A series of compounds with a novel phosphate layer of the composition M-II(OH)(PO4)(2-) (M = Ni, Co, Mg) were hydrothermally prepared. Structures of compounds Na(H3O)(2){Ni-4(OH)(4)(HPO4)(3)(HzPo(4))} (I) and (H3O){Co-2(OH)(2)(HPO4)(H2PO4)} (4) were determined by the single-crystal X-ray diffraction. Crystal data for 1 : monoclinic P2(1), a = 8.374(1) Angstrom, b = 12.810(3) Angstrom, c = 8.307(4) Angstrom, beta = 106.19(2)degrees Z = 2. Cyrstal data for 4 : orthorhombic, Pcab, a = 8.343(2) Angstrom, b = 13.093(4) Angstrom, c 15.384(4) Angstrom, Z = 8. The phosphate layers of these compounds have similar structures but belong to different layer groups. They are composed of zigzag chains of MO6 octahedra sharing skew edges, and the chains are linked by shared corners and also by bridging PO4 tetrahedra. The space between the layers is occupied by sodium and oxonium ions in 1 and by only oxonium ions in 4. Both 1 and 4 are paramagnetic with antiferromagnetic transition at 6 and 5 K, respectively. A lithium analogue of I, Li0.39H1.61- Ni(OH)(PO4)(H2O)(0.5) (isostructural with 1), a nickel phosphate without alkali cations H2Ni(OH)(PO4)(H2O)(0.5) (isostructural with 3), and a magnesium phosphate Na0.27H1.73Mg(OH)(PO4)(H2O)(0.5) (isostructural With 1) were also identified by powder X-ray diffraction.