Abstract
A precursor compound of a dioxygen adduct, [CuII2(Sp)2(µ-OH)2](ClO4)2·CH2Cl2 (Sp = (-)-sparteine) (1·(ClO4)2·CH2Cl2), has been investigated by X-ray structural analysis, magnetic measurement, and molecular orbital calculations. The crystal structure of 1·(ClO4)2·CH2Cl2 showed that the coordination structure is spirally twisted and both of the two edged CuN2 planes with ligating nitrogen atoms of Sp are almost orthogonally crossed, the dihedral angle being 84°. The magnetic susceptibility measurement of 1·(ClO4)2·CH2Cl2 showed an ineffective antiferromagnetic coupling interaction between the two copper(II) centers (2J = -260 cm-1). The density functional theory (DFT) calculation confirmed that the spirally twisted coordination of Sp-nitrogen atoms in 1 contributed to a decrease in energy gap between the two singly occupied molecular orbitals (SOMOs), making the magnitude of antiferromagnetic coupling smaller.