Quest for Double M?bius Aromaticity

Neutral four-membered rings with 4n electrons are generally Huckel antiaromatic. On the other hand, 4n electron system can also be Mobius aromatic, although identification has escaped so far. A recent study of double Mobius aromaticity has been put forwarded in the D2h symmetric singlet ground state of four member Pa2B2 ring. Although interesting, but the synthesis possesses a significant challenge as Pa is rare, highly radioactive and toxic. Herein, a synthetically viable four membered Rh2B2 cluster is proposed which contains double Mobius aromaticity. Interestingly, the three membered RhB2- cluster also possess Mobius aromaticity and is the smallest ring to show such phenomenon. Quantum chemical calculation predict double and single Mobius aromaticity in the global minimum geometries of Rh2B2 and RhB2- clusters. Heavier analogue Ir2B2 follows the same type of aromaticity, albeit being non-planar. Aromaticity of these clusters have been confirmed by various analysis. image