Photoluminescent and cytotoxic properties of multinuclear complexes and multinuclear-based polymers with group 12 metals and a tripodal ligand

Abstract

Four novel multinuclear complexes and multinuclear-based polymers with group 12 metal centers, namely, Zn₃(tpbb)Cl₆ (1), {[Cd₆(tpbb)₂Cl₁₂]·2CHCl₃·0.5H₂O}_n (2), Hg₄(tpbb)Br₈ (3), and Hg₄(tpbb)I₈ (4), have been synthesized with respect to a new flexible tripodal ligand, 1,3,5-tris((2-(pyridine-2-yl)-1H-benzo[d]imidazol-1-yl)methyl)benzene (tpbb). Complex 1 is a trinuclear cluster, as determined by X-ray crystallography, while 2 features an unprecedented hexanuclear metallacycle-based 2D network with chloride ion bridges. The similar umbrella-like tetranuclear architectures of 3 and 4 with different Hg(II)-halide salts demonstrate that halides with the same tetrahedral coordination geometries of metal centers do not greatly affect the structure of the complexes. Photoluminescent studies indicate that complexes 1 and 2 reveal enhanced and red-shifted solid-state fluorescence at room temperature compared with the ligand, tpbb, while 3 and 4 show prominent phosphorescence behaviors at cryogenic temperatures with lifetimes in the microsecond range. In addition, when tested against a panel of several human carcinoma cell lines (SH-SY5Y, QBC939 and EC109) by standard MTT assay, complex 1 displayed potential cytotoxicity against SH-SY5Y and QBC939 cells and selectivity to different tumor cell lines.