Luminescent Dinuclear Lanthanide Complexes of 5-Me-HXTA

The synthesis and characterization of a series of anionic homobimetallic lanthanide complexes of the septadentate
chelate 5-Me-HXTA (N,N-(2 hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine) is described (Ln = Nd,
Sm, Eu, Tb, Dy, Ho, Er, Yb). Single X-ray crystallography confirms that the complexes exist as discrete dimeric
pairs in the solid state. Proton NMR, diffusion-ordered spectroscopy, and luminescence solution studies suggest
that the binuclear stoichiometry is retained in aqueous solution over a range of analytically useful concentrations.
The phenolic chromophores effectively sensitize the visible and near-infrared lanthanide-centered emission in the
terbium, neodymium, and ytterbium derivatives, giving rise to particularly long-lived green and near-infrared emission.
The terbium complex displays a high quantum yield of around 50% in aqueous solution with a low detection limit
of 1 × 10-12 M, rendering this compound a potential candidate for time-resolved applications.