Fluoride‐Bridged {GdIII3MIII2} (M=Cr,Fe, Ga) Molecular Magnetic Refrigerants

The reaction of fac‐[M^IIIF₃(Me₃tacn)]⋅x H₂O with Gd(NO₃)₃⋅5H₂O affords a series of fluoride‐bridged, trigonal bipyramidal {Gd^III₃M^III₂} (M=Cr ( 1 ), Fe ( 2 ), Ga ( 3 )) complexes without signs of concomitant GdF₃ formation, thereby demonstrating the applicability even of labile fluoride‐complexes as precursors for 3d–4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3 J kg⁻¹ K⁻¹ ( 1 ) and 33.1 J kg⁻¹ K⁻¹ ( 2 ) for the field change 7 T→0 T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe–Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close‐lying excited states for successful design of molecular refrigerants.     

Low‐Dimensional Carboxylate‐Bridged GdIII Complexes for Magnetic Refrigeration

Four carboxylate‐bridged Gd^III complexes ( 1 – 4 ) with 1D/2D structures have been synthesized by using the hydrothermal reaction of Gd₂O₃ with various carboxylate ligands. Compounds 1 and 2 contained the same [2n] Gd^III? OH ladders, but with different crystallographically independent Gd^III ions, whilst the structures of compounds 3 and 4 were composed of [Gd₄(μ₃‐OH)₂(piv)₈(H₂O)₂]²⁺ units and 1D ladder Gd^III chains, respectively. Antiferromagnetic interactions occurred in compounds 1 – 3 , owing to their small Gd? O? Gd angles, whereas ferromagnetic coupling occurred in compound 4 , in which the Gd? O? Gd angles were larger. These complexes exhibited a distinct magnetocaloric effect (MCE), which was affected by their different magnetic densities and exchange interactions. Among these compounds, complex 4 presented the largest MCE (?ΔS_m^max=43.6 J kg^?1 K^?1), the lowest M_w/N_Gd ratio (the highest magnetic density), and weak ferromagnetic coupling. Therefore, a lower M_w/N_Gd ratio and weaker exchange interactions (a smaller absolute value of θ) between Gd^III ions resulted in a larger MCE for the Gd^III complexes.     

Magnetocaloric Properties of Heterometallic 3d–Gd Complexes Based on the [Gd(oda)3]3− Metalloligand

A series of heterometallic 3d–Gd³⁺ complexes based on a lanthanide metalloligand, [M(H₂O)₆][Gd(oda)₃] ? 3 H₂O [M=Cr³⁺ ( 1‐Cr )] (H₂oda=2,2′‐oxydiacetic acid), [M(H₂O)₆][MGd(oda)₃]₂ ? 3 H₂O [M=Mn²⁺ ( 2‐Mn ), Fe²⁺ ( 2‐Fe ) and Co²⁺ ( 2‐Co )], and [M₃Gd₂(oda)₆(H₂O)₆] ? 12 H₂O [M=Ni²⁺ ( 3‐Ni ), Cu²⁺ ( 3‐Cu ), and Zn²⁺ ( 3‐Zn )], are reported. Magnetic and heat‐capacity studies revealed a significant impact on the magnetocaloric effect depending on the anisotropy of the 3d transition metal ions, as confirmed by comparison of the observed maximum values of ?ΔS_m between complexes 2‐Co and 1‐Cr . In these two complexes, the 3d metal ions have the same spin (S=3/2 for Co²⁺ and Cr³⁺ ions), and the theoretical calculation suggested a larger ?ΔS_m value for 2‐Co (47.8 J K^?1 kg^?1) than 1‐Cr (37.5 J K^?1 kg^?1); however, the significant anisotropy of Co²⁺ ions in 2‐Co , which can result in smaller effective spins, gives a smaller value of ?ΔS_m for 2‐Co (32.2 J K^?1 kg^?1) than for 1‐Cr (35.4 J K^?1 kg^?1) at ΔH=9 T.     

Three Phenoxo‐Bridged Dinuclear Lanthanide Complexes: Syntheses,Crystal Structures,and Magnetic Properties

Three dinuclear lanthanide complexes [Ln₂(H₂L)₂(NO₃)₄] [Ln = Dy ( 1 ), Tb ( 2 ), and Gd ( 3 )] [H₃L = 2‐hydroxyimino‐N′‐[(2‐hydroxy‐3‐methoxyphenyl)methylidene]‐propanohydrazone] were solvothermally synthesized by varying differently anisotropic rare earth ions. Single‐crystal structural analyses demonstrate that all the three complexes are crystallographically isostructural with two centrosymmetric Ln^III ions aggregated by a pair of monodeprotonated H₂L^– anions. Weak intramolecular antiferromagnetic interactions with different strength were mediated by a pair of phenoxo bridges due to superexchange and/or single‐ion anisotropy. Additionally, the Dy^III‐based entity shows the strongest anisotropy exhibits field‐induced single‐molecule magnetic behavior with two thermally activated relaxation processes. In contrast, 3 with isotropic Gd^III ion has a significant cryogenic magnetocaloric effect with the maximum entropy change of 25.7 J · kg^–1 · K^–1 at 2.0 K and 70.0 kOe.     

Decanuclear Ln10 Wheels and Vertex‐Shared Spirocyclic Ln5 Cores: Synthesis,Structure, SMM Behavior,and MCE Properties

The reaction of a Schiff base ligand (LH₃) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln₁₀ (Ln=Dy( 1 ), Tb( 2 ), and Gd ( 3 )) and pentanuclear Ln₅ complexes (Ln=Gd ( 4 ), Tb ( 5 ), and Dy ( 6 )), respectively. The formation of Ln₁₀ and Ln₅ complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes ( 1 – 6 ) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (U_eff)=16.12(8) K and relaxation time (τ_o)=3.3×10^?5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out‐of‐phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: ?ΔS_m=26.6 J kg^?1 K^?1 at T=2.2 K for 3 and ?ΔS_m=27.1 J kg^?1 K^?1 at T=2.4 K for 4 , both for an applied field change of 7 T.     

Cyano‐Bridged Aqua(N,N‐Dimethylacetamide)(cyanoiron)lanthanides from Samarium,Gadolinium, or Holmium Nitrate and Potassium Hexacyanoferrate: Crystal Structures and Magnetochemistry

Three cyano‐bridged aqua(N,N‐dimethylacetamide)(cyanoiron)lanthanide complexes were synthesized by the reaction of K₃Fe(CN)₆, Ln(NO₃)₃⋅6 H₂O (Ln=Sm, Gd, Ho), and N,N‐dimethylacetamide (DMA). The obtained complexes 1 – 3 exhibit different coordination geometries and crystal structures. The polymeric {[Sm(DMA)₂(H₂O)₄Fe(CN)₆⋅5 H₂O}_n ([SmFe]_n; 1 ) has a one‐dimensional chain structure with approximately parallel trans‐positioned bridging CN ligands between the Sm‐ and Fe‐atoms. [(Gd(DMA)₃(H₂O)₄)₂Fe(CN)₆]⋅[Fe(CN)₆]⋅3 H₂O (Gd₂Fe; 2 ) is an isolated trinuclear Gd(1)−Fe−Gd(2) complex with two approximately perpendicular cis‐positioned bridging CN ligands between the two Gd‐atoms and the Fe‐atom. [Ho(DMA)₃(H₂O)₃Fe(CN)₆]⋅3 H₂O (HoFe; 3 ) adopts a single dinuclear crystal structure with only one bridging CN between the Ho‐ and Fe‐atom. Magnetochemistry experiments establish weak antiferromagnetic interactions between Gd^III (and Ho^III) and Fe^III atoms. Especially the [SmFe]_n complex 1 exhibits long‐range magnetic ordering, T_c=3.5 K, and a stronger coercive force, H_c=1400 Oe.     

Serum Albumin Targeted,pH‐Dependent Magnetic Resonance Relaxation Agents

The objective of this work was the synthesis of serum albumin targeted, Gd^III‐based magnetic resonance imaging (MRI) contrast agents exhibiting a strong pH‐dependent relaxivity. Two new complexes ( Gd‐glu and Gd‐bbu ) were synthesized based on the DO3A macrocycle modified with three carboxyalkyl substituents α to the three ring nitrogen atoms, and a biphenylsulfonamide arm. The sulfonamide nitrogen coordinates the Gd in a pH‐dependent fashion, resulting in a decrease in the hydration state, q, as pH is increased and a resultant decrease in relaxivity (r₁). In the absence of human serum albumin (HSA), r₁ increases from 2.0 to 6.0 mM ^?1 s^?1 for Gd‐glu and from 2.4 to 9.0 mM ^?1 s^?1 for Gd‐bbu from pH 5 to 8.5 at 37 °C, 0.47 T, respectively. These complexes (0.2 mM ) are bound (>98.9 %) to HSA (0.69 mM ) over the pH range 5–8.5. Binding to albumin increases the rotational correlation time and results in higher relaxivity. The r₁ increased 120 % (pH 5) and 550 % (pH 8.5) for Gd‐glu and 42 % (pH 5) and 260 % (pH 8.5) for Gd‐bbu . The increases in r₁ at pH 5 were unexpectedly low for a putative slow tumbling q=2 complex. The Gd‐bbu system was investigated further. At pH 5, it binds in a stepwise fashion to HSA with dissociation constants K_d1=0.65, K_d2=18, K_d3=1360 μM . The relaxivity at each binding site was constant. Luminescence lifetime titration experiments with the Eu^III analogue revealed that the inner‐sphere water ligands are displaced when the complex binds to HSA resulting in lower than expected r₁ at pH 5. Variable pH and temperature nuclear magnetic relaxation dispersion (NMRD) studies showed that the increased r₁ of the albumin‐bound q=0 complexes is due to the presence of a nearby water molecule with a long residency time (1–2 ns). The distance between this water molecule and the Gd ion changes with pH resulting in albumin‐bound pH‐dependent relaxivity.     

Unprecedented Sensitization of Visible and Near‐Infrared Lanthanide Luminescence by Using a Tetrathiafulvalene‐Based Chromophore

Ligand L was synthesized and then coordinated to [Ln(hfac)₃] ? 2 H₂O (Ln^III=Tb, Dy, Er; hfac^?=1,1,1,5,5,5‐hexafluoroacetylacetonate anion) and [Ln(tta)₃]?2 H₂O (Ln^III=Eu, Gd, Tb, Dy, Er, Yb; tta^?=2‐thenoyltrifluoroacetonate) to give two families of dinuclear complexes [Ln₂(hfac)₆( L )] ? C₆H₁₄ and [Ln₂(tta)₆( L )] ? 2 CH₂Cl₂. Irradiation of the ligand at 37 040 cm^?1 and 29 410 cm^?1 leads to tetrathiafulvalene‐centered and 2,6‐di(pyrazol‐1‐yl)‐4‐pyridine‐centered fluorescence, respectively. The ligand acts as an organic chromophore for the sensitization of the infrared Er^III (6535 cm^?1) and Yb^III (10 200 cm^?1) luminescence. The energies of the singlet and triplet states of L are high enough to guarantee an efficient sensitization of the visible Eu^III luminescence (17 300–14 100 cm^?1). The Eu^III luminescence decay can be nicely fitted by a monoexponential function that allows a lifetime estimation of (0.49±0.01) ms. Finally, the magnetic and luminescence properties of [Yb₂(hfac)₆( L )] ? C₆H₁₄ were correlated, which allowed the determination of the crystal field splitting of the ²F_7/2 multiplet state with M_J=±1/2 as ground states.     

Synthesis,structures and magnetic properties of cyano- and amide-bridged FeIII-LnIII tetranuclear heterometallic clusters

Three Fe^III₂Ln^III₂ tetranuclear heterometallic clusters, [H₄LGd(H₂O)Tp*Fe(CN)₃]₂·8H₂O·2MeOH (1) and [H₄LLn(MeOH)Tp*Fe(CN)₃]₂·6MeOH·2MeCN (Ln?=?Tb and Dy for 2 and 3, respectively, H₆L = N,N′-(2,6-pyridine-dicarboxyl)-disalicylhydrazide, Tp* = hydridotris(3,5dimethylpyrazol-1-yl)-borate), were synthesized by use of the [(Tp*)Fe(CN)₃]^? unit as a metalloligand toward LnCl₃ and H₆L species. Structural analyses reveal that Fe^III and Ln^III ions in all complexes are connected to each other by one cyanide to form a heterobinuclear unit of [Ln(H₄L)][(Tp*)Fe(CN)₃], which is dimerized through Ln–N–C?=?O–Ln interaction. Magnetic susceptibility measurements show weak antiferromagnetic interactions between cyano-bridged Fe^III and Gd^III ions and amide-bridged Gd^III ions are operative. Complex 1 displays the magnetocaloric effect with ?ΔS_m^max = 12.70 J·kg^?1·K^?1 at 4.0 K for ΔH?=?7 T. No single-molecule magnetic properties are observed for 2 or 3 down to 1.8 K.     

Rational Electrostatic Design of Easy‐Axis Magnetic Anisotropy in a ZnII–DyIII–ZnII Single‐Molecule Magnet with a High Energy Barrier

Two novel trinuclear complexes [ZnCl(μ‐L)Ln(μ‐L)ClZn][ZnCl₃(CH₃OH)]?3 CH₃OH (Ln^III=Dy ( 1 ) and Er ( 2 )) have been prepared from the compartmental ligand N,N′‐dimethyl‐N,N′‐bis(2‐hydroxy‐3‐formyl‐5‐bromo‐benzyl)ethylenediamine (H₂L). X‐ray studies reveal that Ln^III ions are coordinated by two [ZnCl(L)]^? units through the phenoxo and aldehyde groups, giving rise to a LnO₈ coordination sphere with square‐antiprism geometry and strong easy‐axis anisotropy of the ground state. Ab initio CASSCF+RASSI calculations carried out on 1 confirm that the ground state is an almost pure M_J=±15/2 Kramers doublet with a marked axial anisotropy, the magnetic moment is roughly collinear with the shortest Dy?O distances. This orientation of the local magnetic moment of the Dy^III ion in 1 is adopted to reduce the electronic repulsion between the oblate electron shape of the M_J=±15/2 Kramers doublet and the phenoxo‐oxygen donor atoms involved in the shortest Dy?O bonds. CASSCF+RASSI calculations also show that the ground and first excited states of the Dy^III ion are separated by 129 cm^?1. As expected for this large energy gap, compound 1 exhibits, in a zero direct‐current field, thermally activated slow relaxation of the magnetization with a large U_eff=140 K. The isostructural Zn–Er–Zn species does not present significant SMM behavior as expected for the prolate electron‐density distribution of the Er^III ion leading to an easy‐plane anisotropy of the ground doublet state.     

Two Lanthanide(III)?Copper(II) Organic Frameworks Based on {OLn6} Clusters that Exhibited a Large Magnetocaloric Effect and Slow Relaxation of the Magnetization

Two new 3D lanthanide(III)? copper(II) organic frameworks based on unusual {OLn₆} clusters have been successfully synthesized and fully characterized. Crystallographic studies showed that the {OLn₆} clusters acted as 12‐connected nodes that were linked together by [CuL₂] (H₂L=3‐hydroxypyrazine‐2‐carboxylic acid) moieties to construct an interesting 4,12‐c net with the point symbol {4³⁶.6³⁰}{4⁴.6²}₃. Magnetic studies revealed that these two isostructural heterometallic frameworks exhibited different magnetic properties, depending on the different anisotropies of the lanthanide spin carriers: Gd‐Cu showed a large magnetocaloric effect, with an entropy change (?ΔS_m) of 35.76 J kg^?1 K^?1, which is one of the largest values in high‐dimensional complexes, whilst Dy‐Cu exhibited slow relaxation of the magnetization at low temperatures.     

Enhancement of TbIII–CuII Single‐Molecule Magnet Performance through Structural Modification

We report a series of 3d–4f complexes {Ln₂Cu₃(H₃L)₂X_n} (X=OAc^?, Ln=Gd, Tb or X=NO₃^?, Ln=Gd, Tb, Dy, Ho, Er) using the 2,2′‐(propane‐1,3‐diyldiimino)bis[2‐(hydroxylmethyl)propane‐1,3‐diol] (H₆L) pro‐ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb₂Cu₃(H₃L)₂X_n} complexes is seen by changing the auxiliary ligands (X=OAc^? for NO₃^?). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu‐based single‐molecule magnet. Ab initio CASSCF calculations performed on mononuclear Tb^III models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the Tb^III coordination environment (C_4v versus C_s).     

Comprehensive Evaluation of the Physicochemical Properties of LnIII Complexes of Aminoethyl‐DO3A as pH‐Responsive T1‐MRI Contrast Agents

N‐Substituted aminoethyl groups were attached to 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (DO3A) with the aim to design pH‐responsive Ln^III complexes based on the pH‐dependent on/off ligation of the amine nitrogen to the metal ion. The following ligands were synthesized: AE ‐ DO3A (aminoethyl‐DO3A), MAE ‐ DO3A (N‐methylaminoethyl‐DO3A), DMAE ‐ DO3A (N,N‐dimethylaminoethyl‐DO3A) and MEM ‐ AE ‐ DO3A (N‐methoxyethyl‐N‐methylaminoethyl‐DO3A). The physicochemical properties of the Ln^III complexes were investigated for the evaluation of their potential applicability as magnetic resonance imaging (MRI) contrast agents. In particular, a ¹H and ¹⁷O NMR relaxometric study was carried out for these Gd^III complexes at two different pH values: at basic pH (pendant amino group coordinated to the metal centre) and at acidic pH (protonated amine, not interacting with the metal ion). Eu^III complexes allow one to estimate the number of inner‐sphere water molecules through luminescence lifetime measurements and obtain some structural information through variable‐temperature (VT) high‐resolution ¹H NMR studies. Equilibria between differently hydrated species were found for most of the complexes at both acidic and basic pH. The thermodynamic stability of Ca^II, Zn^II, Cu^II and Ln^III complexes and kinetics of formation and dissociation reactions of Ln^III complexes of AE ‐ DO3A and DMAE ‐ DO3A were investigated showing stabilities comparable to currently approved Gd^III‐based CAs. In detail, higher total basicity (Σlog K_i^H) and higher stability constants of Ln^III complexes were found for AE ‐ DO3A with respect to DMAE ‐ DO3A (i.e., log K_{Gd‐ AE‐DO3A} =22.40 and log K_{Gd‐ DMAE‐DO3A} =20.56). The transmetallation reactions of Gd^III complexes are very slow (Gd‐ AE ‐ DO3A : t_1/2=2.7×10⁴ h; Gd‐ DMAE ‐ DO3A : 1.1×10⁵ h at pH 7.4 and 298 K) and occur through proton‐assisted dissociation.     

Anion‐Templated Assembly and Magnetocaloric Properties of a Nanoscale {Gd38} Cage versus a {Gd48} Barrel

The comprehensive study reported herein provides compelling evidence that anion templates are the main driving force in the formation of two novel nanoscale lanthanide hydroxide clusters, {Gd₃₈(ClO₄)₆} ( 1 ) and {Gd₄₈Cl₂(NO₃)} ( 2 ), characterized by single‐crystal X‐ray crystallography, infrared spectroscopy, and magnetic measurements. {Gd₃₈(ClO₄)₆}, encapsulating six ClO₄^? ions, features a cage core composed of twelve vertex‐sharing {Gd₄} tetrahedrons and one Gd???Gd pillar. When Cl^? and NO₃^? were incorporated in the reaction instead of ClO₄^?, {Gd₄₈Cl₂(NO₃)} is obtained with a barrel shape constituted by twelve vertex‐sharing {Gd₄} tetrahedrons and six {Gd₅} pyramids. What is more, the cage‐like {Gd₃₈} can be dynamically converted into the barrel‐shaped {Gd₄₈} upon Cl^? and NO₃^? stimulus. To our knowledge, it is the first time that the linear M‐O‐M′ fashion and the unique μ₈‐ClO₄^? mode have been crystallized in pure lanthanide complex, and complex 2 represents the largest gadolinium cluster. Both of the complexes display large magnetocaloric effect in units of J kg^?1 K^?1 and mJ cm^?3 K^?1 on account of the weak antiferromagnetic exchange, the high N_Gd/M_W ratio (magnetic density), and the relatively compact crystal lattice (mass density).     

Designing Novel Contrast Agents for Magnetic Resonance Imaging. Synthesis and Relaxometric Characterization of three Gadolinium(III) Complexes Based on Functionalized Pyridine‐Containing Macrocyclic Ligands

The three novel pyridine‐containing 12‐membered macrocyclic ligands 1 – 3 were synthesized. The coordinating arms are represented by three acetate moieties in 1 and 3 and by one acetate and two phosphonate moieties in 2 . In all three ligands, the acetate arm in the distal position is substituted, with a benzyl group in 1 and 2 and with an arylmethyl moiety in 3 . The relaxivities r_1p (20 MHz, 25°) of Gd^III complexes are: GD?1 , r_1p=8.3 mM ^?1 s^?1; GD?2 , r_1p8.1 mM ^?1 s^?1; Gd?3 , r_1p10.5 mM ^?1 s^?1. ¹H‐NMRD and ¹⁷O‐NMR T₂ data show that Gd?1 and Gd?3 contain two H₂O molecules in the inner sphere, whereas the presence of two phosphonate arms allows the coordination of only one H₂O molecule in Gd?2 . Interestingly, the exchange lifetime of coordinated H₂O in the three complexes is similar in spite of the difference in the coordination number of the Gd^III ion (i.e., 9 in Gd?1 and Gd?3 , and 8 in Gd?2 ). ¹H‐Relaxometric measurements at different pH and in the presence of lactate and oxalate were carried out to get some insight into the formation of ternary complexes from Gd?1 and Gd?3 . Finally, it was found that binding to human‐serum albumin (HSA) of Gd?1 and Gd?2 , though weak, yields limited relaxivity enhancements, likely as a consequence of effects on the hydration sphere caused by donor atoms on the surface of the protein.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

Two C3‐Symmetric Dy3III Complexes with Triple Di‐μ‐methoxo‐μ‐phenoxo Bridges,Magnetic Ground State,and Single‐Molecule Magnetic Behavior

Two series of isostructural C₃‐symmetric Ln₃ complexes Ln₃ ? [BPh₄] and Ln₃ ? 0.33[Ln(NO₃)₆] (in which Ln^III=Gd and Dy) have been prepared from an amino‐bis(phenol) ligand. X‐ray studies reveal that Ln^III ions are connected by one μ₂‐phenoxo and two μ₃‐methoxo bridges, thus leading to a hexagonal bipyramidal Ln₃O₅ bridging core in which Ln^III ions exhibit a biaugmented trigonal‐prismatic geometry. Magnetic susceptibility studies and ab initio complete active space self‐consistent field (CASSCF) calculations indicate that the magnetic coupling between the Dy^III ions, which possess a high axial anisotropy in the ground state, is very weakly antiferromagnetic and mainly dipolar in nature. To reduce the electronic repulsion from the coordinating oxygen atom with the shortest Dy?O distance, the local magnetic moments are oriented almost perpendicular to the Dy₃ plane, thus leading to a paramagnetic ground state. CASSCF plus restricted active space state interaction (RASSI) calculations also show that the ground and first excited state of the Dy^III ions are separated by approximately 150 and 177 cm^?1, for Dy₃ ? [BPh₄] and Dy₃ ? 0.33[Dy(NO₃)₆], respectively. As expected for these large energy gaps, Dy₃ ? [BPh₄] and Dy₃ ? 0.33[Dy(NO₃)₆] exhibit, under zero direct‐current (dc) field, thermally activated slow relaxation of the magnetization, which overlap with a quantum tunneling relaxation process. Under an applied H_dc field of 1000 Oe, Dy₃ ? [BPh₄] exhibits two thermally activated processes with U_eff values of 34.7 and 19.5 cm^?1, whereas Dy₃ ? 0.33[Dy(NO₃)₆] shows only one activated process with U_eff=19.5 cm^?1.     

High‐Performance Magnetic Refrigerant Featuring One‐Dimensional Gd‐O Chains and O‐Gd3 Triangles

Magnetic cooling at low temperature has attracted intensive interest in cryogenics research, which may become important as cooling medium for long‐wave photon detectors to support space exploration. Here, we report a Gd‐based quaternary magnetic refrigerant material, Gd₅BSi₂O₁₃, containing chains of face‐shared GdO₉ polyhedra and geometrically frustrated OGd₃ triangles. Magnetic measurements indicate that Gd₅BSi₂O₁₃ exhibits a large magnetocaloric effect (MCE) about 1.74 times that of the practical magnetic refrigerant GGG (−ΔS_m=67.0 J kg⁻¹ K⁻¹). We analyzed the origin of the large MCE by comparing Gd^III‐containing compounds with different structures and concentrations of Gd^III.     

Tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide as Efficient Charge‐Transfer Antenna Ligand for the Sensitization of YbIII Luminescence in a Series of Lanthanide Paramagnetic Coordination Complexes

The tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide ( L ) ligand has been employed to coordinate 4f elements. The architecture of the complexes mainly depends on the ionic radii of the lanthanides. Thus, the reaction of L in the same experimental protocol leads to three different molecular structure series. Binuclear [Ln₂(hfac)₅(O₂CPhCl)( L )₃] ? 2 H₂O (hfac^?=1,1,1,5,5,5‐hexafluoroacetylacetonate anion, O₂CPhCl^?=3‐chlorobenzoate anion) and mononuclear [Ln(hfac)₃( L )₂] complexes were obtained by using rare‐earth ions with either large (Ln^III=Pr, Gd) or small (Ln^III=Y, Yb) ionic radius, respectively, whereas the use of Tb^III that possesses an intermediate ionic radius led to the formation of a binuclear complex of formula [Tb₂(hfac)₄(O₂CPhCl)₂( L )₂]. Antiferromagnetic interactions have been observed in the three dinuclear compounds by using an extended empirical method. Photophysical properties of the coordination complexes have been studied by solid‐state absorption spectroscopy, whereas time‐dependent density functional theory (TD‐DFT) calculations have been carried out on the diamagnetic Y^III derivative to build a molecular orbital diagram and to reproduce the absorption spectrum. For the [Yb(hfac)₃( L )₂] complex, the excitation at 19 600 cm^?1 of the HOMO→LUMO+1/LUMO+2 charge‐transfer transition induces both line‐shape emissions in the near‐IR spectral range assigned to the ²F_5/2→²F_7/2 (9860 cm^?1) ytterbium‐centered transition and a residual charge‐transfer emission around 13 150 cm^?1. An efficient antenna effect that proceeds through energy transfer from the singlet excited state of the tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide chromophore is evidence of the Yb^III sensitization.     

Evaluation of the Oxo‐bridged Dinuclear Ruthenium Ammine Complex as Redox Mediator in an Electrochemical Biosensor

The mediation of electron‐transfer by oxo‐bridged dinuclear ruthenium ammine [(bpy)₂(NH₃)Ru^III(µ‐O)Ru^III(NH₃)(bpy)₂]⁴⁺ for the oxidation of glucose was investigated by cyclic voltammetry. These ruthenium (III) complexes exhibit appropriate redox potentials of 0.131–0.09 V vs. SCE to act as electron‐transfer mediators. The plot of anodic current vs. the glucose concentration was linear in the concentration range between 2.52×10^?5 and 1.00×10^?4 mol L^?1. Moreover, the apparent Michaelis‐Menten kinetic (K_M^app) and the catalytic (K_cat) constants were 8.757×10^?6 mol L^?1 and 1,956 s^?1, respectively, demonstrating the efficiency of the ruthenium dinuclear oxo‐complex [(bpy)₂(NH₃)Ru^III(µ‐O)Ru^III(NH₃)(bpy)₂]⁴⁺ as mediator of redox electron‐transfer.