Pure heterometallic spodium bonding†

In the structures of (C₆F₅)₂Hg·M(acac)₂ (M = Pt, Pd; acacH = acetylacetone), infinite stacks of alternating crisscrossing coformers are held by the pure Hg^II⋯d_z²-[M^II] spodium bond (11–15 kcal mol⁻¹) occurring between the electrophilic mercury(II) ion and d-nucleophilic [M^II] sites of the positively charged Pt^II and Pd^II ions. X-ray diffraction studies reveal short Hg⋯M contacts (3.1051(1) Å for M = Pt; 3.1033(3) Å for M = Pd) significantly less than the sum of their van der Waals radii. Detailed density functional theory calculations, including QTAIM, NBO, and SAPT analyses, demonstrate the multifaceted nature of these interactions. The spodium bonds exhibit predominantly electrostatic character, with significant contributions from dispersion forces and orbital interactions. The Pt^II complex shows slightly stronger interactions compared to its Pd^II counterpart due to the more pronounced d_z²-orbital of platinum. These pure heterometallic spodium bonds, unaffected by other noncovalent interactions, provide valuable insights for theoretical studies on spodium bonding.