Metal-organic hendecahedra assembled from dinuclear paddlewheel nodes and mixtures of ditopic linkers with 120 and 90° bend angles

Article abstract of DOI:10.1002/anie.200904722

Don't be square: The title cages were synthesized by cooperative assembly of four-connected units and mixtures of two bridging dicarboxylate ligands (see pic-ture). This work may open a new synthetic path towards complex coordination polyhedra that are in

Full text of DOI:10.1002/anie.200904722

Angewandte
Chemie
DOI: 10.1002/anie.200904722
Metal–Organic Polyhedra
Metal–Organic Hendecahedra Assembled from Dinuclear
Paddlewheel Nodes and Mixtures of Ditopic Linkers with 120 and 908
Bend Angles**
Jian-Rong Li and Hong-Cai Zhou*
Nature has demonstrated the extraordinary ability of biolog-
ical systems to form large and intricate supramolecular arrays
from small and simple building blocks, giving rise to a wide
variety of structures and functions. In the past two decades,
abiological self-assembly of molecular architectures has
evolved into a field of intense investigation in supramolecular
chemistry.[1] Besides their aesthetic appeal, some of these
assemblies become useful as molecular vessels for selective
guest inclusion, protection of sensitive molecules, asymmetric
catalysis, and chemical sensing.[2] Among them, coordination
Figure 1. The self-assembly of three metal–organic polyhedra with
ditopic angular linkers and four-connected square nodes.
polyhedra are one of the fastest-growing families of such
supramolecular entities, because coordination-driven assem-
bly allows the selection of metal ions or clusters with different
coordination modes and the choice of bridging ligands with a
variety of shapes.[3] Most of the coordination polyhedra were
assembled from single metal ions and organic bridging
ligands, which were mainly pyridine-based.
As a metal cluster node, the dinuclear paddlewheel unit
has emerged as a common four-connected building block in
the synthesis of highly symmetric coordination polyhedra,
also called metal–organic polyhedra (MOPs). It has been used
in the design of a number of MOPs structurally controlled by
the geometry of the bridging ligand. However, only limited
geometric types of polyhedra have been realized with this
popular building unit.[3e,4] Typically, the combination of a
ditopic bridging ligand with a bend angle of 1208 and such a
dinuclear paddlewheel unit gave rise to a coordination
cuboctahedron.[5] Similarly, a 908 bridging ligand led to a
coordination octahedron (Figure 1).[4c,6]
nation polyhedra using a mixture of ditopic carboxylate
ligands with 120 and 908 bend angles and succeeded in
obtaining two isostructural metal–organic hendecahedra
(Figure 1 and Scheme 1). These coordination hendecahedra
However, almost all of the reported coordination poly-
hedra contain bridging ligands with a single bend angle,
leading to Platonic or Archimedean solids with an even
number of edges and an even number of faces. It occurred to
us that the application of a mixture of bridging linkers with
different bend angles in coordination-driven self-assembly
should allow access to novel structural types. With this
background in mind, we attempted the assembly of coordi-
Scheme 1.
[*] Dr. J.-R. Li, Prof. Dr. H.-C. Zhou
have an odd number of faces (eleven) and an odd number of
vertices (nine). To the best of our knowledge, compounds 1
and 2 (Scheme 1) represent the first molecular polyhedra with
an odd number of faces and an odd number of vertices. Prior
to this work, no attempts have been reported in the self-
assembly of coordination polyhedra using bridging ligands
with different bend angles and metal cluster nodes.[7]
Department of Chemistry, Texas A&M University
PO Box 30012, College Station, TX 77842-3012 (USA)
Fax: (+01)979-845-1595
E-mail: zhou@mail.chem.tamu.edu
[**] This work was supported by the U. S. Department of Energy (DE-
FC36-07GO17033) and the U. S. National Science Foundation
(CHE-0449634).
The first combination of ligands adopted for the assembly
of a molecular hendecahedron was 9H-carbazole-3,6-dicar-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200904722.
Angew. Chem. Int. Ed. 2009, 48, 8465 –8468
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8465

Communications
boxylate (9H-3,6-cdc2À) and 4,4’-pyridine-2,6-diyldibenzoate
(pddb2À), which we designed and synthesized. The former has
a bend angle of about 908, the latter of 1208. The reaction of
H2(9H-3,6-cdc), H2pddb, and Cu(NO3)2·2.5H2O in the pres-
ence of base (2,6-dimethylpyridine) in N,N-dimethylaceta-
mide (dma) at room temperature produced the first hendec-
ahedral cage compound, [(Cu2)9(9H-3,6-cdc)6(pddb)12(dma)6-
(H2O)12]·xS (1, S = non-coordinated solvent molecule,
Scheme 1), isolated as blue-green plate-like crystals suitable
for single-crystal X-ray diffraction studies. The identity of the
bulk sample was confirmed by powder X-ray diffraction
(PXRD, see the Supporting Information).
The structure of 1 was determined by single-crystal X-ray
ꢀ
diffraction studies. Compound 1 crystallizes in the R3c space
group. The molecule of 1 has crystallographically imposed D3
symmetry, although the idealized point group symmetry is
D3h. As shown in Figure 2a,c, the molecular structure of 1
consists of nine Cu2 units, six 9H-3,6-cdc2À ligands, and twelve
pddb2À ligands. Three 9H-3,6-cdc2À ligands link three Cu2
units to form a triangular moiety. Two of these moieties are
connected through three additional Cu2 paddlewheel units
and twelve pddb2À entities, six on each triangular moiety. The
compound contains 2 + 6 triangular and three quadrilateral
windows of sizes (atom-to-atom distance along an edge after
considering van der Waalsꢀ radii) 7.0 ꢁ 7.0 ꢁ 7.0, 7.0 ꢁ 11.8 ꢁ
12.3, and 11.8 ꢁ 12.3 ꢁ 11.8 ꢁ 12.3 ꢂ, respectively. The bend
angles of 9H-3,6-cdc2À and pddb2À linkers in 1 are 88 and 1158,
respectively, slightly deviated from the ideal 90 and 1208
angles. The dimensions of 1 are approximately 3.7 nm in
height and 3.0 nm in diameter. It is noteworthy that the ligand
pddb2À also results in a unique nitrogen-rich interior of the
polyhedron. In crystals, these molecules are held together by
p···p interactions between pddb2À ligands from adjacent
molecular polyhedra to form a porous material (Figure 2d)
with an overall 75% solvent-accessible volume calculated
using the PLATON routine.[8]
When the square Cu2 units are viewed as vertices and the
ligands as edges, 1 can be described as a hendecahedron
(Figure 2e, top) with 2 + 6 triangular and three quadrilateral
faces. It can also be viewed as two tapered face-sharing
octahedra, as shown in Figure 2e, bottom. The hendecahe-
dron possesses a [38.43] (face symbol) pattern of polygonal
Figure 2. a,b) The molecular structures of 1 and 2, respectively
(Cu cyan; O red; N blue; C maroon, green, orange, or pink; H white).
c) Space-filling representation of 1 viewed from the [001] direction.
d) Molecular packing of 1 in the crystal structure with space-filling
representation highlighting the intermolecular p–p interactions.
e,f) Schematic representation of the polyhedra when considering the
metal clusters or ligands, respectively, as vertices.
composition and
a
(33.4)6(3.4.3.4)3 topology (vertex
symbol).[9] Such a hendecahedral framework is unprece-
dented and interesting not only in synthetic chemistry but also
in geometry. It is also remarkable to notice how well the two
angular linkers and the square nodes fit together. Alterna-
tively, when each bridging ligand is viewed as a vertex, 1 can
be described as an elongated triangular orthobicupola, a
Johnson solid, which can also be viewed as an anticuboctahe-
dron with the two triangular-cupola moieties separated by a
hexagonal prism (Figure 2 f). It has idealized D3h symmetry
with twenty faces: twelve quadrilateral faces and eight
triangular faces. Only nine quadrilateral faces are occupied
by Cu2 units; three of the six quadrilateral faces of the
hexagonal prism are empty.
metal–organic hendecahedral cage compound, [(Cu2)9(9H-
3,6-cdc)6(3,4’-bpdc)12(dma)6(H2O)12]·xS (2, Scheme 1), the
structure of which was also determined by single-crystal
X-ray diffraction. The phase purity of the bulk sample was
confirmed by PXRD (see Supporting Information). Com-
ꢀ
pound 2 is isostructural with 1 and also crystallizes in the R3c
space group, thus indicating that the molecular hendecahe-
dron is likely a common structural type from a combination of
suitable bridging ligands with 90 and 1208 bend angles and
four-connected planar nodes (Figure 2b). As expected, the
3.2 ꢁ 2.4 nm overall dimensions of 2 and the window sizes are
consistently smaller than those of 1, proportional to the size of
the ligand.
Under synthetic conditions similar to that of 1, biphenyl-
3,4’-dicarboxylate (3,4’-bpdc2À), an unsymmetrically short-
ened ligand with a bend angle of 1208, gave rise to another
8466 www.angewandte.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2009, 48, 8465 –8468

Angewandte
Chemie
excess) was added to this solution to give a green solution after
Preliminary gas sorption studies were also performed with
an evacuated sample of 1 (Figure 3). The N2 sorption isotherm
shows type I gas sorption behavior indicative of a micro-
porous material, with a Langmuir surface area of 372 m2 gÀ1.
thorough mixing. The vial was sealed and allowed to stand at room
temperature. After 15 days, homogeneous blue-green block crystals
of 2 were collected, washed with dma and EtOH, and dried in air
(yield: 30 mg). PXRD, TGA, and FTIR of as-isolated 2 are shown in
Figures S2, S3, and S5, respectively, in the Supporting Information.
Single-crystal X-ray crystallographic studies: Data were collected
on a Bruker-AXS APEXII X-ray diffractometer at 110 K. Raw data
collection and reduction were done using APEX2 software.[11]
Adsorption corrections were applied using the SADABS routine.
The structures were solved by direct methods and refined by full-
matrix least-squares on F2 using the SHELXTL software package.[12]
Non-hydrogen atoms (except some in dma molecules) were refined
with anisotropic displacement parameters during the final cycles.
Hydrogen atoms of ligands and dma were calculated in ideal positions
with isotropic displacement parameters; those of water were origi-
nally found from electron density peaks and then refined with
restrictions. Free solvent molecules were highly disordered, and
attempts to locate and refine the solvent peaks were unsuccessful. The
diffuse electron densities resulting from the these residual solvent
molecules were removed from the data set using the SQUEEZE
routine of PLATON and refined further using the data generated.[8]
The contents of the solvent region are not represented in the unit cell
contents in crystal data. Attempts to determine the final formula of
such compounds from the SQUEEZE results combined with
elemental analysis and TGA data were also unsuccessful because of
the volatility of crystallization solvents; therefore, an accurate data
set could not be obtained. Crystal data for 1: C336H252Cu18N24O90, Mr =
Figure 3. N2 and H2 adsorption isotherms of 1 at 77 K.
Both N2 and H2 uptakes are relatively low with respect to the
calculated accessible surface area, presumably because of the
blockage of the cavity windows in the activated sample.
Indeed, after activation the sample became almost amor-
phous, as verified by PXRD. This loss of crystallinity may be
attributed to position rearrangement of the molecular cages
of 1 with respect to one another upon activation. On the
molecular level, the cage structure of 1 and its porosity should
be maintained.[4c] However, we cannot rule out the possibility
of structural disintegration.
In summary, two metal–organic hendecahedra have been
obtained through self-assembly of paddlewheel Cu2 units and
two mixtures of two ditopic linkers with 90 and 1208 bend
angles. The hendecahedral compounds represent the first
examples of molecular polyhedra with an odd number of faces
and an odd number of vertices. The work reveals the vast
potential of using a mixture of bridging ligands with different
bend angles to obtain novel coordination polyhedra that are
inaccessible using reported synthetic methods.
ꢀ
7209.34, hexagonal, space group R3c, a = b = 38.289(4), c =
120.10(1) ꢂ, V= 152479(30) ꢂ3, Z = 6,
d
calcd = 0.471 gcmÀ3
,
R1-
(I>2s(I)) = 0.0743, wR2(all data) = 0.2375, GOF = 0.934. 2:
ꢀ
C
276H216Cu18N12O90, Mr = 6284.33, hexagonal, space group R3c, a =
b = 33.423(7), c = 107.88(2) ꢂ, V= 104363(36) ꢂ3, Z = 6, dcalcd
=
0.600 gcmÀ3, R1(I>2s(I)) = 0.0774, wR2(all data) = 0.1610, GOF =
0.922; CCDC 745163 (1) and 745164 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Adsorption measurements: Gas adsorption measurements were
performed using an ASAP 2020 gas adsorption analyzer. The gases
used were of ultrapure quality. Before adsorption, the sample was
activated by solvent exchange with subsequent pumping under a
dynamic vacuum at RT and 508C as detailed in the Supporting
Information.
Received: August 25, 2009
Published online: October 6, 2009
Experimental Section
Keywords: angular ligands · hendecahedra · organic–
inorganic hybrid composites · multicomponent reactions ·
self-assembly
Synthesis of ligands: H2(9H-3,6-cdc) was synthesized according to a
reported procedure.[6,10] H2pddb and H2(3,4’-bpdc) were synthesized
by Suzuki coupling reactions. Details can be found in the Supporting
Information.
.
1: N,N-dimethylacetamide (dma, 4 mL) containing H2(9H-3,6-
cdc) (25.6 mg, 0.1 mmol) and H2pddb (32.0 mg, 0.1 mmol) was mixed
thoroughly with dma (2 mL) containing Cu(NO3)2·2.5H2O (48.0 mg,
0.2 mmol). 2,6-dimethylpyridine (44.0 mg, 0.4 mmol) was added to
this solution to give a green solution after thorough mixing. The vial
was sealed and allowed to stand at room temperature. After 10 days,
homogeneous blue-green plate-like crystals of 1 were collected,
washed with dma and EtOH, and dried in air (yield: 35 mg). PXRD,
thermogravimetric analysis (TGA), and FTIR of as-isolated 1 are
shown in Figures S1, S3, and S4, respectively, in the Supporting
Information.
[1] a) G. F. Swiegers, T. J. Malefetse, Chem. Rev. 2000, 100, 3483 –
3538; b) J.-M. Lehn, Science 2002, 295, 2400 – 2403; c) P. J. Steel,
Acc. Chem. Res. 2005, 38, 243 – 250; d) R. M. McKinlay, G. W. V.
Cave, J. L. Atwood, Proc. Natl. Acad. Sci. USA 2005, 102, 5944 –
5948; e) D. Ajami, J. Rebek, Jr., Proc. Natl Acad. Sci. USA 2007,
104, 16000 – 16003; f) J. F. Stoddart, Nat. Chem. 2009, 1, 14 – 15.
[2] a) D. M. Vriezema, M. C. Aragonꢃs, J. A. A. W. Elemans,
J. J. L. M. Cornelissen, A. E. Rowan, R. J. M. Nolte, Chem.
Rev. 2005, 105, 1445 – 1489; b) M. D. Pluth, R. G. Bergman, K. N.
Raymond, Science 2007, 316, 85 – 88; c) K. Harano, S. Hiraoka,
M. Shionoya, J. Am. Chem. Soc. 2007, 129, 5300 – 5301; d) S. J.
Lee, S.-H. Cho, K. L. Mulfort, D. M. Tiede, J. T. Hupp, S. T.
Nguyen, J. Am. Chem. Soc. 2008, 130, 16828 – 16829; e) M.
2: N,N-dimethylacetamide (dma, 3 mL) containing H2(9H-3,6-
cdc) (25.6 mg, 0.1 mmol) and H2(3,4’-bpdc) (24.0 mg, 0.1 mmol) was
mixed thoroughly with dma (3 mL) containing Cu(NO3)2·2.5H2O
(48.0 mg, 0.2 mmol). 2,6-dimethylpyridine (219.0 mg, 2.0 mmol,
Angew. Chem. Int. Ed. 2009, 48, 8465 –8468
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 8467

Communications
Fukuda, R. Sekiya, R. Kuroda, Angew. Chem. 2008, 120, 718 –
Ockwig, M. OꢀKeeffe, O. M. Yaghi, J. Am. Chem. Soc. 2008,
130, 11650 – 11661.
[6] J.-R. Li, D. J. Timmons, H.-C. Zhou, J. Am. Chem. Soc. 2009, 131,
6368 – 6369.
722; Angew. Chem. Int. Ed. 2008, 47, 706 – 710; f) T. Sawada, M.
Yoshizawa, S. Sato, M. Fujita, Nat. Chem. 2009, 1, 53 – 56;
g) T. K. Ronson, J. Fisher, L. P. Harding, P. J. Rizkallah, J. E.
Warren, M. J. Hardie, Nat. Chem. 2009, 1, 212 – 216; h) P. Mal, B.
Breiner, K. Rissanen, J. R. Nitschke, Science 2009, 324, 1697 –
1699.
[7] a) P. N. W. Baxter, J.-M. Lehn, G. Baum, D. Fenske, Chem. Eur.
J. 1999, 5, 102 – 112; b) B. Olenyuk, J. A. Whiteford, A.
Fechtenkꢄtter, P. J. Stang, Nature 1999, 398, 796 – 799; c) M.
Fujita, N. Fujita, K. Ogura, K. Yamaguchik, Nature 1999, 400,
52 – 55; d) K. Kumazawa, K. Biradha, T. Kusukawa, T. Okano,
M. Fujita, Angew. Chem. 2003, 115, 4039 – 4043; Angew. Chem.
Int. Ed. 2003, 42, 3909 – 3913; e) N. K. Al-Rasbi, I. S. Tidmarsh,
S. P. Argent, H. Adams, L. P. Harding, M. D. Ward, J. Am. Chem.
Soc. 2008, 130, 11641 – 11649; f) K. Ghosh, J. Hu, H. S. White,
P. J. Stang, J. Am. Chem. Soc. 2009, 131, 6695 – 6697.
[8] A. L. Spek, J. Appl. Crystallogr. 2003, 36, 7 – 13.
[9] V. A. Blatov, M. OꢀKeeffe, D. M. Proserpio, CrystEngComm
2010, DOI: 10.1039/b910671e.
[3] a) S. R. Seidel, P. J. Stang, Acc. Chem. Res. 2002, 35, 972 – 983;
b) D. Fiedler, D. H. Leung, R. G. Bergman, K. N. Raymond, Acc.
Chem. Res. 2005, 38, 351 – 360; c) M. Fujita, M. Tominaga, A.
Hori, B. Therrien, Acc. Chem. Res. 2005, 38, 369 – 378; d) N. C.
Gianneschi, M. S. Masar, C. A. Mirkin, Acc. Chem. Res. 2005, 38,
825 – 837; e) D. J. Tranchemontagne, Z. Ni, M. OꢀKeeffe, O. M.
Yaghi, Angew. Chem. 2008, 120, 5214 – 5225; Angew. Chem. Int.
Ed. 2008, 47, 5136 – 5147.
[4] a) F. A. Cotton, C. Lin, C. A. Murillo, Proc. Natl. Acad. Sci. USA
2002, 99, 4810 – 4813; b) M. Eddaoudi, J. Kim, D. Vodak, A.
Sudik, J. Wachter, M. OꢀKeeffe, O. M. Yaghi, Proc. Natl. Acad.
Sci. USA 2002, 99, 4900 – 4904; c) Z. Ni, A. Yassar, T. Antoun,
O. M. Yaghi, J. Am. Chem. Soc. 2005, 127, 12752 – 12753; d) M. J.
Prakash, Y. Zou, S. Hong, M. Park, M.-P. N. Bui, G. H. Seong,
M. S. Lah, Inorg. Chem. 2009, 48, 1281 – 1283.
[10] R. W. G. Preston, S. Horwood Tucker, J. M. L. Cameron,
J. Chem. Soc. 1942, 500 – 504.
[11] Bruker AXS, SAINT Software Reference Manual, Madison,
WI, 1998.
[12] G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112.
[5] a) B. Moulton, J. Lu, A. Mondal, M. J. Zaworotko, Chem.
Commun. 2001, 863 – 864; b) H. Furukawa, J. Kim, N. W.
8468 www.angewandte.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2009, 48, 8465 –8468