Two isostructural heterometallic coordination polymers (HCPs) based on {M^IIGd^III₂} clusters (M^II=Mn and Ni) have been obtained from the conventional one-pot self-assembly of Gd^III ions and H₄abtc ligands (H₄abtc=3,3′,5,5′-azobenzenetetracarboxylic acid) with corresponding transition-metal ions in mixed N,N-dimethylformamide (DMF)/H₂O solvents. The formulas are expressed as {[NH₂(CH₃)₂]₂[M^IIGd^III₂(HCOO)₂(abtc)₂]}_n (M^II=Mn for 1 and Ni for 2). The common features of both HCPs are that two Gd^III ions and one M^II ion interconnected through abtc⁴⁻ ligands present “hourglass”-type {M^IIGd^III₂} clusters, which are further linked by HCOO⁻ and abtc⁴⁻ ligands to produce 3D (4,4,10)-connected topological frameworks. Magnetic results reveal that both 1 and 2 possess remarkable magnetocaloric effects (MCE) with maximum −ΔS_m values of 31.9 and 29.5 J kg⁻¹ K⁻¹ at 3.0 K for an applied field of 70 kOe, respectively. Furthermore, the skeletons of two HCPs were stable up to at least 310 °C as supported by thermogravimetric (TG) analyses and in situ variable-temperature powder X-ray diffraction (PXRD) patterns.

Silver nanoparticles were successfully supported on the zeolite-type metal–organic framework MIL-101 to yield Ag@MIL-101 by a simple liquid impregnation method. For the first time, the conversion of terminal alkynes into propiolic acids with CO₂ was achieved by the use of the Ag@MIL-101 catalysts. Owing to the excellent catalytic activity, the reaction proceeded at atmospheric pressure and low temperature (50 °C). The Ag@MIL-101 porous material is of outstanding bifunctional character as it is capable of simultaneously capturing and converting CO₂ with low energy consumption and can be recovered easily by centrifugation.

Luminescent 3D lanthanide metal–organic framework (Ln-MOF) {[Tb₂(TATAB)₂]⋅4 H₂O⋅6 DMF}_n (1) was synthesized under solvothermal conditions by using flexible ligand 4,4′,4′′-s-triazine-1,3,5-triyltri-p-aminobenzoate (TATAB). A phase transition was observed between low temperature and room temperature. The luminescence of 1 could be enhanced by formaldehyde and quenched efficiently by trace amounts of benzaldehyde in solvents such as benzyl alcohol (0.01–2.0 vol %) and ethanol (0.01–2.5 vol %). This is the first use of a Ln-MOF as chemical sensor for both formaldehyde and benzaldehyde. The high sensitivity and selectivity of the luminescence response of 1 to benzaldehyde allows it to be used as an excellent sensor for identifying benzaldehyde and provides a simple and convenient method for detecting traces of benzaldehyde in benzyl alcohol based injections. This work establishes a new strategy for detection of benzaldehyde in benzyl alcohol by luminescent MOFs.

Four isostructural cobalt(II)–lanthanide(III) heterometallic metal–organic frameworks (MOFs), formulated as {[(CH₃)₂NH₂]₃[Co₃Ln(tda)₃(HCOO)₃] 2H₂O 0.75dmf}_n [Ln = Eu (Co-Eu), Gd (Co-Gd), Tb (Co-Tb), and Dy (Co-Dy); H₃tda = 1H-1,2,3-triazole-4,5-dicarboxylic acid] have been successfully synthesized and structurally characterized in detail. In these Co-Ln heterometallic MOFs, three neighboring Co^II ions are connected by HCOO^– anions to form triangular [Co₃(HCO₂)₃]³⁺ clusters. The equivalent triangular [Co₃(HCO₂)₃]³⁺ clusters are connected by six tda^3– anions to generate a 1D trigonal prismatic chain, which are further interconnected through Ln^III ions to give unique 3D (6,6)-connected nia nets with the Schläfli symbol of (4¹² 6³) (4⁹ 6⁶). The magnetic properties of the four isostructural Co-Ln heterometallic MOFs have also been studied.

A series of six-coordinate lanthanide complexes {(H₃O)[Ln(NA)₂]⋅H₂O}_n (H₂NA=5-hydroxynicotinic acid; Ln=Gd^III (1⋅Gd); Tb^III (2⋅Tb); Dy^III (3⋅Dy); Ho^III (4⋅Ho)) have been synthesized from aqueous solution and fully characterized. Slow relaxation of the magnetization was observed in 3⋅Dy. To suppress the quantum tunneling of the magnetization, 3⋅Dy diluted by diamagnetic Y^III ions was also synthesized and magnetically studied. Interesting butterfly-like hysteresis loops and an enhanced energy barrier for the slow relaxation of magnetization were observed in diluted 3⋅Dy. The energy barrier (Δ_τ) and pre-exponential factor (τ₀) of the diluted 3⋅Dy are 75 K and 4.21×10⁻⁵ s, respectively. This work illustrates a successful way to obtain low-coordination-number lanthanide complexes by a framework approach to show single-ion-magnet-like behavior.

Four complexes based on rare earth biradicals [Ln(hfac)₃(NITPhmbis)₂]₂ {Ln = La (1), Nd (2), Gd (3), Tb (4); hfac = hexafluoroacetylacetone; NITPhmbis = [1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene]} were successfully synthesized under appropriate conditions. Single-crystal structures show that 1 is a mononuclear two spin complex and 2–4 are mononuclear three spin complexes, in which a NITPhmbis molecule acts as a bidentate ligand with one coordinated lanthanide ion. The four complexes are isomorphous, the coordination number around the lanthanide ion is eight, and the polyhedron is a 4,4-bicappped trigonal prism. For lanthanum(III) complex 1, the temperature dependence of the magnetic susceptibility indicates that weakly antiferromagnetically coupled radicals exist (J_rad–rad = –1.2 cm^–1). In the case of neodymium(III) complex 2, its magnetic behavior gives antiferromagnetic Nd^III–radical interactions, whereas for complexes 3 and 4, static magnetic properties show that the Gd^III and Tb^III ions interact ferromagnetically with the radical. The dynamic magnetic properties of 4 were also measured, and 4 was found to exhibit slow relaxation of the magnetization at low temperature.

A rare, robust microporous lanthanide metal–organic framework with 1D honeycomb-type channels is presented. Excellent adsorption capabilities for N₂, H₂, and CO₂ and significant selective sorption of CO₂ over N₂ and CH₄ were observed. Moreover, the guest-dependent luminescent behavior of these lanthanide materials shows a potential use for the sensing of small-molecule pollutants such as benzene and acetone.

The combination of the anisotropic Dy^III ion and organic radicals as spin carriers results in discrete and one-dimensional lanthanide–radical magnetic materials, namely, [Dy(hfac)₃(NITThienPh)₂] (1) and [Dy₂(hfac)₆(NITThienPh)₂]_n (2; hfac=hexafluoroacetylacetonate, NITThienPh=2-(5-phenyl-2-thienyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide). Linking monomeric 1 with the Dy^III ion leads to the formation of polymeric 2, and the transformation between them is chemically controllable and reversible. The characterization of both static and dynamic magnetic properties shows that the dominant intrachain exchange interaction is important to observe magnetic bistability in 2 rather than that in 1. Monomeric 1 exhibits paramagnetic behavior, whereas polymeric 2 shows the unusual coexistence of superparamagnetic and two-step field-induced metamagnetic behaviors. The antiferromagnetic ground state of 2 does not prevent the dynamic relaxation of the magnetization with the finite-sized effect in the lanthanide–radical system. Energy barriers to thermally activated relaxation for 2 are 53 and 98 K in the low- and high-temperature regimes, respectively. A hysteresis loop is observed with the coercive field of 99 Oe at 2 K.

A new porous metal-organic framework (MOF) {[CuL]·DMF·2H₂O}_n [1a, H₂L = 5-(4H-1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid; DMF = N,N-dimethylformamide] with zigzag-shaped, narrow channels was prepared by solvothermal synthesis and structurally characterized. 1a has zigzag-shaped, open channels with micropore sizes of approximately 5.6 × 4.6 Ų. The (3,6)-connected network of 1a leads to an α-PbO₂ (apo) topology. The adsorption properties (N₂, H₂, and CO₂) of the desolvated sample 1c have been studied. The results show that 1c has a highly porous structure and a high adsorption capacity: the total capture of CO₂ at 1 bar and 298 K is 22.01 wt.-%, and the total H₂ uptake at 1 bar and 77 K is 1.46 wt.-%. This high adsorption capacity can be attributed to strong interactions between the small gas molecules and the irregularly open channels with their zigzag shape and their narrow pore size.

A series of rare-earth luminescent complexes {[Eu(pta)(H₂O)₃]·H₂O}_n (1, H₃pta=pyridine-2,4,6-tricarboxylic acid) and {[Eu_xY_(1−x)(pta)(H₂O)₃]·H₂O}_n (2–10) have been synthesized. Complexes 1 and 8 were determined by single-crystal X-ray diffraction, while other complexes were characterized by powder X-ray diffraction, displaying the similar structural mode. The luminescent properties of complexes 1–10 were investigated and the results show that the emission intensities of mixed rare-earth complexes 2–10 are the same or even higher than that of homometallic complex 1 with the increasing Y(III) ions.

A robust porous metal–organic framework (MOF), [Co₃(ndc)(HCOO)₃(μ₃-OH)(H₂O)]_n (1) (H₂ndc=5-(4-pyridyl)-isophthalic acid), was synthesized with pronounced porosity. MOF 1 contained two different types of nanotubular channels, which exhibited a new topology with the Schlafli symbol of {4².6⁵.8³}{4².6}. MOF 1 showed high-efficiency for the selective sorption of small molecules, including the energy-correlated gases of H₂, CH₄, and CO₂, and environment-correlated steams of alcohols, acetone, and pyridine. Gas-sorption experiments indicated that MOF 1 exhibited not only a high CO₂-uptake (25.1 wt % at 273 K/1 bar) but also the impressive selective sorption of CO₂ over N₂ and CH₄. High H₂-uptake (2.04 wt % at 77 K/1 bar) was also observed. Moreover, systematic studies on the sorption of steams of organic molecules displayed excellent capacity for the sorption of the homologous series of alcohols (C₁–C₅), acetone, pyridine, as well as water.

Manganese(II), cobalt(II), and zinc(II) coordination polymers, {[Mn(H₂btec)(azopy)(H₂O)₂]·(azopy)}_n (1), {[Co(H₂btec)(azopy)(H₂O)₂]·(azopy)}_n (2), and {[Zn_2.5(btec)(azopy)(μ₃-OH)(H₂O)]·H₂O}_n (3) (H₄btec = 1,2,4,5-benzenetetracarboxylic acid; azopy = 4,4′-azobispyridine), were synthesized by ahydrothermal method and characterized by single-crystal X-ray diffraction, elemental analysis, and powder X-ray diffraction. Compounds 1 and 2 are isomorphic and crystallize in the triclinic space group P, exhibiting a 2D grid framework bridged by two types of ligands. Compound 3 also crystallizes in the triclinic space group P and possess an interesting 3D coordination framework with an unprecedented dodecadentate coordination mode and a unique {4¹⁶.5¹⁰.6¹⁸.7}{4⁴.5.6}² topological structure. The ideal topology of 3 has not been encountered in metal–organic framework chemistry, which has been deposited in the Reticular Chemistry Structure Resource under the name zim net. Magnetic studies show that there are antiferromagnetic interactions in both 1 and 2. The cyclic voltammograms of 1–3 in the solid state were also obtained.

Two zinc(II) complexes, [Zn₉(L1)₆(H₂O)₂]·13.5H₂O (1) and [Zn₉(L2)₆(H₂O)₃]·C₂H₅OH·8.5H₂O (2), were synthesized. Both 1 and 2 are constructed from molecular building units (MBUs) that contain heptanuclear zinc clusters as cores. By introducing an additional chiral site into the original ligand, we achieved the transformation of the MOF from a nonchiral to a chiral structure, which provides a new strategy for designing chiral compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)