Ca- and Sr-tetrafluoroisophthalates: mechanochemical synthesis, characterization, and ab initio structure determination

Mechanochemistry of fluoride solids: from mechanical activation to mechanically stimulated synthesis

Abstract

This lecture text is focused on the comparatively young field of mechanochemistry of fluoride solids, considering both their mechanical activation and their mechanochemical synthesis. Beside a literature survey, the mechanochemical synthesis of binary fluorides MF2, MF3, of complex fluorides MMgF4, of solid solutions MaxMb1−xF2 or M1−xLnxF2+x (Ln: Y, Eu) and of fluorine-containing coordination polymers is presented. Owing to their interesting potential applications in the field of fluoride ion conductivity or luminescence properties when doped, most of the given examples are alkaline earth metal compounds. A short historical survey, remarks on peculiarities and consequences of mechanical activation as well as the necessary technical equipment for mechanochemical reactions precede the section.

Graphic abstract

Metal-Organic Framework (MOF)-Based Biomaterials for Tissue Engineering and Regenerative Medicine

The synthesis of Metal-organic Frameworks (MOFs) and their evaluation for various applications is one of the largest research areas within materials sciences and chemistry. Here, the use of MOFs in biomaterials and implants is summarized as narrative review addressing primarely the Tissue Engineering and Regenerative Medicine (TERM) community. Focus is given on MOFs as bioactive component to aid tissue engineering and to augment clinically established or future therapies in regenerative medicine. A summary of synthesis methods suitable for TERM laboratories and key properties of MOFs relevant to biomaterials is provided. The use of MOFs is categorized according to their targeted organ (bone, cardio-vascular, skin and nervous tissue) and whether the MOFs are used as intrinsically bioactive material or as drug delivery vehicle. Further distinction between in vitro and in vivo studies provides a clear assessment of literature on the current progress of MOF based biomaterials. Although the present review is narrative in nature, systematic literature analysis has been performed, allowing a concise overview of this emerging research direction till the point of writing. While a number of excellent studies have been published, future studies will need to clearly highlight the safety and added value of MOFs compared to established materials for clinical TERM applications. The scope of the present review is clearly delimited from the general 'biomedical application' of MOFs that focuses mainly on drug delivery or diagnostic applications not involving aspects of tissue healing or better implant integration.

New 2D layered structures with direct fluorine–metal bonds: MF(CH3COO) (M: Sr, Ba, Pb)

New coordination polymers with 2D network structures with fluorine directly coordinated to the metal ion were prepared both via mechanochemical synthesis and fluorolytic sol–gel synthesis.

Ca-, Sr-, and Ba-Coordination polymers based on anthranilic acid via mechanochemistry

Ca-, Sr-, and Ba-Based coordination polymers (CPs) were prepared mechanochemically by milling metal-hydroxide samples with anthranilic acid (oABAH). {[Ca(oABA)2(H2O)3]}n (1) consists of one-dimensional polymeric chains that are further connected by a hydrogen-bonding network. {[Sr(oABA)2(H2O)2]·H2O}n (2) is a one-dimensional CP in which water molecules bridge Sr2+ ions and increase the dimensionality by building an extended network. {[Ba(oABA)2(H2O)]}n (3) crystallizes as a two-dimensional CP comprising one bridging water molecule. The cation radii influence the inorganic connectivity and dimensionality of the resulting crystal structures. The crystal structures were refined from powder X-ray diffraction data using the Rietveld method. The local coordination environments were studied via extended X-ray absorption fine structure (EXAFS) measurements. The compounds were further characterized using comprehensive analytical methods such as elemental analysis, thermal analysis, MAS NMR, imaging, and dynamic vapor sorption (DVS) measurements. Compounds 1, 2, and 3 exhibit small surface areas which decrease further after thermal annealing experiments. All compounds exhibit a phase transformation upon heating, which is only reversible in 3.

Ca-Tetrafluorophthalate and Sr-isophthalate: mechanochemical synthesis and characterization in comparison with other Ca-and Sr-coordination polymers

New Ca- and Sr-based coordination polymers (CPs) were mechanochemically synthesized by milling metal hydroxide samples (M = Ca, Sr) with tetrafluorophthalic acid (H2oBDC-F4) and isophthalic acid (H2mBDC). [Ca(oBDC-F4)(H2O)2] (1) exhibits a small surface area which is slightly increased after removing the crystal water. On the other hand, the hydrated sample of the nonfluorinated [Sr(mBDC)(H2O)3.4] (2) reveals a small BET surface area which remains unchanged even after the release of crystal water via thermal treatment. The new compounds 1 and 2 are similar to their Sr- and Ca-analogs, respectively. These findings are confirmed by thermal analysis, MAS NMR, and ATR-IR measurements, in addition to the Le Bail refinements for the measured powder X-ray data of 1 and 2. Ca- and Sr-CPs based on perfluorinated dicarboxylic systems and their nonfluorinated analogs diverse in structural and chemical properties depending on the geometries of the organic linkers and the presence of fluorine atoms. The fluorinations of organic ligands lead to the formation of fluorinated CPs with higher dimensionalities compared to their nonfluorinated counterparts. Conversely, the thermal stabilities of the latter are higher than those of the fluorinated CPs.

Hydrated and dehydrated Ca-coordination polymers based on benzene-dicarboxylates: mechanochemical synthesis, structure refinement, and spectroscopic characterization

Hydrated Ca-CPs were synthesized by milling. Dehydrated phases were obtained by thermal treatments in reversible processes.

New synthetic strategies to prepare metal–organic frameworks

This critical review summarizes the recent developments in the application of new synthetic strategies for preparing MOFs, including the ionothermal method, deep eutectic solvent usage, surfactant-thermal process, and mechanochemistry.

Main group mechanochemistry

Over the past decade, mechanochemistry has emerged as a powerful methodology in the search for sustainable alternatives to conventional solvent-based synthetic routes. Mechanochemistry has already been successfully applied to the synthesis of active pharmaceutical ingredients (APIs), organic compounds, metal oxides, coordination compounds and organometallic complexes. In the main group arena, examples of synthetic mechanochemical methodologies, whilst still relatively sporadic, are on the rise. This short review provides an overview of recent advances and achievements in this area that further validate mechanochemistry as a credible alternative to solution-based methods for the synthesis of main group compounds and frameworks.

Strontium-coordination polymers based on tetrafluorophthalic and phthalic acids: mechanochemical synthesis, ab initio structures determination, and spectroscopic characterization

New fluorinated and fluorine-free Sr-based coordination polymers were synthesized by milling of Sr-hydroxide samples with tetrafluorophthalic acid and phthalic acid, respectively.