Zn(C3H3N2)(C3H2N2–N=N–C6H5)], a Mixed‐Linker ZIF Containing a Photo­switchable Phenylazo Group

Abstract

AbstractWe report the synthesis and characterization of the new switchable Zn‐based zeolitic imidazolate framework (ZIF) [Zn(Im)(aIm)] (1). The high‐throughput investigation of the mixed linker system Zn2+/imidazole (HIm)/2‐phenylazoimidazole (HaIm)/DMF at 85 °C led to 1, which is isostructural to ZIF‐8 and crystallizes in a sodalite (SOD)‐type structure. The preparation was also studied with microwave‐assisted heating and ultrasound‐assisted synthesis. The crystal structure was determined from single‐crystal X‐ray diffraction data. Although Im– and aIm– ions are present in a 1:1 molar ratio, no ordering of the 2‐phenylazo group was observed. Incorporation of the Im– and aIm– linkers as an integral part of the framework structure was confirmed by elemental analysis, 13C and 15N MAS NMR, IR and Raman spectroscopy. In addition, the permanent porosity of 1 was demonstrated by N2 sorption experiments and a specific surface area of SBET = 580 m2 g–1 is observed. The photoswitching properties were investigated by UV/Vis spectroscopy as the cis and trans isomers exhibit different UV absorption spectra. Switching can be achieved by irradiation with UV light (λ = 355 nm), and back‐switching using visible light (λ = 525 nm). Although changes in the UV/Vis spectra are detected, the switching process is only partially reversible.