Synthesis, spectroscopical characterization and biological studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes of 2-amino-5-hydroxyphenyl-1,3,4-thiadiazoles are described. The ligand coordinates through nitrogen at 4th position of thiadiazole moiety and phenolic oxygen of salicylic acid moiety via deprotonation. The characterization involved elemental analysis, molar conductance, IR, 1H NMR, electronic, magnetic susceptibilities, ESR, FAB-mass and thermal studies. From the above studies it is concluded that the ligands act as a bidenate molecule with stoichiometry being 1:2 (metal:ligand) obeying the general formula [ML2 .2H2O]. Co(II), Ni(II) and Zn(II) complexes possessing an octahedral geometry while Cu(II) complexes have exhibited distorted octahedral geometry. The compounds have been screened in vitro for antibacterial and antifungal activities. Active compounds have been assayed with MIC values. The antitubercular activities for the compounds have been carried out against, H37Rv Strain by middle Brook Method. The brine shrimp bioassay was also carried out to study the in vitro cytotoxicity properties for the ligands and their corresponding complexes
