A Series of Robust Copper-Based Triazolyl Isophthalate MOFs: Impact of Linker Functionalization on Gas Sorption and Catalytic Activity †.

Hannes Preißler,Roger Gläser,Jens Möllmer,Oliver Erhart,Merten Kobalz,Jörg Lincke,Harald Krautscheid,Ulrike Junghans

doi:10.3390/ma10040338

Abstract

The synthesis and characterization of an isomorphous series of copper-containing microporous metal-organic frameworks (MOFs) based on triazolyl isophthalate linkers with the general formula [Cu4(μ3-OH)2(R1-R2-trz-ia)3(H2O)x] are presented. Through size adjustment of the alkyl substituents R1 and/or R2 at the linker, the impact of linker functionalization on structure-property relationships was studied. Due to the arrangement of the substituents towards the cavities, the porosity (pore fraction 28%–39%), as well as the pore size can be adjusted by the size of the substituents of the triazole ring. Thermal analysis and temperature-dependent PXRD studies reveal a thermal stability of the MOFs up to 230 °C due to increasing framework stability through fine-tuning of the linker substitution pattern. Adsorption of CO2 (298 K) shows a decreasing maximum loading with increasing steric demand of the substituents of the triazole ring. Furthermore, the selective oxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) is studied over the MOFs at 323 K in liquid chloroform. The catalytic activity increases with the steric demand of the substituents. Additionally, these isomorphous MOFs exhibit considerable robustness under oxidizing conditions confirmed by CO2 adsorption studies, as well as by the catalytic selective oxidation experiments.

Highlights

Since the 1990s, metal-organic frameworks (MOFs) have emerged as an attractive class of porous materials for a broad spectrum of applications, like gas storage [1,2,3,4] and separation [5,6,7,8,9], as well as sensor design [10], biomedicine [11] and heterogeneous catalysis [12,13,14,15]
Suitable crystals were obtained starting from the protonated ligands and Cu(OAc)2 or CuSO4 via solvothermal synthesis using H2 O, H2 O/MeCN or H2 O/MeOH as solvents
The triazolyl isophthalate MOFs 1–5 represent a series of isomorphous MOFs; 3–5 were obtained as single crystals

Summary

Introduction

Since the 1990s, metal-organic frameworks (MOFs) have emerged as an attractive class of porous materials for a broad spectrum of applications, like gas storage [1,2,3,4] and separation [5,6,7,8,9], as well as sensor design [10], biomedicine [11] and heterogeneous catalysis [12,13,14,15] This versatile applicability derives from their large specific surface area, tunable properties, as well as their structural and chemical diversity [16,17]. Several MOFs with nitrogen-containing aromatic moieties within the linker exhibit considerable robustness under these conditions [32,33]

Methods

Results

Conclusion