Pluton Pullumbi

How Can a Hydrophobic MOF be Water-Unstable? Insight into the Hydration Mechanism of IRMOFs

We report an ab initio molecular dynamics study of the hydration process in a model IRMOF material. At low water content (one molecule per unit cell), water physisorption is observed on the zinc cation but the free⇄bound equilibrium strongly favors the free state. This is consistent with the hydrophobic nature of the host matrix and its type-V isotherm observed in a classical Monte Carlo simulation. At higher loading, a water cluster can be formed at the Zn(4)O site and this is shown to stabilize the water-bound state. This structure rapidly transforms into a linker-displaced state, where water has fully displaced one arm of a linker and which corresponds to the loss of the materials fully ordered structure. Thus an overall hydrophobic MOF material can also become water unstable, a feature that has not been fully understood until now.

ELATE: an open-source online application for analysis and visualization of elastic tensors

We report on the implementation of a tool for the analysis of second-order elastic stiffness tensors, provided with both an open-source Python module and a standalone online application allowing the visualization of anisotropic mechanical properties. After describing the software features, how we compute the conventional elastic constants and how we represent them graphically, we explain our technical choices for the implementation. In particular, we focus on why a Python module is used to generate the HTML web page with embedded Javascript for dynamical plots.

Characterization and Photochemistry of the Gallium and Indium Subhydrides Ga2H2 and In2H2

Herein we describe the cocondensation of Ga or In vapor with H2 in an excess of Ar at 10 ± 12 K, and the subsequent irradiation of the resulting matrix with light of different wavelengths. We show that the reaction of Ga2 or In2 with H2 directly or indirectly gives rise to three isomers of Ga2H2 and two isomers of In2H2, namely the bis( -hydrido) species Ga( -H)2Ga (1a) and In( -H)2In (1b), the trans-bent species HGaGaH (3a) and HInInH (3b), and GaGaH2 (2a) with two terminal Ga H bonds (Scheme 1). All these molecules have

Synthesis of Macropolycyclic Ligands Based on Tetraazacycloalkanes

A versatile synthesis of spherical macrobicyclic and cylindrical macrotricyclic ligands is described using 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,4,7,10-tetraazacyclododecane (cyclen), or dioxo macrocycles as precursors. Macrobicycles have been obtained by allowing cyclam, cyclen, or 5,12-dioxocyclam (1,4,8,11-tetraazacyclotetradecane-5,12-dione) to react with a bis-electrophilic spacer under high dilution conditions. A surprising selectivity has been observed for 2,6-dioxocyclen (1,4,7,10-tetraazacyclododecane-2,6-dione), which yields only macrotricycles under the same reaction conditions. Molecular modelling studies have been carried out to investigate the selectivity of the reactions, and good agreement has been observed between the theoretical predictions and experimental data. 1D- and 2D-NMR studies reveal a highly rigid structure in the case of macrobicycles. The macropolycyclic ligands show very different basicities, which demonstrates the influence of the cross-linker on the coordination properties of the ligands.

Iron complexes acting as nitric oxide carriers

Abstract A new strategy for NO-carrier synthesis depending on the strength of the ligand field, the configuration of the complex and the oxidation state of the metal is developed. The preparation of the trans- and cis -[Fe( 1 )(NO)(Cl)]Cl and trans -[Fe( 2 )(NO)(Cl)]Cl complexes, where 1 is 1,4,8,11-tetraaza-cyclotetradecane or cyclam and 2 is 6,6,13,13-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane, is reported. On the basis of spectroscopic data and PM3(tm) molecular modeling calculations, both species are characterized as complexes of the [FeNO] 7 type possessing an S =1/2 and S =3/2 ground state for the trans - and cis -[Fe( 1 )(NO)(Cl)]Cl, respectively. The cis isomer can act as a NO carrier.

Molecular Simulation of a Zn–Triazamacrocyle Metal–Organic Frameworks Family with Extraframework Anions

We report an investigation by means of adsorption experiments and molecular simulation of the behavior of a recently synthesized cationic metal–organic framework. We used a combination of quantum chemistry calculations and classical forcefield-based Grand Canonical Monte Carlo simulations to shed light onto the localization of extra-framework halogenide anions in the material. We also studied the adsorption of small gas molecules into the pores of the material using molecular simulation and investigated the coadsorption of binary gas mixtures.

Cobalt complex based on cyclam for reversible binding of nitric oxide

We report the synthesis and theoretical calculations of nitrosyl cobalt complexes based on saturated tetraazamacrocycle for the reversible binding of nitric oxide (NO). Density-functional theory provides a rigorous theoretical framework for analysing, interpreting and investigating important parameters in order to further tune the properties of these complexes to the target application. We focus on understanding the stability of complexes in methanol solution as well as their reactivity and stability evolution in the presence of NO, O2 and higher nitrogen oxides intermediates. Calculations have been used to explore appropriate combinations of different macrocycles, metal centres and ligands that could be used for efficient NO release.

Density functional theory calculations of Henry's constant for N2, O2 and Ar molecules in Ca-A and Ca-LSX zeolites

Zeolites are widely used in industry as gas-separation adsorbents or heterogeneous catalysts. An understanding of the adsorption properties of these materials (adsorption isotherms, Henry constants and isosteric heats) is vital to efficient separation process design and operation. In this paper we propose a method for the prediction of Henry constants and isosteric heats at zero coverage. By embedding a quantum mechanics calculation (QM) in a classical molecular mechanics (MM) model of the environment, the hybrid QM/MM scheme attempts to incorporate environmental effects at an atomistic level, including influences as accessibility hindrance, electrostatic perturbations and dielectric screening.

Gas Separation by Adsorption : Molecular Simulation of Adsorption Properties of Zeolitic materials

Zeolites are crystalline inorganic materials whose pores rangp from nearly 3A to over 10A. They are mainly used as heterogeneous catalysts, with an increasing use as gas-separation adsorbents. The great industrial applicability of this class of materials has generated many molecular modeling studies of their properties starting from empirical force fields to completely quantum mechanical methods. As quantum-chemical studies of zeolites used for gas separation must treat very largp unit cells, fully periodic ab initio simulations are unfortunately not yet practical due to largp CPU time requirements. Embedded QM/MM methods can be used to study the behavior of adsorbed molecules within zeolitic materials including the effect of the field and field gradient upon adsorption energies. In the present contribution, we show that this approach can be used to complement Grand Canonical Monte Carlo simulations which are currently applied to predict the N2/O2 adsorption isotherms in silicalite, Na-X, Na-LSX, Li-X and Li-LSX, in good agreement with experiment. The N2 molecule, due to its larger quadrupole moment, interacts more strongly with the extra-framework cations than O2, giving rise to a localization of N2 distribution near the accessible cations in contrast to a more diffused O2 distribution. The LSX zeolites provide a highly energetic heterogeneous surface toward N2 adsorption.