Supramolecular Approaches to Molecular Magnetism

Abstract

An extended family of molecules based upon a rotaxane methodology is reported, comprising an antiferromagnetically coupled transition metal (Cr7Ni) ring, with a delocalised S = 1/2 ground state, bound to a second, dissimilar spin component via an organic thread. A number of complementary electron paramagnetic resonance (EPR) spectroscopy techniques are performed to examine the interactions between the dissimilar spins, on compounds containing up to four individual spin systems formed from elegant [2]- [3]- and [4]rotaxane chemistry. A collection of molecules comprising a copper(II) ion bound to a [2]rotaxane, hence featuring two S = 1/2 systems, are synthesised. These are studied via continuous wave EPR measurements to examine the limitations of the 'weak' exchange interactions, which manifest as a perturbation of J coupling on the Zeeman interaction: this is achieved by altering the distance between the two spin systems. Similar work based upon S > 1/2 systems coupled to the spin S = 1/2 ring, using manganese(II) and cobalt(II) ions, is performed with eight new compounds reported. Continuous wave EPR measurements show that for the Mn(II) chemistry, partial chemical exchange of Mn(II) ions and the Ni(II) ions of the Cr7Ni ring occurs. [3]- and [4]rotaxanes are synthesised containing two and three {Cr7Ni} S = 1/2 systems, respectively, centred around a second, dissimilar delocalised {Ni2Cr} S = 1/2 spin system. Continuous wave and advanced pulse EPR techniques reveal a large and well resolved difference in the relative g factors between the spin systems, and double electron-electron resonance (DEER) was performed on the {Cr7Ni} rings in these systems, i.e. on molecule containing twenty-seven paramagnetic ions. The distance distributions between the metal ions correlate to the X-ray structures.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Eric Mcinnes (Supervisor) & Richard Winpenny (Supervisor)