resulting in a frontier orbital, which points toward the removed ligand. Cleaving the bond between the metal center and one ligand results in a radical complex. In order to satisfy the zero-charge criteria the metal center must be changed. For example, a MoL6 complex is d6 and neutral. However, removing a ligand to form the first frontier orbital would result in a complex because Mo has obtained an additional electron making it d7. To remedy this, Mo can be exchanged for Mn, which would form a neutral d7 complex in this case, as shown in Figure 3. This trend can continue until only one ligand is left coordinated to the metal center. Relationship between tetrahedral and octahedral fragments Isolobal fragments of tetrahedral and octahedral molecules can be related. Structures with the same number of frontier orbitals are isolobal to one another. For example, the methane with two hydrogen atoms removed, CH2 is isolobal to a d7 ML4 complex formed from an octahedral starting complex (Figure 4). MO theory dependence Any sort of saturated molecule can be the starting point for generating isolobal fragments. The molecule's bonding and nonbonding molecular orbitals (MOs) should be filled and the antibonding MOs empty. With each consecutive generation of an isolobal fragment, electrons are removed from the bonding orbitals and a frontier orbital is created. The frontier orbitals are at a higher energy level than the bonding and nonbonding MOs. Each frontier orbital contains one electron. For example, consider Figure 5, which shows the production of frontier orbitals in tetrahedral and octahedral molecules. As seen above, when a fragment is formed from CH4, one of the sp3 hybrid orbitals involved in bonding becomes a nonbonding singly occupied frontier orbital. The frontier orbital’s increased energy level is also shown in the figure. Similarly when starting with a metal complex such as d6-ML6, the d2sp3 hybrid orbitals are affected. Furthermore, the t2g nonbonding metal orbitals are unaltered. Extensions of the analogy The isolobal analogy has applications beyond simple octahedral complexes. It can be used with a variety of ligands, charged species and non-octahedral complexes. Isoelectronic fragments The isolobal analogy can also be used with isoelectronic fragments having the same coordination number, which allows charged species to be considered. For example, Re(CO)5 is isolobal with CH3 and therefore, [Ru(CO)5]+ and [Mo(CO)5]− are also isolobal with CH3. Any 17-electron metal complex would be isolobal in this example. In a