Abstract: | Two polymorphs of the title compound, (4R,5R,6R,7R)‐4,7‐bis(hydroxymethyl)‐1,3‐dioxepane‐5,6‐diol, C7H14O6, both have Z′ = 2 at 100 K, and differ in their hydrogen‐bonding patterns. The sodium iodide complex, NaI·C7H14O6, is isomorphous with the NaCl complex, and has the mannitol, cation and anion all lying on twofold axes. The dioxepane rings of all three molecules are in the twist‐chair conformation. |