A DFT and Matrix–Isolation IR/UV-Visible Study of High-Coordinated Lanthanide-CO Complexes

Abstract

Recent joint mass spectrometric and IR photodissociation studies have provided proof on the existence of octa-coordinated ionic lanthanide-carbonyl complexes under those extreme gaseous conditions. In contrast, in older literature concerning cryogenic studies of neutral Ln(CO)x species, the highest coordination was assigned to hexa-coordinated Ln(CO)6 molecules. The present study aims to clarify the above controversy using matrix isolation spectroscopy and DFT calculations. In order to ensure the maximum possible coordination, the Ln(CO)x complexes were synthesized in neat CO cryogenic matrices at 10 K and were investigated by infrared and UV-visible spectroscopy. The formed complexes were identified on the basis of the characteristic CO stretching frequencies of the ground-state molecules predicted by DFT calculations. Our joint experimental–theoretical analysis confirmed the preference of octa-coordinated Ln(CO)8 complexes in cryogenic neat CO matrices.

Preference of C2v Symmetry in Low-Spin Hexacarbonyls of Rare-Earth and f Elements

“…In order to facilitate an easier visual overview, the overestimated B3LYP frequencies were corrected by the scale factor 0.96 from ref. [56]. Visual inspection of the bonding molecular orbitals did not show any difference for the low-spin D4h or high-spin Oh species (cf.…”

“…As described in detail previously [56,93], basically, a Displex closed-cycle helium refrigerator was used to cool a NaCl optical window to 10 K in a specialized vacuum system. Monoatomic scandium and yttrium vapors were generated by direct resistive heating of a metal filament (Goodfellow 0.25 mm, 99%) in a water-cooled oven, and highpurity gases were obtained from Messer-Griesheim (Ar 5.7, CO 4.7).…”

“…The net natural charge of M (q M ) corresponds to the difference in CT to and from M. A negative q M means that the number of donated electrons exceeds the backdonated ones-a case reported recently for several neutral and ionic metal carbonyls [37,56]. It can occur with a sufficiently large number of donor CO groups, while the surrounded M has only a limited number of electrons for backdonation.…”

“…In order to facilitate an easier visual overview, the overestimated B3LYP frequencies were corrected by the scale factor 0.96 from ref. [56].…”

“…Neutral lanthanide carbonyls were reported recently from a matrix isolation study [56], where the interpretation of the spectra was facilitated by Density Fun Theory (DFT) calculations. The most abundant species in the cryogenic CO matrix p to be Ln(CO)8, but in a few cases, Ln(CO)7 and Ln(CO)6 could also be identified.…”