Interactions of 1-hydroxyanthraquinone (1-HAQ) and 1,4- and 1,8-dihydroxyanthraquinone (1,4-DHAQ, 1,8-DHAQ) with Co2+ and Cu2+ have been examined by UV-visible and EPR spectroscopies. These hydroxyanthraquinones form high-spin complexes with Co2+. It has been estimated that these Co2+ complexes in dichloromethane and ethanol have a tetragonal coordination structure, while in dimethlyformamide (DMF) or in mixed solvents containing DMF the complex having a tetrahedral structure is simultaneously formed. 1-HAQ forms the ML and ML2 type complexes with Cu2+, their relative concentration depending on the ligand to metal mole ratio, R, in solution. 1,4-DHAQ forms also the ML2 type complex with Cu2+, but the ML-type mononuclear Cu2+ complex was not directly detected by EPR, though 1,4-DHAQ was estimated to form a polymer-type complex with Cu2+ having metal-ligand ratio of ~ 1:1. For the case of 1,8-DHAQ, the formation of S = 1 M2L2-type dinuclear complex was observed, in addition to the formation of ML- and ML2-type complexes. The ML2-type Cu2+ complexes of 1,4- and 1,8-DHAQ were found to have two forms, the cis and trans configurations. These properties for metal complex formation of the hydroxyanthraquinones are compared with those of adriamycin, which has a similar anthraquinone structure in the molecule.
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