Ai-Ling Cheng

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.

Novel frustrated magnetic lattice based on triangular [Mn3(μ3-F)] clusters with tetrazole ligands

Unprecedented [Mn(II)(3)(micro(3)-F)(micro-N-N)(3)] triangular clusters with tetrazole ligands are linked by Mn(II) ions to generate a novel spin-frustrated 2D lattice exhibiting antiferromagnetic ordering.

Unprecedented 3D entanglement of 1D zigzag coordination polymers leading to a robust microporous framework

One-dimensional zigzag coordination chains in four different directions are hierarchically entangled to generate an unprecedented 3D interwoven framework, which exhibits permanent porosity and guest selectivity.

Magnetic Ordering in Three-Dimensional Metal–Organic Frameworks Based on Carboxylate Bridged Square-Grid Layers

Three isomorphous metal-organic frameworks of formula [M(ppdc)(H(2)O)(2)](n) [M = Mn(II), Fe(II), and Co(II)] were synthesized from sodium p-phenylenediacrylic (Na(2)ppdc). Crystallographic studies revealed that the compounds are layer-pillared 3D frameworks in which the square-grid M(II) layers with single carboxylate bridges are interlinked by long organic spacers with large interlayer separations of about 13 Å. Magnetic investigations indicated that they all display intralayer antiferromagnetic interactions through the carboxylate bridges in the unusual skew-skew coordination mode but the bulk behaviors are quite different. The Co(II) compound, like most compounds containing similar M-O-C-O-M layers, shows no 3D magnetic ordering down to 2 K, while the Mn(II) and Fe(II) compounds exhibit spin-canted ordering, behaving as a weak ferromagnet (T(C) = 3.8 K) and a metamagnet (T(N) = 3.8 K, H(c) = 650 Oe), respectively. Spin-canted ordering is still a rarity in this series of materials. Magnetostructural comparisons with analogous compounds indicate that the occurrence of spin-canted ordering can be related to the uncommon skew-skew and anti-anti coordination modes of carboxylate bridges, which induce stronger antiferromagnetic interactions than the common syn-anti mode.

Unusual composition dependence of magnetic relaxation for CoII1−xNiIIx chain-based metal–organic frameworks

A series of isomorphous 3D Co(II)(1-x)Ni(II)(x) MOFs based on ferromagnetic chains show SCM-type slow relaxation and the Co-rich system can exhibit a higher blocking temperature than both Co(II) and Ni(II) parent materials.

Manganese(II)-carboxylate-pseudohalide systems derived from 1,4-bis(4-carboxylatopyridinium-1-methylene)benzene: structures and magnetism

The reactions of manganese(II) acetate or perchlorate, sodium azide or sodium cyanate, and the zwitterionic dicarboxylate ligand 1,4-bis(4-carboxylatopyridinium-1-methylene)benzene (L) under different conditions yielded three different Mn(II) coordination polymers with mixed carboxylate and azide (or cyanate) bridges: {[Mn (L(1))(0.5)(N(3))(OAc)]·3H(2)O}(n) (1), {[Mn(4)(L(1))(N(3))(8)(H(2)O)(4)(CH(3)OH)(2)]·[L(1)]}(n) (2), and {[Mn(3)(L(1))(NCO)(6)(H(2)O)(4)]·[L(1)]·[H(2)O](2)}(n) (3). The compounds exhibit diverse structures and magnetic properties. In 1, the 1D uniform anionic [Mn(N(3))(COO)(2)](n) chains with the (μ-EO-N(3))(μ-COO)(2) triple bridges (EO = end-on) are interlinked by the dipyridinium L ligands into highly undulated 2D layers. Magnetic studies on 1 reveal that the mixed triple bridges induce antiferromagnetic coupling between Mn(II) ions. Compounds 2 and 3 consist of 1D neutral polymeric chains and co-crystallized zwitterions, and the chains are formed by the L ligands interlinking linear polynuclear units. The polynuclear unit in 2 is tetranuclear with (μ-EO-N(3))(2) as central bridges and (μ-EO-N(3))(2)(μ-COO) as peripheral bridges, while that in 3 is trinuclear with (μ-NCO)(2)(μ-COO) bridges. Magnetic studies demonstrate that the magnetic coupling through the mixed azide/isocyanate and carboxylate bridges in 2 and 3 is antiferromagnetic. An expression of magnetic susceptibility based on a 2-J model for linear tetranuclear systems of classical spins has been deduced and applied to 2.

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.

Layered and pillar-layered metal–organic frameworks based on pinwheel trinuclear zinc-carboxylate clusters

Three new Zn(II) metal–organic coordination polymers, [Zn3(STDC)3(py)2] (1), [Zn3(STDC)3(4,4′-bpy)] (2), [Zn3(STDC)3(bpea)] · 3H2O (3), where H2STDC = trans-stilbene-4,4′-dicarboxylic acid, py = pyridine, 4,4′-bipy = 4,4′-bipyridine, bpea = 1,2-bis(4-pyridyl)ethane, were prepared by solvothermal reactions of Zn(II) acetate with H2STDC in the presence of py or linear bis(pyridyl) molecules. Compound 1 is a 2D triangle-tessellated layered network based on a pinwheel trinuclear zinc-carboxylate clusters as secondary building unit with py as the terminal ligand. Compounds 2 and 3 contain similar layers, which are linked into layer-pillared 3D frameworks by the ditopic bipy or bpea ligand in place of py. Comparing the structures of 2 and 3, the increase in pillar length does not lead to increased multiplicity in interpenetration, due to the limitation of the intralayer space dimensions, but it induces expanded and unequal interlayer separations.

Mixed azide and carboxylate bridged trinuclear Mn(II) and Co(II) motifs in coordination ladders: structures and magnetism

Two isomorphous Mn(II) and Co(II) coordination polymers with an azide and zwitterionic dicarboxylate ligand as coligands were synthesized and structurally characterized, and their magnetic properties were studied. They are formulated as [M3(L)2(N3)6(H2O)2]·2H2O (M = Mn (1), Co (2), L = 1,2-bis(4-carboxylatopyridinium-1-methylene)benzene). The compounds contain anionic linear [Mn3(N3)6(COO)4(H2O)2]4− units built from the simultaneous bridges of a syn–syn carboxylate and two end-on azides. The anionic trinuclear units are linked into ladder-like coordination polymers by the cationic bis(pyridinium) tether of the organic ligand. Analyses of the temperature- and field-dependent magnetic data of the compounds revealed that the mixed [(COO)(EO–N3)2] triple bridges transmit antiferromagnetic and ferromagnetic coupling in 1 and 2, respectively.

Supramolecular networks assembled from binuclear complexes with pyridazine-3,6-dicarboxylate

Solvothermal reactions of dimethyl pyridazine-3,6-dicarboxylate and appropriate metal chlorides in the absence/presence of KCl, NaCl or NH4Cl yielded a series of coordination compounds of pyridazine-3,6-dicarboxylate (pzdc) with Mn(II), Co(II), Ni(II) and Zn(II). All the Mn(II) compounds contain the anionic binuclear motif [Mn2(pzdc)3]2− with the trigonal prismatic shape. Through the K/Na-O electrostatic coordination, charge-assisted N–H⋯O hydrogen bonds, and weak C–H⋯O hydrogen-bonds, the binuclear prismatic anion co-assembles with different cations ([Mn(H2O)6]2+, K+, Na+ or NH4+) to generate 3D architectures. Under similar synthetic conditions, the Co(II) and Ni(II) ions always give the neutral binuclear molecules [M2(pzdc)2(H2O)4], which are self-assembled into 3D hydrogen-bonded networks. The Zn(II) ion seems to be amphibious: in the presence of NH4+, K+ and Na+, it forms the [Zn2(pzdc)3]2− species that are isostructural with the Mn(II) species, but the absence of the above cations leads to [Zn2(pzdc)2(H2O)4], which is isomorphous with the Co(II) and Ni(II) compounds. The different structures have been qualitatively explained based on the metal ionic size, ligand constraints, inter-ligand repulsion, ligand-field effects, and anionic–cationic interactions. Magnetic studies on selected Mn(II) compounds reveal that weak antiferromagnetic coupling is operative through the triple pyridazine bridges within the prismatic anions.