The increase in the fullerene cage volume upon its chemical functionalization

The nuclear volume increase of the fullerene cage upon [2+1] and [1+1] has been studied in the series of C-60 cycloadducts C60Xn (X=O, NH, and CH2; n=1-30) and halogenides C(60)Hal(n) (Hal=F and Cl), respectively. As found, the cage volume increases linearly with the number of addends in the case of the [2+1]-adducts C60Xn due to the elongation of the 5.6 and 6.6 carbon-carbon bonds upon functionalization as compared with the bond lengths of intact C-60. As shown with the example of totally epoxidized derivatives of different fullerenes, the increase of the volume becomes more pronounced for higher fullerenes. The correlation between the fullerene cage volume and number of addends attached is quadratic for C-60 fluorides/chlorides and there are several structures with the volumes smaller than the correlation predicts. These falling values correspond to the structures containing aromatic rings (C60F18 (C-3v), isomeric C60F36 (C-1), C60F36 (C-3), C60F36 (T), and C60Cl30 (D-3d)). Sphericity and volume are inversely correlated within the sets of C60Fn and C60Cln with variable n and the correlation is direct within the series of isomeric halogenides (C60F36, C60F48, and C60Cl30).