Three azido-bridged Mn(II) complexes based on open-chain Diazine Schiff-base ligands: Crystal structures and magnetic properties

Three new Mn(II)-azido polymeric complexes [MnL¹(N ₃)₂·CH₃OH]_n (1) (L ¹ = 1-(2-pyridyl)-1-amino-4-(6-bromo-2-pyridyl)-2,3-diaza-1,3- butadiene), [MnL²(N₃)₂]_n (2a) and [Mn₂(L²)₂(N₃)₄] _n (2b) (L² = 1-(2-pyridyl)-1-amino-4-benzyl-2,3-diaza-1,3- butadiene) have been synthesized and crystallographically characterized, and their magnetic properties are studied. Complexes 1 and 2b show similar one-dimensional (1D) coordination polymeric structure, in which Mn(II) ions are alternately bridged by two end-to-end (EE) and two end-on (EO) azido ligands, resulting in zigzag Mn(II)-azido chains. Complex 2a has a 1D structure, and the Mn(II) ions are connected by double EO azido ligands, forming a neutral 1D uniform chain. Standing in their mother liquor for ca. 2 weeks or more, 2a is transformed to 2b completely. The structures of 2a and 2b are characterized, and the quite different magnetic properties based on this transformation of kinetic favored phase to thermodynamic favored phase are discussed. Magnetic analyses reveal that alternating ferro- and antiferromagnetic interactions are mediated through the alternating EO and EE azido bridges, and the J_F and J_AF parameters are 7.8(1) and -10.8(1) for complex 1, respectively, 7.7(4) and -11.2(1) cm^-1 for complex 2b, respectively. For 2a, on the contrary, magnetic analyses reveal that the ferromagnetic coupling interactions are mediated through the double EO azido bridges, and the J_F is 1.4 cm^-1.