Supramolecular Self-Assembly of Novel Double Chloride-Bridging Trinuclear Ni(II) Mono-Salamo-Type Cluster: Experimental and Theoretical Analysis

Abstract

A mono-salamo-type ligand H₂L was prepared to utilize 3-methoxysalicylaldehyde and a semi-salamo-type compound, and its novel trinuclear Ni(II) cluster with two significantly various configurations in the solid state was obtained by reaction of H₂L with Ni(II) ions. The trinuclear structure of the Ni(II) cluster was validated by x-ray technique, and Ni(II) ions exhibited hexa-coordinated twisted octahedrons. Its structural formula is [Ni₃(L)₂(μ₂-Cl)₂(EtOH)₂]. Chloride ions have also successfully double bridged to participate in coordination, and play a critical impact in the trinuclear configuration's stability and charge balance. Two solvent ethanol molecules are also participated in coordination. The coordination ratio of the ligand to the metal ion was verified to be 2:3 by UV–Vis absorption titration spectroscopy. The HOMO and LUMO energies of the frontline molecular orbitals of H₂L and the complex were analyzed by DFT calculations, and the energy gap value of the ligand H₂L was 4.29 eV, and that of the complex was 0.72 eV. The ligand combined with the metal decreased the energy gap value and produced a more active complex. Furthermore, Hirshfeld surface analysis visualizes the weak interactions of crystalline molecules, and these abundant weak interactions play an especially critical effect in the supramolecular structural self-assembling. The fluorescent researches proclaimed that the fluorescence intensity of the cluster significantly decreased compared with the ligand, suggesting that this ligand and complex have greater promise for fluorescence sensing.