Spectroscopic and theoretical studies of oxygenated dicopper(I) complexes containing hydrocarbon-linked bis[2-(2-pyridyl)ethyl]amine units: Investigation of a butterfly [Cu-2(mu-eta(2):eta(2))(O-2)](2+) core
E. Pidcock et al., Spectroscopic and theoretical studies of oxygenated dicopper(I) complexes containing hydrocarbon-linked bis[2-(2-pyridyl)ethyl]amine units: Investigation of a butterfly [Cu-2(mu-eta(2):eta(2))(O-2)](2+) core, J AM CHEM S, 121(6), 1999, pp. 1299-1308
A series of side-on peroxide-bridged binuclear copper complexes [CU2(NnPY2)
(O-2)](2+) (where n = 3-5), which have been proposed to adopt a butterfly C
u2O2 geometry due to the constraints placed on the Cu-Cu distance by the al
kyl chain linker of length -(CH2)(n)- have been studied using absorption an
d resonance Raman spectroscopy and theoretical techniques. The four compone
nts of the peroxide to copper(II) charge-transfer transitions have been ide
ntified for the first time in the [Cu-2(NnPY2)(O-2)](2+) (where n = 3-5) co
mplexes. The observed shift of the peroxide O-O stretch by 25 cm(-1) to hig
her energy and the changes observed in the energy and intensity of absorpti
on bands including the presence of an additional band at 23 800-20 400 cm(-
1) (420-490 nm) (not seen in planar Side-on peroxide-bridged dicopper cores
) are correlated to the butterfly structure using transition dipole vector
coupling and valence bond configuration interaction models. The identificat
ion of an absorption band at 23 800-20 400 cm(-1) (420-490 nm) associated w
ith the butterfly side-on peroxide-bridged dicopper core is important since
the isomeric, bis(mu-oxo) core is also characterized by an absorption band
in this region. The changes in bonding associated with a butterfly distort
ion of the Cu2O2 core are defined, and the reactivity of the butterfly core
with respect to electrophilic aromatic substitution and H atom abstraction
reactions is compared with that of the planar side-on peroxide-bridged dic
opper core using the frontier molecular orbital description.