Single-Source Precursors for the Synthesis of Layered Metal Chalcogenide Nanomaterials: LnX2, CuCrX2, and Bi2X3
Stoll, Sarah L
Layered materials belong to a class of compounds in which individual, 2-dimensional units are stacked upon each other and held together by weak intermolecular forces. The layered nature of these materials render them ideal for techniques like intercalation, exfoliation, alloying, among others in order to tune their properties. Here, single-source precursors (SSP) from the lanthanides, transition metals, and main group metals will be synthesized and utilized to yield different classes of layered compounds: LnX2, CuCrX2, and Bi2X3, respectively. First, we describe the synthesis of a series of novel lanthanide SSPs, [Ln(Se2PPh2)3(MeCN)x], which were thermolyzed to yield LnSe2-x, an understudied class of 2D layered materials. In a group known for work with rare earth materials, particularly EuS, it was exciting to have discovered a mild route to other lanthanide chalcogenide materials. We explore the synthetic versatility of these precursors through synthesizing alloys of LnSe2-x as well understanding the growth mechanisms in order to yield single- or few- layered sheets. Next, we describe the synthesis of layered ternary transition metal chalcogenides, CuCrX2 and CuCr2X4 which form as hexagonal nanoplates. We utilized SSPs of Cr(III) and Cu(I)/(II) to understand the role of oxidation state, as well as precursor ratio and reaction temperatures, in order to gain phase control and avoid secondary phases. Lastly, we briefly discuss SSPs for synthesizing layered main group chalcogenide nanomaterials, Bi2X3. Bismuth based materials are in interesting comparison to lanthanides due to their similarity in size and charge but lack of f-block valence electrons. Here, we demonstrate the clear advantage of utilizing a SSP through affording defect-free phase-pure material as clear hexagonal nanoplates (compared to separate Bi(III) and Se reagents).
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