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Characterization of a New Porous Pt-Containing Metal-Organic Framework Containing Potentially Catalytically Active Sites: Local Electronic Structure at the Metal Centers
journal contribution
posted on 2007-01-23, 00:00 authored by Kai Chung Szeto, Carmelo Prestipino, Carlo Lamberti, Adriano Zecchina, Silvia Bordiga, Morten Bjørgen, Mats Tilset, Karl Petter LillerudA crystalline and thermally stable metal-organic framework (MOF) with PtII and GdIII sites incorporated
in the structure has been recently reported. This material has been synthesized with the aim to develop
a heterogeneous PtII counterpart to homogeneous metal-organic complexes having C−H activating
properties. The first account focused on the MOF synthesis and on structural and stability characterization
of the material. In the present work, a multitechnique approach has been adopted to investigate the effect
of solvent removal and the reversibility of this process. Structural features have been investigated by
means of powder X-ray diffraction and extended X-ray absorption fine structure spectroscopy at both Pt
and Gd L3-edges. Electronic properties have been studied with diffuse reflectance surface UV−vis and
X-ray absorption near-edge spectroscopies. Finally, IR spectroscopy has been used to determine the
vibration properties. Thermogravimetric methods have been used to quantify the water loss. X-ray
absorption spectroscopy has been used to compare the Pt environment in the periodic MOF structure, in
related molecular complexes, and in the linkers. Our results demonstrate that the environment around Pt
is more or less unaffected by the incorporation of the Pt centers in the molecular complexes into the 3D
extended framework of the Pt−Gd MOF. The principle of using known homogeneous complexes as
building blocks for the construction of single-site heterogeneous catalysts therefore seems applicable in
the present case. Removal of solvent water molecules from the internal voids of the as-prepared MOF
presents an opportunity to attain a porous material with accessible PtII sites. We observe that the structure
undergoes a reversible loss of long-range order upon dehydration at ambient temperature. The environment
of Gd is somewhat perturbed in the dehydration/hydration process, while that of Pt is almost unaffected.
When a total dehydration is achieved, the original structure is only partially recovered upon rehydration.
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PtII counterpartdehydrationabsorptionmaterialPtII sitesPt centersstructure spectroscopywater losswater moleculesstability characterizationmultitechnique approachUVIR spectroscopyGdIII sitesbuilding blocksMOF structureambient temperaturePt environmentThermogravimetric methodsElectronic StructureMetal CentersA3 DMOF synthesisvibration propertiescomplexStructural features
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