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

Abstract

A novel hetero-hexanuclear [Cu^II₄Gd^III₂] complex with a symmetrical bis(salamo)-like tetraoxime ligand (H₄L), [{Cu₂(L)(MeOH)Gd(NO₃)₂(μ₂-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 C2/c 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 (μ₂-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.

Keywords:

• Synthesis
• hetero-hexanuclear complex
• bis(salamo)-like tetraoxime ligand
• fluorescence property
• DFT calculation

Additional information

Funding

This research was funded by the National Natural Science Foundation of China (grant no. 21761018), the Science and Technology Program of Gansu Province (grant no. 18YF1GA057) and the Program for Excellent Team of Scientific Research in Lanzhou Jiaotong University (grant no. 201706)