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 [Cu-2(L)Ce(NO3)(3)] and [{Cu-2(L)Y(NO3)(2)(mu-AcO)}{Cu-2(L)Y(NO3)(2)(mu-NO3)(CH3OH)}]center dot 4CH(3)OH, were synthesized through the reaction of a newly synthesized bis(salamo)-based ligand (H4L), Cu(OAc)(2)center dot H2O and Ln(NO3)(3)center dot 6H(2)O (Ln = Ce and Y), respectively. Single crystal structure analyses showed that the [(Cu2CeIII)-Ce-II] and [(Cu4Y2III)-Y-II] complexes contained similar trinuclear [Cu(2)(II)Ln(III)] structures. The difference was that the [(Cu4Y2III)-Y-II] 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 [(Cu2CeIII)-Ce-II] complex showed catecholase activity and benzoxazinone synthase activity under normal temperature and aerobic conditions. For catecholase activity, the calculated K-cat of the [(Cu2CeIII)-Ce-II] complex was 346.5 h(-1), and the K-cat of p-benzoxazinone synthase activity was 9.73 h(-1). Compared with the [(Cu4Y2III)-Y-II] complex, we speculated that the main reason for the high catalytic function of the [(Cu2CeIII)-Ce-II] complex is the presence of three nitrate groups coordinated with the central Ce-III atom. Evidence from mass spectrometry and cyclic voltammetry curves indicated that there may be heterometallic cooperation, in which Ce-III binds to the substrate, while the metallic copper transformed between Cu-II and Cu-I 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.