The new Ag 2 T1 2 P 2 S 11 quaternary phosphosulfide disilver dititanium undecathiodiphosphate is obtained by heating the elements at ca 850K in an evacuated silica tube. It crystallizes in orthorhombic symmetry, Pnma space group, with a = 8.5222(11), b = 6.8359 (10), c = 24,142 (4) A, V = 1406A (4)A 3 and Z=4 at 293K. The refinement of the room-temperature structure leads to a reliability factor of R = 0.0378 for 1556 independent reflections and 128 variables. Ag 2 Ti 2 P 2 S 11 is composed of layers, separated by van der Waals gaps. The layers are composed of [T1 2 S 9 ] chains built from [TiS 7 ] units (TiS 6 octahedra in which a corner has been replaced by an S 2 pair) and linked through regular [PS 4 ] and highly distorted [AgS 4 ] tetrahedra. The formula of the compound can be written as Ag I 2 Ti IV 2 P V 2 (S 2 )-II S 9 -II . A Gram-Charlier anharmonic development of the atomic displacement factor for Ag atoms reveals a strong non-harmonic probability density deformation, especially in the direction of two empty neighbouring tetrahedra, away from the Ti and P cations. The temperature dependence of the effective one-particle potential shows that the Ag distribution is primarily static in nature. At high temperature the tetrahedrally coordinated site is the preferential site. At lower temperature the Ag atoms are redistributed over the tetrahedral site and the adjacent triangular site. The disorder could not be resolved due to a phase transition with splitting of spots just below room temperature.