Cadmium Amido Alkoxide and Alkoxide Precursors for the Synthesis of Nanocrystalline CdE (E = S, Se, Te)

The synthesis and characterization of a family of alternative precursors for the production of CdE nanoparticles (E
= S, Se, and Te) is reported. The reaction of Cd(NR2)2 where NR2 = N(SiMe3)2 with n HOR led to the isolation
of the following:  n = 1 [Cd(μ-OCH2CMe3)(NR2)(py)]2 (1, py = pyridine), Cd[(μ-OC6H3(Me)2-2,6)2Cd(NR2)(py)]2 (2),
[Cd(μ-OC6H3(CHMe2)2-2,6)(NR2)(py)]2 (3), [Cd(μ-OC6H3(CMe3)2-2,6)(NR2)(py)]2 (4), [Cd(μ-OC6H2(NH2)3-2,4,6)(NR2)(py)]2 (5), and n = 2 [Cd(μ-OC6H3(Me)2-2,6)(OC6H3(Me)2-2,6)(py)2]2 (6), and [Cd(μ-OC6H3(CMe3)2-2,6)(OC6H3(CMe3)2-2,6)(THF)]2 (7). For all but 2, the X-ray crystal structures were solved as discrete dinuclear units bridged
by alkoxide ligands and either terminal −NR2 or −OR ligands depending on the stoichiometry of the initial reaction.
For 2, a trinuclear species was isolated using four μ-OR and two terminal −NR2 ligands. The coordination of the
Cd metal center varied from 3 to 5 where the higher coordination numbers were achieved by binding Lewis basic
solvents for the less sterically demanding ligands. These complexes were further characterized in solution by 1H,
13C, and 113Cd NMR along with solid-state 113Cd NMR spectroscopy. The utility of these complexes as “alternative
precursors” for the controlled preparation of nanocrystalline CdS, CdSe, and CdTe was explored. To synthesize
CdE nanocrystals, select species from this family of compounds were individually heated in a coordinating solvent
(trioctylphosphine oxide) and then injected with the appropriate chalcogenide stock solution. Transmission electron
spectroscopy and UV−vis spectroscopy were used to characterize the resultant particles.