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

We synthesized two new porous coordination polymers (PCPs) {Ln7 (OH)5 [Ru(dcbpy)3 ]4 ·4nH2 O} (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 the3 MLCT 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 .3 MLCT 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 the1 MLCT transition of [4Ru]), suggesting the transfer of energy from the [4Ru]3 MLCT excited state to the 4f-4f transition state of the Nd3+ ions.