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New Schiff base complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) were synthesized by template condensation of quinoxaline-2-carboxaldehyde, L-histidine, and the metal compound, and were characterized by elemental analysis, fourier transform infrared spectroscopy, electronic spectra, conductance measurements, magnetic susceptibility measurements, ESR spectra, and thermal analysis. In all the complexes, the Schiff base coordinates through azomethine nitrogen, quinoxaline nitrogen, and carboxylato oxygen. The physicochemical and spectroscopic measurements reveal square planar geometry for the copper(II) complex, tetrahedral geometry for the manganese(II), cobalt(II), and zinc(II) complexes, and octahedral geometry for the iron(III) and nickel(II) complexes.

The mononuclear cobalt(II) complex [CoL2] · H2O (where HL is quinoxaline-2-carboxalidine-2-amino-5-methylphenol) has been prepared and characterized by elemental analysis, conductivity measurement, IR, UV-Vis spectroscopy, TG−DTA, and X-ray structure determination. The crystallographic study shows that cobalt(II) is distorted octahedral with each tridentate NNO Schiff base in a cis arrangement. The crystal exhibits a 2-D polymeric structure parallel to [010] plane, formed by O−H ··· N and O−H ··· O intermolecular hydrogen bonds and π−π stacking interactions, as a racemic mixture of optical enantiomers. The ligand is a Schiff base derived from quinoxaline-2-carboxaldehyde.

The Schiff base compounds N,N'-bis[(E)-quinoxalin-2-ylmethylidene]propane-1,3-diamine, C(21)H(18)N(6), (I), and N,N'-bis[(E)-quinoxalin-2-ylmethylidene]butane-1,4-diamine, C(22)H(20)N(6), (II), crystallize in the monoclinic crystal system. These molecules have crystallographically imposed symmetry. Compound (I) is located on a crystallographic twofold axis and (II) is located on an inversion centre. The molecular conformations of these crystal structures are stabilized by aromatic pi-pi stacking interactions.

In the title molecule, C16H11N5, the mean planes of the quinoxaline and indazole fragments form a dihedral angle of 10.62 (5)°. In the crystal, weak intermolecular N—H...N hydrogen bonds link the molecules into zigzag chains extending in the [001] direction. The crystal packing also exhibits π–π interactions [centroid–centroid distances of 3.7080 (2) and 3.8220 (5) Å], which form stacks of the molecules parallel to the a axis.