A triclinic polymorph of hexanedioic acid

Hexanedioic acid ( or adipic acid), C6H10O4, crystallizes with two crystallographically independent half-molecules in the asymmetric unit of the triclinic unit cell, space group P (1) over bar, as each molecule lies across a crystallographic inversion centre. A monoclinic polymorph has been reported previously, most recently by Ranganathan, Kulkarni & Rao [J. Phys. Chem. A, (2003), 107, 6073-6081]. The molecules adopt the expected zigzag structure and are linked via centrosymmetric pairs of O-H center dot center dot center dot O hydrogen bonds, forming infinite one-dimensional chains along [011]. These chains are stacked along the a axis. The crystal is further stabilized by weak C-H center dot center dot center dot O interactions.