New one-dimensional azido-bridged manganese(II) coordination polymers exhibiting alternating ferromagnetic-antiferromagnetic interactions: Structural and magnetic studies

Five Mn(II)-azido coordination polymers of formula [Mn(L)(N₃)₂]_n have been synthesized and crystallographically characterized, and their magnetic properties studied, where L's are the bidentate Schiff bases obtained from the condensation of pyridine-2-carbaldehyde with aniline (1) and its derivatives p-toluidine (2), m-toluidine (3), p-chloroaniline (4), and m-chloroaniline (5). All the complexes consist of the zigzag Mn(II)-azido chains in which the MN(II) ions are alternately bridged by two end-to-end (EE) and two end-on (EO) azido ligands, the cis-octahedral coordination being completed by the two nitrogen atoms of the Schiff base ligands. Compound 2 is unique in that the Mn-(EE-N₃)₂-Mn ring adopts an unusual twist conformation with the two linear azido bridges crossing each other. By contrast, the rings in the other compounds take the usual chair conformation with the two azido bridges parallel. The double EO bridging fragments in the complexes are similar with the bridging angles (Mn-N-Mn) ranging from 99.6° to 104.0°. Magnetic analyses reveal that alternating ferro- and antiferromagnetic interactions are mediated through the alternating EO and EE azido bridges with the J_F and J_AF parameters in the ranges of 4.1-8.0 and -11.8 to -15.4 cm^-1, respectively. Finally, the magnetostructural correlations are investigated. The present complexes follow the general trend that the ferromagnetic interaction through the double EO bridge increases with the Mn-N-Mn bridging angle, while the antiferromagnetic interaction through the double EE bridge is dependent on the distortion of the Mn-(N₃)₂-Mn ring from planarity toward the chair conformation and the Mn-N-N angle.