Electronic structures of organometallic complexes of f elements LXVI : Parametric analysis of the linear dichroism spectrum of an oriented tris(η5-tetramethylcyclopentadienyl)samarium(III) single crystal

The absorption spectra of pseudo (ψ) trigonal planar Sm(η5-C5Me4H)3 (1) and La(η5-C5Me4H)3 (2) in KBr pellets have been measured at room temperature and 77 K, respectively. Additionally, the linear dichroism spectra of σ and π type of an oriented single crystal of 1 have been recorded at ambient temperature. The observed polarization properties of the f–f transitions allowed the assignment of the transitions. The free parameters of a phenomenological Hamiltonian were fitted to the energies of the assigned terminal levels, leading to a reduced r.m.s. deviation of 19.1 cm−1 for 19 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Sm3+ central ion was estimated, and seems to be the largest one ever encountered in samarium(III) chemistry. The obtained Slater parameter F2 and the spin–orbit coupling parameter ζ4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively. On the basis of these models, complex 1 turns out to be the most covalent SmIII compound found to date. The experimentally-based non-relativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous Xα-SW calculation on the ψ trigonal planar model compound Sm(η5-C5H5)3.

Applying the selection rules of forced electric dipole transitions (D3h symmetry) to the absorption spectrum of pseudo trigonal planar Sm(η5-C5Me4H)3 in a KBr pellet, and the σ and π absorption spectra of an oriented single crystal, an assigned truncated crystal field splitting pattern could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian.Figure optionsDownload as PowerPoint slide