Correlation of the Electronic and Geometric Structures in Mononuclear Copper(II) Superoxide Complexes

The geometry of mononuclear copper(II) superoxide complexes has been shown to determine their ground state where side-on bonding leads to a singlet ground state and end-on complexes have triplet ground states. In an apparent contrast to this trend, the recently synthesized (HIPT3tren)CuIIO2 •– (1) was proposed to have an end-on geometry and a singlet ground state. However, reexamination of 1 with resonance Raman, magnetic circular dichroism, and 2H NMR spectroscopies indicate that 1 is, in fact, an end-on superoxide species with a triplet ground state that results from the single CuIIO2 •– bonding interaction being weaker than the spin-pairing energy.