Magnetic properties and magnetocaloric effect of Ln = Dy, Tb carborane-based metal-organic frameworks

We present the synthesis and magneto-thermal properties of carborane-based lanthanide metal-organic frameworks (MOFs) with the formula {[(Ln)3(mCB-L)4(NO3)(DMF)n]·Solv}, where Ln = Dy or Tb, characterized by dc and ac susceptibility, X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and heat capacity measurements. The MOF structure is formed by polymeric 1D chains of Ln ions with three different coordination environments (Ln1, Ln2, Ln3) running along the b-axis, linked by carborane-based linkers thus to provide a 3D structure. Static magnetic measurements reveal that these MOFs behave at low temperature as a system of S* = 1/2 Ising spins, weakly interacting ferromagnetically along the 1D polymeric chain (J*/kB = +0.45 K (+0.5 K) interaction constant estimated for Dy-MOF (Tb-MOF)) and coupled to Ln ions in adjacent chains through dipolar antiferromagnetic interactions. The Dy MOF exhibits slow relaxation of magnetization through a thermally activated process, transitioning to quantum tunneling of the magnetization at low temperatures, while both compounds exhibit field-induced relaxation through a very slow, direct process. The maximum magnetic entropy changes (-ΔSmaxm) for an applied magnetic field change of 2-0 T are 5.71 J kg-1 K-1 and 4.78 J kg-1 K-1, for Dy and Tb MOFs, respectively, while the magnetocaloric effect (MCE) peak for both occurs at T ∼ 1.6 K, approximately double that for the Gd counterpart.

The crystal structure of catena-[nitrato-κ 2 O,O′-(μ 3-3-iodobenzene-1,2-dicarboxylato-κ 4 O:O′:O″,O‴)-(2,2′:6′,2″-terpyridine-κ 3 N,N′,N″)lanthanum(III)], C23H14IN4O7La

C23H14IN4O7La, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 8.2438(3) Å, b = 12.3786(5) Å, c = 12.6230(5) Å, α = 111.802(1)°, β = 91.144(1)°, γ = 100.6470(10)°, V = 1169.86(8) Å3, Z = 2, R gt(F) = 0.0313, wR ref(F 2) = 0.1051, T = 296 K.

Lanthanide ternary mixed-ligand coordination polymers as fluorescent sensors for the sensitive and selective detection of chlorogenic acid

A series of lanthanide coordination polymers constructed from ternary mixed ligands were synthesized. The Eu-CP has fluorescence sensing properties for chlorogenic acid. The film loaded with Eu-CP can be used for visual fluorescence detection.

A series of lanthanide(III) metal-organic frameworks derived from a pyridyl-dicarboxylate ligand: single-molecule magnet behaviour and luminescence properties

The reactions of LnIII ions with a versatile pyridyl-decorated dicarboxylic acid ligand lead to the formation of a series of novel three-dimensional (3D) Ln-MOFs, [Ln3(pta)4(Hpta)(H2O)]·xH2O (Ln = Dy (1), Eu (2), Gd (3), Tb (4), H2pta = 2-(4-pyridyl)-terephthalic acid, x = 6 for 1, 2.5 for 2, 1.5 for 3 and 2 for 4). The Ln3+ ions act as nine-coordinated muffin spheres, linking to each other to generate trinuclear {Ln3(OOC)6N2} SBUs, which are further extended to be interesting 3D topological architectures. To the best of our knowledge, the Dy-MOF exhibits zero-field single-molecule magnet (SMM) behaviour with the largest effective energy barrier among the previously reported 3D MOF-based Dy-SMMs. The combined analyses of a diluted sample (1@Y) and ab initio calculations demonstrate that the thermally assisted slow relaxation is mainly attributed to the single-ion magnetism. Furthermore, fluorescence measurements reveal that H2pta can sensitize EuIII and TbIII characteristic luminescence.

Water-stable LnIII-based coordination polymers displaying slow magnetic relaxation and luminescence sensing properties

Six Ln-CPs were synthesized: Dy-CP shows slow magnetic relaxation, and Eu-CP and Tb-CP exhibit recyclable and multi-responsive sensing for Fe³⁺, MnO₄⁻, Cr^VI-anions (CrO₄²⁻, Cr₂O₇²⁻) and TNP in an aqueous system.

Field induced slow magnetic relaxation in a zig-zag chain-like Dy(iii) complex with the ligand o-phenylenedioxydiacetato

Three relaxation channels in field-induced SMM [Dy(PDOA)(NO₃)(H₂O)₂]_n·nH₂O with DyO₉ chromophore.

Two topologically different 3D CuII metal-organic frameworks assembled from the same ligands: control of reaction conditions

Bifunctional ligands containing both carboxylic and sulfonate groups can adopt versatile coordination modes to produce novel metal-organic frameworks (MOFs) with high-dimensional networks and interesting topologies. Using 2,2'-disulfonylbiphenyl-4,4'-dicarboxylic acid (H₄L) as a linker and 4,4'-bipyridine (4,4'-bpy) as a co-ligand, two novel 3D Cu^II MOFs, {[Cu₂(L)(4,4'-bpy)_2.5(H₂O)]·1.7H₂O}_n, (1), and {[Cu₂(L)(4,4'-bpy)₂]·DMA·3H₂O}_n, (2), have been synthesized and structurally characterized by X-ray crystallography (DMA is N,N-dimethylacetamide). MOF (1) shows an unprecedented trinodal 4,4,5-connected topology network with the Schläfli symbol (4.6².7³)(4³.6⁵.7.8)(6.7³.8.10), while MOF (2) indicates a binodal 4,6-connected fsc network with the Schläfli symbol (4⁴.6¹⁰.8)(4⁴.6²). MOFs (1) and (2) were further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction and thermogravimetric analysis. MOF (1) shows a high water and chemical stability. The proton conductivity of (1) and CO₂ adsorption of (2) were also investigated.

Lanthanide coordination polymers based on designed bifunctional 2-(2,2':6',2″-terpyridin-4'-yl)benzenesulfonate ligand: syntheses, structural diversity and highly tunable emission

Seven novel lanthanide coordination polymers, [Eu(STP)(glu)]_n (1), [Ln₄(STP)₂(glu)₅]_n·4nH₂O [Ln = Er (2), Yb (3)], [Ln(STP)(1,3-bdc)]_n·0.5nH₂O [Ln = Tb (4), Yb (5)], and [Ln(STP)(1,2-bdc)]_n [Ln = Eu (6), Tb (7)] [NaSTP = sodium 2-(2,2':6',2″-terpyridin-4'-yl)benzenesulfonate, H₂glu = glutaric acid, H₂(1,3-bdc) = benzene-1,3-dicarboxylic acid, H₂(1,2-bdc) = benzene-1,2-dicarboxylic acid], have been prepared under hydrothermal conditions and characterized by elemental analysis, IR and single-crystal X-ray diffraction. Compound (1) possesses a 2D layered structure based on 1D chains with STP^- and glu^2- anions acting as bridges. Compounds (2) and (3) are isomorphous and show a rare 3D tcj/hc net with a tetranuclear Ln³⁺ unit regarded as a seven-connected node and a glu^2- anion serving as a three-connected node. Compounds (4) and (5) are isomorphous and exhibit six-connected pcu nets by denoting binuclear units to six-connected nodes. Compounds (6) and (7) display 3D 3,5T1 nets with (1,2-bdc)^2- anions and dimetallic units serving as three- and five-connected nodes, respectively. The Eu compounds (1) and (6) demonstrate typically red emission, while the Tb compounds (4) and (7) exhibit characteristic green emission. The emission spectra of heteronuclear compounds [Eu_xTb_1-x(STP)(1,2-bdc)]_n (0 ≤ x ≤ 1) as efficient luminescent tags were investigated. The intermetallic energy transfer of Tb to Eu was also evaluated.