The truncated octahedron is well-known as the only Archimedean solid which can fill space, by itself, without leaving any gaps. The cluster below shows this, and has the overall shape of a rhombic dodecahedron.

It’s easier to see the rhombic dodecahedral shape of this cluster when looking at its convex hull:

Both images here were made using Stella 4d, which you can try for free right here.