Synthesis, structural properties, and catalytic behavior of Cu-BTC and mixed-linker Cu-BTC-PyDC in the oxidation of benzene derivatives

Abstract

a b s t r a c tMixed-linker metal-organic frameworks based on the Cu-BTC structure have been synthesized in which the benzene-1,3,5-tricarboxylate (BTC) linkers have been partially replaced by pyridine-3,5-dicarboxylate (PyDC). X-ray-based techniques (powder XRD and XAS), thermal analysis, and infrared spectroscopy proved that a desired amount of PyDC (up to 50%) can be incorporated without changing significantly the crystal structure. The pyridine unit can be seen as a defect site in the local coordination environment of the dimeric copper units, which is significantly altering their electronic structure and the catalytic properties. Both Cu-BTC and the mixed Cu-BTC-PyDCs catalyze the demanding direct hydroxylation of toluene both in acetonitrile and in neat substrate. Different selectivity toward the desired ortho-and para-cresol and other oxidation products (benzaldehyde, benzyl alcohol, methylbenzoquinone) was observed for Cu-BTC and the Cu-BTC-PyDCs, respectively. Leaching tests and comparison with homogeneously dissolved Cu catalysts indicate mainly a heterogeneous reaction pathway.

Synthesis and Crystal Structure of Two CuII‐benzene‐1,2,4,5‐tetracarboxylates with Three‐Dimensional Open Frameworks

“…for example peroxidative oxidation processes, for hydroxylation reactions, and for the reduction of nitrite. [32,36,37] Herein we report on two new three-dimensional coordination polymers with wide channels as a result of the connection between Cu 2+ cations and benzene-1,2,4,5-tetracarboxylate anions in the presence of 1,6-diaminohexane as template at two different temperatures of synthesis. anions coordinate the Cu 2+ -cations in a monodentate manner.…”

Metal–organic framework MIL-53(Al)-supported copper catalyst for CO catalytic oxidation reaction

“…With high pore volume, large surface area and geometrical control, MOFs have more extensive applications than other porous materials, such as for adsorption separation, catalysts, optical and battery materials [6][7][8][9][10]. Catalysis based on MOFs includes cyanosilylation of benzaldehyde and acetone [11], oxidation of alkanes, olefins, alcohols, and amines [12][13][14][15][16][17], hydroxylation of aromatic compounds [18], hydrolysis of esters, esterification of acetic acid with 1-propanol [19], and regioselective ring opening of epoxides [20]. Most of these MOFs catalyzed reactions are in liquid phase [21].…”

Defects and Disorder in MOFs

“…On the other hand, one of the most common strategies in the creation of defects is direct copolymerization of the so-called defect linker (DL) along with the basic linker L of a given MOF or a combination of distinct metal ions -a solid solution (or linker-fragmentation) approach [13,15,[55][56][57][58]61] (Figures 26.1 and 26.2). From a broader perspective, an oligotopic molecule of similar or almost identical topology and coordination chemistry as the parent linker L but lacking some of the connector sites or having one or more of these exchanged by weaker interacting connectors could act as DL.…”

“…For instance, on a basis of EXAFS and XANES measurements, the general decrease of the mCN of Cu ions in HKUST-1 (doped with pydc DL) [55] and thus quantitative framework incorporation of DL and formation of respective defects were proved. Moreover, EXAFS in conjunction with X-ray photoelectron spectroscopy (XPS) and energydispersive X-ray spectroscopy (EDS) data enabled to confirm the presence of metal-ion vacancies in MOF-505 and even determine their concentration [68].…”