Reversible Z-Type to L-Type Ligand Exchange on Zinc-Blende Cadmium Selenide Nanoplatelets

Three-monolayer CdSe nanoplatelets having the composition (CdSe)3[Cd(OAc)0.77(oleate)1.23]0.78, large lateral dimensions, minimal strain distortions, and the zinc-blende crystal structure undergo Z-type to L-type ligand exchange with ethylenediamine, affording NPLs of composition (CdSe)3[en]0.67 (en = ethylenediamine). The L-type ligation of the (CdSe)3[en]0.67 (en = ethylenediamine) NPLs is exchanged for Z-type ligation with Cd(oleate)2, Cd(OAc)2, CdCl2, Zn(oleate)2, and ZnCl2, giving NPLs having near to the ideal compositions of (CdSe)3[MX2]. All of the Z-type to L-type and L-type to Z-type ligand exchanges are kinetically slow, requiring several hours to reach completion, suggesting that a considerable surface reconstruction is required. In contrast, three-monolayer NPLs having a significant rolling distortion and four- and five-monolayer NPLs having small lateral dimensions are unstable to ethylenediamine, and Z-type to L-type ligand exchange is not achieved.