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

Abstract

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-(mu-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 similar to 100 G over similar to 7000 G with Mn-55 nuclear hyperfine structures at 600-1800 G. For [Mn2LCl4], a typical high-spin Mn(II) signal was observed near g = similar to 2 with an average Mn-55 nuclear hyperfine coupling constant of 91 G and small ZFS. (C) 2008 Elsevier Ltd. All rights reserved.