  Hypothesis: Colloidal molecules with anisotropic shapes and interactions are
powerful model systems for deciphering the behavior of real molecules and
building units for creating materials with designed properties. While many
strategies for their assembly have been developed, they typically yield a broad
distribution or are limited to a specific type. We hypothesize that the shape
and relative sizes of colloidal particles can be exploited to efficiently
direct their assembly into colloidal molecules of desired valence.
  Experiments: We exploit electrostatic self-assembly of negatively charged
spheres made from either polystyrene or silica onto positively charged hematite
cubes. We thoroughly analyze the role of the shape and size ratio of particles
on the cluster size and yield of colloidal molecules.
  Findings: Using a combination of experiments and simulations, we demonstrate
that cubic particle shape is crucial to generate high yields of distinct
colloidal molecules over a wide variety of size ratios. We find that
electrostatic repulsion between the satellite spheres is important to leverage
the templating effect of the cubes, leading the spheres to preferentially
assemble on the facets rather than the edges and corners of the cube.
Furthermore, we reveal that our protocol is not affected by the specific choice
of the material of the colloidal particles. Finally, we show that the permanent
magnetic dipole moment of the hematite cubes can be utilized to separate
colloidal molecules from non-assembled satellite particles. Our simple and
effective strategy might be extended to other templating particle shapes,
thereby greatly expanding the library of colloidal molecules that can be
achieved with high yield and purity.
