Diverse Manganese(II) Coordination Polymers with Mixed Azide and Zwitterionic Dicarboxylate Ligands: Structure and Magnetic Properties

The reactions of manganese(II) acetate or perchlorate, sodium azide, and the inner-salt-type dicarboxylate ligand 1,3-bis(4-carboxylato-1-pyridinium)propane (L) under different conditions yielded four different MnII coordination polymers with mixed azide and carboxylate bridges: {[Mn(L)(N3)]ClO4·0.5H2O}n (1), {[Mn2(L)2(N3)2][Mn(N3)4(H2O)2]·2H2O}n (2), {[Mn2(L)2(N3)2(H2O)2]Br(N3)·2H2O}n (3), and [Mn4 (L)2(N3)8]n (4). The compounds exhibit great diversity in their structures and magnetic properties. Both 1 and 2 contain anionic chains featuring a mixed (OCO)2(EO-N3) triple bridge (EO = end-on) between adjacent MnII ions. In 1, two independent sets of triple bridges with apparently different structural parameters alternate in the AABB sequence, and the resulting alternating chains are cross-linked into a cationic 3D framework by the cationic dipyridinium spacers. Differently, the chains in 2 have uniform bridges and are interlinked into a 2D coordination layer. An expression of the magnetic susceptibility for 1D systems with alternating J1J1J2J2 interactions has been deduced and applied to 1. Magnetic studies on 1 and 2 reveal that the (OCO)2(EO-N3) triple bridges induce antiferromagnetic coupling between MnII ions, and magnetostructural analyses suggest that the magnitude of the coupling can be correlated to the Mn−N and Mn−N−Mn parameters. Compound 3 contains 2D coordination layers in which the chains with alternating double EO-azide and double carboxylate bridges are interlinked by the dipyridinium spacers, and magnetic studies suggest alternating ferro- and antiferromagnetic interactions through the alternating bridges. The 3D framework of compound 4 is formed by the organic ligands interlinking the unique manganese−azide−carboxylate layers in which the [Mn4(μ3-N3)2(μ2-N3)2(μ2-COO)4] clusters are interlinked through EE-azide bridges (EE = end-to-end). The structure represents a novel type of self-catenated 8-connected 3D net. Magnetostructural analyses suggest that all of the short bridging moieties in 4, including (μ3-EO-N3)2, (OCO)(EO-N3), (OCO)(EO-N3)2, and single EE-N3, propagate antiferromagnetic coupling.