Three-Dimensional Extended Frameworks Constructed from Dinuclear Lanthanide(III) 1,4-Naphthalenedicarboxylate Units with Bis(2,2′-biimidazole) Templates: Syntheses, Structures, and Magnetic and Luminescent Properties

Eight unprecedented Ln-NDC coordination
polymers with BBI as templates
{[HBBI]­[Ln­(NDC)2(H2O)]·H2O [Ln
= La (1), Pr (2)], [HBBI]2[Sm­(NDC)2(H2O)]2·1/2H2O (3), and [HBBI]­[Ln­(NDC)2(H2O)] [Ln =
Eu (4), Gd (5), Tb (6), Dy
(7), Er (8)] [Ln = lanthanide, H2NDC = 1,4-naphthalenedicarboxylic acid, BBI = bis­(2,2′-biimidazole)]}
have been hydrothermally synthesized and structurally characterized
by elemental analyses, IR spectra, and single-crystal X-ray diffraction.
Complexes 1–8 crystallize in the
monoclinic space group P21/c and display similar (8,8)-connected 3-D frameworks with different
dinuclear Ln secondary building units due to the effect of Ln contraction
and diverse coordination modes of NDC2– ligands.
As the ionic radii of Ln ions decrease, the coordination numbers of
Ln ions decrease from 10, to 9, to 8. The variable-temperature magnetic
properties of 2–8 have been investigated.
The strong fluorescent emissions of 4 demonstrate that
ligand-to-EuIII energy transfer is efficient. In addition,
thermogravimetric analyses and optical diffuse reflectance spectra
of these compounds are also described.