Zur Elektronenstruktur metallorganischer Komplexe der ƒ -Elemente, 81. Berechnung der Normalschwingungen von La(η⁵-C₅H₅)₃(NCCH₃)₂ auf der Basis der Dichtefunktionaltheorie sowie vibronische Kopplungen und Auffindung weiterer rein elektronischer Absorptions- und Lumineszenzüberg¨ange bei [La(η⁵-C₅H₅)₃(NCCH₃)₂:Nd³⁺] / Electronic Structures of Organometallic Complexe

Abstract

The planned model calculations of normal modes of pseudo-trigonal-bipyramidal LaCp 3 (NCCH 3 ) 2 (Cp = η 5 -C 5 H 5 − ) (1) adopting density functional theory (DFT), and using the molecular structure as suggested by X-ray investigations, did not converge. Alternatively, DFT calculations assuming molecular C 3h symmetry were performed. Unfortunately, these calculations did not reproduce the experimentally derived frequencies of the skeletal modes very well, including a wrong energetic sequence of the four previously unambiguously assigned (close lying) Raman-active ν(La-Cp) skeletal modes. The same presumably also holds for DFT calculations made for LaCp 3 ·NCCH 3 (2) and base-free LaCp 3 (3), assuming molecular C 3 and C 3h symmetry, respectively. In order to check whether the calculated incorrect sequence is produced by the five-membered Cp rings, a DFT calculation also has been performed for the hypothetical model complex [La(η 6 -C 6 H 6 ) 3 ] 3+ (4) of D 3 symmetry.A closer examination of the vibronic sidebands of the hypersensitive absorption transition 4 I 9/2 → 4 G 5/2 of [LaCp 3 (NCCH 3 ) 2 :Nd 3+ ] (5) showed that first of all, totally symmetric intraligand and not skeletal vibrations are coupling as it was the case for [LaCp 3 (NCCH 3 ) 2 :Ln 3+ ] (Ln = Pr, Sm). Applying this result to the vibronic sidebands of some purely electronic crystal field (CF) transitions, which are hampered by strong binary combination vibrations, the energies of these CF levels could be determined. The CF state 1Γ 8 of the ground multiplet 4 I 9/2 of [LaCp 3 (NCCH 3 ) 2 :Nd 3+ ], which previously could not be detected by absorption measurements, could be derived from the luminescence transition 4 F 3/2 → 4 I 9/2 . Considering these additional assignments, the goodness of the fit increased from 32.3 to 29.9 cm −1 for 61 assignments.