Crystal Field in Rare‐Earth Complexes: From Electrostatics to Bonding

• Published in: Chemistry : a European journal 2018-04, Vol.24 (21), p.5538-5550
• Main Authors: Alessandri, Riccardo, Zulfikri, Habiburrahman, Autschbach, Jochen, Bolvin, Hélène
• Format: Article
• Language: English
• Subjects: ab initio calculations; bond theory; Chemical bonds; Chemical Sciences; Chemistry; Coupling (molecular); crystal field effects; Crystal field theory; Crystals; Electrostatic properties; Electrostatics; lanthanides; ligand effects; Ligands; or physical chemistry; Theoretical and
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201705748

The flexibility of first‐principles (ab initio) calculations with the SO‐CASSCF (complete active space self‐consistent field theory with a treatment of the spin‐orbit (SO) coupling by state interaction) method is used to quantify the electrostatic and covalent contributions to crystal field parameters. Two types of systems are chosen for illustration: 1) The ionic and experimentally well‐characterized PrCl3 crystal; this study permits a revisitation of the partition of contributions proposed in the early days of crystal field theory; and 2) a series of sandwich molecules [Ln(ηn‐CnHn)2]q, with Ln=Dy, Ho, Er, and Tm and n=5, 6, and 8, in which the interaction between LnIII and the aromatic ligands is more difficult to describe within an electrostatic approach. It is shown that a model with three layers of charges reproduces the electrostatic field generated by the ligands and that the covalency plays a qualitative role. The one‐electron character of crystal field theory is discussed and shown to be valuable, although it is not completely quantitative. This permits a reduction of the many‐electron problem to a discussion of the energy of the seven 4f orbitals. Separating key components: The flexibility of first‐principles (ab initio) calculations is used to quantify the electrostatic and covalent contributions to crystal field parameters for a selection of rare‐earth complexes. The one‐electron character of crystal field theory is discussed and, although valuable, it is not completely quantitative. This permits a reduction of the many‐electron problem to a discussion of the energy of the seven 4f orbitals