X-ray structure and crystal packing analysis of triphenylbromomethane, C₁₉H₁₅Br

Charge Density of Intra‐ and Intermolecular Halogen Contacts

“…In principle, triphenylbromomethane 12 could be an even more attractive prototypic compound for a charge density analysis of short interhalogen contacts than its congener 11 because in general more attractive forces between neighboring halogen atoms can be expected for the heavier elements. This hypothesis is corroborated by the classical structure reports at room temperature according to which the shortest Cl ··· Cl in 11 3 and Br ··· Br in 12 4 both amount to 3.2 Å, despite the larger van‐der‐Waals radius for Br. We have been able to prepare suitable crystals of 12 , but our attempts to collect diffraction data at low temperatures showed that the compound undergoes a phase transition around 150 K and therefore is not suitable for an experimental charge density study based on high resolution X‐ray diffraction.…”

“…A few years later, Landais published his results on triphenylbromomethane, in which the molecules „..paraissent s'associer par paires, car les atomes de brome sont distants de 3, 3 Å seulement.” (…the molecules seem to be associated in pairs, because the distance between Br atoms is 3.3 Å only) 2. In their more recent publications concerning the triphenylhalogenmethane structures,3,4 Dunand and Gerdil even addressed the short X···X contacts in the abstracts of their articles. As early as 1963, Sakurai et al5 suggested that short intermolecular distances Cl ··· Cl might be classified into two different groups later called “type I” and “type II” interactions 6.…”

“…In Scheme , mononuclear compounds with peripheric halides have been compiled; complexes 8 and 9 feature short intermolecular X ··· X distances, and compound 10 has been included for comparison. With respect to intermolecular contacts, we also address the “classical“ organic molecules 11 and 12 already investigated by Landais ,2 Dunand and Gerdil 3,4 and later by Kahr and Carter 18. Charge density results from the recent literature which deal with short interhalogen contacts will be covered in our discussion, too.…”

Halogen bonds in some dihalogenated phenols: applications to crystal engineering

“…Being positioned between these two extremes, Br is more difficult to interpret and understand. The slightly shorter BrÁ Á ÁBr contact (3.203 Å ) in triphenylbromomethane (Dunand & Gerdil, 1984) when compared with the corresponding ClÁ Á ÁCl contact (3.21 Å ) in the isomorphous triphenylchloromethane (Dunand & Gerdil, 1982) indicates that BrÁ Á ÁBr is stronger than ClÁ Á ÁCl and that Br is more polarizable than Cl. Ample evidence of type II BrÁ Á ÁBr synthons, say Br 3 synthons, in crystal engineering also confirms the polarizable nature of Br (Bosch & Barnes, 2002).…”

Molecules isoelectronic with triphenylmethanol: diphenyl(4-pyridyl)methanol and triphenylmethylamine

“…Other close analogues which have been structurally characterized include Ph3CC1 (Dunand & Gerdil, 1982) and PhaCBr (Dunand & Gerdil, 1984), in which the molecules are stacked in a head-to-head arrangement along crystallographic threefold axes, with X...X (X = C1, Br) distances being significantly shorter than the sum of van der Waals radii. Ph 3 CF has been characterized in a mixed crystal with phenyltropylium tetrafluoroborate (Takusagawa, Jacobson, Trahanovsky & Robbins, 1976).…”