The influence of inductive ligand electronics on the metrical parameters and redox potentials of a series of manganese(II) compounds

In order to assess the changes in the redox activity of a metal ion that result from inductive effects, three electronically modified derivatives of the ligand, N-benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LH), have been prepared: N-(4-nitro)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LNO2), N-(4-chloro)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LCl), and N-(4-methoxy)benzyl-N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine (LOMe). Due to the lack of a fully conjugated π-system between the 4-benzyl substituent and the N-donors, the electronic perturbation should influence a bound metal ion’s redox properties through primarily inductive pathways. The organic ligands react with MnCl2 to form mononuclear complexes with the general formula [Mn(LR)Cl2]. The parent ligand, LH, and its three derivatives each coordinate Mn(II) ions in a cis-α conformation, with the amine N-donors installed trans to the Mn–Cl bonds. Despite its distance from the metal ion, the electron-donating or – withdrawing group has a notable impact on both the metrical parameters of the Mn(II) compounds and the Mn(III/II) reduction potential. A single inductive perturbation can vary the reduction potential by as much as 50 mV.