First crystal structure determination and high-frequency EPR study of an organoarsanecopper radical complex

The red radical complex {(μ-bptz)[Cu(AsPh3)2]2}(BF4) 1, bptz=3,6-bis(2-pyridyl)-1,2,4,5-tetrazine, was obtained as a stable species and characterized by X-ray crystallography, spectroelectrochemistry and EPR at 9.5 and 285 GHz. Comparison with the previously reported {(μ-bptz)[Cu(PPh3)2]2}(BF4) 2 reveals longer Cu-element bonds by about 0.1 Å but otherwise a similar “organic sandwich” structure involving intramolecular π(phenyl)–π(tetrazine)–π(phenyl) interactions, a 3+1 coordination at the copper(I) centers, and averaged tetrazine intraring bond distances. Reversible oxidation to a blue dication with an intense MLCT band at 650 nm occurs at −0.24 V vs. Fc+/o. EPR studies show the effect of the higher spin–orbit coupling constant of the As vs. P atoms through slightly larger g anisotropy as determined through high frequency measurements.