π-Complexation of Biphenyl, Naphthalene, and Triphenylene to Trimeric Perfluoro-ortho-phenylene Mercury. Formation of Extended Binary Stacks with Unusual Luminescent Properties

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Abstract
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 Å). In the dimer, the indivdual components are associated via long mercury−π interactions (3.443 < Hg···C < 3.650 Å). Interestingly, this arrangement leads to the existence of relatively short intermolecular mercury−mercury distances (3.811 < Hg···Hg < 4.093 Å). 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 π-interactions occur between the arene and the mercury centers of 1. The resulting Hg···C distances range from 3.25 to 3.55 Å and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto−π 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 Å). 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.