Direct relationship between intermolecular charge-transfer and charge-resonance complexes via structural changes in the arene donor with various pi-acceptors
P. Le Magueres et al., Direct relationship between intermolecular charge-transfer and charge-resonance complexes via structural changes in the arene donor with various pi-acceptors, J CHEM S P2, (7), 2001, pp. 1180-1185
Citations number
37
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
Aromatic donors (D) spontaneously form a series of colored intermolecular c
harge-resonance (CR) complexes with their cation radicals (D+.) as well as
charge-transfer (CT) complexes with various pi -acceptors (A). Spectroscopi
c changes during the formation of these CR and CT complexes are both includ
ed in a single Mulliken plot of E-CR,E-CT versus E-ox(o)-E-red(o). Precise
X-ray crystallographic studies now reveal almost identical structural featu
res of the CR and CT complexes, especially with a prototypical strong elect
ron donor such as octamethylbiphenylene (OMB). Whereas most weaker donors d
o not show perceptible alterations of their molecular geometry during compl
ex formation, OMB exhibits pronounced bond elongation/contraction of almost
2 pm both in its CT complexes with strong acceptors (TCNE and TCNQ) and in
its CR complex (OMB2)(+.). In both cases, the structural changes lie midwa
y between geometries of the neutral OMB donor and its fully oxidized cation
radical OMB+.. The CT and CR complexes of OMB in the solid state also show
similar crystal packing features that maintain interplanar separations as
short as 3.1-3.2 Angstrom with significant distortion (similar to6 degrees)
from planar molecular geometry. Together with the similar values of K-CR=3
50 M-1 and K-EDA=440-490 M-1, we acknowledge the common nature of the CT an
d CR complexes through an orbital consideration (Chart 1) that recognizes t
he antibonding component in CR complex formation.