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.