Crystal engineering in the gem-alkynol family: interplay between strong and weak interactions in structures of 2,3,5,6-tetrahalo

Structures of the title compounds are all mediated by strong cooperative arrangements of O-H.O hydrogen bonds, supported by a variety of weaker interactions which affect the type of O-H.O synthon that is formed. The tetrafluoro compound contains hexameric O-H.O synthons in a supramolecular chair conformation, together with C identical withC-H.F interactions. However, the tetrachloro and tetrabromo compounds both form tetrameric O-H.O synthons. This dominant pattern is supported by halogen.halogen interactions having one C-Cl[Br].Cl[Br] angle close to 180 degrees and the other close to 90 degrees, and by C identical withC-H.Cl[Br] interactions.

Crystal engineering in the gem-alkynol family; synthon repetitivity and topological similarity in diphenylethynylmethanols: structures that lack O-H.O hydrogen bonds

The structures of four para-substituted derivatives of diphenylethynylmethanol have been determined [ditolylethynylmethanol, di(4-chlorophenyl)ethynylmethanol, di(4-bromophenyl)ethynylmethanol and bis(4,4'-biphenylyl)ethynylmethanol]. The dimethyl, dichloro, dibromo and diphenyl compounds have been analysed using X-ray diffraction at 150 K, and the dichloro compound has also been studied using neutron diffraction at 150 K. In common with the parent diphenylethynylmethanol [Garcia, Ramos, Rodriguez & Fronczek (1995). Acta Cryst. C51, 2674-2676], all four derivatives fail to form the expected strong O-H.O hydrogen bonds due to steric hindrance. Instead, the supramolecular structural organization in this family of gem-alkynols is mediated by a variety of weaker interactions. The two most acidic protons, O-H and C[triple-bond]C-H, participate in weak hydrogen bonds to pi-acceptors, forming synthons that stabilize all five structures. These primary interactions are reinforced by a variety of other weak hydrogen bonds involving C-H donors and the hydroxy-O as an acceptor, and by halogen.halogen interactions in the dichloro and dibromo compounds.

Halogen trimer synthons in crystal engineering: low-temperature X-ray and neutron diffraction study of the 1:1 complex of 2,4, 6-tris(4-chlorophenoxy)-1,3,5-triazine with tribromobenzene

The title complex has been studied using low-temperature X-ray (150 K) and neutron (100 K) diffraction. Molecules of the triazine host form a two-dimensional hexagonal network mediated by trigonally symmetric Cl(3) synthons having Cl.Cl interactions of 3.441 (3) A, a C-Cl.Cl angle of 165 degrees and a Cl.Cl-C angle of 105 degrees, close to the ideal values of 180 and 90 degrees, respectively. The guest molecules are of an appropriate size to fit the hexagonal networks and interact with the host via C-H.pi (phenyl) and C-Br.pi (phenyl) interactions which stabilize the overall structure. Both C-donor bond vectors are directed more closely towards the mid-point (X) of an individual aromatic bond, rather than the ring centroid, with H.X 2.817 (9) A and C-H.X 174.0 (9) degrees, and Br.X 3.353 (4) A and C-Br.X 158.1 (2) degrees.

Benzyltriphenylphosphonium glutaconaldehyde

The title compound, C(25)H(22)P(+).C(5)H(5)O(2)(-), crystallizes in space group P2(1)/c. The phosphonium cations form zigzag chains with P.P distances of 6.475 (1) and 8.287 (2) A, and are related by inversion centres. Two types of attractive edge-to-face phenyl interactions exist, resulting in a dominant supramolecular motif. The glutaconaldehyde anions occupy the interchain spacing and hold adjacent chains together via multiple C-H.O hydrogen bonds. The bond-length alternation, a parameter which reveals the non-linear optical efficiency at the molecular level, is optimized in the chromophore anion.

A comparative study of the crystal structures of tetrahalogenated hydroquinones and gamma-hydroquinone.

gamma-Hydroquinone (1) and its tetrafluoro, tetrachloro and tetrabromo derivatives (2), (3) and (4) adopt crystal structures that have an almost invariant system of O-H.O hydrogen bonds. However, within this O-H.O framework, the four structures display variations that are characteristic of the C-H, C-F, C-Cl and C-Br groups. In the parent compound (1) aromatic rings are packed with a herringbone geometry, whilst in the halogenated derivatives (3) and (4), polarization-type halogen.halogen contacts are optimized. The fluoro derivative (2) is exceptional in that neither of the above possibilities is adopted, even though the O-H.O scaffolding does not per se prohibit either of them geometrically.