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

Abstract

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 Mn(II) coordination polymers with mixed azide and carboxylate bridges: {[Mn(L)(N(3))]ClO(4).0.5H(2)O}(n) (1), {[Mn(2)(L)(2)(N(3))(2)][Mn(N(3))(4)(H(2)O)(2)].2H(2)O}(n) (2), {[Mn(2)(L)(2)(N(3))(2)(H(2)O)(2)]Br(N(3)).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.