Central Metal Ion Research Articles

Remarkably Enhanced Luminol/H2O2 Chemiluminescence with Excellent Peroxidase-like Activity of FeCoNi-based Metal-Organic Xerogels for the Sensitive Detection of Dopamine.

Metal-organic gels (MOGs) are a category of metal-organic smart soft materials with large specific surface areas, loose porous structures, and open metal active sites. In this work, trimetallic Fe(III)Co(II)Ni(II)-based MOGs (FeCoNi-MOGs) were synthesized at room temperature via a simple and mild one-step procedure. Fe3+, Co2+, and Ni2+ were the three central metal ions in it, while 1,3,5-benzenetricarboxylic acid (H3BTC) served as the ligand. The solvent enclosed in it was then removed by freeze-drying to get the corresponding metal-organic xerogels (MOXs). The as-prepared FeCoNi-MOXs have excellent peroxidase-like activity and can significantly enhance luminol/H2O2 chemiluminescence (CL) by more than 3000 times, which is very effective compared with other reported MOXs. Based on the inhibitory effect of dopamine on the CL of the FeCoNi-MOXs/luminol/H2O2 system, a simple, rapid, sensitive, and selective CL method for dopamine detection was established with a linear range of 5-1000 nM and a limit of detection of 2.9 nM (LOD, S/N = 3). Furthermore, it has been effectively used for the quantitative measurement of dopamine in dopamine injections and human serum samples, with a recovery rate of 99.5-109.1%. This research brings up prospects for the application of MOXs with peroxidase-like activity in CL.

Photoactive hourglass-type M{P 4Mo 6} 2 networks for efficient removal of hexavalent chromium

The exploration of high-efficiency photocatalysts to drive the conversion of highly toxic heavy metal hexavalent chromium (Cr(VI)) in wastewater to low-toxic trivalent chromium (Cr(III)) is of great significance for purifying water that contains emerging contaminants. Herein, four hourglass-type phosphomolybdate-based hybrid networks—(H₂bpe)₂[M(H₂O)₃]₂{M[P₄Mo₆O₃₁H₇]₂}·8H₂O <strong>(</strong>M = Mn for <strong>1</strong>, Co for <strong>2</strong>) and (Hbpe)(H₂bpe)Na[M(H₂O)₃]₂{M[P₄Mo₆O₃₁H₇]₂}·9H₂O <strong>(</strong>M = Mn for <strong>3</strong>, Co for <strong>4</strong>; {M[P₄Mo₆O₃₁H₇]₂}⁸⁻ (abbr. M{P₄Mo₆}₂); bpe = 1,2-di(4-pyridyl)ethylene)—were hydrothermally synthesized as heterogeneous photocatalysts for Cr(VI) reduction. A structural analysis showed that the four hybrids <strong>1</strong>–<strong>4</strong> exhibited two-dimensional inorganic sheet-like structures with a 3,6-connected <i>kgd</i> topology built of hourglass phosphomolybdate clusters having different central metal ions, which further interacted with organic bpe cations via abundant hydrogen-bonding interactions to extend the structure to a three-dimensional (3D) supramolecular network. The four hybrids displayed excellent redox properties and wide visible-light absorption. When used as heterogeneous photocatalysts, hybrids <strong>1</strong>–<strong>4</strong> exhibited excellent photocatalytic activity for Cr(VI) reduction under 10 W white light irradiation, with reduction rates of 91% for <strong>1</strong>, 74% for <strong>2</strong>, 90% for <strong>3,</strong> and 71% for <strong>4</strong>, respectively, within 80 min. The Cr(VI) reduction reaction over hybrids <strong>1</strong>–<strong>4</strong> followed the pseudo first-order kinetics model with reaction rate constants <i>k</i> of 0.0237 min⁻¹ for <strong>1</strong>, 0.0143 min⁻¹ for <strong>2</strong>, 0.0221 min⁻¹ for <strong>3</strong> and 0.0134 min⁻¹ for <strong>4</strong>, respectively. The Mn{P₄Mo₆}₂-based hybrids <strong>1</strong> and <strong>3</strong> showed better photocatalytic performance than the Co{P₄Mo₆}₂-based hybrids <strong>2</strong> and <strong>4</strong>, along with excellent recycle stability. This mechanism study shows that the different central metals M in the M{P₄Mo₆}₂ cluster have a considerable impact on photocatalytic performance due to their regulation effect on the electronic structure. This work provides evidence for the important role of the central metal in hourglass-type phosphomolybdate in the regulation of photocatalytic performance, and it brings inspiration for the design of highly efficient photocatalysts based on polyoxometalates.

Improving yields by switching central metal ions in porphyrazine-catalyzed oxidation of glucose into value-added organic acids with SnO2 in aqueous solution.

Photocatalysis has exhibited huge potential in selective conversion of glucose into value-added chemicals. Therefore, modulation of photocatalytic material for selective upgrading of glucose is significant. Here, we have investigated the insertion of different central metal ions, Fe, Co, Mn, and Zn, into porphyrazine loading with SnO2 for access to more efficient transformation of glucose into value-added organic acids in aqueous solution at mild reaction conditions. The best selectivity for organic acids containing glucaric acid, gluconic acid, and formic acid of 85.9% at 41.2% glucose conversion was attained by using the SnO2/CoPz composite after reacting for 3h. The effects of central metal ions on surficial potential and related possible factors have been studied. Experimental results showed that the introduction of metalloporphyrazine with different central metal ions on the surface of SnO2 has a significant effect on the separation of photogenerated charges, changing the adsorption and desorption of glucose and products on the catalyst surface. The central metal ions of cobalt and iron contributed more to the positive effects toward enhancing conversion of glucose and yields of products, and manganese and zinc contributed more to the negative effects, resulting in the poor yield of products. The differences from the central metals may attribute to the surficial potential change of the composite and the coordination effects between the metal and oxygen atom. An appropriate surficial potential environment of the photocatalyst may achieve a better interactive relationship between the catalyst and reactant, while appropriate ability of producing active species matched with adsorption and desorption abilities would gain a better yield of products. These results have provided valued ideas for designing more efficient photocatalysts in selective oxidation of glucose utilizing clean solar energy in the future.

Effect of solvent and auxiliary ligand on catecholase activities of Mn(III) complexes: A comparative study

A mononuclear Mn(III) complex with composition [MnIIIL(Cl)] (1) has been utilized to prepare two new complexes, [MnIIIL(N3)(CH3OH)] (2) and [MnIIIL(μ1,3-NCS)]n (3), by substitution of the auxiliary ligand. The ligand utilized for preparation of 1 is a Schiff base (H2L), obtained by 2:1 condensation of 3-Chlorosalicylaldehyde and ethylene diamine in methanol. The chloride anion, present in the coordination sphere of the central metal ion in 1 has been replaced by two other auxiliary ligands, azide and thiocyanate, in 2 and 3, respectively. All of the three complexes behaved as bio-functional models of catechol oxidase toward oxidation of 3,5-di-tert butyl catechol (3,5-DTBC). A detailed kinetic investigations were carried out for 2 and 3 in methanol, acetonitrile and N,N′-Dimethyl formamide (DMF) separately and the corresponding turn-over numbers have been determined. The ESI-MS spectra of the substrate-catalyst mixtures in acetonitrile and methanol confirmed formation of catecholate bound Mn(III) intermediate in the mass spectral time scale. The progress of the catechol oxidation was monitored by 1H-NMR spectroscopy with the reaction mixtures containing complex-substrate ratio at 1:20 after stirring in acetonitrile as well as methanol at room temperature in open air. NMR spectral data confirmed completion of the process in 90 minutes and 45 minutes for 2 and 3, respectively. Notably, in absence of any of these complexes, aerobic oxidation of 3,5-DTBC to the corresponding quinone is negligible even after twenty four hours of mixing in the same solvent. This observation is a clear indicative of high catalytic efficiencies of the prepared complexes.

Modeling of transition metals coordination polymers of benzene tricarboxylate and pyridyl oxime-based ligands for application as antibacterial agents

Theoretical simulation involving density functional theory (DFT) computation and molecular docking has been utilized to investigate in detailed the reactivity, stability, bond interactions, and the antibacterial potential of coordination polymers constructed with pyridyl oxime and benzene tricarboxylate linkers is based on the earlier experimental studies reported by Ioannis et al., Molecules, 26 (2), 491, 2021. Five (5) complexes: [Zn(BTC)2(PyOx)2] [Cu(BTC)2(PyOx)2], [Ni(BTC)2(PyOx)2], [Co(BTC)2(PyOx)2], [Fe(BTC)2(PyOx)2] were investigated and the DFT calculations was accomplished using a combined basis sets of 6-311++G (2d,2p) and LanL2DZ for the ligands and central metal ions respectively at the B3LYP functional. Structurally, all five complexes showed tetrahedral geometry after optimization due to the bulkiness of the linkers with excellent linearity in bond lengths. Based on quantum chemical simulations, [Ni(BTC)2(PyOx)2] was observed to be the most reactive complex with lower energy gap of 1.45 eV whereas Co(BTC)2(PyOx)2] was said to be the most stable complex with high energy gap of 7.19eV which is in tandem with results from the natural bond orbital analysis (NBO). The potency of all complexes in combating multidrug resistance pathogens were studied by molecular docking analysis, [Ni(BTC)2(PyOx)2] have the most favorable docking score of -9.2 kcal/mol and excellent hydrogen bond interaction. This result is also in good agreement with the quantum descriptors. Thus, [Ni(BTC)2(PyOx)2] exhibits potentials to combat multidrug resistance pathogens.

Investigation of Biological Activities of Tetra‐substituted Phthalocyanines Bearing Tetraethyleneglycol Monomethyl Ether Chains at Peripheral and Non‐peripheral Positions

AbstractThis study describes the synthesis and characterization of peripherally and non‐peripherally substituted copper(II) and cobalt(II) phthalocyanines bearing tetraethyleneglycol monomethyl ether chains. In addition, the metal‐free and zinc(II) phthalocyanine derivatives were prepared according to the referred procedure. All newly synthesized phthalocyanines were characterized using some spectroscopic techniques such as elemental analysis and fourier transform infrared, ultraviolet‐visible, and mass spectroscopies. The effects of solvent type and concentration on aggregation properties of phthalocyanines were studied, as well. The biological activities of a series of these peripherally and non‐peripherally tetra‐substituted phthalocyanines were investigated. The effects of the central metal ion and the position of the substituent on biological activities of phthalocyanines were also compared. When the antioxidant activities of the synthesized molecules were evaluated by the 2,2‐diphenyl‐1‐picrylhydrazyl method, 1,8/11,15/18,22/25‐tetrakis[2‐(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)ethoxy]phthalocyaninatocobalt(II) (63.17±0.012 %) showed the highest activity. The highest reducing power activity was obtained with the 2,9/10,16/17,23/24‐tetrakis[2‐(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)ethoxy]phthalocyaninatozinc(II) molecule. In the antibacterial activity studies using the disc diffusion method, 2,9/10,16/17,23/24‐tetrakis[2‐(2‐(2‐(2‐methoxyethoxy) ethoxy)ethoxy)ethoxy]phthalocyaninatocopper(II) exhibited the highest inhibition activity on both gram negative (18±0.23 mm) and gram positive (23±0.07 mm) strains. On the other hand, 2,9/10,16/17,23/24‐tetrakis[2‐(2‐(2‐(2‐methoxyethoxy)ethoxy) ethoxy)ethoxy]phthalocyaninatozinc(II) and 1,8/11,15/18,22/25‐tetrakis[2‐(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)ethoxy]phthalo‐cyaninatozinc(II) compounds presented hemolytic activity against sheep blood in the hemolytic activity studies. The results confirmed that the synthesized molecules demonstrated average antioxidant activity compared to standard antioxidants. 2,9/10,16/17,23/24‐Tetrakis[2‐(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)ethoxy]phthalo‐cyaninatocopper(II), 2,9/10,16/17,23/24‐tetrakis[2‐(2‐(2‐(2‐methoxy ethoxy)ethoxy)ethoxy)ethoxy]phthalocyaninatozinc(II) and 1,8/11, 15/18,22/25‐tetrakis[2‐(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy) ethoxy]phthalocyaninatozinc(II) complexes could remarkably inhibit S. aureus and CuPc‐1 complex E. coli growth.

Synthesis, characterization, photocatalytic activity, DNA interaction and antimicrobial studies of some lanthanide(III) complexes with a tridentate Schiff base ligand

Lanthanide complexes of Sm(III), Nd(III), and Dy(III) with a Schiff base ligand, (potassium2-((4-hydroxy-3-methoxybenzylidene)amino)acetate, derived from condensation of 4-hydroxy-3-methoxybenzaldehyde and 2-aminoethanoic acid were synthesized. The compounds were characterized by elemental analysis, IR, UV–Vis, 1H-NMR, ESI-MS, photoluminescence spectra, thermogravimetric analysis, magnetic susceptibility, and molar conductivity measurements. No well-defined peaks were observed in X-ray diffractograms of the synthesized complexes, indicating an amorphous nature. The Schiff base ligand is tridentate and coordinated with the metal ion through phenolic oxygen, azomethine nitrogen, and carboxylic oxygen. Thermal properties of the metal complexes were studied using thermogravimetric analysis (TG/DTG) and revealed good thermal stability. The photocatalytic efficiencies of the complexes were explored using solar water-splitting. The optical band gaps (E g) were measured and found to be 2.94, 2.86, and 2.82 eV for Sm(III), Nd(III), and Dy(III) complexes, respectively. These values indicated the semi-conducting nature of the investigated complexes. At room temperature, samarium and dysprosium complexes showed characteristic luminescence of the central metal ions ascribed to the efficient transfer of energy from the Schiff base ligand to the metal center under excitation at 390 nm. The binding properties of these complexes with calf-thymus DNA (CT-DNA) have been investigated using absorption spectrophotometry and fluorescence studies. The physicochemical properties such as hydrodynamic size, zeta potential, and stability of the DNA/complexes were also investigated. DNA cleavage activities of the compounds were assayed using the Agarose gel electrophoresis method. In-vitro antimicrobial activities of the compounds were screened against selected pathogenic strains by Agar well diffusion method.

Binuclear Mn(III) and Fe(III) porphyrin nanostructured materials in catalytic reduction of 4-nitrophenol

Biomimetic reduction reactions may disclose alternatives to the use of noble metals or transition metals of late series that are expensive, toxic, or scarcer. In this work, binary nanostructured materials carrying positive and negative iron (III) and manganese (III) porphyrins were prepared by ionic self-assembly, in a simple and eco-sustainable way, and characterized by SEM, XRD, UV–vis and XPS. The materials were evaluated as catalysts in the reduction of 4-nitrophenol in water, using NaBH4 as a reductant. The effect of the crystallite structures, of the nature of the dual metal ion centers and of solar light, in the catalyst activity were also evaluated. The highest activity was observed for a heterobimetallic [Mn/Fe] material carrying Fe(III) and Mn(III) porphyrins as positive and negative tectons, respectively, leading to complete conversion of the 4-nitrophenol in 3 min under simulated solar light, and the results evidence a synergy between the two metal centers. This material was reused in successive catalytic cycles until the 7th cycle.

Liquid-assisted mechanochemical synthesis, crystallographic, theoretical and molecular docking study on HIV instasome of novel copper complexes: (µ-acetato)-bis(2,2'-bipyridine)-copper and bromidotetrakis(2-methyl-1H-imidazole)-copper bromide.

In the present work the two new Cu(II) complexes, (µ-acetato)-bis(2,2'-bipyridine)-copper [Cu(bpy)2(CH3CO2)] and bromidotetrakis(2-methyl-1H-imidazole)-copper bromide [Cu(2-methylimid)4Br]Br have been synthesized by liquid assisted mechanochemical method. The [Cu(bpy)2(CH3CO2)] complex (1) and [Cu(2-methylimid)4Br]Br complex (2) characterised by IR and UV-visible spectroscopy and the structure are confirmed by XRD diffraction studies. Complex (1) crystallized in the Monoclinic with the space group of C2/c where a = 24.312(5)Å, b = 8.5892(18)Å, c = 14.559(3)Å, α = 90°, β = 106.177(7)° and γ = 90° and Complex (2) crystallized in the Tetragonal with the space group of P4nc, a = 9.9259(2)Å, b = 9.9259(2)Å, c = 10.9357(2)Å, α = 90°, β = 90° and γ = 90°. The complex (1) has distorted octahedral geometry where the acetate ligand showed bidentate bridging with the central metal ion and complex (2) has slightly deformed square pyramidal geometry. The HOMO-LUMO energy gap value and the low chemical potential showed that the complex (2) is stable and difficult to polarize compare to complex (1). The molecular docking study of complexes with the HIV instasome nucleoprotein showed the binding energy values -7.1 and -5.3kcal/mol for complex (1) and complex (2) respectively. The negative binding energy values showed the complexes have affinity to bind with HIV instasome nucleoproteins. The in-silico pharmacokinetic study of the complex (1) and complex (2) showed non AMES toxicity, non-carcinogens and low honey Bee toxicity but weakly inhibit Human Ether-a-go-go-related gene.

Complexes of 2-Amino-3-methylpyridine and 2-Amino-4-methylbenzothiazole with Ag(I) and Cu(II): Structure and Biological Applications

Coordination complexes (1–4) of 2-amino-4-methylbenzothiazole and 2-amino-3-methylpyridine with Cu(CH3COO)2 and AgNO3 were prepared and characterized by UV/Vis and FT-IR spectroscopy. The molecular structure for single crystals of silver complexes (2 and 4) were determined by X-ray diffraction. The coordination complex (2) is monoclinic with space group P21/c, wherein two ligands are coordinated to a metal ion, affording distorted trigonal geometry around the central Ag metal ion. The efficient nucleophilic center, i.e., the endocyclic nitrogen of the organic ligand, binds to the silver metal. Ligands are coordinated to adopt cis arrangement, predominantly due to steric reasons. The O(2) and O(3) atoms of the NO3− group further play an important role in such type of ligand arrangement by hydrogen bonding with the NH2 group of ligands. Complex (4) is orthorhombic, P212121, comprising two molecules of 2-amino-3-methylpyridine as ligand coordinated with the metal ion, affording a polymeric structure. The coordination behavior of the ligand is identical to that in complex 2, wherein ring nitrogen is coordinated to the metal center and bridged to another metal ion through an NH2 group. The resulting product is polymeric in nature with the Ag metal in the backbone and ligand as the bridge. Compounds (2–4) were found to be luminescent, while 1 did not show such activity. All compounds were screened for their preliminary biological activities such as antibacterial, antioxidant and enzyme inhibition. Compounds exhibited moderate activity in these tests.

Influence of the transition metals central atom nature on the optical and electrophysical properties of phthalocyanine nanowires

In the present work, phthalocyanine nanowires were obtained on the surface of glass substrates with an ITO coating. The presence of α, β, and χ crystalline phases, which are formed in the course of synthesis was demonstrated using XRD. Measurement of the absorption spectra showed that the observed change in the shape of the absorption bands is associated with the formation of phase states and the relationship between the tendency of the central metal ion to leave the phthalocyanine plane and the value of the Davydov splitting. It was found that the high-value conductivity of the nanowires is explained by the possibility of the π-electrons transition depending on the metal ion, over the states of overlapping phthalocyanine rings. An analysis of the obtained results showed that additional energy states are involved in the charge transfer mechanism, which is formed during the coordination interaction of metal ions with an organic ligand.

Front Cover: A Thermodynamic Model for the Insertion Electrochemistry of Battery Cathodes (ChemElectroChem 7/2023)

The Front Cover illustrates a crystal layer of nickel hydroxide that undergoes phase separation during electrochemical ion deinsertion (oxidation) and its corresponding cyclic voltammogram (CV). This phase separation phenomenon is revealed by a thermodynamic modelling of solid-solution and phase-separation reaction modes in battery cathodes. Furthermore, according to this model, the hysteresis observed during charge-discharge in the CV curves results from this phase separation which itself is a consequence of large radius changes in the crystal's central metal ion. More information can be found in the Research Article by K. Malaie, F. Scholz and U. Schröder.

Meso‐substituted Metalloporphyrin‐based Composites for Electrocatalytic Oxygen Reduction Reactions

AbstractMetalloporphyrins have been regarded as one of the most promising electrocatalysts for oxygen reduction reactions (ORRs) due to their ease of structure modification and the robust coordinated M−N4 environment. However, the electrocatalytic activity, selectivity and stability of the metalloporphyrin‐based composite catalysts are often reported to be much poorer than those of the Pt‐based materials, arousing researchers to devote to exploring a thorough understanding of the relationship between the catalyst structures and ORR performance/mechanisms. Here we will review the design ofmeso‐positioned porphyrin structures from the aspects of selection of central metal ion species in both monometallic and bimetallic molecules, and modulation of peripheral functional substituents to introduce beneficial effects, including electron affinity, steric effects, interfacial charge states and proton management. Influences from different carbon materials as the support for composite catalysts as well as the electrolytes on oxygen reduction properties will be briefly illustrated before presenting the perspectives and insights for future works in conclusion remarks. We hope that this Review will serve as a roadmap for advancing the insights of the molecular structural and substrate morphological factors impacting ORR properties with the ultimate goal of developing and improving novel metalloporphyrins as efficient and durable electrocatalysts to champion the precious Pt/C.

Synthesis, Molecular, and Supramolecular Structures of Two Azide-Bridged Cd(II) and Cu(II) Coordination Polymers

Two 1D coordination polymers were synthesized by reaction of two ligands, 2-amino-4-picoline (2A4Pic) and quinoline-6-carboxylic acid (Qu-6-COOH) with two metal (II) nitrate (M = Cd and Cu) in the presence of azide as a linker. The synthesized metal complexes [Cd(2A4Pic)2(N3)2]n; (1) and [Cu(Qu-6-COO)(N3)(H2O)]n; (2) were isolated in single crystals and their X-ray structures revealed a 1D polymeric structure. Due to symmetry considerations, the asymmetric formula is half a [Cd(2A4Pic)2(N3)2] unit for 1 and one [Cu(Qu-6-COO)(N3)(H2O)] unit for 2. In complex 1, the Cd(II) is hexa-coordinated with two 2A4Pic molecules and four μ(1,1) azide units. Hence, the CdN6 coordination environment has a slightly distorted octahedral geometry. In 2, the Cu(II) is hexa-coordinated with three different ligands (Qu-6-COO¯, H2O and μ(1,1) N3¯) where all are connectors between the crystallographically related Cu(II) sites. Additionally, complex 2 distorted CuN2O4 octahedral geometry. In both complexes, the polymer arrays are connected by N…H hydrogen bonds and π–π stacking interactions. Based on Hirshfeld analysis, the percentages of N…H contacts are 43.1 and 27.4% for 1 and 2, respectively, while %C...C are 5.6 and 9.3%, respectively. Analysis of Cu-N, Cu-O, and Cd-N bonds using DFT calculations showed predominantly closed-shell coordination interactions with little covalent characters. Additionally, the negatively charged ligand groups were found to compensate the positive charge of the central metal ion to a larger extent than the electrically neutral ligands.

Observation of Exchange Interaction in Iron(II) Spin Crossover Molecules in Contact with Passivated Ferromagnetic Surface of Co/Au(111).

Spin crossover (SCO) complexes sensitively react on changes of the environment by a change in the spin of the central metallic ion making them ideal candidates for molecular spintronics. In particular, the composite of SCO complexes and ferromagnetic (FM) surfaces would allow spin-state switching of the molecules in combination with the magnetic exchange interaction to the magnetic substrate. Unfortunately, when depositing SCO complexes on ferromagnetic surfaces, spin-state switching is blocked by the relatively strong interaction between the adsorbed molecules and the surface. Here, the Fe(II) SCO complex [FeII (Pyrz)2 ] (Pyrz = 3,5-dimethylpyrazolylborate) with sub-monolayer thickness in contact with a passivated FM film of Co on Au(111) is studied. In this case, the molecules preserve thermal spin crossover and at the same time the high-spin species show a sizable exchange interaction of > 0.9 T with the FM Co substrate. These observations provide a feasible design strategy in fabricating SCO-FM hybrid devices.

Crystal Design for Tuning the Mechanical Flexibilities of M(salophen) Complexes

Elastic crystals are a novel class of materials for use in optoelectronics and solar cells. Although controlling mechanical flexibility is critical when developing functional soft crystals, the number of reported metal-coordination-complex-based elastic crystals is limited. When developing such crystals, the flexibility of the crystals may be tuned via ligand substitution of the central metals or by exchange of the central metal ions; however, this has not been demonstrated experimentally to date. Thus, we herein report the preparation of mechanically flexible compounds using a synthetic procedure based on metal coordination complexes. It was found that the packing structure was considerably affected by the crystallization solvent, and control over the packing process was critical in obtaining complex molecules with designed flexibilities and structures. Furthermore, we demonstrate new Pd and Pt complexes with the salophen ligand, which exhibit the second and third highest elastic strains (ε values) reported to date, respectively, and the highest and second highest ε values (ε = 11.95% for Pd; 10.65% for Pt), respectively, among metal coordination complexes. These effects can be attributed to the microscopic changes in bond distance between the metals and ligands. Our findings are expected to inspire the tuning and development of metal-complex-based flexible crystals.

Electrochemical, Antimicrobial, and Theoretical Investigations of Synthetic tetra-aza/penta-aza-Macrocyclic Complexes

The tailoring of the coordination environment around a central metal ion by changing ligands in macrocyclic complexes is one of the key approaches to monitoring their functions in various applications. Herein, two macrocyclic complexes of Co(II) transition metal ion, tetra-aza and penta-aza, were synthesized using a condensation reaction between different diamine and dicarboxylic precursors. The prepared complexes were analyzed using various characterization techniques. Further, the electrochemical behavior of both the tetra-aza and penta-aza complexes was investigated using cyclic voltammetry. The Co(II)-penta-aza-complex exhibited a quasi-reversible redox couple for Co(III)/Co(II) transition in the more anodic region as compared to Co(II)-tetra-aza-complex. According to theoretical calculations, the fifth N-coordination transferred a high electron density in the eg-orbital of Co-atom of penta-aza-complex, resulting in an anodic shift in the Co(III)/Co(II) redox potential when compared to the Co(II)-tetra-aza-complex. Furthermore, both complexes were tested for antimicrobial activity against P. aeruginosa, E. coli, S. aureus, and B. subtilis, with the results indicating that Co(II)-penta-aza-complex had higher antimicrobial activity against these bacteria than Co(II)-tetra-aza-complex. This study offers new insight into tailoring the electrochemical and biological features of macrocyclic complexes by tuning the coordination environment around the central metal ion.

Nanostructured binuclear Fe(III) and Mn(III) porphyrin materials: Tuning the mimics of catalase and peroxidase activity

Tuning of the structures and electronic effects of nanocrystals is of great relevance to the preparation of specialized materials such as artificial enzymes.In this study, binary porphyrin materials have been prepared by ionic self-assembly of oppositely charged Fe(III) and Mn(III) porphyrins. The materials have been characterized by SEM, XPS and UV–vis spectroscopy and tested as biomimetic models of catalase. The heterometallic material [Mn/Fe], prepared by association of MnTHPyP and FeTSPP, showed the highest activity for H2O2 dismutation reaction, 89–95 U·mg−1, over a pH range of 4–7. An enhancement in activity of one to two orders of magnitude can be observed relatively to the individual Fe(III) or Mn(III) porphyrins and to the mono-metallic materials that were prepared by association of a metalloporphyrin (MP) and a metal free porphyrin (H2P). These results support the occurrence of cooperative mechanisms between two metal ion centers within the structure. The materials with the highest catalase-like activity were also tested as peroxidase mimetics in ABTS oxidation. Best activity was observed for the [Mn/Fe] material at pH 4, while at pH 6 the activity decreases by 97%. EPR studies at pH 6 demonstrate the absence of free hydroxyl or superoxide radicals in the mechanism and thus support the activity of the [Mn/Fe] material as a catalytic antioxidant under these conditions.

Synthesis and Characterization of Zinc(II), Cadmium(II), and Palladium(II) Complexes with the Thiophene-Derived Schiff Base Ligand.

Zn(II), Pd(II), and Cd(II) complexes, [L TH MCl 2 ] (M = Zn, Pd; X = Br, Cl) and [L TH Cd(μ-X)X] n (X = Cl, Br; n = n, 2), supported by the (E)-N 1,N 1-dimethyl-N 2-(thiophen-2-ylmethylene)ethane-1,2-diamine (L TH ) ligand are synthesized and structurally characterized. Density functional theory (DFT) electronic structure calculations and variable-temperature NMR support the presence of two conformers and a dynamic interconversion process of the minor conformer to the major one in solution. It is found that the existence of two relevant complex conformers and their respective ratios in solution depend on the central metal ions and counter ions, either Cl- or Br-. Among the two relevant conformers, a single conformer is crystallized and X-ray diffraction analysis revealed a distorted tetrahedral geometry for Zn(II) complexes, and a distorted square planar and square pyramidal geometry for Pd(II) and Cd(II) complexes, respectively. It is shown that [L TH MCl 2 ]/LiO i Pr (M = Zn, Pd) and [L TH Cd(μ-Cl)Cl] n /LiO i Pr can effectively catalyze the ring-opening polymerization (ROP) reaction of rac-lactide (rac-LA) with 94% conversion within 30 s with [L TH ZnCl 2 ]/LiO i Pr at 0 °C. Overall, hetero-enriched poly(lactic acid)s (PLAs) were provided by these catalytic systems with [L TH ZnCl 2 ]/LiO i Pr producing PLA with higher heterotactic bias (P r up to 0.74 at 0 °C).

Intramolecular Ferromagnetism in Di-Nuclear 3 d-Transition-Metal Single-Molecule Magnets by Pseudo-Serial Arrangement.

Di-nuclear citrate complexes, [CH6 N3 ]2 [M2 (citH)2 (H2 O)4 ] ⋅ 2H2 O (citH4 =citric acid; M=FeII (Fe-2), CoII (Co-2), and NiII (Ni-2)), are synthesized. The ligand, citH3- , is deprotonated only at the three carboxy groups, which is different from the previously reported tetra-nuclear structures with cit4- ligands. Magnetic measurements reveal that these complexes have intramolecular ferromagnetism with J=∼0 cm-1 (Ni-2), 0.02 cm-1 (Co-2), and 0.04 cm-1 (Fe-2). Co-2 and Fe-2 show slow magnetic relaxation, and are field-induced SMMs with activation energy of spin-reversal Ueff =27 cm-1 (Co-2) and 4.2 cm-1 (Fe-2). Density functional theory calculations indicate that the uniaxial anisotropy along the z-axis of each metal ion center forms the pseudo-serial arrangement, leading to intramolecular ferromagnetism via the magnetic dipole interaction. This work demonstrates the creation of ferromagnetic SMMs by the magnetic dipole engineering of 3d di-nuclear metal ion centers.