Secondary bonding in a six-coordinate Mn(II) complex as a model of associative substitution

The new hexadentate, bis-pincer ligand, (dipyCH₂)MeNCH₂CH₂NMe(CH₂dipy) (dipy = 2,2′-dipyridyl-6-yl) forms a crystallographically characterized Mn(II) complex in which each half of the ligand binds a separate Mn(OAc)₂ unit. The structure consists of a distorted N₃Mn(η²-OAc)(η¹-OAc) core with six normal coordinate bonds and a long (2.85 Å) secondary bond to a seventh ligand atom, an oxygen of the η¹-acetate. In addition to demonstrating an interesting coordination mode, the structure also mimics a predicted transition state in the associative ligand exchange of octahedral Mn(II) complexes.