CFA-1: the first chiral metal–organic framework containing Kuratowski-type secondary building units

Abstract

The novel homochiral metal–organic framework CFA-1 (Coordination Framework Augsburg-1), [Zn₅(OAc)₄(bibta)₃], containing the achiral linker {H₂-bibta = 1H,1′H-5,5′-bibenzo[d][1,2,3]triazole}, has been synthesised. The reaction of H₂-bibta and Zn(OAc)₂·2H₂O in N-methylformamide (NMF) (90 °C, 3 d) yields CFA-1 as trigonal prismatic single crystals. CFA-1 serves as a convenient precursor for the synthesis of isostructural frameworks with redox-active metal centres, which is demonstrated by the postsynthetic exchange of Zn²⁺ by Co²⁺ ions. The framework is robust to solvent removal and has been structurally characterized by synchrotron single-crystal X-ray diffraction and solid state NMR measurements (¹³C MAS- and ¹H MAS-NMR at 10 kHz). Results from MAS-NMR and IR spectroscopy studies are corroborated by cluster and periodic DFT calculations performed on CFA-1 cluster fragments.