Covalent and Ionic Capacity of MOFs To Sorb Small Gas Molecules

In this work, the aim is to characterize how an Fe-based metal–organic framework (MOF) behaves when gases, like carbon dioxide, are inserted through their channels and to characterize the nature and strength of those interactions. Despite the computational nature of the project, it is based on the experimental results obtained in 2016 by Mı́nguez-Espallargas and co-workers (<i>J. Am. Chem. Soc.</i> <b>2013</b>, <i>135</i>, 15986−15989). Those MOFs were found to selectively allocate/adsorb CO₂, having as a drawback that apparently each cavity allocates only one CO₂ molecule. Despite truncating the MOF to its unitary cell, the whole cavity of the MOF can be described in detail by precise ab initio calculations. Another computational goal is to unravel why experimentally CO₂ was preferred with respect to N₂, and for the sake of consistency, a list of common gases will be further studied, such as H₂, O₂, H₂O, CH₄, C₂H₆, N₂O, or NO

Covalent and Ionic Capacity of MOFs To Sorb Small Gas Molecules

In this work, the aim is to characterize how an Fe-based metal–organic framework (MOF) behaves when gases, like carbon dioxide, are inserted through their channels and to characterize the nature and strength of those interactions. Despite the computational nature of the project, it is based on the experimental results obtained in 2016 by Mı́nguez-Espallargas and co-workers (<i>J. Am. Chem. Soc.</i> <b>2013</b>, <i>135</i>, 15986−15989). Those MOFs were found to selectively allocate/adsorb CO₂, having as a drawback that apparently each cavity allocates only one CO₂ molecule. Despite truncating the MOF to its unitary cell, the whole cavity of the MOF can be described in detail by precise ab initio calculations. Another computational goal is to unravel why experimentally CO₂ was preferred with respect to N₂, and for the sake of consistency, a list of common gases will be further studied, such as H₂, O₂, H₂O, CH₄, C₂H₆, N₂O, or NO

Analysis of the Aromaticity of Five-Membered Heterometallacycles Containing Os, Ru, Rh, and Ir

We study the molecular structure and aromaticity in a series of experimental and new in silico designed five-membered heterometallacycles with general formula M­(XC₃H₃)­(PH₃)₂, where M = OsH₃, OsCl₃, OsCl₂, RuCl₂, RhCl₂ or IrCl₂ and X = NH, O, S, CH^–, or CH⁺. The electron delocalization of the five-membered rings in these complexes is analyzed using the induced magnetic field, NICS, and MCI descriptors of aromaticity. Our results indicate that the five-membered rings in all complexes with X = NH, O, S, and CH^– have a low aromatic character denoted by nonintense diatropic behavior and low MCI values. Five-membered rings in complexes with X = CH⁺ are clearly paratropic and antiaromatic according to MCI values with the exception of M = OsCl₃. The reason for this exception is discussed

An Analysis of the Isomerization Energies of 1,2-/1,3-Diazacyclobutadiene, Pyrazole/Imidazole, and Pyridazine/Pyrimidine with the Turn-Upside-Down Approach

The isomerization energies of 1,2- and 1,3-diazacyclobutadiene, pyrazole and imidazole, and pyridazine and pyrimidine are 10.6, 9.4, and 20.9 kcal/mol, respectively, at the BP86/TZ2P level of theory. These energies are analyzed using a Morokuma-like energy decomposition analysis in conjunction with what we have called turn-upside-down approach. Our results indicate that, in the three cases, the higher stability of the 1,3-isomers is not due to lower Pauli repulsions but because of the more favorable σ-orbital interactions involved in the formation of two C–N bonds in comparison with the generation of C–C and N–N bonds in the 1,2-isomers

Comparison between Alkalimetal and Group 11 Transition Metal Halide and Hydride Tetramers: Molecular Structure and Bonding

A comparison between alkalimetal (M = Li, Na, K, and Rb) and group 11 transition metal (M = Cu, Ag, and Au) (MX)₄ tetramers with X = H, F, Cl, Br, and I has been carried out by means of the Amsterdam Density Functional software using density functional theory at the BP86/QZ4P level of theory and including relativistic effects through the ZORA approximation. We have obtained that, in the case of alkalimetals, the cubic isomer of <i>T</i>_<i>d</i> geometry is more stable than the ring structure with <i>D</i>_4<i>h</i> symmetry, whereas in the case of group 11 transition metal tetramers, the isomer with <i>D</i>_4<i>h</i> symmetry (or <i>D</i>_2<i>d</i> symmetry) is more stable than the <i>T</i>_<i>d</i> form. To better understand the results obtained we have made energy decomposition analyses of the tetramerization energies. The results show that in alkalimetal halide and hydride tetramers, the cubic geometry is the most stable because the larger Pauli repulsion energies are compensated by the attractive electrostatic and orbital interaction terms. In the case of group 11 transition metal tetramers, the <i>D</i>_4<i>h</i>/<i>D</i>_2<i>d</i> geometry is more stable than the <i>T</i>_<i>d</i> one due to the reduction of electrostatic stabilization and the dominant effect of the Pauli repulsion

SingleNot Double3D-Aromaticity in an Oxidized <i>Closo</i> Icosahedral Dodecaiodo-Dodecaborate Cluster

3D-aromatic molecules with (distorted) tetrahedral, octahedral, or spherical structures are much less common than typical 2D-aromatic species or even 2D-aromatic-in-3D systems. Closo boranes, [BnHn]2– (5 ≤ n ≤ 14) and carboranes are examples of compounds that are singly 3D-aromatic, and we now explore if there are species that are doubly 3D-aromatic. The most widely known example of a species with double 2D-aromaticity is the hexaiodobenzene dication, [C6I6]2+. This species shows π-aromaticity in the benzene ring and σ-aromaticity in the outer ring formed by the iodine substituents. Inspired by the hexaiodobenzene dication example, in this work, we explore the potential for double 3D-aromaticity in [B12I12]0/2+. Our results based on magnetic and electronic descriptors of aromaticity together with 11B{1H} NMR experimental spectra of boron-iodinated o-carboranes suggest that these two oxidized forms of a closo icosahedral dodecaiodo-dodecaborate cluster, [B12I12] and [B12I12]2+, behave as doubly 3D-aromatic compounds. However, an evaluation of the energetic contribution of the potential double 3D-aromaticity through homodesmotic reactions shows that delocalization in the I12 shell, in contrast to the 10σ-electron I62+ ring in the hexaiodobenzene dication, does not contribute to any stabilization of the system. Therefore, the [B12I12]0/2+ species cannot be considered as doubly 3D-aromatic

X₂Y₂ Isomers: Tuning Structure and Relative Stability through Electronegativity Differences (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te)

We have studied the XYYX and X₂YY isomers of the X₂Y₂ species (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te) using density functional theory at the ZORA-BP86/QZ4P level. Our computations show that, over the entire range of our model systems, the XYYX isomers are more stable than the X₂YY forms except for X = F and Y = S and Te, for which the F₂SS and F₂TeTe isomers are slightly more stable. Our results also point out that the Y–Y bond length can be tuned quite generally through the X–Y electronegativity difference. The mechanism behind this electronic tuning is the population or depopulation of the π* in the YY fragment

Unraveling the Origin of the Relative Stabilities of Group 14 M₂N₂²⁺ (M, N = C, Si, Ge, Sn, and Pb) Isomer Clusters

We analyze the molecular structure, relative stability, and aromaticity of the lowest-lying isomers of group 14 M₂N₂²⁺ (M and N = C, Si, and Ge) clusters. We use the gradient embedded genetic algorithm to make an exhaustive search for all possible isomers. Group 14 M₂N₂²⁺ clusters are isoelectronic with the previously studied group 13 M₂N₂^2– (M and N = B, Al, and Ga) clusters that includes Al₄^2–, the archetypal all-metal aromatic molecule. In the two groups of clusters, the cyclic isomers present both σ- and π-aromaticity. However, at variance with group 13 M₂N₂^2– clusters, the linear isomer of group 14 M₂N₂²⁺ is the most stable for two of the clusters (C₂Si₂²⁺ and C₂Ge₂²⁺) , and it is isoenergetic with the cyclic <i>D</i>_4<i>h</i> isomer in the case of C₄²⁺. Energy decomposition analyses of the lowest-lying isomers and the calculated magnetic- and electronic-based aromaticity criteria of the cyclic isomers help to understand the nature of the bonding and the origin of the stability of the global minima. Finally, for completeness, we have also analyzed the structure and stability of the heavier Sn and Pb group 14 M₂N₂²⁺ analogues

Media Distribution in Heterogeneous Environments using IP-Multicast

This document discusses problems and solutions around distribution of media in heterogeneous environments when using IP-multicast.Godkänd; 1998; 20080505 (ysko

Ab Initio Design of Chelating Ligands Relevant to Alzheimer’s Disease: Influence of Metalloaromaticity

Evidence supporting the role of metal ions in Alzheimer’s disease (AD) has rendered metal ion chelation as a promising therapeutic treatment. The rational design of efficient chelating ligands requires, however, a good knowledge of the electronic and molecular structure of the complexes formed. In the present work, the coordinative properties of a set of chelating ligands toward Cu(II) have been analyzed by means of DFT(B3LYP) calculations. Special attention has been paid to the aromatic behavior of the metalated rings of the complex and its influence on the chelating ability of the ligand. Ligands considered have identical metal binding sites (through N/O coordination) and only differ on the kind and size of the aromatic moieties. Results indicate that there is a good correlation between the stability constants (log β₂) and the degree of metalloaromaticity determined through the <i>I</i>_NG and HOMA indices; that is, the higher the metalloaromaticity, the larger the log β₂ value. MOs and aromaticity descriptors confirm that present complexes exhibit Möbius metalloaromaticity. Detailed analysis of the nature of the Cu(II)-ligand bonding, performed through an energy decomposition analysis, indicates that ligands with less aromatic moieties have the negative charge more localized in the metalated ring, thus increasing their σ-donor character and the metalloaromaticity of the complexes they form