In this dissertation, selected N-heterocyclic ligands and their metal complexes were studied. The synthesis of heterocyclic compounds, such as derivatives of pyridine, 2,2'-dipyridylamine, benzimidazole and benzothiazole, containing monodentate, bidentate and tridentate coordinating groups, and their coordination complexes with transition metals was carried out. The prepared derivatives are divided into corresponding six classes. The bidentate and tridentate heterocyclic ligands were synthesized by multi-step synthesis using conventional synthetic methods and „green“ microwave-assisted synthesis. The structures of the ligands and metal complexes were confirmed by NMR, UV and IR-spectroscopy and single-crystal X-ray diffraction. Heterobimetallic complexes were additionally characterized by voltammetry and computational analysis. The prepared ligands and metal complexes were evaluated for their antiproliferative activity in vitro against several tumor cell lines, as well as on normal cells with clinical drugs as references. Generally, metal coordination improved activity and selectivity in most cases. The heterobimetallic complex of ferrocene and 2,2'-dipyridylamine conjugate with copper(II) [Cu(A8c)2](CF3SO3)2 showed a selective inhibitory effect on HeLa, MES-OV, A549 and MDA-MB-231 cells with an increase in cell population in the S and G2/M phase of the cell cycle. The activity of 2,2'-dipyridylamine complexes was improved by coordination with Re(I), where [Re(B4a)(CO)3]Cl showed the most pronounced activity, better than cisplatin. The Ni(II) complex of the more structurally flexible bis(2,2'-picolyl)amine ligand, [Ni(C1)2](NO3)2, showed prominent antiproliferative activity by interfering with the DNA replication process and reducing the expression of the antiapoptotic marker Bcl-2. Ruthenium(II) half-sandwich complexes of 2-arylbenzothiazole and 2-picolyl linked by a 1,2,3-triazole bridge showed antiproliferative activity in the submicromolar range, displaying selectivity towards PANC1 cells. Acyl thiourea and benzothiazole conjugates and their Ru(II) complexes exhibited cytostatic activity in the low micromolar and nanomolar range against H460, MCF-7, SW 620 and HepG2 cells, with prominent activity against the MCF-7 breast cancer cell line. Besides, compounds showed weak to moderate antibacterial activity against E. faecalis. Ligand E5c and complexes D4aRu, E4cRu and E5cRu were selected for further evaluation of their mechanism of biological action.