A new organoammonium disphosphopentamolybdate with the formula (C6H18N2)3[P2Mo5O23] · 4H2O was synthesized and characterized by single crystal X‐ray diffraction, thermal study, IR spectra and UV spectra. The complex crystallizes in the triclinic system, space group P‐1 with a=11.1498(15) Å, b=11.1843(15) Å, c=17.973(3) Å, α=95.983(2)°, β=101.143(2)°, γ=96.991(2)°, V=2163.8(5) Å3, Z=2, and R1=0.0385. The structure of heteropoly anion [P2Mo5O23]6− consists of five MoO6 octahedra and two PO4 tetrahedra. The octahedra form a pentagonal ring by sharing four edges and one corner. The PO4 tetrahedra are attached each one to one side of the ring by three oxygen atoms. The anions are arranged in layers and the interactions between anions are established through hydrogen contacts that involve water molecules and hexanediammonium cations.