Lanthanide clusters with internal Ln ions: highly emissive molecules with solid-state cores

"Er(SePh)(2.5)I(0.5)" reacts with elemental S to give (THF)10Er6S6I6, a double cubane cluster with one face of the Er4S4 cube capped by an additional Er2S2. Reactions with a mixture of elemental S/Se results in the formation of (THF)14Er10S6(Se2)6I6, a cluster composed of an Er6S6 double cubane core, with two "Er2(Se2)3" units condensed onto opposing rectangular sides of the Er6S6 fragment. This deposition of Er2Se6 totally encapsulates the two central Er with chalcogen atoms (4 S, 4 Se) and excludes neutral THF donors or iodides from the two primary coordination spheres. The Er10 compound is the first lanthanide cluster to contain internal, chalcogen encapsulated Ln. This cluster shows strong fluorescence at 1544 nm with a measured decay time of 3 ms and an estimated quantum efficiency of 78%, which is comparable to Er doped solid-state materials. The unusual fluorescence spectral properties of (THF)14Er10S6Se12I6 are unprecedented for a molecular Er complex and are attributed to the low phonon energy host environment provided by the I-, S(2-), and Se2(2-) ligands.