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
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Abstract
Eight unprecedented Ln-NDC coordination
polymers with BBI as templates
{[HBBI][Ln(NDC)<sub>2</sub>(H<sub>2</sub>O)]·H<sub>2</sub>O [Ln
= La (<b>1</b>), Pr (<b>2</b>)], [HBBI]<sub>2</sub>[Sm(NDC)<sub>2</sub>(H<sub>2</sub>O)]<sub>2</sub>·1/2H<sub>2</sub>O (<b>3</b>), and [HBBI][Ln(NDC)<sub>2</sub>(H<sub>2</sub>O)] [Ln =
Eu (<b>4</b>), Gd (<b>5</b>), Tb (<b>6</b>), Dy
(<b>7</b>), Er (<b>8</b>)] [Ln = lanthanide, H<sub>2</sub>NDC = 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 <b>1</b>–<b>8</b> crystallize in the
monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i> 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 NDC<sup>2–</sup> 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 <b>2</b>–<b>8</b> have been investigated.
The strong fluorescent emissions of <b>4</b> demonstrate that
ligand-to-Eu<sup>III</sup> energy transfer is efficient. In addition,
thermogravimetric analyses and optical diffuse reflectance spectra
of these compounds are also described
