ON THE INVESTIGATION OF NUCLEATION, GROWTH, STRUCTURE AND MORPHOLOGY OF FUNCTIONAL MATERIALS THROUGH ADVANCED CRYSTALLOGRAPHIC TECHNIQUES
Tesi di Dottorato
Data di Pubblicazione:
2019
Citazione:
ON THE INVESTIGATION OF NUCLEATION, GROWTH, STRUCTURE AND MORPHOLOGY OF FUNCTIONAL MATERIALS THROUGH ADVANCED CRYSTALLOGRAPHIC TECHNIQUES / F. Beghi ; tutor: S. Rizzato; co-tutor: L. Lo Presti, M. Moret. DIPARTIMENTO DI CHIMICA, 2019 Jan 18. 31. ciclo, Anno Accademico 2018. [10.13130/beghi-fabio_phd2019-01-18].
Abstract:
Title of the thesis
On the investigation of nucleation, growth, structure and morphology of functional materials through advanced crystallographic techniques
Description of the research work done
I-Use of gel technique for the crystallization of coordination polymers
A gel is a system where a liquid phase is dispersed within a solid phase. A network of micrometric channels and pores filled by solution characterizes the obtained material. Any mass transport mechanism but slow diffusion is avoided. This creates an interesting media to perform crystal nucleation and growth under purely diffusive conditions. Recently gel technique for crystallization has been extensively adopted, leading to intriguing results about crystals quality, dimension, mechanical and chemical stability. For certain organic molecule were reported the gel ability to induce the formation of new phases and polymorphs.
Inside gel media, slightly different crystallization conditions can be simultaneously created. For a class of compounds known as coordination polymers or MOF, little difference in the crystallization environment can lead the synthesis towards the formation of network completely different from the point of view of dimensionality, topology, coordination geometry of metal centres and ligand behaviours. The aim of the following projects is to map the relevance of gel technique if applied for the synthesis of coordination polymers, considering parameters as solvent composition, gel nature, reagents concentrations ([L]+[M]) and ratio([L]/[M]).
I-A system Cd(II) bpp
We considered water/EtOH solutions of CdCl2 (M) and bis-Pyridyl-propane (bpp) and agarose gel at different concentration. Three different crystalline phases can be obtained:
1D [Cd(bpp)3Cl2]∙H2O (1D-Cd) (L/M=3)
3D [Cd(bpp)2Cl2]·H2O (3D-dia) (L/M=2)
3D [Cd2(bpp)3Cl2]·H2O (3D-sra) (L/M=1,5)
The phases show different compositions in terms of L/M ratio, and also different dimensionality and topology. Their morphologies also are peculiar enough to let they be straightforwardly identified by optical microscopy. We made a strict comparison between system behaviour inside solution and jellified solution, to point out the most important gel effects on crystallization process.
For solution studies, we applied batch technique. For gel studies, we used counterdiffusion methods. We used two different experimental set up: (a) Layering of the solutions of a reagent over the gelified solution of the other reagents inside a test tube; (b) Layering in the opposite branches of a U-shaped tube the solutions of the reagents over a gelified solvent.
I-A.1 solution behaviour
We determined the precipitated phases considering different reagent concentration and ratio at fixed EtOH amount (50%) and different amounts of EtOH and reagents ratio at a fixed concentration (20mM). To confirm the results obtained, we also study powders precipitated from solutions at higher concentrations with the same experimental conditions.
3D-sra phase forms at low L/M value (<2) for any solvent compositions. Increasing [L]/[M] value bring to two different behaviours. For EtOH quantity below than 30% 1D-Cd precipitates as powder, above 30% we observe precipitation of 3D-dia. From solutions, we never observe co-precipitation of all the three phases. But 3D-sra and 3D-dia coexist inside alcoholic solutions.
I-A.2 Gel technique modifies the phase diagram
When we laid ligand alcoholic solutions over water-gelified solutions of the metal salt, the crystals form more in the solutions than in gel. The sra phase appears for a narrower range of L/M values, while dia phase becomes predominant. Instead, when we layer metal salt solution over the ligand solution, the two phases coexist for all the considered value o
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
F. Beghi
Link alla scheda completa: