15.1: Parallels between Main Group and Binary Carbonyl Complexes 15.2: The Isolobal Analogy The isolobal analogy (aka isolobal principle) is a strategy used in organometallic chemistry to relate the structure of organic and inorganic molecular fragments in order to predict bonding properties of organometallic compounds. Roald Hoffmann described molecular fragments as isolobal: "if the number, symmetry properties, approximate energy and shape of the frontier orbitals and the number of electrons in them are similar – not identical, but similar." 15.2.1: Extensions of the Analogy 15.2.2: Some Applications of the Isolobal Analogy 15.3: Metal-Metal Bonds 15.3.1: Metal-Metal Multiple Bonds 15.4: Cluster Compounds 15.4.1: Boranes 15.4.2: Heteroboranes 15.4.3: Metallaboranes and Metallacarboranes 15.4.4: Carbonyl Clusters 15.4.5: Carbon-Centered Clusters 15.4.6: Additional Comments on Clusters 15.5: Problems