Multifunctional Lanthanide-Based Metal–Organic Frameworks Derived from 3-Amino-4-hydroxybenzoate: Single-Molecule Magnet Behavior, Luminescent Properties for Thermometry, and CO₂ Adsorptive Capacity

Abstract

Herein, we describe and study a new family of isostructural multifunctional metal–organic frameworks (MOFs) with the formula {[Ln 5 L 6 (OH) 3 (DMF) 3 ]·5H 2 O} n (where (H 2 L) is 3-amino-4-hydroxybenzoic acid ligand) for magnetism and photoluminescence. Interestingly, three of the materials (Dy-, Er-, and Yb-based MOFs) present single-molecule magnet (SMM) behavior derived from the magnetic anisotropy of the lanthanide ions as a consequence of the adequate electronic distribution of the coordination environment. Additionally, photoluminescence properties of the ligand in combination with Eu and Tb counterparts were studied, including the heterometallic Eu–Tb mixed MOF that shows potential as ratiometric luminescent thermometers. Finally, the porous nature of the framework allowed showing the CO 2 sorption capacity.

Optical Phenomena in Molecule-Based Magnetic Materials

“…The (Hdmbpy)­[Dy III (H 2 dobdc) 2 (H 2 O)]·3H 2 O (H 4 dobdc = 2,5-dihydroxy­terephthalic acid, dmbpy = 4,4′-dimethyl-2,2′-bipyridine) MOF reveals a high proton conduction of 1.2·10 –3 S cm –1 at 100% RH and 343 K, accompanied by the ratiometric detection of pH within the broad luminescence of the H 2 dobdc 2– ligands . Furthermore, the series of [Ln III 5 (L 3a4hb ) 6 (OH) 3 (dmf) 3 ]·5H 2 O (H 2 L 3a4hb = 3-amino-4-hydroxybenzoic acid) frameworks shows various physical phenomena, such as field-induced SMM behavior for the Yb 3+ analog or ratiometric luminescence thermometry for the mixed Gd 3+ –Eu 3+ –Tb 3+ and Y 3+ –Eu 3+ –Tb 3+ systems, which are accompanied by the CO 2 adsorption properties . Among MOF materials, [(CH 3 ) 2 NH 2 ]­[Dy III (bptc)]·2H 2 O (H 4 bptc = biphenyl-3,3′,5,5′-tetracarboxylic acid) framework reveals the combination of field-induced SMM behavior, visible light Dy III -based emission, and selective adsorption of Rhodamine B, while its Gd III -based analog exhibits the similar adsorption property but accompanied by the magnetocaloric effect and proton conduction …”

“…The work on this compound was followed by a considerable number of reports concerning the introduction of proton conductivity into molecule-based materials incorporating lanthanide­(III) complexes. − For instance, [Dy III 2 (phen) 4 (paa) 4 ]­(ClO 4 ) 2 molecules with the 1,10-phenantroline (phen) ligands and 4-hydroxyphenylacetate anions (PAA) reveal the Dy­(III)-centered emission in the visible range, as well as field-induced SMM behavior under H dc = 2 kOe with the effective energy barrier of 86 K . This system also shows proton conductivity reaching the σ value of 1.08·10 –5 S cm –1 at 80°C and 100% RH.…”

Multifunctionality of luminescent molecular nanomagnets based on lanthanide complexes

“…[42][43][44][45][46] Complexes of lanthanide (Ln) ions, especially trivalent ions, have been shown to be one of the most effective molecular building blocks for the construction of multifunctional molecule-based materials. [47][48][49] The primary interest in Ln(III)based coordination assemblies has been devoted to their luminescent properties that are related to emissive f-f or d-f electronic transitions. [50][51][52] The photo-and electroluminescence of materials based on Ln complexes is adjustable through selection of the metal ion as well as the attached ligands which play a crucial role in achieving the high emission intensity through the ligand-to-metal energy-transfer process.…”

Aerogel-Based Single-Ion Magnets: A Case Study of a Cobalt(II) Complex Immobilized in Silica

“…For example, oxygen-responsive porous magnets for the non-cryogenic separation of molecular oxygen from air have been created using layered ruthenium complexes [ 16 ]. Other examples of SIM MOFs include rare earths [ 17 , 18 , 19 ], Mn 12 clusters [ 14 , 20 , 21 ], and cobalt-based MOFs [ 22 , 23 ]. Among them, Co(II)-containing highly porous MOFs have been shown to have excellent sensitivity to various aromatic molecules, including thianthrene, toluene, and pyrrole [ 24 ], and can be used as selective sensors for dimethylformamide and water, and as CO 2 storage materials [ 25 ].…”