Expanding the Variety of Zirconium‐based Inorganic Building Units for Metal–Organic Frameworks

Two new zirconium‐based metal–organic frameworks with the composition Zr₆O₄(OH)₄(OAc)₆(BDC)₃] (CAU‐26) and Zr₅O₄(OH)₄(OAc)₄(BDC)₂] (CAU‐27) are reported, which were synthesized from acetic acid, a rarely utilized but green and sustainable solvent (BDC^2?: 1,4‐benzenedicarboxylate). Structure determination aided by automated electron diffraction tomography revealed that CAU‐26 is composed of layers of well‐known {Zr₆O₈} clusters interconnected by terephthalate ions. In contrast CAU‐27 exhibits a three‐dimensional structure with a so far unknown type of one‐dimensional inorganic building unit (IBU), which can be rationalized as condensed polyhedron‐sharing chains of {Zr₆O₈} clusters. CAU‐26 occurs as an intermediate of the CAU‐27 synthesis and can be isolated easily, when reaction temperature and time are decreased. We were also able to synthesize two isoreticular derivatives of CAU‐27 with extended linker molecules by implementing 4,4′‐biphenyldicarboxylic acid (H₂BPDC) and 5,5′‐dicarboxy‐2,2′‐bipyridine (H₂BIPY). All materials show high thermal and chemical stability as well as permanent microporosity. The excellent stability of CAU‐27‐BIPY was exploited to synthesize a performant iridium‐supported heterogeneous MOF‐based catalyst for the direct C?H borylation of arenes.