Influence of Halogen Substitution in the Ligand Sphere on the Antitumor and Antibacterial Activity of Half‐sandwich Ruthenium(II) Complexes [RuX(η 6 ‐arene)(C 5 H 4 N‐2‐CH=N‐Ar)] +

New complexes [(η 6 ‐ p ‐cymene)Ru(C 5 H 4 N‐2‐CH=N–Ar) X ]PF 6 [ X = Br ( 1 ), I ( 2 ); Ar = 4‐fluorophenyl ( a ), 4‐chlorophenyl ( b ), 4‐bromophenyl ( c ), 4‐iodophenyl ( d ), 2,5‐dichlorophenyl ( e )] were prepared, as well as 3a – 3e ( X = Cl) and the new complexes [(η 6 ‐arene)RuCl(N‐N)]PF 6 (arene = C 6 H 5 OCH 2 CH 2 OH, N‐N = 2,2′‐bipyridine ( 4 ), 2,6‐(dimethylphenyl)‐pyridin‐2‐yl‐methylene amine ( 5 ), 2,6‐(diisopropylphenyl)‐pyridin‐2‐yl‐methylene amine ( 6 ); arene = p ‐cymene, N‐N = 4‐(aminophenyl)‐pyridin‐2‐yl‐methylene amine ( 7 )]. X‐ray diffraction studies were performed for 1a , 1b , 1c , 1d , 2b , 5 , and 7 . Cytotoxicities of 1a – 1d and 2 were established versus human cancer cells epithelial colorectal adenocarcinoma (Caco‐2) (IC 50 : 35.8–631.0 μM), breast adenocarcinoma (MCF7) (IC 50 : 36.3–128.8.0 μM), and hepatocellular carcinoma (HepG2) (IC 50 : 60.6–439.8 μM), 3a – 3e were tested against HepG2 and Caco‐2, and 4 – 7 were tested against Caco‐2. 1 – 7 were tested against non‐cancerous human epithelial kidney cells. 1 and 2 were more selective towards tumor cells than the anticancer drug 5‐fluorouracil (5‐FU), but 3a – 3e ( X = Cl) were not selective. 1 and 2 had good activity against MCF7, some with lower IC 50 than 5‐FU. Complexes with X = Br or I had moderate activity against Caco‐2 and HepG2, but those with Cl were inactive. Antibacterial activities of 1a , 2b , 3a , and 7 were tested against antibacterial susceptible and resistant Gram‐negative and ‐positive bacteria. 1a , 2b , and 3a showed activity against methicillin‐resistant S. aureus (MIC = 31–2000 μg · mL –1 ).