The Perfluoro‐o‐phenylene‐mercury Trimer [Hg(o‐C₆F₄)]₃ – a Textbook Example of Phase‐Dependent Structural Differences

Abstract

The geometric and electronic structure of [Hg(o‐C6F4)]3 (1) in the gas phase, i.e. free of intermolecular interactions, was deter­mined by a synchronous gas‐phase electron diffraction/mass spec­trometry experiment (GED/MS), complemented by quantum chemi­cal calculations. 1 is stable up to 498 K and the gas phase contains a single molecular form: the trimer [Hg(o‐C6F4)]3. It has a planar structure of D3h sym­metry with a Hg–C distance of 2.075(5) Å and a Hg–Hg distance of 3.614(7) Å (both rh1). Structural differences between the crystalline and gaseous state have been analyzed. Different DFT functio­nal‐basis combi­na­tions were tested, demon­stra­ting the importance to consider the relativistic effects of the mercury atoms. The combi­na­tion PBE0/­MWB(Hg),cc‐pVTZ(C,F) turned out to be the most appro­priate for the geometry optimization of such organomercurials. The elec­tronic structure of 1, the nature of the chemical bonding in C–Hg–C fragments and the nature of the Hg···Hg inter­actions have been analyzed in terms of the Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) approaches. The influence of the nature of halogen substi­tution on the structure of the molecules in the series [Hg(o‐C6H4)]3, [Hg(o‐C6F4)]3, [Hg(o‐C6Cl4)]3, [Hg(o‐C6Br4)]3 was also analyzed.