Mandelohydroxamic Acid as Ligand for Copper(II) 15‐Metallacrown‐5 Lanthanide(III) and Copper(II) 15‐Metallacrown‐5 Uranyl Complexes

Abstract

The formation of pentanuclear copper(II) complexes with the mandelohydroxamic ligand was studied in solution by electrospray ionization mass spectrometry (ESI-MS), absorption spectrophotometry, circular dichroism and 1 H NMR spectroscopy. The presence of lanthanide(III) or uranyl ions is essential for the self-assembly of the 15-metallacrown-5 compounds. The negative mode ESI-MS spectra of solutions containing copper(II), mandelohydroxamic acid and lanthanide(III) ions (Ln = La, Ce, Nd, Eu, Gd, Dy, Er, Tm, Lu, Y) or uranyl in the ratio 5:5:1 showed only the peaks that could be unambiguously assigned to the following intact molecular

Copper(II) 15-metallacrown-5 lanthanide(III) complexes derived from l-serine and l-threonine hydroxamic acids

“…the presence of only one set of resonances indicates five-fold pseudo-symmetry of the molecule (Scheme 2). The NMR results are consistent with those of the previously studied lanthanide(III) containing 15-metallacrown-5 copper(II) complexes, which also showed only one set of ligand resonances [6,[12][13][14][15]. Similarly, the relatively sharp NMR signals are indicative of antiferromagnetic coupling between copper(II) ions as it was observed in other 15-metallacrown-5 complexes [6,[12][13][14][15].…”

“…For example, aminohydroximate ligands, which are derivatives of hydroxamic acids with an additional amino group as the potential coordinating group, are suitable ligands for metallacrown formation because they can act as bridging ditopic ligands. In the presence of copper(II) and lanthanide(III) ions, these ligands self-assemble into a planar metallamacrocycle in which five copper(II) ions form a crown structure incorporating lanthanide(III) ion in its cavity [5][6][7][8][9][10][11][12][13][14]. These lanthanide(III)-containing metallacrown compounds are stable in different solvents, including water [8,5].…”

Facile One‐Pot Route toward Water‐Soluble Lanthanide–Copper–Glycinehydrox­imate 15‐Metallacrown‐5 Complexes

“…[2,11,12,25] This simplicity of the spectra is ascribed to the fivefold pseudo-symmetry of the molecule. [2,11,12,25] This simplicity of the spectra is ascribed to the fivefold pseudo-symmetry of the molecule.…”

pH‐Responsive Switching Properties of a Water‐Soluble Metallamacrocyclic Phenylalaninehydroximate La(III)–Cu(II) Complex: Insight into Tuning Protonation Ligand States

“…Nowadays, the popularity of water‐soluble polynuclear metallamacrocyclic Cu(II)‐Ln(III) complexes is largely due to their rich coordination chemistry, diverse properties and ease of synthesis . The remarkable feature of Cu(II)‐Ln(III) 15‐MC‐5 complexes is the deep color . It should be pointed out that the observed ligand‐field bands in visible region near 550 nm have provided the potential ability to obtain useful diagnostic information concerning the structures of transition metal ion‐peptide complexes .…”