Date of Award

2009

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Chemistry and Biochemistry

Keywords

Pure sciences, Heteronuclear compounds, Lanthanide complexes, Mononuclear lanthanides

Supervisor

Samuel Johnson

Rights

info:eu-repo/semantics/openAccess

Abstract

Lanthanides are known for their distinctive magnetic properties and have been utilized for the design of multinuclear single-molecule magnets. Mononuclear trivalent lanthanide complexes were prepared from the reaction of tripodal amido ligands [P(CH2NHArR)3] and Ln[N(SiMe 3)2] (ArR = C6H5, 3,5-Me 2 and 3,5-(CF3)2 and Ln = Y, Tb, Dy, Ho, Er, Tm and Yb) in the presence of THF. These mononuclear lanthanide complexes were then further utilized for the syntheses of d-f heteronuclear compounds, using various transition metal complexes such as Pt(cyclooctadiene)Me 2, Ni(acetylacetonate)2 and Co-porphyrin. Mononuclear trivalent lanthanide complexes, prepared using 2-methyl anthranilate, contained a rigid chelate ring with six proton environments. The 31 p{1H} NMR spectra demonstrated a through-space interaction between the minor lobe of phosphine lone pair and the yttrium metal. Binding of a paramagnetic cobalt metal complex to the unbound phosphine lone pair provided heterodinuclear d-f metal complexes. The EPR spectra and the magnetic study of heterodinuclear complexes indicated the through-space antiferromagnetic coupling between unpaired electrons of gadolinium and cobalt centers. Magnetic anisotropy of lanthanide complexes with more than C2 symmetry can be easily measured by their NMR shifts due to the presence of dipolar contribution. According to Bleaney, temperature dependence of the magnetic anisotropy of lanthanide complexes should be proportional to T–2 and the crystal field parameter (α 20).[special characters omitted] McGarvey later expanded the temperature dependence of the anisotropy by including a term that is proportional to T–3 and other crystal field parameters (equation 2).[special characters omitted] From our calculations, we demonstrated the dependence of higher terms (>T–2) for the calculation of magnetic anisotropy near room temperature. These higher terms showed the contribution of 20-90% of the T–2 term. Estimation of crystal field parameters (related with magnetic properties) generally requires low temperature optical spectroscopy or a SQUID magnetometer. Our trivalent mononuclear lanthanide complexes have C3 symmetry, which required 6 crystal field parameters, B20, B40, B60, B43, B63 and B66. Here, we utilized variable temperature NMR spectra to calculate the set of crystal field parameters. A best set of crystal-field parameters were then obtained by comparing experimental and theoretical magnetic anisotropies. In the future, these parameters can be further utilized for the electronic structure of lanthanide complexes.

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