Multi-Centered Solid-Phase Quasi-Intramolecular Redox Reactions of [(Chlorido)Pentaamminecobalt(III)] Permanganate—An Easy Route to Prepare Phase Pure CoMn2O4 Spinel

Hexakis(urea-O)iron Complex Salts as a Versatile Material Family: Overview of Their Properties and Applications

Due to their Fe- and N-containing reactive urea ligand content, the hexakis(urea-O)iron(II) and hexakis(urea-O)iron(III) complexes were found to be versatile materials in various application fields of industry and environmental protection. In our present work, we have comprehensively reviewed the synthesis, structural and spectroscopic details, and thermal properties of hexakis(urea-O)iron(II) and hexakis(urea-O)iron(III) salts with different anions (NO3-, Cl-, Br- I-, I3-, ClO4-, MnO4-, SO42-, Cr2O72-, and S2O82-). We compared and evaluated the structural, spectroscopic (IR, Raman, UV-vis, Mössbauer, EPR, and X-ray), and thermogravimetric data. Based on the thermal behavior of these complexes, we evaluated the solid-phase quasi-intramolecular redox reactions of anions and urea ligands in these complexes and summarized the available information on the properties of the resulting simple and mixed iron-containing oxides. Furthermore, we give a complete overview of the application of these complexes as catalysts, reagents, absorbers, or agricultural raw materials.

Structural, Spectroscopic, and Thermal Decomposition Features of [Carbonatotetraamminecobalt(III)] Iodide—Insight into the Simultaneous Solid-Phase Quasi-Intramolecular Redox Reactions

[κ2-O,O′-Carbonatotetraamminecobalt(III)] iodide, or [Co(NH3)4CO3]I, named in this paper as compound 1, was prepared and characterized comprehensively with spectroscopic (IR, Raman and UV) and single-crystal X-ray diffraction methods. Compound 1 was orthorhombic, and isomorphous with the analogous bromide. The four ammonia ligands and the carbonate anion were coordinated to the central cobalt cation in a distorted octahedral geometry. The carbonate ion formed a four-membered symmetric planar chelate ring. The complex cations were bound to each other by N-H···O hydrogen bonds and formed zigzag sheets via an extended 2D hydrogen bond network. The complex cations and iodide ions were arranged into ion pairs and each cation bound its iodide pair through three hydrogen bonds. The thermal decomposition started with the oxidation of the iodide ion by CoIII in the solid phase resulting in [Co(NH3)4CO3] and I2. This intermediate CoII-complex in situ decomposed into Co3O4 and C-N bond containing intermediates. In inert atmosphere, CO or C-N bond containing compounds, and also, due to the in situ decomposition of CoCO3 intermediate, Co3O4 was formed. The quasi-intramolecular solid-phase redox reaction of [Co(NH3)4CO3] might have resulted in the formation of C-N bond containing compounds with substoichiometric release of ammonia and CO2 from compound 1. The C-N bond containing intermediates reduced Co3O4 into CoO and Co, whereas in oxygen-containing atmosphere, the end-product was Co3O4, even at 200 °C, and the endothermic ligand loss reaction coincided with the consecutive exothermic oxidation processes.

[Hexaamminecobalt(III)] Dichloride Permanganate—Structural Features and Heat-Induced Transformations into (CoII,MnII)(CoIII,MnIII)2O4 Spinels

We synthesized and characterized (IR, Raman, UV, SXRD) hexaamminecobalt(III) dichloride permanganate, [Co(NH3)6]Cl2(MnO4) (compound 1) as the precursor of Co–Mn–spinel composites with atomic ratios of Co:Mn = 1:1 and 1:3. The 3D−hydrogen bond network includes N–HO–Mn and N–HCl interactions responsible for solid-phase redox reactions between the permanganate anions and ammonia ligands. The temperature-limited thermal decomposition of compound 1 under the temperature of boiling toluene (110 ∘C) resulted in the formation of (NH4)4Co2Mn6O12. which contains a todorokite-like manganese oxide network (MnII4MnIII2O1210−). The heat treatment products of compounds 1 and [Co(NH3)5Cl](MnO4)2 (2) synthesized previously at 500 ∘C were a cubic and a tetragonal spinel with Co1.5Mn1.5O4 and CoMn2O4 composition, respectively. The heating of the decomposition product of compounds 1 and 2 that formed under refluxing toluene (a mixture with an atomic ratio of Co:Mn = 1:1 and 1:2) and after aqueous leaching ((NH4)4Co2Mn6O12, 1:3 Co:Mn atomic ratio in both cases) at 500 ∘C resulted in tetragonal Co0.75Mn2.25O4 spinels. The Co1.5Mn1.5O4 prepared from compound 1 at 500 ∘C during the solid-phase decomposition catalyzes the degradation of Congo red with UV light. The decomposition rate of the dye was found to be nine times faster than in the presence of the tetragonal CoMn2O4 spinel prepared in the solid-phase decomposition of compound 2. The todorokite-like intermediate prepared from compound 1 under N2 at 115 ∘C resulted in a 54 times faster degradation of Congo red, which is a great deal faster than the same todorokite-like phase that formed from compound 2 under N2.

Structure and Vibrational Spectra of Pyridine Solvated Solid Bis(Pyridine)silver(I) Perchlorate, [Agpy2ClO4]·0.5py

A hemipyridine solvate of bis(pyridine)silver(I) perchlorate, [Agpy2ClO4]·0.5py (compound 1) was prepared and characterized by single crystal X-ray analysis and vibrational spectroscopy (R and low-temperature Raman). Compound 1 was prepared via the trituration of [Agpy2ClO4] and 4[Agpy2ClO4]·[Agpy4]ClO4 (as the source of the solvate pyridine) in a mixed solvent of acetone:benzene =1:1 (v = v) at room temperature. The monoclinic crystals of compound 1 were found to be isomorphic with the analogous permanganate complex (a = 19.1093(16) Å, b = 7.7016(8) Å, c = 20.6915(19) Å, β = 105.515(7)°; space group: C2/c). Two [Agpy2]+ cations formed a dimeric unit [Agpy2ClO4]2, and each silver ion was connected to two ClO4− anions via oxygen atoms. The Ag∙∙∙Ag distance was 3.3873(5) Å, the perchlorate ions were coordinated to silver ions, and the Ag∙∙∙O distances were 2.840(2) Å and 2.8749(16) Å in the centrosymmetric rectangle of Ag-O-Ag-O. The stoichiometric ratio of the monomer [Agpy2ClO4] and the solvent pyridine was 1:0.5. The guest pyridine occupied 527.2 Å3, which was 18.0% of the volume of the unit cell. There was no additional residual solvent-accessible void in the crystal lattice. The solvate pyridine was connected via its a-CH to one of the O atoms of the perchlorate anion. Correlation analysis, as well as IR and low-temperature Raman studies, were performed to assign all perchlorate and pyridine vibrational modes. The solvate and coordinated pyridine bands in the IR and Raman spectra were not distinguishable. A perchlorate contribution via Ag-O coordination to low-frequency Raman bands was also assigned.