| 1. |
- George, Sumod, et al.
(author)
-
Crystal engineering of neutral N-arylpyrimidinones and their HCl and HNO3 adducts with a C-HO supramolecular synton : Implications for non-linear optics
- 2001
-
In: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 25:12, s. 1520-1527
-
Journal article (peer-reviewed)abstract
- In a previous crystallographic study of some N-arylpyrimidinones 1, we noted that: (1) C-HO hydrogen bonds connect molecules in a linear array; (2) the charge transfer axis of the chromophore is aligned with the main symmetry operator of point groups 2 or m at ca. 57°, a value that is close to the ideal angle of 54.74°; (3) the methyl and chloro derivatives are isostructural. In this paper, we report the characterisation of chloride and nitrate salt adducts of 1 by X-ray diffraction and the analysis of their packing motifs. Recurrence of the same C-HO supramolecular synthon in three neutral and five HCl and HNO3 adducts of 1 signifies the robustness of this weak hydrogen bond. The occurrence of a mirror plane m in a family of eight crystal structures (four Pnma, two P21/m, one Pbcm, and one Pmn21) is unusual because this symmetry operation is generally avoided due to close packing considerations. Ab initio calculations show that the bisected phenyl conformation present in these crystal structures is the most stable conformation of the pyrimidinone molecule. The presence of aryl and pyrimidinone chromophores in 1, the correct alignment of the aromatic ring in the crystal and the occurrence of 2D polar layers in some crystal structures are favourable factors for non-linear optical applications. However, a strategy for the crystallisation of these achiral molecules in non-centrosymmetric space groups is yet to be achieved. This crystal engineering study simplifies the challenge of complete 3D structural control into a modular 2D+1D problem
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- George, Sumod, et al.
(author)
-
N-(3-Pyridyl)urea
- 2001
-
In: Acta Crystallographica Section E. - 1600-5368. ; 57:8, s. o719-o720
-
Journal article (peer-reviewed)abstract
- The crystal structure of the title compound, C6H7N3O, exhibits packing typical of amides, with N-HO hydrogen-bond dimers forming a corrugated tape and N-HN bonds connecting the tapes
|
|
| 5. |
- George, Sumod, et al.
(author)
-
N-(4-Biphenylyl)urea
- 2001
-
In: Acta Crystallographica Section C. - 0108-2701 .- 1600-5759. ; 57:6, s. 777-778
-
Journal article (peer-reviewed)
|
|
| 6. |
- George, Sumod, et al.
(author)
-
N,N'-Bis(4-biphenylyl)urea
- 2003
-
In: Acta Crystallographica Section E. - 1600-5368. ; 59:6, s. o901-o902
-
Journal article (other academic/artistic)abstract
- The crystal structure of the title compound, C25H20N2O, has the N-HO α-network typical of diaryl ureas.
|
|
| 7. |
- Muthuraman, Meiyappan, et al.
(author)
-
C-H···O and C-H···N Hydrogen Bond Networks in the Crystal Structures of Some 1,2-Dihydro-N-aryl-4,6-dimethylpyrimidin-2-ones
- 2000
-
In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 152:1, s. 221-228
-
Journal article (peer-reviewed)abstract
- A set of three aryl dimethyl pyrimidinones have been studied and their crystal structures described in terms of networks of C-HO and C-HN hydrogen bonds. Two of the three molecules in this study differ in the replacement of a chloro group by a methyl group and obey the chloro-methyl exchange rule in that they have nearly identical crystal structures. However, and in contrast to other pairs of compounds so related, the chloro and methyl groups here are not merely isosteric but also form similar polarization-induced ClPh and CH3Ph contacts. These conjugated molecules may offer some scope for nonlinear optical studies.
|
|
| 8. |
- Reddy, L. Sreenivas, et al.
(author)
-
Crystal Structures of N-Aryl-N′-4-Nitrophenyl Ureas : Molecular Conformation and Weak Interactions Direct the Strong Hydrogen Bond Synthon
- 2007
-
In: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 7:12, s. 2675-2690
-
Journal article (peer-reviewed)abstract
- 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, CONH2, COCH3, OH, Me). These structures are classified into two families depending on the hydrogen bond pattern: urea tape structures contain the well-known α-network assembled via N-HO hydrogen bonds; however, in nonurea tape structures the N-H donors hydrogen bond with NO2 groups or solvent O acceptor atoms. Surprisingly, the urea CO hardly accepts strong H bonds in nonurea type structures sustained by ureanitro and ureasolvent synthons. The carbonyl group accepts intra- and intermolecular C-HO 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-HO tape structure, the dominant pattern in electron-withdrawing aryl urea crystal structures is the ureanitro/ureasolvent synthon and persistence of intramolecular C-HO interactions. Remarkably, the presence of functional groups that can promote specific C-IO or C-HO interactions with the interfering NO2 group, for example, when X = I, C≡CH, NMe2, and Me, steers crystallization toward the N-HO 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 CO 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.
|
|
