Spectroscopic and antimicrobial activity of photoactivatable tricarbonyl Mn(I) terpyridine compounds

The photoinduced fac-[MnBr(CO)₃(L–k²N¹,N²)] (L = 4′-(2-pyridyl)-2,2′:6′,2′'-terpyridine (L^Py) (1) and 4′-(4-phenyl morpholine)-2,2′:6′,2′'-terpyridine (L^morph) (2)) and fac-[Mn₂Br₂(CO)₆(L^DTP–k²N¹,N²)] (L^DTP = 1,4-bis(2,2′:6′,2′'-terpyridin-4′yl)benzene) (3) complexes, capable of release CO at 525 nm, were synthesized and fully characterized using different analytical and spectral tools. Compounds 1–3 had poor solubility or decomposed in most of the organic solvents, and thus they are unsuitable for the phototherapeutic CO applications. Reaction between azide complexes (4–6), prepared by exchange of the axial Br⁻ ligand of 1–3, with ethyl 4,4,4-trifluoro-2-butynoate afforded triazolate complexes (7–9), which had good solubility in the organic solvents. The potential of 7–9 to act as photoinduced CO releasing molecules was studied at two excitation wavelengths, 468 and 525 nm. The ligand L^morph and its complex (8) were strongly potent to Escherichia coli, Candida Albicans and Cryptococcus neoformans. All the ligands and complexes (except 8) exhibited cytotoxicity to the normal human cell line; human embryonic kidney cells (HEK293), but they had good compatibility with the human red blood cells (RBCs) at 32 μg/mL.