Pseudopolymorphism in brucine: brucine–water (1/2), the third crystal hydrate of brucine

The structure of a third pseudopolymorphic hydrate of brucine, brucine–water (1/2) [systematic name: 2,3‐dimethoxystrychnidin‐10‐one–water (1/2)], C 23 H 26 N 2 O 4 ·2H 2 O, has been determined at 130 K. The asymmetric unit comprises two independent brucine molecules and four water molecules of solvation. The four water molecules form uncommon cyclic hydrogen‐bonded homomolecular R 4 4 (8) tetramer rings, which then form primary hydrogen‐bonded chain substructures extending down the 2 1 screw axis in the unit cell. The two brucine molecules are linked peripherally to these substructures by either single O—H...N brucine or asymmetric three‐centre O—H...O brucine hydrogen bonds.