Understanding the
structure and behavior of intermediates in chemical
reactions is the key to developing greater control over the reaction
outcome. This principle is particularly important in the synthesis
of metal nanocrystals (NCs), where the reduction, nucleation, and
growth of the reaction intermediates will determine the final size
and shape of the product. The shape of metal NCs plays a major role
in determining their catalytic, photochemical, and electronic properties
and, thus, the potential applications of the material. In this work,
we demonstrate that layered coordination polymers, called lamellae,
are reaction intermediates in Cu NC synthesis. Importantly, we discover
that the lamella structure can be fine-tuned using organic ligands
of different lengths and that these structural changes control the
shape of the final NC. Specifically, we show that short-chain phosphonate
ligands generate lamellae that are stable enough at the reaction temperature
to facilitate the growth of Cu nuclei into anisotropic Cu NCs, being
primarily triangular plates. In contrast, lamellae formed from long-chain
ligands lose their structure and form spherical Cu NCs. The synthetic
approach presented here provides a versatile tool for the future development
of metal NCs, including other anisotropic structures.