A three dimensional porous metal-organic framework [Fe4L 6·(DMF)3·(H2O)10] constructed from neutral discrete Fe4L6 pyramids [H 2L = 1,3-benzodihydroxamix acid]

Article abstract of DOI:10.1039/b306264c

A 3-D porous zeolite-like metal-organic framework surviving guest removal is assembled from a well-defined tetrahedral Fe₄L₆ cavity by the cooperativity of hydrogen bonds and π-π stacking.

Full text of DOI:10.1039/b306264c

A three dimensional porous metal–organic framework
Fe L ·(DMF) ·(H O) ] constructed from neutral discrete Fe L
[
4
6
3
2
10
4 6
pyramids [H L = 1,3-benzodihydroxamix acid]†
2
Yan Bai, Dong Guo, Chun-ying Duan,* Dong-bin Dang, Ke-liang Pang and Qing-jin Meng*
Coordination Chemistry Institute, The State Key Laboratory of Coordination Chemistry, Nanjing University,
Nanjing 210093, P. R. China. E-mail: duancy@nju.edu.cn
Received (in Cambridge, UK) 3rd June 2003, Accepted 28th October 2003
First published as an Advance Article on the web 24th November 2003
A 3-D porous zeolite-like metal–organic framework surviving
guest removal is assembled from a well-defined tetrahedral
Fe L cavity by the cooperativity of hydrogen bonds and p–p
4 6
4 6
has unequivocally confirmed the tetrahedral geometry of the Fe L
cluster.§ ¶The asymmetry unit consists of two crystallographically
independent units, corresponding to DDDD and LLLL enantiomers,
stacking.
respectively; each lies on a special position with C
3
symmetry, a
subgroup of T . The four metal ions in one polyhedron are separated
d
The coordination paradigm pioneered by Lehn and Sauvage, and as
developed in the groups of Stang, Fujita, Raymond and others for
closed systems, has allowed for the synthesis of an enormous
number and variety of discrete, isolable, supramolecular structures
based on assemblies featuring well-defined nanoscale cavities.1
However, a small number of these have subsequently been used as
building blocks for microporous materials which comprise an
important component of the emerging chemistry of microporous
by an average of 8.85 Å. Fig. 1 shows the DDDD isomer of the
polyhedron; each iron ion is pseudo-octahedrally coordinated by
three bidentate hydroxamate binding units from three separated
ligands in a fac configuration. Each ligand loses two protons and
coordinates to two metal centers as a bridge between two metal ions
to span one edge of the tetrahedron. The polyhedron has a relatively
open, rigid cavity, which is partially filled with three crystallo-
graphically identical DMF molecules.
The most interesting structural feature of the complex in the solid
state is that it forms a three-dimensional porous framework (Fig. 2).
4 6
Each DDDD or LLLL Fe L polyhedron provides three donor
hydrogen bonds and three acceptor hydrogen bonds
[N(11)…O(26C) 2.84 Å, N(11)–H(11A)…O(26C) 162°, or
N(22)…O(14) 2.89 Å, N(22)–H(22A)…O(14) 168°, respectively,
,2
3
molecular materials, since the nominal requirements for functional
microporous molecular materials formation are compounds featur-
ing: accessible cavities of useful size, no catenation, no counter
ions, and sufficient stability to withstand removal of solvent
molecules.
On the other hand, as the simplest platonic polyhedron,
tetrahedral clusters have attracted more attention because of their
intrinsic beauty and interesting host–guest chemistry, as well as the
fact that they illustrate some basic construction principles necessary
4 6
symmetry code C: 1 2 x, 0.5 + y, 1.5 2 z] with six different Fe L
isomers in three directions to form a NaCl-like packing pattern with
larger pores among the polyhedrons. The diameter of the spherical
internal voids is ca. 13–15 Å and the windows of the MOF structure
ca. 7–8 Å. The volume of a van der Waals sphere that would just fit
4
to assemble highly symmetric polyhedra. In this paper we report a
novel and rather beautiful crystalline porous structure assembled
from the neutral platonic polyhedron. The ligand (Scheme 1) used
3
9
inside the void is ca. 900 Å . Three DMF molecules and ten water
molecules per tetrahedral unit are found to fill the 3-D body. The six
phenyl rings of each polyhedron are also stacked with the phenyl
rings of the neighbors to stabilize the three-dimensional porous
here is one of the simplest hydroxamates; it is said that such
5
ligands are suitable for constructing tetrahedral M
4
L
6
cavities with
+
3 charged metal ions of octahedral coordination geometry such as
3+
10
Fe . The polyhedron formed has advantages for the polymeriza-
tion into modular porous open framework solids: a) the hydrogen
atoms attached to the nitrogen atoms and the six phenyl rings of the
ligands in the polyhedron have the potential to contact with others
through hydrogen bonds or p–p interactions, from which the
polyhedron serves as a tetrahedral building block or an octahedral
framework. The dihedral angles of the stacked pairs I and IIID, II
and IVE are 16.1 and 10.6° with the shortest inter-planar
atom…atom separation ca. 3.45 Å, respectively [symmetry code D:
1 + x, 21 + z, x; E: 0.5 2 y, 1 2 z, 0.5 2 x]. Interconnected systems
of non-covalent interactions possess the property of being co-
6
building block; b) the replacement in a vertex of a framework net
4 6
by an Fe L cluster, a process termed decoration, results in open
structures with high rigidity and without a tendency to inter-
7
penetrate, while optimal pore volumes may be achieved; c) the
introduction of a neutral polyhedron as SBU into a porous
framework suggests a number of potentially exciting applications
involving selective molecular transport, sensing, or chemical
transformations.8
Ligand H
dichloride with hydroxylamine. The polyhedron 1 was achieved by
simply diffusing a solution of Fe(NO ·9H O into a solution of
L in the presence of base.‡ Crystallographic study of complex 1
2
L was prepared through the reaction of isophthaloyl
3
)
3
2
H
2
4 6
Fig. 1 Perspective view of the DDDD isomer of the Fe L clusters, showing
the tetrahedral shape of the molecule. Selected bond lengths (Å): Fe(1)–
O(11) 2.067(6), Fe(1)–O(12) 1.968(6), Fe(2)–O(13) 2.020(8), Fe(2)–O(14)
Scheme 1
1
.977(8), Fe(2)–O(15) 2.045(7), Fe(2)–O(16) 1.988(8), Fe(2)–O(17B)
†
Electronic supplementary information (ESI) available: TGA and XRD
2.050(8), Fe(2)–O(18B) 1.987(7). Symmetry code A: 0.5 2 y, 1 2 z, 0.5 +
x; B: 20.5 + z, 0.5 2 x, 1 2 y.
patterns of 1 and 2. See http://www.rsc.org/suppdata/cc/b3/b306264c/
1
86
C h e m . C o m m u n . , 2 0 0 4 , 1 8 6 – 1 8 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

Notes and references
‡
Synthesis of complex 1: A solution of the H
mmol) and KOH (0.002 g, 0.036 mmol) in methanol (6 mL) was layered
onto a solution of Fe(NO ·9H O (0.04 g, 0.1 mmol) in DMF (4 mL). The
2
L ligand (0.018 g, 0.09
)
3 3
2
solutions were left for two weeks at room temperature in darkness to give X-
ray quality red block crystals in good yields. Yield: 86%. Elemental analysis
(
1
§
%) for (C48
H
36
N
12
O
24Fe
1.7; found: C 38.5, H 4.5, N 11.4%.
Crystal data of (C48 24Fe )(C
4 3 7 3 2
)(C H NO) (H O)10 1: calcd: C 38.3, H 4.3, N
H
36 12
N O
4
3 7 3 2 r
H NO) (H O)10, M = 1787.74,
crystallized in the cubic space group P2
1
23
3 with a = 27.642(2) Å, V =
3
21
2
1120(2) Å , Z = 8. rcalc = 1.124 Mg m , T = 293(2), m = 0.612 mm
,
GOOF = 0.986, Intensity data were collected on a Bruker CCD system. The
structure was solved by direct methods. 85354 measured reflections of
which 12373 reflections are independent and all include in the refinement.
2
R
1
= 0.077, wR
2
= 0.208 (all data, refined against ¡F ¡). The water
molecules were refined isotropically and with non-unit occupancies. Since
there are left and right hand molecules in pairs, we tried to resolve the
structure using a centro-symmetric space group such as Pa3 or Pn3,
however, no suitable space group can be found. The mean ¡E*E 21¡ of only
.60 also supports the choice of the reported acentric space group. CCDC
01192. See http://www.rsc.org/suppdata/cc/b3/b306264c/ for crystallo-
Fig. 2 Molecular packing of the clusters showing the large apertures and
voids achieved by the cooperativity of hydrogen bonds and p–p stacking
interactions, the solvent molecules are omitted for clarity.
¯
¯
0
2
graphic data in .cif or other electronic format.¶
operative, namely, the contacts enhance the strengths of each other
and the interaction energy per contact is greater than the energy of
an isolated interaction. There are also hydrogen bonds which are
found to connect the guest DMF molecules, water molecules and
oxygen atoms of the clusters in the porous framework.
1
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1
1
To evaluate the mobility of the guests within the framework, we
examined the as-synthesized crystals by thermal gravimetric
techniques. In flowing nitrogen, a crystalline sample of 1 was
heated at a constant rate of 2 °C min21(see ESI†). A rapid weight
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liberation of all DMF molecules and water molecules, a weight loss
step between 200 °C and 350 °C was observed and is attributed to
decomposition of the framework. A powder X-ray diffraction
pattern of the sample 2, which is obtained by heating complex 1
carefully to 180 °C to remove the solvents, shows that the positions
of the most intense lines remain unchanged relative to the simulated
pattern based upon the single-crystal data of the complex 1. The
good agreement between the peaks in both diagrams demonstrates
that the porous framework is retained in the absence of guest
molecules in the pores. It is said that extensive cooperativity
between discrete molecules throughout the crystals is important for
such materials to maintain the porous framework upon the guest
removal. Since the structure which consists of a network of large
cavities interconnected by channels appears to survive guest
removal, it distinctly exhibits the 3-D porous zeolite-like network.
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(
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crystal phase transition upon guest uptake and release have been
reported,12 and while the cooperativity between the molecules
throughout the crystal maintains the macroscopic integrity upon
guest removal, there is a change in the overall packing arrangement
of the host compounds. It is suggested that even weak dispersive
forces can exert a profound influence on solid-state dynamics.
Controlling the assembly of molecules in the solid state is
currently recognized as one of the most important issues in the
synthesis of functional materials. The present represents the first
example of a 3-D porous framework assembled from discrete,
neutral metal-containing polyhedrons. The ability to control both
the formation and details of the structure of these materials offers an
interesting approach to tune finely the electrical or optical
properties in the crystal.
10 The phenyl rings I, II, III and IV are defined by the atoms C(2), C(3),
C(4), C(5), C(6) and C(7); C(10), C(11), C(12), C(13), C(14) and C(15);
C(18), C(19), C(20), C(21), C(22) and C(23); C(26), C(27), C(28),
C(29), C(30) and C(31), respectively.
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New. J. Chem., 2000, 24, 1057–1062; (b) Z. H. Liu, C. Y. Duan, J. Hu
and X. Z. You, Inorg. Chem., 1999, 38, 1719–1724; (c) H. Mo, D. Guo,
C. Y. Duan, Y. T. Li and Q. J. Meng, J. Chem. Soc., Dalton Trans.,
1
This work was supported by the National Natural Science
Foundation of China. (No. 20131020). We thank Mr Liu Yong-
jiang for collecting the crystal data.
2
002, 3422–3424.
12 (a) J. L. Atwood, L. J. Barbour, A. Jerga and B. L. Schottel, Science,
2002, 298, 1000–1002 and references therein.
C h e m . C o m m u n . , 2 0 0 4 , 1 8 6 – 1 8 7
187