Protonation and Zn(II) complexation with versatile valine and glycylglycine N-pyrimidines derivatives: crystal structures of layered {[Zn(HL₁)₂] • ₂H₂O}_<i>n</i> and [Zn(HL₂)₂ (H₂O)₄]

Protonation and Zn(II) complexation of N-substituted amino acids, valine (H2<b>L1</b>) and glycylglycine (H2<b>L2</b>), with 4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidin-2-yl as substituent, were studied by potentiometric and UV–Vis measurements. Bianions <b>L1</b> and <b>L2</b> suffer three protonation steps in aqueous medium corresponding to the amide and carboxylate groups of the amino acidic moiety, and the nitrogen atom of the nitroso group of the pyrimidine fragment. Both ligands form mononuclear Zn(II) complexes in aqueous solutions. The binding donor groups are the nitroso and/or the oxo groups of the pyrimidinic moiety or the carboxylate group, depending on whether the ligands are neutral or anionic, respectively. Weak metal-to-ligand interactions were observed independently of the functionality used by the corresponding ligand on bonding to Zn(II). The reaction of ZnCl₂ with the monodeprotonated ligands (1:1) yields a polynuclear 2D {[Zn(H<b>L1</b>)₂] • 2H₂O}<i>n</i> and a mononuclear [Zn(H<b>L2</b>)₂(H₂O)₄] complexes, showing the influence of the susbtituent on the amino acids fragment as well as the versatility of this class of compounds when acting as ligands.