Single-Molecule Magnetism in a Pentacoordinate Cobalt(II) Complex Supported by an Antenna Ligand

Pentacoordinate complex [CoL³Cl₂] with a tridentate antenna-like ligand L³ forms a dimer held by short π–π stacking with head-to-head contacts at 3.4 Å. The direct-current (dc) magnetic susceptibility and magnetization data confirm weak ferromagnetic interaction and a large-magnetic anisotropy, <i>D</i>/<i>hc</i> = 150 cm^–1 and <i>E</i>/<i>hc</i> = 11.6 cm^–1. The system shows superparamagnetic behavior at low temperature that depends upon the applied magnetic field. At <i>B</i>_dc = 0.2 T, a low-frequency peak at the out-of-phase susceptibility is seen (ν ∼ 0.3 Hz), whereas the onset of the second peak appears at ν > 1500 Hz, indicating the existence of two slow relaxation processes

Role of π‑Radicals in the Spin Connectivity of Clusters and Networks of Tb Double-Decker Single Molecule Magnets

When single molecule magnets (SMMs) self-assemble into 2D networks on a surface, they interact <i>via</i> the π-electrons of their ligands. This interaction is relevant to the quantum entanglement between molecular qubits, a key issue in quantum computing. Here, we examine the role played by the unpaired radical electron in the top ligand of Tb double-decker SMMs by comparing the spectroscopic features of isolated and 2D assembled entities on surfaces. High-resolution scanning tunneling microscopy (STM) is used to evidence experimentally the Kondo resonance of the unpaired radical spins in clusters and islands and its quenching due to up-pairing at orbital overlaps. The presence or the absence of the Kondo feature in the d<i>I</i>/d<i>V</i> maps turns out to be a good measure of the lateral interaction between molecules in 2D networks. In a 2D cluster of molecules, the π-orbital lobes that are linked through the orbital overlap show paired-up electron wave function (one singly occupied molecular orbital (SOMO) with spin-up and the other with spin-down) and therefore do not experience the Kondo resonance in the experiment. As a result, small clusters built by STM-assisted manipulation of molecules show alternating Kondo features of quantum mechanical origin, from the monomer to the dimer and the trimer. On the other hand, when the TbPc₂ molecular clusters grow larger and form extended domains, a geometric rearrangement occurs, leading to the quenching of the Kondo signal on one lobe out of two. The even distribution of overlapping (SOMO) lobes on the perimeter of the molecule is induced by the square symmetry of the semi-infinite lattice and clearly distinguishes the lattice from the clusters

Role of π‑Radicals in the Spin Connectivity of Clusters and Networks of Tb Double-Decker Single Molecule Magnets

When single molecule magnets (SMMs) self-assemble into 2D networks on a surface, they interact <i>via</i> the π-electrons of their ligands. This interaction is relevant to the quantum entanglement between molecular qubits, a key issue in quantum computing. Here, we examine the role played by the unpaired radical electron in the top ligand of Tb double-decker SMMs by comparing the spectroscopic features of isolated and 2D assembled entities on surfaces. High-resolution scanning tunneling microscopy (STM) is used to evidence experimentally the Kondo resonance of the unpaired radical spins in clusters and islands and its quenching due to up-pairing at orbital overlaps. The presence or the absence of the Kondo feature in the d<i>I</i>/d<i>V</i> maps turns out to be a good measure of the lateral interaction between molecules in 2D networks. In a 2D cluster of molecules, the π-orbital lobes that are linked through the orbital overlap show paired-up electron wave function (one singly occupied molecular orbital (SOMO) with spin-up and the other with spin-down) and therefore do not experience the Kondo resonance in the experiment. As a result, small clusters built by STM-assisted manipulation of molecules show alternating Kondo features of quantum mechanical origin, from the monomer to the dimer and the trimer. On the other hand, when the TbPc₂ molecular clusters grow larger and form extended domains, a geometric rearrangement occurs, leading to the quenching of the Kondo signal on one lobe out of two. The even distribution of overlapping (SOMO) lobes on the perimeter of the molecule is induced by the square symmetry of the semi-infinite lattice and clearly distinguishes the lattice from the clusters

Synthesis, Structural Characterization, and Magnetic Properties of Lanthanide Arsolyl Sandwich Complexes

A series of trivalent lanthanide sandwich complexes [(η5-C4R4As)Ln(η8-C8H8)] using three different arsolyl ligands are reported. The complexes were obtained via salt elimination reactions between potassium arsolyl salts and lanthanide precursors [LnI(COT)(THF)2] (Ln = Sm, Dy, Er; COT = η8-C8H8). The resulting compounds exhibit classical sandwich complex structures with one notable exception. Characterization was conducted in both the solid state using single-crystal X-ray diffraction and in solution for the Sm compounds using NMR spectroscopy. Furthermore, the magnetic properties of an Er complex were investigated, revealing distinctive single-molecule-magnet behavior characterized by an energy barrier of Ueff = 323.3 K. Theoretical calculations were employed to support and interpret the experimental findings, with a comparative analysis performed against previously reported complexes

Mark McKenna was quoted • AP in many articles about software patents issues in the Apple-Samsung court case. on March 30.

Mark McKenna was quoted by AP in many articles about software patents issues in the Apple-Samsung court case. on March 30. There\u27s a widespread suspicion that lots of the kinds of software patents at issue are written in ways that cover more ground than what Apple or any other tech firm actually invented, Notre Dame law professor Mark McKenna said. Overly broad patents allow companies to block competition

Bilayer of Terbium Double-Decker Single-Molecule Magnets

We report a low-temperature scanning tunneling microscopy and spectroscopy study of the structural and electronic properties of a bilayer of terbium double-decker (bis­(phthalocyaninato)­terbium­(III), TbPc₂) molecules on Au(111) at 5 K. The TbPc₂ molecules are found to adsorb flat on top of a first compact TbPc₂ monolayer on Au(111), forming a square-like packing similar to the underlying first layer. Their frontier-orbital electronic structure, measured by tunneling conductance spectroscopy, clearly differs from that of the underlying first monolayer. Our results of second-layer molecules indicate the absence of, both, hybrid molecule–substrate electronic states close to the Fermi level and a zero-bias Kondo resonance. We attribute these findings to a decreased electronic coupling with the Au(111) substrate

Spin-Crossover and Massive Anisotropy Switching of 5d Transition Metal Atoms on Graphene Nanoflakes

In spin crossover phenomena, the magnetic moment of a molecule is switched by external means. Here we theoretically predict that several 5d-transition metals (TMs) adsorbed on finite graphene flakes undergo a spin crossover, resulting from multiple adsorption minima, that are absent in the zero-dimensional limit of benzene and the two-dimensional limit of graphene. The different spin states are stable at finite temperature and can be reversibly switched with an electric field. The system undergoes a change in magnetic anisotropy upon spin crossover, which facilitates read-out of the spin state. The TM-decorated nanoflakes thus act as fully controlled single-ion magnetic switches

Observation of Cooperative Electronic Quantum Tunneling: Increasing Accessible Nuclear States in a Molecular Qudit

As an extension of two-level quantum bits (qubits), multilevel systems, so-called qu<i>d</i>its, where <i>d</i> represents the Hilbert space dimension, have been predicted to reduce the number of iterations in quantum-computation algorithms. This has been tested in the well-known [TbPc₂]⁰ single-molecule magnet (SMM), which allowed implementation of the Grover algorithm in a single molecular unit. In the quest for molecular systems possessing an increased number of accessible nuclear spin states, we explore herein a dimeric Tb₂-SMM via single-crystal μ-SQUID measurements at sub-Kelvin temperatures. We observe ferromagnetic interactions between the Tb^III ions and cooperative quantum tunneling of the electronic spins with spin ground state |<i>J</i>_<i>z</i> = ±6⟩. Strong hyperfine coupling with the Tb^III nuclear spins leads to a multitude of spin-reversal paths, leading to seven strong hyperfine-driven tunneling steps in the hysteresis loops. Our results show the possibility of reading out the Tb^III nuclear spin states via cooperative tunneling of the electronic spins, making the dimeric Tb₂-SMM an excellent nuclear spin qu<i>d</i>it candidate with <i>d</i> = 16

Mixed-Valence Heptanuclear Iron Complexes with Ferromagnetic Interaction

Three new Prussian blue analogues, heptanuclear mixed-valence iron complexes of the type [Fe^II(CN)₆{Fe^III(1_–2H)}₆]­Cl₂·<i>n</i>H₂O, were synthesized and structurally and spectrally characterized, and their magnetic properties were investigated (1_–2H corresponds to doubly deprotoned Schiff-base pentadentate ligands <b>1a</b>, <i>N</i>,<i>N</i>′-bis­(2-hydroxybenzylidene)-1,5-diamino-3-azapentane, <b>1b</b>, <i>N</i>,<i>N</i>′-bis­(3-ethoxy-2-hydroxybenzylidene)-1,7-diamino-4-azaheptane, or <b>1c</b>, <i>N</i>,<i>N</i>′-bis­(3-methoxy-2-hydroxybenzylidene)-1,6-diamino-3-azahexane). These compounds were formed by assembling the [Fe­(CN)₆]^4– building block with mononuclear complexes of the [Fe­(1_–2H)­Cl] type. X-ray structure analysis revealed that the complexes adopt a star-like architecture: the Fe­(II) ion lies at the very center, and on its octahedral nodes the Fe­(III) sites are coordinated in the Fe^II–CN–Fe^III manner. The Schiff-base pentadentate ligand moiety 1_–2H coordinates a single Fe­(III) center in two complexes <b>3b</b> and <b>3c</b>. Ligands 1a_–2H in the complex cation of <b>3a</b> adopt an unusual coordination mode: three donor atoms of the same ligand (one O and two N) coordinate one Fe­(III), whereas the remaining N′ and O′ donor atoms coordinate the neighboring Fe­(III) center creating the {Fe­(ON₂)­(N′O′)­N″} chromophore involving two 1a_–2H ligand moieties. Moreover, three Fe­(III) centers are interconnected with three 1a_–2H ligands in such a manner that two {Fe^III₃(1a_–2H)₃} units form two intramolecular rings. Magnetic investigation of the heptanuclear complexes revealed the high-spin state of all six Fe­(III) coordination sites (<i>s</i> = 5/2), while the very central Fe­(II) site is in the low-spin state (<i>s</i> = 0). At low temperature, the ferromagnetic exchange interactions stay evident for all three complexes. Mössbauer spectra of compounds <b>3a</b> and <b>3b</b> revealed a presence of two different doublets for both compounds: the major doublet is related to six Fe­(III) high-spin coordination sites and the minor doublet refers to the low-spin very central Fe­(II)

Functionalization of Open Two-Dimensional Metal–Organic Templates through the Selective Incorporation of Metal Atoms

Surface-confined molecular networks can serve as templates to steer the adsorption and organization of secondary ligands, metal atoms, and clusters. Here, the incorporation of Ni atoms and clusters into open two-dimensional robust metal–organic templates self-assembled from butadiyne dibenzoic acid molecules and Fe atoms on Au(111) and Ag(100) surfaces is investigated by scanning tunneling microscopy. The metal substrate plays a crucial role in the interaction of Ni atoms with the metal–organic host networks. On Ag(100) the metal–organic template steers the growth of Ni clusters underneath the network pattern near the central butadiyne moiety. In contrast, on Au(111) Ni interacts preferentially with the benzene rings forming size-limited clusters inside the network cavities. Thereby, on both surfaces Ni clusters consisting of a few atoms with both high areal density and thermal stability up to 450 K are realized. The Ni-functionalized networks enable the coordination of additional molecules into the open structures demonstrating the utilization of selective interactions for the assembly of multicomponent architectures at different organizational stages