On the C-60 carbyne links (from 2(1)(2) to 6(3)(2))

The structure and stability of catecarbynes, i.e., nonlinear C-60 carbynes of the link (catenane) type, have been established by ab initio calculation s. For each C-60 catecarbyne topological type examined, the energy changes evaluated with the components size varying in the series (C60-2nC2n), where 20 greater than or equal to n greater than or equal to 5, which exhibit on e to several minima, have been shown to depend on the number of crossings a nd structure type. For the 2(1)(2) C-60 catecarbyne, the lowest structure i s built from two cyclic carbynes of the same size but, for the 4(1)(2) C-60 catecarbyne, the two minimum energy structures are those composed of the C -24 and C-36 cycles and the 4(1)(2) C30C30 molecule is the local maximum st ructure. For the 5(1)(2) C-60 catecarbyne, the minimum energy structure is constructed from the C-20 and C-40 cycles and the local maximum structure i s formed when the first and the second cycles have 42 and 18 C atoms, respe ctively. The six-crossings catecarbynes (6(1)(2), 6(2)(2), and 6(2)(3)) exh ibit an even more complex behavior. Such relationships show that, for the s ame topological catenane type with several crossings, some structures may b e more stable by several hundreds of kilocalories/mole than others. (C) 199 9 John Wiley & Sons, Inc.