| Abstract: | Electronic Structures of Organometallic Complexes of f Elements. 68 Absorption and First Luminescence and Raman Spectroscopic Polarization Measurements of an Oriented Organometallic Single Crystal: Pr(C5Me4H)3 Optical polarization measurements of oriented single crystals of Pr(C5Me4H)3 ( 1 ) were performed at room temperature. In order to separate “cold” and “hot” f‐f‐transitions and νC–H combination vibrations, the absorption spectra of KBr pellets of compound 1 and La(C5Me4H)3 ( 2 ) were additionally recorded at ca. 77 K. To gather additional information about the wavefunctions of the crystal field (CF) states of complex 1 , a magnetic circular dichroism spectrum of 1 was recorded too. From the spectra obtained, a partial CF splitting pattern of 1 was derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian, leading to a reduced r.m.s. deviation of 24.8 cm−1 for 24 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Pr3+ central ion was estimated, and seems to be the largest one ever encountered in PrIII 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, of PrIII compounds. With its low F2 value, complex 1 is the most covalent PrIII compound (considering only f electrons) 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 Pr(η5‐C5H5)3. In the framework of the search for “polarized” luminescence transitions, polarized Raman spectra of 1 were recorded too, and compared to the corresponding FIR and IR spectra run by means of pellets. |
