Manganese(ii)-carboxylate-pseudohalide systems derived from 1,4-bis(4-carboxylatopyridinium-1-methylene)benzene: Structures and magnetism

摘要

The reactions of manganese(ii) acetate or perchlorate, sodium azide or sodium cyanate, and the zwitterionic dicarboxylate ligand 1,4-bis(4- carboxylatopyridinium-1-methylene)benzene (L) under different conditions yielded three different Mn(ii) coordination polymers with mixed carboxylate and azide (or cyanate) bridges: {[Mn (L~1)_(0.5)(N_3)(OAc)] ·3H_2O}_n (1), {[Mn_4(L~1)(N _3)_8(H_2O)_4(CH_3OH) _2]·[L~1]}_n (2), and {[Mn _3(L~1)(NCO)_6(H_2O)_4] ·[L~1]·[H_2O]_2}_n (3). The compounds exhibit diverse structures and magnetic properties. In 1, the 1D uniform anionic [Mn(N_3)(COO)_2]n chains with the (μ-EO-N_3)(μ-COO)_2 triple bridges (EO = end-on) are interlinked by the dipyridinium L ligands into highly undulated 2D layers. Magnetic studies on 1 reveal that the mixed triple bridges induce antiferromagnetic coupling between Mn(ii) ions. Compounds 2 and 3 consist of 1D neutral polymeric chains and co-crystallized zwitterions, and the chains are formed by the L ligands interlinking linear polynuclear units. The polynuclear unit in 2 is tetranuclear with (μ-EO-N_3)_2 as central bridges and (μ-EO-N_3)_2(μ-COO) as peripheral bridges, while that in 3 is trinuclear with (μ-NCO)_2(μ-COO) bridges. Magnetic studies demonstrate that the magnetic coupling through the mixed azide/isocyanate and carboxylate bridges in 2 and 3 is antiferromagnetic. An expression of magnetic susceptibility based on a 2-J model for linear tetranuclear systems of classical spins has been deduced and applied to 2.