Abstract
The synthesis, structures, and properties of a new calix[4]arene ligand with an appended salicylaldimine unit (H4L = 25-[2-((2-methylphenol)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) and four lanthanide complexes (HNEt3)[Ln2(HL)(L)] (Ln = SmIII (4), EuIII (5), GdIII (6), and TbIII (7)) are reported. X-ray crystallographic analysis (for 4 and 6) reveals an isostructural series of dimeric complexes with a triply-bridged NO3Ln(μ-O)2(OHO)LnO3N core and two seven coordinated lanthanide ions. According to UV-vis spectrometric titrations in MeCN and ESI-MS the dimeric nature is maintained in solution. The apparent stability constants range between log K = 5.8 and 6.3. The appended salicylaldimines sensitize EuIII and TbIII emission (λexc 311 nm) in the solid state or immersed in a polycarbonate glass at 77 K (for 5, 7) and at 295 K (for 7).
Highlights
Calix[4]arenes1 have turned out to be versatile backbones for multidentate supporting ligands,2,3 and a large number of donor groups have been appended at the lower and upper rim in order to control the properties of the resulting complexes.4–17 Lanthanide complexes of such ligands have been well investigated,18–24 for their potential in liquid–liquid extraction.25–34 Recently, some research in this area has been directed towards the development of lanthanide-based single-molecule magnets35 and luminescent probes and materials.36–40 The calixarenes are typically designed to saturate the metal’s coordination sphere, and several luminescent complexes have been investigated.41–46Despite the maturity of the field, not many lanthanide complexes of pendant calix[4]arenes were structurally characterized
This study demonstrates that H4L supports dinuclear lanthanide complexes – a property which contrasts the mononucleating behavior of the double and fourfold functionalized calix[4]arene amides
The salicylaldimine-appended calix[4]arene H4L was readily prepared according to a procedure reported by Zhang et al for related bis(salicylaldimine)-p-tert-butylcalix[4]arenes (Scheme 1)
Summary
Calix[4]arenes have turned out to be versatile backbones for multidentate supporting ligands, and a large number of donor groups have been appended at the lower and upper rim in order to control the properties of the resulting complexes. Lanthanide complexes of such ligands have been well investigated, for their potential in liquid–liquid extraction. Recently, some research in this area has been directed towards the development of lanthanide-based single-molecule magnets and luminescent probes and materials. The calixarenes are typically designed to saturate the metal’s coordination sphere, and several luminescent complexes have been investigated.41–46Despite the maturity of the field, not many lanthanide complexes of pendant calix[4]arenes were structurally characterized. Calix[4]arenes have turned out to be versatile backbones for multidentate supporting ligands, and a large number of donor groups have been appended at the lower and upper rim in order to control the properties of the resulting complexes.. Calix[4]arenes have turned out to be versatile backbones for multidentate supporting ligands, and a large number of donor groups have been appended at the lower and upper rim in order to control the properties of the resulting complexes.4–17 Lanthanide complexes of such ligands have been well investigated, for their potential in liquid–liquid extraction.. A handful of structures with triply appended calix[4]arenes have been reported, and as far as we are concerned no structures exist with one-armed calix[4] arenes.50 To fill this gap, we decided to prepare a mono-substituted calix[4]arene-Schiff base ligand H4L and investigate its coordination chemistry towards some lanthanide ions. Hybrid ligands of this sort are known to complex first-row transition metals readily, but their lanthanide chemistry remains largely unexplored.
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