Qin-Xiang Jia

Diverse Structures and Magnetism of Cobalt(II) and Manganese(II) Compounds with Mixed Azido and Carboxylato Bridges Induced by Methylpyridinium Carboxylates

Herein we present a systematic study of the structures and magnetic properties of six coordination compounds with mixed azide and zwitterionic carboxylate ligands, [M(N(3) )(2) (2-mpc)] (2-mpc=N-methylpyridinium-2-carboxylate; M=Co for 1 and Mn for 2), [M(N(3) )(2) (4-mpc)] (4-mpc=N-methylpyridinium-4-carboxylate; M=Co for 3 and Mn for 4), [Co(3) (N(3) )(6) (3-mpc)(2) (CH(3) OH)(2) ] (5), and [Mn(3) (N(3) )(6) (3-mpc)(2) ] (6; 3-mpc=N-methylpyridinium-3-carboxylate). Compounds 1-3 consist of one-dimensional uniform chains with (μ-EO-N(3) )(2) (μ-COO) triple bridges (EO=end-on); 5 is also a chain compound but with alternating [(μ-EO-N(3) )(2) (μ-COO)] triple and [(EO-N(3) )(2) ] double bridges; Compound 4 contains two-dimensional layers with alternating [(μ-EO-N(3) )(2) (μ-COO)] triple, [(μ-EO-N(3) )(μ-COO)] double, and (EE-N(3) ) single bridges (EE=end-to-end); 6 is a layer compound in which chains similar to those in 5 are cross-linked by a μ(3) -1,1,3-N(3) azido group. Magnetically, the three Co(II) compounds (1, 3, and 5) all exhibit intrachain ferromagnetic interactions but show distinct bulk properties: 1 displays relaxation dynamics at very low temperature, 3 is an antiferromagnet with field-induced metamagnetism due to weak antiferromagnetic interchain interactions, and 5 behaves as a noninnocent single-chain magnet influenced by weak antiferromagnetic interchain interactions. The magnetic differences can be related to the interchain interactions through π-π stacking influenced by different substitution positions in the ligands and/or different magnitudes of intrachain coupling. All of the Mn(II) compounds show overall intrachain/intralayer antiferromagnetic interactions. Compound 2 shows the usual one-dimensional antiferromagnetism, whereas 4 and 6 exhibit different weak ferromagnetism due to spin canting below 13.8 and 4.6 K, respectively.

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 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.

Unprecedented Self-Catenated Eight-Connected Network Based on Novel Azide-Bridged Tetramanganese(II) Clusters

The combination of the azide bridge and a neutral inner-salt-type dicarboxylate ligand leads to a three-dimensional coordination framework that contains unprecedented azide-bridged tetramanganese(II) clusters and defines a novel self-catenated, eight-connected net of 4(16) x 6(12) topology.

Syntheses, structures and luminescence properties of cadmium(II) coordination polymers with in situ formed oxalate and bis(chelating) bridging ligands

Hydrothermal reactions of 2-cyanopyrimidine and CdCl2 in the absence and presence of sodium azide yielded two coordination polymers, [Cd3(ox)2(pymc)2]·2H2O (1) and [Cd2(pymtz)2(ox)]·H2O (2), respectively, where pymc = 2-pyrimidinecarboxylate, pymtz = 5-(2′-pyrimidyl)tetrazolate and ox = oxalate. All the ligands in these compounds were generated in situ by the hydrolysis of 2-cyanopyrimidine (pymCN) or the [2 + 3] cycloaddition of the azide ion to the nitrile. In compound 1, seven-coordinated Cd ions are linked by oxalate bridges into a diamond network based on Cd2O2 nodes, and eight-coordinated Cd ions are linked to the network through pymc and oxalate bridges. In compound 2, seven-coordinated Cd ions are bridged by oxalate ions into 1D Cd2(ox) ribbons, which are further linked by bis(chelating) pymtz to give a 3D framework that exhibits the 5-connected 4466 net topology based on Cd2O2 nodes. The compounds exhibit intense luminescence in the solid state.