Syntheses, Structures, and Sensitized Lanthanide Luminescence by Pt → Ln (Ln = Eu, Nd, Yb) Energy Transfer for Heteronuclear PtLn₂ and Pt₂Ln₄ Complexes with a Terpyridyl-Functionalized Alkynyl Ligand

Reaction of Pt(dppm-P,P‘)Cl2 (dppm = 1,2-bis(diphenylphosphino)methane) with HC⋮CPhtpy (HC⋮CPhtpy = 4‘-(4-ethynylphenyl)-2,2‘:6‘,2‘ ‘-terpyridine) in the presence of copper(I) iodide and diisopropylamine induced isolation of mononuclear complex cis-Pt(dppm-P,P‘)(C⋮CPhtpy)2 (1), which can be converted into face-to-face diplatinum(II) species Pt2(μ-dppm)2(C⋮CPhtpy)4 (5) when equivalent dppm is added. Incorporating 1 or 5 to Ln(hfac)3(H2O)2 (Hhfac = hexafluoroacetylacetone) gave PtLn2 (Ln = Nd (2), Eu (3), Yb (4)) or Pt2Ln4 (Ln = Nd (6), Eu (7), Gd (8), Yb (9)) adducts with the lanthanide centers chelated by terdentate terpyridyl in the bridging C⋮CPhtpy. The structures of 1, 6, 7, and 9 were determined by X-ray crystallography. Upon excitation at λex = 360−450 nm (2−4) or 360−500 nm (6−9), where the PtII alkynyl antenna chromophores absorb strongly but the model complexes Ln(hfac)3(HC⋮CPhtpy) lack obvious absorption in this region, these PtLn2 and Pt2Ln4 (Ln = Nd, Eu, Yb) species exhibit bandlike lanthanide luminescence that is typical of the corresponding Ln3+ ions, demonstrating unambiguously that efficient Pt → Ln energy transfer occurs indeed from the PtII alkynyl antenna chromophores to the lanthanide centers across the bridging C⋮CPhtpy with intramolecular Pt···Ln distances being ca. 14.2 Å. The Pt → Ln energy transfer rate (kET) is 6.07 × 107 s-1 for Pt2Nd4 (6) and 2.12 × 105 s-1 for Pt2Yb4 (9) species.