The Bonding Properties Of Lanthanide 4f Orbits In Di-/Trivalent Compounds

Quantum chemical first principle method(Density functional and ab intio methods) with scalar relativistic(SR)/ spin-orbit coupled(SOC) ZORA approach investigations have been done on lanthanide atoms and compounds. The study mainly focused on lanthanide contractions and bonding properties of lanthanide atoms and their 4f orbits. Investigated systems, according to their sizes, ranged from lanthanide atoms, lanthanide trihalides, lanthanide calcogenide diatomics, lanthanide silicon clusters and lanthanide crownether complexes. Included in these systems were 4 kinds of valence states(0, +2, +3 and +4) and 5 different coordination numbers(1, 3, 4, 5, 6). The chemical behavior and bonding properties of lanthanide valence shells were thus studied in a comparative way.The biggest challenge in calculating lanthanide compounds is the converge problem. Due to multi-configuration effect, single-determinant wavefunctions seldom converge. Large time cost, on the other hand, makes multi-reference approaches far from being practical. In this work, the FON-DFT approach has been adopted to treat 4f orbits as a whole and then make the calculations converged. It was also applied for lanthanide chalcogenide diatomics to simulate multi-configuration effect. Reasonable ground states have been found in this way.Our main results are: light lanthanide 4f shells can form covalent bond in appropriate situations like in trihalides or monocalcogenides, the covalent contribution of 4f in monoxides is comparable with 5d contribution in trifluorides, while no 4f participation was found in silicon clusters or crownether complexes; lanthanide contraction was variable in different systems, which increases along with halogen atomic numbers in trihalides but disappeared in monocalcogenides; a difference between SOC bond length and SR results was observed, the bond is contracted for light lanthanide compounds and is extended for the heavy ones in a double periodic pattern; the photoelectron spectra of lanthanide silicon clusters have been successfully simulated and assigned, a 4f charge decrease was observed with the detachment of electrons which is compensated by 5d charge increase that implying a 4f-5d transition; the first theoretical explanation of the selective extraction of lanthanide cations by crowether has been carried out, attributing the selectivity to solvation energy by energy decomposition analysis.The lanthanide 4f electrons should be taken as valence electrons instead of core. It has small distribution even far from the nulear, and participates in covalent bonding in specific situations.When 4f electrons do not make covalent contributions as in silicon clusters, other properties like photoelectron spectra are still relevant with 4f charge. In such cases 4f shells should also be treated as valence shells.