The Crystal and Molecular Structures of Hydrazine Adducts with Isomeric Pyrazine Dicarboxylic Acids

The monoclinic unit cell of Bis(hydrazineH) pyrazine-2,3-dicarboxylate contains singly protonated hydrazine cations and doubly deprotonated pyrazine-2,3-dicarboxylate anions. Atoms forming the pyrazine ring are coplanar (r.m.s. 0.0075(1) A). Carboxylate groups form dihedral angles with the pyrazine ring of 1.7(2)° (C7/O1/O2) and 89.3(2)° (C8/O3/O4). An extended hydrogen bond network is observed in which hydrazine N atoms act as donors in bonds to non- protonated carboxylate O and hetero-ring nitrogen atoms. The monoclinic structure of hydrazine adduct of pyrazine-2,5-dicarboxylic acid is composed of doubly-deprotonated pyrazine-2,5-dicarboxylate anions and singly-protonated hydrazine cations. The anions have their geometrical centres lo- cated at the inversion centres and are planar (r.m.s. 0.0009(1) A). Both carboxylic groups form dihedral angles of +11.7(1)° and -11.7(1)° with the pyrazine ring plane. Hydrazine cations acting as donors bridge the anions via weak hy- drogen bonds in which carboxylate O atoms are the acceptors giving rise to molecular layers. The structure of the adduct with pyrazine-2,6-dicarboxylic acid contains , apart from symmetry independent neutral hy- drazine molecules, symmetry independent acid molecules one half of them with protons attached to the carboxylate oxy- gen atoms as in the parent acid, the second half shows zwitterionic form with proton attached to the hetero-ring nitrogen atom. Carboxylic groups and the pyrazine ring are almost coplanar in both types of acid molecules. The latter are bridged by short hydrogen bonds of 2.435(2) and 2.426(2) A operating between carboxylate oxygen atoms belonging to adjacent symmetry independent acid molecules, forming layers composed of molecular ribbons. Hydrazine molecules acting as donors link the ribbons by a network of hydrogen bonds.