That thiadiazoles derivatives are biologically active as antimicrobial agents. Metal complexes of these derivatives are also active, therefore, five derivatives of the 1,3, 4-thiadiazole have prepared along with series of their metal complexes. 1)The reactions of (H1) ligand; 2-amino-3- [amino-1, 3, 4-thiadiazol-5-yl) dithio] propionic acid with Cu(ll), Fe(ll), Ni(ll), and Pt(IV) ions yield the; following complexes [Cu(H1) 3][Fe(H1) 3]SO4 H2O,[Fe2 H1SO4 (OH)2 (H20)5], [Ni H1CI2(H2O)2]. H2O [Ni Hi (H2O) 2H2O.[Pt(H1)2 (OC2H5)2].2H2O. 2)The reaction of (H2) ligand; 2- (carbethoxy amino-1, 3,4-thiadizol-5-y1)-thio acetic acid with [Co(II) and Ni(ll)] ions gave the following complexes:-[Co (H2)2(H20)2], and [Ni H2(H20)2]. 3). While the reactions of (H3) ligand; 5-amino-,3,4-thiadiazol-2- y1)- thio acetic acid with [Cu(ll),Co(ll),Fe(ll)Zn(lI),and pt(IV)] ions showed to give the following complexes: [Cu(H3)2],[Co(H3)2]H20)[Fe2(H3)2(OH)2(H20)4], [Zn(H3)2].H2O, and K2[Pt(H3)2(OC2H5)2].H20. 4).The H4 ligand; [(5-amino-1, 3, 4-thiadiazol-2-yl) dithio]
acetic acid reacted with [Cu(ll), Co(M) ,Fe(ll) ,Zn(II) and pt (LV)] ions showed to give the following complexes: [Cu2(H4)2(OH)2]1[Co2(H4)2(H20)4])[Fe2(H4)2(OH)2(H20)4].H20I [Zn (H4)2], and [pt(H4)(OC2H5]. 5) The reactions of H2 ligand; 5-(1 -amino-1 -mercapt ethyl thio) - 1,3,4-thiodiazole-2-ethyl carbamate amino-5-thio (2-mercaptoethylamin) 1,3,4-thiadiazole,with [Cu(ll)ICo(ll),NI(ll))Fe(ll)Zn(ll),pt(LV)] ions gave the following complexes: [CuH5(H2O)4].4H2O,[Co(H5).(H2O)2].H20,[Ni2H5(H2O)4].H2O [Fe2 H5 S04(H20)5(OH)2],[ZN(H5)2Cl2]I and K2[pt(H5)2(OC2H5)2J.H2O. All the ligands and their metal complexes were characterized using the appropriate techniques, which included melting point, |R and UV-visible .spectra elemental analysis. According to the data obtained, the structural formulae for these complexes were suggested. The five ligands exhibited different coordination behavior with the metal ions. This depends on the nature of donor groups in each ligand and the type of metal ion. Determination of antimicrobial activity and MIC values of five ligands and their metal complexes were obtained using representative strains of gram-negative and grampositive bacteria , in addition to Candida albicans. Most of the prepared ligands and their metal complexes showed reasonable antimicrobial potency. However, the compounds containing a thiadiazole ring and a disulfide bond (H1 and H4 ligands and their complexes) showed a broader spectrum and were active than other ligands and their metal complexes. From the biological activity study, the relationship between the activity and the structures of the prepared compounds was concluded.