The Synthesis and Magnetochemistry of Transition and Lanthanide Metal Compounds

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Abstract

ABSTRACT OF THESIS, submitted by: Charlene A. Smith to THE UNIVERSITY OF MANCHESTER for the degree of DOCTOR OF PHILOSOPHY and entitled: The Synthesis and Magnetochemistry of Transition and Lanthanide Metal Compounds. Month and Year of Submission: September 2012.The introductory Chapter to this thesis outlines fundamental aspects of 4f lanthanide(III) coordination chemistry, in particular compounds that possess the intriguing properties of slow relaxation of magnetisation, (or the ability to behave as single-molecule magnets, SMMs). The recent renaissance into the study of the magnetic behaviour of 4f-coordination complexes has led to the consideration of utilising organometallic precursors for the development of novel lanthanide containing compounds, which may possess interesting magnetic properties, subsequently forming the basis of Chapter Two. In Chapter Two, the syntheses and structures of the novel lithiated thiolate ligand, lithium triphenylsilylthiolate, (Ph3SiS-Li) (2.1), and the sulfur-bridged, dimetallic dysprosium(III) and gadolinium(III) complexes [(MeCp)2Dy(µ-SSiPh3)]2 (2.2) and [(MeCp)2Gd(µ-SSiPh3)]2 (2.3), are described in detail. The structural and physical properties of these compounds are analysed through NMR, elemental analysis and SQUID magnetometry, alongside supporting theoretical calculations to reveal that compound 2.2 is the first dimetallic, sulfur-bridged SMM reported, giving an energy barrier to the reversal of magnetisation of Ueff = 192 ± 5 K.56bChapter Three reports on the structural development of a series of lanthanide monomers, exhibiting the general motif [Ln(OSiPh3)3(THF)3] (where Ln = Dy(3.4), Er(3.5), Ho(3.6), Gd(3.7), Tb(3.8)), exploiting the siloxide ligand Ph3SiOH through two novel synthetic routes. This Chapter also provides new analytical insight to these complexes by exploring their magnetic properties through a series of SQUID measurements and through the analysis of their electronic properties using air sensitive, variable temperature optical absorption spectroscopy. Compounds 3.4 and 3.5 were revealed to be SMMs, with 3.5 having a much higher thermal barrier to the reversal of magnetisation, Ueff = ~ 28 K, than 3.4, which are supported by theoretical analysis. Chapter Four describes the utility of ligand 2.1 and Ph3SiOH in the context of 3d transition metal cyclopentadienyl chemistry, outlining the syntheses and structures of three distinct compounds; the trimetallic, [Cp2Mn3(µ-OSiPh3)4](4.7), the hetero-cubane tetramer [CpMn(µ-SSiPh3)]4 (4.8) and the dimetallic thiolate-bridged [CpCr(µ-SSiPh3)]2 (4.9) compound. These compounds were formed in reactions exploiting organometallic manganocene and chromocene precursors. Magnetic susceptibility measurements were conducted on these compounds to gain further insight into their structural properties. The magnetic exchange coupling constants for Mn(II) compounds 4.7 and 4.8 were J = - 4.4 cm-1 and J = - 3.0 cm-1 respectively. Furthermore, having demonstrated the use of metal-cyclopentadienyl building blocks in the synthesis of novel SMMs, Chapter Five discusses the possibility of further advancement on the development of this class of magnetic molecules.

Keyword(s)

Lanthanide Metal; Magnetochemistry; Organometallics; Single Ion Magnets; Single Molecule Mganets; Soft Ligands; Transition Metal

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