Remarkable Sensing Behavior of Pyrazole-based Chemosensor Towards Cu(II) Ion Detection: Synthesis, Characterization and Theoretical Investigations

We report the synthesis of a new imine based ligand, 3-((3-methoxybenzylidene)amino)-1H-pyrazol-5-ol (HL) and its Cu(II) complexes in 2:1 (HL:metal) and 1:1:1 (HL:metal:HQ) stoichiometric ratio using 8-hyroxyquinoline (HQ) as an additional bidentate ligand. The synthesized ligand (HL) and its Cu(II) complexes (1 and 2) are structurally characterized using FT-IR, electronic absorption and emission, NMR, MS and TGA techniques. Furthermore, the complexation of Cu²⁺ with HL leads to the immediate formation of brown colored solution which indicates that HL can act as simple colorimetric sensor for Cu²⁺ ions. We further investigated that the sensor could selectively bind to the Cu²⁺ ions even in the presence of competitive ions such as Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Ag⁺ and Na⁺ ions in aqueous solutions which was studied by electronic absorption spectroscopy. The HL ligand and corresponding Cu(II) complexes have been investigated for their reactive properties by density functional theory (DFT) calculations. Quantum molecular descriptors describing local reactive properties have been calculated in order to identify the most reactive molecule sites of title compounds. DFT calculations encompassed molecular electrostatic potential (MEP), local average ionization energies (ALIE), Fukui functions and bond dissociation energies for hydrogen abstraction (H-BDE).