Preparation, Characterization, and Photophysical Properties of <i>cis</i>- or <i>trans</i>-PtLn₂ (Ln = Nd, Eu, Yb) Arrays with 5-Ethynyl-2,2′-bipyridine

Reaction of cis- or trans-Pt(PPh3)2Cl2 (PPh3 = triphenylphosphine) with 5-[2-(trimethylsilyl)-1-ethynyl]-2,2′-bipyridine (bpyCCSiMe3) gave cis-Pt(PPh3)2(CCbpy)2 (1) or trans-Pt(PPh3)2(Cbpy)2 (5). Incorporating 1 or 5 with Ln(hfac)3(H2O)2 (hfac = hexafluoroacetylacetonate) induced formation of the corresponding cis- or trans-PtLn2 heterotrinuclear complexes cis-Pt(PPh3)2{(CCbpy)Ln(hfac)3}2 (Ln = Nd 2, Eu 3, Yb 4) or geometrical isomers trans-Pt(PPh3)2{(CCbpy)Ln(hfac)3}2 (Ln = Nd 6, Eu 7, Yb 8). As verified through 31P NMR characterization as well as determination of the structures of 1, 4, and 8 by X-ray crystallography, the cis- or trans-arranged forms around PtII centers remain unchanged in both solutions and solid states without thermal or light-induced isomerization during the reactions. With excitation at 360 < λex < 450 nm, which is the absorption region of metal-perturbed π→π* (CC) transitions and dπ(Pt)→π*(CCbpy) MLCT transition, sensitized lanthanide luminescence occurs with a microsecond range of lifetimes in both cis- and trans-arranged PtLn2 complexes, revealing that efficient Pt→Ln energy transfer is indeed operating from the platinum(II) acetylide chromophore to lanthanide centers.