On the Bonding Nature in the Crystalline Tri‐Thorium Cluster: Core‐Shell Syngenetic σ‐Aromaticity

Abstract

A unique thorium-thorium bond was observed in the crystalline tri-thorium cluster [{Th(η 8 -C 8 H 8 )(μ 3 -Cl) 2 } 3 {K(THF) 2 } 2 ] ∞ , though the claim of σ-aromaticity for Th 3 bond has been questioned. Herein, a new type of core-shell syngenetic bonding model is proposed to describe the stability of this tri-thorium cluster. The model involves a 3c-2e bond in the Th 3 core and a multicentered (ThCl 2 ) 3 charge-shift bond with 12 electrons scattering along the outer shell. To differentiate the strengths of the 3c-2e bond and the charge-shift bond, the block-localized wavefunction (BLW) method which falls into the ab initio valence bond (VB) theory is employed to construct a strictly core/shell localized state and its contributing covalent resonance structure for the Th 3 core bond. By comparing with the σ-aromatic H 3 + and nonaromatic Li 3 + , the computed resonance energies and extra cyclic resonance energies confirm that this Th 3 core bond is truly delocalized and σaromatic.

Planar Four-Membered Diboron Actinide Compound with Double Möbius Aromaticity

“…30 Remarkably, a unique σ-aromatic thorium−thorium bond was recently observed in the crystalline tri-thorium cluster, 31 and the claim of such σ-aromaticity has been authenticated by the ab initio valence bond (VB) method. 32 Besides, metal clusters [Th@Bi 12 ] 4− and U 4 (NH) 4 have also been found to exhibit single and double aromaticity, respectively. 33,34 It is worthy to note that Kiplinger and co-workers prepared metallabiphenylenes containing an aromatic benzene ring and an antiaromatic cyclobutadiene ring.…”

“…Since the 5 f atomic orbitals (AOs) are rather contracted and 6 d AOs are energetically high, the bonding involving actinides is predicted to be weak and localized. − In other words, actinides are rarely found to participate in strong and delocalized aromaticity, typically with a light 2 p element . Remarkably, a unique σ-aromatic thorium–thorium bond was recently observed in the crystalline tri-thorium cluster, and the claim of such σ-aromaticity has been authenticated by the ab initio valence bond (VB) method . Besides, metal clusters [Th@Bi 12 ] 4– and U 4 (NH) 4 have also been found to exhibit single and double aromaticity, respectively. , It is worthy to note that Kiplinger and co-workers prepared actinide 2-metallabiphenylenes containing an aromatic benzene ring and an antiaromatic cyclobutadiene ring …”

Molecular Aromaticity at the Edge of the Periodic Table

“…[7] Very recently, Lin and Mo provided further computational data supporting the chargeshift bonding in the actinide cluster, and found that the overall charge transfer between thorium and chlorine atoms is about ten times more stabilizing than electron delocalization in the Th3 ring. [8] The authors linked the latter with the stabilization effect resulting from the periodic boundary conditions (PBC) for the electron distribution, [9] and made the conclusion that the trithorium bonding is therefore "truly delocalized and σ-aromatic". [8] Similar conclusions were drawn by Tomeček et al [10] who utilized the entire arsenal of sophisticated computational methods to demonstrate that the Th3 ring contains cyclically delocalized electrons and should be regarded σ-aromatic.…”

“…[8] The authors linked the latter with the stabilization effect resulting from the periodic boundary conditions (PBC) for the electron distribution, [9] and made the conclusion that the trithorium bonding is therefore "truly delocalized and σ-aromatic". [8] Similar conclusions were drawn by Tomeček et al [10] who utilized the entire arsenal of sophisticated computational methods to demonstrate that the Th3 ring contains cyclically delocalized electrons and should be regarded σ-aromatic. However, in both works the simplified highly ionized model cluster Th3Cl6 4+ https://doi.org/10.26434/chemrxiv-2022-hn1vh-v4 ORCID: https://orcid.org/0000-0002-2013-0617 Content not peer-reviewed by ChemRxiv.…”

A trinuclear metallasilsesquioxane of uranium(iii)

“…The design of polymetallic assemblies is attracting high interest in uranium chemistry because of their ability to promote small molecule activation, [1][2][3][4][5][6][7][8][9][10] and their interesting magnetic properties, [11][12][13][14][15] yet synthetic routes to such assemblies remain elusive. Moreover, the recent identification of the first example of actinide metal-metal bonding interactions in a trinuclear thorium complex 16,17 suggests that trinuclear assemblies may be used to promote metal-metal interactions in uranium compounds. Nevertheless, examples of trinuclear uranium complexes [18][19][20][21][22][23][24][25] remain rare with only two examples reported so far for the +III oxidation state.…”