We review the chemistry that leads or could lead to colloidal metal nitride nanocrystals, via solution-based methods.

Lewis acid (LA) activation by coordination to metal oxido species has emerged as a new strategy in catalytic oxidations. Despite the many reports of enhancement of performance in oxidation catalysis, direct evidence for LA-catalyst interactions under catalytically relevant conditions is lacking. Here, we show, using the oxidation of alkenes with H2O2 and the catalyst [Mn2(μ-O)3(tmtacn)2](PF6)2 (1), that Lewis acids commonly used to enhance catalytic activity, e.g., Sc(OTf)3, in fact undergo hydrolysis with adventitious water to release a strong Brønsted acid. The formation of Brønsted acids in situ is demonstrated using a combination of resonance Raman, UV/vis absorption spectroscopy, cyclic voltammetry, isotope labeling, and DFT calculations. The involvement of Brønsted acids in LA enhanced systems shown here holds implications for the conclusions reached in regard to the relevance of direct LA-metal oxido interactions under catalytic conditions.

The precursor conversion chemistry and surface chemistry of Cu 3 N and Cu 3 PdN nanocrystals are unknown or contested. Here, we first obtain phase-pure, colloidally stable nanocubes. Second, we elucidate the pathway by which copper(II) nitrate and oleylamine form Cu 3 N. We find that oleylamine is both a reductant and a nitrogen source. Oleylamine is oxidized by nitrate to a primary aldimine, which reacts further with excess oleylamine to a secondary aldimine, eliminating ammonia. Ammonia reacts with Cu I to form Cu 3 N. Third, we investigated the surface chemistry and find a mixed ligand shell of aliphatic amines and carboxylates (formed in situ). While the carboxylates appear tightly bound, the amines are easily desorbed from the surface. Finally, we show that doping with palladium decreases the band gap and the material becomes semi-metallic. These results bring insight into the chemistry of metal nitrides and might help the development of other metal nitride nanocrystals.

Cu3N and Cu3PdN nanocrystals are attractive materials with numerous applications ranging from optoelectronics to catalysis. However, their chemical formation mechanism and surface chemistry are unknown or contested. In this work, we first optimize the synthesis and purification to yield phase pure, colloidal stable Cu3N and Cu3PdN nanocubes. Second, we elucidate the precursor conversion mechanism that leads to the formation of Cu3N from copper(II) nitrate and oleylamine. We find that oleylamine is both the reductant and nitrogen source. Oleylamine is oxidized to a primary aldimine and the latter reacts further with oleylamine to a secondary aldimine, eliminating ammonia. Ammonia reacts with Cu(I) to form Cu3N. Third, we investigated the surface chemistry of the nanocrystals using solution NMR spectroscopy and X-ray photoelectron spectroscopy (XPS). We find a mixed ligand shell of aliphatic amines and carboxylates. The carboxylate is produced in situ during the synthesis. While the carboxylates appear tightly bound, the amines are easily desorbed from the surface. Finally, we analyze the optoelectronic properties by UV-Vis and XPS. Doping with palladium decreases the bandgap but the material remains a semiconductor. These results bring insight into the chemistry of metal nitrides and will help the development of other metal nitride nanocrystals.

We synthesized two resorcin[4]arene scaffolds with four phosphate binding groups. The superior binding affinity to nanocrystal surfaces is demonstrated using solution NMR spectroscopy and exceeds that of single phosphonates.