An implanted paramagnetic metallofullerene probe within a metal-organic framework.

Paramagnetic endohedral metallofullerene can be used as a molecular probe because of its sensitive electron spin characters, one of which is to sense its surroundings. Metal-organic framework (MOF) materials have significant applications in selective adsorption owing to their porous structures. Herein, we report a ScC@C spin probe implanted in MOF-177 to detect the unusual host-guest interaction between the guest molecules of metallofullerene and the host pores of the MOF. Paramagnetic ScC@C molecules were incorporated into the pores of MOF-177 via absorption method, and there was strong π-π interaction between oleophilic metallofullerene and aromatic framework. The electron paramagnetic resonance (EPR) signals of ScC@C in MOF-177 exhibit anisotropic properties caused by the restricted motion of implanted ScC@C. This unusual host-guest interaction between ScC@C and MOF-177 is gradually strengthened with decreasing temperature as revealed by the EPR signals. In addition, the gas desorption from the MOF-177 pores under subatmospheric pressure can weaken the host-guest interaction and lead to slightly enhanced ScC@C EPR signals. Furthermore, the changes in the host-guest interaction between ScC@C and MOF-177 at different temperatures and pressures exhibit reversibility, as shown by cycling EPR measurements. These results will inspire material design and applications of fullerene and MOF complexes.