Hydrogen-bonding network in metal-pterin complexes: Synthesis and characterization of water-soluble octahedral nickel and cadmium pterine derivatives

New octahedral pterine complexes of the general formula [M(en)(pterin)(2)] (M = Ni (1), Cd (2)) have been synthesized by reaction between the pterin ligand and ethylenediamine complexes of Ni(II) and Cd(II) in a basic aqueous solution. The newly synthesized complexes are surprisingly water soluble, despite the scarce solubility shown by most pteridine complexes reported up to now. In particular, the Ni(II) derivative (1) has been crystallized from water solution, giving rise to very regular brown-yellow needles suitable for single-crystal X-ray analysis. Noncovalent interactions can be identified in the molecular organization of 1 in the 3D space, such as hydrogen bonds of O-H- - -O, N-H- - -N, and N-H- - -O types and pi-pi interactions, which led to a new metallosupramolecular system. The photophysical characterization of these new pterin derivatives highlights their excellent luminescent properties in solution, confirming the metal-binding ability of the pterin ring and the stability of these systems in solution.