Octafluoro-1,4-diiodobutane (ofib, C4F8I2) is also referred to as 1,1,2,2,3,3,4,4-octafluoro-1,4-diiodobutane. It acts as a halogen bond donor compound and its cocrystallization with methyldiphenylphosphine oxide (mdppo) has been investigated. In combination with a calixcrown compound ofib forms a ′binary host′ system, which is employed for the isolation of cesium iodide from aqueous to fluorous phase.