The coordinating properties of a new bis(pyridylhydrazone) ligand derived from iminodiacetic acid diethyl ester and 2-pyridinecarboxaldehyde (picolinaldehyde) H3Imdp and of the bis(salicylhydrazone) H5Imds and H4MeImds ligands derived, respectively, from iminodiacetic acid diethyl ester and from methyl-iminodiacetic acid diethyl ester and salicylaldehyde were considered, by means of analytical and spectroscopic methods, towards first row transition metal ions. These ligands showed various coordination modes in complexation with Cu(II), Co(II), Mn(II) and Zn(II) ions. In particular, we have synthesized and characterized, by analytical, 1H NMR and IR techniques, tri-, di- and mononuclear metal complexes of formula Co3(HImdp)(NO3)4·2H2O, Cu3(HImdp)(NO3)4·C2H5OH·H2O, Cu3(HImdp)Cl4, Zn2(H3Imdp)(ClO4)4·2H2O, Co3(HImds)Cl2·CH3OH·H2O, Zn2(H3Imds)Cl2·2H2O, Co(H4Imds)NO3·2H2O, Mn(H4Imds)Cl·CH3OH·H2O, Cu(H3Imds)·CH3OH·H2O and Cu(H2MeImds).CH3OH·3H2O. Antibacterial, antifungal and antiprotozoal properties of H5Imds and H3Imdp together with three copper(II) trinuclear species of H5Imds of formula Cu3(HImds)(NO3)2.2CH3OH·2H2O, Cu3(HImds)(ClO4)2.EtOH·2H2O and Cu3(HImds)SO4·4H2O are also discussed. The H5Imds ligand and their trinuclear copper(II) complexes showed good activities versus Trichomonas vaginalis, Staphylococcus epidermidis and Acanthamoeba castellanii.