Porous frameworks constructed by non-covalent linking of substitution-inert metal complexes.

Takahiro Itoh,Hirotoshi Sakamoto,Mari Kanaike,Shigeyuki Masaoka,Kenichiro Itami,Mio Kondo,Kaori Wakabayashi

doi:10.1039/c5dt01620g

Abstract

The incorporation of active sites into metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) is an attractive way to functionalise these materials. However, the methodology to organise substitution-inert metal-based secondary building units (SBUs) with active sites into MOFs or PCPs via coordination driven self-assembly is severely limited. In this study, we successfully assembled substitution-inert paddle-wheel Rh(II) dimers to afford three novel porous frameworks, Rh2(ppeb)4(THF)2 (1-THF), Rh2(ppeb)4(3-pentanone)2 (1-PN) and Rh2(ppeb)4(1-adamantylamine)2 (1-AD) (ppeb = 4-[(perfluorophenyl)ethynyl]benzoate), by using non-covalent interactions. Multipoint arene-perfluoroarene (Ar-Ar(F)) interactions, which allow the unidirectional face-to-face interaction mode of aromatic rings, were used to assemble the substitution-inert paddle-wheel Rh(II) dimers. The obtained frameworks were structurally characterisation by single crystal X-ray diffraction, and it is found that all structures exhibited a one-dimensional channel with active axial sites exposed to the pores. The porous properties of the obtained frameworks were also investigated by thermogravimetric analysis, gas adsorption and powder X-ray diffraction measurements. Moreover, the ligand substitution reaction at the active axial sites was examined at the crystalline state and the flexible structural transformation with the change of channel shapes and sizes was observed.

Highlights

We show an effective approach to construct a porous framework based on substitution-inert secondary building units (SBUs) with active sites
The 1H NMR spectrum was acquired on a JEOL JNM-LA500 spectrometer, where chemical shifts in DMF-d7 were referenced to internal tetramethylsilane
The 19F NMR spectrum was acquired on a JEOL JNM-LA500 spectrometer, where chemical shifts in DMF-d7 were referenced to external trifluorotoluene

Summary

Introduction

We show an effective approach to construct a porous framework based on substitution-inert SBUs with active sites. Scheme 1 Schematic illustration of the self-assembly of substitutioninert SBUs via (a) covalent linking and (b) non-covalent linking. 4-[(Perfluorophenyl)ethynyl]benzoic acid (Hppeb) and Na4[Rh2(CO3)4] were prepared by using the literature methods.[15,16] All syntheses were performed under an atmosphere of dry nitrogen or dry argon unless otherwise indicated. The 1H NMR spectrum was acquired on a JEOL JNM-LA500 spectrometer, where chemical shifts in DMF-d7 were referenced to internal tetramethylsilane. The 19F NMR spectrum was acquired on a JEOL JNM-LA500 spectrometer, where chemical shifts in DMF-d7 were referenced to external trifluorotoluene. Thermogravimetric analyses (TGA) were carried out with a SHIMADZU DTG-60 under a nitrogen atmosphere. Scheme 2 Schematic illustration of (a) substitution inert SBU and (b) non-covalent interaction employed in this study.

Synthetic procedures

Results and discussion

Conclusions