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

Trimeric perfluoro-ortho-phenylene mercury (1) crystallizes from CS2 as a pure compound. In the crystal, 1 forms staggered cofacial dimers (centroid distance of 3.38 Angstrom). In the dimer, the indivdual components are associated via long mercury-pi interactions (3.443 < Hg...C < 3.650 Angstrom). Interestingly, this arrangement leads to the existence of relatively short intermolecular mercury-mercury distances (3.811 < Hg...Hg < 4.093 Angstrom). In this form, compound I 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 Angstrom 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 Angstrom). 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.