Supramolecular Stabilization of α,ω-Diphenylpolyynes by Complexation to the Tridentate Lewis Acid [o-C6F4Hg]3

Abstract

The interaction of trimeric (perfluoro-o-phenylene)mercury ([o-C6F4Hg]3, 1) with α,ω-diphenylpolyynes containing 4, 6, 8, and 12 sp carbon atoms in CH2Cl2 leads to the formation of (1)2·Ph(C⋮C)2Ph (2), 1·Ph(C⋮C)3Ph (3), (1)2·Ph(C⋮C)4Ph (4), and (1)2·Ph(C⋮C)6Ph·CH2Cl2 (5). Adducts 2−4 have been characterized by elemental analysis, X-ray crystallography, infrared and fluorescence spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. In the solid state, the α,ω-diphenylpolyynes, which are approximately planar, are associated to molecules of 1 on either side of the molecular plane via secondary Hg−π interactions. The acetylenic stretches of 2−5 measured by IR spectroscopy are essentially identical with those of the free polyyne. While adducts 3−5 give rise to only faint emissions upon UV irradiation, the luminescence spectrum of 2 indicates complete quenching of the fluorescence and displays a heavy-atom-induced emission whose energy and vibronic progression are identical with those reported for the phosphorescence of the pure diyne. DSC/TGA studies indicate that adducts 2−4 are more thermally stable than the respective free α,ω-diphenylpolyynes. For Ph(C⋮C)4Ph, the stability range is increased by almost 120 °C under an oxidizing atmosphere. Similar conclusions are derived by monitoring the acetylenic stretches of Ph(C⋮C)4Ph and 4 as a function of temperature in KBr.