Towards Clathrates: Frozen States of Hydration of tert-Butylamine.

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 H2 O, with n=0, 1/4, 1, 7 1/4, 7 3/4, 9 3/4, 11, and 17. For the two lower hydrates (n= 1/4, 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 H2 O framework. In the intermediate range (1

Design and preparation of co-crystals utilizing the R(4)(2)(8) hydrogen-bonding motif.

An investigation of the feasibility of utilizing a specific, and previously largely unrecognized, hydrogen-bonded synthon for the design and preparation of co-crystals is reported. Structural evidence (i.e., >12,000 instances) indicated the robustness of the cyclic R(4)(2)(8) hydrogen-bonded motif containing, in most cases, four individual (either identical or different) molecules, in which the donor substituent (e.g., an amine) can provide two hydrogen-bond donors, and the acceptor (e.g., a carbonyl oxygen) can provide two hydrogen-bond acceptors. The energetic robustness of the motif with respect to chemical substitution and charge on the component molecules was investigated and confirmed in a series of fully optimized calculations at the MP2/6-31+G(d) level. A proof-of-concept experiment to prepare a co-crystal between a prototypical ketone and a primary amine yielded the crystal structure reported herein, in which the hydrogen bonds between the co-crystal components indeed exhibit exclusively the designed and sought-after R(4)(2)(8) motif.