Chemical recycling of nylon-6 to short-chain oligomers and monomer epsilon-caprolactam via catalytic glycolysis is a potential solution for plastic waste remediation. In this work, the kinetics of amide bond glycolysis (with ethylene glycol) in nylon-6 and the model compound N-phenethyl-3-phenylpropanamide (M1) were evaluated at 473 K in the presence of the cyclic amidine catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene. Rates of polymer glycolysis were determined by the time-dependent shift in molecular weight distribution, whereas rates of M1 glycolysis were determined using liquid chromatography. The similarity of the first-order rate constants for glycolysis of nylon-6 and M1 at 473 K with 0.03 M amidine catalyst (5 mol% relative to amide bonds), 1.22 & times; 10-5 s- 1 and 2.18 & times; 10-5 s- 1, respectively, confirmed the suitability of M1 as a model compound for nylon-6 glycolysis. Similar rates of glycolysis in the presence of other cyclic amidine catalysts as well as sodium methoxide revealed little influence of base strength. Glycolysis rates were unexpectedly non-linear in catalyst loading and deactivation occurred with long reaction times, presumably by non-selective decomposition of products as detected by liquid chromatography.

The presence of strong spin-orbit coupling, which is comparable to the crystal field in certain ferric-porphyrin/phthalocyanine derivatives, results in a spin-admixed state between the high-spin (HS; S = 5/2) and intermediate-spin (IS; S = 3/2) states. However, there are no literature precedents for spin admixing between the IS (S = 3/2) and low-spin (LS; S = 1/2) states, which are purely governed by axial ligation. It is also true that systems showing spin-admixed behavior do not exhibit thermal equilibrium between the spin states, that is, spin crossover (SCO). In this article, we report a unique and rare square planar ferric ion complex, [Na(DME)3][Fe(L12-)2] (1), which exhibits two different physical phenomena: SCO is observed between the spin-admixed states, a phenomenon unprecedented in this context. Field- and temperature-dependent Mössbauer spectra, variable temperature X-band EPR spectra, multifrequency EPR (MF-EPR), and temperature-dependent magnetic susceptibility measurements reveal that the spin-admixed state has contributions from IS (S = 3/2) and LS (S = 1/2), unlike other reports in the literature. The detailed electronic structure of 1, along with the rationale for quantum spin admixing and SCO, is well supported by theoretical calculations.

In modern society, due to rapid urbanization and industry growth, different types of pollutants are accumulating in the environment and making it polluted. The excessive discharge of organic toxins into water bodies is a major contributor to environmental pollution and poses significant health risks to society and the environment. Organic toxins from various chemical and textile industries pollute our water resources, forming breeding centers for different disease pathogens and adversely affecting the natural water cycle. Therefore, to protect and sustain life on the planet, it should be our prime mandate to preserve, manage, and remediate our limited available water resources. Organic pollutant decomposition is a difficult task due to their complex nature; therefore, it is important to understand the structures of different pollutants to decompose them perfectly. This review highlights the classification of various pollutants, their structural properties, and their possible detoxification processes through the advanced photocatalytic processes. In addition, the elaboration for the decomposition mechanism of the different toxins, ranging from azo dyes, phenols, pesticides, and nitrogen-based compounds to halo-compounds, has been explained. This review also briefly explains the underlying charge transfer mechanism used by different photocatalysts, such as metal oxide semiconductors and 2D-layered nanostructures. A brief description of this mechanism is mentioned in the review, along with the fundamental principle, the role of active redox radicals, such as superoxides and hydroxyl ions, in facilitating the photocatalytic degradation process. Lastly, the creation of robust and scalable photocatalytic systems for practical environmental applications is discussed along with the knowledge gaps and future research goals. This review provides invaluable insight into developing the advanced photocatalyst materials for the targeted pollutants.

The observation of slow relaxation of magnetization in low-spin square planar cobalt complexes is exceedingly rare, likely due to the synthetic challenges of stabilizing such geometries, along with the complexities introduced by hyperfine interactions and spin-orbit coupling. Additionally, accurately characterizing the ground-state electronic configuration of these complexes remains a significant challenge. In this article, we report a unique and rare square planar cobalt complex, [Co(L1⋅-)2] (1), where the coordination sites are occupied by the phenanthroiminoquinone (L1). The molecular structure of complex 1 was determined using single-crystal X-ray diffraction studies. A structurally analogous nickel complex, [NiII(L1⋅-)2] (2), was also synthesized and characterized. Detailed DC magnetic susceptibility measurements of 2 reveal strong antiferromagnetic exchange interactions between the radical centers, rendering it diamagnetic. For cobalt complex 1, this strong antiferromagnetic coupling results in a doublet ground state, as corroborated by X-band EPR measurements (at 5 K) conducted on both polycrystalline and frozen solution samples. To gain deeper insights into the electronic structure of the cobalt ion in 1, a comprehensive suite of experimental and theoretical investigations was conducted, including X-ray diffraction, DC magnetic studies, X-band EPR, UV-Vis-NIR spectroscopy, and ab initio calculations. These studies collectively indicate that the cobalt ion in 1 exists in a divalent low-spin state. Furthermore, the observed slow relaxation of magnetization for the doublet state of 1 highlights its potential as an ideal candidate for designing spin-based molecular qubits.

Although several Run+ (n = 2 or 3) complexes have been reported to be excellent biomimetics for the water oxidation process of photosystem II, investigation and spectroscopic characterization of the reactive intermediates such as [Ru-IV/V & boxH;O](n+) involved in the catalytic process are not only scarce but also a daunting task. Here, we report a catalyst [Ru-III(L)(PPh3)(H2O)](+) (2) found to show electrochemical water oxidation efficiency with a considerably low overpotential of 195 mV compared to other Run+ water oxidation catalysts reported in the nonaqueous media. Besides, the Schiff base ligand (L) employed in this study facilitates the stabilization of a [LRuV & boxH;O](+) species. By the use of multispectroscopic techniques (spectroelectrochemistry, electron paramagnetic resonance, and resonance Raman), we have shed light on the electronic structure of the elusive [LRuV & boxH;O](+) species. Based on the experimental results, a plausible intermolecular radical coupling (I2M) mechanism is proposed, which is corroborated by theoretical calculations.

The transesterification reaction kinetics of 2-(benzoyloxy)ethyl benzoate with various alcohols (ethylene glycol, 1,3-propanediol, 1-butanol, propylene glycol and 1,2-butylene glycol) using various cyclic amidine catalysts were investigated. For transesterification with excess glycol (glycolysis), the rate was nearly zero order in diester and glycol concentration, which is substantially different from classical transesterification kinetics with monoalcohols. The measured kinetic parameters during glycolysis are consistent with a reaction path that is kinetically limited by the decomposition of the reaction intermediate formed from the alkoxide and diester. The DFTcalculated reaction energy and activation barrier for decomposition of this intermediate reveal a critical role of intramolecular hydrogen-bond stabilization made possible by the vicinal -OH of the glycol that effectively increases the concentration of the intermediate during reaction resulting in acceleration of the overall transesterification rate. These findings indicate the nature of both the alcohol solvent and the catalyst influence transesterification rate, and results suggest they are also important in the deconstruction of carbonyl-containing condensation polymers.

A series of porous MOF materials, viz., Pdx@IRMOF-9 (x = 2, 5, and 10%) were synthesized by loading varying concentrations of Pd(II) on IRMOF-9. The synthesized MOF materials were characterized by ltravioletisible (UV–Vis) spectroscopy, Fourier transform Infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM) analyses. UV, FT-IR, and PXRD data of Pd(II)@IRMOF-9 were found to be in line with those of IRMOF-9, which suggests that the structure of the IRMOF-9 remained intact upon Pd(II) loading. Surface morphology of IRMOF-9 showed sheet-like structures, and upon incorporation of Pd(II) to IRMOF-9, porous cauliflower-shaped MOFs were obtained. The SEM area mapping of Pd10%@IRMOF-9 confirmed the homogeneous dispersion of Pd(II) on IRMOF-9. BET measurements suggested an increase in the surface area as well as pore size upon incorporation of Pd(II) on IRMOF-9. Due to high porosity and high petal density, Pd10%@IRMOF-9 demonstrated degradation of seven organic dyes, namely, orange G, methylene blue, methyl orange, congo red , methyl red, rhodamine 6G, and neutral red. It showed excellent results with >90% dye degradation efficiency in case of cationic, anionic as well as neutral dyes. Degradation of organic dyes followed the pseudo-first-order kinetics. Kinetic parameters, KM and Vmax, were calculated using the double reciprocal Lineweaver–Burk plot and were found to be 13.2 μM and 26.68 × 10–8 M min–1, respectively. Recyclability studies of heterogeneous Pd10%@IRMOF-9 demonstrated the degradation of CR dye for five consecutive cycles without significant loss of its catalytic activity. Herein, a robust and efficient material for the degradation of organic dyes has been developed and demonstrated.

Copper-catalyzed aziridination of alkenes is dominated in the literature compared to any other metal catalysts. This catalytic reaction is believed to be mediated by the elusive Cu-nitrene intermediate. However, analytical characterization of this intermediate is extremely scarce in the literature. In this article, we intend to shed the light on the electronic structure of the Cu-nitrene intermediate. The reaction of Cu(I) salt in the presence of the redox-active bidentate Schiff base ligand (C21H20N2; L1) led us to isolate a monomeric copper(I) complex with the molecular formula of [Cu(L1)(2)]ClO4. 2C(6)H(6) (1), which was structurally characterized. 1 behaves as an excellent catalyst that promotes the nitrene group transfer to the variety of alkenes in the presence of (N-(p-tolylsulfonyl)imino)phenyliodinane (PhINTs). The intermediate generated from 1 by the addition of PhINTs shows an m/z peak at 832.3079 g/mol which corresponds to an M+ ion peak of the intermediate with the molecular formula of [(L1)(2)Cu-II-NTs](+) (where Ts = Tosyl). Further, based on the detailed experimental studies (in-situ UV-Vis measurement and X-band EPR measurements) we propose that the active catalyst that possesses the copper ion in its +2 oxidation state under our experimental condition, whose electronic structure can be best described as [(L1)(2)Cu-II-NTs](+) nitrene radicals. The optimized structure of the Cu-nitrene intermediate suggests that the triplet state was found to be the ground state. Besides, we propose a mechanism for this catalytic reaction.

A Co dimer with a 3e-reduced NNN pincer ligand [(PMe 3 ) 2 Co II (L 1 3− )Co I (PMe 3 ) 3 ] is an efficient catalyst for the hydrophosphination reaction of both internal and terminal alkynes including α-hydroxy-functionalized alkyne substrates with excellent stereo- and regioselectivity.

A [Ce(L1)(NO 3 ) 3 ] (1) was found to exhibit ferroelectric and magnetic bistability simultaneously. The ferroelectric to paraelectric transition was observed at 303 K and a small external electric field was required to switch the spontaneous polarization in 1.

The reaction of Ln(NO3)3.nH2O (where Ln = Gd, Tb, Dy or Yb) in the presence of sodium acetate led us to isolate a family of structurally analogous dinuclear lanthanide complexes with the general molecular formula of [Ln2(CH3COO)4(NO3)2(H2O)4]. 2H2O (where Ln = Gd (1) or Tb (2) or Dy (3) or Yb (4)), which are characterized by single-crystal X-ray diffraction. The dc magnetic susceptibility measurements were performed on 1 reveal the presence of a weak ferromagnetic exchange between the Gd(III) center (J = +0.01 cm- 1; -2JS1.S2 Hamiltonian). This weak exchange interaction in 1 is presumably overcome by the external magnetic field, and therefore, the Xband EPR spectral features of 1 were simulated by considering the single-ion spin Hamiltonian parameter (g = 1.98, D = 0.03 cm- 1, and divide E/D divide = 0.004). In contrast to 1, complexes 2-4 exhibit a weak antiferromagnetic exchange between the Ln(III) centers. The magnetization relaxation dynamics studies performed on the anisotropic complexes (2-4) show slow relaxation of magnetization in the presence of an optimum external magnetic field. The spin-lattice relaxation predominantly follows the Direct and Raman mechanism exclusively, and the Orbach process was found to be non-existent. By employing ab initio calculations, the electronic structure and the mechanism of magnetization relaxation dynamics of 2-4 have been investigated. The magnetocaloric effect parameter for 1 shows a change in magnetic entropy (-dSm) value of 39 J Kg-1 K-1 at 2.0 K (dH = 70 kOe), which is one of the largest -dSm value registered among the various discrete molecular coolants reported in the literature..

A series of rare six-coordinated dinuclear Ln(III) complexes [Ln2(μ-Cl)2Cl4Li2(L)2(THF)6] were structurally characterized using a bulky amide ligand (L; Ln = Gd(1), Dy(2) and Y(3)). Detailed magnetic studies disclose that a weak antiferromagnetic coupling exists within 1 (-0.09 cm-1) and 2 (-0.07 cm-1; -2J Hamiltonian). Additionally, this study unveils the importance of the amide ligand at the coordination site of Dy(III), which manifests a slow relaxation of magnetization in the absence of an external magnetic field. This has been rationalized by detailed ab initio calculations as well as the electronic structure determination of 1 and 2.

Protein aggregation into amyloid fibrils is a key feature of a multitude of neurodegenerative diseases such as Alzheimer's, Parkinson's, and Prion disease. To detect amyloid fibrils, fluorophores with high sensitivity and better efficiency coupled with the low toxicity are in high demand even to date. In this pursuit, we have unveiled two benzimidazole-based fluorescence sensors ([C15H15N3] (C1) and [C16H16N3O2] (C2), which possess exceptional affinity toward different amyloid fibrils in its submicromolar concentration (8 x 10(-9) M), whereas under a similar concentration, the gold standard Thioflavin-T (ThT) fails to bind with amyloid fibrils. These fluorescent markers bind to alpha-Syn amyloid fibrils as well as amyloid fibrils forming other proteins/peptides including A beta 42 amyloid fibrils. The(1)H-N-15 heteronuclear quantum correlation spectroscopy nuclear magnetic resonance data collected on wild-type alpha-Syn monomer with and without the fluorophores (C1andC2) reveal that there is weak or no interactions betweenC1orC2with residues in alpha-Syn monomer, which indirectly reflects the specific binding ability ofC1andC2to the alpha-Syn amyloid fibrils. Detailed studies further suggest thatC1andC2can detect/bind with the alpha-Syn amyloid fibril as low as 100 x 10(-9) M. Extremely low or no cytotoxicity is observed forC1andC2and they do not interfere with alpha-Syn fibrillation kinetics, unlike ThT. BothC1/C2not only shows selective binding with amyloid fibrils forming various proteins/peptides but also displays excellent affinity and selectivity toward alpha-Syn amyloid aggregates in SH-SY5Y cells and A beta 42 amyloid plaques in animal brain tissues. Overall, our data show that the developed dyes could be used for the detection of amyloid fibrils including alpha-Syn and A beta 42 amyloids with higher sensitivity as compared to currently used ThT.

A family of hetero-trinuclear metal complexes with the general molecular formula [Zn2Dy(L1)2(OAc)4] (X) where X = (NO3)0.92(Br)0.08 (1), ClO4 (2), Cl (3) and PF6 (4) were structurally characterized using a Schiff base ligand (HL1). The Dy(iii) ion in 1-4 exhibits distorted square anti-prism geometry; however, the extent of distortion observed around Dy(iii) in these complexes differ from each other. Consequently, 1-4 show distinct magnetization relaxation dynamics, with the anisotropic energy barrier of 25.4 cm-1, 12.9 cm-1, 14.08 cm-1 and 55.5 cm-1, respectively. The detailed electronic structure of 1-4 and the experimentally observed magnetization relaxation dynamics trends were rationalized using ab initio calculations. The detailed investigation discloses the non-zero influence of the anion themselves and the anion induced geometry change in Zn(ii) affects the electronic structure of Dy(iii), which in turn affects the magnetization relaxation dynamics. Overall, the study unveils an unprecedented methodology i.e. change in geometry of Zn(ii) by altering the anion in the crystal lattice to modulate the relaxation dynamics of Dy(iii).

The reaction of [Ni(COD)2] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis(imino)pyridyl (L1) reveals a susceptibility to oxidation in an inert atmosphere ([O2] level <0.5 ppm), resulting in a transient Ni:dioxygen adduct. This reactive intermediate abstracts a hydrogen atom from THF and stabilizes an uncommon Ni(III) complex. The complex is crystallographically characterized by a molecular formula of [NiIII(L1··)2-(OH)] (1). Various isotopically labeled experiments (16O/18O) assertively endorse the origin of terminal oxygen based ligand in 1 due to the activation of molecular dioxygen. The presence of proton bound to the terminal oxygen in 1 is well supported by NMR, IR spectroscopy, DFT calculations, and hydrogen atom transfer (HAT) reactions promoted by 1. The observation of shakeup satellite peaks for the primary photoelectron lines of Ni(2p) in the X-ray photoelectron spectroscopy (XPS) unambiguously confirms the paramagnetic signature associated with the distorted square planar nickel ion, which is consistent with the trivalent oxidation state assigned for the nickel ion in 1. The variable temperature magnetic susceptibility data of 1 shows dominant antiferromagnetic interactions exist among the paramagnetic centers, resulting in an overall S = 1/2 ground state. Variable temperature X-band EPR studies performed on 1 show evidence for the S = 1/2 ground state, which is consistent with magnetic data. The unusual g-tensor extracted for the ground state S = 1/2 is analyzed under a strong exchange limit of spin-coupled centers. The electronic structure predicted for 1 is in good agreement with theoretical calculations.

A formal E-selective hydrophosphination of terminal and internal alkynes catalyzed by a well-defined [Co(PMe3)4] (A) complex is achieved under mild conditions in good-to-excellent yield. The reaction does not require any additives and/or external base for an efficient hydrophosphination reaction. The reaction provided excellent scope and good functional tolerance. Detailed spectroscopic analysis (NMR, EPR, and UV–vis) revealed that the low valent cobalt(0) complex undergoes oxidative addition with diphenylphosphine, followed by hydrometalation with alkyne, and subsequent reductive elimination led to the expected product. The detailed spectroscopic analyses along with the isotopic labeled experiments facilitate to intercept the active intermediates that are involved in the catalytic cycle, which are detailed. It was revealed that the suprafacial (vide infra) delivery of H and phosphorus to π-alkynes in a syn-fashion led to formal E-vinyl phosphine.