Favorite Orientation of the Carbon Cage and a Unique Two-Dimensional-Layered Packing Model in the Cocrystals of Nd@C82(I,II) Isomers with Decapyrrylcorannulene

To date, the experimental studies on Nd-based metal-lofullerenes are only limited to spectroscopic characterizations. In this work, the molecular structures of Nd@C-82(I,II) isomers, including the isomeric symmetry of the C cage and the position of endohedral Nd atom, as well as their unique two-dimensional (2D)-layered crystallographic packing structures were initially and unambiguously elucidated, based on the X-ray structural analyses of the cocrystals of Nd@C-82(I) or Nd@C-82(II) with cocrystallizing agent decapyrrylcorannulene (DPC). In the V-shaped unit cell, the endohedral Nd atom prefers a site as far away from the DPC molecules as possible because of the unevenly distributed charge on the C cage mainly related to the charge transfers from the endohedral Nd atom, cocrystallizing agent DPC, and solvent toluene molecules to the C-82 cage. Apart from charge transfers, multiple C-H center dot center dot center dot p intermolecular interactions are also confirmed to play important roles both for the orientation of the C cage correlated with the preferential sites of the endohedral Nd atom and for the 2D-layered packing structures within the cocrystals. Density functional theory computations offered theoretical support for the molecular structures of Nd@C-82(I,II) isomers, the valence of the endohedral Nd atom (between II+ and III+), and the global ground state, i.e., the Nd@C-2v(9)-C-82 isomer in the quintet state.

Automated summary

Experimental studies on Nd-based metallofullerenes have been limited to spectroscopic characterizations. However, this work elucidated the molecular structures of Nd@C-82(I,II) isomers and their unique layered crystallographic packing structures based on X-ray structural analyses of cocrystals with decapyrrylcorannulene. The preferential site selection of the endohedral Nd atom and the important role of C-H···p interactions in determining the orientation of the C cage and 2D-layered packing structures were confirmed.