Chiroptical activity is observed from an achiral adenine-containing metal-organic framework (MOF) named ZnFDCA. Such a seemingly counterintuitive phenomenon can, in fact, be predicted by the intrinsic crystal symmetry of 4̅2 m point group. Although theoretically allowed, examples of optically active achiral crystals are extremely rare. ZnFDCA is the first reported achiral MOF showing optical activity, as demonstrated by a pair of circular dichroism signals with opposite signs and enhanced intensity. Moreover, simply through adding an amino substituent to adenine, the chiroptical activity, as well as nonlinear optical activity, of the analogous MOF, namely ZnFDCA-NH2, disappears due to diverse packing pattern giving rise to centrosymmetric crystal symmetry.
Two metallofullerene frameworks (MFFs) constructed from a penta-shell Keplerate cuprofullerene chloride, C60 @Cu24 @Cl44 @Cu12 @Cl12 , have been successfully prepared via a C60 -templated symmetry-driven strategy. The icosahedral cuprofullerene chloride is assembled on a C60 molecule through [η2 -(C=C)]-CuI and CuI -Cl coordination bonds, resulting in the penta-shell Keplerate with the C60 core canopied by 24 Cu, 44 Cl, 12 Cu and 12 Cl atoms that fulfill the tic@rco@oae@ico@ico penta-shell polyhedral configuration. By sharing the outmost-shell Cl atoms, the cuprofullerene chlorides are connected into 2D or 3D (snf net) frameworks. TD-DFT calculations reveal that the charge transfer from the outmost CuI and Cl to C60 core is responsible for their light absorption expansion to near-infrared region, implying anionic halogenation may be an effective strategy to tune the light absorption properties of metallofullerene materials.