COVALENTLY-BONDED ONION TYPE DOUBLE FULLERENIC CARBON CAGES

Three ''onion type'' double carbon cages (consisting of an inner sp(3) -hybridized C-60 buckminsterfullerene skeleton and an outer larger car bon cage with icosahedral symmetry, with covalent bonds between the ca rbon atoms of the 5-membered rings) are described and their strain ene rgies are discussed : (i) when the outer cage is a C-120 Ca derived fr om buckminsterfullerene by replacing each bond between two six-membere d rings by an acetylenic group, the strain is smallest; (ii) when the same derivation concerns each bond between 5- and 6-membered rings lea ding to a C-180 Outer cage, the strain is largest; (iii) when the oute r cage is C-180 With benzenoid rings, the strain is intermediate.