Dinuclear lanthanide complexes supported by a hybrid salicylaldiminato/calix[4]arene-ligand: Synthesis, structure, and magnetic and luminescence properties of (HNEt3)[Ln2(HL)(L)] (Ln = SmIII, EuIII, GdIII, TbIII)

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(OH⋯O)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 logK = 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).