Abstract
Synthesis, characterization and fluorescence study of a benzothiazole based Schiff base ligand N2,N6-bis(benzo[d]thiazol-2-yl)pyridine-2,6-dicarboxamide (H2L) and its zinc complexes are reported. Temperature controlled nuclearities were observed when the ligand was allowed to react with Zn(NO3)2⋅6H2O at different temperature. The reaction didn't proceed at room temperature whereas a dinuclear complex [Zn2(HL)L(µ2OH)]·0.5DMF (1) was formed at 50 °C. The same stoichiometric mixture yielded a hexanuclear Zn complex [Zn6L4(µ4O)2]·6·5H2O·DMSO (2) when the temperature was raised to 80 °C and above. The crystal structure of the zinc complexes show the metal centers are in square pyramidal geometry in 1 whereas two different kinds of coordination geometry (square pyramidal & tetrahedral) were observed in 2. The ligand exhibits variable conformation as well as coordination behavior with changing temperature. The theoretical studies support the formation/transformation of complex 1 & 2 under thermodynamic control. Coordination driven fluorescence enhancement was observed in the Zn complexes which was proportionally dependent on the number of metal sites present.
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