Bridging bonds occur when a mono-valent hydride or halogen anion is held between a pair of Lobe-LUMO Lewis acid centres. The classic example of the bridging bond is found in diborane, B2H6. Bridging bonds are most commonly found in simple inorganic hydrides and halides, such as PdCl2. For more information look in the Chemogenesis
webbook sections on Lewis
acids and Lewis bases and the Lewis
acid/base interaction matrix.