Isomeric Ligands Research Articles

Trivial positional isomerism in ligands triggering different properties in Fe(II)-metallopolymers; design, synthesis, and characterization.

The tunable molecular scaffold of organic moieties in metallopolymers generates variation in their properties, but what could be the minimal change that can produce variation in the properties of these macromolecules is still untouched. This research has meticulously explored the trivial change in the molecular scaffold of the ligand capable of making a mammoth difference in the nonvolatile memory and coordination pattern in two metallopolymers. The significance of this research lies in the fact that it demonstrates how a slight change in the organic building block can significantly alter the memristive and fluorescence properties of iron(II) metallopolymers, opening up new possibilities for their design and synthesis. Two novel positional isomeric ligands and their corresponding iron(II)-polymers were synthesized and thoroughly characterized using NMR, XRD, ATR-IR, FESEM, AFM and other techniques. Bright orange solid and solution state fluorescence was observed both in the solid and solution states for ligand L2 (3,3'-bis((E)-(pyridin-3-ylimino)methyl)-[1,1'-biphenyl]-4,4'-diol), while ligand L1 (3,3'-bis((E)-(pyridin-2-ylimino)methyl)-[1,1'-biphenyl]-4,4'-diol) showed blue fluorescence in the solution state only. A robust memristive property for Fe(II)-L1-poly with a high current ON/OFF ratio of 104, remarkable random access behaviour, and a long retention time greater than 35 000 seconds was observed while its counterpart was entirely silent. Both polymers showed solution-state electrochromism. These synthesised metallopolymers also showed good specific capacitance in the range of 50-60 F g-1 with a remarkable retention of 98% of the initial value even after 5000 charge-discharge cycles. The AFM and FESEM micrographs revealed the formation of long polymer nano-rods, which correlates with the NMR, ATR-IR, and XRD results. The difference in the properties of polymers generated by such a slight change in the organic building block forces different coordination patterns of these two ligands around the same central metal ion, and this is also evident in all the characterization methods.

Pressure-induced single-crystal-to-single-crystal nitrite ligand isomerisation accompanied by a piezochromic effect.

High-pressure structural study of a piezochromic crystal of a rare di-exo-nitrito nickel(II) complex supported by computational analysis is presented. The examined system is not photoswitchable, however, in the 0-6.2 GPa pressure range the crystal undergoes two phase-transitions accompanied by a colour change and the nitrite ligand isomerisation, which is unique.

Rational design of adenine appended synthetic cobalt catalysts via click reaction for electrocatalytic hydrogen production

Green hydrogen has emerged as a critical component in the upcoming renewable energy landscape. Enzyme architecture remains the prime inspiration for designing environment-friendly, efficient, and economical H2 production catalysts from water. The strategic incorporation of peripheral protic functionalities around synthetic metal cores specifically impacts the electrocatalytic H2 evolution reactivity. Here, we have deployed a click chemistry methodology to incorporate a 1,2,3-triazole linker in either meta vs. para position to connect a cobaloxime core with nucleobase adenine. The variation in specific positioning (meta vs. para) of the linker creates two isomeric ligands and their corresponding cobaloxime derivatives. The trifunctional ligand motif positively influences the reactivity of the cobaloximes, as the para-substituted complex produces H2 at a rate of 5350 s−1 with an overpotential <350 mV in near-neutral aqueous conditions. The meta-substituted complex displayed relatively slower catalysis (rate 3700 s−1), albeit with similar energy efficiency under analogous conditions. These robust catalysts also demonstrated substantial H2 production from water under photocatalytic conditions with an appreciable turnover number (TON) of 150 and 100 for the para- and meta-substituted complexes, respectively. The complementary electrochemical and spectroscopic techniques indicate the designed ligand's dual effect (electronic and peripheral) on the catalytic reactivity, where the para-substituted pyridinyl ligand displayed better reactivity than the meta-derivative.

Comparative Analysis of the Donor Properties of Isomeric Pyrrolyl Phosphine Ligands

Comparative Analysis of the Donor Properties of Isomeric Pyrrolyl Phosphine Ligands

A theoretical study of the effect of phosphorus and nitrogen heteroatoms on pentahapto coordination of diazaphospholyl ligands in binuclear ruthenium and iron carbonyl derivatives

The structures and energies of the (Me2C2N2P)2Ru2(CO)n (n = 4, 3) complexes of the four isomeric diazaphospholyl ligands have been studied by density functional theory. Most of the low-energy structures in these systems have one or both diazaphospholyl rings bridging a central RuRu bond through RuN and/or RuP bonds without involvement of the other three ring atoms. A few higher energy structures are found in these systems having either terminal pentahapto η5-Me2C2N2P ligands or bridging η5,η1-Me2C2N2P ligands bonded to one ruthenium atom as a pentahapto ligand and to the other ruthenium atom through a P → Ru or N → Ru dative bond. The potential surfaces of the analogous iron systems (Me2C2N2P)2Fe2(CO)n (n = 4, 3) are complicated considerably by other triplet and even quintet structures of comparable energies to structures analogous to the low-energy ruthenium structures. This relates to the lower ligand field strengths of iron complexes as compared with their ruthenium analogues.

Regulating the Coordination Environment by Using Isomeric Ligands: Enhancing the Energy and Sensitivity of Energetic Coordination Compounds.

Transforming the energy storage structure is an effective approach to achieve a balance between the detonation performance and the sensitivity of energetic compounds, with a goal of high energy and low sensitivity. Building upon previous work, this study employed an isomeric compound 1H-pyrazole-3-carbohydrazide (3-PZCA) as a ligand and creatively designed the energetic coordination compound (ECC) Ag(3-HPZCA)2(ClO4)3 (ECC-1). It is a novel material with a dual structure of ionic salts and coordination compounds, which represents the first report of such a structure in Ag(I)-based ECCs. With its unique structures, ECC-1 exhibits a larger [ClO4-] content, a higher oxygen balance constant (OB = 0%), and superior mechanical sensitivity (IS = 13 J and FS = 40 N). Theoretical calculations indicate that ECC-1 has a higher detonation performance compared to previous work. Furthermore, the explosive experiment testing results demonstrate that it can be ignited by lower-threshold lasers and possesses excellent initiation capability and explosive power, making it suitable not only as a primary explosive but also as a secondary explosive.

Ligand and Linkage Isomers of Bis(ethylthiocarbamato) Copper Complexes with Cyclic C6H8 Backbone Substituents: Synthesis, Characterization, and Antiproliferation Activity.

A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3-methylpentyl (H2L2) and cyclohexyl (H2L3) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL2a/3a have two imino N and two S donors resulting in three five-member chelate rings (555 isomers). The kinetic isomers CuL2b/3b have one imino and one hydrazino N donor and two S donors resulting in four-, six-, and five-member rings (465 isomers). The 555 isomers have more accessible CuII/I potentials (E1/2 = -811/-768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E1/2 = -923/-854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL2a was potent (A549EC50 = 0.080 μM) and selective (IMR-90EC50/A549EC50 = 25) for A549. Its linkage isomer CuL2b had equivalent A549 activity, but lower selectivity (IMR-90EC50/A549EC50 = 12.5). The isomers CuL3a and CuL3b were less potent with A549EC50 values of 1.9 and 0.19 μM and less selective with IMR-90EC50/A549EC50 ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.

How Ligand Geometry Affects the Reactivity of Co(II) Cyclam Complexes

AbstractCobalt complexes are extensively studied as bioinspired models for non‐heme oxygenases as they facilitate both the stabilization and characterization of metal‐oxygen intermediates. As an analog to the well‐known Co(cyclam) complex Co{N4} (cyclam=1,4,8,11‐tetraazacyclotetradecane), the CoII complex Co{i‐N4} with the isomeric isocyclam ligand (isocyclam=1,4,7,11‐tetraazacyclotetradecane) was synthesized and characterized. Despite the identical N4 donor set of both complexes, Co{i‐N4} enables the 2e−/2H+ reduction of O2 with a lower overpotential (ηeff of 385 mV vs. 540 mV for Co{N4}), albeit with a diminished turnover frequency. Characterization of the intermediates formed upon O2 activation of Co{i‐N4} reveals a structurally identified stable μ‐peroxo CoIII dimer as the main product. A superoxo CoIII species is also formed as a minor product, as indicated by EPR spectroscopy. In further reactivity studies, the electrophilicity of these in situ generated Co−O2 species was demonstrated by the oxidation of the O−H bond of TEMPO−H (2,2,6,6‐tetramethylpiperidin‐1‐ol) via a H atom abstraction process. Unlike the known Co(cyclam), Co{i‐N4} can be employed in oxygen atom transfer reactions oxidizing triphenylphosphine to the corresponding phosphine oxide highlighting the impact of geometrical modifications of the ligand while preserving the ring size and donor atom set on the reactivity of biomimetic oxygen activating complexes.

One-Dimensional Coordinated Polymers of Tetraphenylethene Pyridine and Copper-Iodide for Fluorescence Detection of Nitroaromatic Explosives.

The spatial arrangement of molecules plays a crucial role in determining the macroscopic properties of functional materials. Coordinated polymers (CPs) formed by self-assembly of organic isomeric ligands and metals offer unique performance characteristics. In this study, we present the investigation of a one-dimensional CP, named CIT-E, composed of tetraphenylethene pyridine derivative (TPE-2by-2-E) ligands and cuprous iodide. The resulting CP exhibits a one-dimensional bead chain structure with exceptional thermal and chemical stability. By leveraging the competitive absorption between CIT-E and the explosive analog 2,4-dinitroaniline, we achieve detection of the explosive through changes in the absorption intensity of the excitation light source and subsequent fluorescence response. The CP demonstrates high selectivity and anti-interference ability in detecting 2,4-dinitroaniline in aqueous solution, with a detection linear range of 0.1 μM to 300 μM and a detection limit of 0.05 μM, surpassing the national third-level emission standard. These findings highlight the potential of CP CIT-E as a promising material for the detection of explosive nitroaromatic compounds.

The role of ligand isomerism in the solid-state structures of AgI formamidine complexes

The role of ligand isomerism in the solid-state structures of Ag^I formamidine complexes

Crystal Nanoarchitectonics and Characterization of the Octahedral Iron(III)–Nitrate Complexes with Isomer Dimethylurea Ligands

Three octahedral iron(III) nitrate complexes with dimethylated urea ligand isomers, [hexakis(N,N’-dimethylurea-O)iron(III)] nitrate (compound 1), trans-[diaquatetrakis(N,N-dimethylurea-O)iron(III)] nitrate (compound 2), and [hexakis(N,N-dimethylurea-O)iron(III)] nitrate trihydrate (compound 3) were prepared and characterized with single crystal X-ray diffraction, IR, Raman and UV–Vis methods. In compounds 1 and 3, six dimethylurea ligands coordinate to the central FeIII ion via the oxygen in octahedral geometry and the ligands are arranged in a propeller-like manner, dividing the complex cations into two sides. In compound 1, the dimethylurea propellers screw in the opposite direction on the two sides of the complex and in compound 3, they are arranged with the same handedness on the two sides. The complexes have helical chirality. The two sides of the complex cations differ not only in the rotation direction of the ligands but also in the hydrogen bond formation. On one side of the complex cation, the ligands form intermolecular hydrogen bonds only with the crystal waters, meanwhile on the other side of the complex, the ligands form hydrogen bonds only with the nitrate ions. In compound 2, [Fe(N,N-dimethylurea)4(H2O)2]3+ cations form layers that are separated by interconnected NO3− ions forming a hydrogen bonding system and connecting the complex cations A-s and B-s. The three crystallographically different nitrate ions each form four hydrogen bonds in a way that they have one bidentate O atom and two monodentate O atoms; however, the anions differ in their hydrogen bonding. The spectroscopic characteristics of compound 2 were determined by IR measurements on the deuterated compound 2 as well.

Interaction between a photoisomerizable azobenzene compound and alpha-lactalbumin: Spectroscopic and computational simulation studies

The combination of light and photoresponsive compounds provides a peculiar way of regulating biological systems. Azobenzene is a classical organic compound with photoisomerization properties. Exploring the interactions between azobenzene and proteins can deepen the biochemical applications of the azobenzene compounds. In this paper, the interaction of 4-[(2,6-dimethylphenyl)diazenyl]-3,5-dimethylphenol with alpha-lactalbumin was investigated by UV–Vis absorption spectra, multiple fluorescence spectra, computer simulations, and circular dichroism spectra. Most critically, the interaction differences between proteins and the trans- and cis-isomer of ligands have been analyzed and compared. Results showed that both isomers of ligands were bound to alpha-lactalbumin to form ground state complexes and statically quenched the steady-state fluorescence of alpha-lactalbumin. The van der Waals forces and hydrogen bonding dominated the binding; the difference is that the binding of the cis-isomer to alpha-lactalbumin is more rapidly stabilized, and the binding strength is greater than the trans-isomer. These binding differences were modeled and analyzed by molecular docking and kinetic simulations, and we found that both isomers bind through the hydrophobic aromatic cluster 2 of alpha-lactalbumin. However, the bent structure of the cis-isomer is more closely aligned with the construction of the aromatic cluster and may have contributed to the above differences.

Compressed and Expanded Lattices - Barriers to Spin-State Switching in Mn3+ Complexes.

We report the structural and magnetic properties of two new Mn3+ complex cations in the spin crossover (SCO) [Mn(R-sal2323)]+ series, in lattices with seven different counterions in each case. We investigate the effect on the Mn3+ spin state of appending electron-withdrawing and electron-donating groups on the phenolate donors of the ligand. This was achieved by substitution of the ortho and para positions on the phenolate donors with nitro and methoxy substituents in both possible geometric isomeric forms. Using this design paradigm, the [MnL1]+ (a) and [MnL2]+ (b) complex cations were prepared by complexation of Mn3+ to the hexadentate Schiff base ligands with 3-nitro-5-methoxy-phenolate or 3-methoxy-5-nitro-phenolate substituents, respectively. A clear trend emerges with adoption of the spin triplet form in complexes 1a-7a, with the 3-nitro-5-methoxy-phenolate donors, and spin triplet, spin quintet and thermal SCO in complexes 1b-7b with the 3-methoxy-5-nitro-phenolate ligand isomer. The outcomes are discussed in terms of geometric and steric factors in the 14 new compounds and by a wider analysis of electronic choices of Mn3+ with related ligands by comparison of bond length and angular distortion data of previously reported analogues in the [Mn(R-sal2323)]+ family. The structural and magnetic data published to date suggest a barrier to switching may exist for high spin forms of Mn3+ in those complexes with the longest bond lengths and highest distortion parameters. A barrier to switching from low spin to high spin is less clear but may operate in the seven [Mn(3-NO2-5-OMe-sal2323)]+ complexes 1a-7a reported here which were all low spin in the solid state at room temperature.

Consistent zincophosphite 4-ring 'ladder' chain structural motif with isomeric ligands.

The syntheses and crystal structures of four hydro-thermally prepared organo-zinc phosphites, viz. poly[[(2-amino-3-methyl-pyridine)-μ3-phospho-nato-zinc] hemihydrate], {[Zn(HPO3)(C6H8N2)]·0.5H2O} n , (I), poly[(2-amino-4-methyl-pyridine)-μ3-phospho-nato-zinc], [Zn(HPO3)(C6H8N2)] n , (II), poly[(2-amino-5-methyl-pyridine)-μ3-phospho-nato-zinc], [Zn(HPO3)(C6H8N2)] n , (III), and poly[bis-(2-amino-4-methyl-pyridinium) [tetra-μ3-phospho-nato-trizinc] monohydrate], {(C6H9N2)2[Zn3(HPO3)4]·H2O} n , (IV), are described. Compounds (I)-(III) are constructed from vertex-sharing ZnO3N tetra-hedra (the organic mol-ecule acting as a ligand) and HPO3 pseudo pyramids in a 1:1 ratio to generate the same motif of infinite 4-ring 'ladder' chains propagating in the [010], [101] and [100] directions, respectively, whereas (IV) consists of (010) layers of vertex-sharing ZnO4 and HPO3 units in a 3:4 ratio with the protonated organic mol-ecule acting as a template. When an excess of HCl is used in the synthesis, the simple hydrated mol-ecular salt, bis-(2-amino-3-methyl-pyridinium) tetra-chloro-zincate monohydrate, (C6H8N2)2[ZnCl4]·H2O, (V), arises. Com-pounds (I)-(V) feature extensive networks of hydrogen bonds, both classical (N-H⋯O, N-H⋯Cl, O-H⋯O) and non-classical (C-H⋯O, C-H⋯Cl) in nature, which help to consolidate the extended structures.

Reactivities of iron(IV)-oxido compounds with pentadentate bispidine ligands

The FeIVO complexes of bispidines (3,7-diazabicyclo[3.3.1]nonane derivatives) are known to be highly reactive oxidants – with the tetradentate bispidine, the so far most reactive ferryl complex has been reported and two isomeric pentadentate ligands also lead to very reactive high-valent oxidants. With a series of 4 new bispidine derivatives we now try to address the question why the bispidine scaffold in general leads to very reactive oxidants and how this can be tuned by ligand modifications. The study is based on a full structural, spectroscopic and electrochemical analysis of the iron(II) precursors, spectroscopic data of the iron(IV)-oxido complexes, a kinetic analysis of the stoichiometric oxidation of thioanisole by five different bispidine‑iron(IV)-oxido complexes and on product analyses of reactions by the five ferryl oxidants with thioanisole, β-methylstyrene and cis-stilbene as substrates.

Regulation of stability and detonation performance: preparation of coordination compounds by using isomeric ligands

By cutting off the reaction site and maintaining the coordination model, Cu(4-IMCA)2(ClO4)2 (ECC-1) was prepared. Compared to Cu(PZCA)2(ClO4)2, ECC-1 has reduced mechanical sensitivity, enhanced thermal stability, and increased detonation performance.

Nickel(II) Complexes of Octamethyl Tetraazamacrocycle and its N-Pendent Derivative: Syntheses, Characterization, Electrolytic Behaviour and Antimicrobial Activities

Octamethyl tetraazamacrocycle, Me8[14]diene·2HClO4 and its three isomeric ligands (LA, LB and LC) were synthesized and characterized using analytical and spectroscopic data, and the antibacterial activities were evaluated against selected bacteria and yeast. Interaction of LC with excess acrylonitrile resulted in an N-pendent derivative (LCX). Square planar nickel(II) diperchlorate complex of LC, [NiLCα](ClO4)2, underwent axial addition reactions with KI and NaNO2 to yield six coordinated octahedral species, [NiLCαI2]·2H2O and [NiLCα(NO2)(ClO4)]. Five coordinated square pyramidal Ni(II) complexes, [NiLCXCl](ClO4), [NiLCX(NCS)](NO3) and [NiLCXI](NO3), were synthesized from Ni(II) salts and tetraazamacrocyclic ligand LCX. Among the complexes, [NiLCXCl](ClO4) was synthesized through the direct interaction of NiCl2 with LCX, followed by the subsequent addition of NaClO4·6H2O. On the other hand, [NiLCX(NCS)](NO3) and [NiLCXI](NO3) as well as octahedral [NiLCXBr2] and [NiLCX(NO2)(NO3)] were synthesized by the interaction of LCX with different Ni(II) salts.

Optimization of performance and sensitivity: preparation of two Ag(I)-based ECPs by using isomeric ligands.

For energetic compounds, their structure determines their performance, and even minor variations in their structure can have a significant impact on their performance. The application scenarios for energetic materials are diverse, and their performance requirements vary as well. To investigate the influence of different substituent positions on the performance of primary explosives, we prepared two Ag(I)-based complexes, [Ag(2-IZCA)ClO4]n (ECPs-1) and [Ag(4-IZCA)ClO4]n (ECPs-2), using structurally isomeric ligands, 1H-imidazole-2-carbohydrazide (2-IZCA) and 1H-imidazole-4-carbohydrazide (4-IZCA). The structures were confirmed using infrared, elemental analysis, and single-crystal X-ray diffraction. Experimental results demonstrate that both ECPs exhibit good thermal stability. However, compared to ECPs-1, ECPs-2 exhibits a lower thermal initial decomposition temperature (Td = 210 °C), lower mechanical sensitivity (IS = 27 J, FS = 84 N), and more concentrated energy output. Although theoretical predictions suggest similar detonation velocities and pressures for both compounds, actual detonation performance tests indicate that ECPs-2 has stronger explosive power and initiating capability, with potential for use as a laser initiator (E = 126 mJ). The simple preparation method and inexpensive starting materials enrich the research on primary explosives.

Alkali Metal Complexes of an Octamethyl Isomeric Macrocycle: Synthesis, Characterization and Antimicrobial Studies

Fourteen membered octamethyl tetraazamacrocyclic ligand salt, Me8[14]diene·2HClO4 and three isomeric ligands (LA, LB and LC) of its saturated analog have been synthesized as per literature. Interaction between the isomeric ligand LB and KX (X = SCN, NO3, Cl, Br and I) afforded white-coloured five coordinated square pyramidal potassium complexes [KLBX]. Moreover, the reaction between RbCl and LB produced five coordinated [RbLBCl] having square pyramidal geometry. Then, the axial substitution reaction on [RbLBCl] furnished a substituted rubidium complex with the same geometry of the mother complex. All the alkali metal complexes have been characterized by using modern analytical techniques. Furthermore, antibacterial and antifungal activities of ligand LB and its alkali metal (K and Rb) complexes have been investigated against different bacteria and fungi.

Regio-isomerism directed electrocatalysis for energy efficient zinc-air battery

SummaryWe have investigated the role of ligand isomerism in modulating the mechanisms and kinetics associated with charge/discharge chemistry of an aqueous metal-air battery. The dominant electron-withdrawing inductive effect (-I effect) and the diminished electron-withdrawing resonance effect (-R effect) in the α-NO2 isomer noticeably diminishes the rate of oxygen reduction (ORR) and oxygen evolution reactions (OER) on the catalytic Co-center. In their β-counterpart, the cumulative –I and –R effects noticeably enhance the OER and ORR kinetics on the same catalytic Co-center. Therefore, the regioisomerism of the -NO2 functionality amplifies the kinetics of ORR/OER without influencing their mechanistic pathways. When isomeric electrocatalysts are integrated to aid the charge chemistry of a Zn-air battery, the overpotential could be decreased by ∼250 mV with β-NO2 isomer leading to a round-trip efficiency as high as 60%. This work contributes to the design of novel molecular platforms to target the overall round-trip efficiency of energy storage and conversion devices.