The synthesis of lanthanide-based endohedral metallofullerenes (EMFs) was the starting step, which required improvement of the efficiency and accumulation of the necessary amount of target EMFs for their further studies. We therefore optimization synthetic and separation procedures used for fullerenes and synthesized a plethora of new metallofullerenes. Assessment of the production yields revealed that the most suitable EMFs for the dedicated studies of magnetic properties are nitride clusterfullerenes, such as DySc2N@C80 and Dy2ScN@C80, and dimetallofullerenes. Unexpected but very important development was the discovery of metal-metal bonds with variable electron population in dimetallofullerenes. Realization of M–M bond between lanthanides allowed improving magnetic properties by increasing the strength of exchange interaction. We thus developed the synthesis of Ln-based dimetallofullerenes M2@C80(CH2Ph) with single-electron M–M bonds for M = Y, Gd, Tb, Dy, Ho, Er.
Comprehensive magnetic studies of the large number of EMFs synthesized in the project allowed to identify the best fullerene-based single-molecule magnets used in further functionalization and surface depositions. Besides, these studies allowed s to formulate guiding principles for best fullerenes-SMMs and establish EMFs as a unique class of SMM with excellent magnetic properties.
The EMFs combining high production yields and excellent magnetic functionalities were then functionalized with surface-anchoring groups, which facilitate formation of self-assembled monolayers on suitable substrates. Then, monolayers of magnetic fullerenes were grown on conducting substrates either by vacuum sublimation (for unfunctionalized molecules) or by self-assembly from solution (for EMF derivatives with anchor groups). Morphology and electronic properties of monolayers were studied by scanning tunnelling microscopy, and their magnetic properties were then characterized by synchrotron-based X-ray magnetic circular dichroism. These studies proved that excellent magnetic properties for EMFs in powder samples were retained when they were deposited to metallic substrates, which is the necessary prerequisite for the use of SMMs in spintronic devices.
