Pi-complexation of biphenyl, naphthalene, and triphenylene to trimeric perfluoro-ortho-phenylene mercury. Formation of extended binary stacks with unusual luminescent properties.

Abstract

Trimeric perfluoro-ortho-phenylene mercury (1) crystallizes from CS(2) as a pure compound. In the crystal, 1 forms staggered cofacial dimers (centroid distance of 3.38 A). In the dimer, the individual components are associated via long mercury-pi interactions (3.443 < Hg...C < 3.650 A). Interestingly, this arrangement leads to the existence of relatively short intermolecular mercury-mercury distances (3.811 < Hg...Hg < 4.093 A). In this form, compound 1 is photoluminescent and exhibits a broad emission band with a maximum at 440 nm and a shoulder at 530 nm. Compound 1 interacts with biphenyl, naphthalene, or triphenylene to form 1.biphenyl (2), 1.naphthalene (3), and 1.triphenylene (4), respectively. These adducts have been characterized by elemental analysis and X-ray crystallography. Their structure reveals the existence of stacks in which molecules of 1 and molecules of arenes alternate. In each stack, secondary pi-interactions occur between the arene and the mercury centers of 1. The resulting Hg...C distances range from 3.25 to 3.55 A and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto-pi interactions occurring between the electron-rich aromatic molecules and the acidic mercury centers. In the case of the triphenylene adduct 4, a arene-fluoroarene interaction is also observed (centroid distance of 3.605 A). Compounds 2-4 are photoluminescent. The emission observed for 2 and 3 corresponds to the phosphorescence of the aromatic substrate and suggests the occurrence of a mercury heavy atom effect. In the case of 4, the emission appears at longer wavelengths than those typically observed for triphenylene.