We systematically explore the potential energy surface of the B3Al4+ combination of atoms. The putative global minimum corresponds to a structure formed by an Al4 square facing a B3 triangle. Interestingly, the dynamical behavior can be described as a Reuleaux molecular triangle since it involves the rotation of the B3 triangle at the top of the Al4 square. The molecular dynamics simulations, corroborating with the very small rotational barriers of the B3 triangle, show its nearly free rotation on the Al4 ring, confirming the fluxional character of the cluster. Moreover, while the chemical bonding analysis suggests that the multicenter interaction between the two fragments determines its fluxionality, the magnetic response analysis reveals this cluster as a true and fully three-dimensional aromatic system. © 2022 by the authors.National Natural Science Foundation of China, NSFC, (22173053); Academy of Finland, AKA, (314821, 340583); Consejo Nacional de Ciencia y Tecnología, CONACYT, (1561802); Magnus Ehrnroothin Säätiö; Natural Science Foundation of Shanxi Province, (20210302123439); Svenska Kulturfonden