‘Lanthanide contraction’ in [Ln(BTP)3](CF3SO3)3 complexes

Abstract

The FTIR spectra of the complexes of lanthanides (Ln = La -Lu, except for the radioactive Pm) with 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine have been measured in both the mid-and far-IR ranges. The spectra revealed some characteristic bands shifting towards higher wavenumbers with increasing lanthanide atomic number. X-ray diffraction results on several (La, Pr, Nd, Sm, Eu, Tm and Yb) complexes revealed decreasing Lnligand distances in the same direction. DFT calculations using the M062X exchange-correlation functional have been performed on selected model complexes in order to uncover the 'lanthanide contraction' phenomenon and to assist the interpretation of the FTIR spectra. The stronger bonding due to 'lanthanide contraction' is supported by the computed charge transfer interactions. The vibrational study confirmed that the blueshifting bands can be attributed to significant Ln-ligand vibrations.

Comparative Study of Complexes of Rare Earths and Actinides with 2,6-Bis(1,2,4-triazin-3-yl)pyridine

“…We note that the determined X-ray structures of the Sc, Y, and Pu complexes have large uncertainties, due to poor crystallographic quality of the samples. Nevertheless, the crystal analysis verified the structures, being isostructural to lanthanide homologues [27]. Due to the mentioned large uncertainties, a detailed discussion of the experimental structure is not feasible, thus we show only the average of the most important M-N bonds in Table 1.…”

“…Recently, we performed a detailed joint experimental and theoretical study of the lanthanide series, Ln(BTP) 3 , focusing on the structural and energetic effects of "lanthanide contraction" [27]. As one of the main results, we found increasing metal-ligand interactions along the Ln series.…”

“…The main part of the study consists of DFT calculations in order to elucidate the bonding differences between the three groups of metals; namely, transition metals (TM: Sc, Y), lanthanides, and actinides. Due to technical considerations and the previously-found negligible effects upon replacing the n-propyl chains of BTP by hydrogen in lanthanide BTP complexes [27], in the present theoretical modeling we used the reduced ligand molecule, denoted as BTP . The La and Lu complexes (investigated by us, recently [27]) were recomputed with a larger valence basis set, being more comparable with the basis sets used for the other metals.…”

“…Due to technical considerations and the previously-found negligible effects upon replacing the n-propyl chains of BTP by hydrogen in lanthanide BTP complexes [27], in the present theoretical modeling we used the reduced ligand molecule, denoted as BTP . The La and Lu complexes (investigated by us, recently [27]) were recomputed with a larger valence basis set, being more comparable with the basis sets used for the other metals. The bonding properties were analyzed using the natural bond orbital (NBO) [26] and quantum theory of atoms in molecules (QTAIM) [29] model theories, providing quantitative information on the bonding.…”

Structure and bonding of lanthanide dinitrogen complexes, Ln(N2)1‐8

“…[29,30] The following general observations can be made on the basis of Table 1: 1. In contrast to the analogous structures found generally in organometallic complexes across the Ln row, [66,67] there are some differences in the structures of the Ln(N 2 ) x complexes.…”