Stabilization of the Oxidation State +IV in Siloxide‐Supported Terbium Compounds

Abstract

The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of TbIV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six‐coordinate complex [TbIV(OSiPh3)4(MeCN)2], 2‐TbPh, shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong π(O−Tb) interaction which is stronger than in the previously reported TbIV complexes. Cyclic‐voltammetry experiments demonstrate that non‐binding counterions contribute to the stability of TbIV in solution by destabilizing the +III oxidation state, while alkali ions promote TbIV/TbIII electron transfer.

Electron transfer pathways in photoexcited lanthanide(iii) complexes of picolinate ligands

“…A conceivable photochemical reaction would be the oxidation of the photoexcited Tb(III) to Tb(IV) by the electronpoor pyridine. Tb(IV), [78][79][80] along with Ce(IV) [81][82][83][84] and Pr(IV) 85 is more stable than the tetravalent ions of the other Ln. However, the Tb(III)/Tb(IV) oxidation potential is still quite positive, 1.3 V vs NHE in concentrated aqueous carbonate solution, 86 and most examples of Tb(IV) are reported in the solid state rather than as coordination complexes.…”

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

“…44 Remarkable lanthanide-ligand orbital mixing has also been spectroscopically determined in tetravalent lanthanide oxides, LnO 2 (Ln = Ce, Pr, and Tb) 45 , and Pr(IV) and Tb(IV) siloxide compounds. [46][47][48] Inspired by these findings, we are interested in developing and studying cerium(IV) complexes that show red-shifted absorption bands (> 650 nm). We postulate that cerium (IV) complexes with such low energy LMCT bands would have strong metal-ligand interactions, leading to unusual electronic structures.…”

Molecular Complexes of Emerging Tetravalent Rare‐Earth Metals

“…continued their work on tetravalent rare‐ earth chemistry and reported another molecular complex of Tb(IV) 4 from Ph 3 SiO‐substitued trivalent precursor 3 (Scheme 1). [ 7 ] This six‐coordinate complex shows high stability and the MeCN ligands can be replaced by phosphinoxide ligands (Et 3 PO and Ph 3 PO). Unlike 2 , the supporting ligands (OSiPh 3 ) 4 do not saturate the coordination sphere but can also stabilize this complex.…”

“…Since then, four examples of Tb(IV) and Pr(IV) molecular complexes have been reported. [ 6‐9 ] In this emerging topic, we will for the first time cover the field of rare‐earth (except Ce) chemistry contributed to the +4 oxidation state. Meanwhile, we hope that this topic will open a new avenue for the development of tetravalent rare‐earth organometallic chemistry.…”