Theoretical study on the structure and stability of the clusters of tropylium ion solvated by methanol molecules

Density functional theory (DFT) B3LYP calculations characterize the structu re and stability of the clusters of tropylium ion (Tr+) coordinated by meth anol molecules Tr+(MeOH)(n) with n = 1-7. Methanol molecules are bound toge ther through strong O-H . . .O type hydrogen bonds, resulting in a cyclic s tructure when n greater than or equal to 3, and the methanol cluster thus f ormed coordinates to Tr+ through weak C-H . . .O type hydrogen bonds. Thus, the formation of the Tr+(MeOH)(n) clusters is mediated by two kinds of hyd rogen bonds. Calculated distances of the O-H . . .O hydrogen bonds lie in t he range 1.570-1.991 Angstrom (1.712 Angstrom in average) while those of th e C-H . . .O hydrogen bonds lie in the range 2.083-2.319 Angstrom (2.160 An gstrom in average). Mass spectroscopic experiments demonstrated that Tr-(Me OH)(4) is a dominant, magic-numbered species and that Tr+(MeOH)(3) and Tr+( MeOH)(5) are minor [Chemical Communication, (2001) in press]. The experimen tal result is analyzed from the viewpoint of energetics. The specific size effect on the stability of Tr+(MeOH)(n) is a direct consequence of the stab ility of the (MeOH)(n) fragment itself. (C) 2001 Elsevier Science B.V. All rights reserved.