title: The big impact of a small detail: cobalt nanocrystal polymorphism as a result of precursor addition rate during stock solution preparation.
abstract: The control of nanocrystal structures at will is still a challenge, despite the recent progress of colloidal synthetic procedures. It is common knowledge that even small modifications of the reaction parameters during synthesis can alter the characteristics of the resulting nano-objects. In this work we report an unexpected factor which determines the structure of cobalt nanoparticles. Nanocrystals of distinctly different sizes and shapes have resulted from stock solutions containing exactly the same concentrations of [Co{N(SiMe(3))(2)}(2)(thf)], hexadecylamine, and lauric acid. The reduction reaction itself has been performed under identical conditions. In an effort to explain these differences and to analyze the reaction components and any molecular intermediates, we have discovered that the rate at which the cobalt precursor is added to the ligand solution during the stock solution preparation at room temperature becomes determinant by triggering off a nonanticipated side reaction which consumes part of the lauric acid, the main stabilizing ligand, transforming it to a silyl ester. Thus, an innocent mixing, apparently not related to the main reaction which produces the nanoparticles, becomes the parameter which in fine defines nanocrystal characteristics. This side reaction affects in a similar way the morphology of iron nanoparticles prepared from an analogous iron precursor and the same long chain stabilizing ligands. Side reactions are potentially operational in a great number of systems yielding nanocrystals, despite the fact that they are very rarely mentioned in the literature.
authors.affiliation: Université de Toulouse, INSA, UPS, CNRS, LPCNO, 135 avenue de Rangueil, 31077 Toulouse, France.
authors.forename: Nikos
authors.initials: N
authors.lastname: Liakakos
authors.forename: Benoît
authors.initials: B
authors.lastname: Cormary
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Li
authors.forename: Pierre
authors.initials: P
authors.lastname: Lecante
authors.forename: Marc
authors.initials: M
authors.lastname: Respaud
authors.forename: Laurent
authors.initials: L
authors.lastname: Maron
authors.forename: Andrea
authors.initials: A
authors.lastname: Falqui
authors.forename: Alessandro
authors.initials: A
authors.lastname: Genovese
authors.forename: Laure
authors.initials: L
authors.lastname: Vendier
authors.forename: Spyros
authors.initials: S
authors.lastname: Koïnis
authors.forename: Bruno
authors.initials: B
authors.lastname: Chaudret
authors.forename: Katerina
authors.initials: K
authors.lastname: Soulantica