Synthesis, Characterization, and Photoluminescence Properties of Binuclear Co(ll), Ni(ll) and Cu(ll) Schiff Base Complexes with μ -1, 1 Azide Bridges.

Abstract

Three new Co(II) (1), Ni(II) (2), and Cu(II) (3) binuclear complexes with versatile azide bridges and Schiff base derived from 2-hydroxy-1-naphthaldehyde and 2-aminothiophenol have been synthesized. Compounds 1-3 were characterized using various techniques, including microanalysis (CHNS), molar conductance, FTIR, UV-visible, 1H-NMR, mass spec, photoluminescence (PL) spectroscopy, thermogravimetric analysis (TGA-DTG), scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX) techniques. Molar conductance values of the newly synthesized complexes indicate that the complexes are electrolytes in solution. Spectroscopic results suggest that the Schiff base acts as a tridentate ligand, bonding to the metal using imino nitrogen, thiol sulphur, and hydroxy oxygen atoms. Upon the incorporation of the azide pseudohalide, the µ -1, 1 bridge are proposed for all the complexes. Electronic spectra of 1-3 suggest an octahedral environment around the metal ions. Schiff base exhibited fluorescence originating from intra-ligand ( $\pi \to {\pi }^{\ast }$ ) transitions with a quantum yield value of (9 ± 1) %, while the metal complexes exhibited reduced photoluminescence intensity and quantum yield (0.5 - 3.80%) relative to the Schiff base. These results suggest that the Schiff base has a specific recognition for transition metals. It can be used as a turn-off fluorescence sensor specifically for Cu²⁺ ions with a fluorescence quenching efficiency of (94 ± 2) %.