Electronic Structure of Ytterbium(III) Solvates—a Combined Spectroscopic and Theoretical Study

Abstract

The wide range of optical and magnetic properties of lanthanide­(III) ions is associated with their intricate electronic structures which, in contrast to lighter elements, is characterized by strong relativistic effects and spin–orbit coupling. Nevertheless, computational methods are now capable of describing the ladder of electronic energy levels of the simpler trivalent lanthanide ions, as well as the lowest energy term of most of the series. The electronic energy levels result from electron configurations that are first split by spin–orbit coupling into groups of energy levels denoted by the corresponding Russell–Saunders terms. Each of these groups are then split by the ligand field into the actual electronic energy levels known as microstates or sometimes m J levels. The ligand-field splitting directly informs on the coordination geometry and is a valuable tool for determining the structure and thus correlating the structure and properties of metal complexes in solution. The issue with lanthanide complexes is that the determination of complex structures from ligand-field splitting remains a very challenging task. In this paper, the optical spectraabsorption, luminescence excitation, and luminescence emissionof ytterbium­(III) solvates were recorded in water, methanol, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). The electronic energy levels, that is, the microstates, were resolved experimentally. Subsequently, density functional theory calculations were used to model the structures of the solvates, and ab initio relativistic complete active space self-consistent field calculations (CASSCF) were employed to obtain the microstates of the possible structures of each solvate. By comparing the experimental and theoretical data, it was possible to determine both the coordination number and solution structure of each solvate. In water, methanol, and N,N-dimethylformamide, the solvates were found to be eight-coordinated and have a square antiprismatic coordination geometry. In DMSO, the speciation was found to be more complicated. The robust methodology developed for comparing experimental spectra and computational results allows the solution structures of homoleptic lanthanide complexes to be determined.

Delicate, a study of the structural changes in ten-coordinated La(iii), Ce(iii), Pr(iii), Nd(iii), Sm(iii) and Eu(iii) sulfates

“…The electronic properties of transition metal and lanthanide ions are defined by the electrostatic potential acting on the ions. [1][2][3][4] If covalency is possible i.e. in transition metal complexes, this is described by ligand field theory.…”

“…These can be correlated with ideal coordination geometries by assumption and indirect measures. [2][3][4][18][19][20][21] In the solid state, the structure can be determined, and thus be directly related to ideal coordination geometries. [22][23][24] Correlating determined structures to ideal coordination geometries often relies on a visual comparison, and stops with a designation of the structure being a distorted version of an idealized structure.…”

Electronic Energy Levels and Optical Transitions in Samarium(III) Solvates

“…[10][11] Thus, the mapping of photophysical properties of most trivalent ions of the lanthanide series have been focused on solid materials. 9,[12][13][14][15][16][17] We have been interested in the fundamental optical properties in solution, [18][19][20][21][22] while others have focused on developing lanthanide luminescence based bioimaging and bioassay. [23][24][25][26][27][28][29][30] Most of the work has focused on europium centered luminescence, 23,[31][32] while some very elegant work has been done with samarium(III).…”

“…[6][7] Thus we set out to investigate the electronic energy levels and optical transitions in samarium(III) solvates following the methodology we developed in similar work on dysprosium(III) and ytterbium(III). 20,22,[41][42][43][44] Assuming the same chemistry for lanthanide(III) ions along the series may be dangerous. 45 Yet, samarium(III) and europium(III) are neighbors in the periodic table, and as the chemistry is mostly dictated by the size of the ions, 46 we assume that the samarium(III) solvates are isostructural to the corresponding europium(III) solvates.…”

“…Lanthanide(III) ions smaller than europium(III) are 8-coordinated in water, but the nature of the solvent affects the coordination as large, bulkier solvents such as dimethylsulfoxide, can result in 8-coordination for even the larger lanthanides. 20,[47][48][49] The coordination number determines the coordination geometry, where 9-coordinated ions can be either a tricapped trigonal prism (TTP) or a capped square antiprism (cSAP), while 8-coordinated ions primarily adopt a square antiprism (SAP) symmetry. 50 Here, samarium(III) solvates were studied in methanol (MeOH), dimethylsulfoxide (DMSO), and water (H2O).…”