Abstract
The three isomorphous [3.3.1] metallacryptate complexes bis-(pyridinium) di-aqua-dipyridine-hexa-kis-[μ3-salicyl-hydroximato(3-)]bis-[μ2-salicyl-hydroxim-ato(1-)]hexa-aluminiumgadolinium-pyridine-water (1/7.396/1), (C5H6N)2[GdAl6(C7H6NO3)2(C7H4NO3)7(C5H5N)1.855(H2O)2]·7.396C5H5N·H2O or [Hpy]2[GdAl6(H2shi)2(shi)7(py)1.855(H2O)2]·7.396py·H2O, 1, bis-(pyridinium) di-aqua-dipyridine-hexa-kis-[μ3-salicyl-hydroximato(3-)]bis-[μ2-salicyl-hydroxim-ato(1-)]hexa-aluminiumdysprosium-pyridine-water (1/7.429/1), (C5H6N)2[DyAl6(C7H6NO3)2(C7H4NO3)7(C5H5N)1.855(H2O)2]·7.429C5H5N·H2O or [Hpy]2[DyAl6(H2shi)2(shi)7(py)1.891(H2O)2]·7.429py·H2O, 2, and bis-(pyrid-in-ium) di-aqua-dipyridine-hexa-kis-[μ3-salicyl-hydroximato(3-)]bis-[μ2-salicyl-hydrox-imato(1-)]hexa-aluminiumytterbium-pyridine-water (1/7.386/1), (C5H6N)2[YbAl6(C7H6NO3)2(C7H4NO3)7(C5H5N)1.855(H2O)2]·7.429C5H5N·H2O or [Hpy]2[YbAl6(H2shi)2(shi)7(py)1.818(H2O)2]·7.386py·H2O, 3, where Hpy+ is pyridinium, shi3- is salicyl-hydroximate, and py is pyridine, consist of an aluminium-based metallacryptand that captures an Ln III ion in the central cavity. The metallacryptand portions are comprised of an Al-N-O repeat unit; thus, they can be considered three-dimensional metallacrowns. The encapsulated Ln III ions are nine-coordinate with a spherical capped-square-anti-prism geometry, while the six AlIII ions are all octa-hedral. Four of the AlIII ions are chiral centers with 2 Δ and 2 Λ stereoconfigurations. The remaining two AlIII ions have trans chelate rings from two different shi3- ligands. For 1-3, a section of the main mol-ecule is disordered induced by the presence or absence of a pyridine ligand coordinated to one of the AlIII ions. In the absence of the pyridine moiety, an H2shi- ligand moves into the space otherwise occupied by the pyridine and the phenol oxygen atom coordinates to the AlIII ion. The movement of the H2shi- ligand induces movement for the Ln III ion, for another AlIII ion that also binds the same H2shi- ligand, and for one of the shi3- ligands coordinated to the latter AlIII ion. For 1-3 the occupancy ratio of the metallacryptand portions refined to 0.8550 (13):0.1450 (13), to 0.8909 (13):0.1091 (13), and to 0.8181 (14):0.1819 (14), respectively.
Highlights
Since the first report of metallacrowns (MC) in 1989, the chemistry of these molecules has grown to include a number of different structural types and subsequent applications (Pecoraro, 1989)
The first and archetypal metallacrowns are based on a macrocyclic metal–nitrogen–oxygen repeat unit and these molecules typically bind a metal ion in the central cavity similar to crown ethers (Pecoraro et al, 1997)
E76, 1458–1466 research communications metal ion, inverse MCs that bind a non-metal atom in the central cavity, and MC-like metallacryptands – complexes with an M–N–O repeat unit in a three-dimensional pattern (Mezei et al, 2007)
Summary
Since the first report of metallacrowns (MC) in 1989, the chemistry of these molecules has grown to include a number of different structural types and subsequent applications (Pecoraro, 1989). The first and archetypal metallacrowns are based on a macrocyclic metal–nitrogen–oxygen repeat unit and these molecules typically bind a metal ion in the central cavity similar to crown ethers (Pecoraro et al, 1997). E76, 1458–1466 research communications metal ion, inverse MCs that bind a non-metal atom in the central cavity, and MC-like metallacryptands – complexes with an M–N–O repeat unit in a three-dimensional pattern (Mezei et al, 2007). The use of lanthanide ions in particular can yield interesting single-molecule magnet or luminescent properties with the correct choice of the ring metal. To better understand the properties of the central LnIII ion in an MC framework (M–N–O repeat unit), we sought to isolate the LnIII ion from paramagnetic ring metal ions as these ions complicate the magnetism of the complexes and quench any luminescence. Future studies will investigate the magnetic properties of 1–3 to understand the behavior of the LnIII ions in a metallacrown-like framework
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