Isolation of a Square-Planar Th(III) Complex: Synthesis and Structure of [Th(OC₆H₂^tBu₂-2,6-Me-4)₄]^1–

Abstract

Reduction of Th­(OC6H2 tBu2-2,6-Me-4)4 using either KC8 or Li in THF forms a new example of a crystallographically characterizable Th­(III) complex in the salts [K­(THF)5(Et2O)]­[Th­(OC6H2 tBu2-2,6-Me-4)4] and [Li­(THF)4]­[Th­(OC6H2 tBu2-2,6-Me-4)4]. Surprisingly, in each structure the four aryloxide ligands are arranged in a square-planar geometry, the first example of this coordination mode for an f element complex. The Th­(III) ion and four oxygen donor atoms are coplanar to within 0.05 Å with O–Th–O angles of 89.27(8) to 92.02(8)° between cis ligands. The ligands have Th–O–C­(ipso) angles of 173.9(2) to 178.6(4)°, and the aryl rings make angles of 58.5 to 65.1° with the ThO4 plane. The effect of the eight tert-butyl substituents in generating the unusual structure through packing and/or dispersion forces is discussed. EPR spectroscopy reveals an axial signal consistent with a metal-based radical in a planar complex. DFT calculations yield a C 4-symmetric structure that accommodates a low-lying SOMO of 6d z 2 character with 7s Rydberg admixture.

Synthesis of LnII‐in‐Cryptand Complexes by Chemical Reduction of LnIII‐in‐Cryptand Precursors: Isolation of a NdII‐in‐Cryptand Complex

“…To obtain more information about the chemistry of Ln‐in‐crypt complexes in general, we have investigated reactions of lanthanide triflates with crypt. We report here that lanthanide triflates, Ln III (OTf) 3 (Ln=Nd, Sm), form isolable Ln III ‐in‐crypt complexes that are soluble in THF, the solvent commonly used for KC 8 reductions . Reduction of these Ln III complexes with KC 8 demonstrates that chemical transformations of Ln III ‐in‐crypt to Ln II ‐in‐crypt are possible with crystallographically‐characterized precursors and products.…”

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

“…[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. 5 As far as the present work is concerned, it is rather difficult to conclude on a research topic, i.e., Th(IV) complexes with Schiff-base ligands, which is still at its infancy.…”

Oligonuclear Actinoid Complexes with Schiff Bases as Ligands—Older Achievements and Recent Progress

“…Because of its large size, coordination complexes of Th(IV) exhibit high coordination numbers (e.g., Figure 4) and hard donors are preferred. Lower coordination numbers can be stabilized by amido or aryloxido ligands, and the isolation of the first square planar Th(III) complexes (and as a matter of fact the first examples of this geometry for f element complexes) has been just described [70].…”

“…This is mainly due to the potential of Th for the next generation of nuclear fuel, as the development of liquidfluoride thorium reactors is close to commercialization [40,68]. Since the main Th production mineral is monazite, which also contains Ln III ions, there is an urgent need for the discovery of suitable organic ligands and efficient solid adsorbents for the selective extraction of Th 4+ from 4f-metal ions [69,70]. Other research topics of interest in the Th(IV) complexes field are studying the solutions and solid products arising from Th(IV) hydrolysis [35]; the investigation of Th(IV)-peroxide chemistry [71]; the incorporation of this diamagnetic metal ion into isostructural heterometallic d/U IV clusters with the goal of elucidating the d-d magnetic exchange interactions [72]; the structural characterization of complexes with very high coordination numbers and novel polyhedra [41]; the progress in complexes with Th(IV)-ligand multiple bonds [73,74]; the stabilization of novel secondary building units in Th(IV) metal-organic frameworks [75]; the study of the electronic and thermodynamic properties of Th(IV)/An(Z) (Z = various oxidation states) and An(Z)/Th(IV)/3d-metal ion MOFs (Metal-Organic Frameworks) with "structural memory" [76]; and the in-depth investigation of Th(IV) interactions with ionic liquids to model aspects of the An ions extraction from radioactive feeds [42].…”