Multiple Bonding in Lanthanides and Actinides: Direct Comparison of Covalency in Thorium(IV)- and Cerium(IV)-Imido Complexes

Abstract

A series of thorium(IV)-imido complexes was synthesized and characterized. Extensive experimental and computational comparisons with the isostructural cerium(IV)-imido complexes revealed a notably more covalent bonding arrangement for the CeN bond compared with the more ionic ThN bond. The thorium-imido moieties were observed to be 3 orders of magnitude more basic than their cerium congeners. More generally, these results provide unique experimental evidence for the larger covalent character of 4f 0 5d 0 Ce(IV) multiple bonds compared to its 5f 0 6d 0 Th(IV) actinide congener.

Cerium(iv) complexes with guanidinate ligands: intense colors and anomalous electronic structures

“…Overall, the consecutive replacements of the amide ligand by the rigid guanidinate ligand decrease the ligand donation into the metal 5d shell, due to less optimal overlap when going from 2-Cl to [4+] , while simultaneously increasing the 4f participation in the metal–ligand bonding orbitals. Related scenarios have been reported for Ce( iv )/Th( iv ) imido complexes, 42 lanthanide dioxides and sesquioxides, 45,76 [LnCl 6 ] x − ( x = 2, 3; Ln = Ce IV , Ce III , Nd III , Sm III , Eu III , Gd III ), 30 and [AnCl 6 ] 2− (An(IV) = Th, U, Np, Pu). 77 The NLMOs show one Ce–Cl σ bond and two Ce–Cl π bonds, which have similar bonding characteristics to the computed Ce-amide bonds.…”

“…With that fact in mind, metal-ligand covalency in the cerium(IV) imido complexes is more significant than that of the thorium(IV) analogs. 32,41,42 In terms of other lanthanide compounds with low energy LMCT bands, Cp* 2 Yb(bipy) (Cp* = pentamethylcyclopentadienyl, bipy = 2,2'-bipyridine), which has a low-lying LMCT band at ca. 2105 nm, shows significant metal-ligand orbital overlap and strong exchange coupling (2J = −0.11 eV).…”

Isolation and characterization of a covalent CeIV-Aryl complex with an anomalous 13C chemical shift

“…T he bonding between lanthanides and ligands has been described as purely ionic 1,2 . However, modern spectroscopic and computational techniques have challenged this simple assumption [3][4][5][6] . The covalency in M − X interactions can result in anomalous and diagnostic nuclear magnetic resonance shifts, X = 13 C, 15 N, 19 F, 77 Se, 125 Te, resulting from participation of f-element orbital angular momentum [7][8][9][10][11][12][13] .…”

Tetranuclear oxido-bridged thorium(iv) clusters obtained using tridentate Schiff bases

“…Even at the time of submission of the present work, thorium chemistry continues to surprise the inorganic chemistry community. [85][86][87][88][89][90][91] For example, the number of the crystallographically characterised Th(III) complexes (mainly with cyclopentadienyl ancillary ligands) increases and the first example of a square planar thorium complex has been just reported. 89 Many scientists believe that with the harmful effects of global climate change becoming more evident with every passing year, more research activity and allocated resources will help the Z = 90 element realize its great potential and become a truly valuable source of materials in our energy economy.…”