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Running Projects

Rational Design of Azoles and Group 14 element as SCO-ligand

FWF P31076, 1.2.2018 - 31.1.2022

Bistable magnetic materials being switchable between two magnetic states are currently in the focus of research for possible applications in the next generation of miniaturised electronic devices based on magneto-optic technologies. One class of materials being appropriate for such applications is the class of spin-switchable (iron) compounds. They allow the switching of their spin state by external stimuli such as temperature, light, pressure, etc. This effect is called spin crossover being a feature of these molecules thus being the prerequisite for the design of a molecular switch.

Due to the fact that still there does not exist a general valid structure-property relationship to rationally design a desired spin crossover behaviour (e.g. at which temperature and how abrupt such a system switches its spin state), in literature it was tried to derive building principles via comparative studies of rather similar compounds to achieve a rational design. However, it is rather difficult to separately investigate the different factors governing the spin transition behaviour (donicity of the ligands, stereochemistry of the ligands, weak-coordinating anions used, inclusion of non-stoichiometric amounts of solvent, intermolecular interactions, etc...).

Therefore, we have chosen a new approach by selecting 3 different nitrogen-containing five-membered ring systems (tetrazole, imidazole and pyrazole) with always the same set of substituents to keep the steric orientation and interaction of the ligands similar. In one task we start with well-known tetrazole-systems and their iron(II)-spin crossover-complexes synthesizing the analogue imidazol- and pyrazole-ligands and their iron(II)-complexes, whereas in a second task we start from well-known pyrazole-complexes preparing the analogue imidazole and tetrazole-complexes. In both cases we expect the deconvolution of steric factors and intermolecular interactions from the properties merely due to the donor strength of the coordinating azole-rings thus shedding light on the structure-property relationships of spin crossover-complexes.

The most promising ligand systems will be substituted by group 14 elements (Si, Ge, Sn, Pb) instead of C next to the azole ring to upshift the spin transition temperature into the ambient range allowing for possible technological applications.

 

Closed Projects

 

Combining Chirality and Spin Crossover: a promising liaison

FWF P24955; 2012-2015

The technological and industrial application of spin crossover compounds, e.g. for data storage, requires stablecompounds featuring thermal spin transition above room temperature and a LIESST effect around roomtemperature. Furthermore, the intrinsic problem of destructive read-out of the data by laser light needs to be solved.

One possible solution may be the use of polarized laser light for a non-destructive read-out of recorded data. This can be achieved by using chiral compounds. Therefore, the main goal of this project is to synthesize new chiralligands based on the well-characterized 1-substituted tetrazoles via selective halogenation.

The first part of the project is based on the well-defined iron(II) complex of the propyltetrazol. The non-halogenated compound shows an abrupt and complete spin transition at 140K. Previous work on halogenated ethyltetrazol ligands proved are markable upshift of the spin transition temperature. This concept will be applied in a systematic manner on to the propyltetrazol to form beta-halogenated species (variation from fluorine to iodine). Thus we will introduce astereogenic center on the beat-carbon of the substituent.

In the second phase of the project a bridging ligand with two stereogenic centers will be synthesized to open up the new field of multifunctional chiral spin crossover coordination polymers based on functionalized tetrazoles thus paving the path towards a technological application for magneto-optic data storage devices. The performance of the new prepared chiral spin crossover compounds willbe characterised by the concomitant use of polarized Raman spectroscopy and SQUID magnetometry at variabletemperatures.

 

SolidHeat Basic: Systematische Materialforschung für Thermochemische Energiespeicher

FFG 841.150; 1.10.2013 - 30.9.2016

Problems and initial situation

Due to high storage densities, thermochemical storage concepts seem to be promising and auspicious methods for future energy storage. A further advantage is the possibility of more or less loss-free energy storage, if the material can be separated efficiently from the gaseous or liquid reactant which has to be stripped or added (in case of heat release). Preliminary work within a one year´s exploratory study has shown that knowledge about suitable materials is very limited. Even description of material properties is very limited and incomplete.

Targets and method

A data-based search algorithm will be developed within the project and applied for the preselection of materials. The pre-selected materials will be analysed by using various chemical and physical methods like STA, XRD, RFA, FTIR, BET...

Intended results and knowledge

The result of work is a comprehensive, data-based catalogue for thermo-chemical substances. By using this catalogue the selection of appropriate materials dependent on the field of application should be possible. The catalogue will describe the substances according to the field of application (temperature), cycle stability (influence of impurities), materials handling and regulations to be considered (emission of fine dust, materials storage and toxicity). 

"Systematic search algorithm for potential thermochemical energy storage systems", M. Deutsch, D. Müller, C. Aumeyr, C. Jordan, C. Gierl-Mayer, P. Weinberger, F. Winter, A. Werner; Applied Energy, 183 (2016) 113 - 120.

https://doi.org/10.1016/j.apenergy.2016.08.14

SolidHeat Kinetics: Untersuchung der Reaktionskinetik von thermochemischen Energiespeichermaterialien

FFG 848.876; 1.7.2015 - 31.12.2018

Problems and initial situation

Thermochemical energy storage, based on reversible chemical reactions is an auspicious storage method, because: Particle related storage densities are very high Losses during storage period are neglect able new value-added chains can be created concerning new energy distribution systems based on waste heat recovery or increased use of regenerative (solar) sources.

Available literature evaluates thermochemical materials and concepts optimistic concerning e. g. storage density as well as reaction behaviour.

Objectives and methods

So the target of the precursor-project “SolidHeat Basic” and the current proposal “SolidHeat Kinetics” is to identify (SolidHeat Basic) and describe comprehensively all found materials (SolidHeat Kinetics) based on the database initialised in “SolidHeat Basic”.

The following methods of analysis are applied:

  • TGA / DSC
  • Powder X-ray diffraction
  • X-ray fluorescence analysis
  • Infrared spectroscopy
  • Software based identification methods for reaction kinetics

These physical and chemical methods are completed by the (further) development of a flexible and extendible materials data base, where all necessary information about certain thermochemical materials is available.

 

"Combining in-situ X-ray diffraction with thermogravimetry and differential scanning calorimetry - an investigation of Co3O4, MnO2 and PbO2 for thermochemical energy storage", D. Müller, C. Knoll, W. Artner, M. Harasek, C. Gierl-Mayer, J.M. Welch, A. Werner, P. Weinberger; Solar Energy, 153 (2017) 11 - 24.

https://doi.org/10.1016/j.solener.2017.05.037

SolidHeat Pressure: Thermochemical Energy Storage in Solids Under Pressure

FFG 853.593, 1.7.2016 - 29.2.2020

Thermochemical energy storage (TCS) is an interesting concept for thermal energy storage due to:

  • High storage density
  • Unlimited duration of storage without any losses
  • Simple possibilities for transport

Actually, investigations on TCS, taking into consideration only reversible chemical reactions are in the phase of basic research. Development of TC-materials depends on the solution of some technical key problems like attaining sufficient reaction kinetics and cycle stability as well as defining appropriate particle sizes for handling and reaction.

The motivation for the performance of the suggested project is caused by several advantages, resulting from elevated operating pressures, like

  • Influence on state of phase for the reaction partners (e. g. liquid instead of gaseous)
  • Effect on reaction kinetics
  • Introduction of reaction systems, like MgO-sCO2 ( the latter under- or supercritical)

Goals, innovative scope compared to state of the art / state of knowledge

In literature only little or almost no information can be found, describing the influence of ambient pressure on dehydration / hydration, decarbonation / carbonation. Based on findings from project SolidHeat Basic and from SolidHeat Kinetics, under the proposed project investigations on TC-materials will be extended to elevated pressure. Therefore a pressure STA contributed by TU Wien to support these research activities will be applied. According to the applicant’s level of information the pressure STA is one of the few available in Europe. So a unique possibility for top level research in the field of TCS is offered to the applicants by the present proposal.

The affected results will

  • identify reaction pairs, best suitable for TCS-application at elevated pressures
  • help to understand reaction kinetics and mechanisms under high pressure
  • gain an insight into new reaction-systems, e. g. supercritical CO2 used for carbonation, opening new ways for TCS (by combining with ETES-systems)

The takeaway results in knowledge, which is very important for the understanding of coherences of reaction kinetics at elevated pressure.

 

"Pressure effects on the carbonation of MeO (Me=Co, Mn, Pb, Zn) for thermochemical energy storage", G. Gravogl, C. Knoll, W. Artner, J.M. Welch, E. Eitenberger, G. Friedbacher, M. Harasek, K. Hradil, A. Werner, P. Weinberger, D. Müller, R. Miletich; Applied Energy, 252 (2019) 113451, 1-8.

https://doi.org/10.1016/j.apenergy.2019.113451