Polymorphs of gabapentin.

Gabapentin [or 1-(aminomethyl)cyclohexaneacetic acid], C(9)H(17)NO(2), exists as a zwitterion [1-(ammoniomethyl)cyclohexaneacetate] in the solid state. The crystal structures and bonding networks of two new monoclinic polymorphs (beta-gabapentin and gamma-gabapentin) are studied and compared with a previously reported gabapentin polymorph [alpha-gabapentin: Ibers (2001). Acta Cryst. C57, 641-643]. All three polymorphs have extensive networks of hydrogen bonds between the NH(3)(+) and COO(-) groups of neighbouring molecules. In beta-gabapentin, there is an additional weak intramolecular hydrogen bond.