Magnetic ordering in ${\mathrm{C}}_{60}$ polymers with partially broken intermolecular bonds

The possibility of formation of radical centers in a hexagonal ${\mathrm{C}}_{60}$ polymeric layer, without damage to the fullerene cages, is shown. The geometry optimization of ${\mathrm{C}}_{60}$ trimers and tetramers using the semiempirical AM1 method has revealed that linking of molecules through a single bond is preferred for multiplet states of system. The density of unpaired electrons is mainly localized in the vicinity of the single bonds producing narrow energy bands near the Fermi level of hexagonal ${\mathrm{C}}_{60}$ polymers. The magnetic state of the polymer depends on the number and location of single bonds in a polymeric layer.

Figure 1

Molecular clusters of polymerized ${\mathrm{C}}_{60}$ with broken bonds between ${\mathrm{A}}^{\prime }$ and ${\mathrm{B}}^{\prime }$ atoms and ${\mathrm{C}}^{\prime }$ and ${\mathrm{D}}^{\prime }$ atoms. (a) Trimer ${\mathrm{C}}_{60}$ (structure I) with two singly bonded molecules, (b) tetramer ${\mathrm{C}}_{60}$ (structure II) incorporates three adjacent molecules involved in single bonding, and (c) tetramer ${\mathrm{C}}_{60}$ (structure III) links two pairs of singly bonded molecules.

Figure 2

Schematic representation of electronic density distribution for the two highest occupied molecular orbitals of ${\mathrm{C}}_{60}$ trimer in triplet state.

Figure 3

Fragments of hexagonal polymerized ${\mathrm{C}}_{60}$ layers I–III. Unit cells are highlighted.

Figure 4

Band structure of polymerized ${\mathrm{C}}_{60}$ layers: (a) hexagonal layer with standard intermolecular bonding; (b)–(d) model layers I, II, and III, respectively. The flattened upper occupied bands in the electronic structure of layers I–III are highlighted.

Figure 5

Schematic representation of the upper occupied crystal orbital in the center of Brillouin zone of layer I (a), layer II (b), and layer (c). Fragments corresponding to the unit cells of polymerized layers are shown.