Facile Preparation of Face Differentiated, Chiral 15-Metallacrown-5 Complexes

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

“…Since they were first reported by Pecoraro and co-workers in 1989 [3,4], several different types of metallacrown complexes contaning various metals, ligands and ring sizes have been developed [5]. The stoichiometry and the structure of the metallacrown complexes depends on the type of the metal and the ligand used for synthesis.…”

“…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].…”

“…For metal ions with long longitudinal electron spin relaxation times, T 1e and T 2e , like gadolinium(III), the increase of τ R is one of the most important sources of relaxivity enhancement [16]. Moreover, the X-ray single crystal structure of Gd(III) [15- 5 showed that two water molecules are coordinated to gadolinium(III), which can further contribute to the relaxivity enhancement [15]. Water molecules can also coordinate to the copper(II) ions from the ring and may experience an additional paramagnetic way of relaxation.…”

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

“…The key property of these two ligand scaffolds is that they are able to form two fused five-membered chelate rings, which allows five metals and five ligands to form a planar 15-metallacrown-5 structure. [22,23] The planar 15-metallacrown-5 complexes formed in this way are capable to incorporate in their central cavity cations with a larger ionic radius and with a higher coordination number than 12-metallacrown-4 complexes. As a result, lanthanide() [24][25][26][27][28] and uranyl (UO 2 2+ ) [23,28,29] ions have been incorporated in the center of a 15-metallacrown-5 ring.…”

Synthesis, Characterization, and Crystal Structure of Two Manganese Metallacrowns: 30‐Metallacrown‐10 and 18‐Metallacrown‐6 with Ligands Derived from 3‐Hydroxy‐2‐naphthalenecarbohydrazide

“…[2][3][4][5][6][7][8][9][10] At present, the groups of metallacrowns mainly include: (1) metallacrowns with a [M-N-O] n repeating linkage. This type of metallacrown can be synthesized by multidentate ligands such as hydroxamic, [11] ketonoxime, [11a,12] and aminohydroxamic acids [13] and their cyclic size has been enlarged from 9-MC-3 to 24-MC-8, [1,[14][15][16][17][18] including several inverse metallacrowns. [2,[19][20][21] (2) Metallacrowns with the [M-N-N] n repeating linkage, for example, azametallacrown, which can be synthesized by multidentate ligands such as N-substituted salicylhydrazide, salicylhydrazone, or 2-pyridinecarbaldehyde hydrazone.…”