Designing magnetically interesting supramolecular architectures: towards Single-Chain Magnets

by Sebastien Dhers

Institution: University of Otago
Year: 0
Keywords: Single Chain Magnet; Single Molecule Magnet; Molecular magnetism
Record ID: 1311444
Full text PDF: http://hdl.handle.net/10523/4875


Single-Molecule Magnets (SMMs) are single molecules that can behave as magnets. Similarly, Single-Chain Magnet (SCM) are 1D polymers that can exhibit slow relaxation of the magnetisation. Over the last decade, interest in SCMs has increased rapidly, with the main driving force being the possibility of increasing the blocking temperature above that realised by SMMs, in order to meet this requirement for future application as memory devices. In this project, a range of magnetically interesting complexes previously studied in the Brooker research group have been prepared and combined with appropriate linkers for the construction of 1D-chains. This field, which represents a new research direction for this group, is explored herein and the results obtained using various linkers are presented. Chapter 1 presents a review of the field of SCM to date and introduces the most important concepts of magnetism. This is followed by an overview of the methods of crystallisation used to obtain SCMs, an introduction to Schiff base ligands and macrocycles and finishes with the aims of the study. In Chapter 2 the synthesis and magnetic characterisation of the 3d-4f tetrametallic macrocyclic SMM building blocks [CuII3TbIII(L1Et)(NO3)3(MeOH)]∙MeOH ([CuII3TbIII(L1Et)]), [CuII3TbIII(L1Pr)(NO3)2(MeOH)3](NO3) ([CuII3TbIII(L1Pr)]) and [CuII3TbIII(L1Bu)(NO3)2(DMF)(H2O)](NO3) ([CuII3TbIII(L1Pr)]), originally obtained by Dr. Humphrey Feltham during his PhD thesis, is presented, as they are the main building blocks used in this project. The assembly of the macrocyclic building block, [CuII3TbIII(L1Pr)], with K3[MIII(CN)6] linkers, where M = Fe, Cr or Co, results in a range of monomer, dimer and 1D chain architectures, all of which have been structurally and magnetically characterised, and are described in Chapter 3. In Chapter 4 the assembly of the macrocyclic building block, [CuII3TbIII(L1Pr)], with a (TBA)3[WV(CN)8] linker, which results in two different 1D chains depending on the crystallisation conditions, is presented. In these two chapters, a total of nine complexes using [CuII3TbIII(L1Pr)] were structurally characterised. Although no SCM behaviour was seen, metamagnet and SMM behaviour was observed. Following these results with N-donor linkers, a different approach was taken to deliberately link the 3d-4f macrocyclic building block via the Tb(III) ion by using an O-donor linker. In Chapter 5, the assembly of the macrocyclic SMM building block, [CuII3TbIII(L1Et)], with a Na2[tpa] linker (tpa2- terephthalate ion), which results in a structurally and magnetically characterised 1D chain architecture, is described. This is a proof of principle that use of an oxygen donor linker can successfully target linking of the macrocyclic Ising centres via the Tb(III) ions rather than via the Cu(II) ions, to give a 1D chain, and shows enhanced control in the design of the supramolecular architecture by using 3d-4f macrocyclic building blocks. Another strategy envisaged to enhanced the magnetic communication along these 1D-chain systems was to…