Synthesis, Structures and Photophysical Properties of Tetra- and Hexanuclear Zinc Complexes Supported by Tridentate Schiff Base Ligands

The synthesis, structure and photophysical properties of two polynuclear zinc complexes, namely [Zn6L2(& mu;(3)-OH)(2)(OAc)(8)] (1) and [Zn4L4(& mu;(2)-OH)(2)](ClO4)(2) (2), supported by tridentate Schiff base ligand 2,6-bis((N-benzyl)iminomethyl)-4-tert-butylphenol (HL) are presented. The synthesized compounds were investigated using ESI-MS, IR, NMR, UV-vis absorption spectroscopy, photoluminescence spectroscopy and single-crystal X-ray crystallography. The hexanuclear neutral complex 1 comprises six-, five- and four-coordinated Zn2+ ions coordinated by O and N atoms from the supporting ligand and OH- and acetate ligands. The Zn2+ ions in complex cation [Zn4L4(& mu;(2)-OH)(2)](2+) of 2 are all five-coordinated. The complexation of ligand HL by Zn2+ ions leads to a six-fold increase in the intensity and a large blue shift of the ligand-based (1)(& pi;-& pi;)* emission. Other biologically relevant ions, i.e., Na+, K+, Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+ and Cu2+, did not give rise to a fluorescence enhancement.