Multi-Responsive Luminescent Sensors Based on Two-Dimensional Lanthanide–Metal Organic Frameworks for Highly Selective and Sensitive Detection of Cr(III) and Cr(VI) Ions and Benzaldehyde

Four new isostructural two-dimensional lanthanide­(III)–metal organic frameworks (MOFs), namely, [Ln­(L)­(HCOO)­(H₂O)]_<i>n</i> (Ln = Eu <b>1</b>, Gd <b>2</b>, Ho <b>3</b>, and Tb <b>4</b>, H₂L = 5-((2′-cyano-[1,1′-biphenyl]-4-yl)­methoxy)­isophthalic acid), with a uninodal {4⁴.6²}-<i>sql</i> topology have been successfully isolated. Compounds <b>1</b> and <b>4</b> exhibit excellent applications as luminescent sensors for sensing benzaldehyde in methanol and Cr³⁺, CrO₄^2–, and Cr₂O₇^2– in water with high sensitivity and selectivity based on luminescence quenching effects. Interestingly, <b>1</b> and <b>4</b> display excellent recyclable behaviors and can be recycled at least five times for sensing benzaldehyde, Cr­(III) and Cr­(VI) ions. These two compounds are the first multifunctional Ln–MOFs sensors for detecting benzaldehyde, Cr­(III) and Cr­(VI) ions, simultaneously. Therefore, these two materials may be excellent multifunctional recyclable luminescent sensors

Lanthanide–Nitronyl Nitroxide Chains Derived from Multidentate Nitronyl Nitroxides

Unprecedented lanthanide (Ln)-radical loop-chain coordination polymers were achieved using multidentate pyridyl- or triazole- substituted nitronyl nitroxide ligands. Their magnetic units consist of ferromagnetic [Ln₂Radical] moieties, leading for the dysprosium­(III) derivatives to slow relaxation of magnetization, which was found to be dependent on the heterocyclic ligands

[(Cu-Radical)₂‑Ln]: Structure and Magnetic Properties of a Hetero-tri-spin Chain of Rings (Ln = Y^III, Gd^III, Tb^III, Dy^III)

Novel hetero-tri-spin coordination polymers formed of ring-shaped Cu-nitronyl nitroxide spin clusters and Ln^III linkers are reported. These mixed 2p-3d-4f compounds of formula {[Ln­(hfac)₃]­[Cu­(hfac)₂(NIT-3Py)]₂·C₆H₁₄}_<i>n</i> [Ln^III = Y (<b>1</b>), Gd (<b>2</b>), Tb (<b>3</b>), and Dy (<b>4</b>); NIT-3Py = 2-(3-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexa-fluoroacetylacetonate], exhibit a 1D chain structure consisting of [Cu­(NIT-3Py)]₂ rings linked by Ln­(hfac)₃ units. Their magnetic behavior is characteristic for ferromagnetic interactions between the metal centers and the coordinated radical units. The Tb derivative was found to exhibit slow relaxation of its magnetization

Thermal Magnetic Hysteresis in a Copper–Gadolinium–Radical Chain Compound

Magnetic bistability spanning over a temperature domain of 40 K can result from a small structural deformation of the gadolinium aminoxyl coordination. This is illustrated for a nitronyl nitroxide 3d–4f chain, [Ln­(hfac)₃Cu­(hfac)₂(NIT-Pyrim)₂] (Ln^III = Gd, Dy), which is the first example of a bistable lanthanide-based complex

Slow Magnetic Relaxation in Ladder-Type and Single-Strand 2p–3d–4f Heterotrispin Chains

Ladder-type and chain 2p–3d–4f complexes based on a bridging nitronyl nitroxide radical, namely, [LnCu­(hfac)₅(NIT-Ph-<i>p</i>-OCH₂trz)]·0.5C₆H₁₄ [Ln = Y (<b>1a</b>), Dy (<b>1b</b>)] and [LnCu­(hfac)₅(NIT-Ph-<i>p</i>-OCH₂trz)] [Ln = Y (<b>2a</b>), Dy (<b>2b</b>); NIT-Ph-<i>p</i>-OCH₂trz = 2-[4-[(1<i>H</i>-1,2,4-triazol-1-yl)­methoxy]­phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been successfully achieved through a one-pot reaction of the NIT-Ph-<i>p</i>-OCH₂trz radical with Cu­(hfac)₂ and Ln­(hfac)₃·2H₂O. Complexes <b>1a</b> and <b>1b</b> feature a ladder-like structure, where the rails are made of Ln­(III) and Cu­(II) ions alternatively bridged by nitronyl nitroxide and the triazole units while the NIT-Ph-<i>p</i>-OCH₂trz moieties act as the rungs of the ladder. Complexes <b>2a</b> and <b>2b</b> consist of one-dimensional nitronyl nitroxide bridged Ln coordination polymers with dangly Cu­(II) units connected to the triazole moieties. All of compounds exhibit ferromagnetic NIT-Dy and/or NIT-Cu interactions. Both Dy derivatives (<b>1b</b> and <b>2b</b>) show frequency-dependent out-of-phase magnetic susceptibility signals in a zero field indicating slow magnetic relaxation behavior

Functionalized Nitronyl Nitroxide Biradicals for the Construction of 3d–4f Heterometallic Compounds

Functionalized nitronyl nitroxide biradical ligands incorporating pyridine groups hold Co^II and Ln^III ions together, creating biradical-based 3d–4f tetranuclear complexes [Ln₂Co₂(hfac)₁₀(NITPhPybis)₂] [Ln^III = Gd (<b>1</b>), Tb (<b>2</b>), Dy (<b>3</b>), and Ho (<b>4</b>); NITPhPybis = 5-(4-pyridyl)-1,3-bis­(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1<i>H</i>-imidazol-2-yl)­benzene; hfac = hexafluoroacetylacetonate]. These complexes have a centrosymmetric cyclic molecular structure in which two biradicals perform as tetradentate ligands to bind two Co^II and two Ln^III ions, resulting in a rare octaspin system. Direct-current (dc) magnetic susceptibility studies reveal that the strong antiferromagnetic Co^II-NO magnetic exchange dominates the present magnetic system, while magnetic coupling of Gd-ON is ferromagnetic. Analysis of the magnetic data of the Gd complex allows us to determine the magnetic parameters through the appropriate magnetic model. Alternating-current (ac) magnetic susceptibility investigations indicate that <b>2</b> displays frequency-dependent out-of-phase signals under a zero dc field, while ac magnetic susceptibilities of <b>3</b> show field-induced frequency dependence, which is a typical feature of slow relaxation of the magnetization. Complexes <b>1</b>–<b>4</b> represent the first nitronyl nitroxide biradical-based 3d–4f compounds

From Monomeric Species to One-Dimensional Chain: Enhancing Slow Magnetic Relaxation through Coupling Mononuclear Fragments in Ln-rad System

By reacting nitronyl nirtroxide radical NIT-Ph2OEt (NIT-Ph2OEt = 2-(2′-ethoxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) with Ln­(hfac)₃(hfac = hexafluoroacetylacetonate), four new Ln–nitronyl nitroxide complexes, namely, mononuclear species [Ln­(hfac)₃(NIT-Ph2OEt)₂]­(Ln^III = Gd <b>1a</b>, Tb <b>1b</b>) and one-dimensional chains [Ln­(hfac)₃(NIT-Ph2OEt)]_<i>n</i> (Ln^III = Gd <b>2a</b>, Tb <b>2b</b>), have been successfully obtained through controlling the reaction temperature and the ratio of radical ligand and Ln­(hfac)₃. DC magnetic susceptibilities indicate that the ferromagnetic couplings occur between the coordination radicals and the Ln­(III) ions for four complexes. No nonzero out-of-phase signals are observed for mononuclear segment <b>1b</b>, whereas the corresponding 1D chain <b>2b</b> exhibits frequency-dependent out-of-phase signals indicating single-chain magnet behavior, which implies that the intrachain next-nearest-neighbor (NNN) LnLn magnetic interactions play a crucial role for enhancing slow magnetic relaxation in the chain. Moreover, Tb chain exhibits rare three-step field-induced metamagnetic behavior

A New Nitronyl Nitroxide Radical as Building Blocks for a Rare <i>S</i> = 13/2 High Spin Ground State 2p-3d Complex and a 2p-3d-4f Chain

A new nitronyl nitroxide radical L (L = 2-(4-(5-methyl-carbonyl-3-pyriyl)­benzoxo)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) containing N–O groups and the pyridyl nitrogen group was designed and synthesized as a multidentate ligand to obtain compounds with interesting structures and magnetic properties from 3d or 3d-4f precursors. The reaction of Cu­(hfac)₂ and/or Gd­(hfac)₃·2H₂O (hfac = hexafluoroacetylacetonate) with L resulted in a rare <i>S</i> = 13/2 high spin ground state Cu^II complex [(Cu­(hfac)₂)₇(L)₆] (<b>1</b>) and a Cu^II–Gd^III chain complex [Gd­(hfac)₃­Cu­(hfac)₂(L)₂]<i>_n</i>­·0.5CH₂Cl₂ (<b>2</b>). Single crystal X-ray diffraction studies indicate that the N–O groups of the L radicals are all axially bound to Cu^II ions in complex <b>1</b>, which result in the ferromagnetic exchange between Cu^II and radicals and an <i>S</i> = 13/2 high spin ground state. While adding Gd­(hfac)₃ units to the system of Cu­(hfac)₂ and L radical, a one dimension chain structure is obtained, and there are ferromagnetic Gd^III-radical interactions and antiferromagnetic radical–radical coupling in the chain