must be taken to avoid the formation of IF5. F2 attacks I2 to yield IF3 at −45 °C in CCl3F. Alternatively, at low temperatures, the fluorination reaction I2 + 3 XeF2 → 2 IF3 + 3 Xe can be used. Not much is known about iodine trifluoride as it is so unstable. Iodine trichloride (ICl3) forms lemon yellow crystals that melt under pressure to a brown liquid. It can be made from the elements at low temperature, or from iodine pentoxide and hydrogen chloride. It reacts with many metal chlorides to form tetrachloroiodides (), and hydrolyses in water. The molecule is a planar dimer (ICl3)2, with each iodine atom surrounded by four chlorine atoms. Iodine tribromide (IBr3) is a dark brown liquid. Hexatomic interhalogens All stable hexatomic and octatomic interhalogens involve a heavier halogen combined with five or seven fluorine atoms. Unlike the other halogens, fluorine atoms have high electronegativity and small size which is able to stabilize them. Chlorine pentafluoride (ClF5) is a colourless gas, made by reacting chlorine trifluoride with fluorine at high temperatures and high pressures. It reacts violently with water and most metals and nonmetals. Bromine pentafluoride (BrF5) is a colourless fuming liquid, made by reacting bromine trifluoride with fluorine at 200 °C. It is physically stable, but decomposes violently on contact with water, organic substances, and most metals and nonmetals. Iodine pentafluoride (IF5) is a colourless liquid, made by reacting iodine pentoxide with fluorine, or iodine with silver(II) fluoride. It is highly reactive, even slowly with glass. It reacts with water to form hydrofluoric acid and with fluorine gas to form iodine heptafluoride. The molecule has the form of a tetragonal pyramid. Octatomic interhalogens Iodine heptafluoride (IF7) is a colourless gas and a strong fluorinating agent. It is made by reacting iodine pentafluoride with fluorine gas. The molecule is a pentagonal bipyramid. This compound is the only known interhalogen compound where the larger atom is carrying seven of the smaller atoms. All attempts to synthesize bromine or chlorine heptafluoride have met with failure; instead, bromine pentafluoride or chlorine pentafluoride is produced, along with fluorine gas. Properties Typically, interhalogen bonds are more reactive than diatomic halogen bonds—because interhalogen bonds are weaker than diatomic halogen bonds, except for F2. If interhalogens are exposed to water, they convert to halide and oxyhalide ions. With BrF5, this reaction can be explosive. If interhalogens are exposed to silicon dioxide, or