The synthesis, characterization, and properties of dipicolinic acid (dipicH(2)) derivatives are described. Neutralization of hot aqueous concentrated solutions of dipicH(2) showed successive gelifications-liquefaction processes. Isolation of crystalline-phase [(dipicH)(dipicH(2))]Na . 3H(2)O (1) revealed an intricate network of interactions among the acid, the sodium cation, and water molecules. [(dipic)Fe-II(OH2)(3)] (2) was prepared in nearly quantitative yield by reaction of dipic(2-) with an excess of ammonium iron(II) sulfate hexahydrate. 2 reacts with bases (cation(+))OH- to give [(dipic)(2)Fe-II](cation)(2) in high yields (3 : cation = NProp(4)(+)). [(dipic)(2)Fe-II](2-) was solvatochromic, due to interactions between the dipic oxygen lone pairs and solvents. Air or bromine water oxidation of 3 yielded quantitatively the iron(III) complexes [(dipic)(2)Fe-III](cation) (4 : cation = Na+). The crystal structures of 1-4 have been determined. Comparison of the geometries of 3 and 4 showed that the iron-nitrogen bond lengths are insensitive to iron oxidation states whereas the iron-oxygen distances decrease by 0.15 Angstrom upon iron oxidation. This allowed the calculation of the intervalence band energy in dipic mixed-valence systems. 1 crystallized in the triclinic space group with cell constants a = 6.882(1) Angstrom, b = 11.125(2)Angstrom, c = 11.171(2) Angstrom, alpha = 82.65 (4)degrees, beta = 82.13(4)degrees, gamma = 87.38(6)degrees, V = 844(3) Angstrom(3), and Z = 2. 2 was found in the monoclinic space group P2(1)/c with alpha = 12.410(4) Angstrom, b = 9.314(4) Angstrom, c = 8.746(3) Angstrom, beta = 101.44(4)degrees, V = 990(1) Angstrom(3) and Z = 4. 3 . 7.25H(2)O occurred in the monoclinic space group P2(1)/c with a = 15.320(9) Angstrom, b = 33.83(2) Angstrom, c = 17.24(1) Angstrom, beta = 91.55(4)degrees, V = 8932(9) Angstrom(3), and with Z = 8. 4 . H2O crystallized in the monoclinic space group Cc with a = 14.95(1) Angstrom, b = 12.45(3) Angstrom, c = 8.663(5) Angstrom, beta = 92.99(4)degrees, V = 609(4) Angstrom(3), and Z = 4.