As long as product molecules of 2 are not yet aligned in their own crystal lattice, hut in the rebuilt lattice of 1, short-wavelength excitation can cause a photochemical reverse reaction. Only crystalline 2 photodimerizes exclusively to form the cyclobutane derivative [9].The lack of absorption of light at 2. = 365 nm by the crystalline product 2 prevents the formation of its [2 +2]-dimer. Irradiation of 1 (4 h) with light from a 150 W Hanau Hg high-pressure lamp passed through a Wertheimer UVW-55 bandpass filter (isolation of the 365nm light with 2.8% contribution from 334 nm light ( % transmission <1 at 315 nm and at 410 nm)) in a powder cuvette leads to a considerable shift of the diffuse reflectance spectrum to curve bin Figure I. whereas the broad-band irradiation (>. > 300 nm) ofcrystalline 2 produces a decrease in the long-wavelength absorption and an increase in a band of the photodimer 191 at 266 nm.
Fixed in the SiO2 cage at temperatures below 485 K, the [CoCp2]+ ion in the cobaltocenium fluoride nonasil 1 exhibits no rotational disorder. This unusual structural feature for clathrasils is attributed to strong CH…︁OSi interactions, among them hydrogen bonds with a H…︁O distance of 2.31 Å.
5] Anderslautende Angaben bei der [2+2]-Photodimerisierung von a-Zimtsiure 131 konnten von uns nicht reproduziert werden: G. Kaupp, M. Haak, Vortrag auf der Incom'96, Diisseldorf, 26. Marz 1996; hieruber wird in Kurze ausfiihrlich berichtet werden. [6] P 2 J c ; a = 6.241, b = 12.303, c = 12.113 A, B = 95-75", Z = 4, V = 934 A', pbe.. = 2.239 g~m -~, 1659 geniessene Reflexe, davon 1324 beobdchtet rnit F > 4.0 e(0, R = 0.0428, R, = 0.0719. Die kristallographischen Daten (ohne Strukturfaktoren) der in dieser Veroffentlichung beschriebenen Struktur wurden als ,,supplementary publication no. CCDC-179-119" beim Cambridge Crystallographic Data Centre hinterlegt. Kopien der Daten konnen kostenlos bei folgender Adresse angefordert werden: The Director, CCDC. 12 Union Road, GB-Cambridge CB2 1 EZ (Telefax: Int. + 1223/336-033;
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