|Montse Bazaga-García, Maria Papadaki, Rosario M. P. Colodrero, Pascual Olivera-Pastor,Enrique R. Losilla, Belen Nieto-Ortega, Miguel Ángel G. Aranda, Duane Choquesillo-Lazarte,Aurelio Cabeza, and Konstantinos D. Demadis
Tuning Proton Conductivity in Alkali Metal Phosphonocarboxylates by Cation Size-Induced and Water-Facilitated Proton Transfer Pathways,
Chem. Mater. 2015, 27, 424–435.
The structural and functional chemistry of a family of alkali-metal ions with racemic R,S-hydroxyphosphonoacetate (M-HPAA; M = Li, Na, K, Cs) are reported. Crystal structures were determined by X-ray data (Li+, powder diffraction following an ab initio methodology; Na+, K+, Cs+, single crystal). A gradual increase in dimensionality directly proportional to the alkali ionic radius was observed. [Li3(OOCCH(OH)PO3)(H2O)4]•H2O (Li-HPAA) shows a 1D framework built up by Li-ligand “slabs” with Li+ in three different coordination environments (4-, 5-, and 6-coordinated). Na-HPAA, Na2(OOCCH(OH)PO3H)(H2O)4, exhibits a pillared layered “house of cards” structure, while K-HPAA, K2(OOCCH(OH)PO3H)(H2O)2, and Cs-HPAA, Cs(HOOCCH(OH)PO3H), typically present intricate 3D frameworks. Strong hydrogen-bonded networks are created even if no water is present, as is the case in Cs-HPAA. As a result, all compounds show proton conductivity in the range 3.5 × 10–5 S cm–1 (Cs-HPAA) to 5.6 × 10–3 S cm–1 (Na-HPAA) at 98% RH and T = 24 °C. Differences in proton conduction mechanisms, Grothuss (Na+ and Cs+) or vehicular (Li+ and K+), are attributed to the different roles played by water molecules and/or proton transfer pathways between phosphonate and carboxylate groups of the ligand HPAA. Upon slow crystallization, partial enrichment in the S enantiomer of the ligand is observed for Na-HPAA, while the Cs-HPAA is a chiral compound containing only the S enantiomer.
Ayalew H. Assen, Youssef Belmabkhout, Karim Adil, Prashant M. Bhatt, Dong-Xu Xue, Hao Jiang, and Mohamed Eddaoudi
Ultra-Tuning of the Rare-Earth fcu-MOF Aperture Size for SelectiveMolecular Exclusion of Branched Paraffins,
Angew. Chem. Int. Ed. 2015, 54, 14353–14358.
Abstract: Using isoreticular chemistry allows the design and construction of a new rare-earth metal (RE) fcu-MOF with a suitable aperture size for practical steric adsorptive separations. The judicious choice of a relatively short organic building block, namely fumarate, to bridge the 12-connected RE hexanuclear clusters has afforded the contraction of the well-defined RE-fcu-MOF triangular window aperture, the sole access to the two interconnected octahedral and tetrahedral cages. The newly constructed RE (Y3+ and Tb3+) fcu-MOF analogues display unprecedented total exclusion of branched paraffins from normal paraffins. The resultant window aperture size of about 4.7 Å, regarded as a sorbate-size cut-off, enabled a complete sieving of branched paraffins from normal paraffins. The results are supported by collective single gas and mixed gas/vapor adsorption and calorimetric studies.
Juan Manuel Castillo, Juaquin Silvestre-Albero, Francisco Rodriguez-Reinoso, Thijs J. H. Vlugt and Sofia Calero
Water adsorption in hydrophilic zeolites: experiment and simulation, Phys.Chem. Chem. Phys., 15, 17374, August 2013.
DOI: http://dx.doi.org/ 10.1039/C3CP52910J
We have measured experimental adsorption isotherms of water in zeolite LTA4A, and studied the regeneration process by performing subsequent adsorption cycles after degassing at different temperatures. We observed incomplete desorption at low temperatures, and cation rearrangement at successive adsorption cycles. We also developed a new molecular simulation force field able to reproduce experimental adsorption isotherms in the range of temperatures between 273 K and 374 K. Small deviations observed at high pressures are attributed to the change in the water dipole moment at high loadings. The force field correctly describes the preferential adsorption sites of water at different pressures. We tested the influence of the zeolite structure, framework flexibility, and cation mobility when considering adsorption and diffusion of water. Finally, we performed checks on force field transferability between different hydrophilic zeolite types, concluding that classical, non-polarizable water force fields are not transferable.
Mirian E. Casco, Joaquín Silvestre-Albero, Anibal J. Ramírez-Cuesta,
Fernando Rey, Jose L. Jordá, Atul Bansode, Atsushi Urakawa, Inma Peral, Manuel Martínez-Escandell, Katsumi Kaneko & Francisco