The chelating properties of pentadentate hydrazone derived ligands have been intensively studied in several research fields. The variety of structures observed for metal complexes of this type, their pharmacological activity and magnetic properties make these compounds of special interest. The coordination chemistry of manganese(II) has attracted considerable interest due to the crucial role played by the metal in redox and non-redox proteins. Studies involving the synthesis and characterization of manganese complexes are valuable towards the understanding of the structure and reactivity of manganese sites in biological systems. The template condensation of the isonicotinic acid hydrazide with 2,6-diacetylpiridine in combination with Mn(NO3)2x4H2O is favored by the formation of the stable mononuclear complex [Mn(H2L)(H2O)2](NO3)2 (1), where H2L=2,6-diacetylpiridine bis(isonicotinoylhidrazone). X-ray single crystal structure analysis revealed that 1 crystallizes in the triclinic space group P-1: a =8.3541(5), b =10.2910(6), c =16.2970(9) Е, α =73.649(5), β = 83.224(5), γ = 73.874(5)°, V = 1290.32(14) Е3, Z = 2.

The crystal structure of 1 consists of one mononuclear complex cation [Mn(H2L)(H2O)2]2+ and two NO3– anions. Each Mn(II) cation adopts an N3O4 seven-coordinated pentagonal bipyramidal geometry going from the pentadentate Schiff base ligand in the equatorial plane, while the axial vertices are occupied by H2O molecules (figure). Intermolecular OH···O and OH···N hydrogen bonds involving the coordinating water molecules as donors and the nitrate O atoms and pyridine H2L N atoms of hidrazide fragments as acceptors form 3D hydrogen-bonding network.