Synthesis and characterization of mononuclear and dinuclear Mn complexes with N,N′-disubstituted octaaza macrocycle

A new 24-membered octaaza macrocyclic ligand (L) containing two methoxybenzyl pendant arms has been synthesized. While its complexation with MnCl₂ in the presence of perchlorate anion yielded a mononuclear complex, [MnL](ClO₄)₂, a similar reaction in the absence of perchlorate anion led to an endocyclic dinuclear complex, [Mn₂LCl₄]. In [MnL](ClO₄)₂, the Mn(II) ion was tightly surrounded by the N8-macrocyclic ligand to form a distorted bicapped octahedral geometry. In [Mn₂LCl₄], the endomacrocyclic bound two manganese ions are bridged via two chloro ligands to form a bis-(μ-chloro) Mn₂Cl₂ diamond core. Each Mn(II) ion in the dinuclear complex is additionally ligated with a diaminomethyl pyridinyl nitrogen donor atom of the ligand and a terminal chloride, which leads to a distorted octahedral geometry of the N₃Cl₃ donor set. An EPR study of [MnL](ClO₄)₂ in DMSO or DMF showed an unprecedented Mn(II) EPR signal spreading from ∼100 G over ∼7000 G with ⁵⁵Mn nuclear hyperfine structures at 600-1800 G. For [Mn₂LCl₄], a typical high-spin Mn(II) signal was observed near g = ∼2 with an average ⁵⁵Mn nuclear hyperfine coupling constant of 91 G and small ZFS.