Understanding the Optical and Magnetic Properties of Ytterbium(III) Complexes

Abstract

The absorption and emission spectra of three Yb 3+ complexes possessing D 3 , D 2 , and C 2 symmetries were analyzed with the aid of ab initio calculations based on Complete Active Space (CAS) self-consistent field wave functions (CAS(13,7)). The absorption spectra present contributions from both cold and hot bands, involving thermally populated excited sublevels of the 2 F 7/2 manifold. The high-resolution emission spectrum of the tris-picolinate complex [Yb(DPA) 3 ] 3− recorded at 77 K presents four components, while the complexes with macrocyclic ligands show both cold and hot emission bands, resulting in more than four components for the 2 F 5/2 → 2 F 7/2 transition. The combined information provided by the absorption and emission spectra allowed to identify most of the crystal field sublevels of the 2 F 5/2 and 2 F 7/2 states. The energies of these crystal field components are well-reproduced by the ab initio calculations, with deviations typically lower than 100 cm −1 . The crystal field splitting is very sensitive to subtle changes of the Yb 3+ coordination environment. The magnetic anisotropy of [Yb(DPA) 3 ] 3− obtained with ab initio calculations was found to be extremely sensitive to changes in the twist angle of the upper and lower faces of the tricapped trigonal prismatic coordination polyhedron. Ab initio ligand field theory provides a straightforward chemical justification for the changes in magnetic anisotropy, which are responsible for the observed pseudocontact shifts in the NMR spectra.

Periodic trends and hidden dynamics of magnetic properties in three series of triazacyclononane lanthanide complexes

“…For example, the consequences of their unique magnetic properties are being explored actively, ranging from unusual susceptibility anisotropy, [1][2][3][4] to the impact of systematic changes in the coordination environment that determine optical, NMR and EPR behaviour. [5][6][7][8][9][10] Furthermore, such work continues to encourage the development of improved computational and theoretical approaches, that may in due course allow more confident predictions to be made of spectral behaviour in solution. 11,12 Recently, we have been examining several series of ninecoordinate Ln(III) complexes because of their potential as cellular stains 13 and as luminescent probes, e.g.…”

Unravelling the Complexities of Pseudocontact Shift Analysis in Lanthanide Coordination Complexes of Differing Symmetry

“…When the position of the principal magnetic axis changes orientation, the ordering of the M J sub‐levels in a lanthanide complex will alter as well. Such a change is most readily observed by examining very low temperature EPR spectra, from which information on the magnetic anisotropy of the ground state can be ascertained –. X‐band continuous wave EPR spectra were collected at 5 K for solid crystalline and frozen solution (95 % MeOH + 5 % Et 2 O) samples of [YbL 2 ] and [YbL 1b ].…”

pH‐Dependent Hydration Change in a Gd‐Based MRI Contrast Agent with a Phosphonated Ligand

“…The paramagnetic shifts induced by Yb 3 + are dominated by the pseudocontact contributions, which are relatedt ot he magnetic anisotropy of the complex and the location of the observed nuclei with respect to the principal magnetic axes. [38] The pseudocontact shifts of Yb 3 + and other lanthanide complexes were found to be very sensitivet os mall structural changes; [39] for example, induced by changing the polarity of the solvent. [40] Thus, we sought to investigate the 1 Ha nd 31 PNMR spectrao ft he YbL complex at different pH (pD) values.…”