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

The reactions of manganese(I I) 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 Mn-II coordination polymers with mixed azide and carboxylate bridges: [Mn(L)(N-3)]ClO4 center dot 0.5H(2)O)(n) (1), ([Mn-2(L)(2)(N-3)(2)][Mn(N-3)(4)(H2O)(2)]center dot 2H(2)O}(n) (2), {[Mn-2(L)(2)(N-3)(2)(H2O)(2)]Br(N-3)center dot 2H(2)O}(n) (3), and [Mn-4 (L)(2)(N-3)(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-N-3) triple bridge (EO = end-on) between adjacent Mn-II 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 J(1)J(1)J(2)J(2) interactions has been deduced and applied to 1. Magnetic studies on 1 and 2 reveal that the (OCO)(2)(EO-N-3)) triple bridges induce antiferromagnetic coupling between Mn-II 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 [Mn-4(mu(3)-N-3)(2)(mu(2)-N-3)(2)(mu(2)-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 (mu(3)-EO-N-3)(2), (OCO) (EO-N-3), (OCO)(EO-N-3)(2), and single EE-N-3, propagate antiferromagnetic coupling.