Three polymorphs (α, β, and δ) of d-mannitol at 100 K

In the monoclinic δ polymorph of d-mannitol, C₆H₁₄O₆, both the mol­ecule and the packing have approximate twofold rotational symmetry. The P2₁ structure thus approximates space group C222₁, and the α′ polymorph, previously reported in that space group, is almost certainly identical to the δ polymorph. However, torsion angles along the main backbone of the mol­ecule deviate from twofold symmetry by as much as 7.4 (3)° and the hydrogen-bonding pattern does not conform to the higher symmetry. The α polymorph reported here is identical to the previously reported κ polymorph, and the low-temperature structure of the β polymorph agrees well with previously reported room-temperature determinations. The range of C—O bond lengths over the three polymorphs is 1.428 (2)–1.437 (4) Å, and the range of C—C distances is 1.515 (4)–1.5406 (19) Å. The δ polymorph has the highest density of the three, both at room temperature and at 100 K.