Crystal Structures of Water and Tertiary Amines: Hydrates or Ice with a Twist?

Abstract

Structural studies of hydrates with simple tertiary amines are comparatively rare. We here present structures of the hydrated tertiary amines quinuclidine (quin) and tetramethylethylenediamine (tmeda), each with lower and higher water content, which were reproducibly crystallized by adjusting their stoichiometries. Our structures range from simple monohydrates to higher hydrates with extended hydrogen bond networks. Due to the excellent data quality and the absence of disorder, Hirshfeld atom refinements could be performed. This refinement with nonspherical scattering factors further increased the quality of the structure models and allowed fundamental insights into the character of hydrogen bonds and their networks. The dimensionality of the water substructures in our solids correlates with their composition: In our simplest monohydrate, individual water molecules bridge tmeda residues to a chain, the di- and trihydrates of quin feature layers of water, and a 3D network of water molecules is encountered for the tmeda heptahydrate, the compound with the highest ratio between H donor and N acceptor molecules presented.