Guest Solvent Molecules Research Articles

Unravelling Guest Dynamics in Crystalline Molecular Organics Using 2H Solid-State NMR and Molecular Dynamics Simulation.

2H solid-state NMR and atomistic molecular dynamics (MD) simulations are used to understand the disorder of guest solvent molecules in two cocrystal solvates of the pharmaceutical furosemide. Traditional approaches to interpreting the NMR data fail to provide a coherent model of molecular behavior and indeed give misleading kinetic data. In contrast, the direct prediction of the NMR properties from MD simulation trajectories allows the NMR data to be correctly interpreted in terms of combined jump-type and libration-type motions. Time-independent component analysis of the MD trajectories provides additional insights, particularly for motions that are invisible to NMR. This allows a coherent picture of the dynamics of molecules restricted in molecular-sized cavities to be determined.

Synthesis, structure and dielectric behavior study of Mn (II)-4,4′-sulfonyldibenzoate-auxiliary ligand system based coordination polymers (CPs)

Based on MnCl2.4H2O, V-shaped ligand 4,4′-sulfonyldibenzoic acid (H2SBA), and two N-containing auxiliary ligands three new coordination polymers (CPs), namely: [Mn3(SBA)2(pyzc)2(DMA)2].DMA.H2O 1, [Mn3(SBA)2(phen)2(OAc)2].2DMA 2, and [Mn3(SBA)2(phen)2(OAc)2].2EtOH 3 [where, SBA = 4,4′-sulfonyldibenzoate, pyzc = 2-pyrazinecarboxylate, phen = 1,10-phenanthroline, OAc = acetate, DMF = N, N'-dimethylformamide, DMA = N, N'-dimethylacetamide] were synthesized using mixture of polar protic/aprotic solvents under solvothermal conditions. Single crystal X-ray study revealed that solid 1 is composed of tetrameric {Mn4O20N2} and dimeric units {Mn2O8N2}, whereas solids 2 and 3 are built of trimeric cluster {Mn3N2O14}. The structurally similar 2D coordination solids 2 and 3 showed comparable dielectric constant (ɛ'∼15.0) at room temperature. Solid 1 exhibited a higher value of dielectric constant (ɛ'∼30.5) probably due to the contribution from disordered polar guest solvent molecules, and 1D manganese carboxylate chains interaction. The crystal engineering of soluble 1:1 manganese carboxylate complex species, with or without coordination with an auxiliary ligand, is also explained mechanistically in this study. The approach not only provides a rationale for the composition and variation in the coordination linkage but also describes the crystal packing in terms of the dominant directional coordination and H-bonding forces.

Efficient nitro-aromatic sensor via highly luminescent Zn-based metal-organic frameworks

Highly stable zinc-based luminescent metal-organic framework (LMOF) [(Zn2-(NDC)2(bpy)·Gx) where NDC-2,6-naphthalene dicarboxylic acid, bpy - 4,4' bipyridine, and G - guest solvent molecules] is synthesized via solvothermal method at different synthesizing temperatures (120, 150 and 180∘C) for the detection of nitro-aromatics. Sample structure and presence of ligands is confirmed by X-ray diffraction and FTIR measurements, respectively. The photoluminescence properties of synthesized LMOF samples show the strong emission intensity in ethanol at 376 nm when it is excited at 240 nm. The detection limit is calculated using fluorescence quenching for the various nitro-analytes (2,4-DNP, 2-Nitrotoulene, 4-Nitrophenol, and Nitrobenzene) revealed that it is least for the sample synthesized at 150∘C with the maximum percentage in fluorescence decay. The thermal stability of as-synthesized samples is analysed using thermogravimetry analysis (TGA) which reveals that sample synthesized at 150∘C is the most stable sample. The TGA analysis also shows that on further heating from 526∘C to 980∘C decomposition of zinc metal and formation of zinc oxide takes place. FE-SEM confirms the cuboidal morphology with an average particle size of 12.62 nm, corroborated by the TEM analysis. The fluorescence quenching mechanism is explained on the basis of dipole-dipole and π-stacked interactions between the MOF and nitro-aromatics that play a prominent role in the sensing of nitro-analytes. Synthesized MOF samples show excellent recyclability in fluorescence quenching even after the fourth cycle, i.e. more than 95% and is sensitive to detect nitro-aromatics even upto 0.284 µM, and the results can generalize the explosive sensor technology and sensing various nitro-based pollutants.

Spin crossover of a dinuclear Fe(II) complex in the trans-isomeric structure

A trans-isomeric dinuclear complex is synthesized by reacting ligand 4-((1H-pyrrol-2-yl)methylene-amino)-4H-1,2,4-triazole (pyrtrz) with [Fe(NCS)2] in methanol, i.e. trans-[Fe2(pyrtrz)5(NCS)4]·7MeOH (trans-1·7MeOH), which shows complete spin-crossover behaviour from the structural point of view and incomplete spin crossover due to the partial loss of guest solvent molecules.

Polymerizable channel-like stacks derived from cyclic tetrameric diacetylenes

A small series of cyclic diacetylenes has been synthesized and tested by scanning electron microscopy (SEM), single crystal X-ray diffraction, and atomic force microscopy (AFM) to examine their ability to form arrangements of discrete molecules in the solid state. Examining solid state structures clearly demonstrated propensity of diacetylene tetramers to form channel-like stacks. Remarkably, cyclotetradiyne DA-4 monomer tends to produce two types of nano-tubular motifs (i.e., the channel-like arrangement with solvent matrix inside and unprecedented flattened nano-tube incorporated no solvent guest molecules) which is indicative of the weak C–H/π interactions dominating and directing the stacking in such simplistic diacetylene cyclic systems. Noteworthy, DA-4 molecules may be crystallized from organic solvents into birefringent branchy patterns revealed by Polarized Optical Microscopy (POM) and twisted ribbons of both handedness as evidenced by SEM data. We hypothesize that all these secondary structures may arise from the bundling the individual stacks discovered by single crystal X-ray analysis. Overall, engineering the elongated motifs may open up new opportunities for the future applications such as a rational design of synthetic ion channels and carriers, synthesis of the covalent polymeric nanotubes, etc.

Effect of Unsaturated Metal Site Modulation in Highly Stable Microporous Materials on CO2 Capture and Fixation.

We have designed and synthesized two unprecedented microporous three-dimensional metal-organic frameworks, {[Cd6(TPOM)3(L)6]·12DMF·3H2O}n (1) and {[Zn2(TPOM)(L)2]·2DMF·H2O}n (2), based on a flexible quadritopic ligand, tetrakis(4-pyridyloxymethylene)methane (TPOM), and a bent dicarboxylic acid, 4,4'-(dimethylsilanediyl)bis-benzoic acid (H2L). The networks of 1 and 2 share a 4-c uninodal net NbO topology but exhibit different metal environments due to coordination preferences of Cd(II) and Zn(II). The Cd(II) center in 1 is six-coordinated, whereas the Zn(II) center in 2 is only four-coordinated, making the latter an unsaturated metal center. Such modulation of coordination atmosphere of metal centers in MOFs with the same topology is possible due to diverse binding of the carboxylate groups of L2-. Both 1 and 2 have relatively high thermal stability and exhibit permanent porosity after the removal of guest solvent molecules based on variable temperature powder X-ray diffraction and gas adsorption analysis. These materials exhibit similar gas adsorption properties, especially highly selective CO2 uptake/capture over other gases (N2 and CH4). However, because of the presence of an unsaturated Lewis acidic metal site, 2 acts as a very efficient heterogeneous catalyst toward the chemical conversion of CO2 to cyclic carbonates under mild conditions, whereas 1 shows very less activity. This work provides experimental evidence for the postulate that an unsaturated metal site in MOFs enhances adsoprtion of CO2 and promotes its conversion via the Lewis-acid catalysis.

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C 2 H 2 /CO 2 Separation

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C ₂ H ₂ /CO ₂ Separation

Crystal Engineering of Schiff Base Zn(II) and Cd(II) Homo- and Zn(II)M(II) (M = Mn or Cd) Heterometallic Coordination Polymers and Their Ability to Accommodate Solvent Guest Molecules.

Based on solvothermal synthesis, self-assembly of the heptadentate 2,6-diacetylpyridine bis(nicotinoylhydrazone) Schiff base ligand (H2L) and Zn(II) and/or Cd(II) salts has led to the formation of three homometallic [CdL]n (1), {[CdL]∙0.5dmf∙H2O}n (2) and {[ZnL]∙0.5dmf∙1.5H2O}n (3), as well as two heterometallic {[Zn0.75Cd1.25L2]∙dmf∙0.5H2O}n (4) and {[MnZnL2]∙dmf∙3H2O}n coordination polymers. Compound 1 represents a 1D chain, whereas 2–5 are isostructural and isomorphous two-dimensional structures. The entire series was characterized by IR spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction and emission measurements. 2D coordination polymers accommodate water and dmf molecules in their cage-shaped interlayer spaces, which are released when the samples are heated. Thus, three solvated crystals were degassed at two temperatures and their photoluminescent and adsorption–desorption properties were recorded in order to validate this assumption. Solvent-free samples reveal an increase in volume pore, adsorption specific surface area and photoluminescence with regard to synthesized crystals.

Structural and electronic properties of the metal cluster‐based compounds including high concentration of solvent molecules

AbstractRecrystallization of Cs2[Mo6X14] (X=Cl, Br) was examined using typical organic solvents, i. e., methanol (CH3OH), acetone (CH3COCH3) and dichloromethane (CH2Cl2) in order to modify crystal structures and optoelectronic properties by promoting purity or inducing insertion of guest molecules. To this context, we performed recrystallization in solvent liquid and exposure of Cs2[Mo6X14] to vapor of those solvents. Subsequent single crystal X‐ray diffraction analyses revealed that three new types of compounds which contain high concentration of guest organic solvent molecules were obtained. Indeed, the newly found structures are Cs2[Mo6Cl14] ⋅ 3CH3OH and Cs2[Mo6X14] ⋅ 6CH3COCH3 belonging to triclinic space group, and Cs2[Mo6X14] ⋅ 4CH2Cl2 belonging to tetragonal P4/mnc space group. Although breaking of centrosymmetry by insertion of the guest molecule is interesting in terms of optoelectronic properties, all those new compounds belong to centrosymmetric space groups. As DFT calculations for those new compounds show that the guest molecules, such as CH3OH, do not affect the atomic arrangements and electronic features of the [Mo6X14]2− cluster based unit, they incorporated with the lattice while keeping with the electrostatic interaction between the [Mo6X14]2− and Cs+ ions regardless of the very high concentration of the guest solvent molecules.

Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

Summary Zr-carboxylate metal-organic frameworks (MOFs) are structurally robust materials, in part due to their strong coordination bonds. The regioselective Zr–O bond cleavage and formation between 3D architectures are thus challenging and are heretofore unexplored. In this work, by introducing highly flexible 18-crown-6-ether functionalities into a homochiral Zr-MOF, we report an unprecedented topology transition in which a 4,10-connected framework undergoes a rapid solid-state transition into a thermodynamically more stable 4,8-connected analog by a regioselective-linker-elimination under ambient conditions. The transition process was unambiguously unraveled by single-crystal and powder X-ray diffraction studies, and we proposed a possible transition mechanism based on various control experiments and theoretical calculations. The excellent chemical stability and substantially expanded porosity and pore apertures endowed the transformed chiral MOF with an exceptional capacity for the enantioadsorptive and solid-phase extractive separation of the racemic drug molecule of lansoprazole with 98% ee and 93% ee, respectively.

Propargyl-functionalized single arm allied Anthracene based Schiff bases: Crystal structure, solvatochromism and selective recognition of Fe3+ ion

An organic moiety exhibit specific behavior in electronic absorption spectra while accommodating various solvents or metal ions and that specificity depends on particular guest solvent molecules or metal ions. Herein, we report about the photophysical properties of newly synthesized Propargyl-functionalized anthracene based Schiff bases (PASB). The formulated compounds have been thoroughly characterized by elemental analysis, FT-IR, NMR (1H and 13C) and UV-Vis spectroscopy, emphasized with Kamlet-Taft approach to explain the solvatochromic behavior of the synthesized compounds. PASBs were screened for the sensorial aptitude towards various metal ions which were found to act as an excellent UV-Vis probe for selective detection of Fe3+ ion with LOD 1.60 × 10−8M. Additionally, coordination behavior of ligand with Fe3+ ion was examined through the change in magnetic property of Fe3+ ions by VSM (vibrating sample magnetism) study. Moreover, complete structure elucidation of compound 4b was achieved via X-ray crystallography. The binding sites of sensor conjugate 4b-Fe3+ are well supported by FT-IR spectroscopy and computational analysis following DFT approach. The reported contribution focused on the factors determining the ability of propargyl appended Schiff base to present structure, mental picture of solvatochromism and metal ion sensitivity.

Tuning the Atrazine Binding Sites in an Indium-Based Flexible Metal-Organic Framework.

Constructing flexible metal-organic frameworks (MOFs) with targeted properties is of high interest given their demonstrated potential as smart materials that undergo structural transformations in response to external stimuli. Herein, we report a flexible and interpenetrated indium-based MOF, NU-50, comprising four-connected [In(CO2)4]- nodes and tetracarboxylate pyrene-based ligands assembled in the pts topology. The flexible framework of NU-50 exhibits intricate structural transformations upon exposure to external stimuli, namely, guest solvent molecules and elevated temperatures. The high density of pyrene moieties throughout the interpenetrated framework offers numerous sites for the adsorption of highly conjugated guest molecules such as atrazine via π-π interactions. As a result, NU-50 efficiently removes atrazine from water, achieving a maximum atrazine uptake capacity of 74 mg of atrazine per gram of NU-50. Molecular simulations reveal that the dynamic behavior of NU-50 involves the distortion of metal-ligand bonds, resulting in a narrow pore structure that affords effective adsorption of atrazine molecules in a sandwich-like geometry. Moreover, washing in acetone quickly regenerates the sorbent.

Preparation and characterization of several azoxystrobin channel solvates

Azoxystrobin is an important strobilurins fungicide. Nine channel solvates of azoxystrobin were obtained for the first time and six of them could be crystallized in single crystals. The crystallographic data, unit cell porosity, Hirshfeld surface, and fingerprint plot were analyzed. These solvates are isostructural, azoxystrobin forming a host framework through intermolecular interaction and the guest solvent molecules located in channels. These solvates were stabilized by π⋅⋅⋅π interaction, CH⋅⋅⋅π interaction, and weak hydrogen-bonding interactions such as CH⋅⋅⋅O interaction and CH⋅⋅⋅C interaction. All solvates were characterized by PXRD, DSC, TG, FTIR, and FESEM, the stability of them were also examined. Moreover, because of the similarity of the channel solvates, solvent-replacement method could be used to prepare other solvates.

The effect of the coordination orientation of N atoms on polymeric structures: synthesis and characterization of one- and two-dimensional CuII coordination polymers based on 4-amino-3-(pyridin-2-yl)-5-[(pyridin-3-ylmethyl)sulfanyl]-1,2,4-triazole.

Three new one- (1D) and two-dimensional (2D) CuII coordination polymers, namely poly[[bis{μ2-4-amino-3-(pyridin-2-yl)-5-[(pyridin-3-ylmethyl)sulfanyl]-1,2,4-triazole}copper(II)] bis(methanesulfonate) tetrahydrate], {[Cu(C13H12N5S)2](CH3SO3)2·4H2O}n (1), catena-poly[[copper(II)-bis{μ2-4-amino-3-(pyridin-2-yl)-5-[(pyridin-4-ylmethyl)sulfanyl]-1,2,4-triazole}] dinitrate methanol disolvate], {[Cu(C13H12N5S)2](NO3)2·2CH3OH}n (2), and catena-poly[[copper(II)-bis{μ2-4-amino-3-(pyridin-2-yl)-5-[(pyridin-4-ylmethyl)sulfanyl]-1,2,4-triazole}] bis(perchlorate) monohydrate], {[Cu(C13H12N5S)2](ClO4)2·H2O}n (3), were obtained from 4-amino-3-(pyridin-2-yl)-5-[(pyridin-3-ylmethyl)sulfanyl]-1,2,4-triazole with pyridin-3-yl terminal groups and from 4-amino-3-(pyridin-2-yl)-5-[(pyridin-4-ylmethyl)sulfanyl]-1,2,4-triazole with pyridin-4-yl terminal groups. Compound 1 displays a 2D net-like structure. The 2D layers are further linked through hydrogen bonds between methanesulfonate anions and amino groups on the framework and guest H2O molecules in the lattice to form a three-dimensional (3D) structure. Compound 2 and 3 exhibit 1D chain structures, in which the complicated hydrogen-bonding interactions play an important role in the formation of the 3D network. These experimental results indicate that the coordination orientation of the heteroatoms on the ligands has a great influence on the polymeric structures. Moreover, the selection of different counter-anions, together with the inclusion of different guest solvent molecules, would also have a great effect on the hydrogen-bonding systems in the crystal structures.

Three Co(II) coordination polymers constructed from 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole and V-shaped dicarboxylic acids: Syntheses, characterizations, structural diversity and optical properties

Three novel Co(II) coordination polymers, formulated as {[Co(μ3-ipa)(μ-dptztz)]·DMF}n (1), {[Co(μ3-fdc)(μ-dptztz)(H2O)]·DMF}n (2) and {[Co(μ3-tdc)(μ-dptztz)]·G}n (3) (ipa: 1,3-benzenedicarboxylate, fdc: 2,5-furandicarboxylate, tdc: 2,5-thiophenedicarboxylate, dptztz: 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole, G: Guest solvent molecule) were synthesized with dptztz and V-shaped dicarboxylic acids to investigate the effects of these acids on the structural diversity. Single crystal X-ray results demonstrated that compound 1 has a 2D structure, while compounds 2 and 3 display 3D frameworks, depending on these acids. In 1 and 3, although the coordination modes of the ipa and tdc ligands are the same, different dimensions in the compounds are observed owing to the different angles between the two carboxylate arms of the linkers. Moreover, the dimensionalities of the compounds increased with the angle between two carboxylate arms. 3D networks of compound 3 are interpenetrated with each other to form a 3D + 3D → 3D interpenetrated framework with a pcu topology. Diffuse reflectance spectra showed that the optical band gaps of the compounds decreased in the presence of the dptztz ligand. Furthermore, the thermal properties of compounds 1–3 were also studied.

A Flexible Hydrogen Bonded Organic Framework That Reversibly Adsorbs Acetic Acid: γ Trimesic Acid

The elusive γ phase of trimesic acid (TMA, 1,3,5-benzenetricarboxylic acid) has been prepared by recrystallization of commercial α-TMA in acetic acid. This process yields a modified γ-TMA phase that contains guest acetic acid solvent molecules with an approximate stoichiometry of γ-TMA·1HAc. According to 1H NMR and crystal structure determination, guest molecules are located both in the channels and in relatively isolated cavities. Despite the constricted connection between channels and cavities, solvent guest molecules are easily removed, even at room temperature, yielding guest-free γ-TMA. This process is reversible, since pristine γ-TMA can reabsorb acetic acid vapor at room temperature, yielding again γ-TMA·1HAc. Conversely, γ-TMA only adsorbs negligible amounts of N2 at 77 K or CO2 at 273 K, denoting that the guest–adsorbent interaction is a key factor governing adsorption.

Reversible and Site-Dependent Proton-Transfer in Zeolites Uncovered at the Single-Molecule Level.

Zeolite activity and selectivity is often determined by the underlying proton and hydrogen-transfer reaction pathways. For the first time, we use single-molecule fluorescence microscopy to directly follow the real-time behavior of individual styrene-derived carbocationic species formed within zeolite ZSM-5. We find that intermittent fluorescence and remarkable photostability of carbocationic intermediates strongly depend on the local chemical environment imposed by zeolite framework and guest solvent molecules. The carbocationic stability can be additionally altered by changing para-substituent on the styrene moiety, as suggested by DFT calculations. Thermodynamically unstable carbocations are more likely to switch between fluorescent (carbocationic) and dark (neutral) states. However, the rate constants of this reversible change can significantly differ among individual carbocations, depending on their exact location in the zeolite framework. The lifetimes of fluorescent states and reversibility of the process can be additionally altered by changing the interaction between dimeric carbocations and solvated Brønsted acid sites in the MFI framework. Advanced multidimensional magic angle spinning solid-state NMR spectroscopy has been employed for the accurate structural elucidation of the reaction products during the zeolite-catalyzed dimerization of styrene in order to corroborate the single-molecule fluorescence microscopy data. This complementary approach of single-molecule fluorescence microscopy, NMR, and DFT collectively indicates that the relative stability of the carbocationic and the neutral states largely depends on the substituent and the local position of the Brønsted acid site within the zeolite framework. As a consequence, new insights into the host–guest chemistry between the zeolite and aromatics, in terms of their surface mobility and reactivity, have been obtained.

A Three-Dimensional Metal-Organic Framework Displaying Guest-Dependent Spin-Crossover Behaviour

A new three-dimensional metal-organic complex, [{Fe (NCSe)2}3(TPB)4]x(guest), was prepared with the ligand of TPB (1,3,5-tris (4-pyridyl) benzene). The X-ray single crystal diffraction studied in 100 K and 173 K shown the change of bonds and angles of the framework. The guest exchange and magnetic properties indicated that the 3D framework can be responsible to the solvent guest molecules and shows guest-dependent spin-crossover behaviour.

Towards solvent tuning of slow magnetic relaxation and ferroelectric properties in a dysprosium metal–organic framework system

Abstract A new dysprosium metal–organic framework {[Dy2(L)3(H2O)4]·(acetone)2·(H2O)3} n (Dy2-Acetone) with single-molecule magnet and ferroelectric properties was synthesized through a solvent-induced single-crystal-to-single-crystal (SCSC) transformation. Notably, exchange of the coordinated and guest solvent molecules lead to different magnetic relaxation and ferroelectric properties in the dysprosium MOF system, Dy2-DMF and Dy2-Acetone. Study reveals that the tunable magnetic relaxation behaviors are most likely a result of different local coordination sphere and lattice solvent molecules within the pores which influenced and tuned the relaxation rates of the magnetization. Moreover, disparate polar solvent molecules confined in the MOFs may be the key factors for their different ferroelectric properties.

Three-Dimensional Co(II)/Cd(II) Metal–Organic Frameworks: Luminescent Cd-MOF for Detection and Adsorption of 2,4,6-Trinitrophenol in the Aqueous Phase

Sensing and adsorption of hazardous and explosive nitroaromatic compounds using metal–organic frameworks (MOFs) have been a promising research field in the current scenario due to environmental concerns and homeland security. Here, we report two mixed ligand MOFs {[Co2(SDB)2(TIB)(H2O)](H2O)(1,4-dioxane)2}n (CP1) and {[Cd3(SDB)3(TIB)](H2O)2(1,4-dioxane)(G)x}n (CP2) (where SDB = 4,4′-sulfonyldibenzoate, TIB = 1,3,5-tris(imidazol-1-ylmethyl) benzene, and G = guest solvent molecules) synthesized by a hydrothermal method and the application of CP2 as an adsorbent and sensing material for 2,4,6-trinitrophenol (TNP). Both MOFs are characterized by various physicochemical techniques including single crystal X-ray analysis, and the crystal structures of CP1 and CP2 revealed that both MOFs are 3D frameworks composed of trimeric metal clusters linked by SDB ligand further coordinated through the imidazole nitrogen of the TIB moiety. Taking advantage of d10 transition metal present in the case of CP2, the recognition...