Schiff base (SB) ligands and their respective metal complexes are extremely useful in coordination chemistry and interdisciplinary applications such as: catalysis, biomedical, and as building blocks for other compounds. As an example of one the most common SB derivates are the tetradentate salen ligands which are synthesized through a condensation reaction between a diamine and an aryl ketone or aldehyde. Salen ligands can coordinate with transition metals through the SB nitrogens and oxygens generally creating planar geometry. The presented research shows new salen and salen-like naphthalene ligands with their respective Pd and Pt complexes characterized by UV-Vis spectroscopy, FT-IR spectroscopy, proton and carbon nuclear magnetic resonance (<sup>1</sup>H-NMR and <sup>13</sup>C-NMR), and single crystal X-ray diffraction (SC-XRD). The studied ligands show characteristic UV absorption in the 300 – 450 nm range, corresponding to the imine and naphthol moieties. In addition, the salen-like ligand and the 4d and 5d complexes were structurally characterized from suitable crystals for SC-XRD and determining their corresponding space group. Luminescence of the salen-like ligand and complexes was analyzed using emission spectroscopy and the quantum yield was determined. Cyclic voltammetry experiments of the salen and salen-like ligands demonstrated non-innocent behavior at mild potentials. The electrochemical studies performed with the complexes displayed a similar process as the ligands suggesting that the complexes undergo the same redox processes as the ligands. Moreover, the Pd and Pt complexes exhibit additional redox processes at negative potentials involving the metal centers.

Novel Schiff base ligands and their 4d and 5d metal complexes: Synthesis, characterization, luminescence, and electrochemical properties

ACS Fall 2021

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