3d-4f Complexes Research Articles

Impact of paramagnetic CuII and diamagnetic ZnII ions on single-molecule magnetism in heterodinuclear 3d–4f complexes displaying slow relaxation of magnetization

We report the synthesis of heterometallic 3d–4f complexes with paramagnetic CuII and diamagnetic ZnII ions, unveiling rare slow relaxation of magnetization in the Cu–Gd analogue and offering valuable insights into their magnetic dynamics.

Exploiting High Order Magnetic Anisotropy for Advanced Magnetocaloric Refrigerants.

Three new 3 d-4 f complexes of general formula trans-[MF2(py)4][LnDOTA] (M=Cr3+ or Co3+, Ln=Dy3+ or Y3+, py=pyridine and DOTA=tetraazacyclododecane-N,N',N'',N'''-tetraacetate) have been synthetised. The fluoride-bridged systems were designed to achieve perfect tetragonal symmetry by combining four-fold symmetric lanthanide and transition metal building blocks. From single crystal measurements, an unprecedented switch of the tetragonal anisotropy of the Dy3+ complexes has been observed. A combination of spectroscopic observations, magnetometry measurements and ab initio calculations allowed us to pinpoint the origin of this phenomenon, which is related to the peculiar energy level structure of the complexes. Moreover, the fourfold anisotropy of the complex has been exploited to design a rotating magnetocaloric experiment showing that tetragonal anisotropy holds great potential to engineer a new class of more efficient magnetic refrigerants.

Tridentate chelate ligand-based Dy-Cu adduct: synthesis, structure and magnetic properties

One discrete 3d-4f adduct with formula {[Cu(hfac)(Nit-PhCH2-PyN)]+[Dy(hfac)4]–} (hfac=hexafluoroacetylacetonate, Nit-PhCH2-PyN=2-[4-[bi(2-pyridylmethyl)amine]-tolyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been afforded on the basis of a one-pot process of Dy(hfac)3·2H2O, Cu(hfac)2·2H2O and a tridentate chelate ligand Nit-PhCH2-PyN. Interestingly, one discrete [Dy(hfac)4]– anion and [Cu(hfac)(Nit-PhCH2-PyN)]+ serving as the counter-ion are present in the 3d-4f complex. In addition, magnetic studies have shown field-induced slow magnetic relaxation is derived from the [Dy(hfac)4]– anion, involving the eight-coordinated DyIII ion with D4d symmetry.

Single molecule magnet behaviour of CoIIILnIII (Ln = TbIII, GdIII) compounds with compartmental Schiff base ligand and sulfonate co-ligands

In this research, our team synthesized and characterized two heteronuclear 3d-4f complexes, [CoIIICl(μ-valen)(μ-4-HBS)LnIII(NO3)(H2O)(4-HBS)], with Ln representing Tb (1) and Gd (2). Achievement of this was through the utilization of a compartmental Schiff base ligand H2valen, alongside secondary co-ligands Na(4-HBS) [H2valen=6,6′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol); Na(4-HBS)=sodium 4-hydroxybenzenesulfonate]. X-ray crystallography revealed that both complexes feature a similar [Co(III)-Ln(III)] core, connected by the phenoxo-O atoms from the compartmental Schiff base ligand and the sulfonate-O atoms from the co-ligand. In this context, Co(III) displays a distorted octahedral geometry within a CoN2O3Cl coordination sphere, while Ln(III) exhibits a muffin (MFF)-like distorted geometry in a LnO9 coordination sphere. Magnetic analysis shows that the two complexes display unique magnetic properties. Complex 1 exhibits pronounced SMM behavior, with a notable energy barrier of 14.8 K for magnetization reversal. However, complex 2 presents a minor energy barrier of 4.8 K. Additionally, complexes 1 and 2 represent uncommon examples of dinuclear Co(III)-Ln(III) SMMs.

Chiral 4f and 3d-4f Complexes from Enantiopure Salen-Type Schiff Base Ligands

This review summarizes the structural characteristics and physicochemical properties of chiral 4f and 3d-4f complexes based on enantiopure salen-type Schiff base ligands. The chirality originates from the enantiopure diamines and is imparted to the Schiff base ligands and complexes and finally to the crystal structures. The reported enantiopure Schiff base ligands derive from the condensation of aromatic aldehydes, such as salicylaldehyde and its various derivatives, and the enantiopure diamines, (1R,2R) or (1S,2S)-1,2-diamino-cyclohexane, (1R,2R) or (1S,2S)-1,2-diamino-1,2-diphenylethane, (R) or (S)-2,2′-diamino-1,1′-binaphthalene, and 1,2-diaminopropane.

Molecular Fe(II)-Ln(III) dyads for luminescence reading of spin-state equilibria at the molecular level.

Due to the primogenic effect, the valence shells of divalent iron Fe(II) ([Ar]3d6) and trivalent lanthanides Ln(III) ([Xe]4fn) are compact enough to induce spin-state equilibrium for the 3d-block metal and atom-like luminescence for the 4f-block partner in Fe(II)-Ln(III) dyads. In the specific case of homoleptic pseudo-octahedral [Fe(II)N6] units, programming spin crossover (SCO) around room temperature at normal pressure requires the design of unsymmetrical didentate five-membered ring chelating N∩N' ligands, in which a five-membered (benz)imidazole heterocycle (N) is connected to a six-membered pyrimidine heterocycle (N'). Benefiting from the trans influence, the facial isomer fac-[Fe(II)(N∩N')3]2+ is suitable for inducing SCO properties at room temperature in solution. Its connection to luminescent [LnN6O3] chromophores working as non-covalent podates in the triple-stranded [Fe(II)Ln(L10)3]5+ helicates (Ln = Nd, Eu) controls the facial arrangement around Fe(II). The iron-based SCO behaviour of the 3d-4f complex mirrors that programmed in the mononuclear scaffold. Because of the different electronic structures of high-spin and low-spin [Fe(II)N6] units, their associated absorption spectra are different and modulate the luminescence of the appended lanthanide luminophore via intramolecular intermetallic energy transfers. It thus becomes possible to detect the spin state of the Fe(II) center, encoded by an external perturbation (i.e. writing), by lanthanide light emission (i.e. reading) in a single molecule and without disturbance. Shifting from visible emission (Ln = Eu) to the near-infrared domain (Ln = Nd) further transforms a wavy emitted signal intensity into a linear one, a protocol highly desirable for future applications in data storage and thermometry.

Crystal structure and spectral properties of the heterometallic 3d-4f complex of gadolinium (III) – cobalt (II) with ethylenediamine-N,N,N′,N′-tetraacetic acid

The 4f-3d heteronuclear complex Co3Gd2(EDTA)11∙9·5H2O was synthesized by the "block" synthesis method using protonated ethylenediaminetetraacetate Co(II) and Gd(III) nitrate. The complex was fully characterized by means of elemental, thermal and X-ray structural analyses, as well as by the methods of diffuse reflection spectroscopy and IR spectroscopy. The complex crystallizes in monoclinic system (space group C2) with lattice parameters a = 15.8142(3) Å, b = 14.5875(3) Å, c = 14.6808(3) Å, α = γ = 90°, β = 116.5009(10)°.The complex is a 2D coordination polymer in which each Gd(III) ion is connected to with three atoms Co(II) atoms through tridentate bridging carboxylate groups of EDTA, and each Co atom has two neighboring Gd(III) atoms. The polymer layers are packed in parallel, outer-sphere water molecules are located between the layers, forming a branched system of hydrogen bonds.

Tuning Quantum Tunneling in Isomorphic {MII2DyIII2} “Butterfly” System via 3d-4f Magnetic Interaction

In order to probe the magnetic relaxation mechanism of 3d-4f complexes systematically, two “Butterfly” MII2DyIII2 complexes related to our previously reported butterfly compound, [Zn2Dy2(L)4(Ac)2(DMF)2]·4CH3CN (1), and formulated as [Co2Dy2(L)4(Ac)2(DMF)2]·3CH3CN (2) and [Ni2Dy2(L)4(Ac)2(DMF)2]·3CH3CN (3) are prepared and characterized. In comparison to complex 1, the replacement of CoII or NiII with ZnII led to the effective quenching of quantum tunneling of the magnetization (QTM) in complexes 2 and 3. Obviously, the introduction of 3d-4f spin–spin exchange can be important in determining the overall magnetic behaviors of 3d-4f {MII2DyIII2} “Butterfly” systems.

3d Ion-Driven Hexanuclear Heterometallic Clusters with Amazing Structures and Magnetic Properties

By using a heptadentate Schiff base ligand with three NO2 pockets to react with 3d and 4f acetate precursors, three series of M4Ln2 complexes (M, Ln = Ni, Gd for 1NiGd; Ni, Dy for 2NiDy; Co, Gd for 3CoGd; Co, Dy for 4CoDy; Cu, Gd for 5CuGd; Cu, Dy for 6CuDy) have been obtained and characterized. X-ray single-crystal diffraction analyses indicated that Ni4Ln2 series exhibit butterfly structures with extended wings, the Co4Ln2 series are made up of four fused linear defective open cubes, and the Cu4Ln2 series display H-typed topology structures. The dc magnetic susceptibility data revealed that all of the Gd derivatives possess significant magnetic entropy change, whereas the alternating current (ac) magnetic susceptibility measurements identified that only the NiDy derivative displays single-molecule magnet behavior with energy barrier of 15.69 K under zero dc field. These results reveal that 3d ions are important in adjusting the structure and magnetic properties for 3d–4f complexes.

Detailed magnetic properties and theoretical calculation in ferromagnetic coupling DyIII-MII 3d-4f complexes based on a 1,4,7,10‑tetraazacyclododecane derivative

Four Dy-based 3d-4f complexes [MIIDyIII(H2L)(NO3)3](CH3OH)2 (H4L = N,N',N'',N'''-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane, M = Mn (2), Fe (3), Co (4) and Ni (5), the solvent of compound 5 is uncertain) were synthesized through the reference method of complex [ZnIILnIII(H2L)(NO3)3](CH3OH)2 (1). The magnetic properties of all the five complexes were measured for comparison. The magnetic results show that all the complexes except 4 behave as single-molecule magnets (SMMs). The magnetostructural analysis and theoretical calculation indicate the ferromagnetic coupling in 2, 3 and 5 as well as the antiferromagnetic coupling in 4 between DyIII and transition metal ions, while the SMM properties of 1 are caused by the anisotropy of single DyIII ions only. Unexpectedly, neither of the magnetic anisotropic ions in one molecule, namely DyIII and CoII, provides greater advantages for SMM performance. This investigation experimentally proves that the coexistence of magnetic anisotropy of lanthanide ions and ferromagnetic coupling between lanthanide and transition metal ions is important for the design of 3d-4f SMMs.

Synthesis, Characterization and Luminescence Studies of 3d-4f heterometallic Zinc(II)-Lanthanide(III) Complexes Incorporated in Poly(Vinyl Pyrrolidone) Matrix

A series of Lanthanide complexes Nd(btc).4H2O, Eu(btc).3H2O, Tb(btc).3H2O, Er(btc).H2O, Yb(btc). 3H2O and heterometallic 3d-4f complexes, Nd(btc ) (Zn)(C2H5O)2.5H2O, Eu(btc)(Zn)(C2H5O)2.5H2O, Tb (btc)(Zn)(C2H5O)2.H2O, Er(btc)(Zn)(C2H5O)2.H2O, Yb (btc)(Zn)(C2H5O)2.H2O have been prepared by one step reaction of LnIII and LnIII-ZnII with 1,3,5-benzenetricarboxylic acid (H3btc) by reflux method. All the synthesized complexes were incorporated into poly(vinyl pyrrolidone) (PVP) matrix. All these complexes (1-10) have been characterized by elemental analyses (C,H,N), FT-IR-spectra, Transmission electron microscopy (TEM), fluorescence spectra and powder X-ray diffraction (PXRD) analyses to arrive at conclusion regarding their geometrical structure. Transmission electron microscopy (TEM) showed the shape and size of the complexes, which were homogeneously dispersed in the PVP matrix. TEM results showed the complexes were of rod shaped with a mean diameter about 20 nm. The powder X-ray diffraction (PXRD) patterns of 3d-4f complexes showed well defined crystalline peaks.

Heterometallic Hexanuclear [Cu2Ln4] Complexes Showing Zero‐field SMM Behaviour and Magnetocaloric Effect

Three heterometallic hexanuclear 3d-4f complexes bearing the formula [Cu2 (L)2 Ln4 (L)4 (o-van)2 ] [L=2-((E)-((2-hydroxyphenyl)imino]methyl)phenol; o-van=ortho-vanillin] (LnIII =GdIII (1), DyIII (2), and TbIII (3)) have been synthesized and characterized. DC magnetic susceptibility measurements reveal overall antiferromagnetic interactions in 1 and 3, whereas co-existence of ferro- as well as antiferromagnetic interactions were observed in 2. The magnetocaloric effect has been observed for 1 with an entropy change (-ΔSm ) of 22.3 J kg-1 K-1 at 3 K and 7 T. Zero-field single molecule magnet (SMM) behaviour has been observed for 2, where Raman relaxation and quantum tunneling of magnetization (QTM) played a role in magnetization relaxation. The Cu-O-Ln angle well explains the magnetic exchange coupling occurring in the complexes. BS-DFT calculation for the complexes provides an estimate of the exchange interactions between the paramagnetic centres. Ab initio calculations performed for complex 2 established a good correlation to the experimental relaxation dynamics.

Synthesis, crystal structure, fluorescence properties and theoretical calculations of heterobimetallic 3d–4f complex with a flexible bis(salamo)‐type ligand

A new heterobimetallic 3d-4f [Cu(II)2Pr(III)] complex [Cu2Pr(L)(ƞ2-NO3)3(EtOH)2]·2EtOH with a symmetric flexible bis(salamo)-type ligand, (1E,1′E)-2,3-dihydroxynaphthalene-1,4-dicarbaldehyde O,O-di(3-((((E)-3-ethoxy-2-hydroxybenzylidene)amino)oxy)propyl)dioxime (H4L), has been synthesized and characterized structurally. Single crystal X-ray diffraction analysis showed that the ligand was fasten by different metal ions to form a hetero-trinuclear complex with C-shaped structure, where two N2O2-donors of the completely deprotonated ligand (L)4− unit and two oxygen atoms from two ethanol molecules coordinate with Cu(II) atoms (Cu1, Cu2), respectively, to form two five-coordinated square pyramid geometries. Meanwhile, where the O6 cavity coordination sphere of the ligand (L)4− unit and six oxygen atoms from three nitrate groups coordinate with the Pr(III) atom together to form a twelve-coordinated icosahedron. Due to the Cu(II) atom in the O6 cavity was replaced by the Pr(III) atom, it shows that the hetero-trinuclear complex after self-assembly is more stable than the homo-trinuclear complex. At the same time, through UV–Vis titration spectrometric analysis, we can observed that the hetero-trinuclear [Cu(II)2Pr(III)] complex is obtained by 1 equiv. Pr(NO3)3·5H2O and 2 equiv. Cu(NO3)2·3H2O and 1 equiv. H4L. Significantly, fluorescence properties and Hirshfeld surfaces analyses of the [Cu(II)2Pr(III)] complex was also studied.

Coordination-driven self-assemblies of two hetero‐trinuclear [Cu(II)2Ln(III)] (Ln = La and Ce) complexes with a flexible bis(salamo)‐type ligand

d-Block transition metal(II)-lanthanide(III) (3d-4f) hetero‐trinuclear [Cu(II)2Ln(III)] (Ln = La and Ce) complexes [Cu2La(L)(ƞ 2-NO3)3(CH3OH)2]·2CH3OH (1) and [Cu2Ce(L)(ƞ 2-NO3)3(CH3OH)2]·2CH3OH (2) are described, both of which are formed by a flexible symmetrical bis(salamo)-type ligand H4L. The two 3d-4f complexes have been synthesized and characterized by elemental analyses, IR spectra and UV–Vis spectroscopy. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analyses. In 1 and 2, each Cu(II) ion (Cu1 or Cu2) is located in the N2O2 cavity of an (L)4− unit, while the apex is occupied by one oxygen atom of the coordinated methanol molecule, forming a penta-coordinated square pyramidal geometry. The lanthanide(III) (La or Ce) ion is located in the O6-donor coordination sphere of the completely deprotonated (L)4− unit and coordinated with the other six oxygen atoms of the three nitrate ligands to form a twelve-coordinated icosahedron. At the same time, the supramolecular structures are formed by intermolecular hydrogen bonding interactions and quantitatively determined by Hirshfeld surfaces analyses. Fluorescence properties and DFT calculations of 1 and 2 were also studied.

High-Performance Luminescence Thermometer with Field-Induced Slow Magnetic Relaxation Based on a Heterometallic Cyanido-Bridged 3d-4f Complex.

The 1:1:1 reaction of DyCl3·6H2O, K3[Co(CN)6] and bpyO2 in H2O has provided access to a complex with formula [DyCo(CN)6(bpyO2)2(H2O)3]·4H2O (1) in a very good yield, while [DyFe(CN)6(bpyO2)2 (H2O)3]·4H2O (2) was also precipitated (also in a high yield) using K3[Fe(CN)6] instead of K3[Co(CN)6]. Their structures have been determined by single-crystal X-ray crystallography and characterized based on elemental analyses and IR spectra. Combined direct current (dc) and alternating current (ac) magnetic susceptibility revealed slow magnetic relaxation upon application of a dc field. μ-SQUID measurements and CASSCF calculations revealed high-temperature relaxation dynamics for both compounds. Low-temperature magnetic studies show the relaxation characteristics for 1, while for compound 2 the dynamics corresponds to an antiferromagnetically coupled Dy···Fe pair. High-resolution optical studies have been carried out to investigate the performance of compounds 1 and 2 as luminescence thermometers. For 1, a maximum thermal sensitivity of 1.84% K-1 at 70 K has been calculated, which is higher than the acceptable sensitivity boundary of 1% K-1 for high-performance luminescence thermometers in a broad range of temperature between 40 and 140 K. Further optical studies focused on the chromaticity diagram of compound 1 revealed a temperature shift from warm white (3200 K) at 10 K toward a more natural white color near 4000 K at room temperature.

Synergistic Experimental and Theoretical Studies of Luminescent-Magnetic Ln2Zn6 Clusters.

The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl-pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d-4f mixed-metal complexes with a general core of Ln2Zn6 (Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hard and soft coordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu2Zn6 and Tb2Zn6 complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy2Zn6 complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an Ueff value of ∼5 K and a relaxation time of 8.52 × 10-6 s. The Gd2Zn6 complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg-1 K-1 at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCA suite of programs, and MOLCAS calculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.

Heterospin 2p–4f and 2p–3d–4f complexes constructed by a nitronyl nitroxide ligand: syntheses, structures and magnetic properties

Two novel 2p–4f cyclic dimer complexes are presented. By introducing Cu(hfac)2, one 2p–3d–4f compound involving a {[Cu–radical]+}n cation chain and [Tb(hfac)4]− anion is obtained, which exhibits slow magnetization relaxation.

Heterodinuclear Cu–Gd (3d-4f) complex with di-compartmental Schiff base ligand in biological activity: Synthesis, crystal structure, catecholase activity and DNA & BSA-binding studies

A dinuclear CuII-GdIII Schiff base complex (a di-compartmental Schiff base ligand derived from o-vanillin) nominated as: 1,3-propanediyl-bis(2-iminomethylene-6-methoxy-phenol) (H2valpn) was synthesized in two steps. To characterize the compounds, single-crystal X-ray crystallography, UV–Vis spectroscopy, IR spectroscopy, and elemental analyses were used. The crystalline sample of the heterodinuclear complex revealed the structure of general formula [(valpn) (H2O) CuII GdIII (NO3)3], with the copper ion located in a square pyramidal section (with an axial aqua ligand) and the gadolinium (III) ion located in the open compartment, in which 10 oxygen atoms from three chelating nitrate ions and a Schiff base ligand surrounded it. To study the applications of the complex, the binding affinity of the complex with FS-DNA was studied by UV–Vis spectroscopy, fluorescence spectroscopy, viscosity measurements, cyclic voltammetry (CV) and circular dichroism (CD). From all of these methods, intercalation was suggested as the main mode of binding. The complex was also checked in interaction with Bovine serum albumin (BSA) by using UV–Vis and fluorescence spectroscopy. Cytotoxicity was tested by MTT assay toward HeLa, LNCaP, and MCF-7 cancer cell lines. Moreover, the docking calculation was performed and these results confirmed the experimental results. The mechanism and kinetics of the catalytic activity of the complex in the oxidation reaction of 3,5-di-tert-butylcatechol, was studied at 298 K.

A series of zero-dimensional Co(II)-Ln(III) heterometallic complexes derived from 2,3-dichlorobenzoate and 2,2′-bipyridine: Syntheses, structures and magnetic properties

Eight 3d-4f heterometallic complexes were successfully yielded by the solvothermal reactions of Ln(NO3)3·nH2O, Co(NO3)2·6H2O, 2,3-dichlorobenzoic acid (2,3-HDCB), NaOH and 2,2′-bipyridine (2,2′-bpy), namely [Ln2Co2(2,3-DCB)10(2,2′-bpy)2] [Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Er (7) and Yb (8)]. These eight complexes were characterized by single-crystal X-ray diffraction, FT-IR spectrum, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). They show isomorphous zero-dimensional (0D) linear tetranuclear cluster structures. Their magnetic properties were investigated.

Metamagnetic Behavior in a Quadruple Perovskite Oxide.

A cubic quadruple perovskite oxide CeMn3Cr4O12 has been synthesized under high-pressure and high-temperature conditions of 8 GPa and 1273 K. The X-ray absorption spectroscopy reveals that the Ce ions are in a trivalent state, as represented by the ionic model of Ce3+Mn3+3Cr3+4O12. The magnetic study demonstrates three independent antiferromagnetic transitions attributed to Ce (∼10 K), Mn (46 K), and Cr (133 K) ions. Furthermore, a magnetic field-induced antiferromagnetic-to-ferromagnetic (metamagnetic) transition of Ce3+ 4f moments is observed at low temperatures below 20 K, exhibiting a rare example of metamagnetism in the Ce3+-oxides. This finding represents that the 3d-electron magnetic sublattices play a role in the metamagnetism of 4f-electron magnetic moments, demonstrating a new aspect of the 3d-4f complex electron systems.