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In search for future good adsorbents for CO2 capture, a nitrogen-rich triazole-type Metal–Organic Framework (MOF) is proposed based on the rational design and theoretical molecular simulations. The structure of the proposed MOF, named Zinc Triazolate based Framework (ZTF), is obtained by replacing the amine-organic linker of MAF-66 by a triazole, and its structural parameters are deduced. We used grand-canonical Monte Carlo (GCMC) simulations based on generic classical force fields to correctly predict the adsorption isotherms of CO2 and H2O. For water adsorption in MAF-66 and ZTF, simulations revealed that the strong hydrogen bonding interactions of water with the N atoms of triazole rings of the frameworks are the main driving forces for the high adsorption uptake of water. We also show that the proposed ZTF porous material exhibits exceptional high CO2 uptake capacity at low pressure, better than MAF-66. Moreover, the nature of the interactions between CO2 and the MAF-66 and ZTF surface cavities was examined at the microscopic level. Computations show that the interactions occur at two different sites, consisting of Lewis acid–Lewis base interactions and hydrogen bonding, together with obvious electrostatic interactions. In addition, we investigated the influence of the presence of H2O molecules on the CO2 adsorption on the ZTF MOF. GCMC simulations reveal that the addition of H2O molecules leads to an enhancement of the CO2 adsorption at very low pressures but a reduction of this CO2 adsorption at higher pressures. [ABSTRACT FROM AUTHOR]

The present theoretical study was carried out to investigate the NO reduction by CO over a Ti-porphyrin catalyst. Thus, density functional theory with and without the van der Waals correction was employed. The calculated adsorption energies show that the Ti-porphyrin is active in bending the NO and CO molecules. So, we proposed two reaction mechanisms for the NO reduction by CO on Ti-porphyrin. The calculated activation energies show that both mechanisms are plausible and feasible at room temperature. The Ti-porphyrin shows a good catalytic activity to NO reduction by CO compared to conventional Rh cluster catalyst. These results indicate that the Ti-porphyrin is a promising candidate for reducing NO and CO gases from our environment. [ABSTRACT FROM AUTHOR]

Using a first-principle methodology, we investigate the stable structures of the nonreactive and reactive clusters formed between Zn 2+ -triazoles ([Zn 2+ -Tz]) clusters and CO 2 and/or H 2 O. In sum, we characterized two modes of bonding of [Zn 2+ -Tz] with CO 2 /H 2 O: the interaction is established through (i) a covalent bond between Zn 2+ of [Zn 2+ -Tz] and oxygen atoms of CO 2 or H 2 O and (ii) hydrogen bonds through N-H or C-H of [Zn 2+ -Tz] and oxygen atoms of H 2 O or CO 2 , N-H···O. We also identified intramolecular proton transfer processes induced by complexation. Indeed, water drastically changes the shape of the energy profiles of the tautomeric phenomena through strong lowering of the potential barriers to tautomerism. The comparison to [Zn 2+ -Im] subunits formed with Zn 2+ and imidazole shows that the efficiency of Tz-based compounds for CO 2 capture and uptake is due to the incorporation of more accessible nitrogen donor sites in Tzs compared to imidazoles. Since [Zn 2+ -Tz] clusters are subunits of an organometallic nanoporous materials and Zn-proteins, our data are useful for deriving force fields for macromolecular simulations of these materials. Our work also suggests the consideration of traces of water to better model the CO 2 sequestration and reactivity on macromolecular entities such as pores or active sites.

A new Zn-N 4 -Schiff base L=((±)-trans-N,N'-Bis(2-aminobenzylidene)-1,2-diaminocyclohexane) complex was synthesized and fully characterized, showing an unexpected self-assembled double-stranded helicate structure. The X-ray crystal analysis of the Zn 2 L 2 complex ((C 40 H 44 N 8 Zn 2 ,CH 2 Cl 2 , a=14.2375(3) Å, b=16.7976(4) Å, c=16.1613(4) Å, monoclinic, P2 1 /n, Z=4) shows a centrosymmetrical structure in which zinc atoms are in distorted tetrahedral environments, revealing an M- (R, R) left-handed helicity in its asymmetric unit. However, it was observed that this dinuclear complex is thermodynamically unstable in the presence of small water amounts and undergoes demetallation into free N4-Schiff base ligand and ZnO nanoparticles. This hydrolysis process was thoroughly identified and monitored through detailed 1 H NMR, DOSY NMR analysis. The reaction mechanism of this demetallation event was elucidated by using the DFT method, involving an activation energy smaller than 13 kcal/mol. Besides, a theoretical mechanism of the demetallation process is given for the first time., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The aim of this paper is studying the encapsulation effect of carbon nanotubes (CNTs ) on the stabilizing process of titanium dioxide molecule dimers (TiO2)2. First, a theoretical study was performed concerning the guest species that are various titanium dioxide dimers. Five structures were treated as following: i) Cis (C) or ii)Trans (T) relatively to a square shaped fragment Ti2O2, iii) a mixed Tetrahedral/Pyramidal (T/P) disposition while two titanium atoms are sharing three oxygen atoms, and finally not bonded dimers in iv) parallel (P) and v) orthogonal (O) positions respectively. Only the (T), (C) and (T/P) isomers may be considered as stable compounds. The structure of the T-dimer is more stable than the Cis one by only 6.5 kcal mol-1. Typically, intra and extracyclic Ti-O bond lengths are 1.84Å and 1.61Å respectively. (T/P) dimer can be described as a metastable structure since its energy is higher than (T) one by 19 kcal mol-1. NBO analysis highlights the participation of dative bonding between oxygen lone pair and vacant titanium 3d orbitals. (P) and (O) structures represent transitory species that transform into the more stable structure which is the T-dimer. The second and principal part of this work concerns the re-optimization of the studied structures placed inside the CNT (12,0). Only (T), (C) and (P) dimers are stabilized by encapsulation through the establishment of strong interactions with the CNT wall. The (T / P) and (O) isomers which are converted into (T) and (P) dimers respectively, are leaving the nanotube while they still interacting with its edge. These favorable results are indicating in one hand the possibly detection of (T) and (C) isomers, and in another hand that the process of polymerization of the TiO2 molecule which is leading to nanostructured materials could be controlled by encapsulation within the CNTs.