Two new Mn(III) complexes of formulas [MnL 1(N 3)(OMe)] 2 (1) and [MnL 2(N 3) 2] n (2) have been synthesized by using two tridentate NNO-donor Schiff base ligands HL 1{(2-[(3-methylaminoethylimino)- methyl]-phenol)} and HL 2 {(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-N 3 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. © 2012 American Chemical Society.