Solvent-Regulated Formation of Metal/Metal-Oxo Nodes in Two Indium Metal-Organic Frameworks: Syntheses, Structures, Selective Gas Adsorption and Fluorescence Sensor Properties

Two water-stable indium metal-organic frameworks, (NH2Me2)3[In3(BTB)4] ⋅ 12DMA ⋅ 4.5H2O (In-MOF-1) and (NH2Me2)9[In9O6(BTB)8(H2O)4(DMSO)4] ⋅ 27DMSO ⋅ 21H2O (In-MOF-2) (BTB=4,4',4''-benzene-1,3,5-tribenzoate) with 3D interpenetrated structure has been constructed by regulating solvents. Structure analysis revealed that In-MOF-1 has a three-dimensional (3D) structure with a single metal core, while In-MOF-2 features an octahedron cage constructed by three kinds of metal clusters to further form a 3D structure. The fluorescence investigations showed that In-MOF-1 and In-MOF-2 are potential MOF-based fluorescent sensors to detect acetone and Fe3+ ions in EtOH or water with high sensitivity, excellent selectivity, recyclability and a low limit of detection. Moreover, the fluorescence mechanisms of In-MOF-1 and In-MOF-2 toward acetone and Fe3+ ions were further explained. In addition, In-MOF-2 has higher thermal and framework stability than In-MOF-1. The activated In-MOF-2 presents a high BET surface area of 998.82 m2g-1 and a pore size distribution of 8 to 16 Å. At the same time, In-MOF-2 exhibits high selective CO2 adsorption for CO2/CH4 and CO2/N2, respectively. Furthermore, the adsorption sites and adsorption isotherms were predicted using grand canonical Monte Carlo (GCMC) simulations, and the adsorption energy of the lowest-energy adsorption configuration was calculated using molecular dynamics (MD) simulations.

Solvatomorphism in a series of copper(II) complexes with the 5-phenylimidazole/perchlorate system as ligands

In the course of an investigation of the supramolecular behaviour of copper(II) complexes with the 5-phenylimidazole/perchlorate ligand system (`blend') remarkable solvatomorphism has been observed. By employing a variety of crystallization solvents (polar protic, polar/non-polar aprotic), a series of 12 crystalline solvatomorphs with the general formula [Cu(ClO4)2(LH)4]·x(solvent) have been obtained [LH = 5-phenylimidazole, x(solvent) = 3.3(H2O) (1), 2(methanol) (2), 2(ethanol) (3), 2(1-propanol) (4), 2(2-propanol) (5), 2(2-butanol) (6), 2(dimethylformamide) (7), 2(acetone) (8), 2(tetrahydrofurane) (9), 2(1,4-dioxane) (10), 2(ethyl acetate) (11) and 1(diethyl ether) (12)]. The structures have been solved using single-crystal X-ray diffraction and the complexes were characterized by thermal analysis and infrared spectroscopy. The solvatomorphs are isostructural (triclinic, P1), with the exception of compound 9 (monoclinic, P21/n). The supramolecular structures and the role of the various solvents is discussed. All potential hydrogen-bond functionalities, both of the [Cu(ClO4)2(LH)4] units and of the solvents, are utilized in the course of the crystallization process. The supramolecular assembly in all structures is directed by strong recurring Nimidazole-H...Operchlorate motifs leading to robust scaffolds composed of the [Cu(ClO4)2(LH)4] host complexes. The solvents are located in channels and, with the exception of the disordered waters in 1 and the diethyl ether in 12, participate in hydrogen-bonding formation with the [Cu(ClO4)2(LH)4] complexes, serving as both hydrogen-bond acceptors and donors (for the polar protic solvents in 2-6), or solely as hydrogen-bond acceptors (for the polar/non-polar aprotic solvents in 7-11), linking the complexes and contributing to the stability of the crystalline compounds.

Imiquimod Solubility in Different Solvents: An Interpretative Approach

Imiquimod (IMQ) has been successfully formulated to date mainly as semi-solid lipophilic formulations for topical application. In this study, we investigated the solubility of IMQ in solvents suitable for developing innovative formulations in the form of powder obtained, for instance, by spray drying; thus, water, ethanol, methanol, acetone, acetonitrile, and dimethyl sulfoxide were tested at different temperatures. Temperature variations, stirring intensity, and the contact time between IMQ and the solvent greatly affected the evaluation of IMQ equilibrium solubility. The attainment of the solid-liquid equilibrium requires 13 days starting from solid IMQ and 2 days from a cooled-down supersaturated IMQ solution. A correlation between IMQ solubility and the solubility parameters of solvents was not found. IMQ solutions in water, ethanol, methanol, acetonitrile, and dimethyl sulfoxide were neither ideal nor regular. The Scatchard-Hildebrand equation does not apply to IMQ solutions because of association phenomena due to intermolecular hydrogen bonds and/or π-stacking, as supported by the hyperchromic effect that was very pronounced in highly polar solvents, such as water, with the increase in temperature. Finally, IMQ solubility values measured in acetone cannot be considered reliable due to the reaction with the solvent, leading to the formation of new molecules.

In Situ Conversion of Ligand to a Coordination Polymer via a Core@Shell Crystal: A Multi-Step Phase-Dependent Structural Transformation

Two pseudopolymorphic 1D coordination polymers of the formulas [Cd(3,3'-pytz)(CH3OH)2(ClO4)2]n (1) and [Cd(3,3'-pytz)(CH3CN)2(ClO4)2]n (2) have been prepared using the electron-deficient 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3'-pytz) ligand and cadmium perchlorate in the chloroform/methanol and chloroform/acetonitrile solvent system, respectively. It was observed that compounds 1 and 2 experienced one-step (CPreagent → CPproduct) single-crystal-to-powder structural transformation to the pure water-coordinated compound [Cd(3,3'-pytz)(H2O)2(ClO4)2]n (3) by absorbing water vapor from air (solid-gas phase transformation). Interestingly, compounds 1, 2, and 3 undergo a different transformation path and show an in situ unique three-step (CPreagent → CPproduct → Ligandintermediate → CPproduct) single-crystal-to-single-crystal (SCSC) structural transformation process through soaking in deionized water (solid-liquid phase transformation). In this fascinating transformation, we report for the first time the direct conversion of a ligand into a coordination polymer by a rare core-shell pathway in a solid-liquid phase transformation. In this process, we obtained compound {[Cd(3,3'-pytz)(H2O)4](3,3'-pytz)2(ClO4)2(H2O)6}n (4) (single-crystal = S, crystal = C, or microcrystal = P) as mixed compounds of core-shell L@4C and 4S or core-shell L@4P and 4P for compounds (1 and 2) and 3, respectively.

Exfoliation of 2D Metal-Organic Frameworks: toward Advanced Scalable Materials for Optical Sensing

Two-dimensional metal-organic frameworks (MOFs) occupy a special place among the large family of functional 2D materials. Even at a monolayer level, 2D MOFs exhibit unique sensing, separation, catalytic, electronic, and conductive properties due to the combination of porosity and organo-inorganic nature. However, lab-to-fab transfer for 2D MOF layers faces the challenge of their scalability, limited by weak interactions between the organic and inorganic building blocks. Here, comparing three top-down approaches to fabricate 2D MOF layers (sonication, freeze-thaw, and mechanical exfoliation), The technological criteria have established for creation of the layers of the thickness up to 1 nm with a record aspect ratio up to 2*10^4:1. The freezing-thaw and mechanical exfoliation are the most optimal approaches; wherein the rate and manufacturability of the mechanical exfoliation rivaling the greatest scalability of 2D MOF layers obtained by freezing-thaw (21300:1 vs 1330:1 aspect ratio), leaving the sonication approach behind (with a record 900:1 aspect ratio) have discovered. The high quality 2D MOF layers with a record aspect ratio demonstrate unique optical sensitivity to solvents of a varied polarity, which opens the way to fabricate scalable and freestanding 2D MOF-based atomically thin chemo-optical sensors by industry-oriented approach.

Interfacial Tension-Impelled Self-Assembly and Morphology Tuning of Poly(3,4-ethylene dioxythiophene)/Tellurium Nanocomposites at Various Liquid/Liquid Interfaces

Compared to the enormous number of nanostructures that have been documented, the variety of nanostructures produced by organic polymerization is rather limited. We devised an unconventional route and a sustainable approach to distribute tellurium nanoparticles (Te NPs) in a poly(3,4-ethylene dioxythiophene) (PEDOT) matrix to form semiconducting organic-inorganic nanocomposites for potential applications in electrochemical sensing. The adopted strategy of in situ liquid/liquid interface-assisted polymerization aids in the formation of intimately tethered Te NPs on the PEDOT polymer chains, thereby preventing the aggregation of Te NPs. The untapped versatility inherent to using biphasic systems for interfacial polymerization is explored at three interface systems of immiscible solvents: chloroform/water, dichloromethane/water, and hexane/water, giving rise to PEDOT/Te nanocomposite (PTeNC) of distinct morphology. Chemical nature, crystallinity, and morphology investigations proved the successful formation of PTeNC in different interface systems. Consequently, the temporal evolution of interfacial tension in the preferential adsorption of nanoparticles and final product morphology was monitored by pendant drop tensiometry. Owing to the role of morphology, PTeNC synthesized at the hexane/water interface showcased the best electrocatalytic behavior toward nonenzymatic detection of l-ascorbic acid, an essential nutritional factor, and a neuromodulator with a limit of detection of 0.66 μM and excellent sensitivity, selectivity, and reproducibility. Hence, we envision that interface-assisted polymerization offers a nascent and robust strategy for encapsulating unusual electrode materials in polymeric matrices.

Helical fluxionality: numerical frustration drives concerted low-barrier screw motions of a tricopper cluster

Uneven allocation of resources creates frustration, tension, and conflicts. Confronted with an apparent mismatch between the number of donor atoms and the number of metal atoms to be supported, helically twisted ligands cleverly come up with a sustainable symbiotic solution. As an example, we present a tricopper metallohelicate exhibiting screw motions for intramolecular site exchange. A combination of X-ray crystallographic and solution NMR spectroscopic studies revealed thermo-neutral site exchange of three metal centres hopping back and forth inside the helical cavity lined by a spiral staircase-like arrangement of ligand donor atoms. This hitherto unknown helical fluxionality is a superimposition of translational and rotational movements of molecular actuation, taking the shortest path with an extraordinarily low energy barrier without compromising the overall structural integrity of the metal-ligand assembly.

Polydopamine-guarded metal-organic frameworks as co-delivery systems for starvation-assisted chemo-photothermal therapy

Cutting off glucose provision by glucose oxidase (GOx) to famish tumors can be an assistance with chemotherapy to eliminate cancer cells. Co-encapsulation of GOx and chemotherapeutics (doxorubicin) within pH-sensitive metal-organic frameworks (MOFs) could disorder metabolic pathways of cancer cells and generate excessive intracellular reactive oxygen species (ROS), together. To prevent premature leach of GOx from the porous channels of MOFs, polydopamine (PDA) was deposited on the surface of MOFs, which endowed the delivery system with photothermal conversion ability. Our nanoscaled co-delivery system (denoted as DGZPNs) remains stable with low amount of drug leakage under simulated physiological conditions in vitro and internal environment, while they are triggered to release doxorubicin (DOX) and GOx in acid tumor microenvironment and at high temperature for reinforced chemotherapy. NIR laser irradiation also activates superior photothermal conversion efficiency of PDA (36.9 %) to initiate hyperthermia to ablate tumor tissue. After being phagocytized by 4 T1 cells (breast cancer cells), the DGZPNs delivery system showed a superior therapeutic efficacy with a tumor growth inhibition of 88.9 ± 6.6 % under NIR irradiation, which indicated that the starvation-assisted chemo-photothermal therapy prompts the significant advance of synergistic therapy in a parallelly controlled mode.

Nonlinear Optical and Magnetic Properties of FeII-SCN-HgII Isomers: Centrosymmetric Layers and Chiral Networks

Research on isomers is highly desirable due to their prospective role in better understanding of physicochemical properties of similar systems and further development of multifunctional molecular materials. Iron(II) and tetra(thiocyanato)mercury(II) ions self-assembled in the presence of 2-acetylpyridine (2-acpy) excess to form two {[Fe(2-acpy)][Hg(μ-SCN)₄]}_n isomers: two-dimensional (2D) centrosymmetric layers with folded ring structural motifs (1) and three-dimensional (3D) chiral networks with right- or left-handed {···Fe-NCS-Hg-SCN···}_∞ helixes (2). New methods of designing and synthesizing functional thiocyanate-bridged materials have been proposed. In addition, the similarity between 1 and 2 allowed for the description of subtle changes in IR and UV-visible spectra. Moreover, 2 shows spontaneous resolution, and it crystallizes in the noncentrosymmetric space group P2₁, leading to the occurrence of nonlinear optical activity in circular dichroism studies and second harmonic generation (SHG). At room temperature, the SH susceptibility for powder sample 2 reached 6.0 × 10^-11 esu. Ab initio calculations indicated the electric polarization vector and the crystallographic twofold screw axis pass through the aromatic ring. Magnetic studies for 1 and 2 revealed high-spin iron(II) with zero-field splitting at low temperatures. Analysis of magnetic data gave |D| = 37.45 cm^-1, |E/D| = 5.59 cm^-1, and ⟨g⟩ = 2.15 for 1, |D| = 36.78 cm^-1, |E/D| = 4.92 cm^-1, and ⟨g⟩ = 2.18 for 2, and information about the orientation of magnetic anisotropy vectors for both compounds.

Polarity-Evolution Control and Luminescence Regulation in Multiple-Site Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) have shown great potential in separation, sensing and host-guest chemistry, however, the pre-design of HOFs remains challenging due to the uncertainty of solvents' participation in framework formation. Herein, the polarity-evolution-controlled framework/luminescence regulation is demonstrated based on multiple-site hydrogen-bonded organic frameworks. Several distinct HOFs were prepared by changing bonding modes of building units via the evolution of electrostatic forces induced by various solvent polarities. High-polar solvents with strong electrostatic attraction to surrounding units showed the tendency to form cage structures, while low-polar solvents with weak electrostatic attraction only occupy hydrogen-bond sites, conducive to the channel formation. Furthermore, the conformation of optical building unit can be adjusted by affecting the solvent polarity, generating different luminescence outputs. These results pave the way for the rational design of ideal HOFs with on-demand framework regulation and luminescence properties.

Stretchable Self-Healing Plastic Polyurethane with Super-High Modulus by Local Phase-Lock Strategy

In this work, a multiblock polyurethane (PU-Im) consisting of polyether and polyurethane segments with imidazole dangling groups is demonstrated, which can further coordinate with Ni²⁺ . By controlling the ligand content and metal-ligand stoichiometry ratio, PU-Im-Ni complex with vastly different mechanical behavior can be obtained. The elastomer PU-2Im-Ni has extraordinary mechanical strength (61MPa) and excellent toughness (420 MJ m^-3 ), but the plastic PU-4Im-Ni exhibits super-high modulus (515 MPa), strength (63 MPa), and good stretchability (≈800%). The metal-ligand interaction between polyurethane segments and Ni²⁺ is proved by Raman spectra, dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The polyurethane segments domain formed by microphase separation is dynamically "locked" by Ni²⁺ coordinated with imidazole, revealing a local phase-lock effect. The phase-locking hard domains reinforce the PU-Im-Ni complex and maintain stimuli-responsive self-healing ability, while the free polyether segments provide stretchability. Primarily, the water environment with plasticization effect serves as an effective and eco-friendly self-healing approach for PU-Im-Ni plastic. With the excellent mechanical performance, thermal/aquatic self-healing ability, and unique damping properties, the PU-Im-Ni complexes show potential applications in self-healing engineering plastic and cushion protection fields.

Coordination-Guided Conformational Locking of 1D Metal-Organic Frameworks for a Tunable Stimuli-Responsive Luminescence Region

One-dimensional (1D) metal-organic frameworks (MOFs) have shown great potential for designing more sensitive and smart stimuli-responsive photoluminescence metal-organic frameworks (PL-MOFs). Herein, we propose a strategy for constructing the 1D MOFs with tunable stimuli-responsive luminescence regions based on coordination-guided conformational locking. Two flexible 1D MOF microcrystals with trans- and cis-coordination modes, respectively, were synthesized by controlling the spatial constraint of solvents. The two 1D frameworks possess different conformation lockings of gain ligands, which have a great influence on the rotating restrictions and corresponding excited-state behaviors, generating the remarkably distinct color-tunable ranges (cyan-blue to green and cyan-blue to yellow, respectively). On this basis, the two 1D MOF materials, benefiting from the varied stimuli-responsive ranges, have displayed great potential in fulfilling the anticounterfeiting and information encryption applications. These results provide valuable guidance for the development of smart MOF-based stimuli-responsive materials in information identification and data encryption.

Amide-Driven Secondary Building Unit Structural Transformations between Zn(II) Coordination Polymers

The behavior of coordination polymers (CPs) against external stimuli has witnessed remarkable attention, especially when the resulting CPs present reversible molecular arrays. Accordingly, CPs with these characteristics can lead to differences in their properties owing to these structural differences, being promising for their use as potential molecular switches with diverse applications. Herein, we have synthesized four Zn(II) CPs bearing α-acetamidocinnamic acid (HACA) and 4,4'-bipyridine (4,4'-bipy). The reaction between Zn(OAc)₂·2H₂O, HACA, and 4,4'-bipy yields {[Zn(ACA)₂(4,4'-bipy)]·EtOH} _n (1), which was used for the formation of three CPs through dissolution-recrystallization structural transformations (DRSTs): {[Zn(ACA)₂(4,4'-bipy)]·2MeOH} _n (2), {[Zn₂(μ-ACA)₂(ACA)₂(4,4'-bipy)]·2H₂O} _n (3), and {[Zn₃(μ-ACA)₆(4,4'-bipy)]·0.75CHCl₃} _n (4). The study of the four crystal structures revealed that their secondary building units (SBUs) comprise monomeric, dimeric, and trimeric arrangements linked by 4,4'-bipy ligands. The fundamental role of the utilized solvent and/or temperature, as well as their effect on the orientation of the amide moieties driving the formation of the different SBUs is discussed. Furthermore, the reversibility and interconversion between the four CPs have been assayed. Finally, their solid-state photoluminescence has evinced that the effect of the amide moieties not only predetermine a different SBU but also lead to a different emission in 4 compared with 1-3.

Anion-assisted supramolecular assemblies of zinc(II) complexes with isonicotinamide

Five zinc(II) coordination compounds, [ZnCl₂(isn)₂] (1), [ZnBr₂(isn)₂] (2), [Zn(NO₃)₂(H₂O)(isn)₂] (3), [Zn(CH₃COO)₂(isn)]₂ (4) and [Zn(isn)₄(H₂O)₂](ClO₄)₂ (5) (isn = isonicotinamide), were prepared by the reactions of the isonicotinamide (pyridine-4-carboxamide, isn) and corresponding zinc(II) salts. Their crystal structures were determined by the single-crystal X-ray diffraction method. The coordination environment of zinc(II) is tetrahedral in the compounds containing small halide anions (chloride, bromide), 1 and 2. An expansion of the zinc(II) coordination environment to the octahedral is observed in the presence of the monodentate and bridging nitrate ions in 3. The coordination environments of both zinc(II) ions in dimeric acetate complex 4 is also enlarged in the comparison with 1 and 2, one zinc(II) ion being octahedrally coordinated and the other being pentacoordinated. The zinc(II) ion in 5 also reaches higher coordination environment (octahedral), which is enabled by binding of additional water molecules, since the perchlorate ion is uncoordinated. The supramolecular amide-amide homosynthon R 2 2 ( 8 ) is preserved in the presence of halide, nitrate and acetate ions (1-4), but it is completely disrupted in the crystal packing of 5 due to the presence of the bulky perchlorate anion. Spectroscopic analysis of compounds 1-5 was performed by IR spectroscopy in the solid state and by ¹³C NMR spectroscopy in the DMSO solutions. The NMR data support a complete decomposition of 3 in the DMSO solution, but 1, 2, 4 and 5 remain unchanged in the solution. Thermal properties of the coordination compounds were also investigated by TGA and DSC methods.

Solvent media as the driving force in the formation of one-dimensional silver(I) coordination polymers with 2-methylidene-1,3-bis(nicotinoyloxy)propane

Two kinds of silver(I) coordination polymers consisting of the same chemical composition, [Ag(CF3SO3)(L)] [L is 2-methylidene-1,3-bis(nicotinoyloxy)propane], were synthesized and characterized by infrared (IR) and photoluminescence (PL) spectroscopy, elemental and thermal analyses, and single-crystal X-ray diffractometry; these are catena-poly[[(trifluoromethanesulfonato-κO)silver(I)]-μ-2-methylenepropane-1,3-diyl dinicotinate-κ2 N:N′], [Ag(CF3SO3)(C16H14N2O4)] n , and its chloroform monosolvate, {[Ag(CF3SO3)(C16H14N2O4)]·CHCl3} n . The X-ray crystallographic measurements revealed that the silver(I) compounds exhibit one-dimensional sinusoidal or helical molecular structures depending on the solvent used for crystallization. Self-assembly in a methanol/chloroform mixture produces the sinusoidal molecular strand, whereas recrystallization from acetonitrile medium affords a racemic mixture of the helical strands. These compounds display a fluorescence emission arising from both the ligand-centred transition and the ligand-to-metal charge transfer (LMCT) in the solid state under ambient conditions.

Synthesis, Structure, and UV–Vis Characterization of Antimony(III) Phthalocyanine: [(SbPc)2(Sb2I8)(SbBr3)]2

A new antimony(III)–phthalocyanine complex with the formula of [(SbPc)2(Sb2I8)(SbBr3)]2 has been obtained in the reaction of pure antimony powder with phthalonitrile under the oxidation conditions by iodine monobromide vapors. The complex crystallizes in the centrosymmetric space group of the triclinic system. Both independent (SbPc)+ units exhibit non-planar conformation, since the Sb(III) is larger than the equilibrium cavity size of the ring and cannot be accommodated without its expansion; thus, the metal protrudes out of the cavity, forming a saucer shape. The centrosymmetric anionic unit of the crystal consists of two (Sb2I8)2− interacted anionic units forming (Sb4I16)4− anionic complex that interacts with two SbBr3 molecules to form [Sb6I16Br6]4− anionic aggregate. Each [Sb6I16Br6]4− anionic aggregate is surrounded by four (SbPc)+ cations forming a supramolecular centrosymmetric (SbPc)4[Sb6I16Br6] complex. Translationally related (SbPc)4[Sb6I16Br6] molecules form a stacking structure along the [100] and [011] directions with N4–N4 distances of 3.55 and 3.53 Å, respectively, between the back-to-back-oriented saucer-shaped (SbPc)+ units. The interaction between the building units of the crystal was analyzed using the Hirshfeld surface and the analysis of the 2D fingerprint plots. The UV–Vis absorption spectra of crystal 1 were taken in CH2Cl2 and toluene solutions in the concentration range from 10−5 to 10−6 mol/L. No significant changes related to aggregation in solutions were observed. The Q-band in toluene solution is red shifted by ~15 nm in comparison to that in CH2Cl2 solution. Oxidation of (SbPc)4[Sb6I16Br6] yields SbVPc derivative. Both SbIII and SbV phthalocyanine derivatives absorb near infrared light (600–900 nm), which should be intriguing from the point of view of potential use as photosensitizers for PDT and as an infrared cut filter for plasma display and silicon photodiodes.

Construction of Pyrazine-Appended 1D and 3D Cobalt(II) Succinate Coordination Polymers: Influence of Solvent on Architectures and Applications in Gas Adsorption and NAC Detection

An underexplored reaction of pyrazine (rigid and linear) and succinic acid (flexible) with Co(NO₃)₂·6H₂O afforded four new coordination polymers (CPs): [Co(H₂O)(pyz)(suc)] (1), [Co(H₂O)₂(pyz)(suc)] (2), [Co(H₂O)₄(pyz)](suc) (3) and [Co₂(H₂O)₂(pyz)(suc)₂] (4), as well as [Co(HCO₂)₂(pyz)] (5) being lately reported along with well-known 6 and 7. The CPs were obtained as stable crystalline materials and characterized by conventional solid-state techniques, including X-ray crystallography. Hydrothermally produced compounds 1 and 2 were both 3D CPs. While 3 and 4 obtained under ambient/solvothermal conditions in DMSO generated 1D and 3D structures, 5 isolated from DMF under solvothermal conditions had a 3D structure. The topologies of the coordination polymers 1-7 were described by underlying nets 3D 5-c fet, 3D 4-c cds, 1D 2-c 2C1, 3D 5-c bnn, 3D 6-c rob, 1D 2-c 2C1, and 3D 6-c pcu, respectively. The plot of χ_M ^-1 versus T was essentially linear in the entire temperature range following the Curie-Weiss law with a Curie constant (C) of 2.525 and a negative Weiss constant (ϕ) of -46.24 K, suggesting weak antiferromagnetic (AF) exchange interactions. CO₂ and N₂ adsorption studies of 1-5 featured type III isotherms. 1 was found to show remarkably higher quenching efficiencies for nitrophenols (η = 98% for o-NP) over other NACs. The Stern-Volmer plot exhibited deviation in linearity with K _sv values about 200 times greater than that for the simplest nitroaromatic compound (NB), signifying its exclusive quenching ability toward 1. The LOD for p-NP addition to 1 was found to be 0.995 ppm.

Influence of the Lewis basicity hardness of crystallization solvents on the coordination sphere of the complex [Co(3,5-dinitrobenzoate-O,O′)2]: crystallographic and theoretical analysis

Crystal growth of [Co(DNB)2] in different solvents is a thermodynamic process favored by ΔErecrys (kcal mol−1) where mono/trinuclear molecules are obtained. Closeness of HOMO orbitals of solvents to the SOMOs orbitals of Co(ii) ions guide the process.

Guest-Regulated Luminescence and Force-Stimuli Response of a Hydrogen-Bonded Organic Framework

Guest molecules may endow porous materials with new or enhanced properties as well as functions. Here, a porous hydrogen-bonded organic framework (HOF) constructed from a three-armed triphenylamine derivative is used to investigate how guests regulate photoluminescence and trigger force-stimuli response. It was found that guest solvents in pores might regulate HOF's luminescence. Interestingly, acetic acid as a guest endowed HOF materials with longer emission wavelengths and triggered the responses to mechanical force stimuli. Under shear force, an obvious blueshift in emission spectra was observed because of the loss of free guests and the conversion of π-stacking model. Further blue-shifted emission appeared while the bound guests were completely removed by heating. Mechanofluorochromic HOF materials could be regenerated through recrystallization and adsorbing guest. Conversely, HOFs with other guests and activated HOFs only resulted in a slight change in their fluorescence behaviors after force stimuli.

Humidity-Induced Structural Transformation in Pseudopolymorph Coordination Polymers

Three cadmium coordination polymers, namely, {[CdL(OAc)₂](C₂H₅OH)}_n (1), {[CdL(OAc)₂](CH₃CN)}_n (2), and [CdL(OAc)₂(H₂O)]_n (3), were synthesized by an exoditopic 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene Schiff base ligand (L) and cadmium acetate in the presence of different solvent systems. Single-crystal X-ray diffraction, powder X-ray diffraction, and thermogravimetric analysis showed that 1D ladder pseudopolymorphic compounds (1 and 2) transformed to the solvent-free 1D linear compound 3 through a rare case of water absorption from air at room temperature. Interestingly, compound 3 was transformed to compound 1 through a dissolution-recrystallization structural transformation process. The results illustrated that solvents and humidity have an important role in the formation of pseudopolymorphs with the same or different structural motifs.

Modelling drug adsorption in metal-organic frameworks: the role of solvent

Solvent plays a key role in biological functions, catalysis, and drug delivery. Metal-organic frameworks (MOFs) due to their tunable functionalities, porosities and surface areas have been recently used as drug delivery vehicles. To investigate the effect of solvent on drug adsorption in MOFs, we have performed integrated computational and experimental studies in selected biocompatible MOFs, specifically, UiO-AZB, HKUST-1 (or CuBTC) and NH2-MIL-53(Al). The adsorption of three drugs, namely, 5-fluorouracil (5-FU), ibuprofen (IBU), and hydroxyurea (HU) were performed in the presence and absence of the ethanol. Our computational predictions, at 1 atmospheric pressure, showed a reasonable agreement with experimental studies performed in the presence of ethanol. We find that in the presence of ethanol the drug molecules were adsorbed at the interface of solvent and MOFs. Moreover, the computationally calculated adsorption isotherms suggested that the drug adsorption was driven by electrostatic interactions at lower pressures (<10-4 Pa). Our computational predictions in the absence of ethanol were higher compared to those in the presence of ethanol. The MOF-adsorbate interaction (U HA) energy decreased with decrease in the size of a drug molecule in all three MOFs at all simulated pressures. At high pressure the interaction energy increases with increase in the MOFs pore size as the number of molecules adsorbed increases. Thus, our research shows the important role played by solvent in drug adsorption and suggests that it is critical to consider solvent while performing computational studies.

Solvent-Induced Structural Transformation and Luminescence Response in a Dumbbell-Shaped Crystalline Molecular Rotor

Crystalline molecular rotors constitute a new class of stimuli-responsive molecular materials owing to inherent molecular dynamics. However, beyond the molecular level, the role of molecular packings on the bulk structures and related properties has yet to be fully understood. Herein, we report a crystalline molecular rotor showing solvent-induced structural transformation and luminescence response. The molecular rotor has a dumbbell shape with two plates as the stators and one axial bridging ligand as the rotator. The crystals adopt solvated and desolvated forms with strikingly different packing structures. The solvated forms can easily transform into the desolvated form. During the structure transformation, the butterfly-like conformation of the stator undergoes a drastic dihedral angle change of about 30°, resulting in a luminescent change of about 10 nm. These findings afford a new aspect for functional molecular rotor materials.

Effects of alkalinity on interaction between EPS and hydroxy-aluminum with different speciation in wastewater sludge conditioning with aluminum based inorganic polymer flocculant

Extracellular polymeric substances (EPS) form a stable gel-like structure to combine with water molecules through steric hindrance, making the mechanical dewatering of wastewater sludge considerably difficult. Coagulation/flocculation has been widely applied in improving the sludge dewatering performance, while sludge properties (organic fraction and solution chemistry conditions) are highly changeable and have important effects on sludge flocculation process. In this work, the alkalinity effects on sludge conditioning with hydroxy-aluminum were comprehensively investigated, and the interaction mechanisms between EPS and hydroxy-aluminum with different speciation were unraveled. The results showed that the effectiveness of hydroxy-aluminum conditioning gradually deteriorated with increase in alkalinity. Meanwhile, the polymeric hydroxy-aluminum (Al₁₃) and highly polymerized hydroxy-aluminum (Al₃₀) were hydrolysed and converted into amorphous aluminum hydroxide (Al(OH)₃), which changed the flocculation mechanism from charge neutralization and complexing adsorption to hydrogen bond interaction. Additionally, both Al₁₃ and Al₃₀ showed higher binding capacity for proteins and polysaccharides in EPS than monomeric aluminum and Al(OH)₃. Al₁₃ and Al₃₀ coagulation changed the secondary structure of proteins in EPS, which caused a gelation reaction to increase molecular hydrophobicity of proteins and consequently sludge dewaterability. This study provided a guidance for optimizing the hydroxy-aluminum flocculation conditioning of sludge with high solution alkalinity.

Alkali and alkaline earth coordination polymers constructed from benzene-1,2,4,5-tetracarboxylic acid and flexible dicarboxylate acid ligands: syntheses, structures and spectroscopic and thermal properties

Two new metal coordination complexes, namely, poly[aqua(μ₆-benzene-1,2,4,5-tetracarboxylic acid-κ⁸O¹:O¹,O²:O^2':O⁴:O⁴,O⁵:O^5')(μ-but-2-enedioato-κ²O¹:O⁴)potassium(I)], [K₂(C₄H₂O₄)(C₁₀H₆O₈)(H₂O)₂]_n or [K₂(fum)(H₄btec)(H₂O)₂]_n, (1), and poly[aqua(μ₈-2,5-dicarboxybenzene-1,4-dicarboxylato-κ¹²O¹:O^1',O²:O²,O^2':O^2':O⁴:O^4',O⁵:O⁵,O^5':O^5')(μ-ethanedioato-κ⁴O¹,O²:O^1',O^2')strontium(II)], [Sr₂(C₂O₄)(C₁₀H₄O₈)(H₂O)₂]_n or [Sr₂(ox)(H₂btec)(H₂O)₂]_n, (2) (H₄btec = benzene-1,2,4,5-tetracarboxylic acid, H₂btec = 2,5-dicarboxybenzene-1,4-dicarboxylate, fum = fumarate and ox = oxalate), have been obtained under hydrothermal conditions by reacting the different alkali and alkaline earth metal salts with H₄btec, fumaric acid (H₂fum) and oxalic acid (H₂ox). Complexes (1) and (2) were structurally characterized by single-crystal X-ray diffraction, IR and UV-Vis spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetic analysis-differential scanning calorimetry (TGA-DSC). Complex (1) displays a two-dimensional (2D) layer with the K⁺ ion in a distorted pentagonal bipyramidal geometry and exhibits a uninodal 6-connected hxl/Shubnikov plane net (3,6) with {3⁶.4⁶.5³} topology. Complex (2) displays a three-dimensional (3D) network structure, in which the Sr²⁺ ion is in a distorted monocapped square antiprism geometry. The framework possess a binodal (5,8)-connected net with the Schläfli symbol {3².4¹⁰.5⁸.6⁴.7⁴}{3².4⁶.5²}₂. The 3D Hirshfeld surfaces and 2D fingerprint plots show that the main interactions are the O...H/H...O intermolecular interactions. Moreover, the thermal decompositions of (1) and (2) in the temperature range 303-1273 K revealed that they both decompose in three steps and transform to the corresponding metal oxide.

MOFs assembled from C3 symmetric ligands: structure, iodine capture and role as bifunctional catalysts towards the oxidation-Knoevenagel cascade reaction

Three new NiII/CoII-metal organic frameworks were self-assembled by the reaction of C3 symmetric 1,3,5-tribenzoic acid (H3BTC) and 2,4,6-tris(4-pyridyl)-1,3,5-triazine (4-TPT) ligands and NiII/CoII salts under solvothermal conditions. Isomorphous MOF1 and MOF2 exhibit a 3D pillar-layer framework based on binuclear M2(OH)(COO)2 units connected by tritopic BTC3- and 4-TPT ligands with a novel (3,5)-connected topology net. MOF3 displays a 3-fold interpenetrated 3D network exhibiting a (3,4)-connected topology net. The porous MOF3 can reversibly take up I2. The activated MOFs contain both Lewis acid (NiII center) and basic (uncoordinated pyridyl or carboxylic groups) sites, and act as bifunctional acid-base catalysts. The catalytic measurements demonstrate that the activated MOF3 exhibits good activities for benzyl alcohol oxidation and the Knoevenagel reaction and can be recycled and reused for at least four cycles without losing its structural integrity and high catalytic activity. Thus, the catalytic properties for the oxidation-Knoevenagel cascade reaction have also been studied.

A “turn-on” small molecule fluorescent sensor for the determination of Al3+ ion in real samples: theoretical calculations, and photophysical and electrochemical properties

The fluorescence sensing properties of a naphthalene-based acetohydrazide (3) were investigated. A highly selective “turn-on” response was obtained towards Al3+ ions, and this was used for real sample analysis and development of paper test strips.

Steric crowding of a series of pyridine based ligands influencing the photophysical properties of Zn(II) complexes

The combination of α-acetamidocinnamic acid (HACA) and different N, N,N and N,N,N pyridines (dPy) leads to crowded Zn(ii) metal centers. The increasing bulkiness competes with the chelation enhanced effect (CHEF) in the resulting quantum yields.