The mol­ecule of the title compound C₇H₈N₄O·0.5H₂O, alternatively called (E)-1-(pyridin-4-yl­methyl­ene)semi­carb­azide hemihydrate, is in the E conformation and is almost planar; the r.m.s. deviation of the positions of the atoms of the pyridine ring from the best-fit plane is 0.0039 Å. The C, N and O atoms of the rest of the mol­ecule sits close on this plane with a largest deviation of 0.115 (4) Å for the O atom of the semicarbazone moiety. There is an intra­molecular N—HN hydrogen bond. In the crystal, mol­ecules are linked into an infinite three-dimensional network by classical N—HO_s (s = semicarbazone) and O_w—HN (w = water) hydrogen bonds.

The title complex, [VCl₂(dtbeda)(thf)₂] (dtbeda is N,N'-di-tert-butyl­ethane-1,2-di­amine), was prepared from the reaction of [V₂Cl₃(thf)₆]₂[Zn₂Cl₆] with dtbeda in refluxing thf. The crystal structure of [VCl₂(dtbeda)(thf)₂] exhibits chlorides in trans positions in a distorted octahedral geometry around the vanadium site. The asymmetric unit consists of one-half of the complex, which is located on a twofold rotation axis in space group C2/c.

The title complex, (C₆H₁₈N₂)[V₂Cl₅(C₆H₁₆N₂)₂](C₂₄H₂₀B).C₄H₈O, was prepared by the reaction of [V₂Cl₃(THF)₆](BPh₄) with [FeCl₂(tmeda)₂] in the presence of one equivalent of tmeda (tmeda = N,N,N′,N′-tetra­methyl­ethyl­enedi­amine) in methanol. The crystal structure shows the tmeda to be coordinated to the vanadium core groups. The exchange of the di­amine from iron to vanadium sheds new light on the mechanism of self-assembly of triangulo trinuclear complexes.