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

摘要

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 -(mu(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 P2(1)/c, has a unique interdigitated 2D network that consists of double-bridged [Mn-2( 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 mu(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 similar to 2.4 K in addition to a field- induced spin flop transition at 15.6 kOe ( 1.7 K).