Nucleation and Crystal Growth of a {V14Sb8O42} Cluster from a {V15Sb6O42} Polyoxovanadate: In Situ XRD Studies

Emergence of Dynamically-Disordered Phases During Fast Oxygen Deintercalation Reaction of Layered Perovskite

Determination of a reaction pathway is an important issue for the optimization of reactions. However, reactions in solid-state compounds have remained poorly understood because of their complexity and technical limitations. Here, using state-of-the-art high-speed time-resolved synchrotron X-ray techniques, the topochemical solid-gas reduction mechanisms in layered perovskite Sr₃ Fe₂ O_{7- δ} (from δ ∼ 0.4 to δ = 1.0), which is promising for an environmental catalyst material is revealed. Pristine Sr₃ Fe₂ O_{7- δ} shows a gradual single-phase structural evolution during reduction, indicating that the reaction continuously proceeds through thermodynamically stable phases. In contrast, a nonequilibrium dynamically-disordered phase emerges a few seconds before a first-order transition during the reduction of a Pd-loaded sample. This drastic change in the reaction pathway can be explained by a change in the rate-determining step. The synchrotron X-ray technique can be applied to various solid-gas reactions and provides an opportunity for gaining a better understanding and optimizing reactions in solid-state compounds.

Detailed insights into the formation pathway of CdS and ZnS in solution: a multi-modal in situ characterisation approach

The high stability, high availability, and wide size-dependent bandgap energy of sulphidic semiconductor nanoparticles (NPs) render them promising for applications in optoelectronic devices and solar cells. However, the tunability of their optical properties depends on the strict control of their crystal structure and crystallisation process. Herein, we studied the structural evolution during the formation of CdS and ZnS in solution by combining in situ luminescence spectroscopy, synchrotron-based X-ray diffraction (XRD) and pair distribution function (PDF) analyses for the first time. The influence of precursor type, concentration, temperature and heating program on the product formation and on the bandgap or trap emission were investigated in detail. In summary, for CdS, single-source precursor (SSP) polyol strategies using the dichlorobis(thiourea)cadmium(II) complex and double-source precursor approaches combining Cd(CH₃COO)₂·2H₂O and thiourea led to the straightforward product at 100 °C, while the catena((m₂-acetato-O,O')-(acetate-O,O')-(m₂-thiourea)-cadmium) complex was formed at 25 and 80 °C. For ZnS, the reaction between Zn(CH₃COO)₂·2H₂O and thiourea at 100 °C led to the product formation after the crystallisation and dissolution of an unknown intermediate. At 180 °C, besides an unknown phase, the acetato-bis(thiourea)-zinc(II) complex was also detected as a reaction intermediate. The formation of such reaction intermediates, which generally remain undetected applying only ex situ characterisation approaches, reinforce the importance of in situ analysis for promoting the advance on the production of tailored semiconductor materials.

Crystallisation of phosphates revisited: a multi-step formation process for SrHPO4

SrHPO4 is used in a multitude of applications, including biomedicine, catalysts, luminescent materials, and batteries. However, the performance of these materials depends on the ability to control the formation and transformation of strontium phosphates. This work focuses on the application of in situ and ex situ measurements, including synchrotron-based X-ray diffraction (XRD) analysis, luminescence of Ce3+ and Eu3+ dopants, light transmission, reflectance, and thermogravimetry to track structural changes in SrHPO4 under different experimental conditions. Ex situ analysis of aliquots revealed favourable crystallisation of β-SrHPO4 through the formation of Sr6H3(PO4)5·2H2O as an intermediate. Furthermore, in situ analysis showed that the reaction mechanism evolves via the initial formation of amorphous strontium phosphate and Sr5(PO4)3OH, which subsequently transforms to γ-SrHPO4. Analysis of the luminescence properties of the lanthanide dopants provided insights into the coordination environments of the substituted Sr2+ sites.

How do layered double hydroxides evolve? First in situ insights into their synthesis processes

In situ characterisation techniques granted unprecedented experimental access to the formation dynamics of carbonate-intercalated Mg2+/Al3+ LDHs.

Synthesis of Metastable Inorganic Solids with Extended Structures

The number of known inorganic compounds is dramatically less than predicted due to synthetic challenges, which often constrains products to only the thermodynamically most stable compounds. Consequently, a mechanism-based approach to inorganic solids with designed structures is the holy grail of solid state synthesis. This article discusses a number of synthetic approaches using the concept of an energy landscape, which describes the complex relationship between the energy of different atomic configurations as a function of a variety of parameters such as initial structure, temperature, pressure, and composition. Nucleation limited synthesis approaches with high diffusion rates are contrasted with diffusion limited synthesis approaches. One challenge to the synthesis of new compounds is the inability to accurately predict what structures might be local free energy minima in the free energy landscape. Approaches to this challenge include predicting potentially stable compounds thorough the use of structural homologies and/or theoretical calculations. A second challenge to the synthesis of metastable inorganic solids is developing approaches to move across the energy landscape to a desired local free energy minimum while avoiding deeper free energy minima, such as stable binary compounds, as reaction intermediates. An approach using amorphous intermediates is presented, where local composition can be used to prepare metastable compounds. Designed nanoarchitecture built into a precursor can be preserved at low reaction temperatures and used to direct the reaction to specific structural homologs.

New pronounced progress in the synthesis of group 5 polyoxometalates

This highlight summarizes new developments made in group 5 polyoxometalate science of high nuclearity clusters with focus on synthetic approaches.

Soluble Hetero-Polyoxovanadates and Their Solution Chemistry Analyzed by Electrospray Ionization Mass Spectrometry

Polyoxometalates (POMs) are an intriguing class of compounds due to their tremendous structural variety and the wide spectrum of resulting properties, which make them interesting for applications in fields such as catalysis, material science or nanotechnology. Their ability to form large supramolecular architectures by self-assembly offers an entry to complex, functional systems. After an introduction into the structure and synthesis of POMs of the early transition metals, recently discovered water-soluble antimonato polyoxovanadates (Sb-POVs) and the investigation of their chemical reactivity are discussed. Electrospray ionization mass spectrometry (ESI-MS) is presented as an analytical technique suitable to investigate the structure of complex POM assemblies in solution and to probe the underlying reactivity and formation mechanisms. This Minireview highlights the first studies on the soluble Sb-POVs and how the knowledge of their reactivity obtained by ESI-MS has fostered the syntheses of numerous novel Sb-POV compounds.

Mixing SbIII and GeIV occupancy in the polyoxovanadate {V14E8} archetype

The first mixed germanato-antimonato derivative of the {V14E8O42} (E=semi-metal) cluster archetype has been synthesized under hydrothermal conditions and isolated as {Ni(phen)3}2[α-VIV 14SbIII 5GeIV 3O42(OH)3(H2O)]· ≈16H2O (phen=1,10-phenanthroline). In the cluster anion, seven of the eight hetero-metal positions are occupied by disordered Ge/Sb atoms, while one position is fully occupied by Sb atoms. The [V14Sb5Ge3O42(OH)3(H2O)]6− anions are arranged in pairs with remarkably short inter-cluster Sb···O contacts. Bond valence sum calculation strongly suggests that the Sb···O contact must be taken into account as a weak bond. The magnetic properties are dominated by strong intra-cluster antiferromagnetic exchange interactions, and the cluster anion is magnetically quasi-isolated from the spins of the Ni2+ complex cations.

Eliani I, Ströh J, Braun M, Ruser N, Heidenreich N, Rönfeldt P, Bertram F, Näther C, Wöhlbrandt S, Suta M, Terraschke H. From ligand exchange to reaction intermediates: what does really happen during the synthesis of emissive complexes?

The in situ luminescence analysis of coordination sensors (ILACS) technique reveals the influence of synthesis parameters on key features of the crystallization process of [Eu(2,2′bipyridine)₂(NO₃)₃] derivative complexes.

Ordnung muss sein: heteroelement order and disorder in polyoxovanadates

Three new mixed antimonato–germanato polyoxovanadates exhibit different degrees of order of their unique crystallographic heterometal atom positions.

Bi2O2CO3 Growth at Room Temperature: In Situ X-ray Diffraction Monitoring and Thermal Behavior

The room-temperature formation of bismuth oxycarbonate (Bi₂O₂CO₃) from Bi₂O₃ in sodium carbonate buffer was investigated with in situ powder X-ray diffraction (PXRD) in combination with electron microscopy and vibrational spectroscopy. Time-resolved PXRD measurements indicate a pronounced and rather complex pH dependence of the reaction mechanism. Bi₂O₂CO₃ formation proceeds within a narrow window between pH 8 and 10 via different mechanisms. Although a zero-dimensional nucleation model prevails around pH 8, higher pH values induce a change toward a diffusion-controlled model, followed by a transition to regular nucleation kinetics. Ex situ synthetic and spectroscopic studies confirm these trends and demonstrate that in situ monitoring affords vital parameter information for the controlled fabrication of Bi₂O₂CO₃ materials. Furthermore, the β → α bismuth oxide transformation temperatures of Bi₂O₂CO₃ precursors obtained from different synthetic routes differ notably (by min 50 °C) from commercially available bismuth oxide. Parameter studies suggest a stabilizing role of surface carbonate ions in the as-synthesized bismuth oxide sources. Our results reveal the crucial role of multiple preparative history parameters, especially of pH value and source materials, for the controlled access to bismuth oxide-based catalysts and related functional compounds.

A multi-purpose reaction cell for the investigation of reactions under solvothermal conditions

A new versatile and easy-to-use remote-controlled reactor setup aimed at the analysis of chemical reactions under solvothermal conditions has been constructed. The reactor includes a heating system that can precisely control the temperature inside the reaction vessels in a range between ambient temperature and 180 °C. As reaction vessels, two sizes of commercially available borosilicate vessels (V_max = 5 and 11 ml) can be used. The setup furthermore includes the option of stirring and injecting of up to two liquid additives or one solid during the reaction to initiate very fast reactions, quench reactions, or alter chemical parameters. In addition to a detailed description of the general setup and its functionality, three examples of studies conducted using this setup are presented.

In situ luminescence analysis: a new light on monitoring calcium phosphate phase transitions

In situ luminescence measurements allow monitoring the phase transitions of biologically relevant calcium phosphates with high sensitivity, independent of synchrotron radiation.

An unprecedented antimonato-polyoxovanadate (SbPOV) based on both α-[V14Sb8O42]4− and β-[V14Sb8O42]4− isomers

An unprecedented antimonato-polyoxovanadate (SbPOV) based on both α-[V₁₄Sb₈O₄₂]⁴⁻ and β-[V₁₄Sb₈O₄₂]⁴⁻ isomers has been synthesized.

Monitoring the mechanism of formation of [Ce(1,10-phenanthroline)2(NO3)3] by in situ luminescence analysis of 5d–4f electronic transitions

The mechanism of formation of emitting complexes is efficiently elucidated by in situ luminescence measurements of 5d–4f electronic transitions from the early stages of the reaction until the final product crystallization.