Air-stable M(CO)5L (M = Cr, W; L = 4-phenyl-1,2,3-thiadiazole (I), 4-methyl-1,2,3-thiadiazole-5-carboxylic acid and its Et ester, and 4-methyl-1,2,3-selenadiazole (II)) were prepd. from (THF)M(CO)5 and L. IR spectra of products of similar reactions of (THF)Mo(CO)5 provide some evidence of the formation of analogous complexes. The thiadiazole complexes are also accessible directly by photochem. displacement of CO in THF from the parent carbonyl. The x-ray structures of W(CO)5L (L = I) and Cr(CO)5L (L = II) show the coordination of the ligand to the pentacarbonylmetal fragment via the N atom in position 2.