Two manganese phosphonates Mn3(4-piH)2(H2O)3·H2O (1) and Mn5(4-piH)2(4-piH2)2(phen)2(H2O)4 (2) (4-piH4 = 4-phosphonoisophthalic acid, phen = 1,10-phenanthroline) have been synthesized under hydrothermal conditions in the presence of organic co-ligand. Both compounds exhibit layer structures but with different topologies. In compound 1, a complicated “ladder-like” chain of {Mn3O3}O2 which contains three- and six-member rings made up of triangular shaped {Mn3O3} trimers is found. The chains are linked by the PO3C groups to form an inorganic layer. The phenyl and protonated carboxylate groups are pendent between the layers with extensive hydrogen bonds. In compound 2, tetramers of {Mn4O6} are connected by the {MnO6} octahedra through corner-sharing to form an infinite chain, which is further bridged by 4-piH3- ligands into a thick hybrid layer. Magnetic measurements reveal that antiferromagnetic interactions are dominant in both compounds. Metamag- netism is observed in compound 1 at low temperature, while no long range ordering is found in compound 2 down to 1.8 K. Two manganese phosphonates Mn3 (4-piH) 2 (H2O) 3 · H2O (1) and Mn5 (4-piH) 2 (4-piH2) 2 -phosphonoisophthalic acid, phen = 1,10-phenanthroline have been synthesized under hydrothermal conditions in the presence of organic co-ligand. Both compound exhibit layer structures with different topologies. In compound 1, a complicated "ladder- like chain of {Mn3O3} O2 which contains three- and six-member rings made up of triangular shaped {Mn3O3} trimers is found. The chains are linked by the PO3C groups to form an inorganic layer. The phenyl and protonated carboxylate groups are pendent between In compounds 2, tetramers of {Mn4O6} are connected by the {MnO6} octahedra through corner-sharing to form an infinite chain, which is further bridged by 4-piH3-ligands into a thick hybrid layer. Magnetic measurements reveal that antiferromagnetic interactions are dominant in both compounds. Metamag-netism is observed in compound 1 at l ow temperature, while no long range ordering is found in compound 2 down to 1.8 K.