Ligand Geometry Directed Polar Cobalt(II) Phosphonate Displaying Weak Ferromagnetism

The hydrothermal reactions of 4-[(phosphonomethylamino)­methyl]­benzoic acid (H3L) with M­(NO3)2 (M = Co, Zn) afford two metal phosphonates, namely, Co­(HL) and Zn­(HL). Both of them display a 3D polar pillared layered structure. Magnetic measurements confirm that Co­(HL) exhibits a canted antiferromagnetic ordering at about 2 K. A weak ferromagnetic component at low temperature is attributed to the Dzyaloshinskii–Moriya (DM) interactions arising from the polar noncentrosymmetric crystal structure. The ZnII compound exhibits a second harmonic generation (SHG) response of approximately 0.2 times that of potassium dihydrogen phosphate (KDP).