Manganese Complexes Research Articles

Water Oxidation Catalyzed by a Bioinspired Tetranuclear Manganese Complex: Mechanistic Study and Prediction.

Density functional theory calculations were utilized to elucidate the water oxidation mechanism catalyzed by polyanionic tetramanganese complex a [MnIII 3 MnIV O3 (CH3 COO)3 (A-α-SiW9 O34 )]6- . Theoretical results indicated that catalytic active species 1 (Mn4 III,III,IV,IV ) was formed after O2 formation in the first turnover. From 1, three sequential proton-coupled electron transfer (PCET) oxidations led to the MnIV -oxyl radical 4 (Mn4 IV,IV,IV,IV -O⋅). Importantly, 4 had an unusual butterfly-shaped Mn2 O2 core for the two substrate-coordinated Mn sites, which facilitated O-O bond formation via direct coupling of the oxyl radical and the adjacent MnIV -coordinated hydroxide to produce the hydroperoxide intermediate Int1 (Mn4 III,IV,IV,IV -OOH). This step had an overall energy barrier of 24.9 kcal mol-1 . Subsequent PCET oxidation of Int1 to Int2 (Mn4 III,IV,IV,IV -O2 ⋅) enabled the O2 release in a facile process. Furthermore, apart from the Si-centered complex, computational study suggested that tetramanganese polyoxometalates with Ge, P, and S could also catalyze the water oxidation process, where those bearing P and S likely present higher activities.

Modular Difunctionalization of Unactivated Alkenes through Bio-Inspired Radical Ligand Transfer Catalysis.

Development of visible light-mediated atom transfer radical addition of haloalkanes onto unsaturated hydrocarbons has seen rapid growth in recent years. However, due to its radical chain propagation mechanism, diverse functionality other than the pre-existing (pseudo-)halide on the alkyl halide source cannot be incorporated into target molecules in a one-step, economic fashion. Inspired by the prominent reactivities shown by cytochrome P450 hydroxylase and non-heme iron-dependent oxygenases, we herein report the first modular, dual catalytic difunctionalization of unactivated alkenes via manganese-catalyzed radical ligand transfer (RLT). This RLT elementary step involves a coordinated nucleophile rebounding to a carbon-centered radical to form a new C-X bond in analogy to the radical rebound step in metalloenzymes. The protocol leverages the synergetic cooperation of both a photocatalyst and earth-abundant manganese complex to deliver two radical species in succession to minimally functionalized alkenes, enabling modular diversification of the radical intermediate by a high-valent manganese species capable of delivering various external nucleophiles. A broad scope (97 examples, including drugs/natural product motifs), mild conditions, and excellent chemoselectivity were shown for a variety of substrates and fluoroalkyl fragments. Mechanistic and kinetics studies provide insights into the radical nature of the dual catalytic transformation and support radical ligand transfer (RLT) as a new strategy to deliver diverse functionality selectively to carbon-centered radicals.

Synthesis of attapulgite-MnO2 nanocomposite from manganese complex by ultrasound for hydrogen storage

The research included the synthesis of a new complex of manganese with 3,4,5-tri-methoxybenzoic acid in the presence of triethylamine as a base to which gives the complex with formula [Mn (TMB)2].2H2O. This complex was characterized by FTIR, CHN, magnetic susceptibility and thermal analysis. Furthermore, this complex was used as a novel precursor of manganese in preparing the attapulgite-MnO2 nanocomposite by one-pot addition method using ultrasound. The resulting nanocomposite was characterized by X-ray diffraction and TEM and the results prove that this composite was found as nanochannel of the diameter 45 nm decorated with 26–41 nm of MnO2 nanoparticles. The attapulgite-MnO2 nanocomposite was used in the application of hydrogen storage, and the results proved that attapulgite-MnO2 nanocomposite has the ability to store 3.55 wt% of hydrogen under a pressure of 90 bar and a temperature of 77 K. Furthermore, the measurement demonstrated that increasing the pressure increased the stored hydrogen, implying that the stored gas will be liberated by altering the pressure, implying that the storage will be of the physical kind.

Well-Defined Phosphine-Free Manganese(II)-Complex-Catalyzed Synthesis of Quinolines, Pyrroles, and Pyridines.

Herein, we report a simple, phosphine-free, and inexpensive catalytic system based on a manganese(II) complex for synthesizing different important N-heterocycles such as quinolines, pyrroles, and pyridines from amino alcohols and ketones. Several control experiments, kinetic studies, and DFT calculations were carried out to support the plausible reaction mechanism. We also detected two potential intermediates in the catalytic cycle using ESI-MS analysis. Based on these studies, a metal-ligand cooperative mechanism was proposed.

Water Oxidation by a Neoteric Dinuclear Mn(II) Electrocatalyst in Aqueous Medium

AbstractThe employment of manganese complexes towards electrocatalytic water oxidation has gained immense interest among the scientific communities. In this present study, the reaction of Mn(CH3COO)2⋅4H2O with the novel ligand (2‐([2,2′:6′,2“‐terpyridin]‐4′‐yl)quinoline‐8‐ol) (8hq‐tpy) affords a dinuclear manganese complex, [MnII(8hq‐tpy)(H2O)]2(PF6)2 (Mn 1). Various spectroscopic techniques have been implemented for characterization purposes, and Mn 1 is employed as electrocatalysts towards water oxidation catalysis in the aqueous medium. Electrocatalytic responses in the aqueous medium at pH 6.0 lead to the electrodeposition of heterogeneous species (MnOX) which enables the oxidation event at an applied potential of 1.24 V vs. NHE with O2 liberation of 50.2 μmol/L. The XPS analysis performed after executing bulk electrolysis, provide evidence for the generation of MnIV=O as the active species formed by the catalyst precursor complex Mn 1, contributing to O2 evolution during the electrocatalytic water oxidation process.

In silico Design, Synthesis and Antitubercular Activity of Some Metal Complexes Derived from Salicylaldehyde and Amino Acid

Background: A new series of copper (II), cobalt (II), zinc (II), manganese (II), and iron (II) metal complexes were synthesized by the condensation of a novel Schiff base with various metal chlorides in ethanol. Schiff base was synthesized by reacting salicylaldehyde with L-glutamic acid and L-tyrosine dissolved in ethanol, respectively Methods: The structures of all the synthesized metal complexes (4a-e, 7a-e) were investigated using elemental analysis, FT-IR,1H NMR,13C NMR and MS spectral data. The metal complexes were also screened for their anti-bacterial, anti-fungal, and anti-tubercular activities against various tested strains. Results: Assessment of in silico ADMET properties of all metal complexes showed to be in accordance with Lipinski’s rule of five. Further enzymatic assay was aided by a molecular docking study of Enoyl CoA reductase (INHA) using Autodock Vina and evaluated by Autodock 4.0. Conclusion: The metal complexes, 4b,4c, 4d,7b and 7d, containing metals, like Zn, Co, and Fe, exhibited good anti-bacterial, anti-fungal and anti-tubercular activities against the tested strains.

Heterogenized manganese catalyst for C-, and N-alkylation of ketones and amines with alcohols by pyrolysis of molecularly defined complexes

Series of organic transformations are known to be catalyzed by molecularly well-defined homogeneous catalysts, however, it is difficult to recycle. Meanwhile, heterogeneous catalysts are required in many industrial processes due to their stability, and recyclability, but it is challenging to control on a molecular level. Herein, we set out the conversion of homogenous manganese complex into heterogeneous manganese-based catalyst via pyrolyzing the pre-formed crystalline polymer. The catalyst thus produced are then utilized for C–C/C–N bond-forming reactions, such as alkylation of ketones and/or amines, utilizing primary alcohols as an alkylating agent, under nearly mild conditions liberating water as the sole by-product.

Electrochemical Studies on Manganese (III) Complex with meso-5, 10, 15, 20-Tetrakis (o-nitrophenyl) porphyrin by Cyclic Voltammetry and UV-Visible Spectrophotometry

Meso-5,10,15,20-Tetrakis(o-nitrophenyl)porphyrin, [T (o-NO2)PP] and manganese (III) meso-5,10,15,20- Tetrakis(2,5-dimethoxyphenyl)porphyrin, Mn[T(o- NO2)PP] have been prepared. The Mn[T(o-NO2)PP] complex is characterized by UV-Vis spectrophotometric and cyclic voltametric (CV) studies. The preparation of Mn(III) porphyrin complex may be attributed due to a significant metal-porphyrin π interaction. In Mn(III) porphyrin, Mn is in a high spin d4 configuration with octahedral geometry. Mn(III) porphyrin geometry has been altered to square pyramidal Mn(II) porphyrin after addition of ethylamine. In square pyramidal Mn(II) porphyrin, Mn atom is in a high-spin d5 configuration with the occupied d(x 2 - y 2 ) orbital whose orbital energy is low. This shows that Mn(III) will be out of the plane of porphyrin. Successive addition of diethylamine, Mn(III) porphyrin geometry has been changed to tetragonal complex due to a weak π back bonding. It appears that π -bonding is lowered when the tetragonal complexes are formed. This might arise due to the expansion of the in-plane metal to porphyrin in a direction to occupy two axial ligands of ethylamine. The geometry changes indicate that the two ethyl amines groups occupy 5th and 6th places as axial coordination site due to the availability of two ethylamine from ethyl, diethyl and triethyl amines. Cyclic voltammogram confirmed the oxidation state and reduction behavior of Mn porphyrin complex.

Mechanistic Studies on the Epoxidation of Alkenes by Macrocyclic Manganese Porphyrin Catalysts.

Macrocyclic metal porphyrin complexes can act as shape‐selective catalysts mimicking the action of enzymes. To achieve enzyme‐like reactivity, a mechanistic understanding of the reaction at the molecular level is needed. We report a mechanistic study of alkene epoxidation by the oxidant iodosylbenzene, mediated by an achiral and a chiral manganese(V)oxo porphyrin cage complex. Both complexes convert a great variety of alkenes into epoxides in yields varying between 20–88 %. We monitored the process of the formation of the manganese(V)oxo complexes by oxygen transfer from iodosylbenzene to manganese(III) complexes and their reactivity by ion mobility mass spectrometry. The results show that in the case of the achiral cage complex the initial iodosylbenzene adduct is formed on the inside of the cage and in the case of the chiral one on the outside of the cage. Its decomposition leads to a manganese complex with the oxo ligand on either the inside or outside of the cage. These experimental results are confirmed by DFT calculations. The oxo ligand on the outside of the cage reacts faster with a substrate molecule than the oxo ligand on the inside. The results indicate how the catalytic activity of the macrocyclic porphyrin complex can be tuned and explain why the chiral porphyrin complex does not catalyze the enantioselective epoxidation of alkenes.

Solution Equilibria Formation of Manganese(II) Complexes with Ethylenediamine, 1,3-Propanediamine and 1,4-ButanediaMine in Methanol

Manganese is an abundant element that plays critical roles and is at the reaction center of several enzymes. In order to promote an understanding of the behavior of manganese(II) ion with several aliphatic ligands, in this work, the stability and spectral behavior of the complexes with manganese(II) and ethylenediamine, 1,3-propanediamine or 1,4-butanediamine were explored. A spectrophotometric study of its speciation in methanol was performed at 293 K. The formation constants obtained for these systems were: manganese(II)-ethylenediamine log β110 = 3.98 and log β120 = 7.51; for the manganese(II)-1,3-propanediamine log β110 = 5.08 and log β120 = 8.66; and for manganese(II)-1,4-butanediamine log β110 = 4.36 and log β120 = 8.46. These results were obtained by fitting the experimental spectrophotometric data using the HypSpec software. The complexes reported in this study show a spectral pattern that could be related to a chelate effect in which the molar absorbance is not directly related to the increase in the carbon chain of the ligands.

Dehydrogenation of formic acid mediated by a Phosphorus–Nitrogen PN3P-manganese pincer complex: Catalytic performance and mechanistic insights

The utilization of formic acid as a liquid organic hydrogen carrier has taken a vast interest lately because of several desirable properties. The state-of-the-art homogenous catalysts known for formic acid dehydrogenation are mainly based on noble metals such as iridium or ruthenium. 3d metals are considered to be an attractive alternative due to their abundance and low toxicity. Exploration of 3d metals has achieved exciting results mainly with iron-based catalysts; however, manganese has not received much attention, and only a few examples are available. Here we report a manganese complex [Mn(PN3P)(CO)2]Br containing a pincer backbone, as an efficient catalyst for formic acid dehydrogenation. Under the optimized condition, the complex afforded a TON of 15,200. To the best of our knowledge, this is considered one of the best TON achieved using a manganese-based complex with excellent selectivity. Mechanistic studies suggested that the imine arm participates in the formic acid activation/deprotonation step, emphasizing the importance of metal-ligand cooperativity during substrate activation to promote catalytic efficacy.

Synthetic and Nanotechnological Approaches for a Diagnostic Use of Manganese.

The development of multimodal imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) allows the contemporary obtaining of metabolic and morphological information. To fully exploit the complementarity of the two imaging modalities, the design of probes displaying radioactive and magnetic properties at the same time could be very beneficial. In this regard, transition metals offer appealing options, with manganese representing an ideal candidate. As nanosized imaging probes have demonstrated great value for designing advanced diagnostic/theranostic procedures, this work focuses on the potential of liposomal formulations loaded with a new synthesized paramagnetic Mn(II) chelates. Negatively charged liposomes were produced by thin-layer hydration method and extrusion. The obtained formulations were characterized in terms of size, surface charge, efficiency of encapsulation, stability over time, relaxivity, effective magnetic moment, and in vitro antiproliferative effect on human cells by means of the MTT assay. The negatively charged paramagnetic liposomes were monodisperse, with an average hydrodynamic diameter not exceeding 200 nm, and they displayed good stability and no cytotoxicity. As determined by optical emission spectroscopy, manganese complexes are loaded almost completely on liposomes maintaining their paramagnetic properties.

Achieving large thermal hysteresis in an anthracene-based manganese(II) complex via photo-induced electron transfer

Achieving magnetic bistability with large thermal hysteresis is still a formidable challenge in material science. Here we synthesize a series of isostructural chain complexes using 9,10-anthracene dicarboxylic acid as a photoactive component. The electron transfer photochromic Mn2+ and Zn2+ compounds with photogenerated diradicals are confirmed by structures, optical spectra, magnetic analyses, and density functional theory calculations. For the Mn2+ analog, light irradiation changes the spin topology from a single Mn2+ ion to a radical-Mn2+ single chain, further inducing magnetic bistability with a remarkably wide thermal hysteresis of 177 K. Structural analysis of light irradiated crystals at 300 and 50 K reveals that the rotation of the anthracene rings changes the Mn1–O2–C8 angle and coordination geometries of the Mn2+ center, resulting in magnetic bistability with this wide thermal hysteresis. This work provides a strategy for constructing molecular magnets with large thermal hysteresis via electron transfer photochromism.

The economic efficiency of the use of mixed ligand complexes of Zinc, Man-ganese and Cobalt in the rations of highlyproductive cows of the Ukrainian Black-Spotted Dairy breed

The research results on the cost-effectiveness of using different doses of Zinc, Manganese, and Cobalt due to their mixed ligand complexes in the feeding rations of highly productive cows of the Ukrainian Black-Spotted Dairy breed in the first 100 days of lactation are presented. Experimental studies were conducted on five (one control and four experimental) groups of analogous cows in the conditions of the Kyiv region's ALC “Terezyne” Bila Tserkva district. The optimal dose of mixed-ligand complexes of Zinc, Manganese, and Cobalt was established in previous studies, with a concentration of 1 kg of dry matter (DM) of the feed mixture (FM), mg: Zinc – 60.8; Manganese – 60.8, and Cobalt – 0.78. For the second experimental group, the concentration of these trace elements increased by 10 %, and in the 3rd, fourth, and fifth experimental groups – on the contrary, it decreased by 10 %, 20, and 30 %, respectively, compared with the control. The highest hopes of essential fat milk were in experimental cows of the 4th group and were 4791.7 kg, where due to mixed ligand complexes, the doses of Zinc and Manganese were 48.6 mg, and Cobalt – 0.62 mg per 1 kg of DM. The hopes of essential fat milk, compared with the control, in cows of the second experimental group, was higher by 155.2 kg, the 3rd – by 211.3 kg, the 4th – by 427.0 kg, and the fifth experimental group – by 234.6 kg. The lowest hopes of essential fat milk were in cows of the first control group. Using additives of mixed ligand complexes of Zinc, Manganese, and Cobalt in complete feed mixtures allowed profit, UAH: in the first control group – 7581.5; second experimental group – 7963.1; third – 8004.1; fourth – 8437.6 and 5th – 8119.0. The most significant profit, by UAH 856.1, or 11.29 % more than control, was obtained in the fourth experimental group of cows of the Ukrainian Black-Spotted Dairy breed. The positive effect of feeding different levels of Zinc, Manganese, and Cobalt due to their mixed ligand complexes to cows of the Ukrainian Black-Spotted Dairy breed in the first 100 days of lactation on the indicators of economic efficiency of milk production. The best results were obtained in the fourth experimental group, whose cows were fed a feed mixture containing 1 kg of DM, mg: Zinc – 48.6; Manganese – 48.6; Cobalt – 0.62; Selenium – 0.3; Copper – 12 and Iodine – 1.1.

Synthesis and characterization of alkaloid derived hydrazones and their metal (II) complexes

Abstract Alkaloids have been known overtime to have medicinal uses. Exploring alkaloid derived hydrazones and their complexes as potential therapeutic agents with a view to improving the medicinal uses of alkaloids are imperative. 1,8-dichloroacridone hydrazone hydrochloride, 1-chloro pilocarpine nitrate-3-chlorophenyl hydrazone and 1-phenethyl-4-piperidone formyl hydrazone ligands were synthesized via Wolff–Kishner condensation reaction. Five metal (II) complexes of cobalt, nickel and manganese were prepared by stirring the ligands with the respective metal salts. The ligands and complexes were characterized using elemental analyses, molar conductivity, FTIR, 1H and 13C nmr, UV–Vis spectra, melting point and solubility. Antimicrobial activities of the ligands and their complexes were tested against four bacteria (Staphylococcus aureus, Streptococcus faecalis Escherichia coli, Salmonella paratyphimurium) and a fungus (Candida albican). The molar conductance values indicate that they are 1:1 and 1:2 type electrolytes while the elemental analyses of the complexes reveals a 1:1 metal to ligand stoichiometry. The relevant IR bands suggest coordination is through the C=N, C=O, N=C–O and C–N groups. Both 1H and 13C nmr corroborated the elemental analysis while the UV–Vis reveals intra-ligand charge transfer while the complexes exhibited the expected metal transitions bands. A proposed octahedral geometry is supported by spectral data. Only 1, 8-dichloroacridonehydrazone hydrochloride ligand was found to be active against all the organisms. Cobalt and nickel complexes of 1,8-dichloroacridonehydrazone hydrochloride were active against S. paratyphimurium and S. aureus, respectively, while cobalt complex of 1-chloropilocarpinenitrate-3-chlorophenylhydrazone was active against S. faecalis and S. paratyphimurium. The minimum inhibitory concentrations (MIC) were also recorded.

Manganese-Catalyzed Asymmetric Formal Hydroamination of Allylic Alcohols: A Remarkable Macrocyclic Ligand Effect.

A unique family of chiral peraza N6 -macrocyclic ligands, which are conformationally rigid and have a tunable saddle-shaped cavity, is described. Utilizing their manganese(I) complexes, the first example of earth-abundant transition metal-catalyzed asymmetric formal anti-Markovnikov hydroamination of allylic alcohols was realized, providing a practical access to synthetically important chiral γ-amino alcohols in excellent yields and enantioselectivities (up to 99 % yield and 98 % ee). The single-crystal structure of a MnI complex indicates that the manganese atom coordinates with the chiral dialkylamine moiety in a bidentate fashion. Further DFT calculations revealed that five of the six nitrogen atoms in the ligand were engaged in multiple noncovalent interactions with Mn, an isopropanol molecule, and a β-amino ketone intermediate via coordination, hydrogen bonding, and/or CH⋅⋅⋅π interactions in the transition state, showing a remarkable role of the macrocyclic framework.

Manganese‐Catalyzed Asymmetric Formal Hydroamination of Allylic Alcohols: A Remarkable Macrocyclic Ligand Effect

AbstractA unique family of chiral peraza N6‐macrocyclic ligands, which are conformationally rigid and have a tunable saddle‐shaped cavity, is described. Utilizing their manganese(I) complexes, the first example of earth‐abundant transition metal‐catalyzed asymmetric formal anti‐Markovnikov hydroamination of allylic alcohols was realized, providing a practical access to synthetically important chiral γ‐amino alcohols in excellent yields and enantioselectivities (up to 99 % yield and 98 % ee). The single‐crystal structure of a MnI complex indicates that the manganese atom coordinates with the chiral dialkylamine moiety in a bidentate fashion. Further DFT calculations revealed that five of the six nitrogen atoms in the ligand were engaged in multiple noncovalent interactions with Mn, an isopropanol molecule, and a β‐amino ketone intermediate via coordination, hydrogen bonding, and/or CH⋅⋅⋅π interactions in the transition state, showing a remarkable role of the macrocyclic framework.

Redox chemistry of bis(terpyridine)manganese(II) complexes – A molecular view

Oxidation of bis (terpyridine)manganese(II) complexes with a constrained octahedral geometry, leads to a high spin manganese(III) compression Jahn-Teller distortion geometry, while reduction results in a high spin manganese(II) complex which is antiferromagnetically coupled to one localized π-radical anion ligand. The provided linear relationships between experimental redox potentials and density functional theory calculated energies can be used to predict the redox potentials of related bis (terpyridine)manganese(II) complexes. • [Mn II (tpy) 2 ] 2+ has a constrained octahedral geometry. • [Mn III (tpy) 2 ] 3+ has a compression Jahn-Teller geometry. • [Mn IV (tpy) 2 ] 4+ has a constrained octahedral geometry. • Reduction of [Mn II (tpy) 2 ] 2+ gives the high spin [Mn II (tpy)(tpy) • ] 1+ complex. • Linear relationships between experimental redox potentials and DFT calculated energy. A density functional theory study of the oxidation and reduction of a series of bis (terpyridine)manganese(II) complexes showed that oxidation results in a high spin manganese(III) compression Jahn-Teller distortion geometry, while reduction results in a high spin manganese(II) complex which is antiferromagnetically coupled to one localized π-radical anion ligand. Experimental reports on the redox chemistry of [Mn II (tpy) 2 ] 2+ complexes, reported two oxidation and three reduction processes. The DFT results of this study, on the electronic structure of the molecules involved in the redox processes, assign the oxidation processes metal based, with the formation of [Mn III (tpy) 2 ] 3+ and [Mn IV (tpy) 2 ] 4+ respectively. Contrary to oxidation that is metal based, DFT results show that the reduction processes are ligand based, with the formation of [Mn II (tpy)(tpy) • ] 1+ and [Mn II (tpy • ) 2 ] 0 respectively, where (tpy • ) 1− is a π-radical anion that couples antiferromagnetically to the high spin Mn II ion. Correlations between experimental redox potentials and density functional theory calculated energies were established, which can be used to predict redox potential as well as electrophilic and nucleophilic reactivity of further substituted bis (terpyridine)manganese(II) complexes.

Precursor Engineering for the Synthesis of Mixed Anionic Metal (Cu, Mn) Chalcogenide Nanomaterials via Solvent-Less Synthesis.

Metal-organic ligands with mixed chalcogenides are potential compounds for the preparation of mixed anionic metal chalcogenide alloys. However, only a few of such ligands are known, and their complexes are not well explored. We have prepared homo- and hetero-dichalcogenoimidodiphosphinate [(EE'PiPr2NH)] (E, E' = Se, Se; S, S; S, Se) complexes of manganese and copper through metathetical reactions. The X-ray single crystal structure of [Mn{(SePiPr2)2N}2] 1 revealed a triclinic crystal system, with a MnSe4 core unit, whereas the crystal structure determination of [Mn{(SPiPr2)(SePiPr2)N}2] 2 indicated a triclinic crystal system with a Mn(S/Se)2 unit. Both metal centers are tetrahedral, with two deprotonated bidentate ligands forming the coordination sphere. The free ligand was found to exhibit a gauche configuration in the solid state. The energies of the various rotamers of dithio-analogue were studied by DFT calculations. The decomposition behavior of complexes with homo- and heterochalcogenides was investigated, and the complexes were employed as single-source precursors to generate manganese and copper chalcogenides through solvent-less melt reactions between 500 and 550 °C. The deposited powders were characterized by powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscopy (TEM), and elemental mapping. MnS, MnSe2, and MnSSe phases were obtained from the decomposition of respective manganese complexes. In contrast, the decomposition of copper-based complexes yielded Cu2-xSe and the sulfur-doped Cu3Se2 phase from seleno- and mixed thio/seleno-complexes of Cu, respectively. The morphology ranged from random sheet-like structures to agglomerated platelets, while the selected area electron diffraction (SAED) revealed the crystalline nature of the materials. Depending on the nature of the complex and the temperature, different amounts of phosphorus were present as an impurity in the synthesized products.

Catalase and catecholase-like activities of manganese and copper complexes supported by pentadentate polypyridyl ligands in aqueous solution

Novel manganese(II) complex, [MnII(2PyN2Q*)(OTf)]OTf (1) with racemic pentadentate polypyridyl ligand (2PyN2Q* = N,N-bis(2-quinolylmethyl)-1,2-di(2-pyridyl)ethylamine; OTf = CF3SO3) was synthesized and characterized by IR, UV-Vis, ESI-MS and X-ray measurements. The formation of its high-valent species, [MnIV(2PyN2Q*)(O)](OTf)2 was confirmed by UV-Vis measurements. Catalytic activities of compound 1 for the disproportionation of H2O2 as catalase mimics, and for the oxidation of catechol derivatives as catecholase mimics were investigated in buffered aqueous solution compared to our previously published [CuII(N4Py*)(CH3CN)](OTf)2 (2) (N4Py* = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine), [MnII(N4Py*)(OTf)]OTf (3) and [FeII(N4Py*)(CH3CN)](CO4)2 (4) complexes. Based on preliminary reaction kinetic measurements, an opposite order (trend) of reactivity was observed for the two systems: 4 (KM = 1.39 M) > 3 (1.26 M) > 1 (0.91 M) > 2 (0.31 M) for the catalase-like, and 1 ≈ 2 > 3 > 4 for the catecholase-like activity of the complexes.