Syntheses, Structures, and Magnetic Properties of Acetato- and Diphenolato-Bridged 3d–4f Binuclear Complexes [M(3-MeOsaltn)(MeOH)x(ac)Ln(hfac)2] (M = ZnII, CuII, NiII, CoII; Ln = LaIII, GdIII, TbIII, DyIII; 3-MeOsaltn = N,N′-Bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato; ac = Acetato; hfac = Hexafluoroacetylacetonato; x = 0 or 1)

Insight into ferromagnetic interactions in CuII-LnIII dimers with a compartmental ligand

In the last two decades, efforts have been devoted to obtaining insight into the magnetic interactions between CuII and LnIII utilizing experimental and theoretical means. Experimentally, it has been observed that the exchange coupling (J) in CuII-LnIII systems is often found to be ferromagnetic for ≥4f7 metal ions. However, exchange interactions at sub-Kelvin temperatures between CuII and the anisotropic/isotropic LnIII ions are not often explored. In this report, we have synthesized a series of heterobimetallic [CuLn(HL)(μ-piv)(piv)2] complexes (LnIII = Gd (1), Tb (2), Dy (3) and Er (4)) from a new compartmental Schiff base ligand, N,N'-bis(3-methoxy-5-methylsalicylidene)-1,3-diamino-2-propanol (H3L). X-ray crystallographic analysis reveals that all four complexes are isostructural and isomorphous. Magnetic susceptibility measurements reveal a ferromagnetic coupling between the CuII ion and its respective LnIII ion for all the complexes, as often observed. Moreover, μ-SQUID studies, at sub-Kelvin temperatures, show S-shaped hysteresis loops indicating the presence of antiferromagnetic coupling in complexes 1-3. The antiferromagnetic interaction is explained by considering the shortest Cu⋯Cu distance in the crystal structure. The nearly closed loops for 1-3 highlight their fast relaxation characteristics, while the opened loops for 4 might arise from intermolecular ordering. CASSCF calculations allow the quantitative assessment of the interactions, which are further supported by BS-DFT calculations.

Combined effects of the lewis acidity and electric field of proximal redox innocent metal ions on the redox potential of vanadyl Schiff base complexes: an experimental and theoretical study

The reactivity of biological or synthetic metalloenzymes is modulated in the presence of redox innocent Lewis acidic metal ions as they change the redox potential of the redox active metal ions present in the active site of metalloenzymes. To study this effect, we synthesised a mono-nuclear V(IV) complex (VOL, 1) with an N₂O₄ donor bicompartmental ligand, characterized it by single-crystal X-ray crystallography and recorded its cyclic voltammogram in acetonitrile. The CV revealed a reversible redox process for the V(IV)/V(V) couple. The potential of the V(IV)/V(V) couple shifted to a more positive value when equivalent amounts of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Ba²⁺ ions were added separately to its acetonitrile solution, but the extent of shift for Li⁺ and Mg²⁺ was much less than that of the other metal ions. The guest metal ions except Li⁺ and Mg²⁺ were accommodated in the outer compartment of VOL as confirmed by IR and UV-Vis spectral analysis. Single-crystal structural analysis of [(VOL)KPF₆]₂, (1·K) and [(VOL)Ba(ClO₄)₂(H₂O)]_n, (1·Ba) also confirmed the hetero-metallic adduct formation. The correlation of the shift of the V(IV/V) redox potential with the Lewis acidity of respective metal ions deviated appreciably from linearity. DFT calculations suggest that the shift in potential is probably controlled by local electric fields induced by those ions, as indicated by 2D vector electric field maps.

Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

This review summarizes the data on the synthesis of coordination compounds containing two or more different metal ions based on fluorinated β-diketonates. Heterometallic systems are of high interest in terms of their potential use in catalysis, medicine and diagnostics, as well as in the development of effective sensor devices and functional materials. Having a rich history in coordination chemistry, fluorinated β-diketones are well-known ligands generating a wide variety of heterometallic complexes. In this context, we focused on both the synthetic approaches to β-dicarbonyl ligands with additional coordination centers and their possible transformations in complexation reactions. The review describes bi- and polynuclear structures in which β-diketones are the key building blocks in the formation of a heterometallic framework, including the examples of both homo- and heteroleptic complexes.

Experimental and theoretical insights into Co-Ln magnetic exchange and the rare slow-magnetic relaxation behavior of [CoII2Pr]2+ in a series of linear [CoII2Ln]2+ complexes

We herein report a series of near-linear trinuclear complexes [Co₂Ln(HL)₄(NO₃)](NO₃)₂ (where HL = (2-methoxy-6-[(E)-2'-hydroxymethyl-phenyliminomethyl]-phenolate) with Ln(III) = La (1), Ce (2), Pr (3)). For the comparative study, we have also included the recently reported analogous complexes of Gd(III), Tb(III), and Dy(III) (complexes 4-6) with the same H₂L ligand. The experimental nature of the dc magnetic susceptibilities profile and an empirical approach revealed that the magnetic exchange interaction between Co(II) and Ln(III) having <4f⁷ (complexes 2 and 3) is antiferromagnetic while the dominant interaction between Co(II) and Ln(III) having ≥4f⁷ (complexes 4-6) is ferromagnetic. Dynamic magnetic relaxation studies on complexes 1-3 revealed the field induced single-molecule magnetic (SMM) behavior of 1 and 3 with effective energy barriers of 10.65 K and 15.03 K respectively, for magnetic relaxation. To the best of our knowledge, 3d-Pr(III) based zero or field induced SMMs have not been reported to date. CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations on the X-ray structures of complexes 1-6, followed by POLY_ANISO simulations, estimated the magnetic exchange coupling constants J_Co-Ln and J_Co-Co and also rationalized our experimental findings for the dynamic magnetic properties.

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 U_eff 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.

Slow magnetic relaxation and luminescence properties in neodymium(iii)-4,4,4-trifluoro-1-(2-naphthyl)butane-1,3-dionato complexes incorporating bipyridyl ligands

A new series of eight-coordinated Nd(iii) complexes derived from 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionate and bi-pyridyl ligands revealed multifunctional molecular materials as photoluminescent single-molecule magnets (SMMs).

End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N3O2] Ligand: Synthesis, Structure, and Magnetism

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N₃)C₂H₅OH]C₂H₅OH}_n where H₂DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N₃O₂] ligand and Ln = Dy (1), Y_0.930Dy_0.070 (2), Er (3), Y_0.923Er_0.077 (4), and Gd (5). X-ray diffraction analysis of 1-5 show that the central lanthanide atoms are eight-coordinated with the N₅O₃ donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N₃^- bridges connecting the metal centers into infinite chain. The [LnN₅O₃] coordination polyhedron can be regarded as a distorted dodecahedron (D_2d). AC magnetic measurements revealed that compounds 1-4 show field-induced single-molecule magnet behavior, with estimated energy barriers U_eff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln³⁺ ions mediated by the end-to-end azide bridging groups (J ≈ -0.015 cm^-1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln³⁺ ions.

Influence of ancillary ligands and solvents on the nuclearity of Ni-Ln complexes

A Schiff base ligand resulting from the reaction of ovanillin and 2,2-dimethyl-1,3-diaminopropane allows the preparation of hetero-dinuclear [Ni-Ln]³⁺ or -trinuclear [Ni-Ln-Ni]³⁺ complexes. Although empirical parameters for rationalizing the strength of the ferromagnetic Ni-Gd interaction have already been discussed in several papers, no systematic study has been devoted to the control of the nuclearity of such complexes. With the help of structural determinations, we demonstrate the role of solvent and of the nature of ancillary ligands, linked to the Ln ions, in nuclearity. For instance, the presence of one chelating nitrato ligand is already sufficient to impede an increase in the nuclearity, while the replacement of nitrato ligands by chloride anions still yields dinuclear Ni-Ln complexes. This experimental result evidences the role of protic solvents. In contrast, the use of lanthanide salts, soluble in non-protic solvents, allows the isolation of dinuclear [Ni-Ln]³⁺ or trinuclear cationic [LNi-Ln-NiL]³⁺ complexes, depending on the Ni/Ln ratio. A further synthetic step can be overtaken by the reaction of a Ni-Ln complex, soluble in a non-protic solvent, with a LM complex (M = Cu, Zn). By doing so, a heterotrinuclear complex made of three different metal ions, two distinct 3d ions and a 4f one, has been isolated and structurally characterized. Note that the Ni coordination number decreases from 6 to 5 on going from the dinuclear complex to the trinuclear one. Also, the replacement of water molecules by chloride ligands in the hexacoordinate Ni complexes induces a net increase of the positive zero-field splitting parameter D to 20 cm^-1, which is supported by ab initio calculations. Although the Ni-Ln (Ln = Gd, Tb, Dy) magnetic interactions are ferromagnetic, the corresponding trinuclear complexes are devoid of SMM properties in the absence of an applied magnetic field.

Slow magnetic relaxation in Cu(ii)–Eu(iii) and Cu(ii)–La(iii) complexes

A dinuclear [(H₂O)Cu(HLN₂O₂)Eu(NO₃)₃] complex exhibits paramagnetic behaviour with S = 1/2 ground state. At low temperature it displays slow magnetic relaxation that is supported by a small external magnetic field.

A W-Shaped Ga-Dy-Dy-Dy-Ga Cluster: Synthesis, Characterization, and Magnetic Properties

A W-shaped {Ga-Dy-Dy-Dy-Ga} coordination cluster, [Ga₂ Dy₃ (L)₆ (MeO)₂ (MeOH)₃ ]⋅NO₃ ⋅7 MeOH (1) with H₂ L, (E)-2-(2-hydroxy-3-methoxy-benzylideneamino)phenol was synthesized, characterized, and the magnetic properties investigated. The magnetic measurements indicate that the compound shows single-molecule magnet (SMM) behavior under zero dc field. This suggests that the combination of Ga^III ions and Dy^III ions (4 f) is a successful strategy to assemble SMM clusters. The combination of these metal ions also offers prospects in dual functionality therapeutics for medical applications.

Butterfly M2 IIIEr2 (MIII = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

The reaction of N-(2-pyridylmethyl)iminodiethanol (H₂L, pmide), FeCl₂·4H₂O or AlCl₃·6H₂O with ErCl₃·6H₂O and p-Me-PhCO₂H in the ratio of 2:1:1:4 in the presence of Et₃N in MeOH and MeCN yielded compounds [Fe₂Er₂(μ₃-OH)₂(pmide)₂(p-Me-PhCO₂)₆]·2MeCN (1) and [Al₂Er₂(μ₃-OH)₂(pmide)₂(p-Me-PhCO₂)₆]·2MeCN (2). These two complexes are isostructural, possessing a planar butterfly motif with the Er^III ions in the wingtip positions. Both compounds show single molecule magnet (SMM) behavior. For the [Al₂Er₂] compound, the slow relaxation of the magnetization under zero applied direct current (dc) field does not show maxima, but the relaxation processes could be analyzed using an applied dc field of 1000 Oe. In-depth alternating current measurements under different dc fields on the [Fe₂Er₂] compound reveals that the Fe-Fe and Fe-Er interactions speed up the relaxation and decrease the energy barrier height of the SMM in comparison with the [Al₂Er₂] case.

Tri- and hexa-nuclear NiII–MnII complexes of a N2O2 donor unsymmetrical ligand: synthesis, structures, magnetic properties and catalytic oxidase activities

Among two trinuclear and a hexanuclear Ni^II–Mn^II complexes, synthesized by using a Ni(ii) metalloligand of a N₂O₂ donor unsymmetrical ligand, only those containing a H₂O molecule coordinated to the Mn^II center show very high catalytic oxidase activities.

Long-range magnetic ordering in a metal-organic framework based on octanuclear nickel(ii) clusters

A novel three-dimensional metal-organic framework [Ni₃(BTC)₂(bpp)₂(H₂O)]·3H₂O (1) based on mixed ligands H₃BTC (1,2,4-benzenetricarboxylic acid) and bpp (1,3-bis(4-pyridyl)propane) was obtained under hydrothermal conditions. Crystal structure analysis reveals that 1 is a framework based on cage-like Ni₈(COO)₁₂ units. Furthermore, long-range magnetic ordering is observed at low temperature.

Bis-phenoxido and bis-acetato bridged heteronuclear {Co(III)Dy(III)} single molecule magnets with two slow relaxation branches

Two bis-μ-phenoxido-bis-μ-acetato heterobimetallic {Co(III)Dy(III)} complexes and , formulated as [Co(III)Dy(III)L(μ-OAc)2(NO3)2] derived from the comparable hexadentate Schiff bases N,N'-ethylenebis(3-ethoxysalicylaldimine) and N,N'-ethylenebis(3-methoxysalicylaldimine) were synthesized and X-ray structure analysis confirms their nearly identical structures. These are the first examples of bis(μ-phenoxido)-bis(μ-carboxylato) {Co(III)Dy(III)} systems. The AC susceptibility measurements show that both complexes exhibit a field-induced slow magnetic relaxation with two relaxation branches. While the high-frequency process spans the usual range of the relaxation time for analogous single molecule magnets (τ0 ∼ 10(-7) s), the low-frequency branch is as slow as τ ∼ 0.1 s at T = 1.9 K and B = 0.2 T.

Three series of heterometallic NiII–LnIII Schiff base complexes: synthesis, crystal structures and magnetic characterization

Three series of Ni^II–Ln^III complexes were synthesized using compartmental Schiff base ligands in conjunction with auxiliary ligands. Their magnetic properties have been well studied.

Synthesis, structures and magnetic properties of chiral 3d–3d′–4f heterotrimetallic complexes based on [(Tp*)Fe(CN)3]−

A series of chiral cyano- and phenolate-bridged heterotrimetallic compounds have been obtained. The Dy and Tb derivatives exhibit similar single-molecule magnetic behaviors under a 1000 Oe dc field.

Metallocyclic Ni4Ln2M2 single-molecule magnets

Magnetic studies on nine new octanuclear cyclic heterotrimetallic complexes reveal that in comparison with analogous octanuclear complexes [Ni₄Dy₂M₂] (M³⁺ = Fe, W and Co), the [Ni₄Dy₂Cr₂] species show the highest energy barrier and the [Ni₄Tb₂M₂] (M = Cr or Fe) complexes display single-molecule magnetic properties.