Mn Complexes Research Articles

The effect of complex formation on the static and frequency-dependent nonlinear optical properties: A combined experimental and theoretical investigation

A novel mixed ligand Mn(II) complex of 6-Bromopyridine-2-carboxylic acid (6Brpca) and 4,4′-dimethyl-2,2′-dipyridyl has been prepared and structurally characterized using single-crystal X-ray diffraction. The spectroscopic properties were also analyzed by using FT-IR and UV–Vis spectral techniques. The coordination complexes having transition metal ions are known to have promising optical nonlinearity behavior. Therefore, B3LYP level density functional theory was used to investigate first- and second-order hyperpolarizabilities (β and γ) and provide a deep understanding of the relation between the structure and NLO properties. The calculations of frequency-dependent α, β, and γ at frequencies of ω = 0.0856252 and 0.0428126 au. for 6Brpca and Dmdpy ligands as well as Mn(II) complex have been also carried out using B3LYP/LanL2DZ level. Especially second harmonic generation (SHG) first and second hyperpolarizabilities (β(−2ω;ω,ω) and γ (−2ω;ω,ω,0)) parameters for Mn(II) complex have been calculated as 11448 × 10−30 and 680035 × 10−36 esu, respectively. It has been determined that there is a tremendous increase in β and γ parameters when 6Brpca and Dmdpy ligands coordinate to the high spin multiplicity Mn(II) ion. Theoretical calculations revealed that the large first- and second-order hyperpolarizabilities are caused by strong intramolecular charge transfer between the transition metal and the coordinated ligands. These results indicate that the the organometallic complex under investigation is valuable candidate for optoelectronic and photonic applications.

A novel Co(II) complex with sulfamethoxazole ligand: Isostructuralism, non-covalent interactions, Hirshfeld surfaces, crystal voids and energy calculations

The crystal structure of [Co(H2O)6][Co(SMX)3]2 complex (SMX = sulfamethoxazole), hereafter CoSMXW, has been solved by X-ray diffraction methods. The complex CoSMXW was characterized by Infrared (IR), Raman, and UV-Vis spectroscopies. A comparison with the analogous Mn(II) complex, [Mn(H2O)6][Mn(SMX)3]2 (CSD refcode AJIFUW), indicates 3D isostructurality and packing similarity, as evident from X-ray diffraction and geometric descriptors such as dissimilarity index (X = 2.0 from XPac) and packing similarity (PSab = 0.3070 from CrystalCMP), respectively. This represents the first case of isostructurality observed among eleven metal complexes of sulfamethoxazole reported in the literature. A study of non-covalent interactions shows presence of structural motifs involving N-H…O and N-H…S (Motif I), N-H…O (Motif II), O-H…O and O-H…N (Motif III) H-bonds, as well as C-H…π contacts (Motif IV) for [Co(H2O)6][Co(SMX)3]2 and AJIFUW. Energy analysis using CrystalExplorer indicates that the strongest dimer involves Motifs I and II with total energy of -70.3 kcal/mol for CoSMXW, which is only 2.1 kcal/mol longer than that for AJIFUW. Hirshfeld surface (HS) analysis reveals meaningless effect of metal replacement on the intermolecular contacts, confirming the energetic results. The volume of the crystal voids and the percentage of free space were calculated as 862.35 Å3 and 11.8 % for CoSMXW, and 911.42 Å3 and 12.2 % for AJIFUW. 3D topology and hierarchy of interactions were analyzed with energy framework diagrams. Further, structural motifs, HS, crystal voids and intermolecular energies for the SMX free ligand (CSD refcode SLFNMB08) were also studied. Finally, the present study was complemented with DFT calculations to evaluate the strength and nature of the non-covalent interactions by using the quantum theory of atoms in molecules (QTAIM) and NCIplots computational tools. In addition, we have used the potential energy density predictor obtained from QTAIM analysis to investigate the relative contribution of each interaction to the formation of the assemblies.

CATALYTIC OXIDATION OF AROMATIC ALDEHYDES TO CARBOXYLIC ACIDS IN MILD CONDITIONS WITH NaClO2

This study aimed to improve the conditions for the oxidation of benzaldehyde to benzoic acid using chlorine dioxide generated from sodium chlorite, across various pH ranges and different catalysts. The powerful oxidation capability of chlorine dioxide played a crucial role in enhancing the kinetic efficiency of the reactions. In our research, we examined various reaction conditions, including sodium dihydrogen phosphate, sodium dihydrogen phosphate together with sodium chlorite, sodium dihydrogen phosphate combined with sodium chlorite and potassium permanganate, and sodium dihydrogen phosphate with sodium chlorite and V2O5. Additionally, different oxidation combinations were tested, such as sodium chlorite with sodium tripolyphosphate (STPP), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), and formic acid, as well. The stabilized chlorine dioxide solution was also used directly as an oxidation reagent. The role of chlorine dioxide in these combinations significantly impacted the selectivity and yield in terms of product. Furthermore, some Mn (III) complexes (Cat.1 and Cat.2) were used as catalysts in this study, and the findings revealed that chlorine dioxide is an effective oxidant in the selective oxidation of aromatic aldehydes to aromatic acids. For the catalytic application in buffer solutions, a leveling effect was observed. When Mn (III) complexes were used, it showed a similar leveling effect in buffer solutions with a pH >1, which was resulting in slow ClO₂ formation. With these findings it was found that the use of Mn (III) complexes in NaH2PO4+NaClO2 combination provided the highest yield in the oxidation of aromatic aldehydes to acids. These results underscore the importance of chlorine dioxide as a powerful oxidant in chemical transformation processes.

Synthesis of Co(II), Mn(II), and Ni(II) complexes with 4-(4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazin-2-yl)morpholine; X-ray structure, Hirshfeld, AIM, and biological studies

Three transition metal complexes of s-triazine ligand (MorphBPT) were synthesized, characterized, and their supramolecular structures are explored. Their structures are confirmed to be [Co(MorphBPT)2](ClO4)2 (1), [Mn(MorphBPT)2](ClO4)2 (2), and [Ni(MorphBPT)(H2O)3]Cl2·2H2O (3) using single crystal X-ray diffraction. In all cases, the MorphBPT is a tridentate N-chelator. Hence, the metal ions have hexa-coordination environment in all complexes. In the two homoleptic complexes 1 and 2, the O···H, C···H, and C···O contacts, in addition to some short N···O and H···H contacts detected only in 2, are the most important. For 3, the Cl···H, O···H, and C···H contacts are the most significant. Enrichment ratio was used to detect the atom pairs which have the highest probability to form non-covalent interactions. The nature of MN and MO coordination interactions is analyzed with the aid of AIM calculations. Also, the interactions with the ligand moieties lowers the charge of Co(II), Ni(II), and Mn(II) to 0.8411, 0.9332, and 0.8308 e, respectively. The three complexes 1, 2, and 3 exhibited antibacterial activity exceeds the reference drug gentamicin against P. vulgaris where the diameter of the inhibition zones (DIZs) are determined to be 28, 29, 27, and 25 mm, respectively. In addition, 1 and 2 have antifungal activity better (DIZ = 18 mm) and equal (DIZ = 17 mm) compared to ketoconazole against A. fumigatus, respectively. The Mn(II) complex 2 is the most active against MCF-7 (75.3 ± 3.1 μM) and A-549 (40.2 ± 2.7 μM) cancerous cell lines.

Homogeneous versus heterogeneous Mn(II) oxidation in peroxymonosulfate assisting chlorination: Synergistic role for enhanced Mn(II) oxidation in water treatment

Removal of Mn(II) is an essential step for addressing water discoloration in water treatment utilities worldwide. However, conventional chlorination suffers from poor oxidation of Mn(II) due to its low homogeneous oxidation kinetics. This study explored the oxidation capability of a new chemical dosing strategy employing peroxymonosulfate (PMS) to assist the chlorination process (PMS@Cl2) for effective Mn(II) oxidation. The study comprehensively explored both oxidation kinetics and underlying mechanisms associated with homogeneous and heterogeneous oxidation within the PMS@Cl2 system. At an [Mn(II)]0 of 1 mg/L, chlorination demonstrated inability in oxidizing Mn(II), with <10 % oxidation even at an elevated [Cl2] of 150 μM (∼10 mg/L). By contrast, PMS completely oxidized 100 % Mn(II) within a 30-minute reaction at a much lower [PMS] of 60 μM (kobs = 0.07 min−1 and t1/2 = 9 min), demonstrating its superior Mn(II) oxidation kinetics (over one order of magnitude faster than conventional chlorine). PMS@Cl2 exhibited an interesting synergistic benefit when combining a lower dose PMS with a higher routine dose Cl2 (loPMS@hiCl2), e.g. [PMS]:[Cl2] at 15:30 or 30:30 μM. Both conditions achieved 100 % Mn(II) oxidation, with even better values of kobs and t1/2 (0.16–0.17 min−1 and ∼4 min) relative to PMS alone at 60 µM. The synergic benefit of PMS@Cl2 was attributed to distinct functions played by PMS and Cl2 in both homogeneous and heterogeneous oxidation processes. Reactive species identification excluded the possible involvement of SO4•−, OH•, or chlorine radicals in the homogeneous oxidation of the PMS@Cl2 system. Instead, the dominant species was O2•− radical generated during the reaction of Mn(II) and PMS. Furthermore, the heterogeneous oxidation emphasized the important role of combining Cl2 dosing, which demonstrated an increased reactivity and electron transfer with the Mn−O−Mn complex, surpassing PMS. Overall, heterogeneous oxidation accelerated the oxidation kinetics of the PMS@Cl2 system by 1.1–2 orders of magnitude relative to the homogeneous oxidation of Cl2 alone. We here demonstrated that PMS@Cl2 could offer a more efficient mean of soluble Mn(II) mitigation, achieved with a relatively low routine dose of oxidant in a short reaction period. The outcomes of this study would address the existing limitations of traditional chlorine oxidation, minimizing the trade-offs associated with high residual chlorine levels after treatments for soluble manganese-containing water.

Voltammetric Investigations of Low-Coordinate Manganese As an Electrocatalyst for Organic Coupling and Functionalization

Earth-abundant, first row, low coordinate transition metal complexes are considered promising candidates for the electrocatalysis of many organic reactions. The use of transition metal catalysts is no stranger to the field of synthetic organic chemistry; however, many of the existing catalysts require the use of rare and expensive metals such as platinum, palladium, ruthenium, and iridium. In this study, we seek to identify and understand the mechanism by which an Mn(I) complex may act as an electrocatalyst for simple organic coupling and C-H functionalization reactions, beginning with the radicalization of benzyl bromide and benzyl chloride as representative organic halide substrates. The careful design and evaluation of this manganese complex has the potential to offer an effective non-toxic 3d metal electrocatalyst, provided that common transition metal behaviors, such as disproportionation or carbon-metal bond formation, are avoided. Initial characterization of the complex by cyclic voltammetry (CV) demonstrates general reversibility of the catalyst, while additions of benzyl halide exhibit the execution of the electron transfer and catalytic step. Electrochemical simulations run in parallel with CV experiments provide supplementary guidance into the relationship between the substrate and catalyst. Additional studies conducted using bulk electrolysis, mass spectrometry, nuclear magnetic resonance, and density functional theory (DFT) calculation will help to further characterize the mechanism and supporting details. Elucidation of the catalytic mechanism will allow us to use this electrocatalyst in a series of synthetic organic conditions and aid in our advancement toward sustainable organometallic catalysis.

(Digital Presentation) New Earth-Abundant Photoelectrocatalyst and Pathway for CO2 Electroreduction

The rising levels of carbon dioxide (CO2) in the atmosphere is among the most alarming issues in today’s world: harming the environment, health, and economics of all nations on the planet. CO2 capture and its photochemical and/or photoelectrochemical reduction to fuels are promising methodologies to reduce atmospheric CO2. This is a photochemistry, electrochemistry, and catalysis problem. Transition metal complexes that can be tailored to a desired function utilizing a wide range of ligands, play a crucial role in solar fuels chemistry by reducing the activation energy for catalytic CO2 reduction to fuels. In the last decade, Mn-based complexes have sparked a significant interest owing to their abundance in Earth’s crust and lower prices compared to other transition metals. However, a catalyst that operates with high activity and turnover numbers at low overpotential is still required. We report the synthesis, characterization, and activity toward CO2 electrochemical reduction of Mn complexes containing the photoactive, electron-donating 1-imidazole-2,4,6-tri(carbazole-9-yl)-3,5-dicyanobenzene ligand (3CzImIPN). UV-vis and photoluminescence spectra of the Mn complex containing 3CzImIPN will be reported that investigate its photophysical properties under visible light. Cyclic Voltammetry (CV) studies under nitrogen and CO2 will be reported that investigate the electron transfer between the ligand and the Mn centre, as well as the electrochemical reduction of CO2. Evidence will be presented for a new, low overpotential pathway for the electroreduction of CO2 by these types of complexes. Figure 1

Enter MnIV-NHC: A Dark Photooxidant with a Long-Lived Charge-Transfer Excited State.

Detailed photophysical investigation of a Mn(IV)-carbene complex has revealed that excitation into its lowest-energy absorption band (∼500 nm) results in the formation of an energetic ligand-to-metal charge-transfer (LMCT) state with a lifetime of 15 ns. To the best of our knowledge, this is the longest lifetime reported for charge-transfer states of first-row-based transition metal complexes in solution, barring those based on Cu, with a d10 configuration. A so-called superoxidant, Mn(IV)-carbene exhibits an excited state potential typically only harnessed via excited states of reactive organic radical species. Furthermore, the long-lived excited state in this case is found to be a dark doublet, with its transition to the quartet ground state being spin-forbidden, a contrast to most first-row literature examples, and a possible cause of the long lifetime. Showcasing excited state properties which in some cases exceed those of complexes based on precious metals, these findings not only advance the library of earth-abundant photosensitizers but also shed general insight into the photophysics of d3 and related Mn complexes.

Hydroboration of Terminal Alkynes Catalyzed by a Mn(I) Alkyl PCP Pincer Complex Following Two Diverging Pathways.

A stereo- and regioselective Mn(I)-catalyzed hydroboration of terminal alkynes with pinacolborane (HBPin) is described. The hydroboration reaction is highly Z-selective in the case of aryl alkynes and E-selective in the case of aliphatic alkynes. The reaction requires no additives or solvents and proceeds with a catalyst loading of 1 mol % at 50-70 °C. The most active precatalyst is the bench-stable alkyl Mn(I) complex cis-[Mn(PCP-iPr)(CO)2(CH2CH2CH3)]. The catalytic process is initiated by the migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate. This species undergoes C-H and B-H bond cleavage of the alkyne (aromatic alkynes) and HBPin (in the case of aliphatic alkynes) forming the active Mn(I) alkynyl and boryl catalysts [Mn(PCP-iPr)(CO)(C≡CR)] and [Mn(PCP-iPr)(CO)(BPin)], respectively. A broad variety of aromatic and aliphatic alkynes was efficiently and selectively borylated. Mechanistic insights are provided based on experimental data and DFT calculations. The functionalized alkenes can be used for further applications in cross-coupling reactions.

Transition metal azahemiporphycenes as singlet oxygen sensitizers

Using free-base tris([Formula: see text]-X-phenyl)corrole (X = H, Me, OMe) as starting materials and 4-aminotriazole as the nitrogen source, we used a DDQ-mediated, room-temperature strategy for generating isocorroles to obtain the corresponding 6-azahemiporphycenes, H2[X-AHP], one of which was structurally characterized with single-crystal X-ray diffraction analysis. The free-base ligands were readily derivatized to their Pd(II), Pt(II), and Mn(II) complexes; of these, one Pd(II) complex was structurally characterized. Three of the complexes, M[Me-AHP] (M = Pd, Pt, Mn), were singled out for photophysical and singlet oxygen sensitization studies. Although none of the new complexes proved luminescent, Pd[Me-AHP] was found to be an excellent singlet oxygen sensitizer, with a singlet oxygen quantum yield of 84% in 9:1 v/v ethanol:tetrahydrofuran at room temperature. The corresponding value for Pt[Me-AHP] was found to be only 11% and that for Mn[Me-AHP] was essentially 0%. These singlet oxygen quantum yields were consonant with triplet lifetimes accessed via transition absorption spectroscopy. Combined with their strong absorption in the red, these findings suggest that palladium 6-azahemiporphycenes are worthy of exploration as a new class of triplet photosensitizers for photodynamic therapy of cancer and other diseases.

Photochargeable Mn-Based Metal-Organic Framework and Decoupled Photocatalysis.

Designing multifunctional materials that mimic the light-dark decoupling of natural photosynthesis is a key challenge in the field of energy conversion. Herein, we introduce MnBr-253, a precious metal-free metal-organic framework (MOF) built on Al nodes, bipyridine linkers and MnBr(CO)3(bipyridine) complexes. Upon irradiation, MnBr-253 colloids demonstrate an electron photocharging capacity of ~42 C ⋅ g-1 MOF, with state-of-the-art photocharging rate (1.28 C ⋅ s-1 ⋅ g-1 MOF) and incident photon-to-electron conversion efficiency of ~9.4 % at 450 nm. Spectroscopic and computational studies support effective electron accumulation at the Mn complex while high porosity and Mn loading account for the notable electron storage performance. The charged MnBr-253 powders were successfully applied for hydrogen evolution under dark conditions thus emulating the light-decoupled reactivity of photosynthesis.

Synthesis and crystal structure of new Mn (III) complex; a target catalyst for direct conversion of thiols after heterogenization

In this study, we are interested in the synthesizing of a new water-soluble complex of Mn (III) formulated as [Mn(pzo)(dipic)(H2O)2]2·3H2O; hereafter referred to as complex 1 where pzo− = pyrazonate and dipic2− = pyridine-2,6-dicarboxylate, under hydrothermal conditions. The molecular structure of complex 1 is primarily determined by single crystal X-ray diffraction (SC-XRD) which shows two mono-nuclear complexes of Mn (III) with three lattice water molecules. According to SC-XRD, complex 1 crystallizes in space group P1¯ of a triclinic system. The center of Mn (III) is seven-coordinated with a distorted pentagonal-bipyramidal geometry with three oxygen atoms and two nitrogen atoms in the equatorial plane. Two oxygen atoms of two water molecules are coordinated in the axial positions. In addition, the structure of complex 1 has been studied by elemental analysis (CHN), Fourier-transform infrared spectroscopy (FT-IR (, thermogravimetric analysis/differential thermal analysis/differential thermogravimetry (TGA/DTA/DTG). Complex 1 has been immobilized on the silica-coated Fe3O4 nanoparticles to produce an efficient and recyclable heterogeneous catalyst formulated as Fe3O4@SiO2@1; hereafter referred to as catalyst 1. Catalyst 1 was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), energy-dispersive X-ray spectrometer (EDS), FT-IR, scanning electron micrograph (SEM), powder X-ray diffraction pattern (PXRD), and Brunner-Emmet-Teller (BET). 1 was used as a new heterogeneous catalyst for the oxidative coupling of thiols to their corresponding disulfides using 30 % H2O2. Under optimum reaction conditions, catalyst 1 exhibited high catalytic activity. 1 can be recovered by a magnet and reused for at least 7 consecutive cycles without significant loss of catalytic performance.

Exploring the anticancer activity of 1-(2-methyl-3-furoyl)-4-phenyl-3-thiosemicarbazide and its Mn(II) complex: Synthesis, spectral, crystal structures, and Hirshfeld surface analysis

The chemistry of mixed ligand transition metal complexes has been of interest of researchers owing to its diverse application and bonding features. Herein, a new thiosemicarbazide derivative namely 1-(2-methyl-3-furoyl)-4-phenyl-3-thiosemicarbazide (HmfpTSC) has been synthesized along with its [Mn(mfpTSC)2(o-phen)] (C1) complex. The prepared ligand (HmfpTSC) and the complex have been confirmed via spectroscopic and single-crystal X-ray data. The HmfpTSC and complex crystallize in a monoclinic crystal system with space group P21/c and P21/n, respectively. HmfpTSC behaves as a uninegative bidentate ligand and its two-unit binds with metal ion along with one unit of o-phen. Using Hirshfeld surface analysis, the weak interactions seen in HmfpTSC and complex have been quantitatively investigated. The MTT assay was used to assess the cytotoxicity of HmfpTSC and [Mn(mfpTSC)2(o-phen)] complex against Dalton's lymphoma cells. Further, the mechanism of anticancer action of ligand and complex was investigated through DAPI, AO/EB staining, and flow cytometry. The both AO/EB and DAPI staining provided compelling evidence of complex-induced cellular and nuclear changes consistent with apoptosis and necrosis.

Synthesis of a CCC-NHC pincer Mn complex: An earth abundant catalyst for synthesis of α-alkylated ketones, 2-oxindole derivatives via borrowing hydrogen and one-pot synthesis of quinolines

A CCC-NHC pincer Mn complex was prepared and was characterized by 1H and 13C NMR spectroscopy, mass spectroscopy, elemental analysis, and single crystal X-ray crystallography. Its catalytic activities were demonstrated through diverse chemical transformations including cross-coupling borrowing hydrogen reactions and dehydrogenative cyclization reactions, which resulted in the formation of both C–C and C–N bonds. These cascade reactions involved multiple processes, including dehydrogenation, condensation, and hydrogenation. Under optimized conditions, Mn catalyst affectively converted a broad substrate scope. The different reactions yielded saturated ketones (isolated yields, 42 %–92 %), 2-oxindole derivatives (isolated yields, 70 %–83 %), and quinoline derivatives (isolated yields, 70 %–89 %). These atom economical transformations produce only water molecules as by-products enhancing their environmental friendliness. The catalyst utilized earth-abundant Mn potentially reduce costs. Catalytic cycles were proposed for borrowing hydrogen and acceptorless dehydrogenative cyclization reactions based on control experiments. These included oxidation, aldol condensation, and hydrogenation reactions.

Structures and photochromic behavior of viologen-based compounds: Insights from Mn(II) and Cd(II) complexes

This study investigates the crystal structures and photochromic properties of two viologen-based compounds [Mn(CMbpy)(BTEC)0.5(H2O)4]·0.5(H2BTEC)·3H2O (1) and [Cd(CMbpy)(1,2,4-BTC)(H2O)]n (2) [CMbpyBr = 1-(1-cyclohexylmethane)-4,4′-bipyridinium bromide, H4BTEC=1,2,4,5-benzenetetracarboxylic acid, 1,2,4-H3BTC=1,2,4-benzenetricarboxylic acid]. X-ray diffraction analysis identified compound 1 as a triclinic ionic lattice featuring Mn(II) in an octahedral coordination with CMbpy cations, whereas compound 2 crystallizes in an orthorhombic space group forming a three-dimensional MOF stabilized by CMbpy cations. Compound 1 demonstrated no color change, while compound 2 exhibited a rapid transition to a blue state upon UV irradiation, with an accompanying emergence of new absorption peaks, indicative of viologen radical formation. This behavior was corroborated by electron paramagnetic resonance (EPR) spectroscopy. Our findings provide a profound understanding of the structure–function relationship in these viologen complexes, highlighting the synergy between metal coordination, hydrogen bonding, and the strategic positioning of donor–acceptor components.

CO2-to-CO conversion with over 10% efficiency using earth abundant system in a single-compartment reactor with oxygen tolerant Mn complex catalyst.

The direct conversion of CO2 in flue gas to value-added chemicals is a potentially important cost-effective solar-driven CO2 reduction technology. The present work demonstrates the solar-powered conversion of CO2 to CO with greater than 10% efficiency using a Mn complex cathode and an Fe-Ni anode in a single-compartment reactor without an ion exchange membrane in conjunction with a Si solar cell. Reactors separated by ion exchange membranes are typically used to prevent any effects of oxygen generated by the counter electrode. However, the present Mn complex catalyst maintained its activity even in the presence of 15% O2. Operando surface-enhanced Raman spectroscopy established that the present Mn catalyst preferentially reacted with CO2 without adsorbing O2. This unique characteristic enabled solar-driven CO2 reduction using a single-compartment reactor. In contrast, catalytic metals such as Ag tend to lose activity in such systems as a consequence of reaction with oxygen produced at the anode.

Hydrogen Evolving Mono‐Nuclear Manganese Complexes with Carefully Positioned Pyridine Base Ligands

AbstractEnormous efforts have been made by the scientific community in the development of bio‐mimetic/bio‐inspired hydrogen‐evolving complexes as catalysts for an alternative hydrogen energy carrier and a renewable energy sources. In this regard, new bio‐inspired mono‐nuclear Mn(I) carbonyl model complexes fac‐[(Mn(CO)3(κ2‐SN2C7H5)(κ1‐PPh2Py))] 1 and fac‐[(Mn(CO)3(κ2‐S2NC7H4)(κ1‐PPh2Py))] 2 with 2‐mercaptobenzimidazole (N,N) and 2‐mercaptobenzothiazole (S,N) ligands and a N‐based phosphine ligand (PPh2Py) have been synthesized, spectroscopically characterized and evaluated as electro‐catalysts for hydrogen generation. In contrast to related mono‐nuclear (N,N/S,N)−Mn−PPh3 complexes,, the newly introduced pyridine nitrogen atom of the PPh2Py ligand placed in an axial position in the second coordination sphere of the Mn(I) complexes, provides a first site for protonation and enables a fast intra‐molecular proton transfer to the central metal atom with a weaker acid. Theoretical DFT calculations enable a detailed picture of catalytic pathways, assign redox transitions and structural changes. Both the molecular complexes were tested as electro‐catalysts for hydrogen generation in CH3CN. They effectively catalyzed the electrochemical proton reduction with the weaker acetic acid as the proton source and displayed a turnover frequency (TOF/s−1; O.P., η/V) of 610; 1.02 and 615; 1.12, respectively. The computer‐aided design of dedicated proton transfer pathways from second coordination sphere ligands is thus able to allow a hydrogen evolution reactivity with a weaker acid (acetic acid).

Preparation, characterization, single-crystal analysis, and cytotoxic assessment of complexes formed by Schiff base and 8-hydroxyquinoline co-ligand with Co(II), Ni(II), and Mn(II) metal ions

This study focuses on the preparation of mixed ligand complexes of Ni(II), Co(II), and Mn(II) by combining the co-ligands 2-(((4-fluorophenyl)imino)methyl)-4-methoxy-6-nitrophenol (L1) and 8-hydroxyquinoline (L2). The chemical structures of the all compounds were examined using various techniques, including 1H and 13C NMR, FT-IR, UV–Vis, TGA, molar conductivity, LC-MS/MS, elemental analysis and magnetic susceptibility. The crystal structure of the ligand L1 was determined using single crystal X-ray analysis revealing that the ligand favors the phenol-imine tautomeric form in the solid state. All complexes are suggested to have an octahedral structure. Finally, the MTT assay was used to determine the toxicity level of the mixed ligand complexes in human non-small cell lung cancer (A549) and normal bronchial epithelial cell lines (BEAS-2B). The results showed that the [Ni(L1)(L2).(H2O)2] complex (IC50: 5.97 µM) exhibited high cytotoxic activity at a lower dose than cisplatin compared to the other compounds. In contrast, the [Ni(L1)(L2).(H2O)2] complex was shown to exhibit significantly lower cytotoxic activity (IC50 > 100 s µM) in the BEAS-2B (normal bronchial epithelial cell) cell line. The other compounds [Co(L1)(L2).(H2O)2] and [Mn(L1)(L2).(H2O)2] were shown to have no significant anticancer activity in A549 cells due to their cytotoxic activity at higher doses than cisplatin (IC50 > 100 s µM).

Targeting Manganese Amidinate and ß-Ketoiminate Complexes as Precursors for Mn-Based Thin Film Deposition.

With a focus on Mn based organometallic compounds with suitable physico-chemical properties to serve as precursors for chemical vapor deposition (CVD) and atomic layer deposition (ALD) of Mn-containing materials, systematic synthetic approaches with ligand variation, detailed characterization, and theoretical input from density functional theory (DFT) studies are presented. A series of new homoleptic all-nitrogen and mixed oxygen/nitrogen-coordinated Mn(II) complexes bearing the acetamidinate, formamidinate, guanidinate and ß-ketoiminate ligands have been successfully synthesized for the first time. The specific choice of these ligand classes with changes in structure and coordination sphere and side chain variations result in significant structural differences whereby mononuclear and dinuclear complexes are formed. This was supported by density functional theory (DFT) studies. The compounds were thoroughly characterized by single crystal X-ray diffraction, magnetic measurements, mass spectrometry and elemental analysis. To evaluate their suitability as precursors for deposition of Mn-based materials, the thermal properties were investigated in detail. Mn(II) complexes possessing the most promising thermal properties, namely Bis(N,N'-ditertbutylformamidinato)manganese(II) (IV) and Bis(4-(isopropylamino)pent-3-en-2-onato)manganese(II) (ßIII) were used in reactivity studies with DFT to explore their interaction with oxidizing co-reactants such as oxygen and water which will guide future CVD and ALD process development.

SYNTHESIS, CHARACTERIZATION, AND ANTIBACTERIAL EVALUATION OF DIVALENT METAL COMPLEXES WITH SCHIFF BASES DERIVED FROM 4- ANISALDEHYDE AND ARGININE

In the present study, a new Schiff base, 5-Guanidino-2-[(4-methoxy-benzylidene)-amino]-pentanoic acid, and its metal (II) complexes were synthesized. Structural characterization was done using FTIR, UV-visible spectral analysis, molar conductance, and melting/decomposition temperature determination. Spectral studies revealed the ligand to be bidentate, coordinating with the metal through the carboxylic oxygen and azomethine nitrogen. The antibacterial activity (in vitro) against Escherichia coli and Staphylococcus aureus strains was studied using the agar well diffusion method. The results indicated that the free ligand exhibited no biological activity, whereas the cadmium complex (C28H38CdN8O6) proved to be the best antibacterial agent (up to 27 mm diameter inhibition zone against E. coli), followed by the Mn (II) complex and the Ni (III) complex having the least activity against both Escherichia coli and Staphylococcus aureus. This means that metal chelation significantly affected the anti-bacterial behavior of the organic Schiff base. This study contributes to the growing body of knowledge in the field of bioinorganic chemistry and may have potential implications for pharmaceutical and biomedical applications.