Experimental and theoretical studies of bis(perfluorovinyl)mercury, Hg(CF=CF2)2:: Synthesis, characterization, and structure in the gaseous and crystalline phases

The low-temperature reaction between 2 equiv of (perfluorovinyl)lithium, derived from CF3CH2F and butyllithium, and mercury(II) chloride results in high yields of Hg(CF=CF2)(2). Complete characterization of the air- and moisture-stable liquid product is afforded by multinuclear (C-13, F-19, Hg-199) NMR studies. Crystals of the compound [triclinic, P (1) over bar; a = 4.956(4), b = 5.733(4), c = 6.394(4) Angstrom; alpha = 104.57(5), beta = 109.32(6), gamma = 107.16(6)degrees; Z = 1] were obtained by slow cooling; an X-ray structural determination at 110 K represents the first such report for a (perfluorovinyl)metal complex. The mercury is coordinated linearly [r(Hg-C) = 1.998(5) Angstrom], and ct-stacking of the perfluorovinyl groups is observed. There is considerable variation in the C-F bond distances [1.286(6), 1.312(6), 1.362(6) Angstrom] within each perfluorovinyl group. Structural data for the vapor-phase species were obtained by analysis of the electron-diffraction pattern. There appears to be free rotation of the perfluorovinyl groups around the Ng-C bonds, a significantly longer mercury-carbon distance [2.054(3) Angstrom], and a similar, but smaller, variation in the C-F bond lengths. Theoretical optimization of the geometry at the MP2/DZP level predicts a shallow potential-energy minimum when the two perfluorovinyl groups are nearly perpendicular [Phi(C=C ... C=C) 98.2 degrees] to one another. Analysis of the bonding in the molecule suggests that no significant d(Hg) --> pi*(C=C) interaction is present.