d-p Hybridization Induced Open-Shell Planar Four-Membered\nTransition Metal Carbide Clusters with Double Mobius Aromaticity

Aromaticity is one of the most classical\nconcepts in the field\nof modern chemistry and has been employed to explain and design substances\nwith special stability. Although the knowledge about Hückel’s\nand Baird’s rules has been well established, the understanding\nof Möbius aromaticity remains extremely limited. In this letter,\nby employing density functional theory (DFT) calculations, we demonstrated\nthat the four-membered VIB transition metal (TM) carbide clusters\npossess a highly stable open-shell planar tetrameric structure and\nexhibit double Möbius aromaticity, which was evidenced by analyzing\nmultiple aromaticity criteria, including the electronic, magnetic,\nand energetic indicators. Each cluster was characterized by four delocalized\nπ electrons and four delocalized σ electrons, forming\na novel class exhibiting double Möbius aromaticity. Intriguingly,\nthe unexpected stability of these open-shell clusters was suggested\nto arise from the hybridization of d-p atomic orbitals, as revealed\nby analysis of the composition of delocalized orbitals. Our findings\nhighlight the significance of hybridization between the d orbitals\nof transition metals and the p orbitals of main group elements in\nthe creation of dual Möbius aromatic species, which offers\nnew avenues for the design of single-molecule magnetic inorganic materials.