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.

The complexation of an octaaza macrocyclic ligand containing two 2-methoxybenzyl pendant arms with Mn(II) ion has yielded either a bicapped distorted octahedral mononuclear complex showing an unprecedented EPR characteristic or an endocyclic bis-μ-chloro dinuclear complex depending on conditions.Figure optionsDownload as PowerPoint slide