From Uncommon Ethylzinc Complexes Supported by Ureate Ligands to Water-Soluble ZnO Nanocrystals: A Mechanochemical Approach

Abstract

Urea and its derivatives, due to their unusual versatility of coordination modes to metal centers and the presence of multiple hydrogen-bond donor sites, are widely utilized as neutral or monoanionic ligands in coordination and bioinorganic chemistry and as building units of bioinspired materials. However, metal complexes with ureate ligands have essentially not been applied as precursors of hybrid organic-inorganic nanomaterials. We report on the synthesis and structure characterization of two novel organozinc ureate complexes incorporating N-phenylureate or N,N′-dicyclohexylureate ligands, the latter being the first reported complex with the μ3-μ2(O):κ1(N) ureate coordination mode. These findings not only expand the horizon of urea-zinc chemistry but also pave the way for efficient bottom-up mechanochemical synthesis of sub-10 nm diameter zinc oxide nanocrystals (ZnO NCs) coated by the ureate ligands. We explored the NC formation triggered by mechanical force from both a well-defined monocrystalline precursor and an insoluble hard-to-process amorphous organozinc precursor. Moreover, the organic shell of the N-phenylureate-coated ZnO NCs was modified via a facile, fast, and solventless host-guest complexation with β-cyclodextrin using a mechanochemical approach, which afforded water-soluble ZnO NCs. The reported procedure is the first example of rapid and sustainable mechanochemical synthesis of hybrid nanomaterials from organometallic precursors.