Metal–Organic Frameworks with Internal Urea-Functionalized Dicarboxylate Linkers for SO₂ and NH₃ Adsorption

Introduction of a urea R–NH–CO–NH–R group as a seven-membered diazepine ring at the center of 4,4′-biphenyl-dicarboxylic acid leads to a urea-functionalized dicarboxylate linker (L1^2–) from which four zinc metal–organic frameworks (MOFs) could be obtained, having a {Zn₄(μ₄-O)­(O₂C−)₆} SBU and IRMOF-9 topology (compound [Zn₄(μ₄-O)­(L1)₃], <b>1</b>, from dimethylformamide, DMF) or a {Zn₂(O₂C−)₄} paddle-wheel SBU in a 2D-network (compound [Zn₂(L1)₂(DEF)₂·2.5DEF], <b>2</b>, from diethylformamide, DEF). Pillaring of the 2D-network of <b>2</b> with 4,4′-bipyridine (bipy) or 1,2-bis­(4-pyridyl)­ethane (bpe) gives 3D frameworks with rhombohedrally distorted <b>pcu-a</b> topologies ([Zn₂(L1)₂(bipy)], <b>3</b> and [Zn₂(L1)₂(bpe)], <b>4</b>, respectively). The 3D-frameworks <b>1</b>, <b>3</b>, and <b>4</b> are 2-fold interpenetrated with ∼50% solvent-accessible volume, albeit of apparently dynamic porous character, such that N₂ adsorption at 77 K does not occur, while H₂ at 77 K (up to ∼1 wt %) and CO₂ at 293 K (∼5 wt %) are adsorbed with large hystereses in these flexible MOFs. The urea-functionalized MOF <b>3</b> exhibits an uptake of 10.9 mmol g^–1 (41 wt %) of SO₂ at 293 K, 1 bar, which appears to be the highest value observed so far. Compounds <b>3</b> and <b>4</b> adsorb 14.3 mmol g^–1 (20 wt %) and 17.8 mmol g^–1 (23 wt %) NH₃, respectively, which is at the top of the reported values. These high uptake values are traced to the urea functionality and its hydrogen-bonding interactions to the adsorbents. The gas uptake capacities follow the specific porosity of the frameworks, in combination with pore aperture size and affinity constants from fits of the adsorption isotherms

Effects of Extending the π‑Electron System of Pillaring Linkers on Fluorescence Sensing of Aromatic Compounds in Two Isoreticular Metal–Organic Frameworks

A new porous metal–organic framework (TMU-21) that is isostructural to our recently reported TMU-6 is introduced. The structure of this framework has been determined by X-ray crystallography and further characterized by Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. Its structural features as well as its stability and porosity were studied. These two metal–organic frameworks are interesting candidates for a comparative fluorescence study. Thus, their potential abilities to sense nitrobenzene, benzene, and polycyclic aromatic hydrocarbons, namely, naphthalene, anthracene, and pyrene, were investigated. This study clearly shows an important contribution of extending the π-electron systems of pillaring linkers in the ability of metal–organic frameworks to sense aromatic compounds

Proton Conduction and Long-Range Ferrimagnetic Ordering in Two Isostructural Copper(II) Mesoxalate Metal–Organic Frameworks

Two compounds of formula {(H₃O)­[Cu₇(Hmesox)₅(H₂O)₇]·9H₂O}_<i>n</i> (<b>1a</b>) and {(NH₄)_0.6(H₃O)_0.4[Cu₇(Hmesox)₅(H₂O)₇]·11H₂O}_<i>n</i> (<b>1b</b>) were prepared and structurally characterized by single-crystal X-ray diffraction (H₄mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metal–organic frameworks exhibiting proton conduction and magnetic ordering. Variable-temperature magnetic susceptibility measurements reveal that the copper­(II) ions are strongly ferro- and antiferromagnetically coupled by the alkoxide and carboxylate bridges of the mesoxalate linker to yield long-range magnetic ordering with a <i>T</i>_c of 17.6 K, which is reached by a rare mechanism known as topologic ferrimagnetism. Electric conductivity, measured by impedance methods, shows values as high as 6.5 × 10^–5 S cm^–1 and occurs by proton exchange among the hydronium/ammonium and water molecules of crystallization, which fill the voids left by the three-dimensional copper­(II) mesoxalate anionic network

Charge-Density Distribution and Electrostatic Flexibility of ZIF‑8 Based on High-Resolution X‑ray Diffraction Data and Periodic Calculations

The electron-density distribution in a prototypical porous coordination polymer ZIF-8 has been obtained in an approach combining high-resolution X-ray diffraction data and Invariom refinement. In addition, the periodic quantum-chemical calculation has been used to describe the theoretical density features of ZIF-8 in the same geometry (<b>m1</b>) and also in a “high-pressure” form of ZIF-8 (<b>m2</b>) characterized by conformational change with respect to the methylimidazolate linker. A thorough comparison of the electronic and electrostatic properties in two limiting structural forms of ZIF-8 proposes additional aspects on diffusion and adsorption processes occurring within the framework. The dimensions of the four-membered (FM) and six-membered (SM) apertures of the β cage are reliably determined from the total electron-density distribution. The analysis shows that FM in <b>m2</b> becomes competitive in size to the SM aperture and should be considered for the diffusion of small molecules and cations. Bader’s topological analysis (quantum theory of atoms in molecules) shows similar properties of both ZIF-8 forms. On the other hand, analysis of their electrostatic properties reveals tremendous differences. The study suggests exceptional electrostatic flexibility of the ZIF-8 framework, where small conformational changes lead to a significantly different electrostatic potential (EP) distribution, a feature that could be important for the function and dynamics of the ZIF-8 framework. The cavity surface in <b>m1</b> contains 38 distinct regions with moderately positive, negative, or neutral EP and weakly positive EP in the cavity volume. In contrast to <b>m1</b>, the <b>m2</b> form displays only two regions of different EP, with the positive one taking the whole cavity surface and the strong negative one localized entirely in the FM apertures. The EP in the cavity volume is also more positive than that in <b>m1</b>. A pronounced influence of the linker reorientation on the EP of the ZIF-8 forms is related to the high symmetry of the system and to an amplification of the electrostatic properties by cooperative effects of the proximally arranged structural fragments

Novel C,N-Cyclometalated Benzimidazole Ruthenium(II) and Iridium(III) Complexes as Antitumor and Antiangiogenic Agents: A Structure–Activity Relationship Study

A series of novel C,N-cyclometalated benzimidazole ruthenium­(II) and iridium­(III) complexes of the types [(η⁶-<i>p</i>-cymene)­RuCl­(κ²-<i>N</i>,<i>C</i>-L)] and [(η⁵-C₅Me₅)­IrCl­(κ²-<i>N</i>,<i>C</i>-L)] (HL = methyl 1-butyl-2-arylbenzimidazole­carboxylate) with varying substituents (H, Me, F, CF₃, MeO, NO₂, and Ph) in the R₄ position of the phenyl ring of 2-phenylbenzimidazole chelating ligand of the ruthenium (<b>3a</b>–<b>g</b>) and iridium complexes (<b>4a</b>–<b>g</b>) have been prepared. The cytotoxic activity of the new ruthenium­(II) and iridium­(III) compounds has been evaluated in a panel of cell lines (A2780, A2780cisR, A427, 5637, LCLC, SISO, and HT29) in order to investigate structure–activity relationships. Phenyl substitution at the R₄ position shows increased potency in both Ru and Ir complexes (<b>3g</b> and <b>4g</b>, respectively) as compared to their parent compounds (<b>3a</b> and <b>4a</b>) in all cell lines. In general, ruthenium complexes are more active than the corresponding iridium complexes. The new ruthenium and iridium compounds increased caspase-3 activity in A2780 cells, as shown for <b>3a</b>,<b>d</b> and <b>4a</b>,<b>d</b>. Compound <b>4g</b> is able to increase the production of ROS in A2780 cells. Furthermore, all the new compounds are able to overcome the cisplatin resistance in A2780cisR cells. In addition, some of the metal complexes effectively inhibit angiogenesis in the human umbilical vein endothelial cell line EA.hy926 at 0.5 μM, the ruthenium derivatives <b>3g</b> (Ph) and <b>3d</b> (CF₃) being the best performers. QC calculations performed on some ruthenium model complexes showed only moderate or slight electron depletion at the phenyl ring of the C,N-cyclometalated ligand and the chlorine atom on increasing the electron withdrawing effect of the R substituent

Cytotoxic 14-Membered Macrolides from a Mangrove-Derived Endophytic Fungus, <i>Pestalotiopsis microspora</i>

Seven new 14-membered macrolides, pestalotioprolides C (<b>2</b>), D–H (<b>4</b>–<b>8</b>), and 7-<i>O</i>-methylnigrosporolide (<b>3</b>), together with four known analogues, pestalotioprolide B (<b>1</b>), seiricuprolide (<b>9</b>), nigrosporolide (<b>10</b>), and 4,7-dihydroxy-13-tetradeca-2,5,8-trienolide (<b>11</b>), were isolated from the mangrove-derived endophytic fungus <i>Pestalotiopsis microspora</i>. Their structures were elucidated by analysis of NMR and MS data and by comparison with literature data. Single-crystal X-ray diffraction analysis was used to confirm the absolute configurations of <b>1</b>, <b>2</b>, and <b>10</b>, while Mosher’s method and the TDDFT-ECD approach were applied to determine the absolute configurations of <b>5</b> and <b>6</b>. Compounds <b>3</b>–<b>6</b> showed significant cytotoxicity against the murine lymphoma cell line L5178Y with IC₅₀ values of 0.7, 5.6, 3.4, and 3.9 μM, respectively, while compound <b>5</b> showed potent activity against the human ovarian cancer cell line A2780 with an IC₅₀ value of 1.2 μM. Structure–activity relationships are discussed. Coculture of <i>P. microspora</i> with <i>Streptomyces lividans</i> caused a roughly 10-fold enhanced accumulation of compounds <b>5</b> and <b>6</b> compared to axenic fungal control