Network Flexibility: Control of Gate Opening in an Isostructural Series of Ag-MOFs by Linker Substitution

An isostructural series of 15 structurally flexible microporous silver metal–organic frameworks (MOFs) is presented. The compounds with a dinuclear silver core as secondary building unit (Ag₂N₄) can be obtained under solvothermal conditions from substituted triazolyl benzoate linkers and AgNO₃ or Ag₂SO₄; they exhibit 2-fold network interpenetration with <b>lvt</b> topology. Besides the crystal structures, the calculated pore size distributions of the microporous MOFs are reported. Simultaneous thermal analyses confirm the stability of the compounds up to 250 °C. Interconnected pores result in a three-dimensional pore structure. Although the porosity of the novel coordination polymers is in the range of only 20–36%, this series can be regarded as a model system for investigation of network flexibility, since the pore diameters and volumes can be gradually adjusted by the substituents of the 3-(1,2,4-triazol-4-yl)-5-benzamidobenzoates. The pore volumes of selected materials are experimentally determined by nitrogen adsorption at 77 K and carbon dioxide adsorption at room temperature. On the basis of the flexible behavior of the linkers a reversible framework transformation of the 2-fold interpenetrated network is observed. The resulting adsorption isotherms with one or two hysteresis loops are interpreted by a gate-opening process. Due to external stimuli, namely, the adsorptive pressure, the materials undergo a phase transition confirming the structural flexibility of the porous coordination polymer

Cavitands Incorporating a Lewis Acid Dinickel Chelate Function as Receptors for Halide Anions

The halide binding properties of the cavitand [Ni₂(L^Me2H4)]²⁺ (<b>4</b>) are reported. Cavitand <b>4</b> exhibits a chelating N₃Ni­(μ-S)₂NiN₃ moiety with two square-pyramidal Ni^IIN₃S₂ units situated in an anion binding pocket of ∼4 Å diameter formed by the organic backbone of the (L^Me2H4)^2– macrocycle. The receptor reacts with fluoride, chloride (in MeCN/MeOH), and bromide (in MeCN) ions to afford an isostructural series of halogenido-bridged complexes [Ni₂(L^Me2H4)­(μ-Hal)]⁺ (Hal = F^– (<b>5</b>), Cl^– (<b>6</b>), and Br^– (<b>7</b>)) featuring a N₃Ni­(μ-S)₂(μ-Hal)­NiN₃ core structure. No reaction occurs with iodide or other polyatomic anions (ClO₄^–, NO₃^–, HCO₃^–, H₂PO₄^–, HSO₄^–, SO₄^2–). The binding events are accompanied by discrete UV–vis spectral changes, due to a switch of the coordination geometry from square-pyramidal (N₃S₂ donor set in <b>4</b>) to octahedral in the halogenido-bridged complexes (N₃S₂Hal donor environment in <b>5</b>–<b>7</b>). In MeCN/MeOH (1/1 v/v) the log <i>K</i>₁₁ values for the 1:1 complexes are 7.77(9) (F^–), 4.06(7) (Cl^–), and 2.0(1) (Br^–). X-ray crystallographic analyses for <b>4</b>(ClO₄)₂, <b>4</b>(I)₂, <b>5</b>(F), <b>6</b>(ClO₄), and <b>7</b>(Br) and computational studies reveal a significant increase of the intramolecular distance between two propylene groups at the cavity entrance upon going from F^– to I^– (for the DFT computed structure). In case of the receptor <b>4</b> and fluorido-bridged complex <b>5</b>, the corresponding distances are nearly identical. This indicates a high degree of preorganization of the [Ni₂(L^Me2H4)]²⁺ receptor and a size fit mismatch of the receptor binding cavity for anions larger than F^–

An Isomorphous Series of Cubic, Copper-Based Triazolyl Isophthalate MOFs: Linker Substitution and Adsorption Properties

An isomorphous series of 10 microporous copper-based metal–organic frameworks (MOFs) with the general formulas _∞³[{Cu₃(μ₃-OH)­(X)}₄{Cu₂(H₂O)₂}₃(H-R-trz-ia)₁₂] (R = H, CH₃, Ph; X^2– = SO₄^2–, SeO₄^2–, 2 NO₃^2– (<b>1</b>–<b>8</b>)) and _∞³[{Cu₃(μ₃-OH)­(X)}₈{Cu₂(H₂O)₂}₆(H-3py-trz-ia)₂₄Cu₆]­X₃ (R = <i>3</i>py; X^2– = SO₄^2–, SeO₄^2– (<b>9</b>, <b>10</b>)) is presented together with the closely related compounds _∞³[Cu₆(μ₄-O)­(μ₃-OH)₂(H-Metrz-ia)₄]­[Cu­(H₂O)₆]­(NO₃)₂·10H₂O (<b>11</b>) and _∞³[Cu₂(H-3py-trz-ia)₂(H₂O)₃] (<b>12</b>^<b>Cu</b>), which are obtained under similar reaction conditions. The porosity of the series of cubic MOFs with <b>twf-d</b> topology reaches up to 66%. While the diameters of the spherical pores remain unaffected, adsorption measurements show that the pore volume can be fine-tuned by the substituents of the triazolyl isophthalate ligand and choice of the respective copper salt, that is, copper sulfate, selenate, or nitrate

Unprecedented Trapping of Difluorooctamolybdate Anions within an α‑Polonium Type Coordination Network

New fluorinated hybrid solids [Mo₂F₂O₅(tr₂pr)] (<b>1</b>), [Co₃(tr₂pr)₂(MoO₄)₂F₂]·7H₂O (<b>2</b>), and [Co₃(H₂O)₂(tr₂pr)₃(Mo₈O₂₆F₂)]·3H₂O (<b>3</b>) (tr₂pr = 1,3-bis­(1,2,4-triazol-4-yl)­propane) were prepared from the reaction systems consisting of Co­(OAc)₂/CoF₂ and MoO₃/(NH₄)₆Mo₇O₂₄, as Co^II and Mo^VI sources, in water (<b>2</b>) or in aqueous HF (<b>1</b>, <b>3</b>) employing mild hydrothermal conditions. The tr₂pr ligand serves as a conformationally flexible tetradentate donor. In complex <b>1</b>, the octahedrally coordinated Mo atoms are linked in the discrete corner-sharing {Mo₂(μ₂-O)­F₂O₄N₄} unit in which a pair of tr-heterocycles (tr = 1,2,4-triazole) is arranged in cis-positions opposite to “molybdenyl” oxygen atoms. The <i>anti</i>–<i>anti</i> conformation type of tr₂pr facilitates the tight zigzag chain packing motif. The crystal structure of the mixed-anion complex salt <b>2</b> consists of trinuclear [Co₃(μ₃-MoO₄)₂(μ₂-F)₂] units self-assembling in Co^II-undulating chains (Co···Co 3.0709(15) and 3.3596(7) Å), which are cross-linked by tr₂pr in layers. In <b>3</b>, containing condensed oxyfluoromolybdate species, linear centrosymmetric [Co₃(μ₂-tr)₆]⁶⁺ SBUs are organized at distances of 10.72–12.45 Å in an α-Po-like network using bitopic tr-linkers. The octahedral {N₆} and {N₃O₃} environments of the central and peripheral cobalt atoms, respectively, are filled by triazole N atoms, water molecules, and coordinating [Mo₈O₂₆F₂]^6– anions. Acting as a tetradentate O-donor, each difluorooctamolybdate anion anchors four [Co₃(μ₂-tr)₆]⁶⁺ units through their peripheral Co-sites, which consequently leads to a novel type of a two-nodal 4,10-c net with the Schläfli symbol {3².4³.5}­{3⁴.4²⁰.5¹⁶.6⁵}. The 2D and 3D coordination networks of <b>2</b> and <b>3</b>, respectively, are characterized by significant overall antiferromagnetic exchange interactions (<i>J</i>/<i>k</i>) between the Co^II spin centers on the order of −8 and −4 K. The [Mo₈O₂₆F₂]^6– anion is investigated in detail by quantum chemical calculations

Unprecedented Trapping of Difluorooctamolybdate Anions within an α‑Polonium Type Coordination Network

New fluorinated hybrid solids [Mo₂F₂O₅(tr₂pr)] (<b>1</b>), [Co₃(tr₂pr)₂(MoO₄)₂F₂]·7H₂O (<b>2</b>), and [Co₃(H₂O)₂(tr₂pr)₃(Mo₈O₂₆F₂)]·3H₂O (<b>3</b>) (tr₂pr = 1,3-bis­(1,2,4-triazol-4-yl)­propane) were prepared from the reaction systems consisting of Co­(OAc)₂/CoF₂ and MoO₃/(NH₄)₆Mo₇O₂₄, as Co^II and Mo^VI sources, in water (<b>2</b>) or in aqueous HF (<b>1</b>, <b>3</b>) employing mild hydrothermal conditions. The tr₂pr ligand serves as a conformationally flexible tetradentate donor. In complex <b>1</b>, the octahedrally coordinated Mo atoms are linked in the discrete corner-sharing {Mo₂(μ₂-O)­F₂O₄N₄} unit in which a pair of tr-heterocycles (tr = 1,2,4-triazole) is arranged in cis-positions opposite to “molybdenyl” oxygen atoms. The <i>anti</i>–<i>anti</i> conformation type of tr₂pr facilitates the tight zigzag chain packing motif. The crystal structure of the mixed-anion complex salt <b>2</b> consists of trinuclear [Co₃(μ₃-MoO₄)₂(μ₂-F)₂] units self-assembling in Co^II-undulating chains (Co···Co 3.0709(15) and 3.3596(7) Å), which are cross-linked by tr₂pr in layers. In <b>3</b>, containing condensed oxyfluoromolybdate species, linear centrosymmetric [Co₃(μ₂-tr)₆]⁶⁺ SBUs are organized at distances of 10.72–12.45 Å in an α-Po-like network using bitopic tr-linkers. The octahedral {N₆} and {N₃O₃} environments of the central and peripheral cobalt atoms, respectively, are filled by triazole N atoms, water molecules, and coordinating [Mo₈O₂₆F₂]^6– anions. Acting as a tetradentate O-donor, each difluorooctamolybdate anion anchors four [Co₃(μ₂-tr)₆]⁶⁺ units through their peripheral Co-sites, which consequently leads to a novel type of a two-nodal 4,10-c net with the Schläfli symbol {3².4³.5}­{3⁴.4²⁰.5¹⁶.6⁵}. The 2D and 3D coordination networks of <b>2</b> and <b>3</b>, respectively, are characterized by significant overall antiferromagnetic exchange interactions (<i>J</i>/<i>k</i>) between the Co^II spin centers on the order of −8 and −4 K. The [Mo₈O₂₆F₂]^6– anion is investigated in detail by quantum chemical calculations