Kinetic and Mechanistic Investigations of Hydrothermal Transformations in Zinc Phosphates

Alkylzinc diorganophosphates: synthesis, structural diversity and unique ability to incorporate zincoxane units

New tetrameric alkylzinc organophosphates of a drum-like structure and novel aggregates based on alkylzinc organophosphates with incorporated zincoxane units were synthesized and structurally characterized.

An in situ EDXRD kinetic and mechanistic study of the hydrothermal crystallization of TiO2 nanoparticles from nitric acid peptized sol–gel

In situ EDXRD has been used to probe the reaction kinetics and mechanism of the hydrothermal crystallization of TiO₂ nanoparticles. The process was found to involve a diffusion-controlled mechanism based on the Avrami–Erofe'ev kinetic model.

"CLASSIC NMR": an in-situ NMR strategy for mapping the time-evolution of crystallization processes by combined liquid-state and solid-state measurements

A new in-situ NMR strategy (termed CLASSIC NMR) for mapping the evolution of crystallization processes is reported, involving simultaneous measurement of both liquid-state and solid-state NMR spectra as a function of time. This combined strategy allows complementary information to be obtained on the evolution of both the solid and liquid phases during the crystallization process. In particular, as crystallization proceeds (monitored by solid-state NMR), the solution state becomes more dilute, leading to changes in solution-state speciation and the modes of molecular aggregation in solution, which are monitored by liquid-state NMR. The CLASSIC NMR experiment is applied here to yield new insights into the crystallization of m-aminobenzoic acid.

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.

Dimensionality changes in the solid phase at room temperature: 2D → 1D → 3D evolution induced by ammonia sorption–desorption on zinc phosphates

2D → 1D → 3D dimensionality changes on zinc phosphates induced by ammonia sorption–desorption in the solid phase at room temperature.

A new, facile method to prepare hybrid calcium poly(styrene-phenylvinylphosphonate)–phosphate materials for a superior performance catalyst support

Various pores or channels produced by modification of the PS-PVPA chain could contribute to significant impact on the excellent catalytic activity.

Synthesis, structure, and polymorphism studies in amine-templated open-framework zinc phosphites

Five new zinc phosphites, [C10N4H26][Zn2(HPO3)4].2H2O, 1, [C10N4H26][Zn5(H2O)4(HPO3)6].4H2O, 2, [C10N4H26][Zn4(HPO3)6].2H2O, 3, [C10N4H26][Zn4(HPO3)6].2H2O, 4, and [Zn2(HPO3)2(C10N4H24)], 5, were synthesized employing solvo/hydrothermal reactions in the presence of 1,4-bis (3-aminopropyl) piperazine (APPIP). Single crystal X-ray diffraction studies indicate that all the compounds form a hierarchy of structures. While the structures 1 and 2 are low-dimensional, 3-5 have three-dimensional connectivity. ZnO4 and HPO3 units form a 4-membered ring and are connected through their corners forming a one-dimensional chain structure in 1. 2 has one-dimensional ladders connected by ZnO2(H2O)4 octahedral units forming a layer with 4- and 8-membered apertures. Compounds 3 and 4 have similar molecular formulae and connectivity, which makes them polymorphic in nature. The amine molecules exist in gauche and all-trans form in 3 and 4, respectively. The amine molecule binds with the zinc center in 5 and acts as a pillar between the two zinc phosphite layers. The present study outlines the possible role of synthesis parameters for the isolation of a number of different structures by employing a single amine molecule, APPIP. The observation of polymorphic structures along with the interconvertibilities of one of the phases is important and noteworthy. The 31P chemical shifts observed in NMR studies, consistent with the single crystal data, have been correlated with the valence sum values of the oxygen that are bound with the distinct phosphorus.

Memory Effect of Activated Mg–Al Hydrotalcite: In Situ XRD Studies during Decomposition and Gas-Phase Reconstruction

The thermal decomposition of Mg-Al hydrotalcite and the subsequent reconstruction of the decomposed products in the presence of water vapor (2 vol. % H(2)O in N(2)) have been investigated by in situ XRD. Thermographic analysis and temperature-programmed desorption MS results complemented the diffraction data. Valuable mechanistic and kinetic insights into these processes, which are of prime importance for optimal activation of this type of material for catalytic applications, were obtained. Hydrotalcite decomposition to the mixed oxide proceeds via formation at 423-473 K of an intermediate phase, consisting of a highly disordered, dehydrated, layered structure. The latter evolves by removal of interlayer water on heating, causing a shrinking of the interlayer space (it is up to 45 % smaller than in the as-synthesized hydrotalcite). Above 623 K, Mg(Al)O(x) oxide with the periclase structure is formed. Reversion of the intermediate dehydrated structure to hydrotalcite upon contact with water vapor is complete and very fast at room temperature. Recovery of hydrotalcite from the oxide calcined at 723 K is two orders of magnitude slower than rehydration of the intermediate layered structure and one order of magnitude slower than the typically practiced liquid-phase reconstruction. In contrast to the decomposition, the reconstruction mechanism does not involve an intermediate phase. The gas-phase rehydration and reconstruction was interrupted above 303 K. This is attributed to the poor wetting of the surface of the decomposed materials induced by hampered H(2)O adsorption above room temperature at the water vapor pressure applied. The Avrami-Erofe'ev model describes the reconstruction kinetics well.

An ab Initio Molecular Dynamics and Density Functional Theory Study of the Formation of Phosphate Chains from Metathiophosphates

The reactions that occur between metathiophosphate (MTP) molecules are identified and examined through ab initio molecular dynamics simulations and static quantum chemical calculations at the density functional level of theory. The simulations show that certain types of MTPs can react to yield phosphate chains, while others only dimerize. These differences are rationalized in terms of reaction energies and the electronic structures of these molecules. In the reaction leading to the formation of phosphate chains, the reactive center, a tri-coordinate phosphorus atom, is continually regenerated. A polymerization mechanism linking MTPs to phosphate chains is developed on the basis of these results. This information sheds light on the underlying processes that may be responsible for the formation of phosphates under high-temperature conditions and may prove useful in the development of protocols for the rational synthesis of complex phosphate structures.

Structural diversity and chemical trends in hybrid inorganic–organic framework materials

Hybrid framework compounds, including both metal-organic coordination polymers and systems that contain extended inorganic connectivity (extended inorganic hybrids), have recently developed into an important new class of solid-state materials. We examine the diversity of this complex class of materials, propose a simple but systematic classification, and explore the chemical and geometrical factors that influence their formation. We also discuss the growing evidence that many hybrid frameworks tend to form under thermodynamic rather than kinetic control when the synthesis is carried out under hydrothermal conditions. Finally, we explore the potential applications of hybrid frameworks in areas such as gas separations and storage, heterogeneous catalysis, and photoluminescence.

Formation of zinc phosphate polymers and networks through the insertion of metathiophosphates into zinc dialkyldithiophosphates

The interactions between metathiophosphates (MTPs) and zinc dialkyldithiophosphates (ZnDDPs) were explored through molecular simulation. The results highlight a novel reaction leading to the formation of zinc phosphate polymers and networks through the insertion of MTPs into ZnDDPs.

Novel Zinc Phosphate Topologies Defined by Organic Ligands

Six new zinc phosphates [C18H20N4][Zn4(HPO4)4(H2PO4)2(C18H18N4)3].2H2O (1), [Zn4(HPO4)4(C18H18N4)3].4H2O (2), [Zn3(HPO4)3(H2PO4)(C22H22N8)0.5(C22H24N8)0.5] (3), [Zn2(HPO4)2(C18H16N4)] (4), [Zn(HPO4)(C18H14N2)] (5), and [Zn2(HPO4)2(C12H10N4)] (6) have been synthesized under mild hydrothermal conditions in the presence of 1,4-bis(N-benzimidazolyl)butane (L1), 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L2), 1,4-bis(imidazol-1-ylmethyl)naphthalene (L3), 9-(imidazol-1-ylmethyl)anthracene (L4), and 1,4-bis(1-imidazolyl)benzene (L5), respectively, and their structures were determined by X-ray crystallography. Compound 1 exhibits a unique inorganic motif of isolated 8-rings interconnected by L1. Compound 2, also formed from L1, contains a previously unobserved chain structure composed of edge-sharing 4-rings and 8-rings. Compound 3, prepared from L2, possesses an unusual one-dimensional framework, which is composed of vertex-sharing 4-rings and triple fused 4-rings. The inorganic portions of 4, 5, and 6 each adopt a layer structure. The sheets in 4 and 5 have a 4.8(2) topology, and in 6, a 6(3) topology is observed. The zinc atoms in compounds 1-6 are all tetrahedrally coordinated by a combination of phosphate groups and organic ligands. Potential relationships between the inorganic motifs reported in the present study are identified. These are indicative of a possible pattern of self-assembly of zinc and phosphorus tetrahedra and indicative of the role of the organic ligands in the formation of hybrid structures.

Five New Zinc Phosphite Structures: Tertiary Building Blocks in the Construction of Hybrid Materials

The syntheses and structures of five new zinc phosphites [Zn(HPO(3))(C(4)H(6)N(2))] (1), [Zn(2)(HPO(3))(2)(C(10)H(10)N(2))(2)](2) (2), [Zn(HPO(3))(C(14)H(14)N(4))(0.5)] (3), [Zn(2)(HPO(3))(2)(C(14)H(14)N(4))].0.4H(2)O (4), and [Zn(2)(HPO(3))(2)(C(14)H(14)N(4))] (5) are reported. In compounds 1-3, the zinc atoms are ligated by 1-methylimidazole, 1-benzylimidazole, and 1,4-bis(imidazol-1-ylmethyl)benzene, respectively, while compounds 4 and 5 are synthesized in the presence of the same bifunctional ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. The inorganic framework of compound 1 is composed of vertex-shared ZnO(3)N and HPO(3) tetrahedra that form 4-rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 2, the inorganic framework is composed of 4-rings and 8-rings to form the well-known 4.8(2) 2D network. This is connected via C-H...pi interactions between 1-benzylimidazole ligand to generate a pseudo-pillared-layer structure. In 3, the inorganic framework again has the 4.8(2) topology pillared by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. In 4, a new layer pattern is observed. Specifically, three edge-sharing 4-rings form triple-fused 4-rings. These tertiary building units are further connected to form 12-rings. The alternating triple 4-rings and 12-rings form a previously unknown 2D inorganic sheet. The sheets are joined together by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene, to generate a 3D pillared-layer structure. In 4, benzene rings and imidazole rings stack in a zigzag pattern in the interlayer space. A significant role for the triple 4-ring tertiary building unit in the formation of hybrid inorganic/organic metal phosphite structures is proposed for 4 and 5. In 5, the triple 4-rings fuse to give a 1D stair-step structure. Calculations show that the triple 4-ring pattern observed in the linear ladder structure of 1 is more stable than that in the stair step pattern of 5.