Abstract
The geometric and electronic structures of two mononuclear CuO
2
complexes [Cu(O
2
){HB(3-Ad-5-
i
Prpz)
3
}] (
1
) and [Cu(O
2
)(
β
-diketiminate)] (
2
) have been evaluated using Cu K- and L- edge X-ray absorption spectroscopy studies in combination with valence bond configuration interaction (VBCI) simulations and spin unrestricted broken symmetry density functional theory (DFT) calculations. Cu K- and L-edge XAS data indicate the Cu(II) and Cu(III) nature of
1
and
2
, respectively. Total integrated intensity under the L-edges show that the
ψ
L
U
M
O
∗
’s in
1
and
2
contain 20% and 28% Cu character, respectively, which are indicative of very covalent ground states in both complexes, although more so in
1
. Two state VBCI simulations also indicate that the ground state in
2
has more Cu (|3
d
8
〉) character. DFT calculations show that the
ψ
L
U
M
O
∗
in both complexes is dominated by O
2
n-
character, although the O
2
n-
character is higher in
1
. It is shown that the ligand L plays an important role in modulating Cu-O
2
bonding in these LCuO
2
systems and tunes the ground states of
1
and
2
to have dominant Cu(II)-superoxide like and Cu(III)-peroxide like character, respectively. Ligand field and
Q
M
o
l
M
(charge on the absorbing atom in the molecule) contributions to L- and K-edge energy shifts are evaluated using DFT and TD-DFT calculations. It is found that the ligand field makes a dominant contribution to the edge energy shift, while the effect of
Q
M
o
l
M
is minor. The charge on the Cu in the Cu(III) complex is found to be similar to that in Cu(II) complexes, which indicates a much stronger interaction with the ligand leading to extensive charge transfer.