A study of solid [{Cu(MePY2)}(2)O-2](2+) using resonance Raman and X-ray absorption spectroscopies: An intermediate Cu2O2 core structure or a solid solution?
E. Pidcock et al., A study of solid [{Cu(MePY2)}(2)O-2](2+) using resonance Raman and X-ray absorption spectroscopies: An intermediate Cu2O2 core structure or a solid solution?, J AM CHEM S, 121(9), 1999, pp. 1870-1878
Solid [{Cu(MePY2)}(2)O-2](2+) is spectroscopically characterized using reso
nance Raman and X-ray absorption spectroscopy, for which the former techniq
ue probes the nature of the O-O bond and the latter defines the Cu-Cu inter
action. In contrast to the crystal structure obtained for [{Cu(MePY2)}(2)O-
2](2+), which shows an "intermediate" Cu2O2 core (Cu-Cu = 3.3 Angstrom and
O-O = 1.6 Angstrom), resonance Raman peaks characteristic of both a side-on
peroxide-bridged dicopper(II) core and bis-mu-oxo dicopper(III) core are o
bserved. The bis-mu-oxo isomer is estimated to be present at approximately
5-20%. A good fit is obtained for EXAFS data for solid [{Cu(MePY2)}(2)O-2](
2+) using an 80:20 ratio of Cu-Cu separations of 3.6 Angstrom (characterist
ic of a side-on peroxide-bridged copper core) and 2.8 Angstrom (associated
with a bis-mu-oxo dicopper core). Analysis of the edge region places an upp
er limit on the amount of bis-mu-oxo isomer present in the solid at 40%. Th
e factors governing the presence of bis-mu-oxo and/or side-on peroxide core
s in solution for differing ligand systems are considered, and the contribu
tion of the bite angle of the equatorial nitrogen atom donors is explored.
The reactivity of [{Cu(MePY2)}(2)O-2](2+) in solution is correlated with th
e presence of the bis-mu-oxo core, using frontier molecular orbital theory.