Lanthanide clusters with chalcogen encapsulated Ln: NIR emission from nanoscale NdSe_x

Ln(SePh)₃ (Ln = Ce, Pr, Nd) reacts with elemental Se in the presence of Na ions to give (py)₁₆Ln₁₇NaSe ₁₈(SePh)₁₆, a spherical cluster with a 1 nm diameter. All three rare-earth metals form isostructural products. The molecular structure contains a central Ln ion surrounded by eight five-coordinate Se^2- that are then surrounded by a group of 16 Ln that define the cluster surface, with additional μ₃ and μ₅ Se^2-, μ₃ and μ₄ SePh^-, and pyridine donors saturating the vacant coordination sites of the surface Ln, and a Na ion coordinating to selenolates, a selenido, and pyridine ligands. NIR emission studies of the Nd compound reveal that this material has a 35% quantum efficiency, with four transitions from the excited state ⁴F _3/2 ion to ⁴I_9/2, ⁴I_11/2, ⁴I_13/2, and ⁴I_15/2 states clearly evident. The presence of Na⁺ is key to the formation of these larger clusters, where reactions using identical concentrations of Nd(SePh)₃ and Se with either Li or K led only to the isolation of (py)₈Nd ₈Se₆(SePh)₁₂.