New metal phosphonates containing coordination piperazine or pyridyl groups

Reactions of transition metal(II) salts with three aminophosphonic acids, 1-[(H₂O₃PCH₂)₂NCH₂CH₂−]-piperazine-4-CH₂PO₃H₂ (H₆L¹), 3-pyridyl-CH₂N(CH₂PO₃H₂)₂ (H₄L²) and 4-pyridyl-CH₂N(CH₂PO₃H₂)₂ (H₄L³) afforded three new metal phosphonates, namely, Cu(H₄L¹)·2H₂O (1), Co(H₃L²)₂·H₂O (2) and [Co(H₂L³)(H₂O)]·H₂O (3). The structure of compound 1 features a 1D chain in which the CuN₂O₃ and CPO₃ polyhedra are interconnected by bridging phosphonate ligands to form 1D chains. Compound 2 has a layered structure. The cobalt(II) ions in the octahedral coordination geometries and {CPO₃} tetrahedra are interconnected into an inorganic chain via -N(CH₂PO₃H)₂ moieties, and adjacent chains are further bridged by the coordination pyridyl groups of H₃L² into a 2D layer. The structure of compound 3 features a 2D double layered structure, in which the Co(II) ions are interconnected by bridging phosphonate groups into a 1D chain along b-axis. Neighboring chains are interconnected by coordination pyridyl groups into a double layer perpendicular to the c-axis.