Synthesis, crystal structures, and superoxide dismutase activity of two new multinuclear manganese(III)-salen-4,4′-bipyridine complexes

Manganese(III)-salen complexes have been reported as superoxide dismutase mimics (mSOD) that can scavenge superoxide anion radicals. They are mononuclear complexes with a variety of salen ligands. Here, two new multinuclear manganese(III)-salen complexes with 4,4'-bipyridine (4,4'-bpy) as bridging ligand and ClO4- as axial ligand or PF6- as counter anion, respectively, are reported. The dimeric complex [{Mn(ClO4)(salen)}(2)(mu-4,4'-bpy)] (1) was obtained from [MnCl(salen)]center dot 2H(2)O and 4,4'-bipyridine which followed by addition of NaClO4. While the polymeric complex {[Mn(salen)(4,4'-bpy)]PF6}(n) (2) was prepared by the same procedure of 1, followed by addition of KPF6 replacing NaClO4. Compounds 1 and 2 were characterized by elemental analysis, conductometry, infrared spectroscopy, electrospray-ionization mass spectrometry, and room temperature/variable temperature magnetic susceptibility measurements. The crystal structures of compounds 1 and 2 were determined by single crystal X-ray crystallography. Furthermore, in indirect SOD tests using riboflavin photoreduction, the polymeric compound 2 shows the slightly higher SOD activity with an IC50 of 1.6 +/- 0.2 mu M than the dimeric compounds 1 with an IC50 of 2.0 +/- 0.3 mu M.