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

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We synthesized two new porous coordination polymers (PCPs) {Ln 7 (OH) 5 [Ru(dcbpy) 3 ] 4 ·4 n H 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 Ln 7 -Ru 4 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 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 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 3 MLCT emission of [4Ru]. This vapochromic behavior is also affected by the replacement of the Ln 3+ 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 . 3 MLCT 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 Nd 3+ ion were observed in the near-infrared (NIR) region (arising from the 1 MLCT transition of [4Ru]), suggesting the transfer of energy from the [4Ru] 3 MLCT excited state to the 4f–4f transition state of the Nd 3+ ions.