A XAFS study of the local environment and reactivity of Pt- sites in functionalized UiO-67 MOFs

E Borfecchia,E Gallo,S Bordiga,M A Soldatov,K A Lomachenko,K P Lillerud,G Agostini,S Svelle,S Øien,C Lamberti,L Braglia,A V Soldatov,U Olsbye,L Mino,A A Guda

doi:10.1088/1742-6596/712/1/012125

Abstract

We synthesized UiO-67 Metal Organic Frameworks (MOFs) functionalized with bpydcPt(II)Cl2 and bpydcPt(IV)Cl4 complexes (bpydc = bipyridine-dicarboxylate), as attractive candidates for the heterogenization of homogeneous catalytic reactions. Pt L3-edge XAFS experiments allowed us to thoroughly characterize these materials, in the local environment of the Pt centers. XAFS studies evidenced the rich reactivity of UiO-67-Pt(II) MOFs, including reduction to bpydcPt(0) under H2 flow in the 600-700 K range, room-temperature oxidation to bpydcPt(IV)Br4 through oxidative addition of liquid Br2 and ligand exchange between 2 Cl- and even bulky ligands such as toluene-3,4-dithiol. Preliminary XANES simulations with ADF code provide additional information on the oxidation state of Pt sites.

Highlights

Metal-organic frameworks (MOFs) are crystalline, porous solids consisting of metal ions or clusters, coordinated with organic linkers [1]
In this contribution we present results on UiO-67 functionalized with bpydcPt(II)Cl2 and bpydcPt(IV)Cl4 coordination complexes acting as linkers in the Metal Organic Frameworks (MOFs) framework and prepared following three different synthesis methods: (i) one-pot synthesis (OPS) where ZrCl4 and PtClx (x = 2 or 4) precursors salts react with biphenyl and bipyridine linkers; (ii) premade linker synthesis (PMLS), where a previously prepared PtClx(H2bpydc) linker reacts with biphenyl linkers and ZrCl4; and (iii) post-synthesis functionalization (PSF), where a premade UiO-67-bpy MOF is suspended in a solution of precursor PtClx salt [3]
XRPD and Pt L3-edge XAFS studies proved that the three synthesis methods are equivalent and for Pt(II) samples fully comply with the target structure on both long-range and short-range scales

Summary

Introduction

Metal-organic frameworks (MOFs) are crystalline, porous solids consisting of metal ions or clusters, coordinated with organic linkers [1]. XRPD and Pt L3-edge XAFS studies proved that the three synthesis methods are equivalent and for Pt(II) samples fully comply with the target structure (figure 1a) on both long-range (ordered MOF framework) and short-range (local environment of Pt sites probed by XAFS) scales.

Results

Conclusion