Facile synthesis of benzothiazole- and benzoxazole-substituted pyridine-2-carboxylic acids has been developed. these ligands form mononuclear nine-coordinate complexes n(kappa(3)-ligand)(2)(kappa(1)-ligand)(H2O)(2) with light and heavy trivalent lanthanides, as established from the X-ray analysis of 11 complexes. crystal structure of a minor product, the anhydrous nine-coordinate complex u(kappa(3)-)(3), has also been determined. Photophysical studies of gadolinium chelates indicate that the triplet states of the new ligands are located at 20400-21400 cm(-1). he ligands are good sensitizers of the europium luminescence with ligand-to-metal energy transfer efficiency in the range 60-100%. The overall uantum yields of the europium emission are substantial, 12-14% in the solid state, and increase to 29-39% upon replacement of two metal-coordinated water molecules with dimethylsulfoxide in solution. he luminescence of near-infrared emitting lanthanides is also sensitized, but uantum yields are much smaller, reaching 0.17 for neodymium and 1.25 for ytterbium in SO, while energy transfer efficiencies for these two ions are below 50.