Abstract
Picolinate-based segmented dianionic ligands L12– (5-((4-carboxyphenyl)ethynyl)picolinate) and L22– (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(L1)2] (1) and [(CH3)2NH2][Eu(L2)2]·H2O·CH3COOH (2). Both 1 and 2 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 KSV = 150 M–1 and 160 M–1 for 1 and 2, respectively. Luminescence studies in the presence of different metal ions indicate a high selectivity for Fe3+ detection, with KSV values of 471 M–1 and 706 M–1 for 1 and 2, respectively. Both 1 and 2 possess extremely robust extended structures, leading to emissive properties that are stable in a wide pH range.
Highlights
Coordination polymers (CPs) are crystalline materials formed by the self-assembly of metallic centers and multicoordinating organic molecules as bridging ligands through metal−ligand bonds.[1−5] The common interest in these compounds has been driven by their promising applications in fields such as ion exchange,[6] gas adsorption and separation processes,[7−10] drug delivery,[11] luminescence and sensing,[12−14] and catalysis.[15−17]
We report on the synthesis, structural characterization, and optical properties of highly robust europium(III) coordination polymers based on the segmented ligands (Chart 1) 5-((4-carboxyphenyl)ethynyl)picolinate (L12−) and 5,5′
The phase purity of the bulk materials was confirmed by Powder X-ray Diffraction (PXRD) measurements (Figure S1)
Summary
Coordination polymers (CPs) are crystalline materials formed by the self-assembly of metallic centers and multicoordinating organic molecules as bridging ligands through metal−ligand bonds.[1−5] The common interest in these compounds has been driven by their promising applications in fields such as ion exchange,[6] gas adsorption and separation processes,[7−10] drug delivery,[11] luminescence and sensing,[12−14] and catalysis.[15−17]. Quenching mechanism, electronic absorption spectra were recorded for aqueous solutions of the different metal ions and compared to the emission spectra of 1 and 2, together with those of corresponding ligands (Figure S13). For 1, it was found (Figure 11a) that Eubased emission is almost constant in the pH range comprised between 3 and 12, whereas at extreme acid or basic pH values, there is a complete disappearance of the luminescence, together with the onset of a molecular fluorescence emission (λmax = 396−432 nm), which is attributed to the decomposition of the complex and release of the free ligand in its protonated or fully deprotonated forms.[62] The remarkable stability of 1 was demonstrated after soaking the coordination. The lower stability of 2 outside the 3−8 pH range was confirmed by the presence of minor diffraction peaks in the Xray diffractogram
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