Can Weakly Coordinating Anions Stabilize Mercury in Its Oxidation State +IV?

Authors

  • Sebastian Riedel Dipl.-Chem.,

    1. Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany, Fax: (+49) 931-888-7135
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  • Michal Straka Dr.,

    1. Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany, Fax: (+49) 931-888-7135
    2. Present address: Department of Chemistry, P.O. Box 55 (A.I. Virtasen aukio 1), University of Helsinki, 00014, Helsinki, Finland
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  • Martin Kaupp Prof. Dr.

    1. Universität Würzburg, Institut für Anorganische Chemie, Am Hubland, 97074 Würzburg, Germany, Fax: (+49) 931-888-7135
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Abstract

While the thermochemical stability of gas-phase HgF4 against F2 elimination was predicted by accurate quantum chemical calculations more than a decade ago, experimental verification of “truly transition-metal” mercury(IV) chemistry is still lacking. This work uses detailed density functional calculations to explore alternative species that might provide access to condensed-phase HgIV chemistry. The structures and thermochemical stabilities of complexes HgIVX4 and HgIVF2X2 (X=AlF4, Al2F7, AsF6, SbF6, As2F11, Sb2F11, OSeF5, OTeF5) have been assessed and are compared with each other, with smaller gas-phase HgX4 complexes, and with known related noble gas compounds. Most species eliminate F2 exothermically, with energies ranging from only about −60 kJ mol−1 to appreciable −180 kJ mol−1. The lower stability of these species compared to gas-phase HgF4 is due to relatively high coordination numbers of six in the resulting HgII complexes that stabilize the elimination products. Complexes with AsF6 ligands appear more promising than their SbF6 analogues, due to differential aggregation effects in the HgII and HgIV states. HgF2X2 complexes with X=OSeF5 or OTeF5 exhibit endothermic fluorine elimination and relatively weak interactions in the HgII products. However, elimination of the peroxidic (OEF5)2 coupling products of these ligands provides an alternative exothermic elimination pathway with energies between −120 and −130 kJ mol−1. While all of the complexes investigated here thus have one exothermic decomposition channel, there is indirect evidence that the reactions should exhibit nonnegligible activation barriers. A number of possible synthetic pathways towards the most interesting condensed-phase HgIV target complexes are proposed.

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