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- dimethoxy-strychnidin-10- one - water ( 1/ 2)], C23H26N2O4 center dot 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 21 screw axis in the unit cell. The two brucine molecules are linked peripherally to these substructures by either single O - H center dot center dot center dot N-brucine or asymmetric three-centre O-H center dot center dot center dot O-brucine hydrogen bonds.