Abstract
Previous work has shown that certain steroidal bis-(N-phenyl)ureas, derived from cholic acid, form crystals in the P61 space group with unusually wide unidimensional pores. A key feature of the nanoporous steroidal urea (NPSU) structure is that groups at either end of the steroid are directed into the channels and may in principle be altered without disturbing the crystal packing. Herein we report an expanded study of this system, which increases the structural variety of NPSUs and also examines their inclusion properties. Nineteen new NPSU crystal structures are described, to add to the six which were previously reported. The materials show wide variations in channel size, shape, and chemical nature. Minimum pore diameters vary from ∼0 up to 13.1 Å, while some of the interior surfaces are markedly corrugated. Several variants possess functional groups positioned in the channels with potential to interact with guest molecules. Inclusion studies were performed using a relatively accessible tris-(N-phenyl)urea. Solvent removal was possible without crystal degradation, and gas adsorption could be demonstrated. Organic molecules ranging from simple aromatics (e.g., aniline and chlorobenzene) to the much larger squalene (Mw = 411) could be adsorbed from the liquid state, while several dyes were taken up from solutions in ether. Some dyes gave dichroic complexes, implying alignment of the chromophores in the NPSU channels. Notably, these complexes were formed by direct adsorption rather than cocrystallization, emphasizing the unusually robust nature of these organic molecular hosts.
Highlights
Crystal engineering the rational design of crystalline molecular solids remains an important challenge for chemistry.[1]
We have described a series of three nanoporous steroidal urea (NPSU) with aromatic groups in R2, and the interesting feature of “water wires” in the channels,[18] and a range of NPSU-based organic alloys.[19]
The inclusion of dyes in organic molecular crystals is normally achieved by cocrystallization,[6,32,33] not by the interaction of substrates with macroscopically sized preformed crystals. This ability of NPSUs to adsorb such large guest molecules highlights their unusual combination of robust crystal structures with spacious accessible interiors
Summary
Crystal engineering the rational design of crystalline molecular solids remains an important challenge for chemistry.[1]. The molecular units in the two forms are almost identical, and qualitatively different to those in the NPSUs; in particular, the C3 substituent is positioned so that the NH group points inward, creating a binding site which accommodates two water molecules (see Figures S31 and S32) In both crystals the packing is efficient, leaving no substantial voids (see Figures S57 and S58). It is well-known that dyes may be adsorbed by inorganic crystals, such as zeolites,[30] or by organic−inorganic hybrids (PCPs/ MOFs).[31] the inclusion of dyes in organic molecular crystals is normally achieved by cocrystallization,[6,32,33] not by the interaction of substrates with macroscopically sized preformed crystals This ability of NPSUs to adsorb such large guest molecules highlights their unusual combination of robust crystal structures with spacious accessible interiors
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
