On the way to monodispersed ZnO nanocrystals: structure of a zinc dimer bearing primary amido ligands

Abstract

The two-stage conversion of [Zn(NiBu2)2]2 into nanocrystals of zinc oxide has been studied. The initial reaction of [Zn(N i Bu2)2]2 with hexylamine in ether was conducted under nitrogen and required the addition of two hexylamines for each molecule of [Zn(N i Bu2)2]2. After 18 h the clear precursor solution contained free diisobutylamine, [Zn(N i Bu2)2]2 and an oligomeric zinc species. In the second stage of the reaction, the nitrogen atmosphere was replaced with a flow of moist air. Over a period of 2.5–4 days the water in the atmosphere hydrolyzed the zinc amide bonds, and the CO2 converted much of the hexylamine into hexylammonium hexylcarbamate, which served as the stabilizing surfactant. Based on powder X-ray diffraction there was a long period during which crystalline ZnO nucleated followed by relatively rapid growth. Replacing hexylamine with the bulky aniline derivative, 2,6-diisopropylaniline, in the first stage of the reaction made it possible to isolate and characterize a new crystalline dinuclear product, [Zn(NH-2,6- i Pr2C6H3)2]2(HN i Bu2), bearing two bridging and two terminal primary amido ligands. One of the zincs was tricoordinate, whereas the second zinc was four coordinate as a result of binding a molecule of diisobutylamine.