X-ray diffraction and Raman study of pressure-assisted photopolymerization in the ferrocene-doped C 60 crystals

The pressure-assisted photopolymerization in the fullerene complex with ferrocene C 60 · {Fe(C 5 H 5 ) 2 } 2 was studied for the first time by simultaneous in-situ Raman and X-ray diffraction (XRD) techniques at pressures up to 8 GPa. The irreversible splitting of the A g (2) mode in the Raman spectra, resembling pristine fullerene polymerization, was observed at 4.6 GPa. The structural analysis does not show the formation of covalent bonds between adjacent fullerene molecules at a pressure up to 5 GPa. The unit cell volume and interfullerene distances are smooth and monotonous functions of pressure, and the shortest interfullerene distance 9.4 Å at 5 GPa significantly exceeds 9.06 Å typical of fullerene polymers. The changes in the Raman spectra at 4.6 GPa grow with the laser power and exposure time, showing typical photopolymerization phenomena. The distance between ferrocene and fullerene molecules decreases linearly with pressure changing the slope at 2 GPa due to intermolecular interaction crossover. The length of a ferrocene molecule in the complex increases with pressure in contrast to its decrease in a pristine ferrocene crystal. This behavior is associated with a change in the charge state of an iron atom and indicates a charge transfer from ferrocene to fullerene molecules.