Polymorphs of gabapentin

Gabapentin [or 1‐(aminomethyl)cyclohexaneacetic acid], C₉H₁₇NO₂, exists as a zwitterion [1‐(ammoniomethyl)cyclohexaneacetate] in the solid state. The crystal structures and bonding networks of two new monoclinic polymorphs (β‐gabapentin and γ‐gabapentin) are studied and compared with a previously reported gabapentin polymorph [α‐gabapentin: Ibers (2001). Acta Cryst. C 57 , 641–643]. All three polymorphs have extensive networks of hydrogen bonds between the NH₃⁺ and COO⁻ groups of neighbouring molecules. In β‐gabapentin, there is an additional weak intramolecular hydrogen bond.