The self-assembly of SbCl3 and 1,4-dioxane in a 2:3 ratio leads to an interpenetrating extended cubic structure from X-ray crystallography. The structure is held together by very weak Sb-O bonds (similar to 7 kcal/mol each), which still maintain strong directionality. Parameterization and subsequent simulation of the system using a reactive force field (ReaxFF) gives us insight into the key interactions necessary for self-assembly from a completely random configuration of molecules into the experimentally observed cubic structure. We explain why the porous structure (with no interpenetration of lattices) is not observed, and we trace the important intermediate substructures formed en route to the crystal.