Evaluating f‐Element Bonding from Structure and Thermodynamics

Abstract

The practical goal to measure and understand the thermodynamic properties of molecules and materials containing f-elements is often achieved through indirect methods. Of the characterization tools available to inorganic chemists, few are more powerful than X-ray crystallography. Yet for lanthanides and actinides, interpretation of a bond length is a challenging undertaking that involves a complex interplay of steric and electronic forces. In this Concept article, we perform an analysis of selected examples in which structural criteria alone have been used to draw qualitative conclusions about chemical bonding. In other instances for which such an analysis is not valid, thermodynamic information is evaluated side by side with structural data to provide reasonable interpretations of a covalent/ionic mode of bonding. A geometric variation larger than 3σ is not necessarily correlated to a change in bonding, nor is an increase in bond energy related to a bond with more covalent character. However, careful consideration of thermodynamic information can lead to reasonable interpretations of electronic structure, and may provide a more reliable benchmark for the theoretical methods which can describe f-elements.

f‐Element–Metal Bonding and the Use of the Bond Polarity To Build Molecular Intermetalloids

“…The first mention of direct bonds between actinoids and main group metals (MM) dates back to 1969, when Vdovenko et al described [Cl 5 SnU(O) 2 Cl 2 SnCl 5 ] 2À in a study concerned with determining force constants by evaluating the IR spectra of compounds containing the isotopically labeled uranyl fragment [U 16 O 18 O] 2 + . [13] In the following year, the preparation of various uranium(V) complexes was reported by Selbin et al, [14] including the binuclear cation [Cl 4…”

“…Following a concept developed by Roesky and co-workers for the formation of lanthanoid-Group 13 bonds (see below), [18,19] Minasian et al reported the synthesis of [(Cp TMS ) 3 UAlCp*] (A2, Figure 1) [20] as well as [(Cp TMS ) 3 UGaCp*] (A3, Figure 1) [21] from [(Cp TMS ) 3 U] and (AlCp*) 4 or GaCp*, respectively (Cp TMS = trimethylsilylcyclopentadienyl, Cp* = pentamethylcyclopentadienyl). Being isolobal to CO, the latter compounds are known to act as Lewis-basic ligands towards various coordinatively unsaturated metal complexes.…”

“…Among them unsupported bonds are the most attractive ones to study because ligand bridging is likely to alter the nature of the metal-metal bond. [4] The felements, the footnotes of the periodic table, consist of the actinoid (An) series [5] and the lanthanoid series [6] (Ln). The latter are often called rare-earth (RE) elements, which includes the Group 3 metals scandium and yttrium.…”

Photochemical Route to Actinide-Transition Metal Bonds: Synthesis, Characterization and Reactivity of a Series of Thorium and Uranium Heterobimetallic Complexes

“…[1][2][3][4][5][6] In the case of metal-metal bonds, those involving actinides are fundamentally different from their transition metal and lanthanide counterparts as a result of f orbital participation in bonding, coordinative diversity, and access to a wide range of oxidation states. Understanding these fundamental properties is of importance in nuclear fuel reprocessing, where small differences in covalency between the 4 and 5f elements may provide opportunities to improve separations.…”

“…Metal-based transitions were observed in the NIR region for the corresponding main group and transition metal examples of this ligand. Likewise, the two peaks observed for isocarbonyl 5 5 may arise due to independent cobalt and uranium based transitions. Subsequently, and consistent with the polarization of charge between the metal centers in 7 7, a single transition of increased intensity is seen upon formation of the U-Co bond.…”