Assembly of zinc metallacrowns with an α-amino hydroxamic acid ligand

In the assembly of metallacrowns for molecular recognition, luminescence, and molecular magnetism applications, substituting the ring ion can have profound effects on the structure, stability, and physical properties of the inorganic macrocycle. The assembly of Zn(II) metallacrowns with an α-amino hydroxamic acid ligand (pheHA) was investigated to compare the assembly behavior with the well studied metallacrowns containing Cu(II) and Ni(II). Electrospray ionization mass spectrometry reveals that the benchmark species Zn5(pheHA)42+ and LnZn5(pheHA)53+ assemble in pyridine, which is consistent with the behavior of Cu(II) and Ni(II). A LnZn4(pheHA)43+ species is also observed in a 1:1 DMF-pyridine mixture. An unprecedented La(III)[16-MCZn(II),pheHA,HpheHA-6]5+ complex was crystallographically characterized that possesses unusual C2 symmetry. These results provide insights into the design of functional metallacrowns through ring ion substitution.

The chiral ligand l-phenylalanine hydroxamic acid is shown to assemble the metallacrowns Zn(II)[12-MCZn,pheHA-4]2+, Ln(III)[15-MCZn(II),pheHA-5]3+, and Ln(III)[12-MCZn(II),pheHA-4]3+ using electrospray ionization mass spectrometry. A La(III)[16-MCZn(II),pheHA,HpheHA-6]5+ was crystallographically characterized that uniquely possesses protonated hydroxamate ligands and lower rotationally symmetry than conventional lanthanide metallacrowns.Figure optionsDownload as PowerPoint slide