Mn(dca)2(pym)2 and Mn(dca)2(pym)(H2O) {dca = dicyanamide; pym = pyrimidine}: New coordination polymers exhibiting 1- and 2-D topologies

Abstract

Two new coordination polymers comprised of Mn²⁺, N(CN)₂⁻ (dicyanamide, herein denoted dca) and pyrimidine (pym) have been synthesized and structurally and magnetically characterized. Mn(dca)₂(pym)₂, 1, crystallizes in the orthorhombic space group Pbcn and forms trans bi-bridged Mn–(µ_1,5-dca)₂–Mn ribbons that extend along the b-axis of the unit cell. Two terminally bonded pym ligands are trans-coordinated to the Mn center. Adjacent chains interdigitate in an undulating fashion presumably due to a templating effect imposed by the pym ligands where N-atoms of consecutive pym rings stack parallel to the chain axis. Mn(dca)₂(pym)(H₂O), 2, which crystallizes in the monoclinic space group P2₁/c, has a unique interdigitated 2D network that consists of double-bridged [Mn₂(dca)₂(pym)₂(H₂O)₂]²⁺ “dimers” that are connected via single-bridging dca ligands. Each MnN₅O octahedron is comprised of a coordinated H₂O, a monodentate pym ligand, and four µ_1,5-bridging dca anions. The magnetic data for 1 were fitted to a uniform antiferromagnetic chain model which yielded J/k_B = −0.34(1) K. In contrast, 2 is best described as an alternating chain owing to the presence of both single- and double-bridging dca anions; a least-squares fit afforded J_a = −0.43(1) and J_b = −0.20(2) K, respectively. A transition to long-range magnetic ordering was observed for 2 below ∼2.4 K in addition to a field-induced spin flop transition at 15.6 kOe (1.7 K).