[(n-C4H9)(4)N](2)[Mo6O18(N-1-C10H6-2-CH3)] (1) has been prepared by the reaction of 1-amino-2-methylnaphthalene hydrochloride with [(n-C4H9)(4)N](4)[alpha-Mo8O26] in the presence of 1,3-dicyclohexylcarbodiimide. Three solvent-free crystalline phases are isolated from the mixed solvents of acetone and acetic ether. The X-ray single-crystal structures of the three phases have been determined, showing the packing and supramolecular assembly characters (pseudohigher symmetry, helical chains, and pi-pi stacking) by which the effect of solvent polarity and crystallization speed on polymorphism in organic-inorganic hybrids has been demonstrated.