An insight into the molecular structures, theoretical calculation and catalytic activities of novel heterotrinuclear [CuII2CeIII] and heterohexanuclear [CuII4YIII2] bis(salamo)-based complexes

Two heteropolynuclear complexes, namely [Cu2(L)Ce(NO3)3] and [{Cu2(L)Y(NO3)2(μ-AcO)}{Cu2(L)Y(NO3)2(μ-NO3)(CH3OH)}]·4CH3OH, were synthesized through the reaction of a newly synthesized bis(salamo)-based ligand (H4L), Cu(OAc)2·H2O and Ln(NO3)3·6H2O (Ln = Ce and Y), respectively. Single crystal structure analyses showed that the [CuII2CeIII] and [CuII4YIII2] complexes contained similar trinuclear [CuII2LnIII] structures. The difference was that the [CuII4YIII2] complex consisted of two crystallographically independent and chemically different trinuclear complexes with coordination and free solvent molecules. Among the two heteropolynuclear metal complexes, only the [CuII2CeIII] complex showed catecholase activity and benzoxazinone synthase activity under normal temperature and aerobic conditions. For catecholase activity, the calculated Kcat of the [CuII2CeIII] complex was 346.5 h−1, and the Kcat of p-benzoxazinone synthase activity was 9.73 h−1. Compared with the [CuII4YIII2] complex, we speculated that the main reason for the high catalytic function of the [CuII2CeIII] complex is the presence of three nitrate groups coordinated with the central CeIII atom. Evidence from mass spectrometry and cyclic voltammetry curves indicated that there may be heterometallic cooperation, in which CeIII binds to the substrate, while the metallic copper transformed between CuII and CuI through redox reactions. In addition, the catalytic mechanism was inferred through electrospray mass spectrometry and cyclic voltammetry, and fluorescence properties were studied and Hirshfeld surface analyses were also conducted. [ABSTRACT FROM AUTHOR]