and (III) [Eu III 2 (Habtc) 2 (H 2 O) 6 ]•2.75H 2 O (H 4 abtc = 3,3′,5,5′-azobenzenetetracarboxylic acid), were designed and synthesized for use as catalysts. The framework structures, phase formation, and purity were characterized. The catalytic performances of [Eu IIIwere evaluated based on CO 2 cycloaddition with epichlorohydrin under ambient CO 2 pressure and solvent-free conditions. Discussion has been made with respect to the multiple Lewis and Brønsted acidic and Lewis basic sites coresiding in the frameworks, which were revealed by single-crystal X-ray diffraction and measurements of acidity and basicity. Depending on the reaction conditions, excellent turnover numbers and turnover frequencies (2778 and 694 h −1 for Ib and 2870 and 718 h −1 for IIb) with ≥99% conversion and ≥87% selectivity could be achieved. The robustness of Ib and IIb over 10 cycles of catalysis and the makeup process was disclosed. The potential of Ib and IIb as promising catalysts for other epoxides was also examined.

Inspired by the catalytic potential of lanthanide coordination polymers of 3,3′,5,5′-azobenzenetetracarboxylic acid (H4abtc), two new isostructural [Ln2 III(Habtc)2(DMSO)4]·DMSO·H2O (LnIII = SmIII (I), EuIII = (II), DMSO = dimethyl sulfoxide) were synthesized and characterized. Their single-crystal structures were elucidated and described. Structural transformations of II in the solid state prompted by ligand substitution and thermal treatment were studied, from which genuine reversible transformation of II to [EuIII(Habtc)­(H2O)4]·3H2O (II′) and [EuIII(Habtc)­(H2O)2]·2H2O (II″) was revealed. This illustrates the rare case of reversible transformation in lanthanide coordination polymers. The transformation between II′ and II″ was also investigated. Structural transformations among these frameworks are discussed with regard to the coordination environment of EuIII, coordination modes of Habtc3–, and similarities and disparities in framework architecture and registration. In addition, the catalytic performance of II with and without the prior activation in CO2 cycloaddition reaction with epichlorohydrin was studied in comparison with II′ and II″. The excellent performance of II disregarding the activation process has been demonstrated with the maximum turnover number and turnover frequency of 7682 and 1921 h–1, respectively, for the activated II and 7142 and 1786 h–1, respectively, for the nonactivated II. The maintenance of the catalytic efficiency over 10 cycles of the catalysis and the regeneration process is illustrated and discussed with respect to structural transformation.

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Aiming at ammonia gas detection at ambient temperature, phenoxyacetic acid (Hpoa) and 2,5-pyridinedicarboxylic acid (H2pydc) were employed to construct the isostructural [LnIII(poa)(2,5-pydc)(H2O)2]·3H2O (LnIII = EuIII (I), GdIII (II), and TbIII (III)). Their single crystal structures and photophysical properties as well as the triplet state energies of the sensitizers were characterized. Robustness and responses of I and its composite film with poly(vinyl alcohol) (I/PVA) toward water, ammonia, and common volatile organic compounds were examined. The substantial quenching of EuIII:5D0 → 7F J by only ammonia was disclosed, and the underlying mechanism was postulated based on experimental and computational studies. Referring to EuIII:5D0 → 7F2, the response R parameter was defined. Under ambient temperature (25–35 °C) and humidity (45–55% RH), a linear dependence of R on ammonia concentration (0.50–10.0 ppm) was obtained from I/PVA. Based on the calibration method, the sensitivity (4.04%·ppm–1), detection limit (0.14 ppm), percentage recoveries (103–111% for 3.50, 6.50, and 8.50 ppm), and relative standard deviation (1.5–8.2%) were determined. The reuse of the film for at least 10 cycles was demonstrated with 95–97% repeatability. Limitation of the detection by extreme humidity was presented.