Further synthetic investigation of the general lanthanoid(iii) [Ln(iii)]/copper(ii)/pyridine-2,6-dimethanol/carboxylate reaction system: {CuLn} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(iii) analogue

In addition to previously studied {CuGd₆}, {CuGd₄}, {CuLn₇} and {CuLn₈} coordination clusters (Ln = trivalent lanthanide) containing pdm^2- or Hpdm^- ligands (H₂pdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO₂^-), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [Cu₅Ln₄O₂(OMe)₄(NO₃)₄(O₂CCH₂Bu^t)₂(pdm)₄(MeOH)₂] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO₃)₃·xH₂O (x = 5, 6), CuX₂·yH₂O (X = ClO₄, Cl, NO₃; y = 6, 2 and 3, respectively), H₂pdm, Bu^tCH₂CO₂H and Et₃N (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH. Rather surprisingly, the copper(ii)/yttrium(iii) analogue has a slightly different composition, i.e. [Cu₅Y₄O₂(OMe)₄(NO₃)₂(O₂CCH₂Bu^t)₄(pdm)₄(MeOH)₂] (4). The structures of 1·4MeCN·1.5MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography. The five Cu^II and four Dy^III centres in 1 are held together by two μ₅-O^2-, four μ-MeO^-, two syn,synη¹:η¹:μ Bu^tCH₂CO₂^-, four η²:η¹:η²:μ₃ pdm^2- (each of these groups chelates a Cu^II atom and simultaneously bridges two Dy^III atoms through its two -CH₂O^- arms) and two μ-MeOH ligands. The four terminal nitrato groups each chelate (η¹:η¹) a Dy^III centre. The five Cu^II atoms are co-planar (by symmetry) forming a bow-tie arrangement; the four outer Cu^II atoms form a rectangle with edges of 3.061(1) and 6.076(1) Å. The four Dy^III centres also form a rectangle that lies above and below the plane of the Cu^II centres, with edges of 3.739(1) and 5.328(1) Å. The two strictly planar rectangles are almost perpendicular. Two trigonal bipyramidal μ₅-O^2- groups link the perpendicular Cu₅ and Dy₄ frameworks together. The molecule 4 has a very similar structure to that of 1, differences being the replacement of the two chelating nitrato groups of 1 by two chelating Bu^tCH₂CO₂^- ligands in 4 and the coordination polyhedra of the Ln^III and Y^III atoms (Snub diphenoids in 1 and biaugmented trigonal prisms in 4). Dc magnetic susceptibility data (χ_M) on analytically pure samples of 1-3, collected in the 300-2 K range, indicate that ferromagnetic exchange interactions dominate leading to large spin ground states. The χ_MT vs. T data for 4 suggest moderately strong antiferromagnetic Cu^IICu^II exchange interactions. Studies of the dynamic magnetic properties of the {Cu₅Ln₄} clusters show that 1 behaves as a SMM at zero field and 2 is a very weak field-induced SMM, while 3 exhibits only weak tails in the χ''_Mvs. T plots at various ac frequencies at zero dc field.

{Ni4} Cubanes from enantiomerically pure 2-(1-hydroxyethyl)pyridine ligands: supramolecular chirality

Homometallic {NiII4} cubane-like clusters with a rare chiral core have been prepared via the employment of enantiomerically pure 2-(1-hydroxyethyl)pyridine (Hmpm). Comparison with the achiral cubanes derived from the related 2-pyridinemethanol (Hpym) ligand reveals drastic structural changes as a consequence of the transfer of chirality from the ligands to the whole structure. Their magnetic properties have been related to the structural features of their cubane-type cores.

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.

Regulation of magnetic relaxation behavior by replacing 3d transition metal ions in [M2Dy2] complexes containing two different organic chelating ligands

Two [MIII2DyIII2] complexes (M = Fe for 1 and Co for 2) with mixed organic ligands were obtained. Complex 2 exhibits single molecule magnet behavior with U_eff = 64.0(9) K.

Facile and environmentally friendly synthesis of six heterometallic dumbbell-shaped MLn (M = Co, Ni; Ln = Eu, Gd, Dy) clusters as cryogenic magnetic coolants and molecular magnets

Six analogous dumbbell-shaped 3d-4f complexes MLn were obtained by the reaction of Ln(NO₃)₃ (Ln = Eu, Gd, Dy) and M(OAc)₂ (M = Co, Ni) without any other organic ligands, and M₅Gd₄ exhibited a large magnetocaloric effect (-ΔS_m = 31.0, 37.3 J kg^-1 K^-1 for Co₅Gd₄ and Ni₅Gd₄ respectively), while M₅Dy₄ and Co₅Eu₄ showed single molecule magnet behaviour. To the best of our knowledge, Co₅Eu₄ is the first Eu-based cluster to display single molecule magnet behaviour (U_eff = 16.4 K).

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.

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.

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.

Tuning quantum tunnelling of magnetization through 3d–4f magnetic interactions: an alternative approach for manipulating single-molecule magnetism

The quantum tunnelling of magnetization was observed in [Zn₂Dy₂], contrarily it was quenched in [Mn₂Dy₂] and [Co₂Dy₂] by spin–spin exchange.

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.

Experimental and theoretical investigations of four 3d–4f butterfly single-molecule magnets

Experimental and theoretical investigations of four 3d–4f defect-dicubane single-molecule magnets.

Cu(ii)–Dy(iii) and Co(iii)–Dy(iii) based single molecule magnets with multiple slow magnetic relaxation processes in the Cu(ii)–Dy(iii) complex

Two Cu^II–Dy^III and Co^III–Dy^III dinuclear complexes of a Schiff base ligand (H₃L) exhibit single-molecule magnetic behaviour with multiple slow magnetic relaxation processes for the former.

A new family of high nuclearity CoII/DyIII coordination clusters possessing robust and unseen topologies

Mixing Co(NO₃)₂·6H₂O/Dy(NO₃)₃·6H₂O/(E)-4-(2-hydroxy-3-methoxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one (HL)/pivalic acid/Et₃N in various solvents gives products with robust and unseen topologies.

Trinuclear [CoIII 2 -LnIII] (Ln=Tb, Dy) single-ion magnets with mixed 6-chloro-2-hydroxypyridine and Schiff base ligands

The Schiff base ligand N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H(2)valdien) and the co-ligand 6-chloro-2-hydroxypyridine (Hchp) were used to construct two 3d-4f heterometallic single-ion magnets [Co(2) Dy(valdien)2 (OCH(3))(2) (chp)(2)]⋅ClO(4)⋅5 H(2)O 1 and [Co(2) Tb(valdien)(2) (OCH(3))(2)(chp)(2)]⋅ClO(4)⋅(2) H(2)O⋅CH(3)OH(2). The two trinuclear [Co(III) 2 Ln(III)] complexes behave as a mononuclear Ln(III) magnetic system because of the presence of two diamagnetic cobalt(III) ions. Complex 1 has a molecular symmetry center, and it crystallizes in the C2/c space group, whereas complex 2 shows a lower molecular symmetry and crystallizes in the P(2)1/c space group. Magnetic investigations indicated that both complexes are field-induced single-ion magnets, and the Co(III)(2)-Dy(III) complex possesses a larger energy barrier [74.1(4.2) K] than the Co(III)(2) -Tb(III) complex [32.3(2.6) K].