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3,5-Lutidine pentaaqua sulfate complexes of first-row transition metals: [M(3,5-lutidine)(H2O)5]SO4, with M = Mn, Co, Ni, and Zn

ABSTRACT: The structures of four metal 3,5-lutidine pentaaqua sulfates (Mn, Co, Ni, Zn) are presented and are shown to be isostructural. The reactions of MnSO4·H2O, CoSO4·7H2O, NiSO4·6H2O and ZnSO4·7H2O with 3,5-lutidine (3,5-dimethylpyridine) yield crystals of pentaaqua(3,5-dimethylpyridine-κN)manganese(II) sulfate, [Mn(C7H9N)(H2O)5]SO4, (1), pentaaqua(3,5-dimethylpyridine-κN)cobalt(II) sulfate, [Co(C7H9N)(H2O)5]SO4, (2), pentaaqua(3,5-dimethylpyridine-κN)nickel(II) sulfate, [Ni(C7H9N)(H2O)5]SO4, (3), and pentaaqua(3,5-dimethylpyridine-κN)zinc(II) sulfate, [Zn(C7H9N)(H2O)5]SO4, (4), which were characterized by single-crystal X-ray diffraction. The four crystals are isostructural, demonstrating near identical unit-cell parameters and atomic positions. The metal atoms are all octahedrally coordinated, with one lutidine ligand and five water ligands. The sulfate dianion hydrogen bonds with the coordinated water molecules of the dicationic metal complex salts, generating infinite three-dimensional networks.

SUBMITTER: Golen J

PROVIDER: S-EPMC10439421 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature

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Project description:Transition metal oxides are characterized by an acute structure and composition dependent electrocatalytic activity toward the oxygen evolution (OER) and oxygen reduction (ORR) reactions. For instance, Mn containing oxides are among the most active ORR catalysts, while Ni based compounds tend to show high activity toward the OER in alkaline solutions. In this study, we show that incorporation of Ni into α-MnO2, by adding Ni precursor into the Mn-containing hydrothermal solution, can generate distinctive sites with different electronic configurations and contrasting electrocatalytic activity. The structure and composition of the Ni modified hollandite α-MnO2 phase were investigated by X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy (TEM-EDX), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS). Our analysis suggests that Mn replacement by Ni into the α-MnO2 lattice (site A) occurs up to approximately 5% of the total Mn content, while further increasing Ni content promotes the nucleation of separate Ni phases (site B). XAS and XRD show that the introduction of sites A and B have a negligible effect on the overall Mn oxidation state and bonding characteristics, while very subtle changes in the XPS spectra appear to suggest changes in the electronic configuration upon Ni incorporation into the α-MnO2 lattice. On the other hand, changes in the electronic structure promoted by site A have a significant impact in the pseudocapacitive responses obtained by cyclic voltammetry in KOH solution at pH 13, revealing the appearance of Mn 3d orbitals at the energy (potential) range relevant to the ORR. The evolution of Mn 3d upon Ni replacement significantly increases the catalytic activity of α-MnO2 toward the ORR. Interestingly, the formation of segregated Ni phases (site B) leads to a decrease in the ORR activity while increasing the OER rate.

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3,5-Lutidine pentaaqua sulfate complexes of first-row transition metals: [M(3,5-lutidine)(H2O)5]SO4, with M = Mn, Co, Ni, and Zn

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3,5-Lutidine penta­aqua sulfate complexes of first-row transition metals: [M(3,5-lutidine)(H2O)5]SO4, with M = Mn, Co, Ni, and Zn

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OmicsDI is part of the ELIXIR infrastructure

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3,5-Lutidine pentaaqua sulfate complexes of first-row transition metals: [M(3,5-lutidine)(H2O)5]SO4, with M = Mn, Co, Ni, and Zn