Electronic structure, geometry, and stability of organic cations, dications, and donor-acceptor complexes

Abstract

Geometric, electronic, and energy characteristics of the complexes formed in the CF4 ·nAIF3 (n = I or 2) and CBr4 ·nAIBr3 (n = 1, 2, or 4) systems have been determined by the semiempirical AM I method. Besides the donor-acceptor complexes, the CBr3+...AIBr4−, CBr3+...Al2Br7−, CBr22+...(AlBr4−)2, and CBr22+...(Al2Br7−)2 ionic complexes can be formed in the CBr4 ·nAlBr3 systems. In the cations and dications of polyhalomethanes (when Hal = Cl, Br, or l) in both the free and bound (included in ionic complexes) states, carbon atoms carry negative charges, the C-Hal bonds are substantially shortened, and the positive charges are located on one-coordinate halogen atoms. These cations and dications can be considered as halenium ions that differ from halenium salts with dicoordinate halogen atoms. In the cationic and dicationic complexes of the CBr4 ·nAlBr3 systems, the maximum positive charges on the Br atoms are 0.39 and 0.94, respectively. Fluorine-containing cations and dications have structures similar to those of carbenium ions, whereas in the CF4 ·nAIF3 systems (n = l or 2), only donor-acceptor complexes are formed.