Secondary Building Unit (SBU) controlled formation of a catalytically active Metal–Organic Polyhedron (MOP) derived from a flexible tripodal ligand

Abstract

A nanosized truncated octahedron-shaped metal–organic-polyhedron (MOP) namely [{Cu₁₂(TMBTA)₈(DMA)₄(H₂O)₈}·8H₂O·X] MOP-TO (X = 48 H₂O molecules as per SQUEEZE calculation and TGA data) was successfully derived from a flexible C₃-symmetric ligand (2,4,6-trimethylbenzene)-1,3,5-triacetic acid (TMBTA) and Cu(NO₃)₂ in dimethyl acetamide (DMA) and EtOH under solvothermal conditions. The nanocage was well-characterized by single crystal X-ray diffraction (SXRD) and electron spray ionization mass spectrometry (ESI-MS). Remarkably, the nanocage molecules could be seen under high-resolution transmission electron microscope (HR-TEM). It was evident that the Cu(II) paddle wheel secondary building unit (CPWSBU) was responsible for the formation of the nanocage, as the corresponding reactions of TMBTA with other metal ions (e.g., Co(II) and Zn(II) resulted in the formation of two coordination polymers, namely [{Co(μ-TMBTA)(H₂O)4}]_∝ TMBTA-Co(II) and [{(H₂O)2Zn(μ-TMBTA)Zn·K}·2H₂O]_∝ TMBTA-Zn(II). Interestingly, the nanocage MOP-TO was exploited in catalyzing (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO)-assisted aerobic oxidation of benzyl alcohol to benzaldehyde.