Dimers In Solid State Research Articles

Effect of fluoro substitution on the packing motifs of benzylidene- and dibenzylidene-cyclopentanones

The structure and solid-state reactivity of one fluorinated benzyl(benzylidene)cyclopentanone and two fluorinated dibenzylidenecyclopentanones are reported and the influence of fluoro substitution upon the packing of benzylidenecyclopentanones is discussed. It was shown that intermolecular atom–atom interactions involving the fluoro groups hold sway over the effect of the volume of the substituents upon crystal packing. As a result, the two dibenzylidene compounds have packing motifs very different from that of the unsubstituted parent compound, and thus a different solid-state reactivity pattern. Both the fluorinated dibenzylidene compounds undergo topochemical solid-state dimerisation, whereas the fluorobenzylidene compound was found to be photostable.

A vibrational study of tautomerism and associations of 2-mercaptoimidazole and 2-mercaptothiazole

Infrared and Raman spectra of 2-mercaptoimidazole and 2-mercaptothiazole in solid state as well as i.r. spectra of 2-mercaptothiazole in HCCl3 and CS2 0.05M solutions have been investigated. A general assignment of all the observed bands is proposed for both fundamental vibrations and for overtone and combination bands. For 2-mercaptothiazole, the thiocarbonyl-form, intermolecularly hydrogen-bonded dimers in solid state, and unassociated molecules in dilute solutions of inert solvents have been established. Finally, based on this data, thermodynamic functions have been computed.

Solid state dimerisation of β-nitrostyrene: a disordered photoreactive crystal

The unusual solid state dimerisation of β-nitrostyrene to yield two isomeric cyclobutanes is accounted for by its disordered, photoreactive crystal structure which permits a trans→cis isomerisation.

Viscosity and temperature effects in excited state double proton transfer: Luminescence of 1-azacarbazole dimers in solid state and solution

Luminescence properties of 1-azacarbazole (1AC) dimers in solution and solid state 1AC powders and films were investigated and compared. Fluorescence of tautomeric species, generated in the excited state after a double proton transfer, is quenched by the increase of solution viscosity. On the contrary, this emission exists in solid 1AC, even at 1.5 K. The results strongly suggest that the main portion of activation energy of tautomerization is used for twisting of 1AC moieties. Once the coplanar arrangement of all atoms taking part in proton transfer is achieved (as is the case already in the ground state of solid 1AC) the energy barrier for the reaction becomes very small, although non-zero.

Solid State Dimerization of a Styryl Disperse Dye

During an investigation into structure‐property relationships of a series of ethyl‐α‐cyano‐4‐aminocinnamate disperse dyes, the 4‐(N‐β‐cyanoethyl‐N‐β‐acetoxyethyl) amino derivative showed anomalous behaviour on attempts to purify it. This compound was shown to be susceptible to dimerization to a colourless cyclobutane derivative, the structure of which was established by nmr spectroscopy. The dimerization is interpreted in terms of ‘Topochemical’ factors. Typical nmr spectra characteristics of some monomeric styryl disperse dyes are also indicated.