Aggregation-induced emissive pyridoxal derived tetradentate Schiff base for the fluorescent turn-off sensing of copper(II) in aqueous medium

In this study, a tetradentate Schiff base ligand L was synthesized by condensing o-phenylenediamine with two moles of pyridoxal. The solution of L in EtOH/DMSO showed aggregation-induced emission (AIE) behaviour...

FeI Intermediates in N2O2 Schiff Base Complexes: Effect of Electronic Character of the Ligand and of the Proton Donor on the Reactivity with Carbon Dioxide

The characterization of competent intermediates of metal complexes, involved in catalytic transformations for the activation of small molecules, is an important target for mechanistic comprehension and catalyst design. Iron complexes deserve particular attention, due to the rich chemistry of iron that allows their application both in oxidation and reduction processes. In particular, iron complexes with tetradentate Schiff base ligands show the possibility to electrochemically generate FeI intermediates, capable of reacting with carbon dioxide. In this work, we investigate the electronic and spectroscopic features of FeI intermediates in five Fe(LN2O2) complexes, and evaluate the electrocatalytic reduction of CO2 in the presence of phenol (PhOH) or trifluoroethanol (TFE) as proton donors. The main findings include: (i) a correlation of the potentials of the FeII/I couples with the electronic character of the LN2O2 ligand and the energy of the metal-to-ligand charge transfer absorption of FeI species (determined by spectroelectrochemistry, SEC-UV/Vis); (ii) the reactivity of FeI species with CO2, as proven by cyclic voltammetry and SEC-UV/Vis; (iii) the identification of Fe(salen) as a competent homogeneous electrocatalyst for CO2 reduction to CO, in the presence of phenol or trifluoroethanol proton donors (an overpotential of 0.91 V, a catalytic rate constant estimated at 5 × 104 s−1, and a turnover number of 4); and (iv) the identification of sudden, ligand-assisted decomposition routes for complexes bearing a ketylacetoneimine pendant, likely associated with the protonation under cathodic conditions of the ligands.

Synthesis of Novel Aqua ƞ4-NNNO/Cu(II) Complexes as Rapid and Selective Oxidative Catalysts for O-Catechol: Fluorescence, Spectral, Chromotropism and Thermal Analyses

A new tetradentate Schiff base (SB), (E)-4-fluoro-2-(1-((2-(piperazin-1-yl)ethyl)imino)ethyl)phenol, was synthesized from condensation of 2-(1-piperazinyl)ethylamine and 5-fluoro-2-hydroxyacetophenone. This ligand was coordinated with three copper(II) salts (CuCl2, CuBr2 and Cu(NO3)2⸱3H2O) separately, giving rise to new neutral water-soluble Cu(II)/ƞ4-NNNO complexes (1–3). The new materials were fully characterized by standard spectroscopic, elemental, thermal, electronic, absorption, and fluorescence analyses. The chromotropism investigation of the aqueous solutions of the complexes revealed notable outcomes. A turn off-on halochromism effect was observed, both in the acidic and basic mediums. The green-colored solution was changed to colorless (off) upon the addition of HCl, while the initial green color was reversibly restored (on) after the addition of NaOH. On the other hand, bathochromic solvatochromism shifts were noticed in various solvents. Interestingly, complex 2 displayed a remarkable blue fluorescence shift (Δλ = 90 nm) when compared to its SB ligand. The oxidation capability of the three complexes was successfully demonstrated for the conversion of o-catechol to o-benzoquinone in aqueous solutions and in the presence of H2O2, an environmentally friendly oxidant, under mild reaction conditions.