The first two complexes of the trioxodinitrate anion were prepared by reaction of Zn(bipy)Cl-2 . 1.5H(2)O(1 . 1.5H(2)O) with Na2N2O3 . H2O in water to produce Zn-II(bipy)(H2O)(N2O3) (2) and an analogous reaction of Co(bipy)(2)-Cl-2 . 2.5H(2)O (3 . 2.5H(2)O) to produce Co-II(bipy)(2)(N2O3) (4). Both complexes are air-sensitive and crystallize in the monoclinic space group P2(1)/n. For 2 . H2O T = 24-26 degrees C, Z = 4, a = 7.7595(6) Angstrom, b = 9.4798(7) Angstrom, c = 17.197(1) Angstrom, beta = 98.142(7)degrees, and V = 1252.3(2) Angstrom(3). The final residuals were R1 = 0.4452, wR2 = 0.1172, and quality-of-fit = 1.057. The final model consisted of the main structure and a minor, 4% disordered component. For 4 . 4H(2)O T = -123 degrees C, Z = 4, a = 9.0950(9) Angstrom, b = 17.924(3) Angstrom, c = 13.695(2) Angstrom, beta = 90.32(1)degrees, and V = 2232.5(6) Angstrom(3). The final least-squares residuals were R1 = 0.0859, wR2 = 0.1975, and quality-of-fit = 0.917. A network of hydrogen bonds involving the crystal water molecules and the coordinated trioxodinitrate anion was found in each case; in 4, a series of fused four- and eight-membered rings were found to be a dominant feature in the extended structure. The structural data and the IR spectrum indicate that the N-N bond of trioxodinitrate, 1.264(5) Angstrom in the free anion, is longer for the coordinated anion (1.280(5) Angstrom in 2 and 1.333(11) Angstrom in 4).