Luminescent Lanthanide Metal Organic Frameworks as Chemosensing Platforms towards Agrochemicals and Cations

Since the first studies of luminescent sensors based on metal organic frameworks (MOFs) about ten years ago, there has been an increased interest in the development of specific sensors towards cations, anions, explosives, small molecules, solvents, etc. However, the detection of toxic compounds related to agro-industry and nuclear activity is noticeably scarce or even non-existent. In this work, we report the synthesis and characterization of luminescent lanthanide-based MOFs (Ln-MOFs) with diverse crystalline architectures obtained by solvothermal methods. The luminescent properties of the lanthanides, and the hypersensitive transitions of Eu3+ (5D0→7F2) and Tb3+ (5D4→7F5) intrinsically found in the obtained MOFs in particular, were evaluated and employed as chemical sensors for agrochemical and cationic species. The limit of detection (LOD) of Tb-PSA MOFs (PSA = 2-phenylsuccinate) was 2.9 ppm for [UO22+] and 5.6 ppm for [Cu2+]. The variations of the 4f–4f spectral lines and the quenching/enhancement effects of the Ln-MOFs in the presence of the analytes were fully analyzed and discussed in terms of a combinatorial “host–guest” vibrational and “in-silico” interaction studies.

Complexation studies of 3-substituted β-diketones with selected d- and f-metal ions

Results of spectroscopic investigations related to complex compositions of 3-substituted derivatives of pentane-2,4-dione (β-diketonate) complexes with chosen d- and f-metal ions are presented. Ligands 3-allylacetylacetone (3all-acac) and 3-benzylacetylacetone (3ben-acac) were prepared and used for the complexation study with Cu(II), Co(II), Nd(III), and Ho(III) metal ions. Based on the absorption spectra of lanthanide ions in their hypersensitive transitions, with the use of computer assisted target factor analysis (CAT) and absorption spectra of the ligands with Cu(II) and Co(II), the verification of complex compositions and the determination of their stability constants were achieved. In case of Nd(III) and Ho(III) complexes with β-diketone ligands, absorption of their maxima were studied in the range of hypersensitive transitions 4 I 9/2 → 4 F 7/2 + 4 S 3/2 (λ max ∼ 734 nm and 748 nm) for Nd(III) and in the range of 435–465 nm, corresponding to the hypersensitive transition 5 G 6 → 5 I 8 (λ max ∼ 450 nm), for Ho(III).