Interaction of zinc(II)- and copper(II) perchlorate hexahydrates with nicotinamide (Nia – nicotinamide, niacinamide, 3-pyridinecarboxamide, C
5
H
4
NС(O)NH
2
) has been studied. It has been demonstrated that complex compounds [Zn(Nia)
2
(H
2
O)
4
](ClO
4
)
2
(
1
) and [Cu(Nia)
2
(H
2
O)
2
](ClO
4
)
2
⋅ 2H
2
O (
2
) are formed in aqueous media at the molar ratio M(ClO
4
)
2
⋅ 6H
2
O : Nia = 1 : 2. Both compounds are the ionic ones. Geometry of complex cation (
1
) may be represented as a distorted octahedron in which nicotinamide molecules are in the
trans
-position. The same position of ligands is found for planar complex cation (
2
). Cytotoxicity of the prepared compounds (MTT assay) has been determined with respect to dental pulp stem cells (DPSC) and breast cancer cell line MCF-7. Antiproliferative activity has been studied relative to 10 cancer cell lines, complex compound (
1
) being the most toxic for C6, Panc-1, U251 cell lines (survivability below 15%).