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(III) 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)(mu-bpym)](4-) (bpym = 2,2'-bipyrimidine) with lanthanide(III) 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)(H2O)(5)] (Ru-Ln; Ln = Sm, Nd, and Gd) are one-dimensional helical chains; [Ru(bpym)(CN)(4)](2)[Ln(NO3)(H2O)(2)][Ln(NO3)(0.5)(H2O)(5.5)](NO3)(0.5 center dot 5.5)H2O (Ru-Ln; Ln = Er and Yb) are two-dimensional sheets containing cross-linked chains based on Ru(2)Ln(2)(mu-CN)(4) diamond units, which are linked into one-dimensional chains via shared Ru atoms; [{Ru(CN)(4)}(2)(mu-bpym)][Ln(NO3)(H2O)(5)](2)center dot 3H(2)O (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)(A-bpym)][Ln(H2O)(6)](0.5)[Ln(H2O)(4)]-(NO3)(0.5)center dot nH(2)O (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(2)Ln(2)(mu-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 ((MLCT)-M-3) 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, Ru-2-Nd and Ru-2-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 (MLCT)-M-3 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.