Pyridylbenzimidazole based Re(i)(CO)3 complexes: antimicrobial activity,spectroscopic and density functional theory calculations

fac-[ReBr(CO)₃(L^1,2)] L¹ = 1-ethyl-2-(pyridin-2-yl)benzimidazole (1) and L² = 1-[(pyridin-2-yl) benzimidazole]-propyl-sulfonic acid (2), fac-[Re₂Br₂(CO)₆L³] (3) L³ = 1,1′-(hexane-1,6-diyl)bis[2-(pyridin-2-yl)1H-benzimidazole] and fac-[ReBr(CO)₃(L^4,5-κ²N¹N²)] (L⁴ = 2,6-bis(benzimidazol-2′-yl)pyridine (4) and L⁵ = 2,6-bis(1-ethyl-benzimidazol-2′-yl)pyridine (5) were synthesized and fully characterized using different spectrocopic and analytical tools. The spectrocopic data showed coordination of L^1–3 to fac-ReBr(CO)₃via the benzimidazole and pyridine N-atoms. For 4 and 5, the absence of a two-fold axis of symmetry for L^4,5 in the ¹H NMR spectra reflect the κ²N¹,N² mode of coordination. The electronic properties of 1–5 were investigated by time-dependent density functional theory calculations in the singlet and triplet states. The ligands and their Re(i) complexes were assessed for their potential antimicrobial activity. Compound 5 was screened against non-malignant cell line (noncancerous human embryonic kidney cell line (HEK293)) as well as evaluated for its blood compatibility.

Mono- and binuclear pyridylbenzimidazole based Re(i) tricarbonyl complexes exhibited antibacterial activity against Gram(+) bacterium. TDDFT calculation, in singlet and triplet states, assigned the lowest energy transition to MLCT and MLCT/³IL, respectively.