Ikaite formation and its transformation to calcite occurs via distinct amorphous calcium carbonates (referred to as I and II) that differ in their morphology, particle size, water content and stability.

Copper manganese oxide spinels and related (multiphase) materials with the formula Cu_xMn_3−xO₄ are the active catalysts in a wide variety of industrially important processes due to their great diversity in their phase relations, metal ion valence/site distribution, and chemical properties. In this review, we summarize the preparation methods and their effects on the composition, properties, and catalytic properties of various Cu_xMn_3−xO₄ catalysts with various Cu/Mn ratios. The main summarized catalytic reactions are the oxidation of carbon monoxide, nitrogen oxide, and hydrogen sulfide and the oxidative removal of organic solvents such as benzene, toluene, and xylene from the air. Some industrially important reactions (steam reforming of methanol or synthesis gas) and the manufacture of organic chemicals (methyl formate, propylene oxide, and benzyl alcohol) catalyzed by Cu_xMn_3−xO₄ spinels are also reviewed.

Two monoclinic polymorphs of [Ag(NH₃)₂]MnO₄ containing a unique coordination mode of permanganate ions were prepared, and the high-temperature polymorph was used as a precursor to synthesize pure AgMnO₂. The hydrogen bonds between the permanganate ions and the hydrogen atoms of ammonia were detected by IR spectroscopy and single-crystal X-ray diffraction. Under thermal decomposition, these hydrogen bonds induced a solid-phase quasi-intramolecular redox reaction between the [Ag(NH₃)₂]⁺ cation and MnO₄^– anion even before losing the ammonia ligand or permanganate oxygen atom. The polymorphs decomposed into finely dispersed elementary silver, amorphous MnO_x compounds, and H₂O, N₂ and NO gases. Annealing the primary decomposition product at 573 K, the metallic silver reacted with the manganese oxides and resulted in the formation of amorphous silver manganese oxides, which started to crystallize only at 773 K and completely transformed into AgMnO₂ at 873 K.

The reaction of ammoniacal AgNO₃ solution (or aq. solution of [Ag(NH₃)₂]NO₃) with aq. NaClO₄ resulted in [Ag(NH₃)₂]ClO₄ (compound 1). Detailed spectroscopic (correlation analysis, IR, Raman, and UV) analyses were performed on [Ag(NH₃)₂]ClO₄. The temperature and enthalpy of phase change for compound 1 were determined to be 225.7 K and 103.04 kJ/mol, respectively. We found the thermal decomposition of [Ag(NH₃)₂]ClO₄ involves a solid-phase quasi-intramolecular redox reaction between the perchlorate anion and ammonia ligand, resulting in lower valence chlorine oxyacid (chlorite, chlorate) components. We did not detect thermal ammonia loss during the formation of AgClO₄. However, a redox reaction between the ammonia and perchlorate ion resulted in intermediates containing chlorate/chlorite, which disproportionated (either in the solid phase or in aqueous solutions after the dissolution of these decomposition intermediates in water) into AgCl and silver perchlorate. We propose that the solid phase AgCl-AgClO₄ mixture eutectically melts, and the resulting AgClO₄ decomposes in this melt into AgCl and O₂. Thus, the final product of decomposition is AgCl, N₂, and H₂O. The intermediate (chlorite, chlorate) phases were identified by IR, XPS, and titrimetric methods.

We synthesized and structurally characterized the previously unknown [Co(NH₃)₅Cl](MnO₄)₂ complex as the precursor of CoMn₂O₄. The complex was also deuterated, and its FT-IR, far-IR, low-temperature Raman and UV-VIS spectra were measured as well. The structure of the complex was solved by single-crystal X-ray diffraction and the 3D-hydrogen bonds were evaluated. The N-H…O-Mn hydrogen bonds act as redox centers to initiate a solid-phase quasi-intramolecular redox reaction even at 120 °C involving the Co(III) centers. The product is an amorphous material, which transforms into [Co(NH₃)₅Cl]Cl₂, NH₄NO₃, and a todorokite-like solid Co-Mn oxide on treatment with water. The insoluble residue may contain {Mn₄^IIIMn^IV₂O₁₂}_n⁴ⁿ⁻, {Mn₅^IIIMn^IVO₁₂}_n⁵ⁿ⁻ or {Mn^III₆O₁₂}_n⁶ⁿ⁻ frameworks, which can embed 2 × n (Co^II and/or Co^III) cations in their tunnels, respectively, and 4 × n ammonia ligands are coordinated to the cobalt cations. The decomposition intermediates decompose on further heating via a series of redox reactions, forming a solid Co^IIM^III₂O₄ spinel with an average size of 16.8 nm, and gaseous N₂, N₂O and Cl₂. The CoMn₂O₄ prepared in this reaction has photocatalytic activity in Congo red degradation with UV light. Its activity strongly depends on the synthesis conditions, e.g., Congo red was degraded 9 and 13 times faster in the presence of CoMn₂O₄ prepared at 550 °C (in air) or 420 °C (under N₂), respectively.

We reviewed the synthesis, structure, and properties of pyridine complexes of AgXO₄ (X = Cl, Mn, and Re) compounds with various compositions ([AgPy₂] XO₄, [AgPy₂XO₄]·0.5Py, [AgPy₄] XO₄, and 4 [AgPy₂XO₄] [AgPy₄] XO₄). We also clarified the controversial information about the existence and composition of pyridine complexes of silver permanganate, used widely as mild and selective oxidants in organic chemistry. We discussed in detail the available structural and spectroscopic (IR, Raman, and UV) data and thermal behavior, including the existence and consequence of quasi-intramolecular reactions between the reducing ligand and anions containing oxygen.