In search of the elusive amalgam SrHg8: a mercury-rich intermetallic compound with augmented pentagonal prisms

Abstract

In confirmation of its predicted existence in the Sr–Hg phase diagram, the mercury-rich intermetallic compound SrHg₈ has been prepared by reaction of the elements at 200 °C. Single-crystal X-ray diffraction analysis revealed that it adopts a new structure type (Pearson symbol oP72, space group Pnma, a = 13.328(1) Å, b = 4.9128(5) Å, c = 26.446(3) Å). The Sr atoms are centred within two types of 18-vertex Hg polyhedra formed by augmenting pentagonal prisms with octagonal waists. The condensation of these Sr@Hg₁₈ clusters is associated with the formation of a complex anionic Hg–Hg bonding network, as supported by electronic structure calculations which reveal strong mixing of Hg 6s and 6p states in highly delocalized bands superimposed with a narrower 5d band below the Fermi level.