Synthesis and reactivity of copper(II) metallacrowns with (S)-phenylalanine and 2-picolinehydroxamic acids

The new pentanuclear 12-metallacrown-4 complexes of the formula [Cu5L4]X2 (where H2L is (S)-phenylalanine or 2-picolinehydroxamic acids and X− is NO3-, Cl−, or HSO4-) have been isolated in solid state for the first time and characterized by NMR and UV–Vis spectroscopy, electrospray ionization mass spectrometry and elemental analyses. The 1H NMR spectroscopy was used to follow the transformation of these 12-metallacrown-4 complexes into lanthanide 15-metallacrown-5 complexes [LnCu5L5](NO3)3, and allowed to establish the correlation between the stability of the latter complexes and the lanthanide ionic radius. As indicated by 1H NMR and ESI-MS data, the reaction of [Cu5L4]X2 complexes with Ni2+ ion results in replacement of the central Cu2+ ion and formation of heteronuclear 12-metallacrowns-4 of the [NiCu4L4]X2 type. The crystallization of the complex of 2-picolinehydroxamic acid, [Cu5(picha)4](NO3)2, in the presence of pyridine leads to destruction of the metallacrown core and formation of trinuclear complex, [Cu3(picha)2(py)5(NO3)2], whose X-ray crystal structure has been determined.

Graphical abstractThe new pentanuclear copper(II) complexes of 2-picoline- and (S)-phenylalanine hydroxamic acids have been synthesized and characterized. These complexes react with nickel(II) and lanthanide(III) ions to give heteronuclear metallacrown-4 and metallacrown-5 complexes, respectively. The pentanuclear complex of 2-picolinehydroxamic acid reacts with pyridine to give a trinuclear complex, whose X-ray crystal structure has been determined.Figure optionsDownload full-size imageDownload as PowerPoint slide