engleski

Single-Crystal-to-Single-Crystal Photodissociation of dimer of p-Bromonitrozobenzene

Nitrosobenzenes, with their tendency to dimerise in the solid state, present suitable model compounds for study of reaction mechanisms of solid state chemical reactions. Powdered dimeric compound can be converted to monomers by UV irradiation and reverted by visible light irradiation or by elevation of temperature [1]. This change is rather fast and can be followed by change of colour from white to green. On the other hand, material obtained by sublimation of the dimer is also composed of monomers but affords completely different behavior [2]. This different behaviour is evidently due to different phases of the monomer. In this work we determined the crystal structure of monomer phase obtained by irradiation od dimmer phase. Single crystal of the dimer was irradiated with unfiltered UV radiation in the stream of nitrogen at 100 K while it was still mounted on the diffractometar. During irradiation, the crystal was rotated at angular speed of approximately 5 o/s. The colour of the crystal changed from colourless to green upon transformation to monomeric phase. Both, dimer and monomer crystallize in monoclinic crystal system. Due to irradiation and cleavage of the N-N bond, the a axis of the monomeric phase is shortened to approximately half the length than in the dimer phase with no change in other parameters. Dimers crystallize in the space group P21/a while the space group of the monomeric phase is P21.

pretvorba jedinični-kristal-u-jedinični-kristal ; nitrozobenzeni ; fotodisocijacija

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