Bonding Trends in Molecular Compounds of Lanthanides: The Double‐Bonded Carbene Cations LnCH₂⁺ (Ln=Sc, Y, La–Lu)

Abstract

Quasi-relativistic Douglas-Kroll CASPT2 calculations are reported for the title molecules, mainly to provide primary data for a fit of double-bond covalent radii. Indeed, a well-developed sigma(2)pi(2) double bond is identified in all cases. For Eu and Yb, however, it is an excited state. The main valence orbitals of all Ln ions are 6s and 5d. In the sigma bonds, more 5d than 6s character is found at the Ln. The Ln=C bond lengths show a systematic lanthanide contraction of 13 pm from La to Lu. An agostic symmetry breaking is demonstrated for Ce but its effect on the Ln-C length is small.

Bonding in Cationic MCH2+ (M=K–La, Hf–Rn): A Theoretical Study on Periodic Trends

“…Such interactions, which are related to the empty valence orbitals on the metal, have been analyzed in detail by Roos, Pyykkç, and co-workers. [9,18] The a-hydrogen interaction was also found to be significant in metal À silicon multiple bonds owing to their electron deficiency. [19] One imaginary frequency, which corresponds to the in-plane twist of the CH 2 group, was found in the C 2v symmetry of all C s (a) MCH 2 + species.…”

“…Lanthanides have been excluded because their carbene complexes have been recently analyzed comprehensively by Roos and Pyykkç. [9] We provide energetic and structural data and, in addition, present a comparison of the periodic trends for the s-, d-, and pelements.…”

Progress and Challenges in the Calculation of Electronic Excited States

“…The beautiful work of Gagliardi and others about elucidating multiple bonding in late transition metals (e.g. the quintuple bond between two chromium centers), [134][135][136][137][138] lanthanides [139] and actinides (e.g. the quintuple bond in the uranium molecule) [140,141] is a good example of it.…”

Methylidenkomplexe der Seltenerdmetalle

“…[30] Kurz darauf erweiterten Schwarz und Mitarbeiter diese Studien für die gesamte Reihe der MCH 2 + -Kationen (M = K-La und Hf-Rn), um periodische Trends zu identifizieren. [31] Pyykkç et al berechneten, dass prinzipiell alle Lanthanoide Doppelbindungen zur Methylengruppe ausbilden kçnnen.…”

“…Die Einfachbindung wird zwischen einem 6s-5d-Hybridorbital und dem s-Radikalorbital am Methylen ausgebildet. [30] Für das Element Cer wurde bei der Berechnung der Schwingungsfrequenzen für das doppelt-gebundene CeCH 2 + -Ion eine imaginäre Frequenz [30] so wie es in den Verbindungen 6, 8 und 10 beobachtet wurde. [18,20,22] Diese Ergebnisse sind im Einklang mit früheren DFT-und Matrix-IR-Studien an Uran-und Thoriummethylidenkomplexen, bei denen ebenfalls eine agostische Wechselwirkung zwischen dem Metallzentrum und einem Wasserstoffatom der Methylidengruppe nachgewiesen werden konnte.…”