Combining Chirality and Spin Crossover: a promising liaison

The technological and industrial application of spin crossover compounds, e.g. for data storage, requires stable compounds featuring thermal spin transition above room temperature and a LIESST effect around room temperature. 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 chiral ligands 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 a remarkable 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 a stereogenic 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 will be characterised by the concomitant use of polarized Raman spectroscopy and SQUID magnetometry at variable temperatures.