Zhan-Feng Ju

A two-step field-induced magnetic transition in spin-canted systems observed only for the CoII coordination polymer

Two isostructural 1D compounds {[M3(hpdc)2(H2O)6] 2H2O}n (M = Mn, Co; H3hpde = 2-hydroxypyrimidine-4,6-dicarboxylic acid) were synthesized by the in situ hydrothermal reactions of 2-chloropyrimidine-4,6-dicarboxylic acid with MCl2 (M = Mn, Co) and NaOH; the MnII compound shows spin-canted antiferromagnetism, whereas the CoII compound exhibits the coexistence of spin-canting and a two-step field-induced magnetic phase transition.

Syntheses, structures, and photoluminescent properties of ten metal–organic frameworks constructed by a flexible tetracarboxylate ligand

Reactions of zinc ions with the flexible tetracarboxylate ligand, 5,5′-(1,4-phenylenebis(methylene))bis(oxy)diisophthalic acid (H4L1) gave rise to ten complexes, namely {[Zn3(L1)(OH)2(H2O)2]3H2O}n (1), {[Zn(H2L1)(H2O)2]H2O}n (2), [Zn2(L1)(H2O)4]n (3), {[Zn2(H3L1)2(H2L1)(H2O)2(MeCN)2]}n (4), [Zn2(H3L1)2(H2L1)(2,2′-bipy)2]n (5), [Zn2(H3L1)2(H2L1)(1,10-phen)2]n (6), {[Zn2(L1)(4,4′-bipy)2]4H2O}n (7), {[Zn2(L1)(bpe)2]4H2O}n (bpe = 1,2-bi(4-pyridyl)ethene) (8), {[Zn2(L1)(pdp)2]4H2O}n (pdp = 4-[(E)-4-Pyridinylazo]pyridine) (9) and {[Zn2(L1)(bpmp)2]6H2O}n (bpmp = N,N′-bis-(4-pyridyl-methyl) piperazine) (10). The H4L1 ligand not only displayed different deprotonated forms, but also diverse coordination modes and conformations. Compounds 1–4 are constructed of only zinc atoms with H4L1 ligands while compounds 5–10 are constructed of zinc atoms and H4L1 ligands with various N-donor ligands (Scheme 1). Compound 1 features a 3D architecture constructed of a linear Zn3 cluster with H4L1 ligands. Compound 2 is a 2D waved layer structure with (4,4) grid as sql topology. Compound 3 displays a three-dimensional (3D) network simplified by a (3,6)-connected 2-nodal net with ant topology. Compounds 4, 5 and 6 all exhibit 1D infinite chains coordination structure, in which the H4L1 ligand is displayed as two kinds of deprotonated forms. Compounds 7, 8, 9 and 10 are similar and possess (4,4)-connected 3D frameworks with bbf topology, while also exhibiting an intriguing three-fold interpenetrated structure. These results indicate that subtle environmental factors, such as solvent, pH value and neutral auxiliary ligands play important roles in the formation of the structures of the final framework. At the same time, the photochemical properties of compounds 1–10 were tested in the solid state at room temperature, and the luminescent properties of compound 9 and 10 when dispersed in different solvents were investigated. These showed solvent-dependent luminescent spectra with emission intensities significantly quenched towards nitrobenzene. The quenching effects are observed at a low nitrobenzene concentration of 200 ppm, which indicates high sensitivities of these compounds towards nitrobenzene.

Unprecedented 3D polycatenation based on ribbons of rings found in two metallosupramolecular polymers whose open frameworks show reversible collapse upon de- and rehydration

Two isostructural metallosupramolecular polymers [M(H2O)4–(BCbpy)2]2Cl4·18H2O [M = Co(II), Ni(II); HBCbpyCl = 1-(4-carboxybenzyl)-4,4′-bipyridinium chloride] have been synthesized by the self-assembly reaction of HBCbpyCl salt with MCl2 (M = Co, Ni). The unprecedented catenation of the (1D → 3D) type based on ribbons of rings is found in both supramolecular networks. Interestingly, this catenation mode can help generate channels, and the resulting supramolecular frameworks show recoverable collapse upon de- and rehydration, making them good potential adsorbents of water vapor.

Supramolecular Borromean sheet consisting of threefold parallel interwoven 44-sql layers assembled by a flexible bipyridinium ligand

An infinite two-dimensional supramolecular Borromean sheet consisting of threefold parallel interwoven 44-sql layers was obtained by the assembly of a flexible bipyridinium ligand with NiCl2 and phthalate.

2D self-catenated coordination polymer constructed by triple- and double-helical chains

The hydrothermal reaction of the prochiral amine-containing ligand 4-(4-carboxyphenylamino)-3,5-dinitrobenzoic acid, 1,3-bis(4-pyridyl)propane, zinc nitrate and NaOH results in an unprecedented 2D self-catenated network consisting of triple and double helical chains. The chirality of the stereo-chemically labile amine core can be locked via coordination interactions and transferred to the coordination polymer, facilitating the integration of the N-chirality and helicity in the 2D sheet. An unusual trefoil-type molecular knot is firstly observed in this coordination polymer.

A novel two-dimensional homochiral manganese(II)-carboxylate coordination framework exhibiting field-induced spin-flop transition

The reaction of a unique asymmetric bridging ligand 4-(4-carboxyphenylamino)-3,5-dinitrobenzoic acid (H2cpdba), MnCl2·4H2O and NaOH yields a novel two-dimensional coordination polymer, {[Mn(cpdba)(H2O)3]·H2O}n (1) containing homochiral helical Mn(II) chains linked by syn–anticarboxylate bridges, in which the chirality of a stereochemically labile amine core of a carboxylate ligand can be “locked” by the coordination bonds and consequently transferred throughout the entire coordination framework. Magnetic susceptibility measurements reveal weak antiferromagnetic interactions between adjacent Mn(II) ions, with a field-induced spin-flop magnetic transition occurring at ca. 2.6 T at 2 K.

Wings waving: coordinating solvent-induced structural diversity of new Cu(II) flexible MOFs with crystal to crystal transformation and gas sorption capability

A new semi-rigid 5-(bis(4-carboxybenzyl)amino)isophthalic acid (H4L) is designed and synthesized to obtain novel flexible metal organic frameworks (MOFs). The tetracarboxylate ligand (L4−) links to Cu(II) paddle-wheel second build units (SBUs) under different solvent condition to afford two MOFs, [Cu2(L)(S)2]n (S = DMF, 1 and H2O, 2). Single crystal X-ray diffraction structural analyses reveal that the coordinating solvent molecules are DMF and H2O in the SBUs for 1 and 2, respectively. The torsion angle between two methylene benzoate ring subunits of the ligand is 122.7° in 1 but 175.1° in 2. Three phenyl rings of the ligand are nonplanar and orient in different directions in 1 and 2. A reversible crystal to crystal transformation between 1 and 2 are investigated by exchanging the terminal ligated solvent molecule, in which the phenyl rings of the benzoate subunit act as “a pair of waving wings” accompanying the ligated solvent exchange. Time-dependent powder X-ray diffraction data confirms this reversible dynamic transformation. This hinge within the semi-rigid ligand is a built-in breathing mechanism and suggests a novel approach for general synthesis of breathing MOFs. A gas sorption study for 1 demonstrates 1 has the ability to selectively adsorb CO2 over CH4, H2 and N2.

An unprecedented 9-fold [3 × 3] interpenetrated diamondoid network coordination polymer containing Cu(II)-based “paddlewheels” as connecting node

The self-assembly of 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium dichloride with Cu(NO3)2 affords an unusual 9-fold [3 × 3] interpenetrated diamondoid-like coordination polymer with copper-based paddlewheel as connecting node, which shows interesting electronic transition and magnetic properties.

Strong electron-accepting methylviologen dication confined in magnetic hosts: synthesis, structural characterization, charge-transfer and magnetic properties of {(MV)2[Ni(SCN)5]·Cl·2H2O}n and {(MV)[M(N3)2(SCN)2]}n (M = Mn, Co)

Three hybrid host-guest compounds {(MV)2[Ni(SCN)5].Cl.2H2O}n (1), {(MV)[Mn(N3)2(SCN)2]}n (2) and {(MV)[Co(N3)2(SCN)2}n (3) (where MV2+ = methylviologen dication) have been obtained by self-assembly methods and characterized by X-ray crystallography, spectral methods and magnetic measurements. Compound 1 shows a quasi-two-dimensional structure which is formed by novel single thiocyanate-bridged Ni(II) chains connected through S...S interactions. Compounds 2 and 3 are isostructural, containing single micro(1,3)-azide bridged Mn(II)/Co(II) square layers. MV2+, as a strong electron-acceptor and a template, is embedded between the anionic layers in all three compounds. The charge-transfer (CT) interactions between MV2+ and the anionic hosts have been revealed by structural analysis and UV-vis diffuse reflection spectroscopy. The magnetic studies of the compounds show antiferromagnetic interactions between adjacent metal ions (J = -34.52(7) cm(-1) for 1, J = -3.90(2) cm(-1) for 2 and J = -10.96(6) cm(-1) for 3).

Poly[[hexaaquabis[μ4-2-hydroxy-5-(4-sulfonatophenyldiazenyl)benzoato]dibarium(II)] 4,4′-bipyridine solvate]

The title compound, {[Ba2(C(13)H(8)N(2)O(6)S)2(H2O)6].C(10)H(8)N(2)}n, possesses a novel two-dimensional porous coordination network, in which each Ba(II) ion is nine-coordinated by three carboxylate O atoms, two sulfonate O atoms and four water molecules in an irregular coordination environment. Hydrogen-bond interactions between coordinated water molecules and sulfonate/hydroxyl groups hold the network layers together and produce a three-dimensional supramolecular architecture.