Dimeric mixed-valence oxovanadium citrate [V2O3(phen)(3)(Hcit)]center dot 5H(2)O (1) (H(4)cit = citric acid, phen = 1,10-phenanthroline) was isolated from a weak acidic medium. It could be converted quantitatively into a tetrameric oxovanadium citrate adduct of 1,10-phenanthroline [V2O3(phen)(3)(Hcit)(2)(phen)(3)O3V2]center dot 12H(2)O (2). This was supported by the trace of infrared spectra and X-ray diffraction patterns. The two compounds feature a bidentate citrate group that chelates only to one vanadium center through their negatively charged alpha-alkoxy and alpha-carboxy oxygen atoms, while the other beta-carboxy and beta-carboxylic acid groups are free to participate in strong intramolecular and intermolecular hydrogen bonding [2.45(1) in 1 and 2.487(2) angstrom in 2], respectively. This is also the case of homocitrato vanadate(V/IV) [V2O3(phen)(3)(R,S-H(2)homocit)]Cl center dot 6H(2)O (3) (H(4)homocit = homocitric acid), which features a binding mode similar to that found in the R-homocitrato iron molybdenum cofactor of Mo-nitrogenase. Moreover, the homocitrato vanadate(V) [VO2(phen)(2)](2)[V2O4(R,S-H(2)homocit)(2)]center dot 4H(2)O center dot 2C(2)H(5)OH (4) is isolated as a molecular precursor for the formation of mixed-valence complex 3. The V-O alpha-alkoxy and V-O alpha-carboxy bond distances of homocitrate complexes 3 and 4 are 1.858(4) and 1.968(6)(av) and 2.085(4) and 1.937(5) angstrom, respectively. They are shorter than those of homocitrate to FeVco (2.15 angstrom). The gamma-carboxy groups of coordinated homocitrato complexes 3 and 4, and the free homocitrate salt Na-3(Hhomocit)center dot H2O (5), form strong hydrogen bonds with the chloride ion and the water molecule [2.982(5) in 3, 2.562(9) in 4, and 2.763(1) angstrom in 5], respectively.