Synthesis and structure of bivalent ytterbocenes and their coordination chemistry with pi-acceptor ligands

Thesis/Dissertation · Mon May 01 00:00:00 EDT 2000

DOI:https://doi.org/10.2172/764392· OSTI ID:764392

Schultz, Madeleine ^[1]

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

The bivalent lanthanide metallocenes [1,3-(Me₃C)₂C₅H₃]₂Yb and (Me₄C₅H)₂Yb have been synthesized and their structures have been determined by X-ray crystallography. Comparison with the known structures of (Me₅C₅)₂Yb and [1,3 -(Me₃Si)₂C₅H₃]₂Yb leads to an understanding of the role of intermolecular contacts in stabilizing these coordinatively unsaturated molecules. The optical spectra of the base-free ytterbocenes and their Lewis-base adducts have been measured; the position of the HOMO - LUMO transition can be correlated with the degree of bending of the complexes in solution according to a molecular orbital model. Electron - electron repulsion, resulting from additional σ-donor ligands, also affects the HOMO - LUMO transition by increasing the energy of the filled f-orbitals. The base-free metallocene (Me₅C₅)₂Yb coordinates carbon monoxide, resulting in a decrease in V_co relative to that of fi-ee carbon monoxide. This behavior is reminiscent of d-transition metallocene chemistry. Other base-free ytterbocenes also coordinate carbon monoxide and the degree of back-donation is related to the substituents on the cyclopentadienide rings. Isocyanides are coordinated in a 1:2 ratio by the ytterbocenes, giving complexes having v_cN higher than those of the free isocyanides. An electrostatic bonding model has been used to explain the changes in CN stretching frequencies. The optical spectra of the carbonyl and isocyanide complexes are consistent with the molecular orbital model of the variation in the HOMO - LUMO gap upon bending, and the increase in electron - electron repulsion due to the additional ligands. The complex (Me₅C₅)₂Yb(bipy) exhibits optical, infrared and NMIZ spectroscopy and an X-ray crystal structure consistent with the presence of bipyridyl radical anion. However, the shape of the magnetic susceptibility curve is unusual. 2,2’-Bipyridyl and 1,10- phenanthroline complexes of several ytterbocenes have been prepared for comparison with this molecule, The phenanthroline complexes display coupling, with the degree of coupling dependent on cyclopentadienide rings. The magnetism of the bipyridyl strong electron exchange the substituents complexes may on the also be ascribed to electron exchange coupling, or to an equilibrium between a diamagnetic bivalent ytterbium complex and a trivalent complex resulting from the transfer of one electron from the metal to the bipyridyl Iigand.

• 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: AC03-76SF00098
• OSTI ID: 764392
• Report Number(s): LBNL-45780; R&D Project: 403003; TRN: AH200102%%140
• Resource Relation: Other Information: TH: Thesis (Ph.D.); Submitted to University of California, Berkeley, CA (US); PBD: 10 May 2000
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHEMISTRY
SYNTHESIS
LIGANDS
YTTERBIUM COMPLEXES
MOLECULAR STRUCTURE