A compound having redox-active permanganate and complexed silver ions with reducing pyridine ligands is used as a mild organic and as a precursor for nanocatalyst synthesis in a low-temperature solid-phase quasi-intramolecular redox reaction.

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 {Mn4IIIMnIV2O12}n4n-, {Mn5IIIMnIVO12}n5n- or {MnIII6O12}n6n- frameworks, which can embed 2 × n (CoII and/or CoIII) 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 CoIIMIII2O4 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.

A simple synthetic method was developed to prepare 4[Agpy 2 ClO 4 ]Á[Agpy 4 ]ClO 4 in a low-temperature decomposition process of [Agpy 4 ]ClO 4 . A detailed IR, Raman and far-IR study including factor group analysis has been performed, and the assignation of bands is given. The compound decomposes quickly with a multistep ligand loss process with the formation of [Agpy 2 ]ClO 4 and AgClO 4 intermediates and AgCl as an end product around * 85, * 350 and 450°C, respectively. During the first decomposition step, a small fraction of the ligands is lost in a redox reaction: perchlorate oxidizes the pyridine, forming carbon, carbon dioxide, water and NO, while it itself is reduced into AgCl. In the next step, when AgClO 4 forms after complete ligand loss and reacts with the carbon formed in the degradation of pyridine at lower temperatures and produces NO, CO 2 and H 2 O. This reaction becomes possible because the AgCl formed in the redox reactions makes a eutectic melt with AgClO 4 in situ, which is a favorable medium for the carbon oxidation reaction. AgCl is known to reduce the temperature of decomposition of AgClO 4 , in which process forms AgCl as well as O 2 and so is an autocatalytic process. The loss and degradation of pyridine ligand are endothermic; the redox reactions including carbon oxidation and AgClO 4 decomposition into AgCl and O 2 are exothermic. The amount of absorbed/evolved heats corresponding to these processes was determined by DSC both under N 2 and O 2 atmospheres. Keywords Pyridine-silver complexes Á Perchlorates Á Quasi-intramolecular solid-phase redox reaction Á Evolved gas analysis Á DSC Electronic supplementary material The online version of this article (

Copper manganese oxides (CMO) with CuMn2O4 composition are well-known catalysts, which are widely used for the oxidative removal of dangerous chemicals, e.g., enhancing the CO to CO2 conversion. Their catalytic activity is the highest, close to those of the pre-crystalline and amorphous states. Here we show an easy way to prepare a stable CMO material at the borderline of the amorphous and crystalline state (BAC-CMO) at low temperatures (<100 °C) followed annealing at 300 °C and point out its excellent catalytic activity in CO oxidation reactions. We demonstrate that the temperature-controlled decomposition of [Cu­(NH3)4]­(MnO4)2 in CHCl3 and CCl4 at 61 and 77 °C, respectively, gives rise to the formation of amorphous CMO and NH4NO3, which greatly influences the composition as well as the Cu valence state of the annealed CMOs. Washing with water and annealing at 300 °C result in a BAC-CMO material, whereas the direct annealing of the as-prepared product at 300 °C gives rise to crystalline CuMn2O4 (sCMO, 15–40 nm) and ((Cu,Mn)2O3, bCMO, 35–40 nm) mixture. The annealing temperature influences both the quantity and crystallite size of sCMO and bCMO products. In 0.5% CO/0.5% O2/He mixture the best CO to CO2 conversion rates were achieved at 200 °C with the BAC-CMO sample (0.011 mol CO2/(m2 h)) prepared in CCl4. The activity of this BAC-CMO at 125 °C decreases to half of its original value within 3 h and this activity is almost unchanged during another 20 h. The BAC-CMO catalyst can be regenerated without any loss in its catalytic activity, which provides the possibility for its long-term industrial application.

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.

Detailed vibrational (IR, Raman, far-IR) and thermal (TGA, TG–MS, DSC) analysis has been performed on di[κ1O,κ2O-carbonatotetraamminecobalt(III)] sulfate trihydrate, ([Co(NH3)4CO3]2SO4·3H2O (1). Its isothermic heating at 100 °C leads to formation of [Co(NH3)4CO3]2SO4 (compound 2). UV and IR studies showed that the distorted octahedral arrangement around cis-O2CoN4 core in compound 1 does not change during dehydration, which explains the reversible water loss and ability of compound 2 to rehydrate into compound 1. Compound 2 decomposes at ~ 240 °C in inert atmosphere giving final decomposition products, which are two modifications of nanosized metallic cobalt (hcp-15 nm, fcc-250 nm) and CoO (55 nm). The redox reaction results in N2 as an ammonia oxidation product. The decomposition intermediate is a cobalt(II) compound, Co2O1,14+δ(SO4)0.86 (δ = the oxygen surplus due to the presence of 2.8% of Co(III) ion). The same reaction in air atmosphere resulted in Co2O1.25+δ(SO4)0.75 (δ = the oxygen surplus due to the presence of 5.3% of Co(III) ion (compound 3a). Compound 3a is oxidized in air at 793 °C into Co3O4. The compound 3a exhibits catalytic activity in photodegradation in Congo red. The photodegradation process follows pseudo-first-order kinetic (kapp = 1.0 and 7.0. at pH = 3.4 and 5.25, respectively).

This study aims to describe the thermal decomposition of two solvatomorphs of decakis(dimethylammonium) dihydrogendodecatungstate ((Me2NH2)10H2W12O42·10H2O and 11 H2O) under inert and oxidizing atmospheres. Thermal studies have been done by TG-MS, TG-DSC-MS, XRD and IR methods in both synthetic air and helium atmospheres. The general characteristics of thermal decomposition are similar for both solvatomorphs. Minor differences could be observed in the resolution and shifting of the decomposition peak temperatures depending on the heating rate or atmosphere used. The first step of decomposition is endothermic in both atmospheres and involves 2 and 5 water molecule elimination with ~ 150 and ~ 120 °C peak temperatures for the decahydrate and undecahydrate, respectively. The elimination of further water and dimethylamine was observed with increasing the temperature, as well as the disruption of the lattice of compounds. Until 300 °C, these processes are endothermic in both atmospheres, and the further decomposition processes at higher temperatures are left endothermic in helium, but become exothermic in synthetic air atmosphere. In helium atmosphere, above 350 °C, a solid-phase quasi-intramolecular redox reaction takes place when the dimethylamine degradation products react with the W=O bonds with formation of oxidative coupling products of the organic fragments and reduced tungsten oxide with WO~2.93 composition. In synthetic air, above 350 °C, burning of organic fragments takes place, there are no oxidative coupling products and reduced tungsten oxide formation, and the end product of decomposition is monoclinic WO3.

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.