Longuet-Higgings . This bond is typically present in molecules and solids of electron-deficient elements (hydrogen and elements of groups 1, 2, and 13), such as in boranes (BxHy) and hydrogenonium ion H3 + , and is considered to be a well-established type of bond for whose understanding Lipscomb was awarded the Nobel Prize in Chemistry in 1976 [38]. On the other hand, the ERMB was modeled as a 3c-4e bond (see In relation to the multicenter bonds, it is commonly believed that EDMBs could only be formed by electron-deficient elements and ERMBs could only be formed by electron-rich elements . Since both 3c-2e EDMBs and 3c-4e ERMBs are "half" or "partial" bonds, as deduced from their longer bond lengths when compared with those of the single covalent (two-center two-electron, 2c-2e) bond, it has been also believed that both 3c-2e and 3c-4e bonds have a single electron shared between two atoms. In other words, both multicenter bonds have been considered as two different cases of two-center one-electron (2c-1e) bonds. The reason for such a belief was based on the simple molecular orbitals proposed to describe both kinds of multicenter bonds (see Fig. ). In both 3c-2e and 3c-4e bonds there are two electrons in the low-energy three-center bonding orbital, thus leading to one shared electron between each two atoms. In addition, there are two additional electrons in the case of 3c-4e bonds that are located at the three-center nonbonding orbital (note that this orbital could have a slight antibonding character, as suggested by Hoffmann and coworkers ). These two electrons are considered to be exclusively located in the external atoms of the three-atom molecule, so they are not considered up to now to be even partially shared between the two nearest atoms .