In the three newly-prepared mixed dinuclear penta-coordinated cobalt(II) complexes, with the pendant macrocyclic ligand N,N',N ",N"'-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and pseudohalides, of the general formula [Co-2(NCY)(n)tpmc](ClO4)(4) (n)(Y = O, n = 1; Y = S, Se, n = 2), the NCO group is bridging, and the other two pseudohalides are nonbridging, i.e., singly coordinated to each metal in the trans position. It can be supposed that the pendant ligand assumes the boat conformation, in complex involving the cyanate ligand whereas it is in the chair conformation in the complexes involving the thiocyanate and selenocyanate ligands. It was found that these complexes exhibit biological activity towards the following strains of microorganisms: Esherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Bacillus thuringiensis (ssp. kurstaki), Pseudomonas aeruginosa (ATCC 27853) and Candida albicans
