Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures

[Image: see text] We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb(4)S(3)Br(2), a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS–PbBr(2) phase diagram. The Pb(4)S(3)Br(2) nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb(4)S(3)I(2) phase, and indeed we were able to extend our synthesis scheme to Pb(4)S(3)I(2) colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb(3)S(2)Cl(2), which proved to be a structural analogue of the recently reported bulk Pb(3)Se(2)Br(2) phase. It is remarkable that one high-pressure structure (for Pb(4)S(3)I(2)) and two metastable structures that had not yet been reported (for Pb(4)S(3)Br(2) and Pb(3)S(2)Cl(2)) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.