Supramolecular Stabilization of α,ω-Diphenylpolyynes by Complexation to the Tridentate Lewis Acid [<i>o</i>-C<sub>6</sub>F<sub>4</sub>Hg]<sub>3</sub>

2006-04-24T00:00:00Z (GMT) by Thomas J. Taylor François P. Gabbaï
The interaction of trimeric (perfluoro-<i>o</i>-phenylene)mercury ([<i>o</i>-C<sub>6</sub>F<sub>4</sub>Hg]<sub>3</sub>, <b>1</b>) with α,ω-diphenylpolyynes containing 4, 6, 8, and 12 sp carbon atoms in CH<sub>2</sub>Cl<sub>2</sub> leads to the formation of (<b>1</b>)<sub>2</sub>·Ph(C⋮C)<sub>2</sub>Ph (<b>2</b>), <b>1</b>·Ph(C⋮C)<sub>3</sub>Ph (<b>3</b>), (<b>1</b>)<sub>2</sub>·Ph(C⋮C)<sub>4</sub>Ph (<b>4</b>), and (<b>1</b>)<sub>2</sub>·Ph(C⋮C)<sub>6</sub>Ph·CH<sub>2</sub>Cl<sub>2</sub> (<b>5</b>). Adducts <b>2</b>−<b>4 </b>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 <b>1</b> on either side of the molecular plane via secondary Hg−π interactions. The acetylenic stretches of <b>2</b>−<b>5</b> measured by IR spectroscopy are essentially identical with those of the free polyyne. While adducts <b>3</b>−<b>5</b> give rise to only faint emissions upon UV irradiation, the luminescence spectrum of <b>2</b> 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 <b>2</b>−<b>4</b> are more thermally stable than the respective free α,ω-diphenylpolyynes. For Ph(C⋮C)<sub>4</sub>Ph, 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)<sub>4</sub>Ph and <b>4 </b>as a function of temperature in KBr.