45 research outputs found
Host-guest and guest-guest interactions between xylene isomers confined in the MIL-47(V) pore system
The porous MIL-47 material shows a selective adsorption behavior for para-, ortho-, and meta-isomers of xylenes, making the material a serious candidate for separation applications. The origin of the selectivity lies in the differences in interactions (energetic) and confining (entropic). This paper investigates the xylene-framework interactions and the xylene-xylene interactions with quantum mechanical calculations, using a dispersion-corrected density functional and periodic boundary conditions to describe the crystal. First, the strength and geometrical characteristics of the optimal xylene-xylene interactions are quantified by studying the pure and mixed pairs in gas phase. An extended set of initial structures is created and optimized to sample as many relative orientations and distances as possible. Next, the pairs are brought in the pores of MIL-47. The interaction with the terephthalic linkers and other xylenes increases the stacking energy in gas phase (-31.7 kJ/mol per pair) by roughly a factor four in the fully loaded state (-58.3 kJ/mol per xylene). Our decomposition of the adsorption energy shows various trends in the contributing xylene-xylene interactions. The absence of a significant difference in energetics between the isomers indicates that entropic effects must be mainly responsible for the separation behavior
Magnetic and Photoluminescent Sensors Based on Metal-Organic Frameworks Built up from 2-aminoisonicotinate
Red Guipuzcoana de Ciencia, Tecnologia e Innovacion
OF218/2018
University of Basque Country
GIU 17/13
Basque Government
IT1005-16
IT1291-19
IT1310-19
Junta de Andalucia
FQM-394
Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE)
PGC2018-102052-A-C22
PGC2018-102052-B-C21
MAT2016-75883-C2-1-P
European Union (EU)
ESFIn this work, three isostructural metal-organic frameworks based on frst row transition metal ions
and 2-aminoisonicotinate (2ain) ligands, namely, {[M(μ-2ain)2]·DMF}n [MII=Co (1), Ni (2), Zn (3)], are
evaluated for their sensing capacity of various solvents and metal ions by monitoring the modulation
of their magnetic and photoluminescence properties. The crystal structure consists of an open
diamond-like topological 3D framework that leaves huge voids, which allows crystallizing two-fold
interpenetrated architecture that still retains large porosity. Magnetic measurements performed on 1
reveal the occurrence of feld-induced spin-glass behaviour characterized by a frequency-independent
relaxation. Solvent-exchange experiments lead successfully to the replacement of lattice molecules by
DMSO and MeOH, which, on its part, show dominating SIM behaviour with low blocking temperatures
but substantially high energy barriers for the reversal of the magnetization. Photoluminescence studied
at variable temperature on compound 3 show its capacity to provide bright blue emission under UV
excitation, which proceeds through a ligand-centred charge transfer mechanism as confrmed by timedependent DFT calculations. Turn-of and/or shift of the emission is observed for suspensions of 3 in
diferent solvents and aqueous solutions containing metal ions