Abstract The hydrazino complex [VO(dipic)(NH2NHC(O)Ph)] · NH2NHC(O)Ph · H2O (3) has been prepared by reaction of [VO(dipic)(H2O)] · 2H2O (1) with NH2NHC(O)Ph. (dipic = dianion of pyridine dicarboxylic acid). The hydrazido(2-) complex (guanid)[VO(dipic)(NHNC(O)Ph)] · 2H2O (4) was obtained by reaction of (guanid)[VO2(dipic)]·2H2O and NH2NHC(O)Ph. During the course of this reaction a terminally bonded oxygen atom is abstracted from the vanadium(V) center. 1, 3 and 4 have been characterized by X-ray single crystal diffraction, infrared, Raman and electron spin resonance spectroscopy. In 1 vanadium is six-coordinate, with the nitrogen atom of the dipic ligand in trans position to the oxo group. The two water molecules are also ligated in mutual trans positions. Vanadium is also six-coordinate in 3 and 4. In both, the dipic ligand is cis oriented with respect to the terminal oxo group. In 3 benzoylhydrazine, and in 4 the hydrazido(2 -) species NHNC(O)Ph act as N,O-chelate ligands, donating their NH2-, respectively NH-group to the remaining equatorial site and their CO-group to an axial site. The V - NH2(213.1(4) pm) and V - NH (190.5(2) pm) bond lengths differ considerably, indicating multiple bond character for the latter. In 3 the V -O(oxo) and V-O (carbonyl) bond lengths are 160.1(4) and 219.1(3) pm, and in 4 160.8(2) and 211.9(2) pm, respectively. Crystal data for 1: space group P 1̄, a = 656.2(2), b = 913.2(3), c - 1075.2(2) pm, α= 111.44(2), β = 100.16(2), γ = 94.81(3)°, Z = 2; 3: space group P1̄, a = 801.4(2), b = 1188.7(11), c = 1353.5(12) pm, α = 72.02(7), β = 88.31(7), γ = 70.60(7)°, Z = 2; 4: space group P 1̄, a = 1018.2(5), b = 1222.5(6), c = 1683.2(6) pm, α = 80.02, β = 89.95, γ = 78.73°, Z = 4.