. Phys. 2002, 4, 1968-1971.
9
10.1021/ja039914m CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 3817-3828
3817

A R T I C L E S
Scheme 1
Uemura et al.
could have great contribution to a wide range of framework
formation.
Although there are various combinations of hydrogen bond-
type gadgets in structural motifs, a layer-type motif would
operate well for creating dynamic but reversible porous frame-
work, which exhibits structural transformation caused by
external stimuli, the event occurring either within the layer or
between the layers.19,24 When py-X-py (py ) pyridine, spacer
X ) functional group)-type ligands are employed, two-
dimensional (2-D) networks are readily formed; straight-type
rod ligands have thus far afforded a square grid,12,24,42-56
rectangular grid,57-61 herringbone, brick wall, bilayer, and so
on.7,8 Among all the possible networks from py-X-py, the square
grid or rectangular grid polymers are of particular importance
because they could control the spatial dimensions of grids and
chemistry of the interior of channels by modifying the spacer
group (X) in the ligand. Once the size of channels in such a
square grid system is fixed, another important factor is the
stacking modes of the grids in the nearest-neighbor layers. It
has been reported that for coordination polymers of planar square
grids, three types of stacking modes are typically observed, as
follows (Scheme 2):
porous coordination polymers which show framework trans-
formation accompanying the adsorption and desorption of guest
molecules as shown in eq 1:
H + n‚G a H‚Gn (H ⊃ n‚G)
(1)
where H is the apohost, G is the guest molecule, and n is
stoichiometry of accommodated guest vs apohost.38 These new
types of porous coordination polymers are expected to provide
characteristic functionality such as highly selective guest
inclusions19,30 and reversible magnetic modulation.22,37,39,40
There are two kinds of forms for apohost; one is “crystal”
and the other is “amorphous” (Scheme 1). When an apohost is
amorphous, such structural transformation is regarded as
“recoverable collapse”. Therefore, the approach to create such
a transformation could be applicable to brittle materials sys-
tems.41 A unique adsorption property is expected for this
amorphous-to-crystal phase transformation. Several coordination
polymers recover their crystallinity with the aid of liquid
solvents, such as in a recrystallization process.33-35 On the other
hand, the transformation to a crystal form merely upon exposure
to guest Vapor has been observed for several compounds.36,37
A clue for this flexible but ordered structure is to set a
contrivance for a framework by which amorphous-to-crystal
transformation could be realized. For this purpose, it is useful
to take advantage of organic ligands, which possess weak
interaction such as a hydrogen bond, and therefore the utilization
(i) Edge-to-edge type: grids in the nearest-neighbor layers
eclipse in edge-to-edge fashion (or short-slipped manner),
designated as ...AAA...19,24,46,51
(ii) Interpenetration type: square grids are intimately inter-
locked with other(s) in the same sort of topological relation-
ship.42,49,54,56,62,63
(iii) Staggered type: grids deposit on each other in an offset
fashion, designated as ...ABAB... (or ...ABCABC...).12,43-48,50-53,55
(42) Gable, R. W.; Hoskins, B. F.; Robson, R. J. Chem. Soc., Chem. Commun.
1990, 1677-1678.
(43) Biradha, K.; Hongo, Y.; Fujita, M. Angew. Chem., Int. Ed. 2000, 39, 3843-
3845.
(44) Pschirer, N. G.; Ciurtin, D. M.; Smith, M. D.; Bunz, U. H. F.; Loye, H.-C.
z. Angew. Chem., Int. Ed. 2002, 41, 583-585.
(45) Aoyagi, M.; Biradha, K.; Fujita, M. Bull. Chem. Soc. Jpn. 2002, 73, 1369-
1373.
(46) Biradha, K.; Fujita, M. J. Chem. Soc., Dalton Trans. 2000, 3805-3810.
(47) Bourne, S. A.; Kilkenny, M.; Nassimbeni, L. R. J. Chem. Soc., Dalton
Trans. 2001, 1176-1179.
(48) Lu, J.; Paliwala, T.; Lim, S. C.; Yu, C.; Niu, T.; Jacobson, A. J. Inorg.
Chem. 1997, 36, 923-929.
(49) Kondo, M.; Shimamura, M.; Noro, S.-i.; Minakoshi, S.; Asami, A.; Seki,
K.; Kitagawa, S. Chem. Mater. 2000, 12, 1288-1299.
(50) Haynes, J. S.; Rettig, S. J.; Sams, J. R.; Thompson, R. C.; Trotter, J. Can.
J. Chem. 1987, 65, 420-426.
(28) Takamizawa, S.; Nakata, E.-i.; Yokoyama, H.; Mochizuki, K.; Mori, W.
Angew. Chem., Int. Ed. 2003, 42, 4331-4334.
(29) Serre, C.; Millange, F.; Thouvenot, C.; Nogues, M.; Marsolier, G.; Louer,
D.; Ferey, G. J. Am. Chem. Soc. 2002, 124, 13519-13526.
(30) Makinen, S. K.; Melcer, N. J.; Parvez, M.; Shimizu, G. K. H. Chem.-Eur.
J. 2001, 7, 5176-5182.
(51) Tong, M.-L.; Ye, B.-H.; Cai, J.-W.; Chen, X.-M.; Ng, S. W. Inorg. Chem.
1998, 37, 2645-2650.
(52) Biradha, K.; Domasevitch, K. V.; Moulton, B.; Seward, C.; Zaworotko,
M. J. Chem. Commun. 1999, 1327-1328.
(31) Edgar, M.; Mitchell, R.; Slawin, A. M. Z.; Lightfoot, P.; Wright, P. A.
Chem.-Eur. J. 2001, 7, 5168-5175.
(53) Biradha, K.; Domasevitch, K. V.; Hogg, C.; Moulton, B.; Power, K. N.;
Zaworotko, M. J. Cryst. Eng. 1999, 2, 37-45.
(32) Alberti, G.; Brunet, E.; Dionigi, C.; Juanes, O.; Mata, M. J. d. l.; Rodriguez-
Ubis, J. C.; Vivani, R. Angew. Chem., Int. Ed. 1999, 38, 3351-3353.
(33) Choi, H. J.; Lee, T. S.; Suh, M. P. Angew. Chem., Int. Ed. 1999, 38, 1405-
1408.
(54) Real, J. A.; Andres, E.; Munoz, M. C.; Julve, M.; Granier, T.; Bousseksou,
A.; Varret, F. Science 1995, 268, 265-267.
(55) Real, J. A.; Munno, G. D.; Munoz, M. C.; Julvel, M. Inorg. Chem. 1991,
30, 2701-2704.
(34) Min, K. S.; Suh, M. P. Chem.-Eur. J. 2001, 7, 303-313.
(35) Cao, R.; Sun, D.; Liang, Y.; Hong, M.; Tatsumi, K.; Shi, Q. Inorg. Chem.
2002, 41, 2087-2094.
(56) Park, S. H.; Kim, K. M.; Lee, S.; Jung, O.-S. Bull. Korean Chem. Soc.
1998, 19, 79-82.
(57) MacGillivray, L. R.; Groeneman, R. H.; Atwood, J. L. J. Am. Chem. Soc.
1998, 120, 2676-2677.
(36) Tabares, L. C.; Navarro, J. A. R.; Salas, J. M. J. Am. Chem. Soc. 2001,
123, 383-387.
(58) Groeneman, R. H.; MacGillivray, L. R.; Atwood, J. L. Chem. Commun.
1998, 2735-2736.
(37) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Domingo, N.; Cavallini, M.;
Biscarini, F.; Tejada, J.; Rovira, C.; Veciana, A. J. Nat. Mater. 2003, 2,
190-195.
(59) Tong, M.-L.; Chen, X.-M.; Yu, X.-L.; Mak, T. C. W. J. Chem. Soc., Dalton
Trans. 1998, 5-6.
(38) Hereafter, the number n is defined for the ratio of [the amount of adsorbed
guest molecules]/[asymmetric unit of the crystal].
(60) Kawata, S.; Kitagawa, S.; Kondo, M.; Furuchi, I.; Munakata, M. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1759-1761.
(39) Larionova, J.; Chavan, S. A.; Yakhmi, J. V.; Froystein, A. G.; Sletten, J.;
Sourisseau, C.; Kahn, O. Inorg. Chem. 1997, 36, 6374-6381.
(40) Usuki, N.; Ohba, M.; Okawa, H. Bull. Chem. Soc. Jpn. 2002, 75, 1693-
1698.
(61) Zheng, L.-M.; Fang, X.; Lii, K.-H.; Song, H.-H.; Xin, X.-Q.; Fun, H.-K.;
Chinnakali, K.; Razak, I. A. J. Chem. Soc., Dalton Trans. 1999, 2311-
2316.
(62) Shin, D. M.; Lee, I. S.; Chung, Y. K.; Lah, M. S. Inorg. Chem. 2003, 42,
5459-5461.
(63) Shin, D. M.; Lee, I. S.; Chung, Y. K.; Lah, M. S. Chem. Commun. 2003,
1036-1037.
(41) White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.;
Sriram, S. R.; Brown, E. N.; Viswanathan, S. Nature 2001, 409, 794-
797.
9
3818 J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004

Cooperative Guest Adsorption Based on Square Grids
A R T I C L E S
Scheme 2
Scheme 3
(d, J ) 8.0 Hz, 1H), δ 8.33 (d, J ) 5.0 Hz, 1H), δ 8.78 (d, J ) 5.0 Hz,
1H), δ 8.92 (s, 1H), δ 9.12 (s, 1H), δ 10.64 (s, 1H). Elemental analysis
calcd for C11H9N3O (199.2): C, 66.32; H, 4.55; N, 21.09. Found: C,
65.80; H, 4.47; N, 20.89.
Types ii and iii hinder effective pores, since the cavities in a
layer are usually obstructed by adjacent layers. However, even
if the interpenetration or staggered manner occurs, we expect
the presence of voids for an inclusion of small-molecule when
we use longer ligands.43,49 Square grids of {[Ni(L)2(NO3)2]‚
4(o-xylene)}n (L ) py-PhPh-py, py ) pyridine) in a staggered
manner afford large pores,43 resulting in a three-dimensional
(3-D) held porous network.
On this background, we focus on stacking modes of square
grids controlled by hydrogen bonds, which are associated with
dynamic pores. “Coordination Polymer with Amide Groups”
is one of the candidates relevant to those having square grids
with hydrogen bonds in staggered fashion, where coordination
polymers including L-amide-L-type ligand (L ) ligand-
containing coordination donor atom) form complementary
hydrogen bonding (so-called hydrogen-bond pillar framework)
between 2-D motifs. Such a form of hydrogen bond is similar
to that of amide binding of cyclic peptide64,65 and useful for
achieving pores in coordination polymers. In this article, new
“Coordination Polymer with Amide Groups” (1-3) based on
hydrogen-bond pillar framework were synthesized (Scheme 3),
characterized by X-ray crystallography and sorption measure-
ments, and particularly discussed about the adsorption and
structural transformation of 3 ⊃ 4Me2CO based on thermody-
namic analysis.
Synthesis of N-(2-Pyridin-4-yl-ethyl)-isonicotinamide (4-peia). The
ligand was prepared by the reaction of isonicotinic chloride hydro-
chloride (15.0 g, 84.4 mmol) with 4-(2-aminoethyl)pyridine (10.0 mL,
84.4 mmol) in dry tetrahydrofuran (280 mL) in the presence of
triethylamine (24 mL, 170 mmol) under N2. The product was recrystal-
1
lized from acetone/hexane in 55% yield (10.6 g). H NMR (DMSO):
δ 2.87 (t, J ) 7.0 Hz, 2H), δ 3.54 (q, J ) 7.0 Hz, 2H), δ 7.26 (d, J )
4.5 Hz, 2H), δ 7.67 (d, J ) 4.5 Hz, 2H), δ 8.45 (d, J ) 4.5 Hz, 2H),
δ 8.70 (d, J ) 4.5 Hz, 2H), δ 8.86 (t, J ) 7.0 Hz, 1H). Elemental
analysis calcd for C13H13N3O (227.3): C, 68.70; H, 5.77; N, 18.49.
Found: C, 68.56; H, 5.74; N, 18.54.
[Co(NO3)2(3-pna)2]n (1). An ethanol solution (1.5 mL) of 3-pna (29.9
mg, 1.5 mmol) was carefully layered on an acetone/chloroform mixed
(v/v 9:1) solvent (1.5 mL) of Co(NO3)2 (21.8 mg, 0.75 mmol), where
a mixed solvent of ethanol/chloroform (v/v 19:1) was placed between
two layers (yield: 37%). Elemental analysis calcd for C22H18CoN8O8
(581.4): C, 45.45; H, 3.12; N, 19.27. Found: C, 44.80; H, 3.23; N,
19.06.
[CoBr2(3-pna)2]n (2). An ethanol solution (1.5 mL) of 3-pna (14.9
mg, 0.075 mmol) was carefully layered on a methanol/chloroform mixed
(v/v 9:1) solvent (1.5 mL) of CoBr2 (8.2 mg, 0.038 mmol), where a
mixed solvent of ethanol/chloroform (v/v 19:1) was placed between
two layers (yield: 22%). Elemental analysis calcd for C22H18Br2CoN6O2
(617.2): C, 42.81; H, 2.94; N, 13.62. Found: C, 42.31; H, 3.31; N,
12.92.
{[Co(NCS)2(4-peia)2]‚4Me2CO}n (3 ⊃ 4Me2CO). A solution of
4-peia (6.81 mg, 0.03 mmol) in acetone (1.5 mL) was gently layered
onto a solution of Co(SCN)2 (2.63 mg, 0.015 mmol) in acetone/
chloroform (v/v 9:1, 1.5 mL), with a mixed solvent of acetone/
chloroform (v/v 19:1, 1.5 mL) placed between the two layers (yield:
50%). For elemental analysis these crystals were collected and dried
in vacuo at room temperature for 24 h. Elemental analysis calcd for
C31H32CoN8O3S2 (687.7): C, 54.14; H, 4.69; N, 16.29. Found: C, 53.47;
H, 4.55; N, 16.10. The microcrystalline sample for physicochemical
measurements was prepared in the same solvent, and the crystallinity
was checked by X-ray powder diffraction as shown in Figure S1 in
the Supporting Information.
Experimental Section
Materials. Isonicotinic chloride hydrochloride, nicotinic chloride
hydrochloride, 3-aminopyridine, and 4-(2-aminoethyl)pyridine were
obtained from Tokyo Kasei Industrial. Co(SCN)2 was obtained from
Aldrich Co.
Synthesis of N-(3-Pyridyl)nicotinamide (3-pna). The ligand was
prepared by the reaction of nicotinic chloride hydrochloride (15.2 g,
85 mmol) with 3-aminopyridine (8.0 g, 85 mmol) in dry tetrahydrofuran
(220 mL) in the presence of triethylamine (25 mL, 179 mmol) under
N2. The product was recrystallized from acetone/hexane in 47% yield
1
X-ray Crystal Structure Determination. For each compound, a
single crystal was mounted on a glass fiber and coated with epoxy
resin. X-ray data collection for each crystal was carried out on a Rigaku
Mercury diffractometer with graphite monochromated Mo KR radiation
(λ ) 0.71069 Å) and a CCD 2-D detector. The size of the unit cells
were calculated from the reflections collected on the setting angles of
(8.0 g). H NMR (DMSO): δ 7.58 (dd, J ) 8.5 Hz; 5.0 Hz, 1H), δ
7.58 (dd, J ) 8.0 Hz; 5.0 Hz, 1H), δ 8.18 (d, J ) 8.5 Hz, 1H), δ 8.29
(64) Bong, D. T.; Clark, T. D.; Granja, J. R.; Ghadiri, M. R. Angew. Chem.,
Int. Ed. 2001, 40, 988-1011.
(65) Ghadiri, M. R.; Granja, J. R.; Milligan, R. A.; McRee, D. E.; Khazanovich,
N. Nature 1993, 366, 324-327.
9
J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004 3819

A R T I C L E S
Uemura et al.
Table 1. Crystal Data and Structure Refinement for [Co(NO3)2(3-pna)2]n (1), [CoBr2(3-pna)2]n (2), and {[Co(NCS)2(4-peia)2]‚4Me2CO}n (3 ⊃
4Me2CO)
compound
1
2
3
⊃
4Me2CO
chemical formula
formula weight
crystal dimensions (mm)
crystal system
space group
a (Å)
C22H18CoN8O8
581.37
0.40 × 0.30 × 0.20
orthorhombic
Pbcn
18.3004(6)
10.759(3)
11.458(2)
90
90
90
2255.9(8)
4
1.712
C22H16Br2CoN6O2
615.15
C40H26CoN8O6S2
837.75
0.50 × 0.40 × 0.30
monoclinic
P21/c
11.115(3)
22.046(7)
9.717(3)
90
100.834(7)
90
2338(1)
2
1.190
858
0.505
0.25 × 0.20 × 0.10
orthorhombic
Ccca
10.481(7)
19.03(1)
10.894(8)
90
90
90
2172(2)
4
1.881
1212
4.515
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
F
calcd (g cm-3
)
F(000)
1188
0.832
µ (mm-1
)
radiation (Å)
temp (K)
2θ range
GOF
0.71069
223
5.5° < 2θ < 54.1°
1.45
0.71069
293
5.5° < 2θ < 54.9°
1.44
0.71069
293
5.5° < 2θ < 55.0°
2.58
no. of data collected
no. of unique data
no. of obsd data
no. of variables
Ra
11611
1673
1673
167
11978
1211
1211
24767
5324
2526 (I > 5.00σ(I))
195
86
0.066
0.053
0.083
Rw
0.125b
0.137b
0.132c
a
b
2
2
2
c
2
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) {∑w[(Fo - Fc )2]/[(∑wFo )2]}1/2
.
Rw ) [∑w(|Fo| - |Fc|)2/(∑wFo ]1/2
.
six frames by changing by 0.5° for each frame. Three different settings
were used and were changed by 0.5° per frame. Intensity data were
collected with a scan width of 0.5°. Empirical absorption correction
by using REQABA66 was performed for all data. For 1, the structure
was solved by direct methods by using the SIR88 program67 and
expanded by using Fourier techniques.68 For 2, the structure was solved
by Patterson methods by using the DIRDIF94 program69 and expanded
by using Fourier techniques.68 For 3 ⊃ 4Me2CO, the structure was
solved by direct methods by using the SIR97 program70 and expanded
by using Fourier techniques.68 All calculations were performed with
the teXsan crystallographic software package from Molecular Structure
Corporation.71 For all compounds, the non-hydrogen atoms were refined
anisotropically and all hydrogen atoms were placed in the ideal
positions. In compound 1, nitrate anions containing O(3) and 3-pna
containing C(7) were refined isotropically. In compound 3 ⊃ 4Me2CO,
acetone molecules containing O(2), O(3), and C(15)-C(20) were found
at the final stage, and thus its atom positions were isotropically refined
under a rigid condition.
Tran cryostat. The microwave frequency was measured using an
Advantest R5372 frequency counter, and the magnetic field was
repeatedly calibrated with diphenylpicrylhydrazyl (DPPH) and Mn2+
in MgO.
Measurement of Adsorption. The adsorption isotherm of CH4 was
measured by using FMS-BG gravimetric adsorption equipment from
BEL Japan. The adsorption isotherms and kinetics measurements of
gaseous acetone and N2 were measured by using BELSORP18-Plus
volumetric adsorption equipment from BEL Japan. In the sample
chamber (∼17.5 mL) maintained at T ( 0.03 K was placed the
adsorbent sample (∼50 mg), which had been prepared at 373 K and
10-1 Pa prior to measurement of the isotherms. The larger gas chamber
(179.85 mL) with a pressure gauge was kept at (T + 20) ( 0.1 K. The
acetone used to generate the vapor was degassed fully by repeated
evacuation and vapor equilibration cycles of the liquid supply side of
the vapor reservoir. Helium gas at a certain pressure was introduced in
the gas chamber and was allowed to diffuse into the sample chamber
by opening a valve. The change in pressure allowed an accurate
determination of the volume of the total gas phase. The complexation
was monitored in a similar manner by using a guest vapor in place of
helium. The amount of guest adsorbed was calculated readily from
pressure difference (Pcal - Pe), where Pcal is the calculated pressure
with no guest adsorption and Pe is the observed equilibrium pressure.
All operations were computer-controlled and automatic.
Physical Measurements. Thermal gravimetry (TG) was carried out
with a Rigaku Instrument TG8120 in a nitrogen atmosphere. IR spectra
were recorded on a Perkin-Elmer 2000 FTIR spectrophotometer with
samples prepared with Nujol. X-ray powder diffraction (XRPD) data
were collected on a Rigaku RINT-2200HF (Ultima) diffractometer with
Cu KR radiation. Continuous-wave (CW) EPR spectra were recorded
on a JEOL RE-3X spectrometer equipped with an Air-Product Heli-
Results and Discussion
(66) Jacobson, R. A. REQABA Empirical Absorption Correction, version 1.1-
0301998; Molecular Structure Corp.: The Woodlands, TX, 1996-1998.
(67) Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.; Polidori, G.;
Spagna, R.; Viterbo, D. J. Appl. Crystallogr. 1989, 22, 389-303.
(68) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; deGelder,
R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 Program System; Technical
Report of the Crystallography Laboratory; University of Nijmegen:
Nijmegen, The Netherlands, 1994.
(69) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF
Program System; Technical Report of the Crystallography Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1992.
(70) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115-119.
(71) teXsan Crystal Structure Analysis Package; Molecular structure Corpora-
tion: The Woodlands, TX, 2000.
Crystal Structures. Crystallographic data for 1-3 are
summarized in Table 1.
[Co(NO3)2(3-pna)2]n (1). In 1, the cobalt(II) center is
octahedrally coordinated to each nitrogen atom of four 3-pna
in equatorial plane, where two types of the nitrogen donors,
carbonylpyridyl (NC), and amino pyridyl (NA), are located in a
cis fashion (Figure 1a). The two Co-N bond distances are close
to each other: Co-N(1) ) 2.174(5) Å, Co-N(2) ) 2.167(5)
-
Å. In addition, the two oxygen atoms of NO3 groups are
coordinated axially with the distance of 2.089(5) Å. The cis
N-Co-N or N-Co-O bond angles range from 83 to 104°,
9
3820 J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004

Cooperative Guest Adsorption Based on Square Grids
A R T I C L E S
Figure 1. Crystal structure of [Co(NO3)2(3-pna)2]n (1) and [Co(Br)2(3-pna)2]n (2). (a) ORTEP drawing of the cobalt center of 1 at the 30% probability level.
Hydrogen atoms are omitted for clarity. (b) Crystal view of complementary hydrogen bonds among amide moieties in 1. (c) Crystal view of 1 along the b
axis. Two-layer stack with hydrogen bond of amide moieties between the layers. The thin and thick lines show the upper and lower layer, respectively. (d)
ORTEP drawing of the cobalt center of 2 at the 30% probability level. Hydrogen atoms are omitted for clarity. The amide moiety is disordered about the
2-fold axis running through the 3-pna ligand. (e) Crystal view of 2 along the c axis. Two-layer stack with hydrogen bonds of amide moieties between the
layers. The thin and thick lines show the upper and lower layer, respectively.
indicative of a distorted octahedral environment. The cobalt ions
are linked by 3-pna to yield a honeycomb-shaped grid with the
dimension of 10.8 Å × 10.8 Å. The square grids do not
interpenetrate, affording a layered structure. It is worth noting
that hydrogen-bonding links of the NH- - -OdC (N- - -O )
3.170(7) Å) groups between the adjacent layers create a
complementary-amide binding network (Figure 1b). Adjacent
layers are slipped in one direction by approximately 5.7 Å so
that the axial NO3- groups on one layer project into the channels
along the b axis (Figure 1c). The framework contains no solvent
molecules, attributed to a closely packed layer structure with
hydrogen bonds between the layers. The nearest Co-Co distance
is about 10.8 Å in a layer and 7.5 Å in the adjacent layer.
[Co(Br)2(3-pna)2]n (2). In 2, the cobalt(II) center is also
coordinated to the four nitrogen atoms of 3-pna in equatorial
plane (Figure 1d). In addition, two bromide atoms are coordi-
nated axially with the distance of 2.594(2) Å. The trans Br-
Co-Br bond angle is 180°. The cis N-Co-N bond angles range
from 87 to 93°, indicative of a distorted octahedron. The cobalt
ions are linked by 3-pna to afford a honeycomb-shaped grid
9
J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004 3821

A R T I C L E S
Uemura et al.
Figure 2. Crystal structure of {[Co(NCS)2(4-peia)2]‚4Me2CO}n (3 ⊃ 4Me2CO). (a) ORTEP drawing of the cobalt center of 3 ⊃ 4Me2CO at the 30%
probability level. Hydrogen atoms and acetone molecules are omitted for clarity. (b) Two-layer stack of 3 ⊃ 4Me2CO along the c axis with hydrogen bonds
of amide moieties between the layers. Acetone molecules are omitted for clarity. The thin and thick lines show the upper and lower layer, respectively. (c)
Crystal structure of 3 ⊃ 4Me2CO along the c axis without acetone molecules. (d) Crystal view of 3 ⊃ 4Me2CO around complementary hydrogen bonds
among amide moieties. Acetone molecules are represented by the space-filling model.
with the dimension of 10.9 Å × 10.9 Å (Figure 1e), as well as
1. These layers also do not interpenetrate, affording a layered
structure. As shown in Figure 1d, the amide moiety is disordered
about the 2-fold axis running through the 3-pna ligands.
Noticeably, the 2-D layers stack in a slipped fashion along the
a axis with hydrogen bonding links of NH- - -OdC (N- - -O )
3.263(8) Å) between the layers. Coordinated bromide anions
on one layer project into the channels along the c axis with a
close distance of Br- - -Br ) 5.294(4) Å. The nearest Co-Co
distance is about 10.5 Å in a layer and 7.6 Å in the adjacent
layer.
{[Co(NCS)2(4-peia)2]‚4Me2CO}n (3 ⊃ 4Me2CO). In 3 ⊃
4Me2CO, the cobalt(II) center is octahedrally coordinated to
each nitrogen atom of four 4-peia in equatorial plane, where
two types of the nitrogen donors, carbonylpyridyl (NC) and
ethylpyridyl (NE), are located in a trans fashion (Figure 2a).
All the Co-N bond distances are close to each other: Co-NC
) 2.220(5) Å, Co-NE ) 2.191(6) Å. The trans N-Co-N bond
angles for NCS and pyridine ligands are 180°. The cis N-Co-N
bond angles range from 88.2(2) to 91.8(2)°. The NCS groups
are coordinated axially in a slightly bending mode with the
angles of 172.5(6)° (Co-N(4)-C(14)) and 177.3(8)° (N-C-
S). The cobalt ions are linked by 4-peia to form a 2-D layer
composed of a square grid motif with the dimension of 15.8 Å
× 15.8 Å. Interestingly, the adjacent layers stack along the c
axis with an offset by 0.5(a + b) along the ab plane, and the
NCS group protrudes through the midpoint of the cavity of the
adjacent layer eschewing interpenetration (Figure 2b). It is worth
noting that hydrogen-bonding links of the NH- - -OdC (N- - -
O ) 2.780(7) Å) groups between the adjacent layers create a
complementary amide binding network. A channel with the
dimension of 4.4 Å × 4.4 Å is observed72 running along the c
axis, despite the mutual slip of the neighboring layers (Figure
2b,c). These channels create a 46% void, where acetone
molecules are accommodated with no significant interaction
(Figure 2d). All pyridine planes in this crystal are parallel to
the c axis, forming interior panels and, therefore, resulting in
hydrophobic space. Acetone molecules show a guest column
in the channel, but it is highly disordered. The ethylene moiety
in 4-peia assumes a staggered ethane conformation about the
C-C bond. The hydrogen bonds between the amide groups
afford a dipole vector array; however, these dipole vectors are
canceled out with the neighboring one. Compound 3 ⊃ 4THF,
which includes THF molecules, has similar cell parameters and
isostructure as 3 ⊃ 4Me2CO. 3 ⊃ 4THF also forms 2-D layers
which are connected by a hydrogen-bonding link (NH- - -Od
C (N- - -O ) 2.79(1) Å) between the adjacent layers as shown
in the Supporting Information.
Comparison of 1-3 with Other Square Grids. Selected
2-D square grids composed of octahedral metal cations and bpy
(4,4′-bipyridine) analogues ()1:2) are summarized in Table 2.
From Co(NCS)2 and bpy analogues ()1:2), 2-D layers are
rationally obtained because two thiocyanate ions tend to
terminally coordinate to a cobalt(II) ion at the axial posi-
tion.19,48,49,56 What is important at this stage is the mutual
relationship between the layer motifs. Among compounds
(72) The size is measured by considering van der Waals radii for constituting
atoms. Hereafter, all the size estimation of pore is made in this way.
9
3822 J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004

Cooperative Guest Adsorption Based on Square Grids
A R T I C L E S
Table 2. Summary of the Bridging Ligands, Ligand Lengths, Open Areas, and Stacking Manners Found in Selected Square Grids
ligand
ligand length (Å)
open area (Å2)c
stacking mannerd
metal
+
anion
reference
pyrazine
pyrazine
2.8
2.8
7.1
7.1
7.1
9.4
9.5
9.5
9.0
11.4
11.4
15.7
19.8
8.5
8.5
8.4
11.4
none
none
none
6.8
(iii)
(iii)
(ii)
(iii)
(iii)
(ii)
(ii)
(ii)
Co(II) + SCN-
Zn(II) + Br-
48
47
42
12
48
56
56
63
49
46
46
43
44
19
19
19
-
4,4′-bipyridine
4,4′-bipyridine
4,4′-bipyridine
py-CH2CH2-py
py-CHCH-py
mppea
py-azo-py
py-antharacene-py
py-Ph-py
Zn(II) + SiF6 -
Cd(II) + NO3
16.4
Co(II) + SCN-
Co(II) + SCN-
Co(II) + SCN-
Co(II) + SCN-
Co(II) + SCN-
none
none
none
9.0
17.6
4.2
47.3
11.5
9.0 × 2.5
3.5 × 10.5
none
19.4
(ii)
(i)
-
Ni(II) + NO3-
(iii), HBe
(iii), HBe
(iii)
Ni(II) + NO3-
Ni(II) + NO3 -
Cu(II) + NO3
Co(II) + SCN-
Co(II) + SCN-
Co(II) + SCN-
Co(II) + SCN-
py-PhPh-py
py-X-pyb
3-pia (guest ) EtOH, H2O)
3-pia (guest ) Me2CO)
3-pna
4-peia (3 ⊃ 4Me2CO)
(i)
(i)
(iii), HBe
(iii), HBe
this study
a
b
c
1-Methyl-1′-(4-pyridyl)-2-(4-pyrimidyl)ethylene. 9,9-Bis[(S)-2-methylbutyl]-2,7-bis(4-pyridylethynyl)fluorine. The size is measured by considering
d
the van der Waals radii for constituent atoms. Three types of packing manner are typically observed: (i) edge-to-edge manner, (ii) interpenetration, and
(iii) staggered manner (see Scheme 2). Each sheet is connected with an adjacent sheet by an interlayer hydrogen bond.
e
synthesized to date, a ligand longer than bpy prefers the
formation of interpenetrating (type ii) to noninterpenetrating grid
structures (see Scheme 2),1 precluding their frames from porous
materials. On the other hand, short bridging ligands favor the
formation of the staggered fashion of grids in the adjacent layers
(type iii), resulting in no pores. Therefore, to create useful
cavities, a certain gadget is required. Inspection of Table 2
reveals that the gadgets are (1) template of guests43,46 or (2)
interlayer hydrogen bonds with a staggered fashion.19,43,46
To attain a pore frame, each grid must preclude interpenetra-
tion. Herein, “Coordination Polymer with Amide Groups” fulfills
that requirement because complementary hydrogen bonds
between amide moieties in neighboring layers take an important
role in superposing each layers in staggered fashion. In 1 and
2, despite the difference in counteranions, all square grids show
staggered relationship ascribed to complementary amide binding.
Figure 3. TG analysis of 3 ⊃ 4Me2CO over the temperature range from
30 to 500 °C at a heating rate of â ) 5 °C/min under the N2 atmosphere.
Although interpenetration is eschewed, “ABAB” stacking does
not afford channels due to cavities occupied with metals and
anions in neighboring layers. In 3 ⊃ 4Me2CO containing
relatively longer 4-peia ligands, 1-dimensional (1-D) channels
successfully form, because the SCN groups protrude perpen-
dicular to layers. Moreover, 2-D layers of {[Co(NCS)2(3-pia)2]‚
2EtOH‚11H2O}n and {[Co(NCS)2(3-pia)2]‚4Me2CO}n (3-pia )
N-3-pyridylisonicotinamide) form in an edge-to-edge manner
(type i) and afford channels, which accommodate guest mol-
ecules by hydrogen bonds with the amide group.19 Therefore,
“Coordination Polymer with Amide Groups” is suitable for
construction of channels.
Thermal Analysis of 3 ⊃ 4Me2CO. As seen in crystal
structure analysis, 3 ⊃ 4Me2CO includes acetone molecules as
a guest. The acetone desorption was monitored by TG. Figure
3 shows the TG thermograms for 3 ⊃ 4Me2CO over the
temperature range from 30 to 500 °C at a heating rate of â )
5 °C/min. The observed weight loss of acetone molecules is in
agreement with that calculated for the corresponding crystal
structure. The TG data for compound 3 ⊃ 4Me2CO indicate
two stages for weight loss of the guest molecules: three acetone
molecules (observed 19.0%, calculated 20.2%) in the temper-
ature range 30-80 °C, immediately followed by another weight
loss of one acetone molecule (observed 4.3%, calculated 6.7%).
The resultant species, [Co(NCS)2(4-peia)2]n (3), is stable up to
215 °C and then gradually decomposes with loss of two 4-peia
ligands (observed 53.7%, calculated 52.7%).
Recoverable Collapsing of 3 ⊃ 4Me2CO. Removal of the
guest molecules causes a significant change on the framework
of 3 ⊃ 4Me2CO. The two stages on desorption by heating 3 ⊃
4Me2CO reveal the formation of [Co(NCS)2(4-peia)2]n (3) via
{[Co(NCS)2(4-peia)2]‚Me2CO}n (3 ⊃ Me2CO). 3 ⊃ Me2CO
was also obtained by treating 3 ⊃ 4Me2CO under reduced
pressure at room temperature, which was readily detected by
XRPD and IR. The XRPD pattern of 3 ⊃ Me2CO shows an
amorphous form with submaximum peaks (Figure 4b). Since
positions of those submaximum peaks are different from those
in 3 ⊃ 4Me2CO, 3 ⊃ Me2CO is a new form. Guest-free solid,
3, was obtained by treating 3 ⊃ 4Me2CO under reduced pressure
at 373 K. The framework of 3 ⊃ 4Me2CO cannot withstand a
high level of stress on an extensive loss of the guest, resulting
in an amorphous form as shown in Figure 4c. On the other hand,
the XRPD pattern in Figure 4d is in good agreement with those
of as-synthesized and calculated from single-crystal data of 3
⊃ 4Me2CO. Therefore, it is concluded that the original crystal
structure comes back completely upon being exposed to acetone
vapor.
9
J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004 3823

A R T I C L E S
Uemura et al.
Figure 4. XRPD patterns (right) and IR spectra (left) in the region of N-H stretching, amide-I and amide-II bands at room temperature of (a) as-synthesized
3 ⊃ 4Me2CO, (b) 3 ⊃ Me2CO obtained by drying 3 ⊃ 4Me2CO in vacuo for 20 h at room temperature, (c) 3 obtained by drying 3 ⊃ 4Me2CO in vacuo
for 20 h at 373 K, and (d) 3 ⊃ 4Me2CO obtained by exposing 3 to an acetone vapor for 4 days. Asterisk exhibits the CdO stretching band of acetone
molecule.
IR spectra show the information of the amide environments
of 3 ⊃ Me2CO and 3. The N-H stretching and amide-I/-II
bands appear in the regions of 3500-3100 cm-1 and 1700-
1500 cm-1, respectively.65,73-75 The amide moieties in 3 ⊃
4Me2CO provide structured bands which are characteristic of
s-trans complementary amide hydrogen bond as shown in Figure
4a; N-H stretching vibration and the amide-I/-II bands are
observed at 3303, 1644, and 1553 cm-1, respectively. In 3 ⊃
Me2CO, the broadening of the bandwidth is observed at 3299,
1649, and 1548 cm-1, respectively. In 3, N-H stretching and
amide-I/-II bands are observed at 3276, 1650, and 1533 cm-1
(1553 cm-1, shoulder), respectively, and they encounter further
broadening. Since the amide-II is a bending band, the lower
shifts indicate weakening of the hydrogen bonds.73,76 Therefore,
the strength of complementary amide-amide hydrogen bonds
in 3 becomes weaker in 3 ⊃ 4Me2CO.
crystalline 3 ⊃ 4THF” regeneration is also induced by THF
vapor, which is shown in the Supporting Information. We
concluded that there are three different states, characterized by
guest accommodation, namely, {[Co(NCS)2(4-peia)2]‚4Me2-
CO}n (3 ⊃ 4Me2CO), {[Co(NCS)2(4-peia)2]‚Me2CO}n (3 ⊃
Me2CO), and [Co(NCS)2(4-peia)2]n (3), which are summarized
as reaction eqs 2 and 3:
3 + Me2CO a 3 ⊃ Me2CO
3 ⊃ Me2CO + 3Me2CO a 3 ⊃ 4Me2CO
(2)
(3)
In addition to the information of hydrogen bonding modes
among layers, it is necessary to investigate the integrity of layers
in amorphous 3. To gain information concerning the coordina-
tion structures around the CoII ion in 3, EPR measurements were
performed. Figure 5 shows the EPR spectra of 3 ⊃ 4Me2CO,
3 ⊃ Me2CO, and 3 measured at ∼15 K. The EPR spectrum of
3 ⊃ 4Me2CO indicates well-resolved features, and their EPR
parameters have been determined by computer simulation as
g′1, g′2, g′3 ) 5.7, 4.0, 2.8; A1 ) 8.0 mT;77 the peak-to-peak
line widths W1, W2, W3 ) 20, 40, 25 mT. On the other hand, 3
⊃ Me2CO and 3 exhibit broad EPR spectra in accordance with
the amorphous nature of these compounds. The g values are
estimated as g′center ≈ 4.0 (3 ⊃ Me2CO) and g′center ≈ 3.9 (3).
IR data also show the reconstruction of the porous structure
by the complementary amide hydrogen bond; broader bands of
3 in the N-H stretching and amide-I/-II bands change to the
original ones (3301, 1644, and 1553 cm-1). “Amorphous 3 f
(73) Bellamy, L. J. AdVances in Infrared Group Frequencies; Methuen: London,
1968.
(74) Haris, P. I.; Chapman, D. Biopolymers 1995, 37, 251-263.
(75) Hartgerink, J. D.; Granja, J. R.; Milligan, R. A.; Ghadiri, M. R. J. Am.
Chem. Soc. 1996, 118, 43-50.
(76) As the NH bond becomes longer (hydrogen bond becomes stronger) and
easier to stretch, the orbitals of the nitrogen atom take on more p character,
which makes the bond more directional and harder to bend. Therefore,
hydrogen shifts the amide-II band to higher frequencies.
(77) Hyperfine coupling (HFC) is not included for the peaks g′2, g′3.
9
3824 J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004

Cooperative Guest Adsorption Based on Square Grids
A R T I C L E S
Figure 6. Thermogravimetric curves of 3 ⊃ 4Me2CO plotted against the
reciprocal absolute temperature. Heating rate: 2, 3, 5, 7, 10, and 20 °C/
min. Insert: Plots of logarithms of heating rate (â) versus the conversions
of reciprocal absolute temperature of 50% desorption for 3 ⊃ 4Me2CO
(open squares) and 3 ⊃ Me2CO (open circles).
4
4
the ligand-field splitting between | T1;xy> and | T1;z> with the
4
value being positive when | T1;z> is upper, and λ is the spin-
orbit coupling constant. We estimate ∆/|λ| ) 2.1, ∼0, ∼0 for
3 ⊃ 4Me2CO, 3 ⊃ Me2CO, and 3, respectively.86 The present
EPR results are in good agreement with the theory, and
therefore, the CoII ion in 3 ⊃ Me2CO and 3 are in octahedral
coordination environment as well as 3 ⊃ 4Me2CO.
Figure 5. CW EPR spectra of powdered samples of (a) 3 ⊃ 4Me2CO, (b)
3 ⊃ Me2CO, and (c) 3. Experimental setting: microwave frequency, (a)
8.998, (b) 8.993, and (c) 8.996 GHz. Microwave power, 1 mW; field
modulation, 1 mT; temperature, 15 K.
Throughout the characterization of series of 3 by XRPD, IR,
and EPR, we conclude that the 2-D motif of 3 does not collapse.
Although the layer framework in 3 is maintained, the XRPD
pattern shows that 3 crystalline order over a long range is not
seen (Figure 4c). The pattern is attributed to the random layer
slip against the neighboring layers, accompanying with the
deformation of grid framework.
(Computer simulation of the spectra of 3 ⊃ Me2CO and 3 was
found to be difficult because of their broad nature.)
Several types of high-spin CoII complexes have thus far been
studied by EPR spectroscopy,78 and the differences in the EPR
pattern between tetrahedral and octahedral CoII have been well-
documented.79-82 In tetrahedral CoII, the ground orbital state is
4A2, and thus the orbital angular momentum is well-quenched,
which makes the spin Hamiltonian approach appropriate.82,83
However, the observed g values for three compounds do not
accord, similar to the case reported previously.19 In the case of
an octahedral CoII, on the other hand, the ground orbital state
Desorption and Energetics. As mentioned previously, 3 ⊃
4Me2CO is desolvated, via 3 ⊃ Me2CO, to be amorphous 3.
In both desorption processes, “3 ⊃ Me2CO f 3” and “3 ⊃
4Me2CO f 3 ⊃ Me2CO”, the activation energies of desorption
(Ede1 and Ede2, respectively) are estimated by recording TG
curves at various heating rates (â) and by plotting logâ vs 1/T
at a given extent of desorption, according to the eq 4.87,88
4
is T1, and thus orbital degeneracy still remains.84 Theoretical
treatment of the EPR parameters of octahedral CoII was made
by Abragam and Pryce,85 who gave theoretical expressions for
the effective g value and HFC parameters considering up to
the second-order perturbation effects. The perturbation result
for the effective g values are plotted against ∆/|λ|, where ∆ is
lnâ ) -1.0516Ede/RT + constant
(4)
The results of the thermogravimetry at various heating rates
are plotted against the reciprocal absolute temperature in Figure
6. It is apparent that these curves can be superposed by lateral
shifts. For the process of “3 ⊃ 4Me2CO f 3 ⊃ Me2CO” at
50% desorption, T ) 49.6 (322.6), 53.0 (326.0), 57.9 (330.9),
65.1 (338.1), 66.2 (339.2), and 78.3 °C (351.3 K) at â ) 2, 3,
5, 7, 10, and 20 °C/min. For the process of “3 ⊃ Me2CO f 3”
at 50% desorption, T ) 97.4 (370.4), 103.2 (376.2), 108.1
(78) Weckhuysen, B. M.; Verberckmoes, A. A.; Uytterhoeven, M. G.; Mabbs,
F. E.; Collison, D.; Boer, E. d.; Schoonheydt, R. A. J. Phys. Chem. B 2000,
104, 37-42.
(79) Bencini, A.; Benelli, C.; Gattenschi, D.; Zanchini, C. Inorg. Chem. 1980,
19, 1301-1304.
(80) Banci, L.; Benelli, C.; Gatteschi, D.; Mani, F. Inorg. Chem. 1982, 21, 1133-
1136.
(81) Makinen, M. W.; Kuo, L. C.; Yim, M. B.; Wells, G. B.; Fukuyama, J. M.;
Kim, J. E. J. Am. Chem. Soc. 1985, 107, 5245-5255.
(82) Drulis, H.; Dyrek, K.; Hoffmann, K. P.; Hoffmann, S. K.; Weselucha-
Birczynska, A. Inorg. Chem. 1985, 24, 4009-40125.
(83) Pilbrow, J. R. J. Magn. Reson. 1978, 31, 479-490.
(84) Griffith, J. S. In The Theory of Transition Metal Ions; Cambridge University
Press: London, 1961.
(86) Effective g values calculated from the first-order perturbation equations
are plotted versus ∆/|λ| and are depicted in Figure S4.
(87) Flynn, J. H.; Wall, L. A. J. Polym. Sci., Part B: Polym. Phys. 1966, 4,
323-328.
(85) Abragam, A.; Pryce, M. H. Proc. R. Soc. London, Ser. A 1951, 205, 173-
191.
(88) Ozawa, T. Bull. Chem. Soc. Jpn. 1965, 38, 1881-1886.
9
J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004 3825

A R T I C L E S
Uemura et al.
Figure 7. (a) Isotherm for N2 adsorption (filled circles) at 77 K of 3 over the pressure range from 0.003 to 0.939 atoms. P0 is a saturated vapor pressure,
1.022 atoms, of N2 at 77 K. (b) Isotherm for acetone vapor adsorption (crosses) and desorption (open squares) at 298 K of 3 over the pressure range from
0.507 to 27.756 kPa. P0 is a saturated vapor pressure, 30.593 kPa, of acetone at 298 K. (c) Hill plot for the adsorption curve of (b), where Y (0 < Y < 1)
and P are the extent of complexation and pressure (kPa), respectively.
(381.1), 111.1 (384.1), 114.6 (387.6), and 122.8 °C (395.8 K)
at â ) 2, 3, 5, 7, 10, and 20 °C/min. In the insert of Figure 6,
the logarithms of the heating rates are plotted against the
reciprocal absolute temperature, until which point the weight
of the sample decreases to a 50% desorption. Straight lines are
obtained, and the method of the least squares affords the
one looks more carefully at the behavior of the adsorption, the
actual porous coordination polymers, responsible for uptaking
the adsorbates, tend to undergo guest-directed framework
transformation,19,20,27,92,94 dissimilar to zeolites and activated
carbons. The mechanism of this transformation should be
investigated in detail, and the present 3 system is suitable for
in-depth study on adsorption and desorption properties.
3 shows no N2 adsorption at 77 K as shown in Figure 7a.
Moreover, the adsorption isotherm of CH4 for 3 at 298 K reveals
no uptake into the micropores but only surface adsorption.95
These results indicate that 3 does not maintain channels available
for N2 (3.64 Å) and CH4 molecules (3.8 Å).20,93
activation energies determined: Ede1 ) 108 kJ/mol and Ede2
)
71 kJ/mol.
Isothermal Adsorption and Desorption Experiment. Re-
cently, several articles on adsorption behavior of porous
coordination polymers have been published.2,14,19,20,27,89-93 When
(89) Kondo, M.; Okubo, T.; Asami, A.; Noro, S.-I.; Yoshitomi, T.; Kitagawa,
S.; Ishii, T.; Matsuzaka, H.; Seki, K. Angew. Chem., Int. Ed. 1999, 38,
140-143.
(90) Kepert, C. J.; Rosseinsky, M. J. Chem. Commun. 1999, 375-376.
(91) Fletcher, A. J.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. J.; Kepert, C. J.;
Thomas, K. M. J. Am. Chem. Soc. 2001, 123, 10001-10011.
(92) Li, D.; Kaneko, K. Chem. Phys. Lett. 2001, 335, 50-56.
(93) Pan, L.; Adams, K. M.; Hernandez, H. E.; Wang, X.; Zheng, C.; Hattori,
Y.; Kaneko, K. J. Am. Chem. Soc. 2003, 125, 3062-3067.
(94) Dewa, T.; Endo, K.; Aoyama, Y. J. Am. Chem. Soc. 1998, 120, 8933-
8940.
(95) Isotherm for methane adsorption at 298 K of 3 from 0.5 to 70 atoms is
depicted in Figure S5.
9
3826 J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004

Cooperative Guest Adsorption Based on Square Grids
A R T I C L E S
ature: the Pth values decrease with decrease in temperature:
17.3 (288), 21.2 (293), 23.2 (298), 28.8 (303), 34.8 (308) and
40.9 kPa (313 K). Since Pth values could be regarded as the
equilibrium pressure for the reaction of acetone inclusion, their
temperature dependence allows us to evaluate the associated
enthalpy change on acetone adsorption process based on eq 6:
d ln Pth/d(1/T) ) ∆Had/R
(6)
where R and ∆Had denote the gas constant and the adsorption
enthalpy of gas, respectively. The plot of ln Pth vs 1/T, according
to eq 6, yields a straight line (Figure 8b), whose slope leads to
∆Had ) -25 kJ/mol for the inclusion of acetone.
Mechanism and Thermodynamics in Relation to Struc-
tural Regeneration. 3 does not contain channels, but neverthe-
less undergoes the inclusion of acetone molecules. Several
organic hosts and metal-organic architectures exhibit the ability
to switch between dense and open forms responding to guest
molecules.94,96-105 The new aspect of 3 ⊃ 4Me2CO is solid
form conversion based on infinite 2-D layers bound by
complementary hydrogen bonds. As mentioned previously, it
is apparent that the 2-D structural integrity is maintained during
the reaction. The structural regeneration by the inclusion of
acetone is associated with change of the hydrogen-bonding
mode: the accommodation of acetone molecules in each grid
of the 2-D motif could control the orientation of the amide
hydrogen bonds; thus, the overall relationship between the motifs
comes back to the former 3 ⊃ 4Me2CO, where extensive
cooperativity must exist.
Previously, the energy diagram for the adsorption and
desorption of some organic networks was fortunately constructed
and reported.94 In general, it is difficult to discuss the mechanism
of a solid-state reaction, because the reaction is composed of
many kinds of elementary reactions. Figure 9 shows a schematic
energy diagram for the acetone adsorption and desorption of 3,
based on the results of TG and adsorption measurements. DSC
measurement shows two separated endotherms of desorption
for 3 ⊃ 4Me2CO; however, it is difficult to estimate the
desorption enthalpy because 3 ⊃ 4Me2CO is unstable at room
temperature and decomposes with loss of acetone molecules,
usually with concomitant rearrangement of the host compound
to the nonporous compound. Therefore, the energy difference
among states could be calculated from ∆Had (-25 kJ/mol), that
is, ∆Had1 ) ∆Had ) -25 kJ/mol and ∆Had2 ) 3∆Had ) -75
Figure 8. (a) Hill plot for the acetone adsorption curve of 3 at 288, 293,
303, 308, and 313 K. (b) Plot of ln Pth against T-1
.
Since 3 shows structural regeneration when exposed to
acetone vapor, the acetone adsorption and desorption experiment
was carried out on 3. Figure 7b shows the adsorption and
desorption isotherms for acetone over the relative pressure range
from 0 to 0.9 at 298 K. The adsorption isotherm shows a slight
increase and an abrupt rise at P/P0 ) 0.76. This characteristic
adsorption profile clearly indicates a conversion of amorphous
3 to a crystalline 3 ⊃ 4Me2CO.92 On the other hand, the
desorption isotherm shows a monotonic decrease as if the pores
were maintained until a sudden drop at P/P0 ) 0.05. A large
range of hysteresis loop based on the structural conversion is
realized in this compound, which could not be obtained in rigid
porous materials.
Threshold Points for Adsorption. Figure 7c shows the Hill
plot (eq 5) of acetone adsorption on 3 at 298 K.
log [Y/(1 - Y)] ) n log P + log K
(5)
kJ/mol, and activation energy (Ede1 ) 108 kJ/mol and Ede2
)
71 kJ/mol) was obtained as mentioned previously. Although
the thermal decomposition of 3 ⊃ 4Me2CO f 3 ⊃ Me2CO is
where Y (0 < Y < 1) is the extent of complexation (adsorption),
which is often used to describe cooperative or allosteric binding
processes in homogeneous solutions. It may be more important,
however, that this treatment of the binding data according to a
homogeneous host-guest complexation fails to give a linear
correlation for the whole pressure range. The acetone adsorption
curve is characterized by a sharp threshold point (Pth) consisting
of three stages, which are characterized by different slopes: a
prebinding region at P < Pth, the vertical region at P = Pth,
and a milder follow-up region at P > Pth. The vertical one at P
= Pth (Pth/P0 ) 0.76) indicates a remarkably cooperative nature
of adsorption around Pth.
(96) Miyata, M.; Shibakami, M.; Chirachanchai, S.; Takemoto, K.; Kasai, N.;
Miki, K. Nature 1990, 343, 446-447.
(97) Bourne, S. A.; Nassimbeni, L. R.; Toda, F. J. Chem. Soc., Perkin Trans.
2 1991, 1335-1341.
(98) Barbour, L. J.; Caira, M. R.; Coetzee, A.; Nassimbeni, L. R. J. Chem. Soc.,
Perkin Trans. 2 1995, 1345-1349.
(99) Ung, A. T.; Gizachew, D.; Bishop, R.; Scudder, M. L.; Dance, I. G.; Craig,
D. C. J. Am. Chem. Soc. 1995, 117, 8745-8756.
(100) Endo, K.; Sawaki, T.; Koyanagi, M.; Kobayashi, K.; Masuda, H.; Aoyama,
Y. J. Am. Chem. Soc. 1995, 117, 8341-8352.
(101) Endo, K.; Koike, T.; Sawaki, T.; Hayashida, O.; Masuda, H.; Aoyama,
Y. J. Am. Chem. Soc. 1997, 119, 4117-4122.
(102) Thaimattam, R.; Xue, F.; Sarma, J. A. R. P.; Mak, T. C. W.; Desiraju, G.
R. J. Am. Chem. Soc. 2001, 123, 4432-4445.
(103) Atwood, J. L.; Barbour, L. J.; Jerga, A.; Schottel, B. L. Science 2002,
298, 1000-1002.
Isothermal acetone adsorption curves were obtained at various
temperatures: 288, 293, 298, 303, 308, and 313 K. The three
stages of the Hill plots are also observed for all the temperatures.
Figure 8a clearly shows the dependence of Pth on the temper-
(104) Soldatov, D. V.; Ripmeester, J. A.; Shergina, S. I.; Sokolov, I. E.; Zanina,
A. S.; Gromilov, S. A.; Dyadin, Y. A. J. Am. Chem. Soc. 1999, 121,
4179-4188.
(105) Soldatov, D. V.; Ripmeester, J. A. Chem.-Eur. J. 2001, 7, 2979-2994.
9
J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004 3827

A R T I C L E S
Uemura et al.
(1) From Co(SCN)2 and bipyridyl derivatives containing an
amide group, we succeeded in producing new square grid
frameworks, 1-3, which have complementary amide binding
manner eschewing interpenetrating. Particularly, 3 ⊃ 4Me2CO
affords micropores fulfilled with guest molecules and shows
that structural transformation via amorphous is caused by
adsorption and desorption of guest molecules. Such flexible
porous coordination polymers offer an application to a unique
class of materials, which cannot be obtained in rigid porous
material, in this case, large hysteresis loop on adsorption and
desorption measurements, and leading to amplification of
adsorption for specific guest.
(2) On the basis of well-defined 3 ⊃ 4Me2CO, the energy
diagram was achieved. Our results imply that the coordination
polymer is often much more dynamic than generally believed
and that weak dispersive forces induce structural rearrangement
in a well-concerted fashion. Although many porous coordination
polymers have been synthesized and reported, to the best of
our knowledge, the report of thermal analysis is sparse.
Thermodynamic parameters calculated in the present course of
study are also useful to analyze the thermal behavior of porous
coordination polymers.
Figure 9. Schematic energy diagram for the solid-gas complexation of 3
with gaseous acetone. Definitions are as follows: Ede1 and Ede2 are activation
energies of acetone desorption in the processes of 3 ⊃ Me2CO f 3 and 3
⊃ 4Me2CO f 3 ⊃ Me2CO, respectively. ∆Had1 and ∆Had2 are heats of
guest binding in the processes of 3 f 3 ⊃ Me2CO and 3 ⊃ Me2CO f 3
⊃ 4Me2CO, respectively.
an endothermic reaction, the activation energy (Ede2 ) 71 kJ/
mol) is lower than the thermodynamic value for the reaction
(∆Had2 ) -75 kJ/mol). This is because the activation energy
is obtained based on the rate-determining step of some
elementary reaction.
As seen in the energy diagram of the acetone adsorption
process, 3 transfers to 3 ⊃ Me2CO with the energy barrier and
smoothly follows the second transformation to be 3 ⊃ 4Me2CO.
It is surprising that acetone inclusion enthalpy (∆Had (-25 kJ/
mol)) is close to acetone vaporization enthalpy (∆Hvap ) 30.99
kJ/mol).106 Thus, even weak dispersive forces can exert a
profound influence over solid-sate transformation.
This research is particularly relevant in the context of solid-
state chemistry since rational design of solids has important
ramifications for the development of new materials with unusual
properties. We anticipate this approach to be viable for the
construction of cavity-containing frameworks possessing bridg-
ing ligands not described here, and we also anticipate this
approach to be applicable for the design of flexible porous
materials.
Acknowledgment. This work was supported by a Grant-In-
Aid for Science Research in a Priority Area “Metal-Assembled
Complexes” (No. 401-10149106) from the Ministry of Educa-
tion, Science, Sports, and Culture, Japan.
Conclusion
This work demonstrates (1) the rational construction of
flexible porous frameworks using square grids and (2) charac-
terization of cooperative adsorption with thermal analysis. In
addition, we showed a new contrivance for dynamic porous
coordination polymers based on flexible amide-amide hydrogen
bonds.
Supporting Information Available: XRPD, detailed crystal
views, IR spectra of the materials (4-peia and Co(SCN)2),
effective g values of 3 plotted versus ∆/|λ|, isotherm for CH4
adsorption at 298 K of 3 (PDF), and X-ray crystallographic files
(CIF) for 1-3. This material is available free of charge via the
Internet at http://pubs.acs.org.
(106) Weast, R. C.; Astle, M. J.; Beyer, W. H. CRC Handbook of Chemistry
and Physics, 80th ed.; CRC Press: Boca Raton, FL, 1999.
JA039914M
9
3828 J. AM. CHEM. SOC. VOL. 126, NO. 12, 2004