Spodium bonding to anticrown-Hg3 boosts phosphorescence of cyclometalated-PtII complexes

Abstract

The moderately phosphorescent platinum(II) complexes [Pt(ppy)(acac)] (1; ppyH = 2-phenylpyridine, acacH = acetylacetone), [Pt(ppy)(hd)] (2; hdH = heptanedione-3,5), [Pt(ppy)(tmhd)] (3; tmhdH = 2,2,6,6-tetramethylheptanedione-3,5), [Pt(dfppy)(acac)] (4; dfppyH = 2-(2′,4′-difluorophenyl)pyridine), and [Pt(dfppy)(tmhd)] (5) were precipitated on cocrystallization with anticrown Hg₃(1,2-C₆F₄)₃ (Hg₃) to give Hg^II–Pt^II stacked heteroplanar architectures (1–3)·Hg₃ and (4–5)·Hg₃·Me₂CO. Synchrotron X-ray diffraction studies of these cocrystals along with in-depth theoretical density functional theory (DFT; PBE0-D3BJ) calculations, employing a set of computational tools (QTAIM, ELF, IGMH, MEP, CDF, ETS-NOCV, and SAPT methods), allowed the recognition of the spodium bonds Hg⋯Pt and Hg⋯C (the former is significantly stronger than the latter) as the stacking-directing contacts. The major part (57%) of the total interaction energy between 3 and Hg₃ (−32.9 kcal mol⁻¹), as a model system, comes from Hg⋯Pt bonding. Heteroplanar stacking is mostly controlled by dispersion and electrostatic forces, but the d_z²(Pt) → σ*(Hg–C) charge transfer also provides a noticeable contribution; Hg^II functions as an electrophilic component of the Hg⋯Pt and Hg⋯C contacts. The spodium bond-driven supramolecular integration provides enhanced phosphorescence lifetimes and up to 6-fold solid-state quantum yield enhancement for all cocrystals compared to the parent Pt^II species. Appropriate DFT studies along with the analysis of calculated radiative and nonradiative decay rate constants indicate that the heteroplanar stacking reduces the population of the ³MC state, thus increasing the quantum yield.