Metal phosphonates based on (4-carboxypiperidyl)-N-methylenephosphonate: in situligand cleavage and metamagnetism in Co3(O3PCH2-NHC5H9-COO)2(O3PCH2-NC5H10)(H2O)

Abstract

Hydrothermal reaction of (4-carboxypiperidyl)-N-methylenephosphonic acid (4-cpmpH₃) and zinc sulfate results in compound Zn(O₃PCH₂-NHC₅H₉-COO) (1). It has a pillared layered structure in which the inorganic layers made up of corner-sharing {CPO₃} and {ZnO₄} tetrahedra are connected by the organic groups. When cobalt sulfate is allowed to react with 4-cpmpH₃ under similar conditions, a proportion of the ligands undergo decarboxylation, leading to the formation of a novel mixed ligated compound Co₃(O₃PCH₂-NHC₅H₉-COO)₂(O₃PCH₂-NC₅H₁₀)(H₂O) (2). Compound 2 also shows a pillared layered structure with the topology of the inorganic layer similar to that of 1. The Co^II ions in 2 are all tetrahedrally coordinated. Significant difference between the two structures lies in the packing of the layers, e.g.…AAA… in 1 while …AABAAB… in 2. More interestingly, compound 2 behaves as a metamagnet at low temperature. The critical field is 40.1 kOe at 1.8 K.