This paper reports the syntheses and characterization of four isomorphous compounds (NH3C6H4NH3)M-2(hedpH)2 center dot H2O [M = Fe (1), Co (2), Mn (3), Zn (4); hedp = C(CH3)(OH)(PO3)(2)], Each contains two crystallographically different kinds of {M-2(hedpH)(2)}, double chains, where the {M-2(mu-O)(2)} dimer units are connected by O-P-O bridges. The double chains are connected through extensive hydrogen bonds, hence generating a three-dimensional supramolecular network. The temperature-dependent magnetic susceptibility measurements show dominant antiferromagnetic interactions in compounds 1-3, mediated through the mu-O and/or O-P-O bridges between the metal(II) centers, The magnetization measurements reveal that compounds 1-3 experience field-induced magnetic transitions at low temperatures.