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Magnetic multifunctional molecules based on 4f and 3d/4f metal complexes

Periodic Reporting for period 1 - MAGMOLMET (Magnetic multifunctional molecules based on 4f and 3d/4f metal complexes)

Reporting period: 2019-09-01 to 2021-08-31

Positioning different metal centers with well-defined electronic environments in a predefined separation and relative orientation so as to achieve the desired bonding interactions still remains an experimental-synthetic challenge. The project primarily focused on the synthesis and characterization of new homo- and hetero-bimetallic complexes containing one and more metal atoms. In these complexes, metal centers are typically bound through bridging ligands, in particular by types of bridging ligands which allow for systematic variation of metal-to-metal distances. Such complexes remain unsatisfactorily characterized and the project proposed to provide insights for a better understanding of their structure-property relations. They are of significant applications interest in the context of magnetic information storage, magnetic refrigeration and optically active materials.
Two main goals for the project were set:
- development of new original synthetic protocols which would allow the obtaining of metal combinations in a way that allows to influence and control their structure;
- finding for unusual magnetic, spectroscopic and optical behaviours by using physical methods that include magnetic susceptibility measurements (d.c. and a.c.) heat capacity measurements, luminescence spectroscopy.
By completing this project, it was proved that by chosing suitable synthetic protocols, salicylaldehyde and its derivatives were able to generate a rich variety of 3d and 3d/4f complexes, both with nuclearity ranging from dinuclear up to tetradecanuclear metallic cores, and one-dimensional coordination networks. The objectives to expand the library of compounds with single-molecule magnet (SMM) behaviour and to better understand the factors that govern magnetic properties were reached. The achieved results are being prepared for publication and the established chemistry of polynuclear complexes will reveal new features and strategies improving their performances as magnetic/luminescent materials and the consequent development of multifunctional molecules.
The novelty of the project arises from the chemistry that has been developed, based upon quite simple ligands - salicylaldehyde and its derivatives, but with a big potential in assembling multimetallic complexes. Two families of compounds have been obtained: homometallic 4f, and heterometallic 3d-4f polynuclear complexes of 3d metal ions, using original precursors (e. g. polynuclear carboxylate complexes, hexafluoroacetylacetonates). X-ray diffraction studies on single crystal have been used to structurally characterize new compounds. Their magnetic and luminescent properties have been investigated. Performed magnetic studies of synthesised compounds have been correlated in order to understand factors influencing the magnetic anisotropy. Also, the influence of ligands’ electronic and steric features on physical properties as slow relaxation of magnetization and luminescence have been investigated.
The project pursued a joint experimental and theoretical research, which, together, aimed at understanding how cooperative effects determine these properties and how the properties can be controlled by appropriate variation of the coupling between metal centers.
Another part of the work consisted in assembling of 1D cyanido-bridged 3d-4f coordination polymers by following the building-block approach and using a pentadentate bis-semicarbazone ligand. Part of the results has been published via open access to a peer-reviewed scientific journal. A manuscript describing hepta-coordinated Co(II) assemblies is also about to be submitted.
By following the building-block approach new 1D cyanido-bridged 3d-4f coordination polymers have been assembled. The investigation of the magnetic properties revealed slow relaxation of the magnetization, one of the compounds behaving like a chain of Single Ion Magnets. These results open interesting perspectives for the synthesis of new cyanido-bridged 3d-4f complexes, using not only homoleptic but also heteroleptic cyanido tectons, as well as other types of metalloligands. Hence, future efforts will be devoted to investigate the related family of compounds with interesting physical properties, mainly magnetic and optical, and in some cases combined slow magnetic relaxation and light emission.
1D cyanido-bridged 3d-4f coordination polymers