Ring Atoms Research Articles

Insights into the crystal structure investigation and virtual screening approach of quinoxaline derivatives as potent against c-Jun N-terminal kinases 1

Quinoxaline derivatives are an important class of heterocyclic compounds in which N replaces one or more carbon atoms of the naphthalene ring and exhibit a wide spectrum of biological activities and therapeutic applications. As a result, we were encouraged to explore a new synthetic approach to quinoxaline derivatives. In this work, we synthesized two new derivatives namely, ethyl 4-(2-ethoxy-2-oxoethyl)-3-oxo-3,4-dihydroquinoxaline-2-carboxylate (2) and 3-oxo-3,4-dihydroquinoxaline-2-carbohydrazide (3) respectively. Their structures were confirmed by single-crystal X-ray analysis. Hirshfeld surface (HS) analysis is performed to understand the nature and magnitude of intermolecular interactions in the crystal packing. Density functional theory using the wb97xd/def2-TZVP method was chosen to explore their reactivity, electronic stability and optical properties. Charge transfer (CT) and orbital energies were analyzed via natural population analysis (NPA), and frontier molecular orbital (FMO) theory. The calculated excellent static hyperpolarizability (βo) indicates nonlinear optical (NLO) properties for 2 and 3. Both compounds show potent activity against c-Jun N-terminal kinases 1 (JNK 1) based on structural activity relationship studies, further subjected to molecular docking, molecular dynamics and ADMET analysis to understand their potential as drug candidates. Communicated by Ramaswamy H. Sarma

Atomic-level mechanisms of short-circuit diffusion in materials

Abstract This paper reviews the recent progress in understanding the atomic mechanisms of short-circuit diffusion along materials interfaces, such as grain and interphase boundaries, as well as lattice and interfacial dislocations/disconnections. Recent atomistic computer simulations have shown that short-circuit diffusion is dominated by collective atomic rearrangements in the form of strings and rings of mobile atoms. The process is dynamically heterogeneous in space and time and has many features in common with atomic dynamics in supercooled glass-forming liquids. We discuss examples of grain boundary, interphase boundary, and dislocation diffusion in metals and alloys, including the solute effect on the diffusion rates and mechanisms. Interphase boundaries are exemplified by Al–Si interfaces with diverse orientation relationships and atomic structures. The hierarchy of short-circuit diffusion paths in materials is reviewed by comparing the rates of grain boundary, interphase boundary, and dislocation diffusion. Future directions in the field of short-circuit diffusion in defect core regions are discussed.

Synthesis, characterization and theoretical aspects of copper and zinc divalent ion complexes with azo dye derived from 4,5-diphenylimidazole

Azo dye ligand derived from 4,5-diphenyl imidazole and 4,4-diaminodiphenylmethane was synthesized by diazomium coupling reaction. In this reaction an amine (4,4-diaminodiphenylmethane was converted to the diazonium salt and coupled with 4,5-diphenyl imidazole. The bright coloured Cu(II) and Zn(II) complexes with this ligand were synthesized by refluxing the latest with both metals chloride salts. The prepared compounds were characterized by 1H-NMR, 13C-NMR, FTIR, UV-Visible, molar conductivity and atomic absorption. By the infrared data, the coordination between copper and zinc ions and the azo ligand achieved through the nitrogen of the azo group and one of the nitrogen atoms in the imidazole ring. By the molar conductivity test, the non- electrolytic nature of both complexes was also confirmed. The suggested structure for these complexes is octahedral. Using density functional theory (DFT) some theoretical data was obtained for the synthesized complexes. The obtained data include the highest occupied and the lowest unoccupied molecular orbitals energy (HOMO and LUMO), electron density, thermodynamic functions (ΔG°, ΔS°, ΔH°, ΔE°), ionization potential (IP), electron affinity (EA), electrophilicity(ὠ), electronegativity (En), chemical hardness (η) and dipole moment (μ). According to these studied parameters some properties of the two complexes were explained and discussed.
 KEY WORDS: Cu(II) and Zn(II) complexes, Azo ligand, 4,5-Diphenylimidazole, 4,4-Diaminodiphenylmethane, Theoretical study
 Bull. Chem. Soc. Ethiop. 2024, 38(2), 313-323. 
 DOI: https://dx.doi.org/10.4314/bcse.v38i2.4

4-Thiaproline accelerates the slow folding phase of proteins containing cis prolines in the native state by two orders of magnitude.

The cis/trans isomerization of peptidyl-prolyl peptide bonds is often the bottleneck of the refolding reaction for proteins containing cis proline residues in the native state. Proline (Pro) analogues, especially C4-substituted fluoroprolines, have been widely used in protein engineering to enhance the thermodynamic stability of peptides and proteins and to investigate folding kinetics. 4-thiaproline (Thp) has been shown to bias the ring pucker of Pro, to increase the cis population percentage of model peptides in comparison to Pro, and to diminish the activation energy barrier for the cis/trans isomerization reaction. Despite its intriguing properties, Thp has been seldom incorporated into proteins. Moreover, the impact of Thp on the folding kinetics of globular proteins has never been reported. In this study, we show that upon incorporation of Thp at cisPro76 into the thioredoxin variant Trx1P the half-life of the refolding reaction decreased from ~2 h to ~35 s. A dramatic acceleration of the refolding rate could be observed also for the protein pseudo wild-type barstar upon replacement of cisPro48 with Thp. Quantum chemical calculations suggested that the replacement of the Cγ H2 group by a sulfur atom in the pyrrolidine ring, might lower the barrier for cis/trans rotation due to a weakened peptide bond. The protein variants retained their thermodynamic stability upon incorporation of Thp, while the catalytic and enzymatic activities of the modified Trx1P remained unchanged. Our results show that the Pro isostere Thp might accelerate the rate of the slow refolding reaction for proteins containing cis proline residues in the native state, independent from the local structural environment.

Understanding into atomic structures and electronic properties from the analysis of intramolecular junctions in carbon nanotubes

Octuplet arrangements of intra-molecular junctions (IJs) are selected and studied in order to forecast each one's atomic structure, quantum density of states of CNTs with imperfections, and electronic transmittals. Each of these can be divided into groups of triplets, specifically those that exhibit comparable characteristics to one another, such as Semiconductor_Semiconductor IJs (SC_SC IJs) (in arrangements of first, second, fifth and eight), Metal_Metal IJs (in arrangements of third and seventh) and Semiconductor_Metal IJs (in arrangements of fourth and sixth). The quantum density of states of SC_SC IJs results in semiconductors with the same order as before, but with a reduced band gap as compared to the primary standards. Additionally, a resized image of quantum density of states is provided to demonstrate the specifics of the divergence near the Fermi limit. quantum density of states for CNTs-IJs (fifth, fourth) – (fifth, fourth) (SC_SC) estimated across a handful of rings at the intersection indicated by the blue lines is shown through the illustration. The hexagonal-assembly of CNTs contains pentagons & heptagon-paired imperfections, which can alter CNTs’ helicity and their basic electronic framework. The red lines indicate the quantum density of states of Perfect-CNTs with indices (fifth, fourth). Despite being semiconductors by nature, Perfect-CNTs (fifth, fourth) exhibit a band gap around 1.22 eV. The semiconductor Perfect-CNTs with indices (seventh, fourth) have a quantum density of states that is mirrored around the Fermi limit (E = 0). Additionally, at the Fermi limit, it has a value that does not equal zero, along with a difference in particle energy. The picture shows that the behavior of CNTs-IJs quantum density of states changes from being purely semiconductor-like to becoming less like a semiconductor when mixed with metallic CNTs at the intersection. The combination of metal and semiconductor is tangible. It changes from one system to another, beginning as a semiconductor and changing into a semiconductor with a considerable number of switching operations. The observation shows that the semiconductor with the indices (seventh, third) and the metal carbon nanotubes with the indices (seventh, fourth) both have zero QDS at the Fermi energy level. Despite being diluted within a few atomic rings, the quantum density of states in the case of CNTs-IJs (seventh, third) – (seventh, fourth) remains at 0.0 at the Fermi energy level due to being diluted within a few atomic rings.

Covalent triazine reducing the defects by coordination roles and inhibiting I− migration by anion-π interaction for efficient perovskite solar cell

The grain boundary defects related non-radiative recombination, I− migration, and lead leakage problems are the foundational and fundamental aspects for the perovskite solar cells. Herein, covalent triazine frameworks (CTFs) are introduced into the perovskite film to address these problems. CTFs can passivate the uncoordinated Pb2+ defects at grain boundary and reduce the lead leakage based on the coordination interaction between nitrogen atoms in triazine ring and Pb2+. CTFs can also inhibit the I− migration and reduce the I− vacancy defects based on the anion-π interaction between electron-deficient triazine ring and I−. Benefited from the passivated grain boundary defects and inhibited I− migration by CTFs, the modified target device achieves a power conversion efficiency of 23.05 % with improved humidity stability and thermal stability. Therefore, this work lays the foundation for obtaining effective, stable, and environmentally friendly perovskite solar cells.

Deoxygenation of Oxiranes by λ3 σ3 -Phosphorus Reagents: A Computational, Mechanistic, and Stereochemical Study.

Invited for this month's cover is Prof. Arturo Espinosa Ferao at the University of Murcia, Spain. The cover picture shows two different ways of reacting a phosphane (R3 P) with the oxirane (epoxide) ring. They arise from phosphorus attacking either the carbon or oxygen ring atoms and promoting carbene or oxygen transfer reactions with eliminations of H2 C=O or CH2 =CH2 , respectively. More information can be found in the Research Article by Arturo Espinosa Ferao .

An unexpected tautomer: synthesis and crystal structure of N-[6-amino-4-(methylsulfanyl)-1,2-dihydro-1,3,5-triazin-2-ylidene]benzenesulfonamide

The title compound, C10H11N5O2S2, consists of an unexpected tautomer with a protonated nitrogen atom in the triazine ring and a formal exocyclic double bond C=N to the sulfonamide moiety. The ring angles at the unsubstituted nitrogen atoms are narrow, at 115.57 (12) and 115.19 (12)°, respectively, whereas the angle at the carbon atom between these N atoms is very wide, 127.97 (13)°. The interplanar angle between the two rings is 79.56 (5)°. The molecules are linked by three classical hydrogen bonds, forming a ribbon structure. There are also unusual linkages involving three short contacts (< 3 Å) from a sulfonamide oxygen atom to the C—NH—C part of a triazine ring.

Topological superconducting phase competition in magnetic atomic rings

A magnetic flux threading through magnetic atomic rings can induce topological superconductivity. It provides a novel approach to achieving low-dimensional (2D) topological superconductivity, which requires neither spin-orbit coupling nor helical magnetic order. In this paper, we introduce a topological superconductor model by depositing a ferromagnetic atomic ring on the surface of a 2D s-wave superconductor. When the moments of the magnetic atoms are perpendicular to the external magnetic field, a magnetic flux can induce topological superconductivity. Considering practical experiments, because the magnetic atomic chain breaks the inversion symmetry of the surface of the 2D substrate, the Rashba spin-orbit coupling (SOC) is introduced, leading to the appearance of helical magnetic order in the atomic chain. According to previous researches, this helical magnetic order ensures that the magnetic moments of the ring are perpendicular to the external magnetic field, and the patch angle of neighbor moment of the helical order is proportional to the strength of the SOC. However, the helical order or Rashba SOC may introduce topological superconductivity on their own. It is meaningful to investigate the influence of the effects of the Rashba SOC and helical magnetic order on the flux induced topological superconducting states. We find that the Rashba SOC has a disruptive effect on the existing topological state, while helical magnetic order merely shifts its transition position in the parameter space. Therefore, when selecting materials for experiment, it is recommended to choose materials with lower Rashba SOC strength.

Second-order nonlinear optical properties of X-shaped pyrazine derivatives.

This work reports an investigation of the second-order NLO properties of two isomer series of X-shaped pyrazine derivatives, by means of HRS measurements and DFT calculations. The systems differ in the relative position of the donor and acceptor substituents with respect to the axis formed by the nitrogen atoms of the central pyrazine ring. Although the magnitude of the second harmonic signal is similar, HRS measurements revealed that the anisotropy of the NLO response strongly differs in the two chromophore series, the one of the 2,3-isomers being strikingly dipolar, while the one of the 2,6-isomers is mostly octupolar. The experimental observations are well supported by DFT calculations. In particular, the sum-over-states approach allows us to rationalize the different NLO anisotropies observed in the two isomer series through a detailed analysis of the symmetry of the low-lying excited states.

Carbon pre-protected iron strategy to construct Fe, C-codoped g-C3N4 for effective photodegradation of organic pollutants via hole oxidation mechanism

Improving photocatalytic activity in graphitic carbon nitride (g-C3N4) by enhancing charge transfer and light absorption remains a challenge. Herein, iron-loaded carbon (FeC) was first prepared at low temperature, and then the Fe, C-codoped g-C3N4 (FeC–CN) was synthesized by high temperature thermal copolymerization of FeC with melamine. The carbon shell of FeC prevented the formation of iron oxide during high temperature thermal copolymerization, and Fe as electron channels existed in the interlayer, meanwhile, C atoms of FeC replaced part of the N atoms in the triazine ring. This designed structure facilitates in-plane and interlayer transfer of photogenerated carriers, as well as the separation of photogenerated carriers. Additionally, the UV–visible absorption spectra have demonstrated that the substitution of C atoms can greatly enhance visible light absorption. The catalyst exhibits significantly increased photocatalytic activity and excellent stability compared to g-C3N4. Interestingly, different from the reactive oxygen species-based g-C3N4 catalysis reaction, the degradation of organic pollutants was found to initiate from a hole-involved non-radical pathway. The increased electron transfer facilitates the reduction of O2 via a one-step two-electron pathway to generate hydrogen peroxide.

Tuning spin dynamics of binuclear Dy complexes using different nitroxide biradical derivatives.

By employing nitronyl/imino nitroxide biradicals, three Ln-Zn complexes, namely, [Ln2Zn2(hfac)10(ImPhPyobis)2] (LnIII = Gd 1, Dy 2; hfac = hexafluoroacetylacetonate; ImPhPyobis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene) and [Dy2Zn2(hfac)10(NITPhPyobis)2] 3 (NITPhPyobis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene), have been successfully prepared. The three complexes possess {Ln2O2} cores bridged by the oxygen atoms of the 4-oxypyridinium rings of the biradical ligands and one of the imino/nitronyl nitroxide groups of the biradical is coordinated to a ZnII ion, then producing a centrosymmetric tetranuclear six-spin structure. The studies of spin dynamics indicate that complexes 2 and 3 exhibit distinct magnetic relaxation behaviors at zero dc field: complex 2 presents single relaxation with an effective energy barrier (Ueff) of 69.8 K, while complex 3 exhibits double relaxation processes with Ueff values for the fast and slow relaxation being 15.8 K and 50.9 K, respectively. The observed different magnetic relaxation behaviors for the two Dy complexes could be mainly ascribed to the influence of the distinct nitroxide biradical derivatives.

Six-coordinated nickel(II) complexes with benzothiadiazole Schiff-base ligands: synthesis, crystal structure, magnetic and HFEPR study.

Two new nickel(II) complexes, namely Ni(L1)2 (1) and Ni(L2)2·CH2Cl2(2) were obtained by reacting nickel(II) acetate tetrahydrate with the benzothiadiazole Schiff base ligands HL1 = 2-[4-(2,1,3-benzothiadiazole)imino]methyl-phenol or HL2 = 2-[(2,1,3-benzothiadiazol-4-ylimino)methyl]-6-methoxyphenol in the presence of Et3N. The tridentate NNO chelate ligands induce a distorted octahedral environment around the nickel(II) ions. Single crystal X-ray diffraction analysis reveals elongated Ni-N bonds with the nitrogen atom of the benzothiadiazole ring in both complexes. Intermolecular hydrogen bonds and π-π stacking interactions create two-dimensional and three-dimensional supramolecular arrays, respectively, for complexes 1 and 2. Magnetic susceptibility and high-field electron paramagnetic resonance measurements show the presence of significant magnetic anisotropy, with an axial distortion parameter D of -8--10 cm-1.

Uncovering tetrazoles as building blocks for constructing discrete and polymeric assemblies.

Metal-organic self-assembly with flexible moieties is a budding field of research due to the possibility of the formation of unique architectures. Tetrazole, characterised by four nitrogen atoms in a five-member ring, exhibits immense potential as a component. Tetrazole offers four coordination sites for binding to the metal centre with nine distinct binding modes, leading to various assemblies. This review highlights different polymeric and discrete tetrazole-based assemblies and their functions. The meticulous manipulation of stoichiometry, ligands, and metal ions required for constructing discrete assemblies has also been discussed. The different applications of these architectures in separation, catalysis and detection have also been accentuated. The latter section of the review consolidates tetrazole-based cage composites, highlighting their applications in cell imaging and photocatalytic applications.

Probing assembly/disassembly of ordered molecular hydrogels.

Supramolecular hydrogels have a wide range of applications in the biomedical field, acting as scaffolds for cell culture, matrices for tissue engineering and vehicles for drug delivery. L-Phenylalanine (Phe) is a natural amino acid that plays a significant role in several physiological and pathophysiological processes (phenylketonuria and assembly of fibrils linked to tissue damage). Since Myerson et al. [Chem. Eng. Commun., 2002, 189(8), 1079-1090] reported that Phe forms a fibrous network in vitro, Phe's self-assembly processes in water have been thoroughly investigated. We have reported structural control over gelation by introduction of a halogen atom in the aromatic ring of Phe, driving changes in the packing motifs, and therefore, dictating gelation functionality. The additional level of control gained over supramolecular gelation via the preparation of multi-component gel systems offers significant advantages in tuning functional properties of such materials. Gaining molecular-level information on the distribution of gelators between the inherent structural and dynamic heterogeneities of these materials remains a considerable challenge. Using multicomponent gels based on Phe and amino-L-phenylalanine (NH2-Phe), we will explore the patterns of ordered/disordered domains in the gel fibres and will attempt to come up with general trends of interactions in the gel fibres and at the fibre/solution interfaces. Phe and NH2-Phe were found to self-assemble in water into crystalline hydrogels. The determined faster dynamics of exchange between the gel and solution states of NH2-Phe in comparison with Phe were correlated with weaker intermolecular interactions, highlighting the role of head groups in dictating the strength of intermolecular interactions. In the mixed Phe/NH2-Phe systems, at a low concentration of NH2-Phe, disruption of the network was promoted by interference of the aliphatics of NH2-Phe with the electrostatic interactions between Phe molecules. At high concentrations of NH2-Phe, multiple-gelator hydrogels were formed with crystal habits different from those of the pure gel fibres. NMR crystallography approaches combining the strengths of solid- and solution-state NMR proved particularly suitable to obtain structural and dynamic insights into the "ordered" fibres, solution phase and fibre/solution interfaces in these gels. These findings are supported by a plethora of experimental (diffraction, rheology, microscopy and thermal analysis) and computational methods.

Group 13 five- and six-membered rings with rare 2π aromaticity.

According to Hückel's rule, cyclic species are aromatic if they have 4n + 2 (n = 0, 1, 2, etc.) π electrons. However, large aromatic rings (atom number > 4) with minimum 2π electrons (i.e., n = 0) are rather rare because of the structural instability stemming from the deficient π electrons compared to the ring size. To date, the largest 2π-aromatic ring is a five-membered Ga5 core reported in a recent experiment. Herein, density functional theory calculations predicted seven inverse-sandwich Na2(MH)5 and half-sandwich Ca(MH)5 or Ca(MH)6 (M = Al, Ga or In) structures. They all have planar central five- or six-membered Al/Ga/In rings, rather negative binding energies and large HOMO-LUMO gaps. Their dianionic metal rings exhibit obvious aromatic characters and appreciable diatropic ring currents due to the good delocalization of 2π electrons donated by the Na/Ca metals. Interestingly, they also have novel collective bonding with the Na/Ca atoms interacting with both the metal ring and surrounding H atoms. These metalloaromatic rings not only greatly enrich the precious family of 2π aromatics, but also increase the maximum ring atom number from five to six, thus paving the way for Hückel-type 2π-aromatic large rings.

Unraveling hydrogen bond interactions between ketoconazole and imidazolium-based ionic liquids: An experimental and theoretical study

The solubility and solvation mechanism of the Biopharmaceutical Classification System class II insoluble drug, ketoconazole (KCZ), were investigated in eight different types of imidazolium-based ionic liquids (ILs). An in vitro cytotoxicity test was conducted on Human immortalized keratinocytes cells to evaluate the potential toxicity of these ILs. The results showed no cytotoxicity for any of the imidazolium-based ILs tested. The solubility of KCZ was then examined in the eight imidazolium-based ILs at temperatures ranging from 298.15 K to 338.15 K. The findings revealed that the solubility of KCZ followed a specific order among the imidazolium-based ILs tested. The imidazolium-based IL [BMIM][Tf2N] exhibited the highest solubility of KCZ, followed by [HMIM][PF6], [EMIM][Tf2N], [BMIM][TfO], [BMIM][PF6], [EMIM][TfO], [BMIM][BF4], and [EMIM][BF4] in decreasing order. To understand the interaction mechanism between the imidazolium-based ILs and KCZ, the cations, anions and KCZ were analyzed using σ-profiles computed from both the COSMO-RS model and quantum chemical calculations. The results indicated that KCZ had strong hydrogen bond (HB) acceptors, particularly the oxygen atom of the carbonyl group and the nitrogen atom of the imidazole ring. These HB acceptors contributed to the formation of stronger HBs with the hydrogen atoms of cations compared to the oxygen atoms of the anions. The trend of HB strength followed [Emim]+ > [Bmim]+ > [Hmim]+ > [Tf2N]− > [TfO]− > [PF6]− > [BF4]−. Based on these findings, it can be concluded that [BMIM][Tf2N], which has a strong HB donor cation and a strong HB acceptor anion, displayed the most effective dissolution of KCZ.

Structure of Tris[2-(4-pyridyl)ethyl]phosphine, Tris[2-(2-pyridyl)ethyl]phosphine, and Their Chalcogenides in Solution: Dipole Moments, IR Spectroscopy, and DFT Study.

Tris(hetaryl)substituted phosphines and their chalcogenides are promising polydentate ligands for the design of metal complexes. An experimental and theoretical conformational analysis of tris[2-(4-pyridyl)ethyl]phosphine, tris[2-(2-pyridyl)ethyl]phosphine, and their chalcogenides was carried out by the methods of dipole moments, IR spectroscopy and DFT B3PW91/6-311++G(df,p) calculations. In solution, these compounds exist as an equilibrium of mainly non-eclipsed (synclinal or antiperiplanar) forms with a predominance of a symmetrical conformer having a gauche-orientation of the Csp3-Csp3 bonds of pyridylethyl substituents relative to the P=X bond (X = lone pair, O, S, Se) and a gauche-orientation of the pyridyl rings relative to the zigzag ethylene bridges. Regardless of the presence and nature of the chalcogen atom (oxygen, sulfur, or selenium) in the studied molecules with many axes of internal rotation, steric factors-the different position of the nitrogen atoms in the pyridyl rings and the configuration of ethylene bridges-determine the realization and spatial structure of preferred conformers.

Ion valence-gated photochromism of an aza-crowned diarylethene.

A non-photochromic diarylethene 2o with an N-phenylaza-15-crown-5 was synthesized. When the nitrogen atom in the aza-crown ring was protonated, it became photochromic due to the prevention of a twisted intramolecular charge transfer (TICT). Although addition of a monovalent metal cation (Li+, Na+, K+, Rb+, Cs+, Cu+, Ag+) in acetonitrile could not stop the TICT so that it was not photochromic, the addition of a multivalent metal cation (Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, Ni2+, Al3+, Sb5+) changed 2o to be photochromic due to the strong attraction of the lone pair on the nitrogen atom. In the presence of excess Cu2+, 2o was oxidized to be EPR-detectable 2o·+, which was thermally unstable as well as inert towards visible-light irradiation. However, 2o·+ was further oxidized to be fairly stable 2o2+ by the irradiation of 365-nm light in the presence of Cu2+. ESI-MS measurements strongly suggested the generation of 2o·+ by mixing 2o with Cu(ClO4)2 in acetonitrile, and the transformation of 2o·+ to 2o2+ by successive 365-nm light irradiation. Fe3+ similarly worked as the oxidant, but the two-step oxidation of 2o to 2o2+ occurred more easily.

Two Isomers of a Novel Ag(I) Complex with Pyrazole-Type Ligand—Synthesis, Structural, Thermal, and Antioxidative Characterization

The synthesis of the first Ag(I) complexes with ethyl-5-amino-1-methyl-1H-pyrazole-4-carboxylate (L) is presented. The reaction of AgClO4 with the ligand in a molar ratio of 1:1 gives a bis(ligand) complex [AgL2]ClO4 (1) in the presence of 4-formylbenzonitrile, monoperiodic polymer {[AgL2]ClO4}n (2). Characterization involved IR spectroscopy, conductometric measurements, thermogravimetric analysis, antioxidant tests, powder, and single crystal X-ray diffraction. Structural analysis revealed ligand coordination in a monodentate manner through the nitrogen atom of the pyrazole ring in both complexes. Complex 1 displayed a linear coordination environment for Ag(I), whereas, in complex 2, square-planar coordination was achieved with the additional involvement of two oxygen atoms from bridging perchlorate anions. Notably, the thermal properties of both isomers are found to be nearly identical. The significant antioxidant activity of the isomer with a reverse-oriented pyrazole-type ligand suggests its potential relevance in biological studies.