Robust Lanthanoid Picolinate-Based Coordination Polymers for Luminescence and Sensing Applications

Abstract

Picolinate-based segmented dianionic ligands <b>L</b>_<b>1</b>^<b>2-</b> (5-((4-carboxyphenyl)ethynyl)picolinate) and <b>L</b>_<b>2</b>^<b>2-</b> (5,5'-(ethyne-1,2-diyl)dipicolinate) have been used in the synthesis of the highly robust and luminescent europium(III) coordination polymers [(CH₃)₂NH₂][Eu(H₂O)₂(<b>L</b>_<b>1</b>)₂] (<b>1</b>) and [(CH₃)₂NH₂][Eu(<b>L</b>_<b>2</b>)₂]·H₂O·CH₃COOH (<b>2</b>). Both <b>1</b> and <b>2</b> exhibit high selectivity for detection of nitroaromatic compounds since they act as quenchers of the Eu³⁺ emission. Stern-Volmer plots, using nitrobenzene as a quencher, yielded values of <i>K</i>_SV = 150 M^-1 and 160 M^-1 for <b>1</b> and <b>2</b>, respectively. Luminescence studies in the presence of different metal ions indicate a high selectivity for Fe³⁺ detection, with <i>K</i>_SV values of 471 M^-1 and 706 M^-1 for <b>1</b> and <b>2</b>, respectively. Both <b>1</b> and <b>2</b> possess extremely robust extended structures, leading to emissive properties that are stable in a wide pH range.