RUB-15 layered silicate solved by assuming Ibam symmetry (a = 27.91, b = 8.41, c = 11.52 Å). Superimposed Fourier sections (y/b = 0.00–0.45) show the silicate sheets normal to . The phases were obtained by S-TF from laboratory PD data at moderate resolution (d ≥ 2.2 Å). At this resolution, the tetrahedral Si units appear as spheres. The tetramethylammonium molecules are placed on the mirror planes.