Hydrothermal Synthesis, Crystal Structure and Characterizations of Four New Metal Phosphonates with Layered Structure

By using piperazine as a structure‐directing agent, four new metal phosphonates with layered structure, [pzH 2 ] 0.5 [ M L(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 M O 6 octahedra and CPO 3 tetrahedra connected by [O 3 PCH(OH)CO 2 ] 3– to form a 2D layered structure with a one‐dimensional channel system along the a axis direction. In compound 4 , two SbO 4 E trigonal bipyramids ( E is a lone pair of electrons, which occupy an axial position) are interconnected into a dimer by corner‐sharing. The so‐built dimers are bridged by the CPO 3 tetrahedra into a 2D layered structure with a one‐dimensional channel system in the c axis direction. The protonated piperazine cations for compounds 1 – 3 and the piperazine molecules for compound 4 are located between two adjacent layers.