Helical or Polar Guest-Dependent <i>Z</i>‘ = 1.5 or <i>Z</i>‘ = 2 Forms of a Sterically Hindered Bis(urea) Clathrate

Todd, Adam M.; Anderson, Kirsty M.; Byrne, Peter; Goeta, and Andrés E.; Steed, Jonathan W.

doi:10.1021/cg060318o

Cited by 40 publications

(47 citation statements)

References 19 publications

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“…Intramolecular C-H · · · O interactions are present in synthons II-IV but absent in I. (8) 8.0360 (5) 7.9974 (8) 7.919 (4) 8.4419 (17) 8.4078 (9) 6.8807 (5) 9.4442 (19) 7.9488 (7) 7.4728 (10) 10.184 (2) b /Å 12.9932 (12) 13.3397 (8) 13.4826 (13) 13.692 (6) 12.987 (3) 12.7289 (13) 12.7415 (10) 7.3883 (15) 10.4797 (9) 10.2624 (14) 13.346 (3) c /Å 11.6524 (11) 11.8513 (7) 12.0227 (12) 11.777 (6) 12.399 (3) 12.3376 (13) 15.2876 (11) 23.863 (5) 11.9563 (10) 12.5410 (17) 15.502 ( (13) 16.0665 (10) 6.0509 (6) 9.1958 (10) 6.7307 (10) 13.552 (3) 13.422 (3) 6.0710 (12) 14.3837 (15) 9.851 (3) b /Å 9.5690 (14) 5.7448 (4) 12.4575 (12) 9.5491 (10) 10.2019 (15) 4.6722 (9) 4.6511 (9) 7.5613 (15) 9.3167 (10) 56.994 (18) c /Å 11.8457 (18)<...>…”

Section: Resultsunclassified

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Crystal Structures of N-Aryl-N′-4-Nitrophenyl Ureas: Molecular Conformation and Weak Interactions Direct the Strong Hydrogen Bond Synthon

Reddy

Chandran

George

et al. 2007

Crystal Growth & Design

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Hydrogen bond competition was studied in 21 X-ray crystal structures of N-X-phenyl-N′-p-nitrophenyl urea compounds (X ) H, F, Cl, Br, I, CN, C≡CH, CONH 2 , COCH 3 , OH, Me). These structures are classified into two families depending on the hydrogen bond pattern: urea tape structures contain the well-known R-network assembled via N-H · · · O hydrogen bonds; however, in nonurea tape structures the N-H donors hydrogen bond with NO 2 groups or solvent O acceptor atoms. Surprisingly, the urea CdO hardly accepts strong H bonds in nonurea type structures sustained by urea · · · nitro and urea · · · solvent synthons. The carbonyl group accepts intra-and intermolecular C-H · · · O interactions. The molecular conformation and H bonding motifs are different in the two categories of structures: the phenyl rings are twisted out of the urea plane in the tape motif, but they are coplanar in the nonurea category. Even though hydrogen bond synthon energy and urea carbonyl acceptor strength favor the N-H · · · O tape structure, the dominant pattern in electron-withdrawing aryl urea crystal structures is the urea · · · nitro/urea · · · solvent synthon and persistence of intramolecular C-H · · · O interactions. Remarkably, the presence of functional groups that can promote specific C-I · · · O or C-H · · · O interactions with the interfering NO 2 group, for example, when X ) I, C≡CH, NMe 2 , and Me, steers crystallization toward the N-H · · · O urea tape structure, and now the diaryl urea molecule adopts the metastable, twisted conformation. Molecular conformer energy calculations and difference nuclear Overhauser enhancement NMR experiments show that the planar, trans-trans-N,N′-diphenyl urea conformation is more stable than the N-Ph twisted rotamer. However, the urea CdO is a better hydrogen bond acceptor in the twisted conformer compared to the planar one, based on electrostatic surface potential (ESP) charges. These diaryl ureas together with previously reported crystal structures provide a global structural model to understand how functional groups, molecular conformation, hydrogen bonding, and crystal packing are closely related and influence each other in subtle yet definitive ways. Our strategy simultaneously exploits weak, soft intermolecular interactions and strong, hard hydrogen bonds [supramolecular hard and soft acid-base (HSAB) principle] in the crystal engineering of multifunctional molecules.

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Section: Resultsunclassified

“…Urea R-network (synthon I) in the crystal structure of N,N-dimethylamino compound 5 19. and lateral C-H · · · O interactions of synthon VII.…”

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confidence: 99%

Crystal Structures of N-Aryl-N′-4-Nitrophenyl Ureas: Molecular Conformation and Weak Interactions Direct the Strong Hydrogen Bond Synthon

Reddy

Chandran

George

et al. 2007

Crystal Growth & Design

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“…In contrast, the sterically hindered 2 exhibits either a highly asymmetrical, helical urea hydrogen-bonded motif or interactions with included solvent. 50 Compounds 1 and 2 are non-gelators as free ligands, but form a variety of metallogels in the presence of copper(II) and silver(I) salts [32][33][34] . e.g.…”

Section: Gelation By Competitive Inhibitionmentioning

confidence: 99%

Halogen-bonding-triggered supramolecular gel formation

et al. 2012

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Tunable gel phase materials with novel properties such as switchable rheology and controlled flow characteristics are an emerging topic of interest in potential applications as diverse as pharmaceutical crystallization, catalysis, drug delivery and controlled release, wound healing, and stabilization of drilling mud [1][2][3][4][5][6][7][8][9] . Within this context supramolecular low molecular weight gelators (LMWG), with their reversible and dynamic intermolecular interactions are achieving increasing prominence [10][11][12][13][14][15] . Work on switchable gels includes 2 systems involving photo-, pH, and redox based switching, ultrasound induced gelation, and switchable catalysis [16][17][18][19][20][21][22][23] . In order to systematically develop smart materials with controllable and well understood changes in bulk properties, an understanding of the intermolecular interactions in the system and the way in which they engage in hierarchical self-assembly in order to produce emergent morphologies with complex behavior is required. The link between even primary supramolecular interactions and bulk material properties is often unclear, however. Recent work has highlighted some simple approaches to controllable or smart materials that have met with considerable success. A key theme in particular is setting up a 'tipping point' in a system comprising competing intermolecular interactions which contribute to either gel assembly or gel dissolution. In this way a number of research groups have shown that anion binding in competition with urea self-assembly can be used to 'turn-down' and ultimately 'turn-off' gelation behavior 24,25 . Interestingly, in alternative systems, anion binding has also been used to induce gelation 26,27 . In a similar way metal coordination has also been used to tune gel properties 25 . In a series of bis(urea) gels we have shown how a combination of metal-and anion-binding can allow comprehensive control over the system. Competitive anion binding reduces gel strength by inhibiting urea -tape hydrogen-bond formation [28][29][30][31] .Conversely, metal coordination in pyridyl-urea compounds results in metal binding to the pyridyl group which suppresses the alternative, gel-inhibiting urea-pyridyl hydrogenbonding interaction, freeing the urea groups to form fibrils, and hence gels, as a result of the urea tape hydrogen-bonding motif [32][33][34] . These competitive interaction modes are summarised in Figure 1. 3

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“…One example is a dipyridyl bis(urea) compound, which incorporates one molecule of water per 6 molecules of host [28]. The water molecules are located in discrete cavities enclosed by host molecules.…”

Section: Single Crystal X-ray Structures Of Hydratesmentioning

confidence: 99%

X-ray and Neutron Diffraction in the Study of Organic Crystalline Hydrates

Fucke

Steed

2010

Water

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A review. Diffraction methods are a powerful tool to investigate the crystal structure of organic compounds in general and their hydrates in particular. The laboratory standard technique of single crystal X-ray diffraction gives information about the molecular conformation, packing and hydrogen bonding in the crystal structure, while powder X-ray diffraction on bulk material can trace hydration/dehydration processes and phase transitions under non-ambient conditions. Neutron diffraction is a valuable complementary technique to X-ray diffraction and gives highly accurate hydrogen atom positions due to the interaction of the radiation with the atomic nuclei.Although not yet often applied to organic hydrates, neutron single crystal and neutron powder diffraction give precise structural data on hydrogen bonding networks which will help explain why hydrates form in the first place.

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Helical or Polar Guest-Dependent Z‘ = 1.5 or Z‘ = 2 Forms of a Sterically Hindered Bis(urea) Clathrate

Abstract: A sterically hindered bis(pyridylurea) species forms clathrates with water, methanol, and ethanol, all exhibiting unusual polar structures with Z′ > 1. This crystal packing is due to the hindered geometry about the urea oxygen acceptor atoms.

Cited by 40 publications

References 19 publications

Crystal Structures of N-Aryl-N′-4-Nitrophenyl Ureas: Molecular Conformation and Weak Interactions Direct the Strong Hydrogen Bond Synthon

Crystal Structures of N-Aryl-N′-4-Nitrophenyl Ureas: Molecular Conformation and Weak Interactions Direct the Strong Hydrogen Bond Synthon

Halogen-bonding-triggered supramolecular gel formation

X-ray and Neutron Diffraction in the Study of Organic Crystalline Hydrates

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