Perchlorophenalenyl radical, C13Cl9: a modulated structure with nine threefold-symmetric molecules in the asymmetric unit

Citation
Pa. Koutentis et al., Perchlorophenalenyl radical, C13Cl9: a modulated structure with nine threefold-symmetric molecules in the asymmetric unit, ACT CRYST B, 57, 2001, pp. 680-691
Citations number
36
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE
ISSN journal
0108-7681 → ACNP
Volume
57
Year of publication
2001
Part
5
Pages
680 - 691
Database
ISI
SICI code
0108-7681(200110)57:<680:PRCAMS>2.0.ZU;2-X
Abstract
The odd-alternant perchlorophenalenyl radical, C13Cl9, forms molecular stac ks centered on crystallographic threefold rotation axes, but the spacing wi thin the stacks (3.78 Angstrom) is too large to allow good overlap of the o rbitals in which the spin density is localized. The radical is ruffled beca use of the intramolecular repulsions between alpha Cl atoms (the Cl . . . C l peri interactions); the average displacement of an alpha Cl atom from the molecular plane is similar to0.7 Angstrom. The deviations from molecular p lanarity do not, however, determine the spacing within the stacks, which is determined instead by interactions between stacks. The modulations found i n the P3c1 super-structure are a response to the short interstack contacts that would occur in the average pseudocell structure (R (3) over barm, c' = c/6). The primary modulation is a pattern of enantiomeric alternation; a s econdary modulation involves small rotations of the molecules around their threefold axes. The number (9) of independent molecules in the true cell is exceptionally large because of the conflict between the preference within the molecular stacks for threefold rotational symmetry and the preference i n directions perpendicular to the stack axes for twofold alternation of ena ntiomers. The structural complexity reduces the precision of the distances and angles determined, but the average values found are in excellent agreem ent with those calculated by density functional theory.