cis-Conformation of indigo in the coordination complex (indigo-O,O)(Cp*CrIICl)

Abstract

The interaction of decamethylchromocene (Cp*₂Cr) with indigo in the presence of a Cl⁻ source yields the coordination complex (indigo-O,O)(Cp*Cr^IICl) (1) in which one Cp* ligand at chromium is substituted by indigo. Indigo adopts an unusual cis-conformation in 1, allowing the coordination of both indigo carbonyl groups to one Cr^II center. Complex 1 contains Cr^II with an S = 1 spin state and indigo⁰. At the same time, calculations show that an excited ionic state is positioned close to the neutral ground state, providing the appearance of intense low-energy NIR bands in the spectrum of 1 at 820 and 1002 nm attributed to metal-to-ligand charge transfer.