LAUSR

We synthesized two new porous coordination polymers (PCPs) {Ln7(OH)5[Ru(dcbpy)3]4·4nH2O} (Ln7-Ru4; 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 Ln3+ (Ln = Ce, Nd). These two PCPs Ln7-Ru4 are isomorphous with the previously reported PCP La7-Ru4, and the lattice constants (a, c, and unit cell volume V) changed systematically according to the lanthanide contraction. All three Ln7-Ru4 compounds have OH- 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 (RH) and 298 K. In contrast, the structural transformation of Ln7-Ru4 associated with water-vapor adsorption/desorption strongly depends on the lanthanide ion; the Ln7-Ru4 compounds with larger Ln3+ 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 Ln3+ ion plays an important role in the formation of the ion-conductive pathways. La7-Ru4 and Ce7-Ru4 exhibit vapochromic luminescence associated with water vapor adsorption/desorption, arising from the 3MLCT emission of [4Ru]. This vapochromic behavior is also affected by the replacement of the Ln3+ ion; the vapochromic shift of Ce7-Ru4 was observed at RH values (near 100% RH) higher than that of La7-Ru4. 3MLCT emissions of the [4Ru] metalloligand in Nd7-Ru4 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 1MLCT transition of [4Ru]), suggesting the transfer of energy from the [4Ru] 3MLCT excited state to the 4f-4f transition state of the Nd3+ ions.