Coupling of the 4f Electrons in Lanthanide Molecules

Thesis/Dissertation · Mon Sep 01 00:00:00 EDT 2008

DOI:https://doi.org/10.2172/941061· OSTI ID:941061

Kazhdan, Daniel ^[1]

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1. Univ. of California, Berkeley, CA (United States)

(C₅Me₅)₂LnOTf where Ln = La, Ce, Sm, Gd, and Yb have been synthesized and these derivatives are good starting materials for the synthesis of (C₅Me₅)₂LnX derivatives. (C₅Me₅)₂Ln(2,2'-bipyridine), where Ln = La, Ce, Sm, and Gd, along with several methylated bipyridine analogues have been synthesized and their magnetic moments have been measured as a function of temperature. In lanthanum, cerium, and gadolinium complexes the bipyridine ligand ligand is unequivocally the radical anion, and the observed magnetic moment is the result of intramolecular coupling of the unpaired electron on the lanthanide fragment with the unpaired electron on the bipyridine along with the intermolecular coupling between radicals. Comparison with the magnetic moments of the known compounds (C₅Me₅)₂Sm(2,2'-bipyridine) and (C₅Me₅)₂Yb(2,2'-bipyridine) leads to an understanding of the role of the Sm^II/Sm^III and Yb^II/Yb^III couple in the magnetic properties of (C₅Me₅)₂Sm(2,2'-bipyridine) and (C₅Me₅)₂Yb(2,2'-bipyridine). In addition, crystal structures of (C₅Me₅)₂Ln(2,2'-bipyridine) and [(C₅Me₅)₂Ln(2,2'-bipyridine)][BPh4](Ln= Ce and Gd), where the lanthanide is unequivocally in the +3 oxidation state, give the crystallographic characteristics of bipyridine as an anion and as a neutral ligand in the same coordination environment, respectively. Substituted bipyridine ligands coordinated to (C₅Me₅)₂Yb are studied to further understand how the magnetic coupling in (C5Me5)2Yb(2,2'-bipyridine) changes with substitutions. In the cases of (C₅Me₅)₂Yb(5,5'-dimethyl-2,2'-bipyridine) and (C₅Me₅)₂Yb(6-methyl-2,2'-bipyridine), the valence, as measured by XANES, changes as a function of temperature. In general, the magnetism in complexes of the type (C₅Me₅)₂Yb(bipy.-), where bipyo represents 2,2'-bipyridine and substituted 2,2'-bipyridine ligands, is described by a multiconfiguration model, in which the ground state is an open-shell singlet composed of two configurations: Yb(III, f¹³)(bipy.-) and Yb(II, f¹⁴)(bipyo). The relative contributions of the two configurations depends on the substituents on the bipyridine ligand.[(C₅Me₅)₃Ln]₂(L) (Ln = Ce, Tb; L = 4,4'-bipyridine, 1,4-benzoquinone) are synthesized in order to study the effect of these ligands on the oxidation states of the metal as well as to study intramolecular coupling between two lanthanides fragments.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 941061
• Report Number(s): LBNL-1063E; TRN: US200824%%523
• Resource Relation: Related Information: Designation of Academic Dissertation: doctoral thesis; Academic Degree: Doctor of Philosophy; Name of Academic Institution: University of California - Berkeley; Location of Academic Institution: Berkeley, CA, USA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ANIONS
BIPYRIDINES
CERIUM
CRYSTAL STRUCTURE
ELECTRONS
GADOLINIUM COMPLEXES
GROUND STATES
LANTHANUM
MAGNETIC MOMENTS
MAGNETIC PROPERTIES
MAGNETISM
RADICALS
RARE EARTHS
SYNTHESIS
VALENCE
lanthanide magnetism organometallic bipyridyl cyclopentadienyl