Crystal Engineering - Structural Chemistry Group

With alkoxy groups

The crystal structures of E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,5-dimethoxybenzene, E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,5-diisopropoxybenzene, E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,5-dihexoxybenzene and E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,5-bis(2-phenylethoxy)benzene have been determined. A weak intramolecular hydrogen bond between protons on the olefinic link and the ortho-methoxy groups on the adjacent benzene rings has been commented on. In general, however, the crystal packing for these structures is primarily determined by weak methoxy-pi interactions. Their numbers change with the structure and length of the side chains and with the accommodation of the extended chains in the lattice. A discussion on the effects of these interactions on the possibility of lattice formation explains why these four compounds crystallize and several similar ones with different alkoxy side chains do not.

Vande Velde, C.M.L.; Chen, L.J.; Baeke, J.K.; Moens, M.; Dieltiens, P.; Geise, H.J.; Zeller, M.; Hunter, A.D.; Blockhuys, F. Cryst. Growth Des. 2004, 4, 823-830.

In (E,E)-2,5-dimethoxy-1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene molecular symmetry is coincident with crystallographic inversion symmetry. A three-dimensional network is generated containing both CH...pi and CH...O interactions. A comparison of the geometry of this molecule and the structure of a number of 2,4,6-trimethoxy-substituted analogues is provided.

Vande Velde, C.M.L.; Geise, H.J.; Blockhuys, F. Acta Cryst. C 2005, 61, o21-o24.

(E,E)-2,5-Dipropoxy-1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene crystallizes with one-half of a molecule in the asymmetric unit. A three-dimensional network is generated by methoxy-pi and CH...pi interactions. The conformation of the C-C bond exocyclic to the central benzene ring is different from that of every other known derivative. A comparison of the geometry of (E,E)-2,5-dipropoxy-1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene with other 2,4,6-trimethoxy-substituted PPV oligomers, in particular the isopropoxy-substituted compound, is provided.

Vande Velde, C.M.L.; Baeke, J.K.; Geise, H.J.; Blockhuys, F. Acta Cryst. C 2005, 61, o284-o287.

E,E-1,4-Bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,3,5,6-tetramethoxybenzene forms a packing that consists of an intricate network of both CH...O hydrogen bonds and  methoxy-pi interactions. The packing schemes of all known methoxy-substituted distyrylbenzenes are compared and explained on the basis of the observations made made on E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,3,5,6-tetramethoxybenzene. In general, intramolecular CH...O contacts are greatly preferred over intermolecular ones. Intermolecular CH...O contacts are more common than intermolecular methoxy-pi interactions. The latter are adopted only when the number of free methoxy groups, not involved in intramolecular CH...O contacts, is small enough.

Vande Velde, C.M.L.; Geise, H.J.; Blockhuys, F. Cryst. Growth Des. 2006, 6, 241-246.

With fluorine atoms

Three derivatives of E,E-1,4-bis[2-(2,3,4,5,6-pentafluorophenyl)ethenyl]benzene, two of which bear nitrogen atoms in the ethenyl spacers, while in a third the central benzene ring is replaced by a pyrazine moiety, have been synthesized. The supramolecular structures of the resulting set of four compounds have been studied using single-crystal X-ray diffraction to gauge the influence of the position of the nitrogen atoms on the organisation of the molecules in the solid state. The crystal packing patterns were analyzed in terms of intermolecular interactions involving the fluorine and nitrogen atoms, i.e., CH...F, F...F, F...pi and CH...N interactions. The analysis shows that in two of the three solid-state structures the main effect of the nitrogen atoms in an indirect one: they do not participate in intermolecular contacts themselves, but activate nearby hydrogen atoms and phenyl rings in fluorine synthons to form new interactions.

Collas, A.; De Borger, R.; Amanova, T.; Blockhuys, F. CrystEngComm 2011, 13, 702-710.

With methoxy groups

Four new methoxy-substituted derivatives of E,E-2,5-bis(2-phenylethenyl)pyrazine have been synthesized. The supramolecular structures of the resulting set of five polymorphs have been studied using single-crystal X-ray diffraction to gauge the influence of the position of the methoxy groups on the organization of the molecules in the solid state, as part of an attempt to dispense with the particular polymorphism of the parent compound. The crystal packing patterns were analyzed in terms of the two pyrazine-based synthons found in the parent compound's crystal structure, the pi(pyrazine)...pi(phenyl) stacking synthon, and the pyrazine hydrogen-bonded synthon, as well as in terms of weak intermolecular interactions such as CH...O, CH...N, and CH...pi. The analysis shows that the introduction of methoxy groups in positions other than only the para position of the peripheral benzene rings successfully switches off the two synthons seen in the parent compound and that the new compounds adopt other packing strategies, based on methoxy...methoxy and –OCH3...pi contacts. Polymorphism, however, remains.

Collas, A.; Bagrowska, I.; Aleksandrzak, K.; Zeller, M.; Blockhuys, F. Cryst. Growth Des. 2011, 11, 1299-1309.

With fluorine atomsThree derivatives of E,E-1,4-bis[2-(2,3,4,5,6-pentafluorophenyl)ethenyl]benzene, two of which bear nitrogen atoms in the ethenyl spacers, while in a third the central benzene ring is replaced by a pyrazine moiety, have been synthesized. The supramolecular structures of the resulting set of four compounds have been studied using single-crystal X-ray diffraction to gauge the influence of the position of the nitrogen atoms on the organisation of the molecules in the solid state. The crystal packing patterns were analyzed in terms of intermolecular interactions involving the fluorine and nitrogen atoms, i.e., CH...F, F...F, F...pi and CH...N interactions. The analysis shows that in two of the three solid-state structures the main effect of the nitrogen atoms in an indirect one: they do not participate in intermolecular contacts themselves, but activate nearby hydrogen atoms and phenyl rings in fluorine synthons to form new interactions.

Collas, A.; De Borger, R.; Amanova, T.; Blockhuys, F. CrystEngComm 2011, 13, 702-710.

With fluorine atomsThree derivatives of E,E-1,4-bis[2-(2,3,4,5,6-pentafluorophenyl)ethenyl]benzene, two of which bear nitrogen atoms in the ethenyl spacers, while in a third the central benzene ring is replaced by a pyrazine moiety, have been synthesized. The supramolecular structures of the resulting set of four compounds have been studied using single-crystal X-ray diffraction to gauge the influence of the position of the nitrogen atoms on the organisation of the molecules in the solid state. The crystal packing patterns were analyzed in terms of intermolecular interactions involving the fluorine and nitrogen atoms, i.e., CH...F, F...F, F...pi and CH...N interactions. The analysis shows that in two of the three solid-state structures the main effect of the nitrogen atoms in an indirect one: they do not participate in intermolecular contacts themselves, but activate nearby hydrogen atoms and phenyl rings in fluorine synthons to form new interactions.

Collas, A.; De Borger, R.; Amanova, T.; Blockhuys, F. CrystEngComm 2011, 13, 702-710.

With nitro groups

Two polymorphs of (E,E)-N,N'-bis(4-nitrobenzylidene)benzene-1,4-diamine have been identified. In each case, the molecules lies across a crystallographic inversion centre. the supramolecular structure of the first polymorph features stacking based on pi...pi interactions assisted by weak hydrogen bonds involving the nitro groups. The second polymorph displays a perpendicular arrangement of molecules linked via the nitro groups, combined with weak CH...O hydrogen bonds. Both crystal structures are compared with that of the carbon analogue (E,E)-1,4-bis[(4-nitrophenyl)ethenyl]benzene.

Collas, A.; Zeller, M.; Blockhuys, F. Acta Cryst. C 2011, 67, o171-o174.

With methoxy groups

The solid-state structures of three push-pull acceptor-pi-donor (A-pi-D) systems differing only in the nature of the pi-spacer have been determined. (E)-1-nitro-4-[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene and its 'bridge-flipped' imine analogues, (E)-3,4,5-trimethoxy-N-(4-nitrobenzylidene)aniline and (E)-4-nitro-N-(3,4,5-trimethoxybenzylidene)aniline, display different kinds of supramolecular networks, viz. corrugated planes, a herringbone pattern and a layered structure, respectively, all with zero overall dipole moments. Only the latter crystallizes in a noncentrosymmetric space group and is, therefore, a potential material for second-harmonic generation (SHG).

Collas, A.; Blockhuys, F. Acta Cryst. C 2011, 67, o364-o369.