Isotope effect of crystal water on emission lifetime of Ru(dbb)2(CN)2·2H2O (dbb = 4,4′-di-tert-butyl-2,2′-bipyridine) crystal

Abstract

We studied the isotope effect of crystal water on the emission lifetime of Ru(dbb)₂(CN)₂·2H₂O in the solid state. The emission lifetime ratio of Ru(dbb)₂(CN)₂·2D₂O (dbb = 4,4′-di-tert-butyl-2,2′-bipyridine) and Ru(dbb)₂(CN)₂·2H₂O was determined to be τ_D/τ_H = 1.14 ± 0.05 at 298 K. From a crystal structural analysis, it was concluded that hydrogen bonding between crystal water and the 5,5′- and/or 3,3′-H atoms of the dbb ligands contributed more effectively to the isotope effect of crystal water on emission lifetime than that between water and the CN ligands. With increasing temperature, two water molecules were released at 310–345 K and over 385 K stepwise from hydrophobic channels constructed from dbb moieties. Exposure of the non-hydrated crystal, Ru(dbb)₂(CN)₂, to H₂O or D₂O vapor at 298 K gave Ru(dbb)₂(CN)₂·2H₂O or Ru(dbb)₂(CN)₂·2D₂O, respectively. Under a H₂O–D₂O mixed atmosphere, there was no correlation between the ratio of H₂O and D₂O in crystal water and the statistical distribution of H₂O and D₂O in the mixed atmosphere. Even under a 70% D₂O atmosphere, selective sorption of H₂O in the crystal of Ru(dbb)₂(CN)₂ was observed.