Loading of a Phenanthroline-Based Platinum(II) Complex onto the Surface of a Carbon Nanotube via pi-pi Stacking

Stacking of the metal complex [(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)](2+) (56MESS) onto the surface of two different fullerenes, a carbon nanotube (CNT), and a C-60-buckyball was examined. The metal complex forms a supramolecular complex with multi-walled CNTs but not with buckyballs. Binding of 56MESS to the CNTs is highly efficient (90%) but can be further stabilized by the addition of the surfactant, pluronic F-127, which resulted in a loading efficiency of 95%. Molecular modelling shows that binding of 56MESS to the CNT is supported by the large surface area of the fullerene, whereas the more pronounced curvature and lack of a flat surface on the buckyball affects the ability of 56MESS to form bonds to its surface. The loading of 56MESS onto the CNT is via pi-pi stacking from the metal complex phenanthroline ligand and C-H center dot center dot center dot pi bonding from the diaminocyclohexane ligand. 56MESS has 13 critical bonding points with the CNT, eight of which are pi-pi stacking bonds, but the metal complex forms only seven bonds with the buckyball. In addition, the loading of 56MESS onto the CNT results in a charge transfer of -0.111 eV; however, charge transfer is almost negligible for binding to the buckyball.