Counteranion-solvent-dependent construction of two octahedral homopolynuclear Ni(II) complexes with a symmetrical multi-halogen-substituted bis(salamo)-based ligand

Two octahedral homopolynuclear Ni(II) complexes, [Ni2(L)(OAc)(MeOH)]·CH3CN·MeOH (1) and [Ni4(L)2(acac)2(EtOH)2]·2CH3CN (2) have been synthesized and characterized structurally. Hirshfeld surfaces, DFT calculation and fluorescence properties of complexes 1 and 2 were investigated. [Display omitted] •Anion-solvent-dependent construction of two homopolynuclear Ni(II) complexes 1 and 2 were synthesized and characterized structurally.•Complex 2 possesses a novel centrosymmetric tetra-nuclear structure with two dinuclear [Ni2(L)(acac)(EtOH)] units.•Hirshfeld surfaces, DFT calculation and fluorescence properties of complexes 1 and 2 were investigated. Two counteranion-solvent-dependent homopolynuclear Ni(II) complexes, [Ni2(L)(OAc)(MeOH)]·CH3CN·MeOH (1) and [Ni4(L)2(acac)2(EtOH)2]·2CH3CN (2) have been constructed by exploiting the flexibility of a symmetrical multi-halogen-substituted bis(salamo)-based ligand H3L. The structures of complexes 1 and 2 were confirmed by single crystal X-ray diffraction studies. Complex 1 is a di-nuclear Ni(II) complex, where two octahedral Ni(II) atoms are located in the N2O2 cavities of the salamo units, and bridged via a acetate ion. Complex 2 possesses a centrosymmetric tetra-nuclear structure with two di-nuclear [Ni2(L)(acac)(EtOH)] units. It is worth noting that one acetylacetonate anion is coordinated to Ni2 atom in bidentate fashion along with one methanol molecule that completes its hexa-coordinated geometry. It is possible that the existence of the acetylacetone anion makes the ligand (L)3- unit exhibit its flexibility, which promotes the formation of tetra-nuclear complex 2. The close surveillance of the crystal structure of complexes 1 and 2 discloses some notable non-covalent interactions like H-bonding, CH⋯π and π⋯π. Moreover, both complexes 1 and 2 form three-dimensional supramolecular structures with the help of intermolecular hydrogen bonds. It was found that the synthesis of complexes 1 and 2 weakened the fluorescence intensity of H3L until quenching. Hirshfeld surfaces analyses confirmed that hydrogen bond interactions play the most important role in the stability of crystal structures. The high kinetic stability and low chemical reactivity of complexes 1 and 2 were investigated based on the band gap energy.