Two manganese 2,6-naphthalenedicarboxylates, [Mn(ndc)(DMF)] (1) and [Mn-3(ndc)(3)(DMF)(4)] (2) (ndc: 2,6-naphthalenedicarboxylate), have been isolated from a one-pot reaction system. Single-crystal X-ray diffraction results indicate that both compounds exhibit three-dimensional porous structures. Compounds 1 and 2 can be considered pseudopolymorphs. Careful inspection of the structures of compounds 1 and 2 suggests that the spatial arrangement of a secondary ligand of DMF plays a crucial role in the formation of the two supramolecular isomers.