A Ferromagnetic methoxido-bridged Mn(III) dimer and a spin-canted metamagnetic μ_1,3-azido-bridged chain

Abstract

Two new Mn(III) complexes of formulas [MnL¹(N₃)(OMe)]₂ (1) and [MnL²(N₃)₂]n (2) have been synthesized by using two tridentate NNO-donor Schiff base ligands HL¹{(2-[(3-methylaminoethylimino)-methyl]-phenol)} and HL² {(2-[1-(2-dimethylaminoethylimino)methyl]phenol)}, respectively. Substitution of the H atom on the secondary amine group of the N-methyldiamine fragment of the Schiff base by a methyl group leads to a drastic structural change from a methoxido-bridged dimer (1) to a single μ_1,3-azido-bridged 1D helical polymer (2). Both complexes were characterized by single-crystal X-ray structural analyses and variable-temperature magnetic susceptibility measurements. The magnetic properties of compound 1 show the presence of weak ferromagnetic exchange interactions mediated by double methoxido bridges (J = 0.95 cm^-1). Compound 2 shows the existence of a weak antiferromangetic coupling along the chain (J = −8.5 cm^-1) through the single μ_1,3-N₃ bridge with a spin canting that leads to a long-range antiferromagnetic order at T_c ≈ 9.3 K and a canting leading to a weak ferromagnetic long-range order at T_c ≈ 8.5 K. It also exibits metamagnetic behavior at low temperatures with a critical field of ca.1.2 T due to the weak antiferromagnetic interchain interactions that appear in the canted ordered phase.