Molecular and crystal structure of a new polymorph of malonic acid with Z′ = 3

• Molecular and crystal structure of a simple diacid.
• Investigation of structure by single crystal X-ray diffraction.
• Malonic acid forms continuous hydrogen bonded chains through carboxylic acid.

The crystal structure of a fifth polymorph of malonic acid has been determined by single crystal X-ray diffraction. The unit cell parameters, crystal structure and calculated powder diffraction lines for the new polymorph (monoclinic, Z′ = 3) are distinctly different from those of the reported forms. There are both similarities as well as differences in the arrangement of molecules in the crystal lattice in all the forms. The molecules, in all the polymorphs, interact through the formation of O–H⋯O hydrogen bonded dimers by –COOH group with significant differences between the forms within this packing pattern.