Theoretical Investigation on the Complexation and Decomplexation of (He@C₆₀)

The quantum-chemical method EHMO/ ASED is used to theoretically investigate the complexation and dccomplexation of （He@C₆₀）. Four possible paths are studied as follows:（1） He penetrates the C₆₀ cage through the center or pentagon（C₅）; （2） He penetrates the C₆₀ cage through the center of hexagon （C₃）; （3） He penetrates the C₆₀ cage through the center of short bond （C₂）; （4） He penetrates the C₆₀ cage through the center of long bond （Cs）. It is postulated that while He approaches and penetrates the C₆₀ cage, the pentagon or hexagon or short bond or long bond will be extended along its plane and will form a window （rcf. Fig. l）. Itis given that the probability through path （2） is larger than that througll path （l）, which is inagreement with other works. The probability through path （4） is the largest, when the planar extension forming a window is 0.4Å which is the optimized value （re f. Fig.2）. During the reaction,the symmetry of system I_h will be destroyed as He deviates the coenter or C₆₀ cage and is not atinfinity. At this case, the degeneracy of the frontier molecular orbitals will be reduced, althoughthe splitting is not large since the energy or He（ls） is much lower than the frontier orbitals of C₆₀ （ref. Table 1）. Obviously, the charge distribution in C₆₀ is different when He is at different POsitions. Since He and C have different electronegativities, the electrons originally belonging to He will partially transfer to C₆₀. But when He is at the center of C₆₀ or at infinity, He and 60 C's of C₆₀ all are electroneutrality within the calculated precision because or the long distance between He and C. When He deviates the center and approaches the C₆₀ cage, along the longitude corresponding to the symmetry axes, there will be a charge distribution on 60 C's with changing in size and even in plus-minus sign, of which the absolute value is gradually decrease （ref. Table 2）. This is similar to the charge transfer on carbons in straight-chain-conjugated polyene. This is very interesting to see that the charges on C's being nearest to He arc positive although these C's obtain the electrons from He. The reason is that thest C's obtain a few of electrons from He and then lose a lot of electrons to next C's.