Skip to main content

Radical Solutions for Hysteresis in Single-Molecule Magnets

Periodic Reporting for period 3 - RadMag (Radical Solutions for Hysteresis in Single-Molecule Magnets)

Reporting period: 2018-05-01 to 2019-10-31

Single-molecule magnets (SMMs) display magnetic hysteresis that is molecular in origin, and these materials have huge potential to be developed as nano-scale devices. The big challenge is to create SMMs that function without the need for liquid-helium cooling.

This project will develop new SMMs that combine the strong magnetic anisotropy of lanthanide ions with a series of novel radical ligands. Our innovative SMMs will have controllable molecular and electronic structures, which will ultimately enable hysteresis at unprecedented temperatures.

Highly unusual di- and tri-metallic Ln-SMMs are proposed in which the metals are bridged by radicals with heavy Group 15 (phosphorus-bismuth) and Group 16 (sulphur-tellurium) donor atoms. Trimetallic SMMs will also be based on hexaazatriphenylene (HAT) radicals, and dimetallic SMMs will also be based on nindigo radicals, both of which are nitrogen-donor ligands.

The SMM field is dominated by systems with diamagnetic ligands. Our radical ligands have never been used in SMM studies: their diffuse unpaired spin provides a way of switching off the quantum tunnelling mechanisms that otherwise prevent hysteresis. We will exploit the rich electrochemistry of the target ligands: heavy p-block radicals have huge spin densities on the donor atoms; HAT radicals can have up to three unpaired electrons; reduced or oxidized nindigo radicals allow access to redox-switchable SMMs. In the HAT-bridged SMMs, the use of ligands with more than one unpaired electron is unprecedented. The heavy p-block ligands are themselves are novel.

The PI’s approach to SMMs has already established new directions in lanthanide chemistry and in molecular magnetism.1,2 He now proposes a new, radical approach to SMMs with potential to re-define the state of the art, and to extend the frontiers of a vibrant multi-disciplinary field. Achieving the aims will provide a major step towards using SMMs for applications at practical temperatures.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In accordance with Annex 1, we have achieved the following goals at the mid-term report stage:

Work-package 1
The targeted synthesis of dimetallic and trimetallic lanthanide complexes has been achieved. We are able to modify the steric properties of capping and bridging ligands in order to target di- and tri-metallic SMMs with bridging phosphorus and sulphur ligands.

The initial WP1 SMMs have been characterized and their magnetic properties understood. Enhancement of the SMM properties can now be achieved synthetically by, e.g. changing donor atom, lanthanide or capping ligands.

Following on from the above, we have also characterized a series of novel sulphur radicals as their potassium salts. This places us in a strong position to move forward with the next stage of WP1, which is to transfer the radical ligands to the coordination environment of a lanthanide.

Work-package 2.1
Synthetic routes to a series of Ln3HAT complexes have been developed. Radical-bridged versions have been developed. The next step is to extend this to derivatives with control over ligand spin.

We have developed an understanding of the reasons why SMMs such as those studied in WP2 show slow relaxation of the magnetization. This approach involved the development of a novel magneto-structural correlation in which the magnetic axiality of SMMs containing the [Cp2Dy]+ functional unit was proposed for the first time. An important output from these results is a firm link between WP2 and WP1 since the common factor is the [Cp2Dy]+ magnetic building block. As a result, we have clear synergies between the two work packages, hence developments with one will inform developments with the other. Moving forward at the mid-point of the project, we are now in a firm position to extend the initial findings and use them to develop and understand a wide range of the originally proposed radical-bridged SMMs in WP2.
Having achieved a series of intermediate goals essentially on time, we can be optimistic that progress towards achieving the project milestones will continue for the second half of the project.

We are now in a strong position to capitalize on early progress, and with the full RADMAG team now assembled we expect to make rapid progress towards advancing the state of the art.