C 120 O 2 has been prepared, characterised by MALDI-TOF MS, UV-VIS, FTIR, and shown by 13 C NMR spectroscopy to have C 2v symmetry, the [60]fullerene cages being linked by adjacent furanoid rings; thus the structure has a connecting bridge containing a four-membered ring, reminiscent of that conjectured for the [2 + 2] fullerene cycloadduct.Recently, we described the preparation and characterisation of C 120 O, the first dimeric fullerene derivative. 1 The structure was subsequently confirmed. 2 As part of our ongoing interest in fullerene oxides, and the search for C 119 precursors, 3 we prepared and isolated C 120 O 2 by thermolysis of C 120 O. 4 Solid C 120 O was heated to 400 °C for 1 h at normal pressure in an Ar atmosphere. Under these conditions we observed (i) decay of C 120 O into C 60 (up to 60% with respect to the initial C 120 O), (ii) the formation of C 120 O 2 (ca. 15%) together with oligomeric oxides (C 60 ) n O m (n = 3-5; m = 3-9), and (iii) an insoluble uncharacterised residue (ca. 10%). 4 C 120 O 2 , isolated from the obtained mixture by a two-stage HPLC separation, † is a brown solid, stable under ambient conditions and in solution (HPLC analysis).The mass spectrum of C 120 O 2 [matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS, negative mode of ionisation, matrix 9-nitroanthracene] shows ( Fig. 1) the intense molecular ion peak at 1473.3 amu (calculated for C 120 O 2 , 1473.32 amu). Weak peaks at 720.2 and 736.6 amu indicate minor fragmentation of C 120 O 2 into C 60 and C 60 O; a similarly weak peak at 1489.8 amu (C 120 O 3 ) may indicate oxidation by the matrix under MALDI conditions.Our initial attempts to obtain a 13 C NMR spectrum failed due to the low solubility of the substance in CS 2 . To overcome this problem we produced enriched material with ca. 7% 13 C. ‡ The 13 C NMR spectrum is shown in Fig. 2 and consists of two lines in the sp 3 region and 27 in the sp 2 region (with three coincident peaks). § The number of lines, and their intensity distribution is consistent with a molecule of C 2v symmetry. The two groups of four equivalent sp 3 -hybridised carbon atoms indicate that each [60]fullerene cage is bis-linked by adjacent furanoid rings.Thus, the connecting bridge contains a four-membered ring. The four half-intensity sp 2 peaks are due to the carbons on one of the s v planes.The 13 C NMR data suggest two most likely structures, in both of which a four-membered ring is part of the linkage between the cages: in one, the two furanoid rings link the cages via 6,6 junctions as in the case of C 120 O 1 1, whereas the other structure involves 6,5 junctions for this purpose 2 (Fig. 3). Whilst structure 2 has a four-membered ring exactly analogous to that conjectured for photopolymerised fullerenes, 5 2 may be disputed on two grounds: (i) it contains unfavourable double bonds in pentagons 6 (calculated to destabilise by ca. 8.5 kcal mol 21 per double bond); 7 (ii) the structure is inappropriate to explain the position in the spectrum of the signals for the on-pla...
