Decay of Hexaniobate Complexes of Mn(IV) and Pt(IV) in Alkaline Solutions: Some New Hexaniobate Salts

Шмакова, А. А.; Shiriyazdanov, R. R.; Karimova, A. R.; Kompankov, Nikolay B.; Abramov, Pavel A.; Sokolov, Maxim N.

doi:10.1007/s10876-018-1439-6

Cited by 5 publications

(4 citation statements)

References 41 publications

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“…When the hydroxide concentration was increased to 2 M (OH 2 ) and 4 M (OH 4 ), hexaniobate [K x Na 8− x Nb 6 O 19 . n H 2 O, PDF K4Na4Nb6O19.9H2O :00‐014‐0360], that is, KNN‐hydrate started to be seen akin to previous works in which such phase was considered as an intermediate product 41–43,52,57 . When the concentration was further increased to 6, 8, and then to 10 M, orthorhombic K‐rich KNN and NaNbO 3 phases were found to be co‐existing for all samples.…”

Section: Resultsmentioning

confidence: 51%

“…It was already demonstrated that higher pH values promote Nb 2 O 5 hydrolysis, one of the first steps for KNN , that is, KNN-hydrate started to be seen akin to previous works in which such phase was considered as an intermediate product. [41][42][43]52,57 When the concentration was further increased to 6, 8, and then to 10 M, orthorhombic K-rich KNN and NaNbO 3 phases were found to be co-existing for all samples. It is worth mentioning that when the alkalinity was increased, peak shift (up to ∼ 0.2 • at low 2θ-angles, and reaching up to 1 • at higher angles) toward lower 2θ values indicated further potassium accumulation in the crystal lattice, as can also be recognized in Figure 1 (see the enlarged area representing KNN at higher total hydroxide concentrations).…”

Section: Total Hydroxide Concentrationmentioning

confidence: 96%

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Hydrothermal synthesis of potassium–sodium niobate powders

et al. 2022

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Potassium–sodium niobates (KxNa1−xNbO3, 0 < x < 1, KNN) were hydrothermally synthesized under varying alkaline ratios (K+/Na+), total hydroxide concentration, reaction temperature, and time. Compositional surveys were developed by using Rietveld analyses derived quantitative volume fractions. The data demonstrated that phase pure KNN synthesis can be achieved by reacting the niobium source with the hydroxide solution having 6 M total hydroxide concentration, cation ratio (K+/Na+) of above 6 at temperatures ≥200°C for 24 h. Dissolution–precipitation events through intermediate products including hexaniobates were postulated as a plausible formation mechanism. It was shown also that the single‐phase KNN approaching the morphotropic phase boundary (MPB) could be obtained by further incorporation of sodium ions into the crystal via post‐annealing at 800°C/2 h, following the hydrothermal synthesis.

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Section: Resultsmentioning

confidence: 51%

Section: Total Hydroxide Concentrationmentioning

confidence: 96%

Hydrothermal synthesis of potassium–sodium niobate powders

et al. 2022

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“…Polyoxometalates (POMs; M = V, Nb, Ta, Mo, and W) are an important class of compounds that is characterized by a large variety of high-nuclearity cluster anions exhibiting different chemical compositions, properties, shapes, sizes, and topologies. − In most cases POMs contain an appreciable amount of water, which in several cases is emitted already at room temperature. Focusing on polyoxoniobates (PONb), examples include K 12 [Ti 2 O 2 ][SiNb 12 O 40 ]·16H 2 O, Na 14 [H 2 Si 4 Nb 16 O 56 ]·45.5H 2 O, Li 7 K[Nb 6 O 19 ]·15H 2 O, Li 13 K[SiNb 12 (OH) 2 O 38 ]·17H 2 O, (TMA) 9 [V 3 Nb 12 O 42 ]·18H 2 O (TMA = tetramethylammonium), Na 7 [HNb 6 O 19 ]·15H 2 O, [Cu(en) 2 (H 2 O) 2 ] 5 K 10 [K(GeOH) 2 Ge 2 Nb 16 H 3 O 54 ] 2 ·38H 2 O (en = ethylenediamine), [Cu(en) 2 ] 3 {[Cu(en) 2 ][H 6 SiNb 18 O 54 ]}·22H 2 O, (TMA) 5 [H 2 TeNb 5 O 19 ]·20H 2 O, (TMA) 5 [H 3 Nb 6 O 19 ]·20H 2 O, H 4 Na 6 K 22 Cs 4 [H 4 Nb 52 O 150 ]·63H 2 O, Na 12 [Pt(Nb 6 O 19 ) 2 ]·52H 2 O . We note that this list of compounds is not complete, and we are also aware that PONb compounds with a lower number of crystal water molecules were also reported.…”

Section: Introductionmentioning

confidence: 99%

“…Polyoxometalates (POMs; M = V, Nb, Ta, Mo, and W) are an important class of compounds that is characterized by a large variety of high-nuclearity cluster anions exhibiting different chemical compositions, properties, shapes, sizes, and topologies. 16−30 40 We note that this list of compounds is not complete, and we are also aware that PONb compounds with a lower number of crystal water molecules were also reported. In most cases the thermal stability and water removal of the samples was investigated with thermoanalytical methods, but no further efforts were undertaken to characterize partially or fully dehydrated decomposition products in more detail.…”

Section: ■ Introductionmentioning

confidence: 99%

Bond Formation upon Water Removal in an Unusual “Pseudo”-Topotactic Reaction Investigated by Single-Crystal Structure and in Situ Synchrotron X-ray Powder Diffraction Analysis

Dopta

Hansen

Pienack

et al. 2019

Crystal Growth & Design

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The new compound [Cu(cyclam)(H 2 O)]-{[Cu(cyclam)] 2 [HTiNb 9 O 28 ]}•26H 2 O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane) was obtained under solvothermal conditions. Its crystal structure contains a monotitano-nonaniobate anion in which one position is equally occupied by Nb(V) and Ti(IV). The anions are expanded by [Cu(cyclam)] 2+ cations via Nb−O−Cu bridges generating {[Cu(cyclam)] 2 [HTiNb 9 O 28 ]} 2− cluster units, which are arranged into layers. Between these layers there are additionally isolated [Cu(cyclam)(H 2 O) 2 ] 2+ cations as well as hydrate water molecules. Storage of 1 at room temperature leads to loss of ∼13 water molecules, and a new crystalline phase (2) crystallizes that, with heating, transforms into the anhydrate. The reversibility of this reaction was investigated by thermogravimetry and X-ray powder diffraction (XRPD). Temperaturedependent in situ synchrotron XRPD investigations prove an abrupt phase transition, in which especially the a axis is dramatically shortened and the {[Cu(cyclam)] 2 [HTiNb 9 O 28 ] 2− } cluster is rearranged. Single-crystal X-ray diffraction of 2 reveals that, despite the unusual large shrinking of the unit cell volume, the domains formed by water removal exhibit some preferred orientation close to that expected for a topotactic reaction, which allowed the performance of a structure analysis. In the structure of 2, the two water molecules of the isolated [Cu(cyclam)(H 2 O) 2 ] 2+ cation in 1 are replaced by two terminal cluster O atoms, leading to the formation of chains via Nb−O−Cu bonds, and this phase transition is accompanied by an ordering of one of the two cyclam ligands. 50 the formation of domains, without changing the crystal 51 morphology. In most cases there is no structural relationship 52 between the hydrate and the intermediate phase, and therefore, 53 the domains show a random orientation, and the diffraction 54 pattern corresponds to that of a powder. However, in very few 55 cases there is a strong relationship between the structures of 56 the reactant and the product, and in this case the domains 57 formed in a reaction exhibit a strong preferred orientation 58 simulating the diffraction pattern of a single crystal. The 59 presence of such a reaction, called topotactic, can only be 60 proven by single-crystal X-ray diffraction, and in ideal cases 61 differences between the diffraction pattern of the pristine and 62 the product phase are only detected in the mosaic spread. 12−15 63 For such reactions the question arises what will happen if 64 larger structural changes occur for which the orientation of the 65 domains are far from perfect and if structural information can 66 be retrieved in such cases. In the course of our ongoing

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Synthesis, Characterization, and Catalytic Property of a Hybrid Nanoscale Polyoxoniobate

Bian

Zhou

et al. 2020

J Clust Sci

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Decay of Hexaniobate Complexes of Mn(IV) and Pt(IV) in Alkaline Solutions: Some New Hexaniobate Salts

Cited by 5 publications

References 41 publications

Hydrothermal synthesis of potassium–sodium niobate powders

Hydrothermal synthesis of potassium–sodium niobate powders

Bond Formation upon Water Removal in an Unusual “Pseudo”-Topotactic Reaction Investigated by Single-Crystal Structure and in Situ Synchrotron X-ray Powder Diffraction Analysis

Synthesis, Characterization, and Catalytic Property of a Hybrid Nanoscale Polyoxoniobate

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