Three new noncentrosymmetric cyclohexaphosphates with the general formula M(C 6 H 5 NH 3 ) 4 P 6 O 18 ·8H 2 O (M: Cd, Cu, Co) are synthesized. They crystallize in the monoclinic system, space group P 2 1 , Z = 2 and are isostructural. We have determined their structure from the Cd salt. This Cd salt exhibits the following unit-cell parameters: a = 9.852(1), b = 24.784(4), c = 9.2078(8)Å, β = 107.92(9) • , V = 2139.2(9)Å 3 . The structure has been solved using direct method and refined to a reliability R factor of 0.042. The structure can be described as infinite anionic layers with composition of [Cd(P 6 O 18 )(H 2 O) 8 ] 4− and parallel to the (1 0 1) plane. The charge compensation and the three-dimensional cohesion are performed by the protonated amine located between these inorganic layers.