Synthesis, structural, electrochemical and spectroscopic characterization, and theoretical calculations of two new Cu(II) and Ni(II) complexes from 2-(1-((pyridine-2-ylmethyl)imino)ethyl)naphtalen-1-ol

We present the synthesis of the tridentate Schiff base 2-(1-((pyridine-2-ylmethyl)imino)ethyl)naphtalen-1-ol (LH) providing a NNO coordination environment. Two new Ni(II) and Cu(II) complexes with a ligand to metal stoichiometric ratio of 1:1 and 2:1, respectively, were synthesized from LH. The Cu(II) complex of general formula [Cu(L)(MeOH)](ClO₄)·MeOH (2) has a square planar geometry in the central ion completed by a MeOH molecule. In the case of the mononuclear Ni(II) complex [NiL₂]·MeOH (3) the central ion has a distorted octahedral geometry. These new compounds were structurally, spectroscopically and electrochemically characterized using X-ray diffraction, UV-vis, IR, ¹H NMR, ¹³C NMR spectroscopies, and cyclic voltammetry. LH is electroactive in the potential window of −1.0 to 1.0 V with one irreversible oxidation at 0.44 V, a quasi-reversible oxidation at 0.60 V, and one irreversible reduction at 0.24 V. For 2, there is a quasi-reversible oxidation at 0.43 V and one irreversible oxidation at 0.64 V. Complex 3 has two quasi-reversible oxidations at 0.19 V and at 0.58 V, one irreversible oxidation at 0.37 V, and one irreversible reduction at 0.38 V. DFT calculations were undertaken to obtain optimized structures and relative stability for 2 and 3 and their intermediates.