Reversible Waves Research Articles

Electron-Deficient Indenofluorene-Based Systems: Multicolor and Visible-To-Near-Infrared (NIR) Electrochromism and OFF-OFF-ON Electrofluorochromism.

Multifunctional electrochromic systems with divergent functions are highly sought after but rare and challenging to develop. Here, we report the synthesis and multi-functional electrochromic behaviour (multi-colour modulation, visible-to-near IR absorption switching, and electrofluorochromism) of electron-deficient indenofluorene-based systems. The compounds (IF1-IF5) have been obtained via Knoevenagel condensation of indenofluorenone (IFK) with various nucleophiles (malononitrile, benzylcyanide, dimethyl malonate, methyl cyanoacetate, benzothiazole-2-acetonitrile). IF1-IF5 possess strong colours and absorb in the visible region (λmax=295-388 nm). These compounds are electroactive and exhibit two reversible reduction waves (-0.35--0.88 V and -0.65--1.30 V vs Ag/AgCl), generating radical anion and dianion systems. For the electrochromic studies, upon applying the one-electron reduction potential (-0.35 V vs Ag/AgCl), the absorption maximum of IF1 redshift from 382 nm to 1240 nm (IF1 -⋅), which subsequently blueshifts to 466 & 745 nm (IF1 2-⋅) upon increasing to two-electron reduction potential (-0.65 V vs Ag/AgCl). The color of the solution was switched from green to dark blue and further to light orange. The electrochromic behaviour is highly reversible and cycling. In addition, unlike the non-fluorescent (IF1 and IF1 -⋅), the two-electron reduced system (IF1 2-⋅) is red-emissive (λem=630 nm) due to the combination of radicals leading to the formation of antiaromatic quinoidal π-conjugated system (IF1 2-).

Effect of the alkyl chain length of α,ω-dichloroalkane on the Gibbs energy of transfer for functional groups.

Ion-transfer reactions of alkyl and perfluoroalkyl carboxylate ions (CH3(CH2)n-2COO- with n = 8-12 and CF3(CF2)n-2COO- with n = 3-9) were investigated at the polarized Cl-(CH2)m-Cl with m = 2, 4, 6, and 8 (O) | water (W) interface to evaluate the effects of n and m on the solvation energy of the ions, as well as on their methylene and terminal groups. These ions exhibited reversible or quasi-reversible voltammetric waves due to their transfer across the O | W interfaces, enabling the determination of formal potentials and formal Gibbs transfer energies from O to W, . The values for CH3(CH2)n-2COO- and CF3(CF2)n-2COO- increased linearly with n, allowing the estimation of for methylene and difluoromethylene groups, (CH2) and (CF2), and for their terminal groups, (COO- + CH3) and (COO- + CF3). Whereas the (CH2) and (CF2) hardly changed with the variation in m, the (COO- + CH3) and (COO- + CF3) decreased noticeably. These results suggest that the solvation energy for ions in Cl-(CH2)m-Cl increases with m, regardless of hydrophilic or lipophilic nature of the ions. Based on these findings, the advantage of using Cl-(CH2)m-Cl with a large m as a non-aqueous solvent for ion-transfer voltammetry was discussed.

Cyclic (Alkyl)(Amino)Carbene-Iminoboryl Compounds with Three Formal Oxidation States.

BN/CC isosterism is an effective strategy to build hybrid functional molecules with unique properties. In contrast to the alkynyl iminium salts derived from cyclic (alkyl)(amino)carbenes (CAACs) that feature only one reversible reduction wave, the isoelectronic cationic CAAC-iminoboryl adducts could be singly and doubly reduced smoothly. Both the resultant neutral radical and anionic azaborataallenes bear NBC-mixed allenic structures. The former radical has a high spin-density of 0.55e at CCAAC carbon, yet exhibits formal boron-centered radical reactivity. The latter azaborataallenes feature the nucleophilic CCAAC center and polar N(δ-)═B(δ+)═C(δ-) unit, and readily undergo nucleophilic substitution, isocyanide insertion, dipolar addition and cycloaddition reactions etc. The N-substituents have been shown to have a significant influence on the solid-state structure, thermal stability, and reactivity of azaborataallenes. This work showcases the allenic BN-unsaturated species as versatile building blocks in organic synthesis.

A Nonbenzenoid 3D Nanographene Containing 5/6/7/8-Membered Rings

Nanographenes (NGs) have attracted continuous attention in recent years owing to their opened bandgaps and optoelectronic applications. Especially, nonbenzenoid NGs containing non-six-membered rings have been developed rapidly due to their unique structures and properties. In this work, we employ nonbenzenoid acepleiadylene (APD) and the cyclooctatetraene (COT) moiety to construct the first three-dimensional (3D) NG containing 5/6/7/8-membered rings in one molecule (COT-APD). The calculated results prove that COT-APD has a saddle-like configuration similar to that of other COT-type molecules. Each APD segment in COT-APD keeps the inherent aromaticity of the APD moiety. Compared with other COT-type molecules, COT-APD shows a narrower bandgap, which indicates the superiority of APD in bandgap regulation. Furthermore, four reversible reductive waves are observed in electrochemical characterizations, demonstrating the excellent electron-accepting capability of COT-APD.

First electrochemical investigation and determination of non-steroidal anti-inflammatory drug etofenamate using disposable pencil graphite electrode with voltammetric techniques

In this study, the electrochemical properties of etofenamate, an active ingredient belonging to the non-steroidal anti-inflammatory drug group, were investigated using cyclic voltammetry (CV) and square wave voltammetry (SW) techniques on a disposable pencil graphite electrode (PGE). With the CV technique, reversible voltammetric waves of around +0.470 V and irreversible voltammetric waves of around +1.02 V were produced on the PGE. An environmentally friendly, selective and highly sensitive SW voltammetric method was developed using disposable PGE. This voltammetric method gave very good analytical working range on PGE in PBS (pH = 3.0) medium at concentrations ranging from 0.017 μM to 0.306 μM. The LOD value of this analytical method in PBS (pH = 3.0) medium was calculated as 0.0011 μM (0.406 μg L−1). The developed voltammetric method was successfully applied to urine and drug samples. The results of the voltammetric method were compared with the results of the spectrophotometric method. The results were found to be compatible with each other.

Catalytic Oxidation of Methanol to Formaldehyde Catalyzed by Iron Complex with N3S3-type Tripodal Ligand.

A Fe3+ complex with N3S3-type tripod ligand, 1, reacts with O2 in CH3OH to generate formaldehyde, which has been studied structurally, spectroscopically, and electrochemically. Complex 1 crystallizes as an octahedral structure with crystallographic C3 symmetry around the metal, with Fe-N=2.2917(17) Å and Fe-S=2.3574(6) Å. UV-vis spectrum of 1 in CH3OH under Ar shows an intense band at 572 nm (ϵ 4,100 M-1cm-1), which shifts to 590 nm (ϵ 2,860 M-1cm-1) by the addition of O2, and a new peak appeared at 781 nm (ϵ 790 M-1cm-1). Such a spectral change is not observed in CH2Cl2. Cyclic voltammogram (CV) of 1 in CH2Cl2 under Ar gives reversible redox waves assigned to Fe2+/Fe3+ and Fe3+/Fe4+ couples at -1.60 V (ΔE=69 mV) and -0.53 V (ΔE=71 mV) vs Fc/Fc+, respectively. In contrast, in CH3OH, the reversible redox waves, albeit accompanied by a positive shift of the Fe2+/Fe3+ couple, are observed at -1.20 V (ΔE=85 mV) and -0.53 V (ΔE=64 mV) vs Fc/Fc+ under Ar. Interestingly, a catalytic current was observed for the CV of 1 in CH3OH in the presence of CH3ONa under Ar, when the sweep rate was slowed down.

Crystal structure and photophysical and electrochemical properties of the first octamolybdate porphyrin

A novel molybdenum polyoxometalate (POM) porphyrinic compound, i.e. (Mo8O26)(5,10,15,20-tetra-3-H-pyridinyl-21H,23H-porphine)·2H2O (1) was synthesized via a hydrothermal reaction of MoCl5, 5,10,15,20-tetra-3-pyridinyl-21H,23H-porphine and distilled water. This is the first octamolybdate porphyrinic compound. Its crystal structure and properties have been unlocked thoroughly by virtue of single-crystal X-ray diffraction, PXRD (powder X-ray diffraction), UV/vis, FTIR, photoluminescence, CIE (Commission Internationale de I'Éclairage), CT (color temperature) and cyclic voltammetric (CV) spectral analyses. The crystal structure of this compound is characteristic of an isolated (0D) motif and it is comprised of a (Mo8O26)4− anion, a (5,10,15,20-tetra-3-H-pyridinyl-21H,23H-porphine)4+ cation and two lattice water molecues. A three-dimensional (3D) framework is formed by the π-π stacking and hydrogen bonding interactions. The solid state photoluminescence measurements show that compound 1 emits red photoluminescence which results from the (5,10,15,20-tetra-3-H-pyridinyl-21H,23H-porphine)4+ cations. Compound 1 has CIE chromaticity coordinates of (0.7236, 0.2764). The CT is 7978 K. The slow sweep CV of 1 exhibits a reversible wave with E1/2 being of 0.78 V.

Photo- and electrochemical properties of newly synthesized thioxathone-viologen-fluorene ternary compound and its electrochromic device

External stimuli-responsive materials exhibit widespread potential applications in sensors, smart windows, displays, and opto-electronic molecular devices. In this study, we report light-/electrochemically induced chromic behaviors of newly synthesized ternary compound in the device. This compound is composed of a light-harvesting unit of thioxathone (TX), an electron donor of fluorene (FL), and an electron mediator of viologen (VIO), and thus it can act as a photochromic species with an intramolecular electron transfer under irradiation. The precursors of TX and FL substituents give off broad emissions at approximately 437 and 310 − 330 nm, respectively. Both emissions are largely quenched in the TX-VIO-FL ternary compound, which is caused by an intramolecular transduction of energy from the excited singlet FL and TX to the electroactive VIO substituent. Based on cyclic voltammogram of TX-VIO-FL modified electrodes, two reversible waves are observed at around − 0.44 and − 0.89 V (vs Hg/Hg2Cl2), attributed to the electron transport processes of TX-VIO2+-FL ↔ TX-VIO+•-FL and TX-VIO+•-FL ↔ TX-VIO0-FL, respectively. Sandwiched type of photo-/electrochromic devices are constructed, displaying a good transmittance and reversible viologen color change behavior under irradiation or an applied bias of − 2.6 V.

A triradical-containing trinuclear Pd(II) complex: spin-polarized electronic transmission, analog resistive switching and neuromorphic advancements.

Neuromorphic computation has emerged as a potential alternative to subvert the von Neumann bottleneck issue in conventional computing. In this context, the development of resistive switching-based memristor devices mimicking various synaptic functionalities has engendered paramount attention. Here, we report a triradical-containing trinuclear Pd(II) cluster with a cyclohexane-like framework constituted by the Pd-Se coordination motif displaying facile memristor property with neuromorphic functionality as a thin-film device. The metal-ligand complex (complex 1) possessed an St = 1/2 ground state by experiencing a spin-frustrated-type magnetic coupling phenomenon amongst the three ligand-based organic radicals (SR = 1/2), coordinated to the Pd(II) ions. Three reversible one-electron reduction waves countered with a one-electron and one two-electron reversible oxidation waves were noticed in the cyclic voltammogram of the complex, confirming electrons accepting and releasing capacity of the complex at low potentials, i.e., within +0.2 V to -1.1 V. Employing the radical-containing complex 1 as the active thin-film sandwiched between two orthogonal electrodes, resistive switching based memristor property with biological synaptic actions were successfully emulated. Intriguingly, the artificial neural network (ANN) simulated efficient pattern recognition demonstrated using the recorded potentiation and depression curves from the device, which is a step ahead for the hardware realization of neuromorphic computing. The performance of the ANN on MNIST data with reduced image resolution has further been evaluated. Density functional theory (DFT)-based theoretical calculation predicted that the spin-polarized electronic transmission substantiated the memristive property in the neutral complex 1.

A benzoquinone-imidazole hybrid organic anolyte for aqueous redox flow batteries.

A benzoquinone derivative annelated by two imidazole rings was investigated as an organic anolyte of aqueous redox flow batteries. The anolyte showed a high solubility of 0.18 M in 1 M KOH aqueous solution and exhibited a one-step two-electron reversible redox wave with a half-wave potential of -0.59 V VS. SHE. An aqueous redox flow cell comprising the benzoquinone-imidazole hybrid as the anolyte and potassium ferrocyanide as the catholyte showed an operating voltage of ∼1.1 V and minimum capacity fading of over 220 cycles.

Synthesis of NiII porphyrin-NiII 5,15-diazaporphyrin hybrid tapes.

NiII porphyrin (P) and NiII 5,15-diazaporphyrin (DAP) hybrid tapes were synthesized by Suzuki-Miyaura cross-coupling reactions of meso- or β-borylated P with β-brominated DAP followed by intramolecular oxidative fusion reactions. Meso-β doubly linked hybrid tapes were synthesized by oxidation of singly linked precursors with DDQ-FeCl3. Synthesis of triply linked hybrid tapes was achieved by oxidation with DDQ-FeCl3-AgOTf with suppression of peripheral β-chlorination. In these tapes, DAP segments were present as a 20π-electronic unit, but their local antiaromatic contribution was trivial. Remarkably, these hybrid tapes were stable and exhibited extremely enhanced absorption bands in the NIR region and multiple reversible redox waves. A pentameric hybrid tape showed a remarkably sharp and red-shifted band at 1168 nm with ε = 5.75 × 105 M-1 cm-1. Singly linked P-DAP dyads were oxidized with DDQ-FeCl3 to give stable radicals, which were oxidized further to afford dimeric hybrid tapes possessing a nitrogen atom at the peripheral-side meso-position.

Ligand redox controlled amine dehydrogenation and imine hemilability in singlet diradical azo-aromatic Ni(II) complexes: characterization of the electron transfer series of azo-imine complexes of Ni(II).

Herein, using azo-amine (H2L) and azo-imine (L1-3) ligands, singlet diradical Ni(II) complexes [1] and [2] were synthesized from Ni(0)(COD)2 in THF. In separate reactions, homoleptic NiII complexes, [3a]2+-[3c]2+, were synthesized from [NiII(H2O)6](ClO4)2 and L1-3, respectively. All these complexes were characterized thoroughly. The X-ray structures of [1] and [2] showed that the amine side arm in [1] and the imine side arm in [2] are de-coordinated. The dN-N lengths in these two complexes were found to be ∼1.32 Å, which corresponds to the one-electron reduced azo-bond length. These complexes, [1] and [2], showed 1H NMR signals characteristic of diamagnetic compounds. These studies, along with DFT calculations, indicated that the unpaired spins on ligands coupled antiferromagnetically with the two unpaired spins on NiII to result in s = 0 ground states. Complex [1] showed ligand-based redox-induced dehydrogenation of the distal amine side arm to result in L1. Complexes [3a]2+-[3c]2+ have dN-N lengths of ∼1.27 Å and dC-N lengths of ∼1.28 Å. In cyclic voltammetry, complex [3a]2+ showed four well-resolved reversible reductive waves at 0.5 V to -1.6 V in dichloromethane. The first two waves became irreversible when they were measured in acetonitrile solution. The electron transfer series of [3a]2+ was further characterized by spectro-electrochemistry, EPR, and DFT calculations. These showed that all the reductions were associated with the ligand. It was further probed by redox events in complexes [3b]2+ and [3c]2+. While the electron donor -OMe group on the phenyl ring of the azo moiety in [3b]2+ showed a prominent cathodic shift of the potentials, the -F substitution on the phenyl group on the imine side arm of [3c]2+ has almost no effect. It has to be noted here that the oxidation of [2] by two electrons returns it back to complex [3a]2+. Reduction of [3a]2+ by two electrons also resulted in complex [2], indicating reversible ligand redox-induced hemilability of the imine moiety between [3a]2+ and [2]. Moreover, characterization of the electron transfer series of [3a]2+ and [2] has shown superior redox non-innocent behaviour and coordination ability of the azo-pyridine moiety in nickel(II) complexes over the imino-pyridine moiety of the ligand.

Coordination-triggered redox activity of early and late lanthanide calix[4]arene complexes.

The methylation of p-tert-butylcalix[4]arene in the distal 1,3-phenolic sites provides H2L = {p-tert-butylcalix[4](OMe)2(OH)2arene}. This unit acts as a rigid coordinating ligand to early and late lanthanide metal ions, enabling the construction of two families of mononuclear compounds featuring (N(nBu)4)[LnIIIL(acac)2]·CH3CN (Ln = Pr (1), Nd (2), Ho (3), and Er (4)) and (N(nBu)4)2[LnIIIL{Mo5O13(OMe)4(NO)}]·CH2Cl2 (Ln = Nd (5) and Er (6)). The metal ions adopt distorted bicapped trigonal prismatic coordination environments, resulting in slow relaxation of the magnetization for 4. These compounds exhibit reversible redox waves at positive potentials, centered within the calix[4]arene ligand, representing a new type of calix[n]arene-based electrochemical activity induced by coordination to the metal centers.

Synthesis, photophysical, computational characterizations, electrochemical and photovoltaic characteristics of some new quinoline-based hybrid fluorescent dyes

In this work, we have designed and synthesized some new fluorescent heterocyclic systems based on quinoline unit with the aim of providing new and highly effective synthetic dyes for the development of more effective photosensitive materials. The reaction of 8-(4-chlorophenyl)-3-alkyl-5-nitro-3H-imidazo[4′,5':3,4]benzo[1,2-c]isoxazoles with heteroaryl acetonitriles in KOH/MeOH led to the formation of novel 6H-furo[3,2-b]imidazo[4,5-f]isoxazolo[4,3-h]quinoline, 6H-imidazo[4,5-f]isoxazolo[4,3-h]thieno[3,2-b]quinoline and imidazo[4,5-f]isoxazolo[4,3-h]pyrrolo[3,2-b]quinoline at rt. The experimental results of the elemental analysis and spectroscopic data proved the proposed structures of the new fluorescent heterocyclic dyes. The optical properties of the title compounds such as wavelengths of maximum absorbance, fluorescence excitation, fluorescence emission, fluorescence quantum yields, and extinction coefficients were also obtained. The electrochemical characteristics of the title dyes were investigated using the cyclic voltammetry technique and reversible oxidation waves were observed at half-wave potential for these compounds. The HOMO and LUMO energy levels of the dyes were also determined by electrochemical, optical measurements and theoretical calculation. Additionally, I–V curves and the IPCE spectra of the title dyes were screened to investigate their photovoltaic performance parameters. Our experimental results discovered that the photovoltaic performances of the title dyes are in the range of 3.17–4.27 %. Electrochemical impedance spectroscopy (EIS) analysis was also performed to further elucidate the photovoltaic properties of the dyes.

A Nitronyl Nitroxide-Substituted Benzotriazinyl Tetraradical.

High-spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but those synthesized to date possess limited stability and processability. In this work, we have designed a tetraradical based on the Blatter's radical and nitronyl nitroxide radical moieties and successfully synthesized it by using the palladium-catalyzed cross-coupling reaction of a triiodo-derivative of the 1,2,4-benzotriazinyl radical with gold(I) nitronyl nitroxide-2-ide complex in the presence of a newly developed efficient catalytic system. The molecular and crystal structure of the tetraradical was confirmed by X-ray diffraction analysis. The tetraradical possesses good thermal stability with decomposition onset at ∼150 °C under an inert atmosphere and exhibits reversible redox waves at -0.54 and 0.45 V versus Ag/AgCl. The magnetic properties of the tetraradical were characterized by SQUID magnetometry of polycrystalline powders and EPR spectroscopy in various matrices. The collected data, analyzed by using high-level quantum chemical calculations, confirmed that the tetraradical has a triplet ground state and a nearby excited quintet state. The unique high stability of the prepared triazinyl-nitronylnitroxide tetraradical is a new milestone in the field of creating high-spin systems.

O2 Activation by a Coordinated -NH- Function: Hydrogen Atom Transfer and Aromatic Ring Oxidation.

Herein, we disclose a unique method of oxidation of a 1,4-naphthoquinone ring in air. We report that (1,4-naphthoquinone)-NH-N=C(OH)Ph (H3L) coordinated to octahedral ruthenium(II) and osmium(II) ions activates an 3O2 molecule spontaneously. Hydrogen atom transfer (HAT) from the -NH- function of H3L to 3O2 and subsequent (2e + 2H+) oxidation forming (1,3,4-trioxonaphthalen)=N-N=C(OH)Ph (HLOX) have been established. The H3L → HLOX transformation occurs via (3-hydroperoxy-1,4-naphthoquinone)=N-N=C(O-)Ph (HLOOH-) as an intermediate. The primary step is HAT generating H2L•- and hydroperoxide (OOH•) radicals. H2L•- is delocalized over the aromatic ring and incites coupling reactions via ortho carbon and produces coordinated HLOOH-. In solution, the homolytic cleavage of the peroxo bond leads to aromatic ring oxidation, affording LOX-. Ruthenium(II) and osmium(II) complexes of the types [MII(H2L-)(PPh3)2X], [MII(HLOOH-)(PPh3)2X], and trans-[MII(LOX-)(PPh3)2X] were successfully isolated in good yields. Notably, the cyclic voltammograms of all of the complexes exhibit reversible anodic waves due to MIII/MII redox couples. The rate constants of the [MII(H2L-)(PPh3)2X] → [MII(HLOOH-)(PPh3)2X] conversions determined by time-driven UV-vis spectroscopy in dry CH2Cl2, wet CH2Cl2, and D2O wet CH2Cl2 in air at 298 K follow the order > > . It is established that the rate constants are dependent on the 3O2 content of the solution but not on the concentration of the complex.

Synthese und Charakterisierung eines stabilen Nickelocenium‐Dikation‐Salzes

AbstractWir berichten über die Synthese und Charakterisierung der Nickelocenium‐Kationen [NiCp2]⋅+ und [NiCp2]2+ als deren [F‐{Al(ORF)3}2]− (Cp = C5H5; RF=C(CF3)3) Salze. Das diamagnetische [NiCp2]2+ ist das erste Beispiel für die Isolierung eines unsubstituierten Metallocen Dikations. Beide Salze wurden durch Reaktion von neutralem NiCp2 mit [NO]+[F‐{Al(ORF)3}2]− in 1,2,3,4‐Tetrafluorbenzol (4FB) erzeugt. Die Salze konnten durch Einkristall‐Röntgenbeugung charakterisiert werden, wobei kürzere Metall‐Ligand‐Bindungslängen für das höher geladene Salz gemessen wurden. Pulver‐Röntgenbeugung zeigte, dass die Salze phasenrein erhalten wurden. Cyclovoltammetrie in 4FB ergab quasi‐reversibel Redoxwellen bei −0.44 (0→1) und +1.17 V (1→2) gegen Fc/Fc+. Das 1H NMR von [NiCp2]2+ weist ein Singulett bei 8.6 ppm auf, während das paramagnetische [NiCp2]⋅+ deutlich Hochfeld auf −103.1 ppm verschoben ist.

Synthesis and Characterization of a Stable Nickelocenium Dication Salt.

We report the synthesis and characterization of the nickelocenium cations [NiCp2 ]⋅+ and [NiCp2 ]2+ as their [F-{Al(ORF )3 }2 ]- (Cp = C5 H5 ; RF =C(CF3 )3 ) salts. Diamagnetic [NiCp2 ]2+ represents the first example for the isolation of an unsubstituted parent metallocene dication. Both salts were generated by reacting neutral NiCp2 with [NO]+ [F-{Al(ORF )3 }2 ]- in 1,2,3,4-tetrafluorobenzene (4FB). The salts were characterized by single crystal X-ray diffraction (XRD), indicating shorter metal-ligand bond lengths for the higher charged salt. Powder XRD shows the salts to be phase pure, cyclic voltammetry in 4FB gave quasi reversible redox waves at -0.44 (0→1) and +1.17 V (1→2) vs Fc/Fc+ . The 1 H NMR of [NiCp2 ]2+ is a singlet at 8.6 ppm, whereas paramagnetic [NiCp2 ]⋅+ is significantly shifted upfield to -103.1 ppm.

Suffusion behavior of crushed calcareous sand under reversed cyclic hydraulic conditions

Due to the unique properties of calcareous sand in reclamation projects, soil foundations consisting of calcareous sand-filled land are often exposed to reversible tidal waves. This may induce continuous long-term internal erosion of the soil that differs from monotonic seepage conditions, which has not yet been studied from a microscopic perspective. In this study, a selected particle size distribution (PSD) based on the breakage experiments of calcareous sand is adopted. Then, a series of reversed seepage flows is generated using CFD-DEM, taking into account both cyclic frequency and hydraulic gradient. Numerical results examine the overall suffused fine mass, the migration and suffusion degree across the divided layers along seepage, and the microscopic origins of continuous suffusion under reversed hydraulic conditions. Furthermore, the micro-mechanical and energetic evolution of soil skeletons is analyzed. The findings reveal that hydraulic gradient is the primary factor influencing suffusion outcomes at the initial stage (PEM increases from roughly 21% to 24%), while the cyclic frequency determines the long-term result (PEM increases from roughly 30% to 37%). From a microscopic point, the elimination of clogging, combined with energetic instability and force chain network rearrangement, is identified as the origin of continuous suffusion under reversed hydraulic loading.

Synthesis and characterization of iron(II) Schiff-base complexes of tridentate mixed amine/imine ligands with cis- and trans-1,2-diaminocyclohexane backbones

The synthesis and characterization of two low-spin iron(II) complexes of tridentate mixed amine/imine Schiff bases is described. The complexes bear two tridentate ligands having either a cis- or trans-(1R,2R)-1,2-diaminocyclohexane backbone accompanied by a single pyridine-imino fragment. The complexes can be synthesized in protic solvents via ligand hydrolysis or by self-assembly. X-ray crystallography of the hexafluorophosphate salts is indicative that the tridentate ligands adopt a meridional configuration around the metal center. Synthesis using trans-(1R,2R)-diaminocyclohexane yields only one chiral stereoisomer of the iron complex. In the cis-1,2-diaminocyclohexane complex, the ligand amino groups form hydrogen-bonds to co-crystallized water, which in turn forms an extended hydrogen-bonding network with hexafluorophosphate counterions. The water molecule resides in a cavity formed from the two cyclohexyl backbones. The imine CN stretch frequencies and long CN bonds suggest a large degree of metal to ligand backbonding. Both complexes exhibit moderate solvatochromism. The circular dichroism (CD) spectrum of the enantiopure [trans-(1R,2R)-L2Fe]2+ cation has intense signals across the entire visible range. Mössbauer spectroscopy on the cis- complex confirms no noticeable spin-crossover behavior between 10 K and 300 K, as might be expected for a C2-symmetrial coordination complex of iron(II) with a high degree of π-backbonding. Electrochemical experiments are indicative of one reversible oxidation wave which was assigned based on the spectroelectrochemical and theoretical data to the FeII/FeIII couple. Density Functional Theory (DFT) calculations suggest that the HOMO in the cis- and trans- complexes is iron(II) centered, while the LUMO is delocalized over the organic ligands. Time-dependent density functional theory (TDDFT) confirms the presence of the numerous metal-to-ligand charge-transfer transitions between 380 and 620 nm.