We synthesized a porous twofold interpenetrated MOF [Zn 2 (NDC) 2 (1)] (coined CAU-5) using 3-azo-phenyl-4,4¢-bipyridine (1), 2,6-naphthalenedicarboxylic acid, and Zn(NO 3 ) 2 ·6H 2 O. The azo-functionality protrudes into the pores, and can be switched, by irradiation with UV light (365 nm), from the thermodynamically stable trans-isomer to the cis-isomer. Back-switching was achieved thermally and with an irradiation wavelength of l max = 440 nm.

For the first time an azo functionality was covalently introduced into a MOF by post-synthetic modification. The reaction of Cr-MIL-101-NH 2 with p-phenylazobenzoylchloride (1) and 4-( phenylazo)-phenylisocyanate (2) as the reactants led to the compounds Cr-MIL-101_amide and Cr-MIL-101_urea, with the azo groups protruding into the mesoporous cages. XRPD and N 2 sorption measurements confirm the intactness of the framework and the successful covalent modification was proven by IR-and NMRspectroscopy. Furthermore, cis/trans isomerisation upon irradiation with light was demonstrated by UV/ Vis spectroscopy. More distinct changes in the UV/Vis spectra were observed for Cr-MIL-101_amide compared to Cr-MIL-101_urea, while the degree of functionalization, i.e. the number of reacted NH 2 -groups, seems to have a less pronounced effect. The variation of the sorption properties due to the cis/trans isomerisation was proven by methane adsorption measurements.

We 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.

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Four new compounds [Co 2 (NDC) 2 (AzBIPY)] (1), [Cu 2 (NDC) 2 (AzBIPY)] (2), [Zn 2 (BPDC) 2 (AzBIPY)] (3) and [Zn 2 (CCA) 2 (AzBIPY)] (4) (with H 2 NDC: 2,6-naphthalenedicarboxylic acid, AzBIPY: 3-azo-phenyl-4,4Ј-bipyridine, H 2 BPDC: 4,4Ј-biphenyldicarboxylic acid and H 2 CCA: 4-carboxy-cinnamic acid) were synthesized and characterized. All compounds have paddle-wheel units and * Prof. Dr. N. Stock