Synthesis And Structural Characterization Of Metal Bisphosphonates In Deep Eutectic Solvents

As an important kind of organic-inorganic hybrid material,metal phosphonate compounds have excellent performance in the field of catalysis, adsorption and photoelectromagnetic. Compared with most compounds based on the carboxylic acid or nitrogen-containing ligands, phosphonate group can provide more binding sites for connecting with metal ions and forming stronger bonds, which make it easier to form metal phosphonate compounds with rich structures and high thermal stability. Currently, most of the metal phosphonate compounds are synthesized by hydrothermal or solvothermal route and the choice of solvent, organic phosphonate ligand and organic amine are the important factors that influences the structure of product.Recently, ionic liquids or eutectic mixture (DES) are widely used as both solvent and template agent in ionothermal synthesis, which shows the potential value in the synthesis of new inorganic porous materials. Herein, the synthesis of metal phosphonates were systematically investigated with HEDP and Hpmd as organic ligands in the DESs (urea-based compounds/quaternary ammonium salt,carboxylic acid/quaternary ammonium salt).As a result, eight metal bisphosphonate compounds were successfully synthesized by changing synthetic conditions, five of which have novel crystal structures and their structures were determined by single-crystal diffraction data. Also, TGA, SEM,CHN elemental analysis and FT-IR were used to characterize the physico-chemical properties of the obtained compounds. The main contents and conclusions are as follows.1、Urea-based derivatives (urea and imidazolone) and choline chloride were used to form deep eutectic sovents as reaction solvents, four novel phosphonates were producted with HEDP as ligand and zinc and cobalt as metal inons by controlling the synthetic conditions. The structural formula of the four compounds are (NH4)2Zn(C2H4O7P2)(Ⅰ).(NH4)2Co(C2H4O7P2)(Ⅱ), (C2H10N2)Zn(C2H407P2) (Ⅲ) and (C2H8N2)(C2H10N2)2Zn(C2H4O7P2) (Ⅳ) respectively.Crystal structure analysis and elemental analysis show the compounds mentioned above have new crystal structures,both compounds Ⅰ and Ⅳ have three-dimensional open framework structures, compound Ⅱ exhibits two-dimensional layered structure and compound Ⅲ has a one-dimensional chain structure. The TG analysis shows those compounds have a low thermal stability with less 300℃. In addition, adding a small amount of water to initial reaction mixture has a significant influence on the structure of compound I. It is also found that the inorganic amine derived from urea and ethylenediamine from imidazolone have a strong template role in the final structures, and were located in channels of compounds. The template agent were released slowly from in-situ decomposition in reaction may resulted in a large size single crystal.2、oxalic acid and a variety of quaternary ammonium salt(ChCl、TMACl、 TEABr、TPABr) were used to form deep eutectic systems as reaction solvents. We obtained two novel materials and two known substances with Hpmd as the organic ligand zinc and cobalt as metal inons by changing the conditions.one of the novel material is being resolved now. Other synthetic products and formulas are as follows:Zn[HO3PCH2(C6H4)CH2PO3H] (Ⅴ).; Co2(H2O)2[O3PCH2(C6H4)CH2PO3] (Ⅵ);NaZn (C8P2H]006)0.5(C8P2H806)0.5·1.5H2O (Ⅶ);Among those compounds, compound V and VI are known metal bisphosphonates and compound Ⅶ is a new one, all of them have typical three-dimensional structures with a pillared type. For compound Ⅶ, it was synthesized in the presence of a small amount of water and Na cations, and sodium ions were coordinated by five oxygen atom in the final structures. This result also indicates that the Na ions in the initial reaction mixtures are beneficial to form new structures. Compared to compounds Ⅰ-Ⅳ, other metal bisphosphonates with Hpmd as a ligand have higher thermal stability (> 500 ℃).