Lanthanide contraction in linear lanthanide–oxygen clusters

<div><p>Five coordination polymers containing linear lanthanide–oxygen clusters <b>1–5</b> have been synthesized by a hydrothermal reaction of 3-(quinolin-8-yloxy) phthalic acid (H<sub>2</sub>L) with the respective lanthanide salt. The X-ray single crystal structural analyses revealed that these five crystalline materials belong to two isostructures with formulas [LnHL<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]<sub>n</sub> (<b>Ln1</b>, where Ln = La <b>1</b>, Ce <b>2</b>, Pr <b>3</b>) and [Ln(HL)(L)(H<sub>2</sub>O)]<sub>n</sub> (<b>Ln2</b>, where Ln = Nd <b>4</b>, Sm <b>5</b>), respectively, which are attributed to the effect of lanthanide contraction. In both structures, the lanthanide cations were bridged by two carboxyl groups of L<sup>2−</sup> through Ln–O bonds to form 1-D linear lanthanide<b>–</b>oxygen clusters, which were further connected by intermolecular <i>π</i>–<i>π</i> stacking interactions between quinolinyl units to generate 3-D supramolecular polymers with moderate luminescence and high thermal stability.</p></div>