The Schiff base ligand derived from salicylaldehyde and benzoic acid hydrazide (H 2 salhyph) reacts with potassium metavanadate in methanol solution to yield the potassium salt of the corresponding cis-dioxovanadium(V) complex K[VO 2 (salhyph)] (1). 1 crystallizes with one molecule of methanol in the monoclinic space group P2 1 /c with a=1332.3(7), b=669.9(2), c=1809.0(8) pm, β=100.96(4) o , and Z=4. The reactions of 1 with several proton acidic compounds including water, methanol, ethane-1,2-diol (H 2 ed), and proton acids lead to neutral monooxovanadium(V) and cis-dioxovanadium(V) complexes ([VO 2 (Hsalhyph)] (2); [V 2 O 3 (salhyph) 2 ] (3); [VO(OMe)(salhyph)(HOMe)] (4); [VO(Hed)(salhyph)] (5)). The crystal structure of 2 (triclinic space group P1 with a=677.79(5), b=842.89(7), c=1214.66(9) pm, α=79.931(1), β=75.466(1), γ=73.391(1) o , and Z=2) reveals that the protonation of the cis-dioxovanadium(V) complex 1 occurs at the hydrazide nitrogen atom of the ligand system. This was confirmed by the spectroscopic properties of the deuterium derivative.