N-Salicylidenehydrazides as versatile tridentate ligands for dioxovanadium(V) complexes

The Schiff base ligand derived from salicylaldehyde and benzoic acid hydrazide (H2salhyph) reacts with potassium metavanadate in methanol solution to yield the potassium salt of the corresponding cis-dioxovanadium(V) complex K[VO2(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, beta = 100.96(4) degrees, and Z = 4. The reactions of 1 with several proton acidic compounds including water, methanol, ethane-1,2-diol (H2ed), and proton acids lead to neutral monooxovanadium(V) and cis-dioxovanadium(V) complexes ([VO2(Hsalhyph)] (2); [V2O3(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, alpha = 79.931(1), beta = 75.466(1), gamma = 73.391(1) degrees, 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.