alpha-Hydroxy acids (H(2)L = R(1)R(2)C(OH)COOH) react with tungstate ions in aqueous acidic solution to form mononuclear complexes [WO(2)L(2)](2-) and 2:2 species that may be either mononuclear bis chelates (the tartrate compound) or dinuclear complexes (the isocitrate and mandelate compounds). Ligands with R(1) not equal R(2) afford a pair of 1:2 diastereoisomers. The formation constants of the colorless complexes were determined by indirect photometry, using a ligand-ligand exchange reaction. The stabilities of the 1:2 complexes depend on the nature of the substituents R(1) and R(2), whereas the acidity constants of the ligands are practically identical. Further structural characterization was achieved using C-13 and W-183 NMR data. All ligands chelate tungstate through the C(OH)-COOH system. The dinuclear 2:2 complexes are characterized by a single tungsten signal with sigma(w) close to -120 ppm. In the 1:2 complexes, substitution of the ligand by alkyl groups has a large shielding effect on the chemical shift of the tungsten nucleus (sigma(w) +81.2 to -13.9 ppm), which is correlated with the magnitude of the formation constant (log K-122 16.85 to 18.75).