By using piperazine as a structure-directing agent, four new metal phosphonates with layered structure, [pzH 2 ] 0.5 [ML(H 2 O)]· 1.5H 2 O [M = Co (1), Ni (2), Zn (3)] and [pz] 0.5 [Sb 2 L 2 ]·H 2 O (4) (H 3 L = 2-hydroxyphosphonoacetic acid; pz = piperazine), have been hydrothermally synthesized and structurally characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, elemental analysis and thermogravimetric analysis. Compounds 1-3 are isostructural and comprise MO 6 octahedra and CPO 3 tetrahedra connected by [O 3 PCH(OH)CO 2 ] 3to form a 2D layered structure with a one-dimen-