1,720,977 research outputs found
Host-Guest Chemistry of M12L8 Poly-[n]-catenanes: Inclusion Process by Switchable ''losed-Open'' ynamic Channels
No full textDirect guest exchange reactions in one-dimensional (1D) poly-[n]-catenanes self-assembled by elusive M12L8 large nanocages (similar to 2600 angstrom(3) of internal volume) have never been documented. Herein, we report for the first time the guest behavior of a TPB poly-[n]-catenane (1) self-assembled from M12L8 icosahedral nanocages in the absence of permanent communicating voids. High-resolution synchrotron X-ray data obtained by means of crystal-to-crystal guest exchange reactions unambiguously demonstrate the uptake of o-dichlorobenzene and p-chloroanisole. Density functional theory calculations aimed at studying local interaction energy variation among 1D chains of catenated M12L8 cages provided insights that help us further understand the intrinsic dynamic behavior of the 1D porous rods. The guest uptake by the icosahedral M12L8 nanocages is rationalized via a switchable closed-open process considering both the weak interchain interactions and the stronger intrachain mechanical bond. Mechanistic aspects of the molecular exchange consider both the sliding motion of the 1D chains of interlocked M12L8 nanocages and the dynamic aspects of single M12L8 cages within the 1D chains (i.e., cage compression/extension) in a concerted cooperative dynamic behavior. Thermal treatment of the ZnBr2-TPB poly-[n]-catenane demonstrates that the mechanical bond remains up to similar to 500 K. The exceptional structural properties of 1 have been studied for potential applications such as selectivity of chlorobenzenes. The labile nature of the Zn-N coordination bond allows the recyclability of the TPB ligand in water, thus making these materials candidates in green chemistry applications
Polycatenanes Formed of Self-Assembled Metal-Organic Cages
No full textPoly-[n]-catenanes (PCs) self-assembled of three-dimensional (3D) metal organic cages (MOCs) (hereafter referred to as PCs-MOCs) are a relatively new class of mechanically interlocked molecules (MIMs) that combine the properties of MOCs and polymers. The synthesis of PCs-MOCs is challenging because of the difficulties associated with interlocking MOCs, the occurrence of multiple weak supramolecular electrostatic interactions between cages, and the importance of solvent templating effects. The high density of mechanical bonds interlocking the MOCs endows the MOCs with mechanical and physical properties such as enhanced stability, responsive dynamic behavior and low solubility, which can unlock new functional properties. In this Minireview, we highlight the benefit of interlocking MOCs in the formation of PCs-MOCs structures as well as the synthetic approaches exploited in their preparation, from thermodynamic to kinetic methods, both in the solution and solid-states. Examples of PCs-MOCs self-assembled from various types of nanosized cages (i.e., tetrahedral, trigonal prismatic, octahedral and icosahedral) are described in this article, providing an overview of the research carried out in this area. The focus is on the structure-property relationship with examples of functional applications such as electron conductivity, X-ray attenuation, gas adsorption and molecular sensing. We believe that the structural and functional aspects of the reviewed PCs-MOCs will attract chemists in this research field with great potential as new functional materials in nanotechnological disciplines such as gas adsorption, sensing and photophysical properties such as X-ray attenuation or electron conductivity.This article reviews the most relevant examples of polycatenanes in which the catenating subcomponents forming the mechanical bonds are interlocked three-dimensional metal organic cages (MOCs). We emphasize the beneficial aspects of mechanical bond formation among MOCs, synthetic approaches, supramolecular topologies, and structure-function correlations. The experimental and theoretical aspects of polycatenanes made of MOCs have also been investigated. imag
Mechanochemical synthesis of mechanical bonds inM12L8poly-[n]-catenanes
No full textUsing mechanochemistry by grindingTPBand ZnBr2, anamorphouspoly-[n]-catenane of interlockedM12L8nanocages is obtained in good yields (∼80%) and within 15 minutes. The mechanical bond among the icosahedralM12L8cages in the amorphous phase has been demonstrated by single crystal XRD, powder XRD and FT-IR spectroscopy following anamorphous-to-crystallinetransformation by guest uptake of the amorphous phase. High-resolution solid-state13C NMR spectroscopy gives insights into the local structure of theamorphouscatenane focusing onTPBaromatic-aromatic interactions
ON/OFF Control of the Flipping Motion of Diuranyl Bis(Salophen) Macrocycle by Extremely Strong Binding with Fluoride Ion
No full textDiuranyl bis(salophen) complex 1 features a relatively slow conformational motion, induced by an intramolecular O═U═O···UO2 binding motif, which interconverts the two nonsymmetric halves of the ligand. This flipping motion, which constitutes one of the fundamental molecular motions, can be completely halted by addition of fluoride anion, which is bound to 1, reaching one of the highest affinities reported to date. This system represents a model to study flipping dynamics in light of the possibility of developing novel types of molecular machines based on it
Crystal Engineering of a Two-Dimensional Lead-Free Perovskite with Functional Organic Cations by Second-Sphere Coordination
No full textHybrid lead halide perovskite semiconductors are attracting increasing attention for applications in optoelectronics. However, the high lead content calls for the development of greener and smarter alternatives through crystal engineering. This is extremely challenging since the use of functional cations often results in the disruption of the metal halide framework. Here we show the rational design of a new lead-free, copper-based hybrid perovskite following a second-sphere coordination approach. Our synthetic strategy allows the incorporation of an organic cationic fluorophore within the two-dimensional Cu−Cl framework of a layered copper perovskite. The functionalization results in a moisture-stable and near-UV/blue-emitting copper perovskite. Along with the possibility of extending the emission in the visible range by further synthetic design, our approach paves the way for the development of a new class of Pb-free perovskites with potential applications in solid-state lighting
Reactivity among first and second coordination spheres using a multiprotonated ligand and Cu(ii) in the solid-state
No full textSecond sphere interactions by means of charge-assisted hydrogen bonds have been used to study the solid-state reactivity of two new Cu(ii) super-complexes. A tetradentate flexible ligand (1R,2R)-N,N '-bis(pyridine-3-ylmethyl)cyclohexane-1,2-diamine (L) with two pyridine and two amine groups self-assembled with [CuCl4](2-) and Cl- anions gave the second sphere complex [H4L](4+)center dot[CuCl4](2-)center dot 2Cl(-) (2). In air, 2 transforms into a new hydrated outer sphere structure [H4L](4+)center dot[CuCl3(H2O)](-)center dot 3Cl(-) (3) differing in the chemistry and geometry of the Cu(ii) metal center. Upon heating, 3 reversibly transforms into 2 in the solid-state. The 3 -> 2 reaction occurs via ligand exchange with the transfer of a Cl- from the outer sphere to the Cu(ii) first sphere replacing the coordinated H2O. Adduct 3 reacted using mechanochemistry with KOH to form a neutral first sphere coordination complex [LCuCl2] (4). The transformation from first-to-second coordination spheres 3 -> 4 with the formation of a five-membered chelated ring and its reversible process (second-to-first coordination sphere) 4 -> 3 can be carried out upon chemisorption of HCl. The gas-solid chemisorption process occurs in a dynamic non-porous material able to adapt to the incoming HCl and H2O molecules. The amines in the internal part of L appear to be more reactive towards the formation/destruction of coordination of bonds than the external pyridine groups. Insights into the relative stabilities of key crystalline phases have been obtained by means of quantum-mechanical calculations. Considering that the reaction [CuCl4](2-) + H2O -> [CuCl3H2O](-) + Cl- is exothermic, a simple rationalisation of the experimental results has been provided
Exploring the sensing behavior in the detection of nitroaromatics using coordination complexes based on 4,4′-(1,3-phenylenedioxy)-dianiline ligand
Full text linkThe aromatic ligand 4,4'-(1,3-phenylenedioxy)-dianiline (L), has been used to explore its coordination chemistry behaviour and nitroaromatic sensing ability by crystallizing it with a variety of transition metals. The supra molecular structures [CuCl2(L)] (1), [Mn(H2O)(2)Cl-2(L)2] (2), [Ni(H2O)(2) (L)(2)] Cl-2 (3) and [Co(H2O)(2) (L)(2)] Cl-2 (4) have been characterized by single crystal X-ray diffraction (SC-XRD) and X-ray powder diffraction (XRPD) analysis. While 1 and 2 do not form polymeric structures but discrete (0D) arrays, 3 and 4 resulted in extended isostructural 2D coordination polymers. The solid-state fluorescence properties of the reported crystals have been investigated. Interestingly, coordination polymers 3 and 4 showed a better solid-state fluorescence emission compared to that of complexes 1 and 2. Coordination polymer 3 has been successfully used as a sensor for the detection of trace amounts of nitrobenzene, 2-nitrotoluene and 3-nitrotoluene with a high quenching efficiency of 96% for 3-nitrotoluene. The quenching efficiency of 3 is better than that of the free ligand L. The polymeric nature of 3 is maintained after the sensing experiment and thus can be used in a recyclable manner. Due to the fact that 3 is a nonporous and its structure does not change in the presence of the quenchers, the quenching effect occurs in the surface of the solids when is in a suspension
Chain-Walking Polymerization of α-Olefins by α-Diimine Ni(II) Complexes: Effect of Reducing the Steric Hindrance of Ortho- and Para-Aryl Substituents on the Catalytic Behavior, Monomer Enchainment, and Polymer Properties
Full text linkWith Brookhart type α-diimine Ni(II) based catalysts, it is highly challenging to tune polymers branching level and branch-type distribution, which in turn strongly affects thermal and mechanical properties, through the aryl ortho-positions modification, while maintaining high turnover frequencies (TOFs). Herein, we are interested in performing a systematic investigation on the polymerization of 1-octene, 1-decene, and 1-octadecene catalyzed by a series of α-diimine nickel(II) complexes with methyl ligand backbone and different substituents in aryl positions (Ni1-Ni6). In addition to bulky isopropyl and tert-butyl substituents described in the original Brookhart's work, complexes with different aryl ortho- and para-substituted α-diimine ligands, including the less sterically demanding methyl and ethyl substituents, are investigated. The 13C NMR spectra of the polymers have been assigned in detail, and some unique features have been identified and related to the chain-walking coordination/insertion mechanism. Changes in the ligand structure and monomer size have important effects on the numerous combinations of insertion and chain-walking paths from which different branches are installed. We have also carried out a comprehensive investigation of the mechanical behavior of the polymers by means of uniaxial stretching until failure, step-cycle, and creep tensile tests. Overall, the resulting polymers exhibited a broad spectrum of tensile properties, depending on their microstructure and crystallinity which in turn are strongly affected by monomer length and type of α-diimine ligand. 1-Octene and 1-decene polymers behave as elastomers with excellent mechanical properties, i.e., high elongation at break (up to 2000%) and good strain recovery, while 1-octadecene polymers behave as plastomers
Concerted Electron Transfer in Iminopyridine Chromium Complexes: Ligand Effects on the Polymerization of Various (Di)olefins
No full textA study of reactions among CrCl2, CrCl3(THF)3, and iminopyridine ligands differing in the nature of the substituents at the iminic carbon and at the ortho positions of the aryl ring (2,6-R12C6H3N=CR2(C5H3N) (R1 = R2 = H (L1); R1 = iPr, R2 = H (L2); R1 = H, R2 = CH3 (L3)) but featuring close electron-accepting properties has provided a new example of the redox chemistry of chromium complexes. The reactions of unsubstituted aniline L1 and of L3 with CrCl2 give rise to [(L1•)CrIIICl2(THF)]- (Cr1) and [(L3•)CrIIICl2(THF)]- (Cr3) complexes, respectively, containing chromium in the physical trivalent oxidation state and the ligand in the monoanionic radical state (L•)- as a result of a one-electron transfer from the metal to the ligand. In contrast, the reactions of CrCl2 with the ortho-substituted L2 and of CrCl3(THF)3 with the unsubstituted L1 give rise to [(L2)CrIICl2(THF)]0 (Cr2) and [(L1)CrIIICl3(THF)]0 (Cr4) having the chromium in the divalent and trivalent oxidation states, respectively, and the unperturbed ligand in the neutral state. All four complexes were used, in combination with methylaluminoxane (MAO), as catalyst precursors for the polymerization of ethylene, cyclic olefins (i.e., norbornene and dicyclopentadiene), and 1,3-butadiene. A chromium to ligand synergy, coupled with a good stability of the active intermediate in the presence of the Al activator, proven particularly effective in the polymerization of ethylene, especially for Cr1, giving high molecular weight linear poly(ethylene)s. The formalism in the metal oxidation state does not affect the reactivity toward the cyclic olefins and 1,3-butadiene, while ligand steric effects emerge clearly. The use of bulky ortho substituents shuts down the activity in the polymerization of cyclic olefins, particularly for the bulkier dicyclopentadiene, and reverses the catalyst chemoselectivity in the polymerization of 1,3-butadiene
Solid-state stability of Z′ < 1 and Z′ = 2 polymorphs of N,N,N′,N′-tetrabenzylethylenediamine: a combined experimental and theoretical study
Full text linkThe synthesis and structural analysis by means of single crystal X-ray diffraction (SC-XRD) and DFT calculations, of two additional new polymorphs of the flexible organic molecule N,N,N′,N′-tetrabenzylethylenediamine (L) which is used as first sphere ligand in outer sphere adducts are reported. Slow crystallization of L in the solution-state yields two polymorphs (Lα-phase and Lβ-phase) with Z′ = 0.5, while fast crystallization by rapid cooling from solution and directly from melt, allows a third, less stable polymorph with Z′ = 2 (Lγ-phase). The latter structure can be seen as a low-density metastable phase obtained by trapping L molecules after they reached high mobility by thermal treatment (i.e., high energy state). The three L polymorphs have been also studied using quantum mechanical (QM) calculations specific for the solid state by comparing the sublimation energy for each polymorph, and by comparing the experimental X-ray structures against the optimized structures from DFT, showing that Lβ-phase is the most stable and Lγ-phase is the least stable phase. The high Z′ structure can be considered as a “crystal on the way” of a more stable form. These results provide insights about crystallization mechanisms and polymorphism in organic crystals. The potential use of conformational polymorphs of flexible ligands to prepare second sphere adducts with marked polymorphism is commented
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