Colloidal atomic layer deposition (c-ALD) enables the growth of hybrid organic/inorganic oxide shells with tunable thickness at the nanometer scale around ligand-functionalized inorganic nanoparticles (NPs). This recently developed method has demonstrated improved stability of NPs and of their dispersions, a key requirement for their application. Nevertheless, the mechanism by which the inorganic shells forms is still unknown, as is the nature of the multiple complex interfaces between the NPs, the organic ligands functionalizing the surface, and the shell. Here, we demonstrate that carboxylate ligands are the key element that enables the synthesis of these core–shell structures. Dynamic nuclear polarization surface enhanced nuclear magnetic resonance spectroscopy (DNP SENS) in combination with density functional theory (DFT) structure calculations show that the addition of the aluminum organometallic precursor forms a ligand–precursor complex that interacts with the NP surface. This ligand–precursor complex is the first step for the nucleation of the shell and enables its further growth.