Pressure-Induced Donor–Acceptor Charge Transfer in a Fullerene Molecular Complex with Ferrocene

Abstract

The pressure-induced charge transfer in a molecular complex of fullerene with ferrocene, C60·{Fe2+(η5 -C5H5)2•}2, was studied by ab initio calculations, single-crystal X-ray diffraction analysis, and Raman spectroscopy at pressures up to 5.3 GPa. The calculations based on high-pressure crystal structure data, performed by the fragment molecular orbital method and hybrid density functional level chemistry, show a pressure-dependent partial ionization of the C60 and Fe2+(η5 -C5H5)2• molecules. At pressures up to 2 GPa, the calculated charges of the two molecules nearest to the C60 ferrocenes grow equally, while at P > 2 GPa, the transferred charges are clearly different. The unequal charge transfer is due to the different orientations of the two neighboring ferrocene molecules with respect to a fullerene molecule cage. The Raman spectra of the complex show a peculiarity near 2 GPa in the pressure dependence of the frequency and bandwidth of the ferrocene intramolecular breathing mode associated with unequal charge transfer.