pH-Independent Selective Formation of VO 2 + Motif Incorporating a Family of Hydrazone Ligands: Synthesis, Structure, and Luminescence-Based Sensing Studies toward Selective Metal Ions.

Two new dioxidovanadium(V) compounds with the general formula [V ^V O ₂ (L)] (L = hydrazone ligand) were synthesized using three different methods (acidic, neutral, and basic media) with either V ^IV OSO ₄ . 5H ₂ O, [V ^IV O(acac) ₂ ], or NH ₄ V ^V O ₃ as the starting material and hydrazone ligands. In both cases, five coordinated V ⁵⁺ ions adopted distorted square pyramidal geometry through the coordination of two oxido ligands and one hydrazone ligand. In compound 1 , the presence of free hydroxyl groups stabilized the molecular species through intramolecular O-H•••N type hydrogen bond interactions. In compound 2 , the free amino groups are involved in both intramolecular N-H•••N type and intermolecular N-H•••O type hydrogen bond interactions. Compound 1 showed highly selective luminescence turn-on behavior, along with a 33-nm blue shift in the presence of Al ³⁺ ions in an aqueous medium. The experimental limit of detection (LOD) was found to be 66 nM. Whereas compound 2 showed luminescence quenching behavior in the presence of Fe ³⁺ , Al ³⁺ , and Cr ³⁺ ions. The LODs were observed to be 312, 408, and 280 nM for Fe ³⁺ , Al ³⁺ , and Cr ³⁺ ions, respectively. The luminescence response mechanisms of both compounds in the presence of metal ions have been correlated with molecular-level interactions.