Zinc and cadmium coordination polymers assembled with 2,2′-bipyridine and bithiophenedicarboxylic acid: Effect of metal ions on the conformation of ligand

A Series of Metal-Organic Frameworks with 2,2'-Bipyridyl Derivatives: Synthesis vs. Structure Relationships, Adsorption, and Magnetic Studies

Five new metal-organic frameworks based on Mn(II) and 2,2'-bithiophen-5,5'-dicarboxylate (btdc^2-) with various chelating N-donor ligands (2,2'-bipyridyl = bpy; 5,5'-dimethyl-2,2'-bipyridyl = 5,5'-dmbpy; 4,4'-dimethyl-2,2'-bipyridyl = 4,4'-dmbpy) [Mn₃(btdc)₃(bpy)₂]·4DMF, 1; [Mn₃(btdc)₃(5,5'-dmbpy)₂]·5DMF, 2; [Mn(btdc)(4,4;-dmbpy)], 3; [Mn₂(btdc)₂(bpy)(dmf)]·0.5DMF, 4; [Mn₂(btdc)₂(5,5'-dmbpy)(dmf)]·DMF, 5 (dmf, DMF = N,N-dimethylformamide) have been synthesized, and their crystal structure has been established using single-crystal X-ray diffraction analysis (XRD). The chemical and phase purities of Compounds 1-3 have been confirmed via powder X-ray diffraction, thermogravimetric, and chemical analyses as well as IR spectroscopy. The influence of the bulkiness of the chelating N-donor ligand on the dimensionality and structure of the coordination polymer has been analyzed, and the decrease in the framework dimensionality, as well as the secondary building unit's nuclearity and connectivity, has been observed for bulkier ligands. For three-dimensional (3D) coordination polymer 1, the textural and gas adsorption properties have been studied, revealing noticeable ideal adsorbed solution theory (IAST) CO₂/N₂ and CO₂/CO selectivity factors (31.0 at 273 K and 19.1 at 298 K and 25.7 at 273 K and 17.0 at 298 K, respectively, for the equimolar composition and the total pressure of 1 bar). Moreover, significant adsorption selectivity for binary C₂-C₁ hydrocarbons mixtures (33.4 and 24.9 for C₂H₆/CH₄, 24.8 and 17.7 for C₂H₄/CH₄, 29.3 and 19.1 for C₂H₂/CH₄ at 273 K and 298 K, respectively, for the equimolar composition and the total pressure of 1 bar) has been observed, making it possible to separate on 1 natural, shale, and associated petroleum gas into valuable individual components. The ability of Compound 1 to separate benzene and cyclohexane in a vapor phase has also been analyzed based on the adsorption isotherms of individual components measured at 298 K. The preferable adsorption of C₆H₆ over C₆H₁₂ by 1 at high vapor pressures (V_B/V_CH = 1.36) can be explained by the existence of multiple van der Waals interactions between guest benzene molecules and the metal-organic host revealed by the XRD analysis of 1 immersed in pure benzene for several days (1≅2C₆H₆). Interestingly, at low vapor pressures, an inversed behavior of 1 with preferable adsorption of C₆H₁₂ over C₆H₆ (K_CH/K_B = 6.33) was observed; this is a very rare phenomenon. Moreover, magnetic properties (the temperature-dependent molar magnetic susceptibility, χ_p(T) and effective magnetic moments, μ_eff(T), as well as the field-dependent magnetization, M(H)) have been studied for Compounds 1-3, revealing paramagnetic behavior consistent with their crystal structure.

Coordination Polymers of Scandium(III) and Thiophenedicarboxylic Acid

Abstract

Three new metal−organic frameworks based on scandium(III) cations and 2,5-thiophenedicarboxylic acid (H2Tdc) are synthesized: [Sc(Tdc)(OH)]·1.2DMF (I), [Sc(Tdc)(OH)]·2/3DMF (II), and (Me2NH2)[Sc3(Tdc)4(OH)2]·DMF (III) (DMF is N,N-dimethylformamide). The structures of the compounds are determined by single-crystal X-ray structure analysis (CIF file CCDC nos. 2067819 (I), 2067820 (II), and 2067821 (III)). The chemical and phase purity of compound I is proved by elemental analysis, thermogravimetry, X-ray diffraction analysis, and IR spectroscopy.

3D Metal-Organic Frameworks Based on Co(II) and Bithiophendicarboxylate: Synthesis, Crystal Structures, Gas Adsorption, and Magnetic Properties

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2′-bithiophen-5,5′-dicarboxylate (btdc²⁻) [Co₃(btdc)₃(bpy)₂]·4DMF, 1; [Co₃(btdc)₃(pz)(dmf)₂]·4DMF·1.5H₂O, 2; [Co₃(btdc)₃(dmf)₄]∙2DMF∙2H₂O, 3 (bpy = 2,2′-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co₃(RCOO)₆}, connected either by btdc^2– ligands (1, 3) or by both btdc^2– and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N₂, O₂, CO, CO₂, CH₄ adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m²⋅g⁻¹ and promising gas separation performance with selectivity factors up to 35.7 for CO₂/N₂, 45.4 for CO₂/O₂, 20.8 for CO₂/CO, and 4.8 for CO₂/CH₄. The molar magnetic susceptibilities χ_p(T) were measured for 1 and 2 in the temperature range 1.77–330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are μ_eff (300 K) ≈ 4.93 μ_B. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2.

One-pot concomitant preparation of two copper(II) coordination polymers with different configurations of bridging bithiophene ligands

By employing the conjugated bithiophene ligand 5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene (bibp), which can exhibit trans and cis conformations, two different Cu^II coordination polymers, namely, poly[[μ-5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene-κ²N:N'](μ₂-4,4'-oxydibenzoato-κ²O:O')copper(II)], [Cu(C₁₄H₈O₅)(C₁₄H₁₀N₄S₂)]_n or [Cu(bibp)(oba)]_n, (I), and catena-poly[μ-aqua-bis[μ-5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene-κ²N:N']bis(μ₃-4,4'-oxydibenzoato)-κ³O:O':O'';κ⁴O:O',O'':O'-dicopper(II)], [Cu₂(C₁₄H₈O₅)₂(C₁₄H₁₀N₄S₂)(H₂O)]_n or [Cu₂(bibp)(oba)₂(H₂O)]_n, (II), have been prepared through one-pot concomitant crystallization and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD) and thermogravimetric (TG) analysis. Single-crystal X-ray diffraction indicates that the most interesting aspect of the structure is the existence of sole trans and cis conformations of the bibp ligand in a single net of (I) and (II), respectively. Compound (I) displays a threefold interpenetrating three-dimensional framework with a 4-connected {6⁵.8} cds topology, whereas (II) features a one-dimensional chain structure. In the crystal of (II), the polymeric chains are further extended through C-H...O hydrogen bonds and C-H...π interactions into a three-dimensional supramolecular architecture. In addition, strong intramolecular O-H...O hydrogen bonds formed between the bridging water molecules and the carboxylate O atoms improve the stability of the framework of (II). Furthermore, solid-state UV-Vis spectroscopy experiments show that compounds (I) and (II) exhibit optical band gaps which are characteristic for optical semiconductors, with values of 2.70 and 2.26 eV, respectively.

Topological polymorphism and temperature-driven topotactic transitions of metal–organic coordination polymers

A facile crystal-to-crystal solid-state phase transition between a low-temperature phase and a high temperature phase changes the MOF topology and involves a significant rearrangement of bulky organic ligands.

A new CdII coordination polymer with a self-penetrating architecture induced by the molecular conformation of a rigid bithiophene ligand

The design and synthesis of coordination polymers with a self-penetrating architecture has attracted much interest not only due to their interesting structures but also due to their potential applications. 5,5'-Bis(pyridin-4-yl)-2,2'-bithiophene (bpbp), as a conjugated bithiophene ligand, can exhibit trans and cis conformations and this can lead to the construction of a self-penetrating architecture. In addition, the semi-rigid ancillary ligand 4,4'-oxybis(benzoic acid) (H₂oba) can adopt different coordination modes, resulting in coordination polymers with high-dimensional skeletons. A new Cd^II coordination polymer based on mixed ligands, namely poly[diaquapentakis[μ-5,5'-bis(pyridin-4-yl)-2,2'-bithiophene-κ²N:N']bis(nitrato-κ²O,O')tetrakis(μ₃-4,4'-oxydibenzoato)-κ¹⁰O:O,O':O'',O''';κ⁶O:O':O''-pentacadmium(II)], [Cd₅(C₁₄H₁₄O₅)₄(NO₃)₂(C₁₈H₁₂N₂S₂)₅(H₂O)₂]_n, (I), has been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction indicates that there are three crystallographically independent Cd^II cations, three bpbp ligands, two deprotonated oba^2- ligands, one nitrate ligand and one coordinated water molecule in the asymmetric unit. One Cd^II centre is seven-coordinated, exhibiting a distorted {CdN₂O₅} pentagonal bipyramidal geometry, while the other two Cd centres are both six-coordinated, showing slightly distorted {CdN₂O₄} octahedral geometries. The most interesting feature is the co-existence of trans and cis conformations in a single net, allowing structural interpenetration via self-threading and yet the expected self-penetrating structure was obtained. Topological analysis shows that the whole three-dimensional framework can be classified as a 3-nodal (4,6,6)-c net with Schläfli symbol {6¹³.8²}₂{6⁶}, which is a new topology. Furthermore, the luminescence properties of (I) were examined in the solid state at room temperature.

Nitroaromatic sensing with a new lanthanide coordination polymer [Er2(C10H4O4S2)3(H2O)6]n assembled by 2,2′-bithiophene-5,5′-dicarboxylate

A new three dimensional lanthanide-containing coordination polymer assembled from 2,2′-bithiophene-5,5′-dicarboxylic acid ([Ln₂(C₁₀H₄O₄S₂)₃(H₂O)₆]_n, Ln = Sm–Yb) was solvothermally synthesized and used as a sensor to detect nitroaromatic compounds via luminescence quenching.