Low-spin manganese(II) and high-spin manganese(III) complexes derived from disalicylaldehyde oxaloyldihydrazone: Synthesis, spectral characterization and electrochemical studies

Adapting Atomic Configuration Steers Dynamic Half-Occupied State for Efficient CO2 Electroreduction to CO

Electronic structures stand at the center to essentially understand the catalytic performance and reaction mechanism of atomically dispersed transition-metal-nitrogen-carbon catalysts (ADTCs). However, under realistic electrocatalytic conditions, the dynamic electronic disturbance at metal centers originating from complicated interactions with microenvironments is commonly neglected, which makes a true structure-property correlation highly ambiguous. Here, we employ operando time-resolved X-ray absorption spectroscopy to delve deeply into dynamic electronic behaviors of a family of transition-metal centers that are observed to adaptively vary in the metal-ligand configuration during the CO2 electroreduction reaction. We identify dynamic electronic/geometric configuration and d-orbital occupation under working conditions, demonstrating an unprecedentedly precise activity descriptor, i.e., dynamic axial dz2 electron, for the CO2-to-CO conversion. Direct results validate that the half-occupied state suggests the optimum binding behaviors with intermediates, significantly promoting CO production, which has been demonstrated by a significant kinetics enhancement of 1 to 2 orders of magnitude as compared with fully occupied and unoccupied states. This work presents the first empirical demonstration for a real correlation between the dynamic electronic/geometric configuration and catalytic kinetics in ADTCs, paving a new way for modulating catalysts and designing highly efficient reaction pathways.

Structural elucidation of a Mn(III) derivative anchored with a tetradentate Schiff base precursor: in vitro cytotoxicity study

A new mononuclear Mn(III) derivative, [Mn(L)(H2O)2]ClO4 (1) was obtained by reacting manganese perchlorate with the tetradentate Schiff base precursor, H2L, [where H2L=C6H3(OMe)(OH)CH=N(CH2)3N=CH(OH)(OMe)C6H3] and characterized by various spectral techniques. Single crystal X-ray diffraction analysis revealed that in 1, the central Mn atom is hexa-coordinated via the NNOO donor sites of the Schiff base precursor and two water molecules, yielding a distorted octahedral geometry. Also, the EPR spectra of 1 were recorded at the solid state by varying the temperature (from 90 to 300 K) as well as in different organic solvents; DMSO, MeOH and a mixture CH2Cl2/toluene; the results obtained agree with the geometrical environment around the metal. The cytotoxic activity of the Mn(III) derivative was evaluated against normal and cancer cell lines. The derivative exhibited comparatively better cytotoxic activity against MCF-7 cells compared to SiHa and fibroblast cells.

Tetramer Compound of Manganese Ions with Mixed Valence [MnII MnIII MnIV] and Its Spatial, Electronic, Magnetic, and Theoretical Studies

Using different spectroscopic techniques and computational calculations, we describe the structural and electromagnetic relationship that causes many interesting phenomena within a novel coordination compound with mixed valence manganese (II, III and IV) in its crystal and powder state. The novel compound [MnII MnIII MnIV(HL)2(H2L)2(H2O)4](NO3)2(H2O) 1 was obtained with the Schiff base (E)-2-((2-hydroxybenzylidene)amine)-2-(hydroximethyl)propane-1,3-diol, (H4L), and Mn(NO3)2.4H2O. The coordination reaction was promoted by the deprotonation of the ligand by the soft base triethylamine. The paper’s main contribution is the integration of the experimental and computational studies to explain the interesting magnetic behavior that the mixed valence manganese multimetallic core shows. The results presented herein, which are rarely found for Mn(II), (III) and (IV) complexes, will contribute to the understanding of the magnetic communication generated by the valence electrons and its repercussion in the local geometry and in the overall crystalline structure.

Monodisperse Ultrasmall Manganese-Doped Multimetallic Oxysulfide Nanoparticles as Highly Efficient Oxygen Reduction Electrocatalyst

The highly efficient and cheap non-Pt-based electrocatalysts such as transition-based catalysts prepared via facile methods for oxygen reduction reaction (ORR) are desirable for large-scale practical industry applications in energy conversion and storage systems. Herein, we report a straightforward top-down synthesis of monodisperse ultrasmall manganese-doped multimetallic (ZnGe) oxysulfide nanoparticles (NPs) as an efficient ORR electrocatalyst by simple ultrasonic treatment of the Mn-doped Zn-Ge-S chalcogenidometalate crystal precursors in H₂O/EtOH for only 1 h at room temperature. Thus obtained ultrasmall monodisperse Mn-doped oxysulfide NPs with ultralow Mn loading level (3.92 wt %) not only exhibit comparable onset and half-wave potential (0.92 and 0.86 V vs reversible hydrogen electrode, respectively) to the commercial 20 wt % Pt/C but also exceptionally high metal mass activity (189 mA/mg at 0.8 V) and good methanol tolerance. A combination of transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical analysis demonstrated that the homogenous distribution of a large amount of Mn(III) on the surface of NPs mainly accounts for the high ORR activity. We believe that this simple synthesis of Mn-doped multimetallic (ZnGe) oxysulfide NPs derived from chalcogenidometalates will open a new route to explore the utilization of discrete-cluster-based chalcogenidometalates as novel non-Pt electrocatalysts for energy applications and provide a facile way to realize the effective reduction of the amount of catalyst while keeping desired catalytic performances.