Coordination compounds containing 2-pyridylselenium ligands: synthesis, structural characterization, and antibacterial evaluation

Reactions between 3-amine-2-((pyridin-2-ylmethyl)selanyl)pyridine (L) and MX2 (M = Co, Cu, Zn; X = Cl, Br) result in the formation of the metal(II) molecular complexes 1–5 with the general formula [MX2(L)]. The organic ligand is coordinated to the metal center through nitrogen atoms of the pyridine rings, without interaction with the selenium atom. The rhenium(V) complex [ReO(apySe)2]Cl (6) is formed in two different ways, using [ReOCl3(PPh3)2] as precursor. Firstly, the formation of 6 was observed in the mother liquor, through Csp3–Se bond cleavage of the ligand L and formation of new Re–Se bonds. Secondly, the direct reaction between bis(3-amino-2-pyridyl)diselane (apySe)2 and [ReOCl3(PPh3)2] gave complex 6 in higher yields. The coordination compounds were characterized by spectroscopic and crystallographic methods. Furthermore, the antibacterial activity of the complexes 1–5 was evaluated against Gram-positive bacteria, Staphylococcus aureus (ATCC® 25923), and Gram-negative bacteria, Escherichia coli (ATCC® 25922). The results suggest that the complexes [CoCl2(L)] (1), [CuCl2(L)] (3), [CuBr2(L)] (4) and, [ZnCl2(L)] (5) possess significant bactericidal activity when compared with those of the free ligand and metal salts used in the synthesis.