Synthesis, structural characterization, fluorescence properties, and DFT calculations of a novel hetero-hexanuclear [Cu^II₄Gd^III₂] bis(salamo)-like complex involving bidentate chelating and bridging nitrate groups

A novel hetero-hexanuclear [Cu^II₄Gd^III₂] complex with a symmetrical bis(salamo)-like tetraoxime ligand (H₄L), [{Cu₂(L)(MeOH)Gd(NO₃)₂(<i>μ</i>₂-NO₃)}₂]·2CH₃OH was obtained after careful design and synthesis. The structure of the [Cu^II₄Gd^III₂] complex was adequately characterized by elemental analysis, FTIR, and UV–vis spectroscopy. The [Cu^II₄Gd^III₂] complex crystallized in the monoclinic system, space group <i>C2/c</i> embraces four Cu^II ions with two coordination geometries: tetragonal pyramid and octahedron, two Gd^III ions with nine coordinated tricapped trigonal prism geometry, two completely deprotonated octadentate (L)^4– units, two coordinated methanol molecules, two bidentate bridging nitrate groups (<i>μ</i>₂-NO₃^–), four bidentate chelating nitrate groups and two crystallized methanol molecules. The [Cu^II₄Gd^III₂] complex ultimately constructs infinite 2D and 3D supramolecular structures via the intermolecular hydrogen bond interactions. Meanwhile, the fluorescence properties of the ligand (H₄L) and its [Cu^II₄Gd^III₂] complex were studied. The electronic structure and stability of the [Cu^II₄Gd^III₂] complex were proved by density functional theory calculation.