C-60 cyclized hook-and-ladder carbynes

In 1992, Walba, Zheng, and Schilling synthesized and discussed the first st ructure of cyclized hook-and-ladder topological type [J. Am. Chem. Sec., 11 4 (1992) 6259-6260]. Here, the structure and stability of C-60 hook carbyne s, i.e., carbynes of the hook-and-ladder type, have been estimated by semi- empirical and ab initio calculations. Such a hookcarbyne may be a product o f cycloaddition of two unlinked or linked cyclic carbynes or two segments i n knotted carbynes and, as a result, a bicyclic structure or its topologica l isomer with crossings can be formed. Several topological types of hookcar bynes from zero to four crossings are considered here. For each C-60 hookca rbyne topological type, we examined the energy changes evaluated with the c omponents size varying in the series (C60-2nC2n), where 20 greater than or equal to n greater than or equal to 5, which exhibit one to several minima. The energy is shown to be related to the number of crossings and to the st ructure type. For the simplest unknotted bicyclic structure (0(1)(2), zero crossings, two cycles, structure type 1), the lowest energy structure is bu ilt from two cyclic carbynes of the same size. For the one-crossing hookcar bynes there exist three conformers: the conformer "out" with cycles outside to each other, the confirmer "in" with one cycle entirely inside the other cycle, and the "letter Q" conformer when the cycle sizes in conformer "in" are interchanged and the larger cycle has not enough room inside smaller c ycle. For one out of two types of two-crossing C-60 hookcarbynes, two confo rmers are observed: one with two minimum energy structures composed of the C-26 and C-34 cycles and other with a single minimum built from two C-30 mo lecules. For the three- and four-crossing C-60 hookcarbynes the isomers hav e at least two minimum energy structures and usually a local maximum for th e C30C30 molecule. (C) 2000 John Wiley & Sons, Inc.