Dicopper(II) Metallacyclophanes with Oligo(p-phenylene-ethynylene) Spacers: Experimental Foundations and Theoretical Predictions on Potential Molecular Magnetic Wires

Building-up host-guest helicate motifs and chains: a magneto-structural study of new field-induced cobalt-based single-ion magnets

In this work, we present the synthetic pathway, a refined structural description, complete solid-state characterization and the magnetic properties of four new cobalt(ii) compounds of formulas [Co(H₂O)₆][Co₂(H₂mpba)₃]·2H₂O·0.5dmso (1), [Co(H₂O)₆][Co₂(H₂mpba)₃]·3H₂O·0.5dpss (2), [Co₂(H₂mpba)₂(H₂O)₄]_n·4nH₂O (3), and [Co₂(H₂mpba)₂(CH₃OH)₂(H₂O)₂]_n·0.5nH₂O·2ndpss (4) [dpss = 2,2'-dipyridyldisulfide and H₄mpba = 1,3-phenylenebis(oxamic) acid], where 2 and 4 were obtained from [Co(dpss)Cl₂] (Pre-I) as the source of cobalt(ii). All four compounds are air-stable and were prepared under ambient conditions. 1 and 2 were obtained from a slow diffusion method [cobalt(ii) : H₂mpba^2- molar ratio used 1 : 1] and their structures are made up of [Co₂(H₂mpba)₃]^2- anionic helicate units and [Co(H₂O)₆]²⁺ cations, exhibiting supramolecular three-dimensional structures. Interestingly, a supramolecular honeycomb network between the helicate units interacting with each other through R₂²(10) type hydrogen bonds occurs in 2 hosting one co-crystallized dpss molecule. On the other hand, for the first time, linear (3) and zigzag (4) cobalt(ii) chains were isolated by slow evaporation of stirred solutions of mixed solvents with cobalt(ii) : H₂mpba^2- in 1 : 2 molar ratio at room temperature. Magnetic measurements of Pre-I revealed a quasi magnetically isolated S = 3/2 spin state with a significant second-order spin-orbit contribution as expected for tetrahedrally coordinated cobalt(ii) ions. The analysis of the variable temperature static (dc) magnetic susceptibility data through first- (1 and 3) and second-order spin-orbit coupling models (2 and 4) reveals the presence of magnetically non-interacting high-spin cobalt(ii) ions with easy-axis (1 and 4)/easy-plane magnetic anisotropies (2 and 4) with low rhombic distortions. Dynamic (ac) magnetic measurements for Pre-I and 1-4 below 8.0 K show that they are examples of field-induced Single-Ion Magnets (SIMs).

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.

Electronic Communication as a Transferable Property of Molecular Bridges?

Electronic communication through molecular bridges is important for different types of experiments, such as single-molecule conductance, electron transfer, superexchange spin coupling, and intramolecular singlet fission. In many instances, the chemical structure of the bridge determines how the two parts it is connecting communicate, and does so in ways that are transferable between these different manifestations (for example, high conductance often correlates with strong antiferromagnetic spin coupling, and low conductance due to destructive quantum interference correlates with ferromagnetic coupling). Defining electronic communication as a transferable property of the bridge can help transfer knowledge between these different areas of research. Examples and limits of such transferability are discussed here, along with some possible directions for future research, such as employing spin-coupled and mixed-valence systems as structurally well-controlled proxies for understanding molecular conductance and for validating first-principles theoretical methodologies, building conceptual understanding for the growing experimental work on intramolecular singlet fission, and developing measures for the transferability of electronic communication as a bridge property.

Structurally characterized dipalladium(ii)-oxamate metallacyclophanes as efficient catalysts for sustainable Heck and Suzuki reactions in ionic liquids

Dipalladium-oxamate metallacyclophanes were synthesised, structurally characterized and applied in carbon–carbon cross couplings in ionic liquids.

Synthetic ability of dinuclear mesocates containing 1,3-bis(diazinecarboxamide)benzene bridging ligands to form complexes of increased nuclearity. Crystal structures, magnetic properties and theoretical studies

Triple stranded Ni-metallacyclic complexes Na_2.5[Ni₂(bpcb)₃]·0.5OH·18.5H₂O (1) and Na₂[Ni₂(bpzcb)₃]·16H₂O (2), and double stranded Cu-metallacyclic complexes [Cu₂(bpcb)₂(H₂O)₂]·8H₂O (3) and [Cu₂(bpzcb)₂(H₂O)₂]·4H₂O (4) have been assembled from the tailored bisbidentate bridging ligands, 1,3-bis(pyrimidine-2-carboxamide)benzene (H₂bpcb) and 1,3-bis(pyrazine-2-carboxamide)benzene (H₂bpzcb), and the corresponding nitrate salts of the metal ions. Following the "complex as ligand" strategy, 1 can be assembled with either Ni²⁺, Co²⁺ ions or the [Mn(acen)Cl] complex to afford unique, neutral, bent trinuclear molecules [M^IINi(bpcb)₃]·xH₂O (5 and 6) and the 2D honeycomb-like complex (PPh₄){[Ni₂(bpcb)₃]₂[Mn(acen)]₃} (7), respectively. In these cases, the Ni₂ units are linked to the corresponding metal ions through amidate oxygen atoms and the outward nitrogen atom of one of the pyrimidine rings of the bcpb ligand. The assembly of 2 with Ln³⁺ ions (Ln³⁺ = Tb, Gd) leads to one dimensional complexes of formula [{[Ni₂(bpzcb)₃]Tb(H₂O)₅}(CF₃SO₃)·THF·5H₂O]_n (8) and [{[Ni₂(bpzcb)₃]Ln(H₂O)₄(NO₃)}·2THF·nH₂O]_n (9 and 10) (Ln³⁺ = Gd and Tb), where the dinuclear Ni₂ units are joined to two Ln³⁺ ions exclusively through amidate oxygen atoms of two different ligands. The analyses of the magnetic data indicate that 1-4 exhibit intradinuclear ferromagnetic interactions between the metal ions through a spin polarisation mechanism, as supported by DFT calculations. Trinuclear complexes 5 and 6 show predominant antiferromagnetic coupling, which is a result of an antiferromagnetic interaction between one of the Ni²⁺ ions of the Ni₂ unit and the M²⁺ ion through the pyrimidine bridging fragment that is stronger than the polarised ferromagnetic interaction between the Ni²⁺ ions through the bpcb ligand in the dinuclear [Ni₂(bpcb)₃]^2- moiety. Complex 7 shows a dominant antiferromagnetic interaction between the Ni²⁺ and Mn²⁺, whereas the Ni₂Ln (Ln³⁺ = Gd, Tb) chain complexes present ferromagnetic interactions inside the Ni₂ mesocate unit as well as between the Ni²⁺ ions of the Ni₂ unit and the Ln³⁺ ions. The magnetic exchange interactions in these new materials have been experimentally analysed and supported by theoretical DFT studies.

Dicopper(II) Metallacyclophanes with N,N'-2,6-Pyridinebis(oxamate): Solution Study, Synthesis, Crystal Structures, and Magnetic Properties

The complexing ability of copper(II) in solution by the ligand N,N'-2,6-pyridinebis(oxamic acid) (H4mpyba, H4L) was determined through potentiometric and UV-vis spectroscopy at 25 °C and 0.15 M NaCl. The logarithms of the equilibrium constants for its copper(II) complexes according to the eqs 2H2L + 2Cu ⇆ [Cu2(H2L)2], 2H2L + 2Cu ⇆ [Cu2(H2L) (HL)] + H, 2H2L + 2Cu ⇆ [Cu2(HL)2] + 2H, 2H2L + 2Cu ⇆ [Cu2(HL)(L)] + 3H, and 2H2L + 2Cu ⇆ [Cu2L2] + 4H were 12.02(7), 8.04(5), 1.26(6), -7.51(6), and -16.36(6), respectively. The knowledge of the solution behavior has supported the synthesis of three new compounds bearing the common building block Cu2L2(4-). Their formulas are (Me4N)4[Cu2(mpyba)2(H2O)2]·H2O (1), (Me4N)4[K2Na2Cu4(mpyba)4(H2O)6.8]·1.6H2O (2), and [Na6Cu2(mpyba)2Cl2(H2O)8]·7H2O (3) (Me4N(+) = tetramethylammonium cation). The [Cu2(mpyba)2(H2O)2](4-) tetraanionic unit, which is present in 1, has a [3,3] metallacyclophane-type motif connected by two N-Cu-N bonds. In 2, a heterotrimetallic decanuclear nanocage is formed through front-to-front assembly of two [Cu2(mpyba)2](4-) units, which also coordinate to potassium(I) and sodium(I) cations by means of carboxylate oxygens from oxamate. The structure of 3 consists of heterobimetallic layers of formula [Na6Cu2(mpyba)2Cl2(H2O)8] and crystallization water molecules, which are interlinked by hydrogen bonds leading to a supramolecular three-dimensional network. The investigation of the magnetic properties of 1-3 in the temperature range 1.9-300 K shows the occurrence of ferromagnetic interactions between the dicopper(II) metallacyclophane unit [J = +6.85 (1), +7.40 (2), and +7.90 cm(-1) (3); H = -JSCu1·SCu2, where SCu1 = SCu2 = 1/2]. Theoretical calculations on 1-3 were carried to substantiate the nature and magnitude of the involved magnetic interactions and to support the occurrence of a spin polarization mechanism accounting for them.

Theoretical design of magnetic wires from acene and nanocorone derivatives

A theoretical design of molecular magnetic wires based on linear and cyclic oligoacene-bridged dicopper(ii) model complexes is highlighted in the present contribution.

Self-assembly, binding ability and magnetic properties of dicopper(ii) pyrazolenophanes

The nature of the blocking α-diimine ligand controls of the molecular folding and binding ability of the resulting “butterfly-shaped”, antiferromagnetically coupled dicopper(ii) pyrazolenophanes in the solid state.

Dicopper(II) metallacyclophanes as multifunctional magnetic devices: a joint experimental and computational study

Metallosupramolecular complexes constitute an important advance in the emerging fields of molecular spintronics and quantum computation and a useful platform in the development of active components of spintronic circuits and quantum computers for applications in information processing and storage. The external control of chemical reactivity (electro- and photochemical) and physical properties (electronic and magnetic) in metallosupramolecular complexes is a current challenge in supramolecular coordination chemistry, which lies at the interface of several other supramolecular disciplines, including electro-, photo-, and magnetochemistry. The specific control of current flow or spin delocalization through a molecular assembly in response to one or many input signals leads to the concept of developing a molecule-based spintronics that can be viewed as a potential alternative to the classical molecule-based electronics. A great variety of factors can influence over these electronically or magnetically coupled, metallosupramolecular complexes in a reversible manner, electronic or photonic external stimuli being the most promising ones. The response ability of the metal centers and/or the organic bridging ligands to the application of an electric field or light irradiation, together with the geometrical features that allow the precise positioning in space of substituent groups, make these metal-organic systems particularly suitable to build highly integrated molecular spintronic circuits. In this Account, we describe the chemistry and physics of dinuclear copper(II) metallacyclophanes with oxamato-containing dinucleating ligands featuring redox- and photoactive aromatic spacers. Our recent works on dicopper(II) metallacyclophanes and earlier ones on related organic cyclophanes are now compared in a critical manner. Special focus is placed on the ligand design as well as in the combination of experimental and computational methods to demonstrate the multifunctionality nature of these metallosupramolecular complexes. This new class of oxamato-based dicopper(II) metallacyclophanes affords an excellent synthetic and theoretical set of models for both chemical and physical fundamental studies on redox- and photo-triggered, long-distance electron exchange phenomena, which are two major topics in molecular magnetism and molecular electronics. Apart from their use as ground tests for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the electron exchange interaction through extended π-conjugated aromatic ligands in polymetallic complexes, oxamato-based dicopper(II) metallacyclophanes possessing spin-containing electro- and chromophores at the metal and/or the ligand counterparts emerge as potentially active (magnetic and electronic) molecular components to build a metal-based spintronic circuit. They are thus unique examples of multifunctional magnetic complexes to get single-molecule spintronic devices by controlling and allowing the spin communication, when serving as molecular magnetic couplers and wires, or by exhibiting bistable spin behavior, when acting as molecular magnetic rectifiers and switches. Oxamato-based dicopper(II) metallacyclophanes also emerge as potential candidates for the study of coherent electron transport through single molecules, both experimentally and theoretically. The results presented herein, which are a first step in the metallosupramolecular approach to molecular spintronics, intend to attract the attention of physicists and materials scientists with a large expertice in the manipulation and measurement of single-molecule electron transport properties, as well as in the processing and addressing of molecules on different supports.

Structural, spectroscopic, magnetic behavior and DFT investigations ofl-tyrosinato nickel(ii) coordination polymer

The 4,4′-bpy molecules are weakly bonded with nickel(ii) ions in 1Dl-tyrosinato coordination polymer.

A bilayer triangular lattice with crown-like Co7 spin cluster SBUs exhibiting high spin frustration

An unprecedented crown-like Co₇(OH)₆ spin cluster is assembled in a bilayer triangular lattice, showing high spin frustration.