Structural and photophysical properties of coordination networks combining [Ru(Bpym)(CN)4]2- or [{Ru(CN)4}2(μ-bpym)] 4- anions (bpym = 2,2′-bipyrimidine) with lanthanide(lll) cations: Sensitized near-infrared luminescence from Yb(III), Nd(III), and Er(III) following Ru-to-lanthanide energy transfer

Reaction of the cyanoruthenate anions [Ru(bpym)(CN)4] 2- and [{Ru(CN)4}2(μ-bpym)]4- (bpym - 2,2′-bipyrimidine) with lanthanide(lll) salts resulted in the crystallization of coordination networks based on Ru-CN-Ln bridges. Four types of structure were obtained: [Ru(bpym)(CN)4][Ln(NO3)(H 2O)5] (Ru-Ln; Ln -Sm, Nd, and Gd) are one-dimensional helical chains; [Ru(bpym)(CN)4]2[Ln(NO3)(H 2O)2][Ln(NO3)0.5(H 2O)5.5](NO3)0.5·5.5H 2O (Ru-Ln; Ln = Er and Yb) are two-dimensional sheets containing cross-linked chains based on Ru2Ln2(μ-CN)4 diamond units, which are linked into one-dimensional chains via shared Ru atoms; [{Ru(CN)4}2(μ-bpym)][Ln(NO3)(H 2O)5]2·3H2O (Ru 2-Ln; Ln = Nd and Sm) are one-dimensional ladders with parallel Ln-NC-Ru-CN-Ln-NC strands connected by the bipyrimidine "cross pieces" acting as rungs on the ladder; and [{Ru(CN)4}2(μbpym)] [Ln(H2O)6]0.5[Ln(H2O) 4]-(NO3)0.5·nH2O (Ru 2-Ln; Ln = Eu, Gd, and Yb; n = 8.5, 8.5, and 8, respectively) are three-dimensional networks in which two-dimensional sheets of Ru 2Ln2(μ-CN)4 diamonds are connected via cyanide bridges to Ln(III) ions between the layers. Whereas Ru-Gd shows weak triplet metal-to-ligand charge-transfer (3MLCT) luminescence in the solid state from the Ru-bipyrimidine chromophore, in Ru-Nd, Ru-Er, and Ru-Yb, the Ru-based emission is quenched, and all of these show, instead, sensitized lanthanide-based near-IR luminescence following a Ru → Ln energy transfer. Similarly, Ru2-Nd and Ru2-Yb show lanthanide-based near-IR emission following excitation of the Ru-bipyrimidine chromophore. Time-resolved luminescence measurements suggest that the Ru → Ln energy-transfer rate is faster (when Ln = Yb and Er) than in related complexes based on the [Ru(bipy)(CN)4]2- chromophore, because the lower energy of the Ru-bpym 3MLCT provides better spectroscopic overlap with the low-energy f-f states of Yb(III) and Er(III). In every case, the lanthanide-based luminescence is relatively short-lived as a result of the CN oscillations in the lattice. © 2006 American Chemical Society.