Controlling Nucleation and Crystal Growth of a Distinct Polyoxovanadate Cluster: An In Situ Energy Dispersive X-ray Diffraction Study under Solvothermal Conditions

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.

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.

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.

Combined in- and ex situ studies of pyrazine adsorption into the aliphatic MOF Al-CAU-13: structures, dynamics and correlations

The intercalation of different pyrazine derivatives into the trans-1,4-cyclohexanedicarboxylate (CDC²⁻) based Al-MOF [Al(OH)(CDC)], denoted as CAU-13, was investigated ex- and in-situ.

The ZIF system zinc(II) 4,5-dichoroimidazolate: theoretical and experimental investigations of the polymorphism and crystallization mechanisms

In this report, we summarize our theoretical and experimental investigations on the zeolitic imidazolate framework (ZIF) system [Zn(dcim)

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.

High Nuclearity Antimonato-Polyoxovanadate Cluster {V15 Sb6 O42 } as a Synthon for the Solvothermal in situ Generation of α- and β-{V14 Sb8 O42 } Isomers

New heteroatom polyoxovanadates (POVs) were synthesized by applying a water-soluble high-nuclearity cluster as new synthon. The [V15 Sb6 O42 ](6-) cluster shell exhibiting D3 symmetry was in situ transformed into completely different cluster shells, namely, the α-[V14 Sb8 O42 ](4-) isomer with D2d and the β-[V14 Sb8 O42 ](4-) isomer with D2h symmetry. The solvothermal reaction of {Ni(en)3 }3 [V15 Sb6 O42 (H2 O)x ]⋅15 H2 O (x=0 or 1; en=ethylenediamine) in water led to the crystallization of [{Ni(en)2 }2 V14 Sb8 O42 ]⋅5.5 H2 O containing the β-isomer. The addition of [Ni(phen)3 ](ClO4 )2 ⋅0.5 H2 O (phen=1,10-phenanthroline) to the reaction slurry gave the new compound {Ni(phen)3 }2 [V14 Sb8 O42 ]⋅phen⋅12 H2 O with the α-isomer. Both transformation reactions are complex due the change of symmetry, the chemical composition, and rearrangement of the VO5 square pyramids and Sb2 O5 handle-like moieties.

Catalysis of "outer-phase" oxygen atom exchange reactions by encapsulated "inner-phase" water in {V15Sb6}-type polyoxovanadates

A water molecule encapsulated inside water-soluble {V₁₅Sb₆} antimonato polyoxovanadate cages accelerates oxygen-exchange reactions in the cluster periphery.

Antimonato polyoxovanadate (POV) cluster compounds {M(en)₃}₃[V₁₅Sb₆O₄₂(H₂O)_x]·nH₂O (M = Fe^II, Co^II, Ni^II and x = 0 or 1) obtained under solvothermal conditions exhibit unusual high water solubility making these compounds promising synthons for generation of new POV structure types. Electrospray ionization mass spectrometry provides evidence (i) for a water molecule encapsulated inside the cavity of a fraction of the spherical cluster shells, (ii) for a post-functionalization in water, namely a slow exchange of VO against Sb₂O, (iii) for the inner-phase reactivity of the encapsulated water that is capable of opening an oxo-bridge, and (iv) for a significant acceleration of the ¹⁶O/¹⁸O exchange reactions of oxygen atoms in the cluster periphery with surrounding H₂¹⁸O, when encapsulated water is present. To the best of our knowledge, this is the first example in polyoxovanadate chemistry for the transduction of inner-phase reactivity of an encapsulated guest molecule into changes in the outer-phase reactivity of the cluster. Magnetic susceptibility measurements reflect the individual contributions of the frustrated {V₁₅} spin polytope and the {M(en)₃}²⁺ complexes, with very weak coupling between these groups.

Semimetal-functionalised polyoxovanadates

Polyoxovanadates (POVs), known for their wide applicability and relevance in chemical, physical and biological sciences, are a subclass of polyoxometalates and usually self-assemble in aqueous-phase, pH-controlled condensation reactions. Archetypical POVs such as the robust [VO42](12-) polyoxoanion can be structurally, electronically and magnetically altered by heavier group 14 and 15 elements to afford Si-, Ge-, As- or Sb-decorated POV structures (heteroPOVs). These main-group semimetals introduce specific chemically engineered functionalities which cause the generally hydrophilic heteroPOV compounds to exhibit interesting reactivity towards organic molecules, late transition metal and lanthanoid ions. The fully-oxidised (V(V)), mixed-valent (V(V)/V(IV) and V(IV)/V(III)), "fully-reduced" (V(IV)) and "highly-reduced" (V(III)) heteroPOVs possess a number of intriguing properties, ranging from catalytic to molecular magnet characteristics. Herein, we review key developments in the synthetic and structural chemistry as well as the reactivity of POVs functionalised with Si-, Ge-, As- or Sb-based heterogroups.

Influence of the synthesis parameters onto nucleation and crystallization of five new tin-sulfur containing compounds

The distinct control of the synthesis parameters achieved crystallization of five new inorganic-organic hybrid tin sulfides with 1,10-phenanthroline (phen) as the organic component: {[Mn(phen)2]2(μ2-Sn2S6)} (1, 3), {[Mn(phen)2]2(μ2-Sn2S6)}·phen (2), {[Mn(phen)2]2(μ2-Sn2S6)}·phen·H2O (4), and {[Mn(phen)2]2[μ-η(2)-η(2)-SnS4]2[Mn(phen)]2}·H2O (5). Compounds 1, 3, and 4 occur successively under static conditions by increasing the reaction time up to 8 weeks. Stirring the reaction mixtures and keeping the educt ratio constant allow preparation of distinct phase pure samples within very short reaction times. At higher autogenous pressure, crystallization and conversion of several compounds are suppressed, and only 1 crystallized. Compound 2 could only be obtained in glass tubes at low pH value of the reaction mixture or at low amine concentration. Adjusting the pH value of the solution, the concentration, and the volume of the solvent, compounds 1-4 crystallize sequentially and were successively converted into each other. Results of thermal stability experiments and solubility studies suggest that compounds 1 and 3 are polymorphs following the density rule. Compounds 2 and 4 may be viewed as pseudopolymorphs of 1 and 3.

In situ studies of solvothermal synthesis of energy materials

Solvothermal and hydrothermal synthesis, that is, synthesis taking place in a solvent at elevated temperature and pressure, is a powerful technique for the production of advanced energy materials as it is versatile, cheap, and environmentally friendly. However, the fundamental reaction mechanisms dictating particle formation and growth under solvothermal conditions are not well understood. In order to produce tailor-made materials with specific properties for advanced energy technologies, it is essential to obtain an improved understanding of these processes and, in this context, in situ studies are an important tool as they provide real time information on the reactions taking place. Here, we present a review of the use of powder diffraction and total scattering methods for in situ studies of synthesis taking place under solvothermal and hydrothermal conditions. The experimental setups used for in situ X-ray and neutron studies are presented, and methods of data analysis are described. Special attention is given to the methods used to extract structural information from the data, for example, Rietveld refinement, whole powder pattern modelling and pair distribution function analysis. Examples of in situ studies are presented to illustrate the types of chemical insight that can be obtained.