Magnetic molecular wheels and grids – the need for novel concepts in “zero-dimensional” magnetism

Quantum Spin Wave Excited from a Cr-Dy Single-Molecule Magnet

The efficient excitation and controlled propagation of nanoscale spin waves remain significant challenges, as their intrinsic dispersion relations are primarily determined by magnetic dipole and exchange interactions. Here we report the first observed coexistence of quantum spin wave excitation and single-molecule magnet behavior in a mixed chromium(III) and dysprosium(III) complex, namely Dy4Cr2(μ3-F)2(mdea)3(piv)10, which shows a large ferrimagnetic ground moment with a restricted quantum tunneling gap (<3.8 × 10-7 cm-1) up to nine levels, leading to an axial anisotropic energy barrier of 12 cm-1 and opened hysteresis loop at 0.4 K. More importantly, quantized spin wave excitations ranging from 108 to 352 GHz have been observed by using inelastic neutron scattering spectroscopy, and the data can be well explained by the L&E-band theory with Δ/2 = 2.08 cm-1 and ε(q) = 2.5 cm-1, providing unambiguous evidence for nanoscale spin waves.

Single-Molecule Magnet Behavior and Spin Structure of an FeIII7 Cartwheel Cluster Revealed by Sub-Kelvin Magnetometry and Mössbauer Spectroscopy: The Final Pieces of the Puzzle

The spin frustration and other magnetic properties of the "cartwheel" heptanuclear cluster [FeIII7O3(O2CtBu)9(Me-dea)3(H2O)3] (Me-deaH2 = N-methyldiethanolamine) have been previously investigated; we present here a Mössbauer spectroscopic study and sub-Kelvin magnetization and ac susceptibility measurements which enable a complete magnetic picture of this frustrated cluster. 57Fe Mössbauer spectra above 150 K showed three doublets in a 1:3:3 ratio, which could be assigned by their respective quadrupole splittings to the central Fe(1) and the peripheral Fe(2) and Fe(3). The field dependence of the corresponding magnetic sextets at 3 K showed that the spins on the central Fe(1) and the three peripheral Fe(2) sites with O5N coordination are oriented mutually coparallel, while these are antiparallel to the spins on the peripheral Fe(3) sites with O6 coordination, resulting in an overall S = 5/2 ground state. This provides experimental confirmation of the previously proposed spin ground state structure. Upon cooling to sub-Kelvin temperatures, a crossover to spin blocking with TB ≈ 0.21 K could be observed. This single-molecule magnet behavior had been expected but had not been observable with a conventional SQUID. The anisotropy barrier, of 3-fold symmetry, can be described in terms of the parameter D/kB = -0.47 K and a fourth-order perturbation; the latter enables thermally activated quantum tunneling through the excited sublevel mz = ± 3/2, with an activation barrier of U/kB = 1.9 K.

When Molecular Magnetism Meets Supramolecular Chemistry: Multifunctional and Multiresponsive Dicopper(II) Metallacyclophanes as Proof-of-Concept for Single-Molecule Spintronics and Quantum Computing Technologies?

Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday.

The Influence of Halide Substituents on the Structural and Magnetic Properties of Fe6Dy3 Rings

We report the synthesis and magnetic properties of three new nine-membered Fe(III)-Dy(III) cyclic coordination clusters (CCCs), with a core motif of [Fe₆Dy₃(μ-OMe)₉(vanox)₆(X-benz)₆] where the benzoate ligands are substituted in the para-position with X = F (1), Cl (2), Br (3). Single crystal X-ray diffraction structure analyses show that for the smaller fluorine or chlorine substituents the resulting structures exhibit an isostructural Fe₆Dy₃ core, whilst the 4-bromobenzoate ligand leads to structural distortions which affect the dynamic magnetic behavior. The magnetic susceptibility and magnetization of 1-3 were investigated and show similar behavior in the dc (direct current) magnetic data. Additional ac (alternating current) magnetic measurements show that all compounds exhibit frequency-dependent and temperature-dependent signals in the in-phase and out-of-phase component of the susceptibility and can therefore be described as field-induced SMMs. The fluoro-substituted benzoate cluster 1 shows a magnetic behavior closely similar to that of the corresponding unsubstituted Fe₆Dy₃ cluster, with U_eff = 21.3 K within the Orbach process. By increasing the size of the substituent toward 4-chlorobenzoate within 2, an increase of the energy barrier to U_eff = 36.1 K was observed. While the energy barrier becomes higher from 1 to 2, highlighting that the introduction of different substituents on the benzoate ligand in the para-position has an impact on the magnetic properties, cluster 3 shows a significantly different SMM behavior where U_eff is reduced in the Orbach regime to only 4.9 K.

The linear and non-linear magnetic response of a tri-uranium single molecule magnet

We report here low temperature magnetization isotherms for the single molecule magnet, (UO₂-L)₃. By analyzing the low temperature magnetization in terms of M  =  χ ₁ B  +  χ ₃ B ³ we extract the linear susceptibility χ ₁ and the leading order nonlinear susceptibility χ ₃. We find that χ ₁ exhibits a peak at a temperature of T ₁  =  10.4 K with χ ₃ also exhibiting a peak but at a reduced temperature T ₃  =  5 K. At the lowest temperatures the isotherms exhibit a critical field B _c  =  11.5 T marked by a clear point of inflection. A minimal Hamiltonian employing S  =  1 (pseudo) spins with only a single energy scale (successfully used to model the behavior of bulk f-electron metamagnets) is shown to provide a good description of the observed linear scaling between T ₁, T ₃ and B _c. We further show that a Heisenberg Hamiltonian previously employed by Carretta et al (2013 J. Phys.: Condens. Matter 25 486001) to model this single molecule magnet gives formulas for the angle averaged susceptibilities (in the Ising limit) very similar to those of the minimal model.

An unusual zig-zag 1D copper(ii) coordination polymer displaying magnetic phase transition

A new Cu(ii)-based 1D chain was prepared and its magnetic behaviour was investigated, which indicated a magnetic phase transition below 25 K as well as long-range magnetic ordering.

A series of six-membered lanthanide rings based on 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol: synthesis, crystal structures and magnetic properties

A series of six-membered ring cyclic lanthanide(iii) clusters have been constructed by utilizing the pentol ligand.

Halogen dependent symmetry change in two series of wheel cluster organic frameworks built from La18 tertiary building units

Two series of wheel cluster organic frameworks (WCOFs) built from La18 tertiary building units are hydrothermally made, which show halogen-dependent structural symmetry, and demonstrate different chiral performances.

Nine members of a family of nine-membered cyclic coordination clusters; Fe6Ln3 wheels (Ln = Gd to Lu and Y)

We report a family of isostructural nonanuclear Fe^III–Ln^III cyclic coordination clusters, [FeIII6LnIII3(μ-OMe)₉(vanox)₆ (benzoate)₆], with a planar core structure built up from three [Fe₂Ln] units to give a giant Ln₃ triangle embedded into an Fe₆ ring.

Cyclic single-molecule magnets: from the odd-numbered heptanuclear to a dimer of heptanuclear dysprosium clusters

A heptanuclear compound and a dimer of heptanuclear dysprosium clusters (Dy₇ and Dy₁₄) have been successfully synthesized, which feature the largest odd-numbered cyclic lanthanide clusters reported thus far. Both exhibit single molecule magnet behaviours at low temperature.

Enlarging the ring by incorporating a phosphonate coligand: from the cyclic hexanuclear to octanuclear dysprosium clusters

Solvothermal reaction of a double pyrazinyl hydrazone ligand EDDC(2-) with Dy(OAc)3 results in a cyclic hexanuclear cluster [Dy6(EDDC)2(OAc)14(H2O)2]·MeOH·2H2O (). The addition of 1-naphthylphosphonate to the reaction mixture expands the ring size with the formation of a cyclic octanuclear cluster [Dy8(EDDC)4(O3PC10H7)4(OAc)8(H2O)4]·12H2O (). The latter shows slow magnetization relaxation below 12 K, characteristic of single molecule magnet behavior.

Magnetic clusters based on octacyanidometallates

A complete review of all known octacyanide-based clusters with an extensive discussion of their structures, magnetic properties and multifunctionality.

Discrete and encapsulated molecular grids: homometallic Mn15 and heterometallic Mn24Ni2 aggregates

Two molecular grid-like clusters are reported, one is a discrete [3 × 5] grid and the other a [3 × 4] grid within a Mn12Ni2 loop. Both Mn24Ni2 and Mn15 aggregates display novel and aesthetically pleasing structures with the former one being among the highest nuclearity heterometallic MnxMy clusters (M = any transition metal ion).

Syntheses, crystal structures, MMCT and magnetic properties of four one-dimensional cyanide-bridged complexes comprised of MII–CN–FeIII (M = Fe, Ru, Os)

Four 1D cyanide-bridged complexes [cis-M^II(L)₂(CN)₂Fe^III(salen)](PF₆) (3–6) have been synthesized, of which 3 and 4 are Class II mixed-valence complexes.

Three-Membered Metal-Nucleobase-Carboxylate System Showing Interesting 2D and 3D Architecture: Synthesis, Structure, Thermostability, and Magnetic Properties

Via hydrothermal synthesis, we constructed four nucleobase metal-organic compounds, viz. Zn2(7H-ade)(oba)2·H2O (1), Zn(1H-hyp)(Hoba) (2), Ni(1H-ade)(ip) (3), and Cd(H2O)(9H-ade)(ip) (4), where ade, hyp, H2oba, and H2ip are adenine, hypoxanthine, 4,4′-oxybisbenzoic acid, and isophthalic acid, respectively. These polymers show novel 2D and 3D structures, such as 3-fold interpenetrating dmp net, supramolecular zeolite-type sra net, and exceptional 2D 44 net composed of three kinds of quadrangle, observed in polymers 1, 2, and 3, respectively. Moreover, thermogravimetric studies of polymers 1, 2, and 4, and the magnetic properties of 3 are also explored.

Self-assembled Co(II) molecular squares incorporating the bridging ligand 4,7-phenanthrolino-5,6:5',6'-pyrazine

Three high-spin tetranuclear cobalt(II) complexes have been prepared with the bridging ligand 4,7-phenanthrolino-5,6:5',6'-pyrazine (ppz) through metal-ion directed self-assembly. The complexes differ by the incorporation of three different coordinating anions: chloride, thiocyanide and selenocyanide. The physical properties of these complexes have been investigated in detail.

Quantum phase interference and Néel-vector tunneling in antiferromagnetic molecular wheels

The antiferromagnetic molecular wheel Fe18 of 18 exchange-coupled Fe;{III} ions has been studied by magnetic torque, magnetization, and inelastic neutron scattering. The combined data show that the low-temperature magnetism of Fe18 is very accurately described by the Néel-vector tunneling (NVT) scenario, as unfolded by semiclassical theory. In addition, the magnetic torque as a function of applied field exhibits oscillations that reflect the oscillations in the NVT splitting with field due to quantum phase interference.