Project

molecular orbital calculations; metal-organic materials; X-ray diffraction; coordination polymers; electron density distribution; distributed atomic polarizabilities

Lead
Materials properties depend on the distribution of electrons. In this project, we correlate the observable electron density (measured experimentally or computed theoretically) and the respons of materials. For example, indexes of refraction of a crystal are calculated from the electron density partitioning of the dipole polarizability of a molecule. This enables to understand how the material property is generated from specific stereoelectronic features of the functionals groups and the bulding blocks.
Lay summary
In this project we correlate the observable optic/electronic properties of hybrid metal organic materials and their ground state electron density distribution in crystals. The materials are modeled with a building blocks approach, where organic linkers, metal connectors and guest molecules are described in multipolar expansion. When this cannot be derived on the actual materials (because experiments cannot be sufficiently accurate or theoretical calculations are too demanding) the isolated building blocks are  simulated based on simple calculations on isolated building blocks, treating the aggregation in crystalline materials as a first order perturbation. In layered or three-dimensional framework materials, the modeling allows addressing the sites more keen to bind guest molecules (for example an absorbed gas, or an ion), by mapping the total interaction between host framework and guest, including electrostatic and non-electrostatic (dispersive) interactions. In this project, reconstructed ground state electron density of the hybrid materials are used to evaluate properties, for example electric susceptibilities, useful for prediction of optical response of a material. We have so far published the basic theoretical framework for the building block reconstruction of the crystal linear susceptibility. Application to a wider class of potentially useful optical materials is currently in due course and a publication has been submitted. Among various materials, an appealing class is that of metal bio-organic frameworks, based on amino acids as linkers, able to produce a quite variable charge of the host hybrid framework (cationic, neutral or anionic depending on reaction conditions) and to infer specific properties to the materials based on their chirality. We started this investigation by analyzing the amino acid linkers in their molecular crystals, in salts with another acid (e.g. oxalic acid) acting as proton donor and eventually in metal coordination polymers. We have so far published results of the investigations in pure amino acids and in their salts. The M-BioF crystals are currently under investigation and further publication is in due course.

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Last update: 19.12.2014

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Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

This project is a continuation of the previous project 200021_125313, aimed at correlating the observable properties of hybrid metal organic materials and their ground state electron density distribution. The first steps were undertaken to test the most reliable and transferable electron density models for building blocks of these kinds of materials, in particular analyzing the coordinative bonds between the organic linkers and the metal connectors, and to study properties derived from the electron density distribution. The project merges theoretical investigations of isolated building blocks, simulations of their aggregation in crystals and experimental validation through accurate X-ray diffraction. In layered or three-dimensional framework materials, the modeling allows addressing the sites more keen to bind guest molecules (for example an absorbed gas, or an ion), by mapping the total interaction between host framework and guest, including electrostatic and non-electrostatic (dispersive) interactions. This put the bases for additional investigations that are proposed through this renewal: a) using ground state electron density to evaluate properties, for example susceptivities, useful for prediction of optical response of a material; b) using the building block modeling to carry out dynamic simulations, for example to predict and understand sorption processes; c) investigating some recent types of metal organic materials, based on zwitterionic amino acids as linkers, hence able to invert the charge of the host hybrid framework (cationic, instead of neutral or anionic).These goals can be achieved, using the approach previously developed, which is based on theoretical modeling of the building blocks (which are stable ions or neutral molecules), and transfer their electron density in the actual hybrid materials, which are usually more difficult to model from first principles (systems are often too big) or from experiments (single crystal samples often do not match the expected quality). The same approach could be used to simulate the dynamics of guest molecules in the host framework. The advantage of this treatment is the accurate evaluation of electrostatic energy, without high computational costs. In addition, some recent work proved that distributed polarizabilities based on electron density approaches are reliable and highly transferable, which could provide a more accurate evaluation of induction and van der Waals energies in these materials and give access to evaluation of optical properties, with potential extension to non linear optics (when using hyper polarizabilities). Moreover, the local polarizability function could be used to map reactive sites in a metal-organic material.In this project, we also propose to study an intriguing class of metal amino acids materials, that have several advantages: a) availability and costs; b) water based chemistry; c) homo-chirality and inverted charge of the framework; d) versatile coordination modes of the linker.This research could impact the scientific community operating in the field of supramolecular chemistry, because of the availability of new tools to perform crystal engineering.