Development of Ion-Conductive and Vapoluminescent Porous Coordination Polymers Composed of Ruthenium(II) Metalloligand

We synthesized two new porous coordination polymers (PCPs) {Ln(7)(OH)(5)[Ru(dcbpy)(3)](4).4nH(2)O} (Ln(7)-Ru-4; Ln = Ce, Nd) composed of the luminescent ruthenium (II) metalloligand [Ru(4,4'-dcbpy)(3)](4-) ([4Ru]; 4,4'-dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and lanthanide ions Ln(3+) (Ln = Ce, Nd). These two PCPs Ln7-Ru4 are isomorphous with the previously reported PCP La-7-Ru-4, and the lattice constants (a, c, and unit cell volume V) changed systematically according to the lanthanide contraction. All three Ln(7)-Ru-4 compounds have OW anion containing porous structures and a large number of hydrate water molecules within the pores, resulting in moderate ion conductivities (10(-6)-10(-7) S cm(-1)) at 90% relative humidity Wavelength / nm (RH) and 298 K. In contrast, the structural transformation of Ln(7)-Ru-4 associated with water-vapor adsorption/desorption strongly depends on the lanthanide ion; the Ln(7)-Ru-4 compounds with larger Ln(3+) ions recover the original porous structure at lower relative humidities (RH). A similar trend was observed for the ion conduction activation energy, suggesting that the bridging Ln(3+) ion plays an important role in the formation of the ion conductive pathways. La-7-Ru-4 and Ce-7-Ru-4 exhibit vapochromic luminescence associated with water vapor adsorption/desorption, arising from the (MLCT)-M-3 emission of [4Ru]. This vapochromic behavior is also affected by the replacement of the Ln3(+) ion; the vapochromic shift of Ce-7-Ru-4 was observed at RH values (near 100% RH) higher than that of La-7-Ru-4. (MLCT)-M-3 emissions of the [4Ru] metalloligand in Nd-7-Ru-4 were barely observable in the visible region, but sharp emission bands characteristic of 4f-4f transitions of the Nd3+ ion were observed in the near -infrared (NIR) region (arising from the (MLCT)-M-1 transition of [4Ru]), suggesting the transfer of energy from the [4Ru] (MLCT)-M-3 excited state to the 4f-4f transition state of the Nd3+ ions.