Synthesis, structure, theoretical studies, and properties of dinuclear Cu(II) and novel trinuclear Co(II) complexes with a more flexible 3-MeOsalamo-like ligand

•A novel three-bridged trinuclear [{Co3(L)2(µ3OAc)2}2] complex with acetate was constructed.•Fluorescence properties of the ligand and its complexes were studied.•A series of theoretical calculations of the ligand and its complexes were investigated.•The softness of the complexes was proposed and energy gaps were analyzed by DFT calculation.•Quantitative analyses of intermolecular interactions in the crystalline structures were performed by Hirshfeld surfaces analysis. A more flexible 3-methoxysalamo-like ligand H2L and its dinuclear Cu(II) complex [Cu2(L)(NO3)2] (1) and novel trinuclear Co(II) complex [{Co3(L)2(µ3OAc)2}2]⋅9CH2Cl2 (2) were synthesized. The self-assembly reaction was driven by the unique N,O-donor coordination environments. Single crystal X-ray diffraction analysis showed that two Cu(II) atoms occupy the N2O2 and O4 cavities of the ligand (L)2− unit in complex 1, respectively, and two oxygen atoms on the two mono-dentate nitrate groups have also participated in the coordination for the charge balance of complex 1. The stretching of chemical bonds of complex 1 can be perfectly explained by the Jahn-Teller effect. The novel salamo-based Co(II) complex 2 containing µ3OAc− coordination mode was discovered for the first time. The trinuclear Co(II) complex embodies the advantage of the salamo-based ligand, which has a good flexible form. The binding ratio of the ligand to the Co(II) center was verified by a UV–Vis titration experiment, which is consistent with the single crystal X-ray diffraction result. The energy gaps between the ligand and complexes 1 and 2 were obtained by DFT calculations, and a new theory-softness was proposed. The degree of softness affected the shapes of the complexes. Hirshfeld analysis, IRI, and electrostatic potential proved the existence of hydrogen bond, π···π, CH···π interactions, and van der Waals force. These weak interaction forces affected the structures of the complexes. Finally, the fluorescence properties of the ligand and its complexes were studied.