Family of Defect-Dicubane Ni4Ln2 (Ln = Gd, Tb, Dy, Ho) and Ni4Y2 Complexes: Rare Tb(III) and Ho(III) Examples Showing SMM Behavior

Strategies to quench quantum tunneling of magnetization in lanthanide single molecule magnets

Enhancing blocking temperature (T_B) is one of the holy grails in Single Molecule Magnets(SMMs), as any future potential application in this class of molecules is directly correlated to this parameter. Among many factors contributing to a reduction of T_B value, Quantum Tunnelling of Magnetisation (QTM), a phenomenon that is a curse or a blessing based on the application sought after, tops the list. Theoretical tools based on density functional and ab initio CASSCF/RASSI-SO methods have played a prominent role in estimating various spin Hamiltonian parameters and establishing the mechanism of magnetization relaxation in this class of molecules. Particularly, various strategies to quench QTM effects go hand-in-hand with experiments, and different methods proposed to quell QTM effects are scattered in the literature. In this perspective, we have explored various approaches that are proposed in the literature to quench QTM effects, and these include the role of (i) local symmetry of lanthanides, (ii) super-exchange interaction in {3d-4f} complexes, (iii) direct-exchange interaction in {radical-4f} and metal-metal bonded complexes to suppress the QTM, (iv) utilizing external stimuli such as an electric field or pressure to modulate the QTM and (v) avoiding QTM effects by stabilising toroidal states in 4f and {3d-4f} clusters. We believe the strategies summarized here will help to design new-generation SMMs.

Exchange-Driven Slow Relaxation of Magnetization in NiII2LnIII2 (LnIII = Y, Gd, Tb and Dy) Butterfly complexes: Experimental and Theoretical Studies

The tetranuclear NiII2LnIII2 complexes, [{L′2{Ni(MeOH)(μ-OAc)}2(μ3-MeO)2Ln2}; LnIII = YIII (1), GdIII (2), TbIII (3), DyIII (4)] were prepared using a Schiff base ligand, H3L [H3L = 3-((2-hydroxy-3-methoxybenzylidene)amino)-2-(2-hydroxy-3-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one, whereas {L′}3- is the...

Toroidal magnetic moments in Tb4 squares

A series of Tb4 complexes isolated from reduced or dimerized Schiff base ligand share a similar µ4-O bridged Tb4 square core with the magnetic moments of the TbIII ions in...

Superb Alkali-Resistant DyIII2NiII4 Single-Molecule Magnet

A superb alkali-resistant single-molecule-magnet (SMM) material with the molecular formula [Dy₂Ni₄(L)₈(CH₃COO)₄(NO₃)₂] (1) (HL = 8-hydroxyquinoline) has been structurally and magnetically characterized. Single-crystal X-ray diffraction revealed that 1 possesses a hexanuclear [Dy^III₂Ni^II₄] cluster, which is built by two triangular [Dy^IIINi^II₂] cores double-bridged through two CH₃COO^- ions. Interestingly, 1 can keep its original structure in dilute acid and common basic solutions (e.g., triethylamine and NaOH). More importantly, 1 is still stable after treatment with a 20 M NaOH aqueous solution for 1 month at room temperature. Magnetic measurements uncovered that 1 is an SMM under zero applied field with U_eff = 7.43 K. To the best of our knowledge, 1 is the first example of a 3d-4f SMM with such extreme alkali resistance. This work will broaden the vision of preparing SMM materials with excellent chemical stability.

Guest-Induced Switching of a Molecule-Based Magnet in a 3d-4f Heterometallic Cluster-Based Chain Structure

With the motivation of controlling a magnetic switch by external stimuli, we report here an infinite chain structure formed from the secondary building units of Cu₃Tb₂ clusters through the linkage of nitrate ions. It behaves as a molecule-based magnet with the highest energy barrier among isolated Tb/Cu-based single-molecule magnets and single-chain magnets, which is close to a dimer of a Cu₃Tb₂ cluster unit from a magnetic point as revealed by its correlation length of 2.23 Cu₃Tb₂ units. This kind of molecule-based magnet in a chain structure is rare. The removal of its guest ethanol molecules leads to the complete disappearance of slow magnetic relaxation behavior. Interestingly, the capture and removal of guest ethanol molecules are reversible, mediating a rare ON/OFF switching of a 3d-4f heterometallic molecule-based magnet, which was interpreted by the theoretical calculations based on the structural difference upon desolvation.

Roles of basicity and steric crowding of anionic coligands in catechol oxidase-like activity of Cu(ii)-Mn(ii) complexes

Five new heterometallic Cu(ii)-Mn(ii) discrete trinuclear complexes, [(CuL)2Mn(CH3COO)2] (1), [(CuL)2Mn(NO3)2] (2), [(CuL)2Mn(C6H5COO)(H2O)]Cl (3), [(CuL)2Mn((p-OH)C6H5COO)(H2O)]ClO4 (4) and [(CuL)2Mn(HCOO)(H2O)]ClO4 (5), have been synthesized using a metalloligand, CuL derived from an N2O2 donor Schiff base, H2L (N,N'-bis(α-methylsalicylidene)-1,3-propanediamine). Single-crystal structural analyses reveal that all five complexes have a common [(CuL)2Mn] core, where two terminal metalloligands, CuL, are connected to the central metal ion, Mn(ii), via double phenoxido bridges. Among the complexes, 1 and 2 possess linear structures where the terminal Cu(ii) atoms are bridged to the central Mn(ii) atoms by acetate and nitrate ions, respectively along with the double phenoxido bridges, whereas 3, 4 and 5 have bent structures in which the respective anionic coligands, benzoate, p-hydroxybenzoate and formate ions are coordinated only to central Mn(ii) in monodentate fashion along with a water molecule that completes its hexa-coordinated geometry. Among the complexes, 1, 3, 4 and 5 show quite high bio-mimicking catecholase-like activity for the aerial oxidation of 3,5-di-tert-butylcatechol with turnover numbers (Kcat) of 139 h-1, 439 h-1, 348 h-1 and 730 h-1, respectively, whereas complex 2 is practically inactive towards this reaction. The presence of the coordinated water molecule to Mn(ii) in the bent complexes, 3-5, appears to be responsible for their high catalytic activity and the difference in their activity may be attributed to steric crowding due to the anionic coligand, whereas the inactivity of 2 seems to be associated with the low basicity of the nitrate ion. The temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 1-5 are antiferromagnetically coupled with the exchange coupling constants (J) = -8.54 cm-1, -11.50 cm-1, -19.83 cm-1, -10.65 cm-1 and -10.27 cm-1 for 1, 2, 3, 4 and 5 respectively as is expected from the Cu-O-Mn bridging angles.

Coordination control of a semicarbazide Schiff base ligand for spontaneous aggregation of a Ni2Ln2 cubane family: influence of ligand arms and carboxylate bridges on the organization of the magnetic core

A new family of tetranuclear [Ni₂Ln₂O₄] cubane complexes has been assembled from carbazido ligand by altering the 4f ions without changing the core topology, which provided weak ferromagnetic and antiferromagnetic interactions.

Synthesis, crystal structures and magnetic properties of a series of chair-like heterometallic [Fe4Ln2] (Ln = GdIII, DyIII, HoIII, and ErIII) complexes with mixed organic ligands

Four chair-like hexanuclear Fe-Ln complexes containing mixed organic ligands, namely, [Fe₄Ln₂{(py)₂CO₂}₄(pdm)₂(NO₃)₂(H₂O)₂Cl₄]·xCH₃CN·yH₂O (Ln = Gd^III (1, x = 1, y = 0), Dy^III (2, x = 1, y = 1), Ho^III (3, x = 0, y = 2), and Er^III (4, x = 1, y = 3); (py)₂CO₂H₂ = the gem-diol form of di-2-pyridyl ketone and pdmH₂ = 2,6-pyridinedimethanol) have been obtained by employing di-2-pyridyl ketone and 2,6-pyridinedimethanol reacting with FeCl₃ and Ln(NO₃)₃ in MeCN. The structures of 1-4 are similar to each other except for the number of lattice solvent molecules. Four Fe^III and two Ln^III in these complexes comprise a chair-like core with the "body" constructed by four Fe^III ions and the "end" constructed by two Ln^III ions. Among the four compounds, 2 shows field-induced single molecule magnet behavior as revealed by ac magnetic susceptibility studies, with the effective energy barrier and the pre-exponential factor of 22.07 K and 8.44 × 10^-7 s, respectively. Ab initio calculations indicated that, among 2_Dy, 3_Ho and 4_Er fragments, the energy gap between the lowest two spin-orbit states for 2_Dy is the largest, while the tunneling gap for 2 is the smallest. These might be the reasons for complex 2 exhibiting SMM behavior. Additionally, the orientations of the magnetic anisotropy of Dy^III in 2 were obtained by electrostatic calculations and ab initio calculations, both indicating that the directions of the main magnetic axis of Dy1 ions are almost aligned along Dy1-O5 (O5 from the pdm^2- ligand).

A family of planar hexanuclear CoLn clusters with lucanidae-like arrangement and single-molecule magnet behavior

A family of planar hexanuclear CoLn clusters with the hydroxyl and nitrogen rich ligand 2-[bis(pyridin-2-ylmethyl) amino]-2-(hydroxymethyl)propane-1,3-diol (H₃L), formulated as [Co₄Ln₂(μ₃-O)₂(μ-N₃)₂(OH)₂(H₂O)₂(HL)₄]·(CH₃CO₂)₂·20H₂O [Ln = Dy (1), Gd (2), Tb (3), Eu (4) and Ho (5)], have been synthesized and structurally characterized. They are isomorphous and feature a lucanidae-like arrangement. They are the first examples of 3d-4f clusters with the H₃L ligand. In addition, the magnetic properties of 1-5 have been investigated and the single-molecule magnet (SMM) behaviour is observed for 1.

M, Ahmad M, Shahid M. Synthesis, characterization, theoretical studies and catecholase like activities of [MO6] type complexes

Co(ii) and Zn(ii) complexes are prepared and characterized through spectral, crystallographic and theoretical studies. The Co(ii) complex is shown to be a catechol oxidase mimic and the activity is corroborated by DFT results.

Variation of nuclearity in NiII complexes of a Schiff base ligand: crystal structures and magnetic studies

Four Ni^II complexes have been synthesized by changing the reaction conditions and stoichiometry of the reactants. The magnetic coupling in the NiII4 complex is ferromagnetic whereas that in the NiII6 complex is antiferromagnetic.

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.

High-nuclear heterometallic oxime clusters assembled from triangular subunits: solvothermal syntheses, crystal structures and magnetic properties

Three series of 3d–4f oxime clusters with slightly low magnetic relaxation or large entropy change were solvothermally constructed through the flexible connectivity of triangular {Ln₃(μ₃-OH)} subunits.

Dinucleating Schiff base ligand in Zn/4f coordination chemistry: synthetic challenges and catalytic activity evaluation

Synthetic challenges and catalytic activity evaluation of Zn/(Dy,Y) coordination clusters derived from a dinucleating Schiff base ligand.

Heterometallic lanthanide-centred [NiII6LnIII] rings

The syntheses, structures and magnetic properties of three new hetero-heptametallic [Ni₆Ln] complexes are reported.

Heterometallic hexanuclear Ni4M2 (M = Dy, Y) complexes: structure and single-molecule magnet for the Dy(iii) derivative

We report here a 3d–4f heterometallic hexanuclear Ni₄Dy₂ single-molecule magnet with an S-shaped double-pocket skeleton.

Polynuclear ampyrone based 3d coordination clusters

The use of a monoanionic Schiff base ligand in transition (Co, Ni and Cu) coordination chemistry yields mono-, tetra- and pentanuclear coordination clusters with different structural motifs.

A Three-Pronged Attack To Investigate the Electronic Structure of a Family of Ferromagnetic Fe4Ln2 Cyclic Coordination Clusters: A Combined Magnetic Susceptibility, High-Field/High-Frequency Electron Paramagnetic Resonance, and 57Fe Mössbauer Study

We present the synthesis, structure, magnetic properties, as well as the Mössbauer and electron paramagnetic resonance studies of a ring-shaped [Fe^III₄Ln^III₂(Htea)₄(μ-N₃)₄(N₃)₃(piv)₃] (Ln = Y 1, Gd 2, Tb 3, Dy 4, Ho 5, Er, 6) coordination cluster. The Dy, Tb, and Ho analogues show blocking of the magnetization at low temperatures without applied fields. The anisotropy of the 3d ion and the exchange interaction between 3d and 4f ions in Fe₄Ln₂ complexes are unambiguously determined by high-field/high-frequency electron paramagnetic resonance measurements at low temperature. Ferromagnetic exchange interaction J_Fe-Ln is found which decreases upon variation of the Ln ions to larger atomic numbers. This dependence is similar to the behavior shown in the effective barrier values of complexes 3-5. Further information about the anisotropy of the Ln³⁺ ions was gathered with ⁵⁷Fe Mössbauer spectroscopy, and the combination of these methods provides detailed information regarding the electronic structure of these complexes.

Anion dependent self-assembly of sandwich 13-metal Ni-Ln nanoclusters with a long-chain Schiff base ligand

Two classes of Ni-Ln clusters [Ln₄Ni₃L₃(OAc)₆(NO₃)₃(OH)₃] (Ln = Gd (1) and Tb (2)) and [Ln₆Ni₇L₆(OAc)₁₂(OH)₆](OH)₂ (Ln = Gd (3) and Dy (4)) were prepared using a specifically designed Schiff base ligand built around a flexible (CH₂)₂O(CH₂)₂O(CH₂)₂ chain. 1 and 2 exhibit cone-like structures, while 3 and 4 have nanosized sandwich architectures. The structures were studied by single-crystal X-ray diffraction and TEM, and magnetic properties were investigated.

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.

Tetranuclear Ni(ii) and Co(ii) Schiff-base complexes with an M4O6 defective dicubane-like core: zero-field SMM behavior in the cobalt analogue

Two tetranuclear Ni₄ and Co₄ complexes were prepared and characterized. Their magnetic properties were thoroughly studied and it was revealed that the Co₄ compound behaves as a zero-field single-molecule magnet.

A Schiff base platform: structures, sensing of Zn(ii) and PPi in aqueous medium and anticancer activity

A Schiff base platform was explored to present structural aspects of its Zn(ii) and Cd(ii) coordination compounds, sensing behavior towards Zn(ii) and PPi in aqueous medium and anticancer activity.

Syntheses, crystal structures, and magnetic properties of a family of heterometallic octanuclear [Cu6Ln2] (Ln = Dy(iii), Tb(iii), Ho(iii), Er(iii), and Gd(iii)) complexes

Five novel [Cu₆Ln₂] complexes were synthesized, wherein Ln^III ions are seven-coordinate and coordinated by one triethanolamine and three di-2-pyridyl ketone ligands, without coordinated solvent molecules and small anions.

Probing the magnetic relaxation and magnetic moment arrangement in a series of Dy4 squares

Modulations of the first and secondary coordination geometries by dimerizing and reducing the Schiff base ligands result in the enhancement of the magnetic relaxation and rearrangement of the magnetic moments in μ₄-O²⁻ bridged Dy₄ squares.

Structural variations in (CuL)2Ln complexes of a series of lanthanide ions with a salen-type unsymmetrical Schiff base(H2L): Dy and Tb derivatives as potential single-molecule magnets

Five heterometallic Cu₂Ln complexes (Ln = Gd, Tb, Dy, Ho and Er) have been synthesized using asymmetric Schiff base ligand. Among these, Cu₂Tb and Cu₂Dy complexes show field induced SMM behaviour.

The ferromagnetic [Ln2Co6] heterometallic complexes

Four 3d–4f [Ln₂Co₆] complexes were fabricated. [Dy₂Co₆] (1) and [Ho₂Co₆] (2) displayed ferromagnetic coupling, and [Dy₂Co₆] (1) exhibited slow magnetic relaxation.