A series of complexes of the type [Ln­(Se2P­(phenyl)2)3(CH3CN) x ] (x = 1 or 2) have been synthesized and structurally characterized for Ln = La–Lu (excluding Pm). The complexes are straightforward to prepare and crystallize and are soluble in solvents typically used in nanoparticle synthesis. Solution-phase thermolysis of these complexes formed lanthanide diselenide or LnSe2–x nanosheets, for Ln = La–Ho, except Eu, which formed EuSe. By contrast, the smallest lanthanides Ln = Er–Lu formed Ln2Se3 nanomaterials. The lanthanide dichalcogenides are rare-earth analogues of the transition metal dichalcogenides and exhibit similar properties, including small band gaps, charge density waves, antiferromagnetism, and superconductivity. The lanthanide diselenide nanomaterials exhibited highly anisotropic growth and were phase pure with the exception of CeSe2 (which also formed a cerium oxide and cerium ultraphosphate). The lateral nanosheet dimensions, based on transmission electron microscopy (TEM), range from ∼50 to 500 nm, and the thickness was found to be ∼4 nm for the thinnest sheets by atomic force microscopy. The nanosheets were further characterized by powder X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Alloy formation was also demonstrated with the combined solution thermolysis of Sm and Gd complexes to form Sm1–x Gd x Se1.8. The alloy was found to have homogeneous composition on the basis of powder X-ray diffraction and TEM.

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In targeting reduced valent lanthanide chalcogenides, we report the first nanoparticle synthesis of the mixedvalent ferromagnets Eu 3 S 4 and EuSm 2 S 4 . Using divalent lanthanide halides with bis(trimethylsilyl)sulfide and oleylamine, we prepared nanoparticles of EuS, Eu 3 S 4 , EuSm 2 S 4 , SmS 1.9 , and Sm 3 S 4 . All nanoparticle phases were identified using powder X-ray diffraction, transmission electron microscopy was used to confirm morphology and nanoparticle size, and magnetic susceptibility measurements for determining the ordering temperatures and valence. The UV/Vis, Raman and X-ray photoelectron spectroscopies for each phase were compared. Surprisingly, the phase is influenced by the halide and the reaction temperature, where EuCl 2 formed EuS while EuI 2 formed Eu 3 S 4 , highlighting the role of kinetics in phase stabilization. Interestingly, at lower temperatures EuI 2 initially forms EuS, and converts over time to Eu 3 S 4 .

In targeting reduced valent lanthanide chalcogenides, we report the first nanoparticle synthesis of the mixedvalent ferromagnets Eu 3 S 4 and EuSm 2 S 4 . Using divalent lanthanide halides with bis(trimethylsilyl)sulfide and oleylamine, we prepared nanoparticles of EuS, Eu 3 S 4 , EuSm 2 S 4 , SmS 1.9 , and Sm 3 S 4 . All nanoparticle phases were identified using powder X-ray diffraction, transmission electron microscopy was used to confirm morphology and nanoparticle size, and magnetic susceptibility measurements for determining the ordering temperatures and valence. The UV/Vis, Raman and X-ray photoelectron spectroscopies for each phase were compared. Surprisingly, the phase is influenced by the halide and the reaction temperature, where EuCl 2 formed EuS while EuI 2 formed Eu 3 S 4 , highlighting the role of kinetics in phase stabilization. Interestingly, at lower temperatures EuI 2 initially forms EuS, and converts over time to Eu 3 S 4 .

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