Hydrate frameworks involving the pyridazino[4,5-d] pyridazine unit as a multiple hydrogen-bond acceptor

1,4,5,8-Tetramethylpyridazino[4,5- d] pyridazine trihydrate, C10H12N4 center dot 3H(2)O, ( I), and 1,2,3,6,7,8-hexahydrocinnolino-[5,4,3-cde] cinnoline tetrahydrate, C12H12N4 center dot 4H(2)O, (II), exhibit exceptional functionality of the condensed N-4-heteroaromatic frame as a symmetric acceptor of four hydrogen bonds [N center dot center dot center dot O = 2.843 ( 2) - 2.8716 ( 10) angstrom]. Thus, all the N atoms of the electron-deficient and highly pi-acidic polynitrogen heterocycles function as lone-pair donors. In ( I), all the molecular components lie on or across special positions; the site symmetry is 2/m for the organic and m2m and m for the two water molecules. In ( II), the organic polycycle lies across a crystallographic inversion center. Both structures involve a hydrogen-bonded centrosymmetric water - pyridazine dimer as the basic supramolecular unit, which is integrated into two-dimensional [ in ( I)] and three-dimensional [in (II)] hydrate frameworks by hydrogen bonding with the additional water molecules [O center dot center dot center dot O = 2.744 ( 2) - 2.8827 ( 19) angstrom]. The hydrate connectivity exists in the form of an ( H2O)(3) trimer in ( I) and as a one-dimensional zigzag (H2O)(n) chain in ( II).