Effect Of Positional Isomerism Research Articles

Modulation of Weak Interactions in Structural Isomers: Positional Isomeric Effects on Crystal Packing and Physical Properties and Solid-State Thin-Film Fabrication.

Selective formation of positional isomers and accordingly tuning the physicochemical properties of small conjugated organic molecules through structural isomers is an effective crystal engineering for a fascinating successful delivery of thermally stable and photophysically exciting compounds. By small structural skeleton changes, the single crystal of the naphthalenemaleonitrile isomers is found to exhibit a drastic change in crystal packing array, which in turn is found to tune the thermal and physicochemical properties. The α-isomer (A) forms the “herringbone packing” (HP) due to peri-interaction-sensitive C–H···(Ar)π (Ar = naphthalene ring) interactions, and the β-isomer (B) forms the “bricklayer packing” (BP) due to π(C≡N)···π(Ar) stacking interactions. These two positional isomers have revealed insight of molecular packing-dependent structure–property relationship. In this report, we show that a simple modification of relatively less common weak interactions, such as C–H···π(Ar) ↔ π(C≡N)···π(Ar), through the preparation of isomers, can lead to a drastic change in crystal packing (HP ↔ BP). Also, this report demonstrates that by a small structural diversity, one can obtain significant changes in the physicochemical properties like melting behavior, enthalpy, entropy, and electrical properties in the solid state. Therefore, it transpires from this study that structural isomer provides a useful complement to intermolecular nonbonding interactions as a tool to design new promising materials.

The positional isomeric effects induced various phosphorescence: Switchable properties through acid-base vapor stimulation

Three novel positional isomers, namely (E)-3-(2-chloroimidazo[1,2-a] pyridin-3-yl)- 1-(pyridin-2-yl)prop-2-en-1-one (1), (E)-3-(2-chloroimidazo[1,2-a]pyridin-3-yl)-1- (pyridin-3-yl)prop-2-en-1-one (2) and (E)-3-(2-chloroimidazo[1,2-a]pyridin-3-yl)- 1-(pyridin-4-yl)prop-2-en-1-one (3), were obtained through a mild approach. Powder X-ray diffraction patterns demonstrate their various stacking structures, attributed to positional isomeric effects. Furthermore, these positional isomers exhibit different phosphorescent colors and quantum yields. Interestingly, these positional isomers also reveal reversible phosphorescent color switching in the response to acid-base vapor stimuli. The present work provides a promising approach for synthesizing organic materials and a new access to develop dynamic functional materials which can be reversibly switched between different phosphorescence based on external acid-base vapor stimuli.

Distributed polarizability of fullerene [2+1]-adducts C60Xn (n = 1 and 2) with symmetric addends X = CH2 and O: A fresh view on the effect of positional isomerism

We have performed a site-specific analysis of the mean polarizability of fullerene [2+1]-adducts C60Xn (n = 1 and 2) with symmetric addends X = CH2 and O using the distributed polarizability model. We have found that the contributions from the fullerene core and addends to the molecular polarizability are not the same for different regioisomeric C60X2: the core contribution linearly decreases and the addend contribution linearly increases with the distance between the addends (or the functionalized bonds of the C60 cage). Additionally, the contributions are sensible to the degree of the fullerene core functionalization: the contribution of the C60 core decreases with the number of the attached addends due to reducing its π-electronic system.

The Positional Isomeric Effect on the Structural Diversity of Cd(II) Coordination Polymers, Using Flexible Positional Isomeric Ligands Containing Pyridyl, Triazole, and Carboxylate Fragments.

To systematically investigate the influence of the positional isomeric effect on the structures of polymer complexes, we prepared two new polymers containing the two positional isomers ethyl 5-methyl-1-(pyridin-3-yl)-1H-1,2,3-triazole-3-carboxylate (L1) and ethyl-5-methyl-1-(pyridin-3-yl)-1H-1,2,3-triazole-4-carboxylate (L2), as well as Cd(II) ions. The structures of the metal–organic frameworks were determined by a single crystal XRD analysis. The compound [Cd(L1)2·4H2O] (1), is a hydrogen bond-induced coordination polymer, whereas the compound [Cd(L2)4·5H2O]n (2) is a three-dimensional (3-D) coordination polymer. Their structures and properties are tuned by the variable N-donor positions of the ligand isomers. This work indicates that the isomeric effect of the ligand isomers plays an important role in the construction of the Cd(II) complexes. In addition, the thermal and luminescent properties are reported in detail.

The positional isomeric effect and structural difference in coordination assemblies system of CoII with 3/4-pmpt ligands

Six Co(II) complexes were synthesized from CoCl2 with positional isomeric ligands: 3-(pyridine-3-yl)-5-(2-methoxyphenol-6-yl)-1H-1,2,4-triazole (3-H2pmpt) and 4-(pyridine-3-yl)-5-(2-methoxyphenol-6-yl)-1H-1,2,4-triazole (4-H2pmpt), namely, {[Co3(3-pmpt)2Cl2(DMF)2]·(DMF)2}n (1), {[Co3(4-pmpt)2Cl2(DMF)2]·(DMF)}n (2), [Co3(3-pmpt)2Cl2(DMF)2]n (3), [Co3(4-pmpt)2Cl2(DMF)2]n (4), {[Co5(3-pmpt)4(HCO2)2(DMF)2]·(H2O)4}n (5), {[Co5(4-pmpt)4(HCO2)2(H2O)2]·(H2O)6}n (6). Structural analysis reveals that pmpt isomers display different coordination modes to manage Co(II) ions to form [Co3] subunits in 1–4, and [Co5] subunits in 5–6, respectively. Which are further extended via different pyridine ring N-orientation to build the 1-D chains (for 1, 5 and 6) and 2-D layers (for 2, 3 and 4). Structural analysis indicate that 3/4-pmpt is an excellent multi-connect linker with pyridine ring at different angles, has an important effect on the structural topologies of such Co(II) complexes. Magnetic susceptibilities reveal weak ferromagnetic and antiferromagnetic exchange interactions between the adjacent metal centers in 5 and 6.

Antioxidant and Cytoprotective Effects of Kukoamines A and B: Comparison and Positional Isomeric Effect.

In this study, two natural phenolic polyamines, kukoamine A and B, were comparatively investigated for their antioxidant and cytoprotective effects in Fenton-damaged bone marrow-derived mesenchymal stem cells (bmMSCs). When compared with kukoamine B, kukoamine A consistently demonstrated higher IC50 values in PTIO•-scavenging (pH 7.4), Cu2+-reducing, DPPH•-scavenging, •O2−-scavenging, and •OH-scavenging assays. However, in the PTIO•-scavenging assay, the IC50 values of each kukoamine varied with pH value. In the Fe2+-chelating assay, kukoamine B presented greater UV-Vis absorption and darker color than kukoamine A. In the HPLC–ESI–MS/MS analysis, kukoamine A with DPPH• produced radical-adduct-formation (RAF) peaks (m/z 922 and 713). The 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl (MTT) assay suggested that both kukoamines concentration-dependently increased the viabilities of Fenton-damaged bmMSCs at 56.5–188.4 μM. However, kukoamine A showed lower viability percentages than kukoamine B. In conclusion, the two isomers kukoamine A and B can protect bmMSCs from Fenton-induced damage, possibly through direct or indirect antioxidant pathways, including electron-transfer, proton-transfer, hydrogen atom transfer, RAF, and Fe2+-chelating. Since kukoamine B possesses higher potentials than kukoamine A in these pathways, kukoamine B is thus superior to kukoamine A in terms of cytoprotection. These differences can ultimately be attributed to positional isomeric effects.

Porphyrin dimers with a bridging chiral amide-bonded benzo-moiety: Influence of positional isomerism on the molecular chirality

The facile synthesis and characterization of four porphyrin dimers which introduced stereomeric centers with chiral amide-bonded para- and meta-disubstituted benzo-moiety is reported. Trends in the electronic structures and optical and redox properties are analyzed through a comparison with theoretical calculations to explore the effect of positional isomerism of the bridging benzene rings.

Joining of trinuclear (CuL)2M (M = MnII and CdII) nodes by 1,3- and 1,4-benzenedicarboxylate linkers: positional isomeric effect on co-crystallization

Among the four one-dimensional coordination polymers obtained by joining (CuL)2M (M = MnII and CdII) nodes with 1,3- and 1,4-benzenedicarboxylate linkers, the chains derived from 1,3-benzenedicarboxylate are co-crystallized with dimeric CuII units.

The effect of positional isomerism of propanediol on the formation of cobalt oxides

The effect of positional isomerism of propanediol on the formation of cobalt oxides

Positional isomeric effects of coupling agents on the temperature-induced gelation of triblock copolymer aqueous solutions

The linking angles of positional isomers in the middle of thermogelling mPEG-PLGA-mPEG polymers were found to affect their microscopic conformations and macroscopic properties.

Positional isomeric effect on CuII and CdII complexes based on perfluorinated dicarboxylate ligands and bipyridyl co-tectons

Five novel CuII and CdII complexes with the formula {[Cu2(HBDO-F4)2(BDO-F4)-(2,2′-bipy)2](CH3OH)} (1), [Cd2(BDO-F4)2(2,2′-bipy)2(H2O)2] (2), {[Cu(BDO-F4)(4,4′-bipy)(H2O)2](CH3OH)2}n (3), {[Cd(BDO-F4)(4,4′-bipy)(H2O)2](CH3OH)2}n (4) and {[Cd(BDC-F4)-(2,2′-bipy)](H2O)2}n (5) have been prepared by reaction of metal perchlorates with H2BDO-F4 (tetrafluorophthalic acid) or H2BDC-F4 (tetrafluoroterephthalic acid) in the presence of different bipyridyl co-ligands (2,2′-bipy=2,2′-bipyridine and 4,4′-bipy=4,4′-bipyridine). All these complexes were characterized by elemental analysis, IR spectra and X-ray single crystal diffraction. Complexes 1 and 2 show binuclear structures, and further connected by hydrogen bonding to result in the final supramolecular 3-D framework and 1-D box-like chain, respectively. Polymers 3 and 4 are isostructural, where the metal centers are connected by BDO-F42− and 4,4′-bipy ligands to generate a 2-D grid-like (4,4) network. These layers are interlinked through hydrogen bonds to form a 3-D architecture. Complex 5 exhibits a distinct (4,4) coordination layer constructed by paddle-wheel [Cd2(COO)4] dinuclear subunits. The results reveal that the diverse structure of 1–5 can be adapted by the different positions of carboxylate groups of perfluorinated ligands, as well as the metal centers and auxiliary ligands. Moreover, their thermal stability and fluorescent properties have also been investigated.

Two Zinc(II) Coordination Polymers Based on 1,3,5-Tris(imidazole-1-yl)benzene and Phenylene-Diacetate Isomers

To investigate the influence of the positional isomeric effect on the structures of their complexes, two zinc(II) coordination polymers, [Zn3(1,3-phda)2(tib)2]·5H2O (1) and [Zn(1,2-phda)(tib)]·4H2O (2) (phda2– = phenylenediacetate and tib = 1,3,5-tris(imidazole-1-yl)benzene), have been synthesized and characterized by IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Structural analyses reveal that complex 1 exhibits a 2-fold interpenetrating two-dimensional (2D) (3,4)-connected framework with an unusual (3.6.7)2(3.62.72.9)2(32.63.7) topology, whereas complex 2 possesses a one-dimensional (1D) tubular structure constructed from 20-membered {Zn2(tib)2} rings and {Zn(1,2-phda)} chains. This work indicates that isomeric effect of the couple of isomers plays an important role in the construction of the Zn(II) complexes. In addition, their thermal stability and luminescence are also reported in detail.

Entrapment of Cyclic Fluoride–Water and Sulfate–Water–Sulfate Cluster Within the Self-Assembled Structure of Linear meta-Phenylenediamine Based Bis-Urea Receptors: Positional Isomeric Effect

meta-Phenylenediamine based two linear bis-urea anion receptors, L1 (meta-nitro) and L2 (para-nitro), have been synthesized which showed strong binding affinities toward halides as well as planar and tetrahedral oxyanions. In the presence of excess fluoride anion, L1 self-assembles to entrap a cyclic fluoride–water tetrameric cluster within its tetrameric pillar-like assembly of each urea arm (complex 1a). In the presence of sulfate anion, L1 self-assembles in an identical fashion to entrap the bigger tetrahedral anion (complex 1b), whereas two urea moieties of two different receptor molecules of L1 have been structurally authenticated to be sufficient to stabilize the simple Y-shaped acetate anion in complex 1c. On the other hand, receptor L2, with a bis(para-nitro urea) functional group, especially in the presence of sulfate anion, self-assembles like long straight pillars entrapping sulfate–water–sulfate cluster {SO42–-(H2O)3-SO42–} (complex 2a). Additionally, L2 forms a host–guest assembly with the ca...

Assembly of 1D, 2D and 3D lanthanum(iii) coordination polymers with perchlorinated benzenedicarboxylates: positional isomeric effect, structural transformation and ring-opening polymerisation of glycolide.

Utilizing a series of positional isomers of tetrachlorinated benzenedicarboxylic acid ligands, seven La(iii)-based coordination polymers were solvothermally synthesized and structurally characterized. Their structural dimensionalities varying from 1D double chains, to the 2D 3,4,5-connected network, to 3D 6-connected pcu topological nets are only governed by the positions of carboxyl groups on the tetrachlorinated benzene ring. A comprehensive analysis and comparison reveals that the size of the carbonyl solvent molecules (DMF, DEF, DMA, and NMP) can affect the coordination geometries around the La(iii) ions, the coordination modes of carboxylate groups, the packing arrangements, and the void volumes of the overall crystal lattices. One as-synthesized framework further shows an unprecedented structural transformation from a 3D 6-connected network to a 3D 4,5-connected net through the dissolution and reformation pathway in water, suggesting that these easily hydrolyzed lanthanide complexes may serve as precursors to produce new high-dimensional frameworks. The bulk solvent-free melt polymerisation of glycolide utilizing these La(iii) complexes as initiators has been reported herein for the first time. All complexes were found to promote the polymerization of glycolide over a temperature range of 200 to 220 °C, producing poly(glycolic acid) (PGA) with a molecular weight up to 93,280. Under the same experimental conditions, the different catalytic activities for these complexes may result from their structural discrepancy.

Molecular tectonics of mixed-ligand metal-organic frameworks: Positional isomeric effect, and structural diversification

To explore the influence of three structurally different polycarboxylate ligands H2L1 to H4L3 in the system Cd(II)/PPAN, three coordination polymers, formulated as {Cd2(PPAA)2(L1)2}n (1), {[Cd2(PPAA)2(HL2) (H2O)].2H2O}n (2), {Cd2(PPAN)2(L3) (H2O)2}n (3) have been obtained under similar conditions (PPAA− = 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetate, PPAN = 2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)acetonitrile, H2L1 = 1,3-benzenedicarboxylic acid, H3L2 = 1,3,5-benzenetricarboxylic acid, H4L3 = 1,2,4,5-benzenetetracarboxylic acid). In 1–2, PPAN are hydrolyzed into a novel PPAA− ligand. The structure determination reveals that complex 1 contains 1D double chains of {[Cd(PPAA)]+}n cation structural units, which are further extended by these μ3-(L1)2− ligands forming a novel 2D three-layered framework with (4.82)2(43.62.8)2(4383)2(48.66.8) topology. Complex 2 is one-dimensional (1D) ribbon-like chains having two kinds of dimerics [Cd(PPAA)]2 and [Cd(COO)]2 subunits and dimeric Cd(II) units bridged by μ3-(HL2)2− ligands. Complex 3 shows an undulating 2D (4, 4)-network by μ4-(L3)4−. In addition, photoluminescent properties of three coordination polymers were also investigated in this paper.

Structural and Magnetic Analysis of Retrosynthetically Designed Architectures Built from a Triply Bridged Heterometallic (CuL)2Co Node and Benzenedicarboxylates

AbstractThe flexible trinuclear metallatecton {(CuL)2Co}2+ [H2L = N,N′‐bis(salicylidene)‐1,3‐propanediamine] has been used as a building block, and its coordinative interaction with ortho‐, meta‐, and para‐benzenedicarboxylates (BDCs) has been investigated to evaluate the positional isomeric effect of these carboxylate ligands on the resulting compounds. Structural characterization reveals that o‐H2BDC produces a discrete trinuclear complex, namely [(CuL)2Co(o‐HBDC)2]·H2O (1). As expected from the retrosynthetic design, one‐dimensional (1D) coordination polymers, i.e., [{(CuL)2Co(m‐BDC)}·CH3OH]∞ (2) and [{(CuL)2Co(p‐BDC)}·2CH3OH]∞ (3), are obtained with m‐BDC and p‐BDC linkers, respectively. In all three complexes, the triply bridged bimetallic trinuclear coordination clusters are linear and solely a syn‐syn bridging mode is observed for the carboxylates. In 2, the nodes are connected sidewise and are inclined toward each other to be accommodated by the 120°‐angular m‐BDC units, whereas in 3, the linear p‐BDC linkers connect the parallel nodes diagonally. These differences in connectivity give rise to one‐dimensional “great wall”‐like chains for 2 and to quasi‐linear coordination chains for 3. These distinct one‐dimensional propagations induced by the different BDC isomers influence the three‐dimensional columnar packing of 2 and 3. Magnetic susceptibility measurements and fitting of the results confirm that these three compounds are made by analogous magnetic building blocks, with very similar antiferromagnetic intramolecular magnetic exchange (with J in the –16.96 to –11.80 cm–1 range, using the –2JS1S2 convention). The structural homogeneity of the magnetic fragment within this family of compounds has allowed magnetostructural correlations to be explored, which has not previously been attempted.

Positional isomeric effect on the structural variation of Cd(ii) coordination polymers based on flexible linear/V-shaped bipyridyl benzene ligands

Solvothermal reactions of Cd(OAc)2·2H2O with 2,2′-azodibenzoic acid and five positional isomeric N-donor bipyridyl benzene ligands in MeOH/H2O at 170 °C gave rise to five coordination polymers. Complexes 1–5 were characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, and single-crystal X-ray diffraction.

Positional isomerism in triarylmethyl carbocation radical salts: positional isomeric effects, crystal structures and properties

Through a simple and mild approach, we unprecedentedly synthesized three novel triarylmethyl carbocation radical salts, namely bisimidazo[1,2-a]pyridin-2-one-yl(2-pyridyl)methyl carbocation radical salt (1), bisimidazo[1,2-a]pyridin-2-one-yl(3-pyridyl)methyl carbocation radical salt (2), and bisimidazo[1,2-a]pyridin-2-one-yl(4-pyridyl)methyl carbocation radical salt (3). Single-crystal X-ray diffraction analyses reveal that 1, 2 and 3 are positional isomers with different one-dimensional (1D) chain structures. Through supramolecular interactions, the 1D chains of 1 are further assembled into a 1D double-stranded chain, then into a two-dimensional (2D) layer structure, and the 1D chains of 2 and 3 are also assembled into 2D layer structures. This work indicates that the positional isomeric effects of pyridyl groups in the three carbocation radical salts are significant in the construction of isomers, because 1, 2 and 3 were synthesized and crystallized under the same conditions. Furthermore, these positional isomers exhibit different magnetic susceptibility values at 300 K. 1 with 1D double-stranded chains consists of one repetitive unit having four carbocation radical moieties, giving a magnetic susceptibility value of 1.636 emu K Oe−1 mol−1 at 300 K. 2 with 1D chains consists of one repetitive unit with two carbocation radical moieties, giving a magnetic susceptibility value of 0.747 emu K Oe−1 mol−1 at 300 K. 3 exhibits a magnetic susceptibility value of 0.326 emu K Oe−1 mol−1 for one isolated spin of the carbocation radical. Compared with 2 and 3, 1 shows broad and stronger NIR absorption bands from 800 nm to 1951 nm, probably ascribed to its 1D double-stranded chain structure, antiparallel arrangements of 2-pyridinium rings in the 1D chains, and/or tetra-connecting hydrogen-bonding bridge.

Physical and Electrolytic Properties of Monofluorinated Ethyl Acetates and Their Application to Lithium Secondary Batteries

Ethyl acetate (EA) shows low viscosity for its relative permittivity. Monofluorinated organic solvents exert the polar effect on the various properties. We have investigated the effect of position isomerism on the physical and electrochemical properties of two monofluorinated carboxylates: 2-fluoroethyl acetate (2FEA) and ethyl fluoroacetate (EFA). Relative permittivity of 2FEA was lower than that of EFA, whereas viscosity of 2FEA was higher. Electrolytic conductivity of a LiPF6 solution in 2FEA was lower than that in EFA, but higher than that in EA at high temperatures. The use of 2FEA as a co-solvent improved cycling efficiency and suppressed fading of discharge capacity of a Li|LiCoO2 coin cell at high cycle numbers.

Five chiral Cd(II) complexes with dual chiral components: Effect of positional isomerism, luminescence and SHG response

Five chiral Cd(II) complexes with dual chiral components have been synthesized by using a series of (1R,2R)–N1,N2-bis(pyridinylmethyl)cyclohexane-1,2-diamine ligands with different N-positions of pyridyl rings and Cd(NO3)2. The circular dichroism (CD) spectra and second-harmonic generation (SHG) efficiency measurements confirmed that they are of structural chirality in the bulk samples. The luminescent properties indicated that they may have potential applications as optical materials. The formation of discrete mononuclear and binuclear complexes, and one-dimensional chains may be attributed to positional isomerism of the ligands.