Synthesis Strategy Guided by Decision Tree for Morphology Control of Metal Phosphonates

The morphology control of metal phosphonates is always a difficulty because there are many challenges derived from the complexity of crystallization and the multivariable synthesis system. Responding to challenges, we propose a synthesis strategy guided by a decision tree for morphology control of metal phosphonates, through which directional design of the morphology-controlled synthesis can be realized. Specifically, any one synthetic condition involving the synthesis of metal phosphonates can be regarded as a decision problem to construct a binary decision tree. By means of the classification principle of the binary decision tree, the samples synthesized under the boundary value of each synthesis condition are classified based on crystal phase and morphology. The key synthetic conditions determining crystal phase and morphology can be precisely screened out to serve as decision nodes for the binary decision tree and are also rapidly optimized by the recursion level by level, whereas others cannot. Here, the β-polymorph of copper phenylphosphonate (β-CuPP) is selected as an example to elaborate the decision-tree-guided synthesis strategy for morphology control of metal phosphonates. From the constructed binary decision tree, it is clear that the right amount of methanol in the solvent is vital to obtain β-phase of CuPP, whereas the reactant concentration, pH value, and reaction time are important for morphology and phase transformation. Under the optimal synthetic conditions screened out by the binary decision tree, β-CuPP can thus be controlled to be hierarchically flower-like microsphere morphology through either the direct synthesis route or the solid-to-solid phase transformation route. This research work confirms that the decision-tree-guided synthesis is highly efficacious for the morphology control of metal phosphonates. Furthermore, the morphology-controlled synthesis guided by a decision tree may provide some valuable inspiration for morphology control of metal-organic frameworks (MOFs) and even coordinate compounds.

A new route to polyoxometalates via mechanochemistry

Mechanochemistry offers a new route to polyoxometalates (POMs) under mild conditions. The molybdenum isoPOM heptamolybdate and the molybdenum heteroPOMs of the Strandberg- and Keggin-type could be achieved from grinding together molybdenum oxide, potassium or ammonium carbonate and phosphate. The reactions were controlled by the stoichiometric ratio of the starting materials and the liquid used, with reaction times between 30 min and 3 h. In situ investigations of the syntheses reveal the formation of intermediates during the reactions. Their identification helps explaining the mechanism of formation of the intermediates as well as the final POMs.

Under mild conditions, molybdenum POMs could be achieved mechanochemically from simple building blocks, within short reaction times. In situ investigations reveal the formation of intermediates and help explaining the mechanism behind the reaction.

Metastability and Seeding Effects in the Mechanochemical Hybrid Lead(II) Iodide Formation

The mechanism for the mechanochemical synthesis of (C(NH₂ )₃ )₃ PbI₅ 3 and (C(NH₂ )₃ )₄ PbI₆ 4 and their conversion into each other is presented. We investigated the synthesis of 3 at different frequencies and energies using in situ powder X-ray diffraction. By splitting the reaction into single parts we could prove that the formation of 3 is simply dependent on the energy and mixing speed. The nucleation of 4 instead is slightly negative dependent on the energy but dependent on the mixing speed, while its growth is mostly independent of any influence. We were able to influence the reaction pathways by seeding the mixture with a small amount of powdery 4. The formation of 4 is very likely an auto-catalytic process. 3 instead is metastable. It can be stabilized by energy, which beside mechanochemistry can also be achieved by temperature. The results showcases the complex nature of mechanochemical reactions.

New Directions in Metal Phosphonate and Phosphinate Chemistry

In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective article is to provide a critical overview of the topics discussed during the workshop, which are divided into two main areas: synthesis and characterisation, and applications. In terms of synthetic methods, there has been a push towards cleaner and more efficient approaches. This has led to the introduction of high-throughput synthesis and mechanochemical synthesis. The recent success of metal–organic frameworks has also promoted renewed interest in the synthesis of porous metal phosphonates and phosphinates. Regarding characterisation, the main advances are the development of electron diffraction as a tool for crystal structure determination and the deployment of in situ characterisation techniques, which have allowed for a better understanding of reaction pathways. In terms of applications, metal phosphonates have been found to be suitable materials for several purposes: they have been employed as heterogeneous catalysts for the synthesis of fine chemicals, as solid sorbents for gas separation, notably CO2 capture, as materials for electrochemical devices, such as fuel cells and rechargeable batteries, and as matrices for drug delivery.

Cadmium benzylphosphonates – the close relationship between structure and properties

Structure-properties relationship of new Cd-benzylphosphonates differing in their fluorine content.

In Situ Investigations of Mechanochemical One-Pot Syntheses

We present an in situ triple coupling of synchrotron X-ray diffraction with Raman spectroscopy, and thermography to study milling reactions in real time. This combination of methods allows a correlation of the structural evolution with temperature information. The temperature information is crucial for understanding both the thermodynamics and reaction kinetics. The reaction mechanisms of three prototypical mechanochemical syntheses, a cocrystal formation, a C-C bond formation (Knoevenagel condensation), and the formation of a manganese-phosphonate, were elucidated. Trends in the temperature development during milling are identified. The heat of reaction and latent heat of crystallization of the product contribute to the overall temperature increase. A decrease in temperature occurs via release of, for example, water as a by-product. Solid and liquid intermediates are detected. The influence of the mechanical impact could be separated from temperature effects caused by the reaction.

The crystallisation of copper(ii) phenylphosphonates

The crystal structures and syntheses of four different copper(ii) phenylphosphonates, the monophenylphosphonates α-, β-, and γ-Cu(O₃PC₆H₅)·H₂O (α-CuPhPmH (1) β-CuPhPmH (2) and γ-CuPhPmH (3)), and the diphosphonate Cu(HO₃PC₆H₅)₂·H₂O (CuPhP2mH (4)), are presented. The compounds were synthesized from solution at room temperature, at elevated temperature, under hydrothermal conditions, and mechanochemical conditions. The structures of α-CuPhPmH (1) and CuPhP2mH (4) were solved from powder X-ray diffraction data. The structure of β-CuPhPmH (2) was solved by single crystal X-ray analysis. The structures were validated by extended X-ray absorption fine structure (EXAFS) and DTA analyses. Disorder of the crystal structure was elucidated by electron diffraction. The relationship between the compounds and their reaction pathways were investigated by in situ synchrotron measurements.

Synthesis, crystal structures, and magnetic properties of six transition metal phosphonates

Six new complexes have been quantificationally investigated for magnetic properties. There are abundant water molecules existing in the complexes with different aggregation modes.

Divalent metal phosphonates – new aspects for syntheses, in situ characterization and structure solution

Divalent metal phosphonates are promising hybrid materials with a broad field of application. The rich coordination chemistry of the phosphonate linkers enables the formation of structures with different dimensionalities ranging from isolated complexes and layered structures to porous frameworks incorporating various functionalities through the choice of the building blocks. In brief, metal phosphonates offer an interesting opportunity for the design of multifunctional materials. Here, we provide a short review on the class of divalent metal phosphonates discussing their syntheses, structures, and applications. We present the advantages of the recently introduced mechanochemical pathway for the synthesis of divalent phosphonates as a possibility to generate new, in certain cases metastable compounds. The benefits of