The use of thiol ligands as a sulfur source for nanocrystal synthesis has recently come en vogue, as the products are often high quality. A comparative study was performed of dodecanethiol-capped Cu2S prepared with elemental sulfur and thiol sulfur reagents. XPS and TGA-MS provide evidence for differing binding modes of the capping thiols. Under conditions where the thiol acts only as a ligand, the capping thiols are "surface-bound" and bond to surface cations in low coordination number sites. In contrast, when thiols are used as a sulfur source, "crystal-bound" thiols result that sit in high coordination sites and are the terminal S layer of the crystal. A (1)H NMR study shows suppressed surface reactivity and ligand exchange with crystal-bound thiols, which could limit further application of the particles. To address the challenge and opportunity of nonlabile ligands, dodecyl-3-mercaptopropanoate, a molecule possessing both a thiol and an ester, was used as the sulfur source for the synthesis of Cu2S and CuInS2. A postsynthetic base hydrolysis cleaves the ester, leaving a carboxylate corona around the nanocrystals and rendering the particles water-soluble.
A new metal oxide framework based on the redox-active Preyssler anion linked with Co(H2O)4 2+ bridging units is presented. The framework can be photochemically reduced, allowing the storage of multiple electrons under mild conditions. Titrations with molecular redox species show that this reduction is reversible and can accommodate up to 10 electrons per Preyssler cluster (corresponding to an electron density on the order of 1021 cm–3) without changing the crystal structure. This addition of delocalized electrons is accompanied by a 1000-fold increase in the conductivity. These results demonstrate that the ability to add delocalized electrons to polyoxometalate clusters can be incorporated into self-assembled extended solids, enabling the development and tuning of metal oxide materials with emergent or complementary properties.
We present the synthesis of metal oxide frameworks composed of [NaP5W30O110]14– assembled with Mn, Fe, Co, Ni, Cu, or Zn bridging metal ions. X-ray diffraction shows that the frameworks adopt the same assembly regardless of bridging metal ion. Furthermore, our synthesis allows for the assembly of isostructural frameworks with mixed-metal ion bridges, or with clusters that have been doped with Mo, providing a high degree of compositional diversity. This consistent assembly enables investigation into the role of the building blocks in the properties of the metal oxide frameworks. The presence of bridging metal ions leads to increased conductivity compared to unbridged frameworks, and frameworks bridged with Fe have the highest conductivity. Additionally, Mo-doping can be used to enhance the conductivities of the frameworks. Similar structures can be obtained from clusters in which the central Na+ has been replaced with Bi3+ or Sm3+. Overall, the optical and electronic properties are tunable via choice of bridging metal ion and cluster building block and reveal emergent properties in these cluster-based frameworks. These results demonstrate the promise of using polyoxometalate clusters as building blocks for tunable complex metal oxide materials with emergent properties.
S Supporting Information E ver-growing demand on our traditional energy resources makes harnessing underutilized alternative energy sources all the more necessary and desirable to the scientific community. 1 Colloidal copper(I) sulfide nanocrystals (NCs) are an attractive photovoltaic device component due to their solar absorption characteristics; 2 Cu 2 S is a p-type semiconductor with a bandgap reported from 1.1 to 1.4 eV, and an absorption coefficient of 10 4 cm −1 . 3 Cu 2 S is also a parent material to ternary and quaternary copper sulfides such as CuInS 2 , which has emissive defects that can be used for LED lighting, biomedical applications and solar concentrating. 4 The light-absorbing characteristics of copper(I) sulfide can be further enhanced by morphologies that increase the absorption cross section of the nanocrystals. Manipulating reaction mixture additives can generate highly faceted Cu 2 S nanocrystals, 5 and careful stabilizer control has been used previously to make Cu 2 S nanoribbons from nanocrystal assemblies in aqueous media. 6 Sadtler et al. were first to synthesize Cu 2 S nanorods through cation exchange with CdS nanorods, a process that lacks atom economy and generates a cadmium byproduct. 7 Additionally, the cation exchange process likely leaves the Cu 2 S doped with Cd ions. Kruszynska et al. discovered that substoichiometric Cu 2−x S nanorods could be grown from nucleations when using tert-DDT as a ligand and sulfur source, 8 but the fully stoichiometric Cu 2 S was not achieved. Further developments to prepare rods structures without cadmium and of controlled stoichiometry are needed.The oriented attachment of Cu 2 S seed particles into larger single crystalline structures offers a means to obtain nanostructures with morphologies, sizes and compositions that may not be possible with traditional monomer-based growth. Oriented attachment of PbSe performed by Cho 9 and later by Koh 10 produced nanowires, nanorings, and nanorods from single-particle building blocks. Oriented attachment has also been used to create single-crystalline chains of TiO 2 crystals, 11 CdTe nanowires, 12 and nanorods of ZnO, 13 CdS and Ag 2 S. 14 The process occurs due to dipole interactions between particles. Hexagonal-like crystal structures (as shown in ZnO, CdS and Ag 2 S) inherently have a dipole due to crystal structure anisotropy, yet control over the surface chemistry was essential to orchestrate the directed attachment in many of these cases. The room temperature crystal structure of stoichiometric Cu 2 S (low chalcocite) and substoichiometric crystal structure djurleite (Cu 1.96 S) consist of copper atoms arranged around a distorted hexagonally close-packed sulfur sublattice 15 (approximated here for simplicity by the hexagonal high chalcocite structure). Provided the surface chemistry can
In this report, we present a new path to the control of quantum dot surface chemistry that can lead to a better understanding of nano-scale interfaces and the development of improved photocatalysts. Control of the synthetic methodology leads to QDs that are concomitantly ligated by crystal-bound organics at the surface anion sites and small X-type ligands on the surface cation sites.
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