Flexible Ligand‐Based Lanthanide Three‐Dimensional Metal–Organic Frameworks with Tunable Solid‐State Photoluminescence and OH‐Solvent‐Sensing Properties

Abstract

Luminescent 3D metal–organic frameworks (MOFs) constructed from trivalent lanthanides Nd3+, Sm3+, Eu3+, Gd3+, Tb3+ and a flexible ligand, 2‐methylsuccinate, (Ln‐msucc) have been hydrothermally obtained as polycrystalline solids. They were fully characterized by X‐ray powder diffraction, thermal analysis, vibrational spectroscopy, and scanning electron microscopy. The crystalline structure and topological features were elucidated and compared with those of related Ln‐MOFs. The magnetic studies reveal that Nd‐msucc and Gd‐msucc present antiferromagnetic and ferromagnetic behavior, respectively. Moreover, the solid‐state photoluminescence properties of all the compounds were fully explored. Depending on the lanthanide content, these materials exhibited luminescence in the near‐infrared and visible regions. In particular, the photophysical behavior of the Eu phase was exhaustively examined and the radiative and nonradiative constants and intrinsic quantum yields were calculated. The hypersensitive nature of the Eu3+ 5D0→7F2 transition allowed an in‐depth study of the optical response in the presence of various protic and aprotic solvents. As far as we know, the chemical‐sensing studies employing Eu‐msucc constitute the first case reported for a lanthanide succinate‐derived framework. The obtained results are promising for the elaboration of specific chemical sensors based on this material.

Two Series of Substituent‐Group‐Directed Adipate‐Based Lanthanide Coordination Polymers: Syntheses, Structures, Photoluminescence, and Magnetism

“…The excitation and emission spectra for 2 , 3 , 5 , 6 , 9 , 11 , and 12 are shown in Figure , Figure , Figure , Figure , Figure , Figure , and Figure . All of the excitation spectra for 2 , 3 , 5 , 6 , 9 , 11 , and 12 recorded by monitoring the strongest emissions of the lanthanide ions exhibit the f–f transitions . For 2 (Figure ), the excitation sharp lines at 295, 307, 318, 332, 346, 363, 376, 391, 403, 418, 441, 453–480, 500, and 531 nm can be ascribed to the 4 H 15/2 → 4 F 9/2 / 4 I 9/2 , 4 H 15/2 → 4 P 5/2 , 4 H 15/2 → 4 P 3/2 , 4 H 15/2 → 4 G 9/2 , 4 H 15/2 → 4 D 7/2 , 4 H 15/2 → 6 P 5/2 / 4 D 5/2 , 4 H 15/2 → 6 P 7/2 , 4 H 15/2 → 4 L 15/2 , 4 H 15/2 → 6 P 3/2 , 4 H 15/2 → 4 P 5/2 / 6 P 5/2 , 4 H 15/2 → 4 M 17/2 / 4 G 9/2 , 4 H 15/2 → 4 I 11/2 / 4 I 13/2 , 4 H 15/2 → 4 G 5/2 , and 4 H 15/2 → 4 F 3/2 transitions of Sm III , respectively.…”

“…For 2 (Figure ), the excitation sharp lines at 295, 307, 318, 332, 346, 363, 376, 391, 403, 418, 441, 453–480, 500, and 531 nm can be ascribed to the 4 H 15/2 → 4 F 9/2 / 4 I 9/2 , 4 H 15/2 → 4 P 5/2 , 4 H 15/2 → 4 P 3/2 , 4 H 15/2 → 4 G 9/2 , 4 H 15/2 → 4 D 7/2 , 4 H 15/2 → 6 P 5/2 / 4 D 5/2 , 4 H 15/2 → 6 P 7/2 , 4 H 15/2 → 4 L 15/2 , 4 H 15/2 → 6 P 3/2 , 4 H 15/2 → 4 P 5/2 / 6 P 5/2 , 4 H 15/2 → 4 M 17/2 / 4 G 9/2 , 4 H 15/2 → 4 I 11/2 / 4 I 13/2 , 4 H 15/2 → 4 G 5/2 , and 4 H 15/2 → 4 F 3/2 transitions of Sm III , respectively. [23a] The emission spectrum of 2 (Figure ) excited at 404 nm displays the characteristic emissions of Sm III at 562 ( 5 G 2 → 6 H 5/2 ), 597 ( 5 G 2 → 6 H 7/2 ), 643 ( 5 G 2 → 6 H 9/2 ), and 705 nm ( 5 G 2 → 6 H 11/2 ), respectively . The most intense 5 G 2 → 6 H 9/2 emission at 643 nm is responsible for the pink luminescence of the Sm III ion.…”

Reviewing Rare Earth Succinate Frameworks from the Reticular Chemistry Point of View: Structures, Nets, Catalytic and Photoluminescence Applications

“…The same underlying net is also associated with a big family of isomorphic compounds that belongs to the 3D‐6 structural type and can be obtained with succ, msucc and 2,3‐dms ligands (see Table and Figure ). These compounds crystallises in the space group with general formulae [Ln 2 (succ) 3 (H 2 O) 2 ]⋅nAr, with Ar=aromatic molecule,, [Ln 2 (msucc) 3 (H 2 O) 2 ] and [Ln 2 (2,3‐dms) 3 (H 2 O) 2 ] . Additionally, a phase with formula [La 2 (2,3‐dms) 3 (H 2 O) 2 ] was also included in 3D‐6 since it exhibits the same structural features as the members of the lanthanide 2,3‐dms series, though it was reported as belonging to the C2/c S.G.…”

“…In the case of 2‐methylsuccinate or 2,3‐dimethylsuccinate as ligands, the stabilisation of the structure is achieved by the filling effect of the methyl substituents oriented to the channels of higher transversal area. Consequently, a diminution of 48 % and 80 % in the cell void volume occurs when one (msuc) or two methyl groups (2,3‐dms) per succinate are added, respectively, when compared with the potential available void volume of the succinate framework if the aromatic molecule is removed.…”

“…Motivated by this attractive application, we chose 3D‐6 Eu‐msucc for sensing protic and aprotic solvents, taking advantages of its strong 4f luminescence based on the hypersensitive transition 5 D 0 → 7 F 2 . A high dependence of the intensity values of such transition with the nature of the solvent was observed in the emission spectra; this fact is particularly marked in case of water which produces a significant quenching effect (Figure ).…”