Naslov
Solid-State Reaction Mechanisms in Monomer-Dimer Interconversions of p- Bromonitrosobenzene. Single-Crystal-to- Single-Crystal Photodissociation and Formation of New Non-van der Waals Close Contact

Autori
Halasz, Ivan ; Meštrović, Ernest ; Čičak, Helena ; Mihalić, Zlatko ; Vančik, Hrvoj

Izvornik
Journal of Organic Chemistry (0022-3263) 70 (2005), 21; 8461-8467

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Solid state reaction mechanism; Non-covalent close contacts; close contacts

Sažetak
Thermal and photochemical reactions and the phase transition mechanisms of solid-state monomer-dimer interconversions of p-bromonitrosobenzene were studied on the basis of kinetics data and single-crystal-to-single-crystal transformations. From the crystal structure and packing of p- bromobenzeneazodioxide, and the previously determined structure of the freshly sublimed monomer, we have explained both consecutive steps in thermal dimerization. While the first reaction (formation of the metastable dimer) with first-order kinetics affords diminishing of the (2 2 0) critical crystal plane that intersects atoms of the nitroso groups, the second phase transformation step includes four critical planes, which show sigmoid kinetics. In the new phase growth, these crystal planes developed in two (Cartesian) dimensions as vectors perpendicular to ab and ac planes, which is in agreement with the dimensionality previously determined on the basis of the Avrami-Erofeyev analysis (with m = 2.01). Photochromic dissociation of the azodioxide at 100 K was followed by structure determination of the single-crystal-to-single crystal transformation. A new metastable monomer was discovered, in which, in spite of bond breaking, the nitrogen atoms of the neighboring monomers remained very close to each other (2.30 ?), i.e., by 23.3% closer than is the sum of two N-atom van der Waals radii. Such an extraordinary close contact was also observed between N and O atoms. This tight packing can explain why the return to dimerization after the low temperature photodissociation occurs so rapidly at a temperature as low as 170 K.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

POVEZANOST RADA