Electrical conductivity and thermoelectric power of liquid Co–Sn alloys

The electrical conductivity and thermoelectric power of liquid Co–Sn alloys were investigated in a wide concentration and temperature range. It was shown that the electrical conductivity of the melts decreased with an increase of the Co content. The results are interpreted in the context of the s–d hybridisation model. The corresponding behaviour is caused by sharing electrons from one metal to another one. This is in agreement with the concept of Fermi enthalpy, according to which up to two electrons from Sn transfer to the uppermost bands of Co.     

In Situ Growth of Ultrafine Pt Nanoparticles onto Hierarchical Co3O4 Nanosheet-Assembled Microflowers for Efficient Electrocatalytic Hydrogen Evolution

The development of Pt-based electrocatalysts with high Pt utilization efficiency toward the hydrogen evolution reaction (HER) is of great significance for the future sustainable hydrogen economy. For rational design of high-performance HER electrocatalyst, the simultaneous consideration of both thermodynamic and kinetic aspects remains greatly challenging. Herein, a simple template-derived strategy is demonstrated for the in situ growth of ultrafine Pt nanoparticles onto Co₃O₄ nanosheet-assembled microflowers (abbreviated as Pt/Co₃O₄ microflowers hereafter) by using the pre-fabricated PtCo-based Hofmann coordination polymer as reactive templates. The elaborate preparation of such intriguing hierarchical architecture with well-dispersed tiny Pt nanoparticles, abundant metal/oxide heterointerfaces and open configuration endows the formed Pt/Co₃O₄ microflowers with high Pt utilization efficiency, rich active sites, lowered energy barrier for water dissociation and expedited reaction kinetics. Consequently, the Pt/Co₃O₄ microflowers exhibit superior HER activity with a relatively low overpotential of 34 mV to deliver a current density of 10 mA cm⁻², small Tafel slope (34 mV dec⁻¹) and outstanding electrochemical stability, representing an attractive electrocatalyst for practical water splitting. What's more, our concept of in situ construction of metal/oxide heterointerfaces may provide a new opportunity to design high-performance electrocatalysts for a variety of applications.     

One-Pot Synthesis of Heterobimetallic Metal–Organic Frameworks (MOFs) for Multifunctional Catalysis

A one-pot synthesis of bimetallic metal–organic frameworks (Co/Fe-MOFs) was achieved by treating stoichiometric amounts of Fe and Co salts with 2-aminoterephthalic acid (NH₂-BDC). Monometallic Fe (catalyst A) and Co (catalyst F) were also prepared along with mixed-metal Fe/Co catalysts (B–E) by changing the Fe/Co ratio. For mixed-metal catalysts (B–E) SEM energy-dispersive X-ray (EDX) analysis confirmed the incorporation of both Fe and Co in the catalysts. However, a spindle-shaped morphology, typically known for the Fe-MIL-88B structure and confirmed by PXRD analysis, was only observed for catalysts A–D. To test the catalytic potential of mixed-metal MOFs, reduction of nitroarenes was selected as a benchmark reaction. Incorporation of Co enhanced the activity of the catalysts compared with the parent NH₂-BDC-Fe catalyst. These MOFs were also tested as electrocatalysts for the oxygen evolution reaction (OER) and the best activity was exhibited by mixed-metal Fe/Co-MOF (Fe/Co batch ratio=1). The catalyst provided a current density of 10 mA cm⁻² at 410 mV overpotential, which is comparable to the benchmark OER catalyst (i.e., RuO₂). Moreover, it showed long-term stability in 1 m KOH. In a third catalytic test, dehydrogenation of sodium borohydride showed high activity (turnover frequency=87 min⁻¹) and hydrogen generation rate (67 L min⁻¹ g⁻¹ catalyst). This is the first example of the synthesis of bimetallic MOFs as multifunctional catalysts particularly for catalytic reduction of nitroarenes and dehydrogenation reactions.     

Four-component relativistic calculations of NMR shielding constants of the transition metal complexes. Part 1: Pentaammines of cobalt,rhodium, and iridium

The nonrelativistic and four-component fully relativistic calculations of ¹H, ¹⁵N, ⁵⁹Co, ¹⁰³Rh, and ¹⁹³Ir shielding constants of pentaammineaquacomplexes of cobalt(III), rhodium(III), and iridium(III) were carried out at the density functional theory (DFT) level of theory. The noticeable deshielding relativistic corrections were observed for nitrogen shielding constants (chemical shifts), whereas those corrections were found to be negligible for protons. For the transition metals cobalt, rhodium, and iridium, relativistic corrections to their nuclear magnetic resonance (NMR) shielding constants were found to be rather small for cobalt and rhodium (some 5–10%), whereas they are essentially larger for iridium (up to 70%).     

Accelerating H2 Evolution by Anodic Semi-dehydrogenation of Tetrahydroisoquinolines in Water over Co3O4 Nanoribbon Arrays Decorated Nickel Foam

Coupling the H₂ evolution reaction in water with thermodynamically favorable organic oxidation reactions is highly desirable, because it can enhance the energy conversion efficiency compared with electrocatalytic water splitting, and produce value-added chemicals instead of O₂ in the anodic reaction. Herein, Co₃O₄ nanoribbon arrays in situ grown on nickel foam (Co₃O₄@NF) was employed as an effective electrocatalyst for the selective oxidation of tetrahydroisoquinolines (THIQs). Various value-added semi-dehydrogenation products including dihydroisoquinolines with electro-deficient or -rich groups could be obtained with moderate yields and faradaic efficiencies. Benefitting from the rich surface active sites of Co₃O₄@NF, a two-electrode (Co₃O₄@NF||Pt) electrolytic system drove a benchmark current density of 10 mA cm⁻² at a cell voltage as low as 1.446 V in 1.0 M KOH aqueous solution containing 0.02 M THIQ, which was reduced by 174 mV in comparison with that of overall water splitting.     

Synthesis,molecular geometry,spectroscopic studies and thermal properties of Co(II) complexes

Co(II) complexes (1‐4) were prepared and characterized by elemental analyses, infrared spectra, spectral studies, magnetic susceptibility measurements, X‐ray diffraction analysis and thermogravimetric analysis (TGA). The X‐ray diffraction patterns of Co(II) complexes were observed many peaks which indicate the polycrystalline nature. The thermodynamic parameters were calculated by using Coats–Redfern and Horowitz–Metzger methods. The bond length, bond angle and quantum chemical parameters of the Co(II) complexes were studied and discussed. The Co(II) complexes were tested against various Gram‐positive bacteria, Gram‐negative bacteria and fungi. It was found that the Co(II) complex (1) has more antifungal activity than miconazole (antifungal standard drug) against P. italicum at all concentration. The Co(II) complex ( 2 ) has more antibacterial activity than the penicillin against K. pneumoniae at all concentration. The interaction between Co(II) complexes and calf thymus DNA show hypochromism effect. The relationship between the values of HOMO–LUMO energy gap (?E) and the values of intrinsic binding constant (K_b) is revealed increasing of HOMO–LUMO energy gap accompanied by the decrease of K_b.     

A Delicate Balance between Antiferromagnetism and Ferromagnetism: Theoretical and Experimental Studies of A2MRu5B2 (A=Zr,Hf; M=Fe,Mn) Metal Borides

Metal-rich borides with the Ti₃Co₅B₂-type structure represent an ideal playground for tuning magnetic interactions through chemical substitutions. In this work, density functional theory (DFT) and experimental studies of Ru-rich quaternary borides with the general composition A₂MRu₅B₂ (A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr₂FeRu₅B₂ and Hf₂FeRu₅B₂ prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M-chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically and creates a strong competition between FM and AFM states with a slight preference for AFM in Zr₂MnRu₅B₂ and for FM in Hf₂MnRu₅B₂. Magnetic property measurements show a field dependence of the AFM transition (T_N): T_N is found at 0.1 T for all phases with predicted AFM states whereas for the predicted FM phase it is found at a much lower magnetic field (0.005 T). Furthermore, T_N is lowest for a Hf-based phase (20 K) and highest for a Zr-based one (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf-based phases. Interestingly, the AFM transitions vanish in all compounds at higher fields (>1 T) in favor of FM transitions, indicating metamagnetic behaviors for these Ru-rich phases.     

X-ray structure and magnetochemical study on a Co(II) complex of 2-acetyl-1,3-indandione

An X-ray structure of a Co(II) complex of bidentate chelating 2-acetyl-1,3-indandione (2AID) is reported–Co(2AID)₂(H₂O)₂ · 2H₂O. The compound crystallizes in the monoclinic space group P2₁/n with four molecules per unit cell. The molecular structure shows distorted octahedral geometry of the metal center. The complex is characterized by EPR and magnetic measurements, which show high-spin electronic structure for the metal ion.     

Metal-Organic Gel-Derived Co/CoO/Co3O4 Composite for the Electrochemical Detection of Diethylstilbestrol

A novel three-phase composite of Co/CoO/Co₃O₄ is synthesized through straightforward calcination treatment towards cobalt-based metal-organic gel (Co MOG) precursor, which is constructed with the metal source of cobalt chloride and organic ligand of 4, 4', 4”-((1, 3, 5-triazine-2, 4, 6-triyl) tris (azanediyl)) tribenzoic acid at room temperature. The morphology, structure and composition of the derived Co/CoO/Co₃O₄ is confirmed through scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectrums (XPS). Furthermore, the composite of Co/CoO/Co₃O₄ is employed as electrode modified material with the excellent electrochemical performances of accelerating the electron transfer and boosting the electrode interface reaction. As a proof of concept, the electrochemical redox behaviors of diethylstilbestrol (DES) have been systemically investigated at the modified electrode interface and the established analytical approach for DES with the broad linear range and satisfied recovery. This work not only provided a facile approach to obtain electrode material with excellent electrochemical performance but also enriched the application of MOG materials in the electrochemical field.