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')Cl-2 (dppm = 1, 2-bis(diphenylphosphino)methane) with HC CPhtpy (HC CPhtpy = 4'-(4-ethynylphenyi)-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 Pt-2(mu-dppm)(2)(C CPhtpy)(4) (5) when equivalent dppm is added. Incorporating 1 or 5 to Ln(hfac)(3)(H2O)(2) (Hhfac = hexafluoroacetylacetone) gave PtLn(2) (Ln = Nd (2), Eu (3), Yb (4)) or Pt(2)Ln(4) (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 lambda(ex) = 360-450 nm (2-4) or 360-500 nm (6-9), where the Pt-II alkynyl antenna chromophores absorb strongly but the model complexes Ln(hfaC)3(HC CPhtpy) lack obvious absorption in this region, these PtLn2 and Pt(2)Ln(4) (Ln = Nd, Eu, Yb) species exhibit bandlike lanthanide luminescence that is typical of the corresponding Ln (3+) ions, demonstrating unambiguously that efficient Pt -> Ln energy transfer occurs indeed from the Pt-II alkynyl antenna chromophores to the lanthanide centers across the bridging C CPhtpy with intramolecular Pt center dot center dot center dot Ln distances being ca. 14.2 angstrom. The Pt -> Ln energy transfer rate (K-ET) is 6.07 x 10(7) s(-1) for Pt2Nd4 (6) and 2.12 x 10(5) s(-1) for Pt2Yb4 (9) species.