Abstract
Two tridentate imine–oxime–amine ligands HL
1 and HL
2 and their corresponding Cu
II complexes were synthesized. These complexes are readily oxidized to give diamagnetic d
8Cu
III complexes.
Two tridentate imine–oxime–amine ligands have been synthesized and their corresponding copper(II) complexes have been isolated. These copper(II) complexes are readily oxidized both chemically and electrochemically to give relatively stable copper(III) complexes. In the pH range 1.5–3.0 the electron transfer process is electrochemically reversible with Δ
E
p
=
60
mV and
i
pa/
i
pc
∼
1. Plots of
E
1/2 versus pH are linear with a slope
=
−60 indicating the involvement of one proton in the electron transfer process. Aqueous solutions of copper(III) complexes have high molar absorption at
λ
max with
ε
>
10
4
M
−1
cm
−1. Solid samples of the complexes are diamagnetic consistent with a d
8 square planar geometry. It seems that only imine–oxime nitrogens are coordinated to copper(II) with the NH
2 group being free as indicated by i.r. spectra. Substitution of a –CH
3 group on the carbon atom adjacent to the oxime group by the more electron donating group –CH(CH
3)
2 lowers electrode potential by more than 90
mV. This is consistent with an earlier observation that electron-donating substituents on the carbon atom adjacent to the oxime group lower the potential of Cu
III/Cu
II couples and stabilize the higher oxidation state.