This paper describes the syntheses and characterization of three novel phosphonate compounds M{(C₅H₄N)CH(OH)PO₃}(H₂O) [M = Mn (1), Fe (2), Co (3)] with isomorphous layered structures. Each {MO₄N} trigonal bipyramid in the structure is corner-shared with three {CPO₃} tetrahedra from three equivalent [hydroxy(4-pyridyl)methyl]phosphonate ligands, forming a one-dimensional inorganic double chain. These inorganic chains are linked together via the organic groups of the ligand, leading to a two-dimensional layer structure. The layers are further connected to each other through extensive hydrogen bonds, thus generating a three-dimensional supramolecular network. The magnetic properties show that weak antiferromagnetic interactions are mediated between the metal centers in all three compounds.