Lanthanide Clusters with Chalcogen Encapsulated Ln: NIR Emission from Nanoscale NdSex

Ln(SePh)3 (Ln = Ce, Pr, Nd) reacts with elemental Se in the presence of Na ions to give (py)16Ln17NaSe18(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 Se2− that are then surrounded by a group of 16 Ln that define the cluster surface, with additional μ3 and μ5 Se2−, 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 4F3/2 ion to 4I9/2, 4I11/2, 4I13/2, and 4I15/2 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)8Nd8Se6(SePh)12.