Bimetallic Mn Research Articles

Bimetallic synergy in non-precious metal Mn/Ba-SSZ-13 zeolite for improving NOx storage capacity at low temperatures.

Pd-zeolite is considered one of the most promising passive NOx adsorber (PNA) materials for NOx purification in diesel vehicles during cold start. Nevertheless, the scarcity and high cost of the precious metal Pd restrict the industrialisation of Pd-zeolites as PNA. This work developed a bimetallic Mn and Ba co-modified SSZ-13 as non-precious metal PNA material. The results of the orthogonal experiments demonstrated that 0.5Ba3Mn-SSZ-13 exhibits an exceptional NOx storage capacity (255 μmol/gcat.). The physicochemical properties, active adsorption sites and NOx adsorption mechanism are deeply analyzed to illustrate the bimetallic synergistic effect between Mn and Ba. The findings demonstrate that the addition of Ba results in the formation of greater quantities of Mn4+ (MnO2) in lieu of Mn3+ (Mn2O3) within the 0.5Ba3Mn-SSZ-13. Moreover, it demonstrates that Mn3+ (Mn2O3) has a higher affinity for NO, NO2 and NO3- than of Mn4+ (MnO2) through density functional theory (DFT) calculations. Concurrently, the introduction of Ba increases the adsorption sites for nitrate and nitrite species in 0.5Ba3Mn-SSZ-13, thereby enhancing the NOx storage capacity of the zeolite. This work offers novel insights and a scientific foundation for the synthesis of non-metallic PNA materials, which will facilitate the substantial advancement of materials that comply with ultra-low emission regulations in the near future.

Sacrificial MOF-derived MnNi hydroxide for high energy storage supercapacitor electrodes via DFT-based quantum capacitance study.

Electrochemical energy storage plays a critical role in the transition to clean energy. With the growing demand for efficient and sustainable energy solutions, supercapacitors have gained significant attention due to their high specific capacitance, rapid charge/discharge capabilities, long lifespan, safe operation across various temperatures, and minimal maintenance needs. This study introduces a novel approach for the synthesis of high-performance supercapacitor electrodes by using MnNi-MOF-74 as a precursor. Bimetallic Mn(OH)₂/Ni(OH)₂ hydroxides (MnNi-x, where x=2, 6, 12) with tailored morphologies were successfully fabricated by treating MnNi-MOF-74 anchored on nickel foam with different concentrations of KOH. Among the various synthesized samples, MnNi-6 exhibited the best performance, with a remarkable specific capacitance of 4031.51mFcm⁻2at 2mAcm⁻2, attributed to its high surface area of 186m2/g, optimized particle size, and abundant micropores. Furthermore, MnNi-6 demonstrated exceptional thermal stability, positioning it as a promising candidate for high-temperature supercapacitors. It also exhibited excellent cycling stability, retaining 86.34% of its capacity after 10,000 cycles at 10mAcm⁻2, highlighting its remarkable durability. Density functional theory (DFT) calculations were conducted to explore the quantum capacitance of the bimetallic hydroxide. The DFT results revealed electron density near the Fermi level, which directly contributes to the high quantum capacitance of Mn(OH)₂/Ni(OH)₂ with a Mn:Ni molar ratio of 3:1. This work underscores the potential of MOF-derived materials as a promising route for the development of high-performance supercapacitor electrodes, paving the way for future advances in electrochemical energy storage technologies.

Syntheses, Structures and Magnetism of Trinuclear Bimetallic MnIILnIIIMnII Complexes (Ln = La, Nd, Sm, Gd, Dy and Er) with 2,6‐Dipicolinoylbis(N,N‐Diethylthiourea)

AbstractSelf‐assembled reactions of 2,6‐dipicolinoylbis(N,N‐diethylthiourea) (H2L) with Mn(CH3COO)2 ⋅ 4H2O and LnCl3, where Ln = La, Nd, Sm, Gd, Dy, Er in MeOH lead to formation of stable trinuclear complexes of the composition [LnMn2(L)2(μ1,3‐CH3COO)2X] (MnIILnIIIMnII), where X− can be κ2‐CH3COO− or κ1‐CH3COO−. Single crystal X‐ray studies reveal their symmetric structures comprising one central Ln(III) ion, two terminal Mn(II) ions sandwiched by two doubly deprotonated ligands {L2−}. The magnetic properties of MnIILaIIIMnII and MnIIGdIIIMnII complexes are successfully simulated using symmetrical magnetic interaction models, giving the best fitted parameters: JMn‐Mn=−0.120(1) cm−1, gMn=1.99(1), TIP=4.45(7) ⋅ 10−4 cm3 mol−1 K for MnIILaIIIMnII and JGd‐Mn=0.042(1) cm−1, JMn‐Mn=−0.076(1) cm−1, gMn=1.96(1), gGd=2.01(1) and TIP=3.59(14) ⋅ 10−4 cm3 mol−1 K for MnIIGdIIIMnII complex. The magnetic interactions between the Mn(II) and Ln(III) ions in the other MnIILnIIIMnII complexes are studied by comparing their χM values to the sum of χM values of the MnIILaIIIMnII and the analogous ZnIILnIIIZnII complexes. The MnIIErIIIMnII complex reveals a strong ferromagnetic interaction, while the Sm, Nd, Gd and Dy complexes show weak ferromagnetic interactions.

Response surface optimization of hydrogen-rich syngas production by methane dry reforming over bimetallic Mn-Ni/La2O3 catalyst in a fixed bed reactor

The present work utilizes a response surface optimization technique to optimize hydrogen-rich syngas production through the process of methane dry reforming (DRM). This optimization is achieved by employing a bimetallic Mn–Ni/La2O3 catalyst. The study aimed to evaluate the impact of three key parameters, namely reaction temperature, time on stream (TOS), and gas hourly space velocity (GHSV), on the hydrogen to carbon monoxide (H2/CO) ratio in syngas during the DRM. The Mn–Ni/La2O3 catalyst, synthesized using the sequential wet impregnation technique, exhibited suitable physicochemical properties necessary for DRM reaction, as evidenced by the obtained characterization data. Among the five models examined, it was found that the quadratic versus 2FI model substantially fit the experimental data, as evidenced by a p-value <0.05. The analysis of variance (ANOVA) conducted on the quadratic response surface model compared to the 2FI model demonstrated that both the reaction temperature and the TOS had a significant impact on the H2/CO ratio in the syngas. The only significant interaction factor was the relationship between the reaction temperature and the TOS. Under the specified optimal circumstances of 15 000 ml/g.h, 850 °C, and 258.15 min, an H2/CO ratio of 0.98 was achieved. The resulting H2/CO ratio of 0.98 is almost 1, indicating its suitability as a feedstock for methanol production in the Fischer-Tropsch synthesis (FTS).

Switching reactive oxygen species reactions derived from Mn–Pt anchored zeolite for selective catalytic ozonation

Rationally switching reactive oxygen species (ROS) reactions in advanced oxidation processes (AOPs) is urgently needed to improve the adaptability and efficiency for the engineering application. Herein we synthesized bimetallic Mn–Pt catalysts based on zeolite to realize the switching of ROS reactions in catalytic ozonation for sustainable degradation of organic pollutants from water. The ROS reactions switched from singlet oxygen (1O2, 71.01%) to radical-dominated (93.79%) pathway by simply introducing defects and changing Pt/Mn ratios. The oxygen vacancy induced by anchoring Mn–Pt species from zeolite external surface (MnPt/H-Beta) to internal framework (MnPt@Si-Beta) exposes more electron-rich Pt2+/Pt4+ redox sites, accelerating the decomposition of O3 to generate •OH via electron transfer and switching ROS reactions. The Mn site acted as a bridge plays a critical role in conducting electrons from organic pollutants to Pt sites, which solidly solves the electron loss of catalysts, facilitating the efficient degradation of pollutants. A 34.7-fold increase in phenol degradation compared with the non-catalytic ozonation and an excellent catalytic stability are achieved by MnPt@Si-Beta/O3. The 1O2-dominated ROS reaction originated from MnPt/H-Beta/O3 exhibits superior performances in anti-interference for Cl−, HCO3−, NO3−, and SO4−. This work establishes a novel strategy for switching ROS reactions to expand the targeted applications of O3 based AOPs for environmental remediation.

Bimetallic Co-Mn catalysts for synergistic enhancement of VOC gas-sensing performance of ZnO hierarchical nanostructures.

The synergistic effect between bonding dissimilar metals is a very effective way to improve the performance of metal catalysts. In this work, we prepared a series of bimetallic co-doped ZnO hierarchical nanostructures by controlling Mn and Co contents. The gas-sensing properties of the sensors based on the bimetallic co-doped ZnO hierarchical nanostructures were studied systematically through different volatile organic compound (VOC) vapors for the temperature range from 160 to 400 °C. In the testing of normal butanol gas by the bimetallic co-doped ZnO sensor, its performance was tens of times higher than that of pure zinc oxide, and the response values to other VOCs tested were very low, which also indicates that the sensor has good selectivity. The promoted performance is attributed to the increase of adsorbed oxygen content on the surface of the sensor material due to the bimetallic synergistic enhancement effect. XPS spectra of O 1s region of the sensor show that the adsorbed oxygen content is 22.4%, which is higher than that of the pure ZnO (8.5%). The synergistic effect between bimetallic Mn and Co leads to electron enrichment on the surface of ZnO. Electron enrichment can not only promote the activation of ZnO, but also can help to improve the gas-sensing performance.

Facile hydrothermal synthesis of a tri-metallic Cu-Mn-Ni oxide-based electrochemical pseudo capacitor.

Transition metal oxide nanocomposites with heterostructures have gained a lot of attention for use in supercapacitors owing to their low cost, high surface area, fast transport of ions and electrons and high specific capacitance due to efficacious interplay between the electrode and the electrolytes. In this study, we fabricated tri-metallic Cu, Mn, Ni(CMNO), bi-metallic Mn, Ni(MNO) and mono-metallic Ni(NO) oxides through a facile hydrothermal route. All the fabricated materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDX), and their electrochemical properties were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). The CMNO material showed remarkable electrochemical performance with a specific capacitance of 790.63 F g-1 at a current density of 1 A g-1, surpassing the performance of MNO (438.4 F g-1) and NO (290.82 F g-1). Furthermore, CMNO showed high cycling stability with a retention of 96.7% specific capacitance after 8000 cycles. Based on remarkable and unique properties, the CMNO material is regarded as a promising material for new-generation pseudo-capacitor applications.

Catalytic oxidation of thymol and carvacrol with Mn(II)-benzoylbenzoate-bipyridine complex

The primary focus of catalytic chemistry is the synthesis of valuable chemicals from cheaper and more abundant substrates. The main objective of catalytic processes is to achieve higher yields at affordable costs under environmentally friendly conditions. Under homogeneous conditions, the synthesized bimetallic Mn(II) complex with (2-benzoylbenzoic acid, bba) and N,N coordinated (2,2-bipyridine, bipy) ligands, [Mn2(μ1,3-(C6H5)CO(C6H4)COO)2(bipy)2].2ClO4 is shown to be an active catalyst for the oxidation of monoterpenes (thymol and carvacrol), using TBHP under mild reaction conditions. The structure of the complex was characterized by single-crystal X-ray diffraction. The six-coordinated Mn(II) centers bridge in a coordination pattern due to the monodentate bonding mode of the carboxylate oxygen atoms of benzoylbenzoate anion. The selectivity of the Mn-catalyst was measured to be 100 % for thymol and carvacrol to thymoquinone. A simple, effective and selective Mn(II)/TBHP/Monoterpene/CH3CN catalyst system was used for the oxidation of thymol (TOF = 2000 h−1, in 15 min) and carvacrol (TOF = 667 h−1, in 45 min.) into a valuable product, thymoquinone (TQ), in acetonitrile at 80 °C.

Preparation of Mn-Co-MCM-41 Molecular Sieve with Thermosensitive Template and Its Degradation Performance for Rhodamine B

Rhodamine B (RhB) in dyes is widely used in various industries, but it poses a great threat to the natural environment and human health. In this work, a series of thermosensitive polymer materials, PNxDy, with controllable morphology and particle size were prepared by free radical polymerization using N-isopropylacrylamide and N,N-dimethylacrylamide as monomers. Then, by using PNxDy as a template, bimetallic Mn- and Co-doped MCM-41 molecular sieves with good morphology and properties were prepared by the microwave-assisted hydrothermal method. The effects of a series of thermosensitive templates on the morphology and properties of the Mn-Co-MCM-41 molecular sieve were investigated. The results demonstrated that the Mn-Co-MCM-41 by PN100D4 as a templating agent showed the best mesoporous ordering and the most regular material morphology with 2 nm nanoparticles. In addition, the molecular sieve with the best structure was selected for the RhB degradation experiments. The Mn-Co-MCM-41 with PN100D4 as the template showed regular morphology and uniform pore channels. It was applied as a catalyst for the degradation of RhB by potassium monopersulfate (PMS). The degradation rate of RhB could reach 98% with a 20 min reaction by Mn-Co-MCM-41 (PN100D4). Meanwhile, the degradation rate could be maintained at 91% after being reused six times. The bimetallic-doped Mn-Co-MCM-41 molecular sieves prepared using the thermosensitive material PN100D4 as a template have good catalytic performance and can be effectively reused.

Synthesis, characterization and catalytic activity of novel monometallic and bimetallic Mn(II) complexes with thiocarboxamide and phenanthroline ligands

Synthesis, characterization and catalytic activity of novel monometallic and bimetallic Mn(II) complexes with thiocarboxamide and phenanthroline ligands

Microwave‐Assisted Rapid Synthesis of Urchin‐Like Bimetallic Mn–Co Carbonate Composites for High‐Performance Supercapacitors

AbstractHerein, we developed a novel microwave‐assisted hydrothermal synthetic method for urchin‐like bimetallic manganese‐cobalt carbonate composites. Compared with the traditional process, the microwave‐assisted hydrothermal process is not only environmentally friendly, but also more convenient. The electrode of supercapacitors prepared at 120 °C for 10 min exhibited the best electrochemical performance, which could deliver a high capacitance of 839.58 F g−1 at 1 mA cm−2 and remain 82.12 % of its initial capacitance even after 8,000 successive charge‐discharge cycles at a high current density of 6 mA cm−2. We have found the possibility of using a microwave‐assisted hydrothermal process to synthesize the urchin‐like bimetallic manganese‐cobalt carbonate composites, which is of great importance for the application of bimetallic manganese‐cobalt carbonate composites in the supercapacitor field.

Bimetallic Mn–Ni oxide nanoparticles: Green synthesis, optimization and its low-cost anode modifier catalyst in microbial fuel cell

Green synthesis of α-MnO2/NiO bimetallic nanocatalyst was achieved in the presence of Vernonia amygdalina leaf extract. The biosynthesized material was optimized by I-optimal Coordinate Exchange Design model by setting 3-operational factors under 9 experimental run. The optimum conditions were 51% nickel ion concentration, 25.3 min reaction time, and 75.3% (v/v) extract ratio to obtain a maximal absorption edge of 376.8 nm (Eg=3.29eV) for a stable particle size estimation. The regression (R2=0.9873) and adjusted (R2=0.9494) coefficients as well as adequacy of precision (16.8772) proved the good correlation between actual and predicted values. Optical spectroscopies (UV–Vis and FTIR), XRD, DSC, SEM, surface roughness, CV, and EIS were performed to characterize the biosynthesized bimetallic nanocatalyst. Oxidation peak current response using bimetallic nanoparticles (NPs) modified electrode was 2.522 mA, which was higher than α-MnO2 (2.442 mA), NiO (1.897 mA), and bare pencil graphite (0.735 mA) electrodes. The corresponding conductivity of α-MnO2/NiO was higher with low solution resistance (10.84 Ω) than other catalysts. As a result, the biosynthesized bimetallic modified pencil graphite electrode produces 412.24 ± 5.98 mW m−2maximum power density than bare pencil graphite (65.74 ± 0.96 mW m−2), α-MnO2 (315.62 ± 4.87 mW m−2), and NiO (140.35 ± 1.68 mW m−2) in the doubled chambered MFC. The results showed that the fabricated bimetallic NPs have an effective and value add role to modify conventional carbon anode electrodes in the MFCs energy conversion device system.

The enhanced visible-light-induced photocatalytic activities of bimetallic Mn-Fe MOFs for the highly efficient reductive removal of Cr(vi).

The photocatalytic efficiencies of bimetallic MOFs, namely STA-12-Mn–Fe, for the reductive removal of Cr(vi) were explored. The best effective variable values were obtained and correlation between the response and influential variables was optimized via experimental design methodology. Complete Cr(vi) removal was achieved under natural sunlight and fluorescent 40 W lamp radiation at pH 2, with an initial Cr(vi) concentration of 20 mg L−1, and 10 mg of photocatalyst within 30 min. A pseudo-first-order rate constant of 0.132 min−1 at T = 298 K was obtained for the Cr(vi) reduction reaction. The title catalysts revealed high performance in the visible region based on photoefficiency measurements, while improved activity was observed compared to the corresponding single-metal MOFs under natural sunlight, highlighting the synergistic effect between the two metal ions. Trapping experiment results proved that direct electron transfer is the main pathway during the photocatalytic Cr(vi) reduction process.

The Influence of the Support on the Activity of Mn–Fe Catalysts Used for the Selective Catalytic Reduction of NOx with Ammonia

Mono and bimetallic Mn–Fe catalysts supported on different materials were prepared and their catalytic performance in the NH3–SCR of NOx was investigated. It was shown that Mn and Fe have a synergic effect that enhances the activity at low temperature. Nevertheless, the activity of the bimetallic catalysts depends very much on the support selected. The influence of the support on the catalyst activity has been studied using materials with different textural and acid–base properties. Microporous (BEA-zeolite), mesoporous (SBA15 and MCM41) and bulk (metallic oxides) materials with different acidity have been used as supports for the Mn–Fe catalysts. It has been shown that the activity depends on the acidity of the support and on the surface area. Acid sites are necessary for ammonia adsorption and high surface area produces a better dispersion of the active sites resulting in improved redox properties. The best results have been obtained with the catalysts supported on alumina and on beta zeolite. The first one is the most active at low temperatures but it presents some reversible deactivation in the presence of water. The Mn–Fe catalyst supported on beta zeolite is the most active at temperatures higher than 350 °C, without any deactivation in the presence of water and with a 100% selectivity towards nitrogen.

Bimetallic Mn and Co encased within bamboo-like N-doped carbon nanotubes as efficient oxygen reduction reaction electrocatalysts

The development of oxygen reaction reduction (ORR) electrocatalysts that are low-cost, highly-active and have long-term stability for use in energy conversion and storage applications such as fuel cells and metal-air batteries is very important. In this paper, a facile one-step pyrolysis method was used to prepare bamboo-like N-doped carbon nanotubes (BNCNTs) as effective ORR electrocatalysts. Manganese and cobalt salts were used as the metal precursors, and urea was the C and N source. The resulting catalysts were characterized by the scanning electron microscopy, high resolution-transmission electron microscopy, X-ray photoelectron spectroscopy, Raman microscopy and X-ray power diffraction. The BNCNTs contained Mn and Co nanoparticles that were coated with graphitic carbon. The electrochemical performances of the catalysts in alkaline media were evaluated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The BNCNTs prepared with a Mn to Co molar ratio of 1:1 at 800 °C had the best catalytic activity. The reaction followed a quasi-4 electron reaction pathway with a smaller Tafel slope (57.5 mV dec−1) than that of the commercial Pt/C (72.8 mV dec−1). In addition, the limiting current density, durability and methanol crossover resistance were all superior to those of Pt/C. The above results indicate that Mn/Co-BNCNTs-800 is an active electrocatalyst with earth-abundant non-precious elements for ORR.

Bi-metallic catalysts of mesoporous Al2O3 supported on Fe, Ni and Mn for methane decomposition: Effect of activation temperature

Abstract Methane decomposition reaction has been studied at three different activation temperatures (500 °C, 800 °C and 950 °C) over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts. On co-impregnation of Ni on Fe/Al2O3 the activity of the catalyst was retained even at the high activation temperature at 950 °C and up to 180 min. The Ni promotion enhanced the reducibility of Fe/Al2O3 oxides showing higher catalytic activity with a hydrogen yield of 69%. The reactivity of bimetallic Mn and Fe over Al2O3 catalyst decreased at 800 °C and 950 °C activation temperatures. Regeneration studies revealed that the catalyst could be effectively recycled up to 9 times. The addition of O2 (1 ml, 2 ml, 4 ml) in the feed enhanced substantially CH4 conversion, the yield of hydrogen and the stability of the catalyst.

Bimetallic Mn–Co Oxide Nanoparticles Anchored on Carbon Nanofibers Wrapped in Nitrogen-Doped Carbon for Application in Zn–Air Batteries and Supercapacitors

The exploration and rational design of cost-effective, highly active, and durable catalysts for oxygen electrochemical reaction is crucial to actualize the prospective technologies such as metal–air batteries and fuel cells. Herein manganese cobalt oxide nanoparticles anchored on carbon nanofibers and wrapped in a nitrogen-doped carbon shell (MCO/CNFs@NC) is successfully prepared. Benefiting from the synergistic effect between the core nanoparticles and nitrogen-doped carbon shell, MCO/CNFs@NC catalyst exhibits oxygen reduction reaction (ORR) activity with comparable onset potential (1.00 V vs RHE) and half-wave potential (0.76 V vs RHE) which is only about 40 mV lower than that of the state of art Pt/C catalyst. Furthermore, the MCO/CNFs@NC catalyst exceeds the Pt/C catalyst by a great margin in terms of stability in alkaline media. Additionally, MCO/CNFs@NC catalyst is strongly tolerant to methanol crossover, promising its applicability as cathode catalyst in alcohol fuel cells. Moreover, MCO/CNFs@NC catalyst exhibits the oxygen evolution reaction (OER) activity with low overpotential of 0.41 V at the current density of 10 mA cm–2 and ORR/OER potential gap (ΔE) as low as 0.88 V, suggesting its strong bifunctionality. The Zn–air battery based on MCO/CNFs@NC catalyst is found to deliver a specific capacity of 695 mA h g–1Zn and an energy density of 778 W h kg–1Zn at a current density of 20 mA cm–2. The mechanically rechargeable Zn–air battery based on MCO/CNFs@NC catalyst is also found to function continually by only reloading the consumed Zn anode and electrolyte. Furthermore, the electrically rechargeable battery based on MCO/CNFs@NC catalyst is found to function for more than 220 cycles with negligible loss of voltaic efficiency. Moreover, MCO/CNFs@NC is found to display a supercapacitive nature with a good discharge capacity of 478 F g–1 at a discharge current density of 1 A g–1.

Density functional theory study of small bimetallic Mn–Fe clusters

Geometric and electronic properties of MnxFey (x+y≤6) clusters have been investigated in the framework of all-electron density-functional theory. It can be seen that the stability of pure Mnx clusters is enhanced by the addition of the Fe atoms. The MnxFey clusters undergo a change in magnetic behavior from ferrimagnetic orderings for the MnxFe (x≤5) clusters to ferromagnetic orderings for MnxFey (2≤x≤4, 2≤y≤4) and then ferrimagnetic orderings for MnFey (y≤5) clusters. The maximum of the total spin moments correspond to the MnxFe2 (x≤4) composition, which is found to be independent of the cluster size. The transition range of the magnetic orderings from ferromagnetic to ferrimagnetic for MnxFey clusters is altered by changing Mn:Fe ratio. The Mn–Fe bond lengths correlate closely with the spin moments of the Fe, Mn atoms and the total spin moments. Fe atoms mix with Mn at every composition, while Mn atoms prefer to segregate at high Fe content. The charge transfers between Mn and Fe atoms are very little, there are internal electron transfers from 4s to 3d and 4p states in Mn and Fe atoms.

Insertion of a Single‐Molecule Magnet inside a Ferromagnetic Lattice Based on a 3D Bimetallic Oxalate Network: Towards Molecular Analogues of Permanent Magnets

The insertion of the single-molecule magnet (SMM) [Mn(III)(salen)(H2O)]2(2+) (salen(2-) = N,N'-ethylenebis-(salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [Mn(III)(salen)(H2O)]2[Mn(II)Cr(III)(ox)3]2⋅(CH3OH)⋅(CH3CN)2 (1). This cationic Mn2 cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn(III)(salen)(H2O)]2[Zn(II)Cr(III)(ox)3]2⋅(CH3OH)⋅(CH3CN)2 (2) and [In(III)(sal2-trien)][Mn(II)Cr(III)(ox)3]⋅(H2O)0.25⋅(CH3OH)0.25⋅(CH3CN)0.25 (3), which are used as reference compounds. In 2 it has been shown that the magnetic isolation of the Mn2 clusters provided by their insertion into a paramagnetic oxalate network of Cr(III) affords a SMM behavior, albeit with blocking temperatures well below 500 mK even for frequencies as high as 160 kHz. In 3 the onset of ferromagnetism in the bimetallic Mn(II) Cr(III) network is observed at Tc = 5 K. Finally, in the hybrid compound 1 the interaction between the two magnetic networks leads to the antiparallel arrangement of their respective magnetizations, that is, to a ferrimagnetic phase. This coupling induces also important changes on the magnetic properties of 1 with respect to those of the reference compounds 2 and 3. In particular, compound 1 shows a large magnetization hysteresis below 1 K, which is in sharp contrast with the near-reversible magnetizations that the SMMs and the oxalate ferromagnetic lattice show under the same conditions.

Mono- and bi-metallic Mn(III) complexes of macroacyclic salen type ligands: Syntheses, characterization and studies of their catalytic activity

Complex 1, a six-coordinated Mn(III) species of a macroacyclic salen type ligand L [L = N, N′-cyclohexanebis(3-formyl-5-methylsalicylaldimine)] having two axial positions occupied by water molecules with chloride as counter anion has been synthesized and characterized by X-ray single crystal structure analysis. Structural analysis reveals that it is the N 2O 2 site, and not the O 4 site, of L that acts as the potential ligating site to accommodate Mn(III) ion. In order to put second metal close to the Mn(III) center the two formyl groups of L were condensed with aniline to generate another O 2N 2 site and subsequent reaction with MCl x produced a series of bimetallic complexes MnML′Cl x · yH 2O [M = Zn(II), Cu(II), Ni(II), Co(II), Fe(III) and Mn(III); x = 3 or 4 depending on the oxidation state of M; L′ = condensation product of L with aniline; y = 2 or 3]. The bimetallic complexes have been characterized by elemental analyses, UV–vis and IR spectroscopic, magnetic susceptibilities and thermogravimetric analyses. The catalytic property of the complexes for epoxidation of alkenes has been investigated in the presence of two terminal oxidants PhIO and NaOCl, with two solvents CH 3CN and CH 2Cl 2. As alkenes styrene and ( E)-stilbene have been chosen for investigation. The study suggests the possibility of atleast another active epoxidizing species, most probably (salen)Mn(III)OCl, in addition to the discrete Mn(V) O(salen) species in epoxidation of olefins depending upon whether NaOCl or PhIO is used as terminal oxidants. Complex 1 is observed to exhibit the highest efficiency to catalyze the epoxidation of both the substrates irrespective of the terminal oxidant and solvent used, whereas the bimetallic complexes exhibit moderate to poor activity. The study has also established that as solvent CH 3CN and as terminal oxidant PhIO are the better options for epoxidation of both styrene and ( E)-stilbene. The UV–vis spectroscopic studies imply that the detrimental effect of the second metal present in the close vicinity of Mn(III) center on the catalytic efficiency of Mn(III) is a consequence of the slow rate of formation of the active intermediate Mn(V) O species as well as the gradual decomposition of the binuclear complexes in the presence of PhIO.