Abstract
The 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.
The new pentanuclear 12-metallacrown-4 complexes of the formula [Cu
5L
4]X
2 (where H
2L is (
S)-phenylalanine or 2-picolinehydroxamic acids and X
− is
NO
3
-
, Cl
−, or
HSO
4
-
) 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 [LnCu
5L
5](NO
3)
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 [Cu
5L
4]X
2 complexes with Ni
2+ ion results in replacement of the central Cu
2+ ion and formation of heteronuclear 12-metallacrowns-4 of the [NiCu
4L
4]X
2 type. The crystallization of the complex of 2-picolinehydroxamic acid, [Cu
5(picha)
4](NO
3)
2, in the presence of pyridine leads to destruction of the metallacrown core and formation of trinuclear complex, [Cu
3(picha)
2(py)
5(NO
3)
2], whose X-ray crystal structure has been determined.