〈100〉-oriented Pt and Pt-Rh supercrystals were directly synthesized in N,N-dimethylformamide (DMF) solution. DMF was demonstrated to serve as the facet-specific agent of the (100) facets and the driving force for the self-assembly of Pt and Pt-Rh building blocks due to the strong bonding interaction between metal atoms on the (100) facets and the carbonyl group of DMF.