Far infrared spectroscopy and other spectral and thermal properties of [Li@C60]PF6

The endohedral fullerene [Li@C60]+PF6− was characterized by differential scanning calorimetry (DSC), by electronic absorption spectroscopy in the spectral range from 195 to 800 nm and by FT-IR and far-infrared spectroscopy. [Li@C60]+PF6− shows a sharp melting point with the onset at 86 °C and peak at 90 °C and melting enthalpy of 9.5 kJ/mol. The electronic absorption spectrum of [Li@C60]+PF6− in the UV shows both a hypsochromic shift and a hyperchromic effect with respect to the corresponding electronic transitions of C60. In the mid-infrared spectrum [Li@C60]+ cation displays the typical four band pattern of C60, with small shifts. The far-infrared spectroscopy appears to be the most effective diagnostic tool to distinguish between C60 and endohedral fullerenes like [Li@C60]+. In fact, while C60 does not show any far-infrared vibration, [Li@C60]+PF6− shows four far-infrared bands. Also in an astrochemical perspective the search of endohedral fullerenes must rely mainly on the far-infrared spectral region.