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

A diamagnetic complex, {(cis-indigo-N,N)2-(Cp*IrIII)} (1), in which deprotonated cis-indigo dianions coordinate an iridium center through two nitrogen atoms was obtained. By employment of the ability of the iridium center in 1 to coordinate an additional ligand, the complex [(Bu4N+)2{[SnII(Pc•3-)](cis-indigo-N,N)2-Cp*IrIII}•-2·0.5(H2Indigo)·2.5C6H4Cl2 (2), which has two functional ligands coordinating an IrIII center, was obtained. This complex has a magnetic moment of 1.71 μB at 300 K, in accordance with an S = 1/2 spin state. The spin density is mainly delocalized over the Pc•3- macrocycle and partially on (cis-indigo-N,N)2-. Due to an effective π-π interaction, a thermally activated charge transfer from [SnII(Pc•3-)]•- to (cis-indigo-N,N)2- is observed, with an estimated Gibbs energy (-ΔG°) of 9.27 ± 0.18 kJ/mol. The deprotonation of indigo associated with the coordination of IrIII by the indigo releases H+ ions, which protonate noncoordinating indigo molecules to produce leuco cis-indigo (H2Indigo). One H2indigo links two (cis-indigo-N,N)2- dianions in 2 to produce strong N-H···O═C and O-H···O═C hydrogen-bonding interactions.