Towards Clathrates: Frozen States of Hydration of tert-Butylamine


  • This work was supported by the Cluster of Excellence RESOLV (EXC 1069) funded by the Deutsche Forschungsgemeinschaft. R.B. and S.A.C. gratefully acknowledge support from the DFG Forschergruppe 618. R.B. acknowledges the Foundation for Polish Science for a Honorary Humboldt Stipend. Ł.D. thanks the Foundation for Polish Science for a “KOLUMB” stipend and a Homing Plus/2011-4/5 grant based on the European Union Regional Development Fund. M.K.C. thanks the National Science Center (NCN 2011/03/B/ST4/02591) for support. We are grateful to Dr. Siân Howard for proofreading the manuscript.


The dilution of tert-butylamine (tBA) with water and subsequent cooling leads to a large series of different crystalline hydrates by an in situ IR laser melting-zone procedure. The crystal structures were determined for tBA⋅n H2O, with n=0, equation image, 1, 7 equation image, 7 equation image, 9 equation image, 11, and 17. For the two lower hydrates (n=equation image, 1), one- and two-dimensional hydrogen-bonded networks are formed, respectively. The higher hydrates (n>1) exhibit a clathrate-like three-dimensional water framework with the tBA molecules as part of, or sitting inside, the cages. In all cases, tBA is hydrogen-bonded to the H2O framework. In the intermediate range (1<n<7 equation image), crystallization is hindered, and no crystalline phases could be observed. The crystal structures that are achieved from the dilution of tBA with water are considered to be frozen stages of hydration, describing the genesis of such clathrate-like structures, finally ending at ice as an example of an infinitely diluted hydrate.