Angewandte
Communications
Chemie
Metal–Organic Layers Hot Paper
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Abstract: Metal–organic layers (MOLs) represent an emerg-
ing class of tunable and functionalizable two-dimensional
materials. In this work, the scalable solvothermal synthesis of
self-supporting MOLs composed of [Hf O (OH) (HCO ) ]
secondary building units (SBUs) and benzene-1,3,5-triben-
zoate (BTB) bridging ligands is reported. The MOL structures
were directly imaged by TEM and AFM, and doped with 4’-(4-
dimensional (2D) metal–organic layers (MOLs), a new
category of 2D materials. MOLs not only provide the benefit
of readily accessible active sites in a thin layer but also inherit
the heterogeneous nature, ordered structure, and molecular
tunability of MOF catalysts.
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2 6
2D coordination layers have been reported in the
[
3]
literature, along with other prominent 2D materials, such
[
4]
benzoate)-(2,2’,2’’-terpyridine)-5,5’’-dicarboxylate
(TPY)
as graphenes and metal dichalcogenides. 2D coordination
[5]
before being coordinated with iron centers to afford highly
active and reusable single-site solid catalysts for the hydro-
silylation of terminal olefins. MOL-based heterogeneous
catalysts are free from the diffusional constraints placed on
all known porous solid catalysts, including metal–organic
frameworks. This work uncovers an entirely new strategy for
designing single-site solid catalysts and opens the door to a new
class of two-dimensional coordination materials with molec-
ular functionalities.
layers were previously assembled on flat metal surfaces or
created at air/liquid or liquid/liquid interfaces by the Lang-
[6]
muir–Blodgett method. However, these methods cannot
produce sufficient quantities of self-supporting nanosheets for
catalytic applications. Recently, top-down chemical or phys-
ical exfoliation has also been used to prepare nanosheets from
[
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layered 3D MOFs. Herein, we report a highly scalable
bottom-up strategy to assemble MOLs directly from molec-
ular building blocks in one-pot solvothermal reactions.
Importantly, the MOLs were functionalized with Fe catalytic
centers to give diffusion-free heterogeneous catalysts.
A
s the majority of industrially used catalysts are heteroge-
neous, it is desirable to immobilize molecular catalysts onto
porous solid supports that are compatible with industrial
processes. Metal–organic frameworks (MOFs), porous solids
that are assembled from organic ligands and metal coordina-
tion nodes, have provided a versatile platform for the
Nanostructures with a high surface energy, such as MOLs,
can in principle be prepared in the presence of surfactants,
which reduce the surface energy through the hydrophobic
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protecting shell but also block the catalytic sites. Alterna-
tively, nanoparticles with high index facets (with high surface
energies) can be prepared by crystallization under super-
[1]
heterogenization of molecular catalysts. However, their
activity is often limited by the rates of diffusion of substrates
and products within the frameworks. This diffusional
constraint can be relieved by reducing one dimension of the
MOF crystal to only a few nanometers to minimize the
diffusion distance. This dimensional reduction results in two-
[
9]
saturation conditions. This strategy can be rationalized by
the Thomson–Gibbs equation,
[
2]
Dm ¼ m
À m
¼ sS
ð1Þ
l
c
which relates the difference between the chemical potentials
Dm) of the species in the supersaturated solution (m ) and the
(
l
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[
*] L. Cao, W. Wang, R. Huang, Prof. C. Wang, Prof. J. Yan,
Prof. Z. Zhang, Prof. L. Long, Prof. W. Lin
crystallized ones (m ) to additional surface energies of the
c
crystallites (sS) as a result of energy conservation. We
combined the above two strategies to create MOLs by
College of Chemistry and Chemical Engineering, iCHEM, PCOSS
Xiamen University, Xiamen 361005 (China)
E-mail: wangchengxmu@xmu.edu.cn
1
) introducing small capping molecules that reduce the sur-
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face energy penalty without blocking the catalytic sites and
2) creating a supersaturation of the building blocks in the
solution for MOL synthesis to tolerate additional surface
energies as compared to the bulk 3D crystals.
Z. Lin, T. Zhang, Prof. W. Lin
Department of Chemistry, University of Chicago
Chicago, IL 60637 (USA)
E-mail: wenbinlin@uchicago.edu
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[10]
F. Peng, J. Liang, Prof. J. Sun
The Hf cluster [Hf (m -O) (m -OH) (carboxylate) ]
6 3 4 3 4 12
Berzelii Center EXCELLENT on Porous Materials
Department of Materials and Environmental Chemistry
Stockholm University, 10691 Stockholm (Sweden)
was chosen for the MOL synthesis because of the tendency
of Hf to form stable coordination bonds with carboxylates.
The 12-connectivity of the Hf cluster, however, violates the
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Prof. J. Sun
geometric requirement of a 2D layer. We used a capping
method to overcome the geometric mismatch. In this method,
six of the connection sites on the cluster were protected by
formate groups, leaving the remaining six in the same plane to
connect to the benzene-1,3,5-tribenzoate (BTB) moieties.
College of Chemistry and Molecular Engineering
Peking University, 100871 Beijing (China)
E-mail: junliang.sun@pku.edu.cn
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[
] These authors contributed equally to this work.
The 6-connected Hf secondary building units (SBUs) and the
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three-connected BTB ligands link to each other to form an
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 4962 –4966