22 resultados para METAL-ORGANIC FRAMEWORK
em BORIS: Bern Open Repository and Information System - Berna - Suiça
Resumo:
A general introduction to the state of the art in modeling metal organic materials using transferable atomic multipoles is provided. The method is based on the building block partitioning of the electron density, which is illustrated with some examples of potential applications and with detailed discussions of the advantages and pitfalls. The interactions taking place between building blocks are summarized and are used to discuss the properties that can be calculated.
Resumo:
The enormous impact of crystal engineering in modern solid state chemistry takes advantage from the connection between a typical basic science field and the word engineering. Regrettably, the engineering aspect of organic or metal organic crystalline materials are limited, so far, to descriptive structural features, sometime entangled with topological aspects, but only rarely with true material design. This should include not only the fabrication and structural description at micro- and nano-scopic level of the solids, but also a proper reverse engineering, a fundamental discipline for engineers. Translated into scientific language, the reverse crystal engineering refers to a dedicated and accurate analysis of how the building blocks contribute to generate a given material property. This would enable a more appropriate design of new crystalline material. We propose here the application of reverse crystal engineering to optical properties of organic and metal organic framework structures, applying the distributed atomic polarizability approach that we have extensively investigated in the past few years[1,2].
Resumo:
Bistriazoles, 1,3-bis(1,2,4-triazol-4-yl)propane (tr2pr) and 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr2ad), were examined in combination with the rigid tetratopic 1,3,5,7-adamantanetetracarboxylic acid (H4-adtc) platform for the construction of neutral heteroleptic copper(II) metal−organic frameworks. Two coordination polymers, [{Cu4(OH)2(H2O)2}{Cu4(OH)2}(tr2pr)2(H-adtc)4]·2H2O (1) and [Cu4(OH)2(tr2ad)2(H-adtc)2(H2O)2]·3H2O (2), were synthesized and structurally characterized. In complexes 1 and 2, the N1,N2-1,2,4-triazolyl (tr) and μ3-OH− groups serve as complementary bridges between adjacent metal centers supporting the tetranuclear dihydroxo clusters. The structure of 1 represents a unique association of two different kinds of centrosymmetrical {Cu4(OH)2} units in a tight 3D framework, while in compound 2, another configuration type of acentric tetranuclear metal clusters is organized in a layered 3,6-hexagonal motif. In both cases, the {Cu4(OH)2} secondary building block and trideprotonated carboxylate H-adtc3− can be viewed as covalently bound six- and three-connected nodes that define the net topology. The tr ligands, showing μ3- or μ4-binding patterns, introduce additional integrating links between the neighboring {Cu4(OH)2} fragments. A variable-temperature magnetic susceptibility study of 2 demonstrates strong antiferromagnetic intracluster coupling (J1 = −109 cm−1 and J2 = −21 cm−1), which combines for the bulk phase with a weak antiferromagnetic intercluster interaction (zj = −2.5 cm−1).
Resumo:
The general goal of this thesis is correlating observable properties of organic and metal-organic materials with their ground-state electron density distribution. In a long-term view, we expect to develop empirical or semi-empirical approaches to predict materials properties from the electron density of their building blocks, thus allowing to rationally engineering molecular materials from their constituent subunits, such as their functional groups. In particular, we have focused on linear optical properties of naturally occurring amino acids and their organic and metal-organic derivatives, and on magnetic properties of metal-organic frameworks. For analysing the optical properties and the magnetic behaviour of the molecular or sub-molecular building blocks in materials, we mostly used the more traditional QTAIM partitioning scheme of the molecular or crystalline electron densities, however, we have also investigated a new approach, namely, X-ray Constrained Extremely Localized Molecular Orbitals (XC-ELMO), that can be used in future to extracted the electron densities of crystal subunits. With the purpose of rationally engineering linear optical materials, we have calculated atomic and functional group polarizabilities of amino acid molecules, their hydrogen-bonded aggregates and their metal-organic frameworks. This has enabled the identification of the most efficient functional groups, able to build-up larger electric susceptibilities in crystals, as well as the quantification of the role played by intermolecular interactions and coordinative bonds on modifying the polarizability of the isolated building blocks. Furthermore, we analysed the dependence of the polarizabilities on the one-electron basis set and the many-electron Hamiltonian. This is useful for selecting the most efficient level of theory to estimate susceptibilities of molecular-based materials. With the purpose of rationally design molecular magnetic materials, we have investigated the electron density distributions and the magnetism of two copper(II) pyrazine nitrate metal-organic polymers. High-resolution X-ray diffraction and DFT calculations were used to characterize the magnetic exchange pathways and to establish relationships between the electron densities and the exchange-coupling constants. Moreover, molecular orbital and spin-density analyses were employed to understand the role of different magnetic exchange mechanisms in determining the bulk magnetic behaviour of these materials. As anticipated, we have finally investigated a modified version of the X-ray constrained wavefunction technique, XC-ELMOs, that is not only a useful tool for determination and analysis of experimental electron densities, but also enables one to derive transferable molecular orbitals strictly localized on atoms, bonds or functional groups. In future, we expect to use XC-ELMOs to predict materials properties of large systems, currently challenging to calculate from first-principles, such as macromolecules or polymers. Here, we point out advantages, needs and pitfalls of the technique. This work fulfils, at least partially, the prerequisites to understand materials properties of organic and metal-organic materials from the perspective of the electron density distribution of their building blocks. Empirical or semi-empirical evaluation of optical or magnetic properties from a preconceived assembling of building blocks could be extremely important for rationally design new materials, a field where accurate but expensive first-principles calculations are generally not used. This research could impact the community in the fields of crystal engineering, supramolecular chemistry and, of course, electron density analysis.
Resumo:
The accurate electron density distribution and magnetic properties of two metal-organic polymeric magnets, the quasi-one-dimensional (1D) Cu(pyz)(NO3)2 and the quasi-two-dimensional (2D) [Cu(pyz)2(NO3)]NO3·H2O, have been investigated by high-resolution single-crystal X-ray diffraction and density functional theory calculations on the whole periodic systems and on selected fragments. Topological analyses, based on quantum theory of atoms in molecules, enabled the characterization of possible magnetic exchange pathways and the establishment of relationships between the electron (charge and spin) densities and the exchange-coupling constants. In both compounds, the experimentally observed antiferromagnetic coupling can be quantitatively explained by the Cu-Cu superexchange pathway mediated by the pyrazine bridging ligands, via a σ-type interaction. From topological analyses of experimental charge-density data, we show for the first time that the pyrazine tilt angle does not play a role in determining the strength of the magnetic interaction. Taken in combination with molecular orbital analysis and spin density calculations, we find a synergistic relationship between spin delocalization and spin polarization mechanisms and that both determine the bulk magnetic behavior of these Cu(II)-pyz coordination polymers.
Resumo:
Organic matter amendments are applied to contaminated soil to provide a better habitat for re-vegetation and remediation, and olive mill waste compost (OMWC) has been described as a promising material for this aim. We report here the results of an incubation experiment carried out in flooded conditions to study its influence in As and metal solubility in a trace elements contaminated soil. NPK fertilisation and especially organic amendment application resulted in increased As, Se and Cu concentrations in pore water. Independent of the amendment, dimethylarsenic acid (DMA) was the most abundant As species in solution. The application of OMWC increased pore water dissolved organic-carbon (DOC) concentrations, which may explain the observed mobilisation of As, Cu and Se; phosphate added in NPK could also be in part responsible of the mobilisation caused in As. Therefore, the application of soil amendments in mine soils may be particularly problematic in flooded systems.