The melting diagram of the system 18-crown-6/water has been set up and the existence of four binary hydrates confirmed. Crystal structures have been determined for three of these, in addition to that for the hexahydrate already published. The hydrates are monoclinic, a tetrahydrate (previously reported as a 4.5-hydrate) with space group P21/c and Z = 2 formula units per unit cell, an octahydrate with I2/a and Z = 4, and a dodecahydrate with P21/n and Z= 2. In each structure the crown ether molecule has the (pseudo) D3d conformation common for many of its complexes, and is immediately hydrogen-bonded by a group of four water molecules in a similar, characteristic pattern. In the tetrahydrate, with one of the waters disordered, the total connectivity is that of a 1D chain, while the overall structures of the octa-and dodecahydrate are 3D networks. Four of the six independent water molecules in the dodecahydrate are linked with each other into a rare 2D ice-like layer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.