Anion-tuned assembly of three double cubane tetranuclear Cd(II)/Zn(II) complexes based on a 2-substituted 8-hydroxyquinoline ligand: Synthesis, crystal structures and fluorescent properties

One unique 2-substituted-8-hydroxyquinoline ligand with 2,3-dimethoxyphenyl groups was synthesized and characterized by ESI-MS, NMR spectroscopy and elemental analysis (EA). Two double cubane tetranuclear Cd(II) complexes [Cd4(L)6(CH3COO)2] (1), [Cd4(L)6(I)2] (2) and one double cubane tetranuclear Zn(II) complex [Zn4(L)6(NO3)2] (3), were prepared by solvothermal reactions of Cd(CH3COO)2, CdI2 and Zn(NO3)2. Complexes 1–3 were characterized with single crystal X-ray diffractions, powder X-ray diffractions (PXRD), thermogravimetry analyses (TGA) and EA. The building blocks exhibited unprecedented structural diversification and their self-assembly afforded tetranuclear Cd(II)/Zn(II) structures binding of different anions and solvent systems. Complexes 1–3 featured three types of supramolecular network controlled by non-covalent interactions, such as C–H⋯O, C–H···π, π···π stacking, hydrogen-bonding, and halogen-related interactions. Investigation of their photoluminescence properties exhibited disparate emission wavelengths and lifetimes in the solid state. This unique capability may provide a useful strategy to tune the optical properties of multinuclear materials, which could be exploited as important components for optoelectronic devices.