The effect of co-ligands on the performance of single-molecule magnet behaviours in a family of linear trinuclear Zn-Dy-Zn complexes with a compartmental Schiff base.

We present herein magneto-structural studies of three heterometallic ZnDy complexes: [ZnDy(L)Cl(HO)](ClO)·4HO (1), [ZnDy(L)Br(HO)](ClO)·4HO (2) and [ZnDy(L)(OAc)I(HO)]I·4HO (3), utilizing a new Schiff base ligand, ,-bis(3-methoxy-5-methylsalicylidene)-1,2-diaminocyclohexane (HL). Complexes 1 and 2 exhibit remarkable magnetic relaxation behaviour with relatively high energy barriers in zero field (: 244 K for 1 and 211 K for 2) and notable hysteresis temperatures, despite the low local geometric symmetry around the central Dy ions. The SMM performance of these complexes is further enhanced under an applied magnetic field, with increasing to 309 K for 1 and 269 K for 2, positioning them as elite members within the Zn-Dy SMM family.

Synthesis and Optical Properties of a Novel Hybrid Nanosystem Based on Covalently Modified nSiO Nanoparticles with a Curcuminoid Molecule.

A new curcuminoid molecule () has been designed and synthesized, containing a central -(CH)-COOH chain at the α carbon of the keto-enol moiety in the structure. The carboxylic acid group is added to react with exposed amino groups on silica oxide nanoparticles (nSiO), forming an amide bond to attach the curcuminoid moiety to the nSiO covalently. The Kaiser test quantifies the functionalization degree, yielding 222 μmol of curcuminoid per gram of nanoparticles.

Understanding Single-Molecule Magnet properties of lanthanide complexes from 4f orbital splitting.

We present an approach for connecting the magnetic anisotropy of lanthanide mononuclear complexes with their f-orbital splitting for both idealized and real coordination environments. Our proposal is straightforward to apply and provides sensible estimations of the energy spacing of the ground multiplet for axial magnetic systems. This energy splitting controls Single-Molecule Magnet properties of lanthanide complexes, determining key parameters such as the demagnetization energy barrier ().

Influence of symmetry on the magneto-optical properties of a bifunctional macrocyclic Dy complex.

In this work, a novel complex, [Dy(L)(NO)]·(HO)·(NO) (1), containing a highly distorted macrocyclic ligand (L) and weak axial anions (NO), was synthesized and characterized. Even though this coordination environment is not ideal for maximizing the magnetic anisotropy of a Dy ion, a magneto-structural analysis reveals that the high distortion of the macrocycle promotes a disposition of the hard plane and easy axis opposite to the expected one. This results in a quite symmetrical environment which allows obtaining a field induced SMM behaviour.

Tuning the Emission of Homometallic Dy, Tb, and Eu 1-D Coordination Polymers with 2,6-Di(1-1,2,4-triazole-1-yl-methyl)-4-R-phenoxo Ligands: Sensitization through the Singlet State.

This work reports the structural characterization and photophysical properties of Dy, Tb, and Eu coordination polymers with two phenoxo-triazole-based ligands [2,6-di(1-1,2,4-triazole-1-yl-methyl)-4-R-phenoxo, LTr (R = CH; Cl)]. These ligands permitted us to obtain isostructural polymers, described as a 1D double chain, with Ln being nona-coordinated. The energies of the ligand triplet (T) states were estimated using low-temperature time-resolved emission spectra of Y analogues.

Luminescence of Macrocyclic Mononuclear Dy Complexes and Their Immobilization on Functionalized Silicon-Based Surfaces.

Two mononuclear Dy complexes, [Dy(L)(NCS)] () and [Dy(L)(NCS)] (), where L ( = 1-2) corresponds to a macrocyclic ligand derived from 2,6-pyridinedicarboxaldehyde and ethylenediamine (L) and 1,3-diaminepropane (L) were immobilized on functionalized silicon-based surfaces. This was achieved by the microcontact printing (μCP) technique, generating patterns on a functionalized surface via covalent bond formation through the auxiliary -NCS ligands present in the macrocyclic complex species. With this strategy, it was possible to control the position of the immobilized molecules on the surface.

Lanthanide SMMs Based on Belt Macrocycles: Recent Advances and General Trends.

Enhancement of axial magnetic anisotropy is the central objective to push forward the performance of Single-Molecule Magnet (SMM) complexes. In the case of mononuclear lanthanide complexes, the chemical environment around the paramagnetic ion must be tuned to place strongly interacting ligands along either the axial positions or the equatorial plane, depending on the oblate or prolate preference of the selected lanthanide. One classical strategy to achieve a precise chemical environment for a metal centre is using highly structured, chelating ligands.

Room-Temperature Spin-Dependent Transport in Metalloporphyrin-Based Supramolecular Wires.

Here we present room-temperature spin-dependent charge transport measurements in single-molecule junctions made of metalloporphyrin-based supramolecular assemblies. They display large conductance switching for magnetoresistance in a single-molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire: those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin-dependent charge transport.

Structure and excited-state dynamics of dimeric copper(i) photosensitizers investigated by time-resolved X-ray and optical transient absorption spectroscopy.

Time-resolved X-ray (tr-XAS) and optical transient absorption (OTA) spectroscopy in the picosecond time scale coupled with Density Functional theory (DFT) and X-ray absorption near-edge structure (XANES) calculations are applied to study three homoleptic Cu(i) dimeric chromophores with ethyl and longer propyl spacers, denoted as [Cu(mphenet)]Cl (C1), [Cu(mphenet)](ClO) (C2) and [Cu(mphenpr)](ClO) (C3) (where mphenet = 1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane and mphenpr = 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane). Tr-XAS analysis after light illumination at ∼ 100 ps illustrate the formation of a flattened triplet excited state in all 3 complexes. Optical transient absorption (OTA) analysis for C1 monitored in water and C2 and C3 measured in acetonitrile reveals distinct excited-state lifetimes of 169 ps, 670 ps and 1600 ps respectively.

Tuning Single-Molecule Conductance in Metalloporphyrin-Based Wires via Supramolecular Interactions.

Nature has developed supramolecular constructs to deliver outstanding charge-transport capabilities using metalloporphyrin-based supramolecular arrays. Herein we incorporate simple, naturally inspired supramolecular interactions via the axial complexation of metalloporphyrins into the formation of a single-molecule wire in a nanoscale gap. Small structural changes in the axial coordinating linkers result in dramatic changes in the transport properties of the metalloporphyrin-based wire.

Control of magnetic anisotropy by macrocyclic ligand distortion in a family of Dy and Er single molecule magnets.

A family of hexaazamacrocyclic lanthanide complexes, [Ln(Ln)(NCS)3] (LnIII = Dy, Er; n = 1-3) has been synthesized and characterized by single-crystal X-ray diffraction, magnetic measurements and ab initio calculations. Macrocyclic ligands (Ln) differ in the lateral spacers, which are aliphatic chains with two and three carbons (for Ln, n = 1 and 2, respectively), and an aromatic ring for Ln = 3. Modification of the macrocycle spacer tunes planarity and rigidity of the equatorial coordination for both oblate (Dy) and prolate (Er) lanthanide ions.

Reactivity of CuN Flattened Complexes: Interplay between Coordination Geometry and Ligand Flexibility.

The relation between redox activity and coordination geometry in CuN complexes indicates that more flattened structures tend to be more reactive. Such a preorganization of the ligand confers to the complex geometries closer to a transition state, which has been termed the "entatic" state in metalloproteins, more recently extending this concept for copper complexes. However, many aspects of the redox chemistry of Cu complexes cannot be explained only by flattening.

Spin dynamics in single-molecule magnets and molecular qubits.

Over recent decades, much effort has been made to lengthen spin relaxation/decoherence times of single-molecule magnets and molecular qubits by following different chemical design rules such as maximizing the total spin value, controlling symmetry, enhancing the ligand field or inhibiting key vibrational modes. Simultaneously, electronic structure calculations have been employed to provide an understanding of the processes involved in the spin dynamics of molecular systems and served to refine or introduce new design rules. This review focuses on contemporary theoretical approaches focused on the calculation of spin relaxation/decoherence times, highlighting their main features and scope.

[UF ] : A Molecular Hexafluorido Actinide(IV) Complex with Compensating Spin and Orbital Magnetic Moments.

The first structurally characterized hexafluorido complex of a tetravalent actinide ion, the [UF ] anion, is reported in the (NEt ) [UF ]⋅2 H O salt (1). The weak magnetic response of 1 results from both U spin and orbital contributions, as established by combining X-ray magnetic circular dichroism (XMCD) spectroscopy and bulk magnetization measurements. The spin and orbital moments are virtually identical in magnitude, but opposite in sign, resulting in an almost perfect cancellation, which is corroborated by ab initio calculations.

Influence of the substituent on the phosphine ligand in novel rhenium(i) aldehydes. Synthesis, computational studies and first insights into the antiproliferative activity.

Cyrhetrenyl aldehyde derivatives [(η5-C5H4CHO)Re(CO)2PR3] with R = methyl (Me, 2a), phenyl (Ph, 2b), and cyclohexyl (Cy, 2c) were synthesized by a photochemical reaction from the starting material [(η5-C5H4CHO)Re(CO)3] (1) and the corresponding phosphines. The complexes were fully characterized by FT-IR, 1H, 13C and 31P NMR spectroscopy, elemental analysis and mass spectrometry. The molecular structures of 2a-c have also been determined.

Ab Initio Prediction of Tunneling Relaxation Times and Effective Demagnetization Barriers in Kramers Lanthanide Single-Molecule Magnets.

Single-molecule magnets (SMMs) are promising candidates for molecule-based quantum information devices. Their main limitation is their cryogenic operative temperature. To achieve devices performing at higher temperatures, demagnetization mechanisms must be suppressed by chemical tuning.

Steric and Electronic Factors Affecting the Conformation of Bimetallic Cu Complexes: Effect of the Aliphatic Spacer of Tetracoordinating Schiff-Base Ligands.

A family of six homoleptic [Cu (L )] (ClO ) and six heteroleptic [Cu (L )(PPh ) ] (ClO ) bimetallic complexes, in which L are bis-Schiff base ligands with alkyl spacers of variable length (n=2-7 -CH -), were prepared to evaluate the role of the spacer on the formation of helicates or mesocates. In the homoleptic series, spectroscopic and theoretical studies indicate that preferences for a conformation are based on energetic parameters, mainly, the establishment of noncovalent interactions. The odd-even nature of the spacers preconditions the superposition of the aromatic rings to allow the juxtaposition necessary for noncovalent interactions, whereas the increase of the length reduces the strength of such interactions.

Effect of Heteroatoms on Field-Induced Slow Magnetic Relaxation of Mononuclear Fe ( S = 5/2) Ions within Polyoxometalates.

In this paper, the synthesis and magnetic properties of mononuclear Fe-containing polyoxometalates (POMs) with different types of heteroatoms, TBAH[(A-α-XWO)Fe] (II, X = Ge, Si; TBA = tetra- n-butylammonium), are reported. In these POMs, mononuclear highly distorted six-coordinate octahedral [FeO] units are sandwiched by two trivacant lacunary units [A-α-XWO] (X = Ge, Si). These POMs exhibit field-induced slow magnetic relaxation based on the single high-spin Fe magnetic center ( S = 5/2).

Designing a Dy Single-Molecule Magnet with Two Well-Differentiated Relaxation Processes by Using a Nonsymmetric Bis-bidentate Bipyrimidine- N-Oxide Ligand: A Comparison with Mononuclear Counterparts.

Herein we report a dinuclear [(μ-mbpymNO){(tmh)Dy}] (1) single-molecule magnet (SMM) showing two nonequivalent Dy centers, which was rationally prepared from the reaction of Dy(tmh) moieties (tmh = 2,2,6,6-tetramethyl-3,5-heptanedionate) and the asymmetric bis-bidentate bridging ligand 4-methylbipyrimidine (mbpymNO). Depending on whether the Dy ions coordinate to the N^O or N^N bidentate donor sets, the Dy sites present a NO ( D geometry) or NO ( D) coordination sphere. As a consequence, two different thermally activated magnetic relaxation processes are observed with anisotropy barriers of 47.

Metal-Controlled Magnetoresistance at Room Temperature in Single-Molecule Devices.

The appropriate choice of the transition metal complex and metal surface electronic structure opens the possibility to control the spin of the charge carriers through the resulting hybrid molecule/metal spinterface in a single-molecule electrical contact at room temperature. The single-molecule conductance of a Au/molecule/Ni junction can be switched by flipping the magnetization direction of the ferromagnetic electrode. The requirements of the molecule include not just the presence of unpaired electrons: the electronic configuration of the metal center has to provide occupied or empty orbitals that strongly interact with the junction metal electrodes and that are close in energy to their Fermi levels for one of the electronic spins only.

A Low Spin Manganese(IV) Nitride Single Molecule Magnet.

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene)borate compound PhB(MesIm)Mn≡N as a four-coordinate manganese(IV) complex with a low spin ( = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e.

Lanthanide Tetrazolate Complexes Combining Single-Molecule Magnet and Luminescence Properties: The Effect of the Replacement of Tetrazolate N3 by β-Diketonate Ligands on the Anisotropy Energy Barrier.

Three new sets of mononuclear Ln(III) complexes of general formulas [LnL3 ]⋅CH3 OH [Ln(III) =Yb (1), Er (2), Dy (3), Gd (4), and Eu (5)], [LnL2 (tmh)(CH3 OH)]⋅n H2 O⋅m CH3 OH [Ln(III) =Yb (1 b), Er (2 b), Dy (3 b), Gd (4 b)], and [LnL2 (tta)(CH3 OH)]⋅CH3 OH [Ln(III) =Yb (1 c), Er (2 c), Dy (3 c), Gd (4 c)] were prepared by the reaction of Ln(CF3 SO3 )⋅n H2 O salts with the tridentate ligand 2-(tetrazol-5-yl)-1,10-phenanthroline (HL) and, for the last two sets, additionally with the β-diketonate ligands 2,2,6,6-tetramethylheptanoate (tmh) and 2-thenoyltrifluoroacetonate (tta), respectively. In the [LnL3 ]⋅CH3 OH complexes the Ln(III) ions are coordinated to three phenanthroline tetrazolate ligands with an LnN9 coordination sphere. Dynamic ac magnetic measurements on 1-3 reveal that these complexes only exhibit single-molecule magnet (SMM) behavior when an external dc magnetic field is applied, with Ueff values of 11.

Single-Molecule Magnet Properties of Transition-Metal Ions Encapsulated in Lacunary Polyoxometalates: A Theoretical Study.

Single-molecule magnet (SMM) properties of transition-metal complexes coordinated to lacunary polyoxometalates (POM) are studied by means of state of the art ab initio methodology. Three [M(γ-SiW10O36)2] (M = Mn(III), Fe(III), Co(II)) complexes synthesized by Sato et al. (Chem.

Periodic Trends in Lanthanide Compounds through the Eyes of Multireference ab Initio Theory.

Regularities among electronic configurations for common oxidation states in lanthanide complexes and the low involvement of f orbitals in bonding result in the appearance of several periodic trends along the lanthanide series. These trends can be observed on relatively different properties, such as bonding distances or ionization potentials. Well-known concepts like the lanthanide contraction, the double-double (tetrad) effect, and the similar chemistry along the lanthanide series stem from these regularities.

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex.

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin Fe(III) ferromagnetically coupled and 24 diamagnetic low-spin Fe(II) ions.