Interligand Charge Transfer in a Complex of Deprotonated <i>cis</i>-Indigo Dianions and Tin(II) Phthalocyanine Radical Anions with Cp*Ir^III

A diamagnetic complex, {(<i>cis</i>-indigo-<i>N</i>,<i>N</i>)^2–(Cp*Ir^III)} (<b>1</b>), in which deprotonated <i>cis</i>-indigo dianions coordinate an iridium center through two nitrogen atoms was obtained. By employment of the ability of the iridium center in <b>1</b> to coordinate an additional ligand, the complex [(Bu₄N⁺)₂{[Sn^II(Pc^•3–)]­(<i>cis</i>-indigo-<i>N</i>,<i>N</i>)^2–Cp*Ir^III}^•–₂·0.5­(H₂Indigo)·2.5C₆H₄C_l2 (<b>2</b>), which has two functional ligands coordinating an Ir^III center, was obtained. This complex has a magnetic moment of 1.71 μ_B at 300 K, in accordance with an <i>S</i> = 1/2 spin state. The spin density is mainly delocalized over the Pc^•3– macrocycle and partially on (<i>cis</i>-indigo-<i>N</i>,<i>N</i>)^2–. Due to an effective π–π interaction, a thermally activated charge transfer from [Sn^II(Pc^•3–)]^•– to (<i>cis</i>-indigo-<i>N</i>,<i>N</i>)^2– is observed, with an estimated Gibbs energy (−Δ<i>G</i>°) of 9.27 ± 0.18 kJ/mol. The deprotonation of indigo associated with the coordination of Ir^III by the indigo releases H⁺ ions, which protonate noncoordinating indigo molecules to produce leuco <i>cis</i>-indigo (H₂Indigo). One H₂indigo links two (<i>cis</i>-indigo-<i>N</i>,<i>N</i>)^2– dianions in <b>2</b> to produce strong N–H···OC and O–H···OC hydrogen-bonding interactions