Structure of decamethylferrocenium tribromide

Abstract

Fe{Cs(CH3)5}2)Br3, Mr=5658, ortho- rhombic, Cmcm, a = 15.162(5), b = 12.358 (5), c = 11-936 (5) A, V = 2236.4 A 3, Z = 4, Dx = 1.681 Mg m -a, A(Mo Ka) = 0.71069 A, /z = 5.985 mm-', F(000) = 1124, room temperature, final R = 0.040, wR = 0-044 for 856 reflections with I_ 2tr(/) and 86 variables. The solid is comprised of layers of alternating cations and anions, no signifi- cant interactions between the layers are observed. Introduction. Although a large number of ferrocene derivatives have been characterized by X-ray studies, only comparatively few compounds containing the ferrocenium ion have been investigated. Among these are ferrocenium triiodide (Bernstein & Herbstein, 1968), ferrocenium tetrachloroferrate (Paulus & Sch~ifer, 1978), 1,1'-dimethylferrocenium triiodide (Bats, de Boer & Bright, 1971) and a series of charge-transfer complexes containing the deca- methylferrocenium ion and spacious anions such as tetracyanoethenide (TCNE) and pentacyano- propenide (PCNP), which interact with the ferro- cenium moieties and give rise to interesting physical properties, for example, metamagnetism (Miller, Calabrese, Rommelmann, Chittipeddi, Zhang, Reiff & Epstein, 1987, and literature cited therein). Whereas the unsubstituted ferrocenium cations are mostly disordered, so that exact structural informa- tion on the cations cannot be obtained, substituted (e.g. decamethylferrocenium) cations do not seem to exhibit disorder. With this in view we have determined the crystal structure of the decamethyl- ferrocenium cation with a simple counterion, the Br3 anion. Experimental. The title compound was prepared by reaction of decamethylferrocene with Br2 in CC14 and recrystallized from methanol. Dark-green crystal plates, dimensions of crystal used for measurement 0.5 x 0.2 × 0-05 mm. Enraf-Nonius CAD-4 diffrac- tometer, graphite-crystal monochromator, Mo Ka radiation, unit-cell parameters determined from the angular settings of 25 reflections with 0.0 ___ 0 ___ 15 °. Intensity data for 1033 unique reflections up to 0 = 25 ° in the range O<_h_< 18, O_<k_< 14, 0<_l<_14 measured, using the oy-20-scan technique with a scan angle of 1.00 ° and a variable scan rate with a maxi- mum scan time of 60 s per reflection. Three check reflections measured at intervals of 200 reflections showed no significant intensity variation during the period of measurement. The data set was corrected for Lorentz and polarization effects, a Gaussian absorption correction procedure (Frenz, 1981) was used (Tmi, = 055, Tma x = 098). Systematic absences (hklwith h+k=2n+l; hOlwith h and l=2n+l;