Aqueous acid–base chemistry involving dioxovanadium(V) complexes of 2,6-pyridinedimethanol, and the X-ray structures of Na[VO2{2,6-(OCH2)2NC5H3}] · 4H2O and [1-H-2,6-(HOCH2)2NC5H3]+Cl−

Reaction of NH4VO3 with 2,6-pyridinedimethanol in water at 85 °C followed by the room temperature addition of HCl (aq) yields [HVO2(pydim)]x (pydim = 2,6-pyridinedimethanolato dianion), as a sparingly soluble off-white solid. This acid may be deprotonated by titration with NaOH (aq), yielding Na[VO2(pydim)] · 4H2O, which has been structurally characterized by single-crystal X-ray diffraction. Treating Na[VO2(pydim)] · 4H2O with HCl (aq) regenerates [HVO2(pydim)]x, but reaction with additional NaOH (aq) displaces the pyridinedimethanolato ligand from the vanadium center. Similarly, treating [HVO2(pydim)]x with excess HCl (aq) strips the pyridinedimethanolato ligand from the vanadium center and yields the adduct [H3(pydim)]+Cl− as one component in a mixture of products. This adduct has been structurally characterized by single-crystal X-ray diffraction. The optimum pH range for stable dioxovanadium(V) complexes stabilized by the 2,6-pyridinedimethanolato ligand is at least 1.5–9.4.

Graphical abstractThe dioxovanadium(V) complexes of 2,6-pyridinedimethanol, namely Na[VO2(pydim)] · 4H2O and [HVO2(pydim)]x (pydim = 2,6-pyridinedimethanolato dianion), have been found to be stable in aqueous solution over the pH range of ca. 1.5 to 9.4. Outside this range, the pydim ligand is displaced from the vanadium center. Na[VO2(pydim)] · 4H2O and [1-H-2,6-(HOCH2)2NC5H3]+Cl− have been structurally characterized by single crystal X-ray diffraction.Figure optionsDownload full-size imageDownload as PowerPoint slide