Numerous coordination complexes of 1,2-diaminoanthraquinone (aqLH2) with ruthenium and osmium were isolated, and their molecular structures were determined by X-ray crystallography. The NN-chelated aqLH2 is redox active and exists in three redox forms, 1,2-diamido-9,10-anthraquinone (aqLNN-AM 2–), 1,2-diimino-9,10-anthraquinone-semiquinonate anion radical (aqLNN-SQ•–), and 1,2-diimine-9,10-anthraquinone (aqLNN-Q 0). The NN-chelated aqLNN-SQ•– and NO-chelated 1-amido-2-amine-9,10-anthraquinone (aqLNO-AM H–) complexes of ruthenium(II) and osmium(II) of types trans-RuII(aqLNN-SQ•–)(PPh3)2(CO)Cl (1), trans-RuII(aqLNO-AM H–)(PPh3)2(CO)Cl (2), trans-RuII(aqLNN-Q 0)(PPh3)2Cl2 (3), trans-OsII(aqLNN-SQ•–)(PPh3)2(CO)Br (4), and trans-OsII(aqLNN-Q 0)(PPh3)2Br2 (5) were successfully isolated. Oxidation of 2 by an I2 solution affords a 1-aminyl-2-amino-9,10-anthraquinone (aqLNO-AR H•) complex of ruthenium(II), trans-RuII(aqLNO-AR H•)(PPh3)2(CO)Cl+ I3– (2+I3–). The electronic structures of the reported complexes were determined by X-ray bond parameters, X-band EPR spectral data, spectro-electrochemistry measurements, and DFT calculations. The investigation infers that the extent of mixing of d-orbitals with the π-orbitals of aqLH2 is more than that of the corresponding o-phenylenediamine (o-PD) derivatives. The notable observation is that the average C–N and C–C bond lengths of aqLNN-SQ•–, aqLNN-Q 0, and aqLNO-AM H– forms are closely similar, while these lengths of the corresponding forms of the o-PD derivatives are distinctly different.
Maji et al. (Fri,) studied this question.