The key role of hydrogen bonding in the nuclearity of three copper(II) complexes with hydrazone-derived ligands and nitrogen donor heterocycles

► Three copper(II) complexes are synthesised by two hydrazone-derived Schiff bases. ► Phenolic-OH side arm in the Schiff base appears as structure directing component. ► Mononuclear complexes result when Schiff base contains phenolic-OH side arm. ► Phenolic-OH of Schiff base also influences hydrogen bonding in the complexes. ► Hydrogen bonding plays the key role in the nuclearity of the complexes.