Synthesis, X-ray characterization, DFT calculations and Hirshfeld surface analysis of Zn(II) and Cd(II) complexes based on isonicotinoylhydrazone ligand

In this manuscript we report the synthesis and X-ray characterization of four Zn(II) complexes and three Cd(II) complexes with an asymmetrical hydrazone-pyridine based ligand {HL = 2-acetyl-pyridylisonicotinoylhydrazone (HAPIH)}; i.e. {[Zn.HL)(2)](NO3)(2)center dot H2O} (1), [Zn(HL)Br-2] (2), [Zn(HL)I-2] (3), [Zn(HL)(NCS)(2)] (4), [Cd(L)(2)] (5), {[Cd(HL)Br-2]center dot CH3OH} (6) and {[Cd(HL)I-2]center dot 2CH(3)OH} (7). The Schiff base acts as a tridentate N-2-Odonor ligand through the oxygen, the imine and pyridine nitrogen atoms in all the complexes. In most complexes, the ligand is observed to coordinate as a zwitterion since the proton in the hydrazine group (=N-NH-C=O) shifted to the uncoordinated pyridine ring, except in 7. On the other hand, in 5 the ligand acts as a negatively charged species and is bound to the cadmium center in the enolic form (=N-N=CO-). In complexes 2-4, 6 and 7, the coordination geometry around each metal center is distorted trigonal bipyramidal, with the coordination sphere of the metal completed by two halide or NCS anions. On the other hand, in homoleptic complexes 1 and 5, the metal, chelated by two tridentate Schiff base ligands, exhibits an octahedral geometry. In the crystal packing of all compounds, the pyridine rings favour pi-pi interactions among the symmetry related complexes. The noncovalent interactions among the complexes have been analyzed using Hirshfeld surface analysis and DFT calculations using Grimme's D3 dispersion correction to properly describe the pi-pi interactions.