A research team from the IMDEA Nanociencia (Madrid) describes the first example of a non-porous dynamic crystalline fullerene C60 hexakis-adduct holding together by weak carbon-hydrogen van der Waals bonds interactions, also known as sticky fingers. Its dynamism allows single-crystal to single-crystal reaction by the inclusion of small molecules in smooth conditions, specifically in this work hydrazine molecules, allowing a toposelective hydrogenation of the buckyballs. The inclusion of the molecule has been illustrated by an X-ray single crystal diffraction performed at the ALBA Synchrotron, at the XALOC beamline.

In this work, published in Angewandte Chemie, scientists have used for the very first time a fullerene hexakis-non-porous adducts as a dynamic host-guest receptor for hydrazine molecules. In this way, it is demonstrated that sticky fingers interactions enables dynamism in a 3D framework allowing molecule inclusions. Exposure to hydrazine vapors of fullerene C60 hexakis-adduct in a reactor, induces structural and chemical changes that evince the hydrogenation of the C60.

Fullerenes are structures of carbon atoms in form of spheres, ellipsoids or tubes. Since they discovery in 1985, which deserved the Chemistry Nobel Prize, they have been the subject of intense research, both for their chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology. The best known fullerene is C60, a sphere also called buckyball for its similarity to a ball where the 60 carbon atoms that form it are situated in the vertex of the hexagonal and pentagonal rings. This C60 hexakis-adduct it’s a C60 sphere with 6 adducts (chemical substitutions).

In this research, IMDEA research team firstly performed the synthesis and characterization of a novel non-porous crystalline structure of a C60 hexakis-adduct. The weak non-covalent carbon-hydrogen interactions are holding together the molecular dynamic crystalline framework. The dynamism of these weak interactions that are presented in the organic fullerene-based material makes possible that this non-porous crystalline structure undergoes the inclusion of small molecules close to the buckyballs. Interestingly, the hydrazine molecules allocated inside these pockets trigger the toposelective hydrogenation of half of the remaining cyclohexatriene rings of the C60 hexakis-adduct in a single-crystal to single-crystal reaction. This reaction has been monitored by different techniques at IMDEA and also synchrotron techniques at Advanced Light Source and ALBA. Nevertheless, the X-ray single crystal diffraction of final product obtained in XALOC beamline, at the ALBA Synchrotron was crucial to unveil the mechanism of this host-guest unique reaction and confirm the toposelective hydrogenation. Furthermore, the reaction can be followed by a visible orange to yellow color change.

Researchers believe that further design of new suitably functionalized hexakis-adducts will allow obtaining materials with customizable pockets ready for capturing different hazardous volatiles and gases. Therefore, the new and groundbreaking strategy described in this work on topochemical solid-state reactions involving fullerenes will contribute to the creation of novel softs and dynamics carbon-based advanced absorbent materials with a variety of direct technological applications, as chemosensor and environmental remediation devices.

a) Orange-reddish single crystals of  b) (before exposure to hydrazine vapors). b) C60 hexakis-adduct obtained by the addition of bromomalonate to a solution of C60 in chlorobenzene, employing DBU as chemical base. c) ORTEP illustration of a single hexakis-adduct of C60 including the malonates groups (only one branch of the distorted malonates is illustrated for clarity). d) iRASPA view of the packing. e) C60 hexakis-adduct visualized at the ALBA Synchrotron. From its X-ray crystal structure, it is concluded that half of the fullerene’s six-membered rings in b) have been hydrogenated after the exposure. f) Single crystals of e) (after exposure to hydrazine vapors). g) MERCURY illustration of the hydrogenated hexaadduct, including the hydrogen atoms incorporated to the C60 and the malonates functional groups (only one branch of the distorted malonates is illustrated for clarity). h) iRASPA view of e).

The team leader researcher of the switchable nanomaterials (SNM) group is Dr. Jose Sánchez Costa, from IMDEA Nanoscience at the Universidad Autónoma de Madrid Campus. The SNM group have strongly worked with the Nazario Martín Group (IMDEA Nano and Univ. Complutense de Madrid). Also, for the achievement of this work, the collaboration with Dr. Roeland Boer (beamline scientist of XALOC/ALBA) and Dr. Simon J. Teat (beamline scientist at 12.2.1 in the Advanced Light Source) was decisive.

Reference: Estefania Fernandez-Bartolome, José Santos, Arturo Gamonal, Saeed Khodabakhshi, Laura J. Mc Cormick, Simon J. Teat, E. Carolina Sañudo, José Sánchez Costa and Nazario Martín. A Three-dimensional Dynamic Supramolecular “Sticky Fingers” Organic Framework. Angew. Chem. 10.1002/anie.201812419