Novel sigma-delocalized aromatic compounds: An X-ray crystal structure of hexaiodobenzene dication and synthesis of related species

Miscellaneous · Fri Jan 01 00:00:00 EST 1993

OSTI ID:6980892

Patel, M K

Structures of benzene and substituted benzene dications continue to attract great interest from chemists; removal of two electrons from the planar, aromatic [pi]-system leads to a very unstable four electron antiaromatic dication, which usually results in a highly distorted geometry. An X-ray crystal structure of hexaiodobenzene dication ditriflate revealed a planar and symmetric [C[sub 6]I[sub 6]][sup 2+] moiety, a structure that is consistent with the earlier hypothesis that the two plus charges are dispersed over the six iodines via a delocalized sigma bond between a pair of adjacent iodine atoms, overall involving ten electrons of Hueckel 4n + 2 number. Magnetic circular dichroism analysis of the strong near IR absorption of [C[sub 6]I[sub 6]][sup 2+] [CF[sub 3]SO[sub 3][sup [minus]]][sup 2], attributed to the [sigma]-HOMO [yields] [sigma]-LUMO electronic transition, is consistent with a ten-electron [sigma]-delocalized aromatic species. An AM1 calculation on bromopentaiodobenzene showed the HOMO to be a completely anti-bonding, non-degenerate orbital of [sigma]-type; the [C[sub 6]I[sub 5]Br][sup 2+] [CF[sub 3]SO[sub 3][sup [minus]]][sub 2] species also demonstrated strong near IR absorption. Interpretation of the X-ray crystal structure and NMR ([sup 19]F, [sup 13]C and [sup 77]Se) of related neutral C[sub 6]F[sub 5]SeC[sub 6]I[sub 5] species revealed tendencies toward stabilization of the non-degenerate HOMO, which would show anti-bonding [sigma]-type interactions between each pair of adjacent iodines and selenium. Near IR and [sup 19]F NMR of [C[sub 6]F[sub 5]SeC[sub 6]I[sub 5]][sup 2+] [CR[sub 3]SO[sub 3][sup [minus]]][sup 2] are consistent with a ten-electron [sigma]-delocalized aromatic species.

• Research Organization: Vanderbilt Univ., Nashville, TN (United States)
• OSTI ID: 6980892
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
IODINATED AROMATIC HYDROCARBONS
CRYSTAL STRUCTURE
SELENIUM COMPOUNDS
BROMINATED AROMATIC HYDROCARBONS
CHEMICAL PREPARATION
ELECTRONIC STRUCTURE
FLUORINATED AROMATIC HYDROCARBONS
TELLURIUM COMPOUNDS
AROMATICS
HALOGENATED AROMATIC HYDROCARBONS
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
SYNTHESIS
400201* - Chemical & Physicochemical Properties