Energy parameters of 1,3,4-thiadiazole derivatives were calculated by the M
NDO semiempirical method, and the calculation results were used to interpre
t competing coordination at the donor nitrogen atoms with regard to the sub
stituent in the heteroring. Prediction of the coordination sites in 2-amino
-1,3,4-thiadiazole and 2-amino-5-ethyl-1,3,4-thiadiazole was consistent wit
h the X-ray diffraction data for Zn(II) complexes with these ligands.