Spectroscopic and Electrochemical Study of the Adsorption of [Co(en)2Cl2]Cl on γ-Alumina: Influence of the Alumina Ligand on Co(III)/(II) Redox Potential

Atmospheric chemistry of CF3O2: a theoretical study on mechanisms and pathways of the CF3O2 + IO reaction

The mechanisms and reaction pathways for the CF3O2 + IO reaction have been investigated by quantum chemistry methods. It has been found that the title reaction takes place on both the singlet and triplet potential energy surfaces (PES). On the singlet PES, the most important products include CF3OOOI, CF3OOIO, CF3OIO2, and CF2O + FIO2, while other products such as CF2O + FOIO, CF2O + FOOI, CF3OOI + O((3)P), CF3OI + O2 ((1)Δ and (3)Σ), and CF3O + OIO are negligible due to high barriers or unstable formations. On the triplet PES, CF3O + OIO is the dominant product with a lower barrier. As for FIO2 and it isomers, the most stable one is FIO2. TDDFT (Time Dependent Density Functional Theory) calculation indicates that CF3OOOI, CF3OOIO and CF3OIO2 undergo photolysis easily under sunlight. Moreover, a minor contribution relative to hydrogen is found in the CX3O2 + IO (X = H and F) reactions.

Thermal decomposition of [Co(en)3][Fe(CN)6]∙ 2H2O: Topotactic dehydration process, valence and spin exchange mechanism elucidation

BACKGROUND

The Prussian blue analogues represent well-known and extensively studied group of coordination species which has many remarkable applications due to their ion-exchange, electron transfer or magnetic properties. Among them, Co-Fe Prussian blue analogues have been extensively studied due to the photoinduced magnetization. Surprisingly, their suitability as precursors for solid-state synthesis of magnetic nanoparticles is almost unexplored. In this paper, the mechanism of thermal decomposition of [Co(en)3][Fe(CN)6] ∙∙ 2H2O (1a) is elucidated, including the topotactic dehydration, valence and spins exchange mechanisms suggestion and the formation of a mixture of CoFe2O4-Co3O4 (3:1) as final products of thermal degradation.

RESULTS

The course of thermal decomposition of 1a in air atmosphere up to 600°C was monitored by TG/DSC techniques, (57)Fe Mössbauer and IR spectroscopy. As first, the topotactic dehydration of 1a to the hemihydrate [Co(en)3][Fe(CN)6] ∙∙ 1/2H2O (1b) occurred with preserving the single-crystal character as was confirmed by the X-ray diffraction analysis. The consequent thermal decomposition proceeded in further four stages including intermediates varying in valence and spin states of both transition metal ions in their structures, i.e. [Fe(II)(en)2(μ-NC)Co(III)(CN)4], Fe(III)(NH2CH2CH3)2(μ-NC)2Co(II)(CN)3] and Fe(III)[Co(II)(CN)5], which were suggested mainly from (57)Fe Mössbauer, IR spectral and elemental analyses data. Thermal decomposition was completed at 400°C when superparamagnetic phases of CoFe2O4 and Co3O4 in the molar ratio of 3:1 were formed. During further temperature increase (450 and 600°C), the ongoing crystallization process gave a new ferromagnetic phase attributed to the CoFe2O4-Co3O4 nanocomposite particles. Their formation was confirmed by XRD and TEM analyses. In-field (5 K / 5 T) Mössbauer spectrum revealed canting of Fe(III) spin in almost fully inverse spinel structure of CoFe2O4.

CONCLUSIONS

It has been found that the thermal decomposition of [Co(en)3][Fe(CN)6] ∙∙ 2H2O in air atmosphere is a gradual multiple process accompanied by the formation of intermediates with different composition, stereochemistry, oxidation as well as spin states of both the central transition metals. The decomposition is finished above 400°C and the ongoing heating to 600°C results in the formation of CoFe2O4-Co3O4 nanocomposite particles as the final decomposition product.