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Among various strategies for CO 2 chemical fixation, the CO 2 cycloaddition with epoxides is one of the most promising and efficient approaches, in which ionic liquid (ILs) is a typical relatively environmentally friendly catalyst and medium. However, ILs decomposition and catalytic stability have not been in-depth investigated, and the structure-activity relationship of cations and anions has remained obscure, which would affect the understanding of catalytic behavior and catalyst loss, and limit the theoretical research and industrial application in CO 2 utilization. Therefore, based on a variety of phosphonium ILs we have designed and synthesized for CO 2 cycloaddition, the structure-activity relationship, steric hindrance and electronic effect of various anions and cations have been systematically studied in main and side reactions. Especially, a regulation strategy of cationic flexible steric hindrance and anionic electron effect have been developed to improve both ILs' activity and stability. Remarkably, the synergistic action of electron-donating effect, hydrogen bond and decreased acidity from flexible steric alkyl groups result in the spatial shielding of cation center and enhancement of the Br's leaving. Consequently, the quaternary phosphonium ILs with asymmetric flexible steric hindrance exhibit the optimal performance, showing propylene oxide (PO) conversion of 99.15% and propylene carbonate (PC) yield of 98.86%, which can efficiently decrease the formation of phosphine oxide, avoiding the decomposition of ILs. This discovery provides a new idea for developing stable and efficient CO 2 fixation system in sustainable industry. • Phosphine oxide generated from ILs' decomposition is first concerned and systematically investigated in CO 2 conversion. • Cationic steric hindrance and anionic electron effect are regulated to enhance both activity and stability. • Quaternary phosphonium ILs with asymmetric flexible groups exhibit excellent performance, avoiding phosphine oxide's formation. • Flexible alkyls' electron-donating effect and hydrogen-bond interaction lead to the spatial shielding and protection to cation center. • This discovery provides a novel avenue for developing CO 2 mitigation and fixation system in sustainable industry. [ABSTRACT FROM AUTHOR]

A new 3D complex namely [Gd 4 (C 7 H 7 N 2 O 4) 6 (H 2 O) 12 ·Cl 6 ·9H 2 O (1) was solvothermally synthesized by using 1,3-bis (carboxymethyl) imidazolium cation as a ligand. Single crystal X-ray analysis reveals that 3D positive charged framework was formed by Gd–O coordination bonds,and Gd3+ ions have two kinds of coordination environments. The free counter Cl− ions and lattice H 2 O locate in cavities of 1 through extensive H-bonds and electrostatic attractions between the Cl−/H 2 O and the positive framework. The thermogravimetric analysis (TGA) shows the organic framework decomposed at temperature above 345 °C, giving the final products Gd 2 O 3. The temperature dependent magnetic susceptibility displays antiferromagnetic interaction at temperature below 15.2 K, once above 15.2 K, compound 1 converts into paramagnetic interaction. The gadolinium-based MOF with 1, 3-bis(carboxymethyl)imidazolium Chloride ionic liquid as ligand has good thermal stability and magnetic property. There is Neel temperature at 15.2 K in compound 1 when study its magnetic, at temperature below 15.2 K there is antiferromagnetic interaction, but at temperature above 15.2 K, it converts into paramagnetic interaction. Image 1 1. This structure has 3D positive charged framework was formed by Gd−O coordination bonds. 2. There are free counter Cl− ions and lattice H 2 O locate in cavities of 1 through extensive H−bonds and electrostatic attractions between the Cl−/H 2 O and the positive framework. 3. The organic framework can be kept stables until 345 °C. There are antiferromagnetic interaction in Gd3+ ions at temperature below 15.2 K, once above 15.2 K, they converts into paramagnetic interaction. [ABSTRACT FROM AUTHOR]

A new lanthanide metal organic framework, namely [Eu(C 7 H 7 O 4 N 2)(H 2 O) 2 (Cl 0.38) 2 Cl 1.24 (1), was solvothermally synthesized using 1,3-bis(carboxymethyl)imidazolium chloride ([H 2 imdc]Cl) ionic liquid as a ligand. This compound was structurally characterized by single crystal X-ray diffraction and its properties were analyzed spectroscopy and theoretical studies. In 1 , Eu (III) ions have only one coordination environment, and the ligands exhibit one coordination mode. The Eu3+ ions and ligands are connected to construct wavelike 2D cationic layers through coordination bonds, and then the 2D networks further interconnected through hydrogen bonds. The luminescent properties were studied at 77 K. The emission spectrum shows that there is one Eu3+ ion site in asymmetric unit, which is consistent with the results of the X-ray crystal structure analysis. Compound 1 exhibits characteristic emission bands of Eu3+ with emission lifetime of 0.336 ms. Single crystal of metal organic framework: [Eu(C 7 H 7 O 4 N 2)(H 2 O) 2 (Cl 0.38) 2 Cl 1.24 1 was solvothermally synthesized by 1,3-bis(carboxymethyl)imidazolium ionic liquid. The single crystal data indicate Eu3+ ions have only one nine-coordinate chemical environment, which is accordance with the results of the luminescence analysis of 1. FT-IR, PXRD, thermogravimetric analysis are also in accordance with the result of single crystal structure data. The time-resolved spectra further display that there is only one Eu3+ ion site in 1 and it has the lifelime of 0.336 ms. The thermal analysis results show the organic framework of 1 can sustain until 299 °C and completely decomposed into Eu 2 O 3 at about 589 °C. Image 1 • Rare earth metal organic framework crystal was synthesized by solvothermal method using ionic liquids as ligand. • The synthesized Eu-MOF is 2D cationic layers, which are further interconnected through hydrogen bonds. • It has good optical properties and the fluorescence lifetime can reach 0.336 ms. [ABSTRACT FROM AUTHOR]

• Two new two dimensional metal organic frameworks namely {Er 2 [(C 9 N 2 O 4 H 11) 3 ·H 2 O·Br]Br·Cl} n (1) and {Yb 2 [(C 9 N 2 O 4 H 11) 3 (H 2 O) 2 ]Br·Cl 2 } n (2) were solvothemally synthesized with Brønsted ionic liquid as ligand. • The effects of the reaction conditions to the growth of 1 and 2 , such as temperature, reaction solvents, as well as the ratio of solvents were explored. • 1 and 2 display good thermal stability and hydrophilicity in this work. • The magnetic measure of 2 shows its antiferromagnetic interaction via the Yb/O-C-O/Yb pathways. Two lanthanide metal organic frameworks (MOFs) {Er 2 [(C 9 N 2 O 4 H 11) 3 (H 2 O)Br]Br·Cl} n (1) and {Yb 2 [(C 9 N 2 O 4 H 11) 3 (H 2 O) 2 ]Br·Cl 2 } n (2) were solvothermally synthesized using Brønsted acidic ionic liquid: 1,3-bis(1-dicarboxylatoethyl) imidazolium bromide ([H 2 bcei]Br) as ligand. The results of single crystal X-ray diffraction show that Er3+ and Yb3+ both possess two different seven-coordinated chemical environments in 1 and 2 , respectively. While coordinating to Er3+ and Yb3+, [bcei]‒ displays same coordination mode because of their similar ionic radius. Although Er3+ and Yb3+ display different chemical environments, they are all linked by [bcei]− via Ln−O coordination bonds affording two three-dimensional structures with Cl− or Br− in the frameworks through H-bonds and electrostatic interaction. Considering the effect of the reaction temperature, solvents and solvent volume ratio on the crystal growth, the optimized synthesis conditions of 1 and 2 were explored. The magnetic behaviors of 2 were measured in the temperature range 2–300 K, which reveals its antiferromagnetic interaction between Yb3+ions. [Display omitted] [ABSTRACT FROM AUTHOR]