The analogue of aromaticity for three-dimensional compounds, i.e. three-dimensional molecules that are particularly stable. Three-dimensional aromaticity occurs in organic compounds, inorganic compounds such as boranes, and cluster compounds. In the case of cluster compounds, aromaticity is sometimes called cluster aromaticity. It is frequently possible to determine which molecules are stable by using electron counting rules such as Wade’s rules, which are the analogues of the Hückel rule. As with aromaticity for planar (flat) compounds, three-dimensional aromaticity is associated with the delocalization of electrons. Just as there are three-dimensional analogues of benzene, there are three-dimensional analogues of naphthalene, with a notable example of this being found in 2016—a borane with metal atoms in which two icosahedra are fused together.