Metal‐Complex Assemblies Constructed from the Flexible Hinge‐Like Ligand H 2 bhnq: Structural Versatility and Dynamic Behavior in the Solid State

Novel metal‐complex assemblies constructed from the flexible hinge‐like ligand H 2 bhnq (H 2 bhnq=2,2′‐bi(3‐hydroxy‐1,4‐naphthoquinone)) have been synthesized. The X‐ray crystal structures of these compounds reveal that four types of architectures are accessible by variation of the metal ions. In copper( II ) compounds 1 – 3 , the chelating bhnq 2− ions bridge copper( II ) centers to form one‐dimensional zigzag chains. The chains of 1 – 3 are arranged by hydrogen‐bonding interactions and stacking interactions to produce porous structures. Cobalt( II ) and zinc( II ) compounds 4 and 5 form one‐dimensional helical chains. In 4 and 5 , the crystal packing induces spontaneous resolution of the helical chains with chiral cavities formed perpendicular to the helices. Nickel( II ) compounds 6 and 7 form cyclic tetramers. The fourth architecture, a dimer (compound 8 ), is obtained by the reaction of zinc( II ) and bhnq 2− in MeOH. In these compounds, changes of the dihedral angles and the metal‐coordination mode of the bhnq 2− ion induce the structural versatility. The assemblies of the zigzag chains of the copper( II ) compounds exhibit reversible vapochromic behavior. UV/Vis, powder X‐ray diffraction, EPR, and adsorption isotherm measurements indicate that this vapochromic behavior is based on the hinge‐like flexibility of the bhnq 2− ion.