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) ). 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 nonprotonated 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 located at the inversion centres and are planar [r.m.s. 0.0009(1) ]. 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 hydrogen 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 hydrazine molecules, symmetry independent acid molecules one half of them with protons attached to the carboxylate oxygen 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) 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.