The title compound, (C(3)H(7)N(6))(2)[Co(H(2)O)(6)][Co(C(7)H(3)NO(4))(2)](2)·4H(2)O, or (tataH)(2)[Co(H(2)O)(6)][Co(pydc)(2)](2)·4H(2)O (where tata is 2,4,6-triamino-1,3,5-triazine and pydc is pyridine-2,6-dicarboxylic acid), was obtained by reaction of Co(NO(3))(2)·6H(2)O with the proton-transfer compound (tataH)(2)(pydc) in aqueous solution. The [Co(pydc)(2)](2-) anion is a six-coordinate Co(II) complex with a distorted octa-hedral coordination geometry. The structure also contains hexa-aqua-cobalt(II) cations (site symmetry ), (tataH)(+) cations and uncoordinated water mol-ecules. The two(pydc)(2-) ligands in each [Co(pydc)(2)](2-) anion are almost perpendicular to each other [dihedral angle between their mean planes = 82.3 (1)°]. There is extensive O-H⋯O, N-H⋯N, O-H⋯N and C-H⋯O hydrogen bonding in the structure, as well as π-π stacking between (pydc)(2-) ligands with an inter-planar distance of 3.484 (15) Å.