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A common criterion for designing performant single molecule magnets and pseudocontact shift tags is a large magnetic anisotropy. In this article we present a dysprosium complex chemically designed to exhibit strong easy-axis type magnetic anisotropy that is preserved in dichloromethane solution at room temperature. Our detailed theoretical and experimental studies on the magnetic properties allowed explaining several features typical of highly performant SMMs. Moreover, the NMR characterization shows remarkably large chemical shifts, outperforming the current state-of-the art PCS tags.

Ovarian cancer recurrence is frequent and associated with chemoresistance, leading to extremely poor prognosis. Herein, we explored the potential anti-cancer effect of a series of highly charged Ru(II)-polypyridyl complexes as photosensitizers in photodynamic therapy (PDT), which were able to efficiently sensitize the formation of singlet oxygen upon irradiation (Ru12+ and Ru22+) and to produce reactive oxygen species (ROS) in their corresponding dinuclear metal complexes with the Fenton active Cu(II) ion/s ([CuRu1]4+ and [Cu2Ru2]6+). Their cytotoxic and anti-tumor effects were evaluated on human ovarian cancer A2780 cells both in the absence or presence of photoirradiation, respectively. All the compounds tested were well tolerated under dark conditions, whereas they switched to exert anti-tumor activity following photoirradiation. The specific effect was mediated by the onset of programed cell death, but only in the case of Ru12+ and Ru22+ was preceded by the loss of mitochondrial membrane potential soon after photoactivation and ROS production, thus supporting the occurrence of apoptosis via type II photochemical reactions. Thus, Ru(II)-polypyridyl-based photosensitizers represent challenging tools to be further investigated in the identification of new therapeutic approaches to overcome the innate chemoresistance to platinum derivatives of some ovarian epithelial cancers and to find innovative drugs for recurrent ovarian cancer.

The combined experimental and computational study of the 13 magnetic complexes belonging to the Na[LnDOTA(H2O)] (H4DOTA = tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid and Ln = Ce-Yb) family allowed us to identify a new trend: the orientation of the magnetic anisotropy tensors of derivatives differing by seven f electrons practically coincide. We name this trend the fn+7 effect. Experiments and theory fully agree on the match between the magnetic reference frames (e.g., the easy, intermediate, and hard direction). The shape of the magnetic anisotropy of some couples of ions differing by seven f electrons might seem instead different at first look, but our analysis explains a hidden similarity. We thus pave the way toward a reliable predictivity of the magnetic anisotropy of lanthanide complexes with a consequent reduced need of computational and synthetical efforts. We also offer a way to gain information on ions with a relatively small total angular momentum (i.e., Sm3+ and Eu3+) and on the radioactive Pm3+, which are difficult to investigate experimentally.

A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripoidal oxazolidine nitroxyl radical were obtained in acetonitrile media starting from nitrates. The compounds, [LnRad(NO3)3] (Ln = Gd, Tb, Dy, Tm, Y; Rad = 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl), have molecular structure. Their coordination polyhedron, LnO7N2, can be described as a tricapped trigonal prism with symmetry close to D3h. The value of 23 cm-1 for the antiferromagnetic coupling Gd-Rad established from the DC magnetic and EPR data is a record strength for the complexes of 4f-elements with nitroxyl radicals. The terbium derivative displays frequency-dependent out-of-phase signals in zero field indicating single-molecule magnetic behavior with an effective barrier of 57 cm-1.

Neptunium was the first actinide element to be artificially synthesized, yet, compared with its more famous neighbours uranium and plutonium, is less conspicuously studied. Most neptunium chemistry involves the neptunyl di(oxo)-motif, and transuranic compounds with one metal–ligand multiple bond are rare, being found only in extended-structure oxide, fluoride or oxyhalide materials. These combinations stabilize the required high oxidation states, which are otherwise challenging to realize for transuranic ions. Here we report the synthesis, isolation and characterization of a stable molecular neptunium(V)–mono(oxo) triamidoamine complex. We describe a strong Np≡O triple bond with dominant 5f-orbital contributions and σ u > π u energy ordering, akin to terminal uranium-nitrides and di(oxo)-actinyls, but not the uranium–mono(oxo) triple bonds or other actinide multiple bonds reported so far. This work demonstrates that molecular high-oxidation-state transuranic complexes with a single metal–ligand bond can be stabilized and studied in isolation. [Figure not available: see fulltext.]

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc)(4))(pyNO(2))](2) (M = Ni or Co) that are linked in the solid state via metallophilic PtMIDLINE HORIZONTAL ELLIPSISPt bridges. This contrasts the terminally capped monomers [M(Pt(SAc)(4))(py)(2)], for which neither metallophilic bridges nor magnetic exchange interactions are found. Computational modeling has shown that the magnetic exchange interaction is facilitated by the pseudo-closed shell d(8)MIDLINE HORIZONTAL ELLIPSISd(8) metallophilic interaction between the filled Pt2+ 5d(z)(2) orbitals. We present here inelastic neutron scattering experiments on these complexes, wherein the dimers present an oscillatory momentum-transfer-dependence of the magnetic transitions. This allows for the unequivocal experimental assignment of the distance between the coupled ions, which matches exactly the coupling pathway via the metallophilic bridges. Furthermore, we have synthesized and magnetically characterized the isostructural palladium-analogues. The magnetic coupling across the PdMIDLINE HORIZONTAL ELLIPSISPd bridge is found through SQUID-magnetometry and FD-FT THz-EPR spectroscopy to be much weaker than via the PtMIDLINE HORIZONTAL ELLIPSISPt bridge. The weaker coupling is traced to the larger radial extent of the 5d(z)(2) orbitals compared to that of the 4d(z)(2) orbitals. The existence of a palladium metallophilic interaction is evaluated computationally from potential surface cuts along the metal stretching direction. Similar behavior is found for the PdMIDLINE HORIZONTAL ELLIPSISPd and PtMIDLINE HORIZONTAL ELLIPSISPt-systems with clear minima along this coordinate and provide estimates for the force constant for this distortion. The estimated MMIDLINE HORIZONTAL ELLIPSISM stretching frequencies are found to match experimental observed, polarized bands in single-crystal Raman spectra close to 45 cm(-1). This substantiates the existence of energetically relevant PdMIDLINE HORIZONTAL ELLIPSISPd metallophilic interactions. The unique properties of both Pt2+ and Pd2+ constitutes an orthogonal reactivity, which can be utilized for steering both the direction and strength of magnetic interactions.

The notion of magnetic anisotropy is very central to the field of molecule-based magnetism, where it is considered to be a key quantity that must be rationalized and controlled in order to improve the performances of, e.g., single-molecule magnets. A rough classification of the magnetic properties is widely done in terms of the qualitative descriptors of magnetic anisotropy: “easy-axis” and “easy-plane”. They can be based on different physical properties, in casu: free energy, magnetization, or magnetic susceptibility. However, this degree of freedom leads in some cases, including very simple ones like [V(H2O)6]3+, to incommensurate descriptions of a system being simultaneously easy-axis and easy-plane, depending only on the choice of the physical quantity on which the descriptor is based. Moreover, it has recently been pointed out that the magnetic anisotropy of a chemical system can be addressed and switched using external stimuli like temperature and magnetic field. These external parameters are, thoug...

The combined experimental and computational study of the 13 magnetic complexes belonging to the Na[LnDOTA(H2O)] (H4DOTA = tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid and Ln = Ce–Yb) family allowed us to identify a new trend: the orientation of the magnetic anisotropy tensors of derivatives differing by seven f electrons practically coincide. We name this trend the fn+7 effect. Experiments and theory fully agree on the match between the magnetic reference frames (e.g., the easy, intermediate, and hard direction). The shape of the magnetic anisotropy of some couples of ions differing by seven f electrons might seem instead different at first look, but our analysis explains a hidden similarity. We thus pave the way toward a reliable predictivity of the magnetic anisotropy of lanthanide complexes with a consequent reduced need of computational and synthetical efforts. We also offer a way to gain information on ions with a relatively small total angular momentum (i.e., Sm3+ and Eu3+) and on the radioactive Pm3+, which are difficult to investigate experimentally.

Neptunium was the first actinide element to be artificially synthesized, yet, compared with its more famous neighbours uranium and plutonium, is less conspicuously studied. Most neptunium chemistry involves the neptunyl di(oxo)-motif, and transuranic compounds with one metal-ligand multiple bond are rare, being found only in extended-structure oxide, fluoride or oxyhalide materials. These combinations stabilize the required high oxidation states, which are otherwise challenging to realize for transuranic ions. Here we report the synthesis, isolation and characterization of a stable molecular neptunium(V)-mono(oxo) triamidoamine complex. We describe a strong Np≡O triple bond with dominant 5f-orbital contributions and σ

The new PtVO(SOCR)4 lantern complexes, 1 (R = CH3) and 2 (R = Ph) behave as neutral O-donor ligands to Ln(OR)3 with Ln = Ce, Nd. Four heterotrimetallic complexes with linear {LnOVPt} units were prepared: [Ln(ODtbp)3{PtVO(SOCR)4}] (Ln = Ce, 3Ce (R = CH3), 4Ce (R = Ph); Nd, 3Nd (R = CH3), 4Nd (R = Ph); ODtbp = 2,6-ditertbutylphenolate). Magnetic characterization confirms slow magnetic relaxation behaviour and suggests antiferromagnetic coupling across {Ln-O[double bond, length as m-dash]V} in all four complexes, with variations tunable as a function of Ln and R.

Longitudinal and transverse 1H nuclear magnetic resonance relaxivities of Ln(III)-DOTA complexes (with Ln = Gd, Tb, Dy, Er; DOTA = 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid) and Mn(II) aqueous solutions were measured in a wide range of frequencies, 10 kHz to 700 MHz. The experimental data were interpreted by means of models derived from the Solomon–Bloembergen–Morgan theory. The data analysis was performed assuming the orbital angular momentum L = 0 for Gd-DOTA and the aqua ion [Mn(H2O)6]2+ and L ≠ 0 for Dy-, Tb-, and Er-DOTA. A refined estimation of the zero-field-splitting barrier Δ and of the modulation correlation time τv was obtained for [Mn(H2O)6]2+ by extending the fitting of nuclear magnetic relaxation dispersion profiles to the low-field regime. The Gd-DOTA fitting parameters resulted in good agreement with the literature, and the fit of transverse relaxivity data confirmed the negligibility of the scalar interaction in the nuclear relaxation mechanism. Larger transverse relaxivities of Dy-DOTA and Tb-DOTA (∼10 mM−1 s−1) with respect to Er-DOTA (∼1 mM−1 s−1) were observed at 16 T. Such higher values are suggested to be due to a shorter residence time τm that is possibly linked to the fluctuations of the hyperfine interaction and the different shape of the magnetic anisotropy. The possible employment of Dy-DOTA, Tb-DOTA, and Er-DOTA as negative magnetic resonance imaging contrast agents for high-field applications was envisaged by collecting spin-echo images at 7 T. Particularly in Dy- and Tb-derivatives, the transverse relaxivity at 16 T is of the order of the Gd-one at 1.5 T.

In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd2+ ion in four metalloligated lanthanide complexes of formula [PPh4][Ln{Pd(SAc)4}2] (SAc- = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd2+ compared to the previously reported isostructural Pt2+-based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt2+-analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.

By combining high spinning speed (60 kHz) and low-field (4.7 T) $^{31}\mathrm{P}$ solid-state NMR with magnetic susceptibility measurements, we experimentally characterized a series of solid solutions belonging to the $\mathrm{L}{\mathrm{a}}_{x}\mathrm{E}{\mathrm{u}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{O}}_{4}$ ($0\ensuremath{\le}x\ensuremath{\le}1$) series. Analyses of the magnetic susceptibility data were carried out using the free ion model and crystal field theory calculations allowing to extract the electronic structure. The paramagnetic shifts of the P sites having one $\mathrm{E}{\mathrm{u}}^{3+}$ cation in their surrounding were predicted by combining the determined crystal field and energy level values with density functional theory (DFT) calculations. For the $\mathrm{L}{\mathrm{a}}_{0.9}\mathrm{E}{\mathrm{u}}_{0.1}\mathrm{P}{\mathrm{O}}_{4}$ sample, these theoretical shifts gave a very good overall trend allowing the unambiguous attribution of each P site. This study paves the way for the future analysis of both magnetic susceptibility and NMR data for a broad range of materials containing paramagnetic rare-earth cations.

A 3D metal-organic framework (MOF) having single-molecule magnet (SMM) linkers was prepared in crystalline form by using a tetrairon(III) complex functionalised with two divergent pyridyl groups, namely [Fe4 (pPy)2 (dpm)6 ] (1; H3 pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane). Reaction of 1 with silver(I) perchlorate afforded {[Fe4 (pPy)2 (dpm)6 ]2 Ag}ClO4 (2), which crystallises in a cubic face-centred lattice and exhibits two interlocked diamondoid networks. In 2, the SMMs act as linear ditopic synthons, and silver(I) ions as tetrahedral nodes coordinated by four pyridyl nitrogen atoms. The magnetic properties of 1 (S=5 and D≈-0.4 cm(-1) in the ground spin state) are largely preserved in 2, which shows slow magnetic relaxation with an anisotropy barrier of Ueff /kB =11.46(10) K in zero field and 14.25(8) K in an applied field of 1 kOe. However, crystal symmetry triggers highly noncollinear magnetic anisotropy contributions oriented at 109.47° from each other along the threefold axes of AgN4 tetrahedra, a unique scenario fully confirmed by a single-crystal cantilever torque magnetometry investigation. Magnetisation curves down to 0.03 K demonstrated the occurrence of a wide hysteresis loop when the magnetic field was swept along one of the four Ag-N bonds. By symmetry, the crystalline compound can then be persistently magnetised parallel or antiparallel to the four main diagonals of the unit cell, although the crystals have no overall second-order anisotropy.

We present the in-depth determination of the magnetic properties and electronic structure of the luminescent and volatile dysprosium-based single molecule magnet [Dy2(bpm)(fod)6] (Hfod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2-bipyrimidine)., We present the in-depth determination of the magnetic properties and electronic structure of the luminescent and volatile dysprosium-based single molecule magnet [Dy2(bpm)(fod)6] (Hfod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2′-bipyrimidine). Ab initio calculations were used to obtain a global picture of the electronic structure and to predict possible single molecule magnet behaviour, confirmed by experiments. The orientation of the susceptibility tensor was determined by means of cantilever torque magnetometry. An experimental determination of the electronic structure of the lanthanide ion was obtained combining Luminescence, Far Infrared and Magnetic Circular Dichroism spectroscopies. Fitting these energies to the full single ion plus crystal field Hamiltonian allowed determination of the eigenstates and crystal field parameters of a lanthanide complex without symmetry idealization. We then discuss the impact of a stepwise symmetry idealization on the modelling of the experimental data. This result is particularly important in view of the misleading outcomes that are often obtained when the symmetry of lanthanide complexes is idealized.

We present the in-depth determination of the magnetic properties and electronic structure of the luminescent and volatile dysprosium-based single molecule magnet [Dy2(bpm)(fod)6] (Hfod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2'-bipyrimidine). Ab initio calculations were used to obtain a global picture of the electronic structure and to predict possible single molecule magnet behaviour, confirmed by experiments. The orientation of the susceptibility tensor was determined by means of cantilever torque magnetometry. An experimental determination of the electronic structure of the lanthanide ion was obtained combining Luminescence, Far Infrared and Magnetic Circular Dichroism spectroscopies. Fitting these energies to the full single ion plus crystal field Hamiltonian allowed determination of the eigenstates and crystal field parameters of a lanthanide complex without symmetry idealization. We then discuss the impact of a stepwise symmetry idealization on the modelling of the experimental data. This result is particularly important in view of the misleading outcomes that are often obtained when the symmetry of lanthanide complexes is idealized. ispartof: CHEMICAL SCIENCE vol:10 issue:7 pages:2101-2110 ispartof: location:England status: published

INTRODUCTION The magnetic properties of a single metal center are determined by a combination of its total spin S and orbital angular momentum L . Orbital angular momentum gives rise to magnetic anisotropy, an essential property for applications such as information storage and high-coercivity magnets. Unquenched L arises from an odd number of electrons in degenerate orbitals and is typically observed only for free ions, as well as for complexes of the f elements. For the majority of transition metal ions, however, orbital angular momentum is quenched by the ligand field, which removes the requisite orbital degeneracies. Maximal L for a transition metal ( L = 3) would require an odd number of electrons in two sets of degenerate orbitals. Such a species would entail a non-Aufbau configuration, wherein the electrons do not fill the d orbitals in the usual order of lowest to highest in energy, and likely exhibit a large magnetic anisotropy. RATIONALE Previous efforts have identified the utility of linear coordination environments for isolating iron complexes with unquenched orbital angular momentum and large magnetic anisotropies. Crucially, transition metals in this environment are unaffected by Jahn-Teller distortions that would otherwise remove orbital degeneracies in the case of partially filled d orbitals. Separately, cobalt atoms deposited on a MgO surface—for which one-coordination of the metal is achieved, provided a vacuum is maintained—were shown to have L = 3, giving rise to near-maximal magnetic anisotropy. Calculations on the hypothetical linear molecule Co(C(SiMe 3 ) 3 ) 2 (where Me is methyl) also predicted that this system would possess a ground state with L = 3. Empirically, maximal L in a transition metal complex thus requires both a linear coordination environment and a sufficiently weak ligand field strength to allow for non-Aufbau electron filling. RESULTS The strongly reducing nature of the carbanion ligand hinders isolation of dialkyl cobalt(II) complexes. However, reducing the basicity of the central carbanion through the use of electron-withdrawing aryloxide groups allowed for the synthesis of the dialkyl cobalt(II) complex Co(C(SiMe 2 ONaph) 3 ) 2 , where Naph is a naphthyl group. Ab initio calculations on this complex predict a ground state with S = 3 / 2 , L = 3, and J = 9 / 2 arising from the non-Aufbau electron configuration (d x 2 –y 2 , d xy ) 3 (d xz , d yz ) 3 (d z 2 ) 1 . Much as for lanthanide complexes, the ligand field is sufficiently weak that interelectron repulsion and spin-orbit coupling play the key roles in determining the electronic ground state. dc magnetic susceptibility measurements reveal a well-isolated M J = ± 9 / 2 ground state, and simulations of the magnetic data from the calculations are in good agreement with the experimental data. Variable-field far-infrared (FIR) spectroscopy shows a magnetically active excited state at 450 cm −1 that, in combination with calculations and variable-temperature ac magnetic susceptibility experiments, is assigned to the M J = ± 7 / 2 state. Modeling of experimental charge density maps also suggests a d-orbital filling with equally occupied (d x 2 –y 2 , d xy ), and (d xz , d yz ) orbital sets. As a consequence of its large orbital angular momentum, the molecule exhibits slow magnetic relaxation and, in a magnetically dilute sample, a coercive field of 600 Oe at 1.8 K. CONCLUSION Isolation of Co(C(SiMe 2 ONaph) 3 ) 2 illustrates how an extreme coordination environment can confer an f-element–like electronic structure on a transition metal complex. The non-Aufbau ground state enables realization of maximal orbital angular momentum and magnetic anisotropy near the physical limit for a 3d metal. In this respect, the linear L–Co–L motif may prove useful in the design of new materials with high magnetic coercivity.

Early actinide ions have large spin-orbit couplings and crystal field interactions, leading to large anisotropies. The success in using actinides as single-molecule magnets has so far been modest, underlining the need for rational strategies. Indeed, the electronic structure of actinide single-molecule magnets and its relation to their magnetic properties remains largely unexplored. A uranium(III) single-molecule magnet, [UIII {SiMe2 NPh}3 -tacn)(OPPh3 )] (tacn=1,4,7-triazacyclononane), has been investigated by means of a combination of magnetic, spectroscopic and theoretical methods to elucidate the origin of its static and dynamic magnetic properties.

The recently discovered thermal elasticity of magnetic anisotropy is not at all an exotic phenomenon. For many lanthanide complexes the qualitative nature of their magnetic anisotropy changes as a function of temperature and magnetic field; for some, even multiple times. The theoretically predicted existence of such multi-switch compounds is experimentally corroborated.

Tetraoxolene radical-bridged lanthanide SMM systems were prepared for the first time by reduction of the respective neutral compounds. Magnetic measurements reveal the profound influence of the radical center on magnetic behavior. Strong magnetic couplings are revealed in the radical species, which switch on SMM behavior under zero applied field for DyIII and TbIII compounds. HFEPR spectra unravel the contributions of the magnetic coupling and the magnetic anisotropy. For GdIII this results in much more accurate magnetic coupling parameters with respect to bulk magnetic measurements.

The rational design of the magnetic anisotropy of molecular materials constitutes a goal of primary importance in molecular magnetism. Indeed, the applications of molecular nanomagnets, such as single-molecule magnets and molecular magnetic refrigerants, depend on the full control over this property. Axially anisotropic magnetic systems are frequently classified as easy axis or easy plane, depending on whether the lowest energy is obtained by application of a magnetic field parallelly or perpendicularly to the unique axis. Here, the magnetic aniso-tropy of three lanthanide complexes is studied as a function of magnetic field and temperature. It is found that for two of these the type of magnetic aniso-tropy switches as a function of these parameters. Thus, this paper experimen-tally demonstrates that the magnetic anisotropy is not uniquely defined by the intrinsic electronic structure of the systems in question but can also be reversibly switched using external stimuli: temperature and magnetic field., This work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland. The project was funded by the Independent Research Fund Denmark through the project “Spin Architecture” and the Danish Agency for Science, Technology and Innovation through DANSCATT. M.P., H.B., P.H., S.L., and J.v.S. thank DFG foundation (Project SL 104/5-1). M.A.S. thanks the Oticon Foundation (16-2669) and the Augustinus Foundation (16-2917) for financial support in relation to a research stay at Institut für Physikalische Chemie, Universität Stuttgart, Germany. E.B., A.A., and J. Bartolomé acknowledge the financial support of Spanish MINECO project MAT2017-83468-R. For the experiments conducted at FRM II, this project has received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under the NMI3-II Grant No. 283883.

The magnetic properties of the pentacoordinate [MII (Me4 cyclam)N3 ]+ (Me4 cyclam=tetramethylcyclam; N3 =azido; M=Ni, Co) complexes were investigated. Magnetization and EPR studies indicate that they have an easy plane of magnetization with axial anisotropy parameters D close to 22 and greater than 30 cm-1 for the Ni and Co complexes, respectively. Ab initio calculations reproduced the experimental values of the zero-field splitting parameters and allowed the orientation of the anisotropy tensor axes with respect to the molecular frame to be determined. For M=Ni, the principal anisotropy axis lies along the Ni-Nazido direction perpendicular to the Ni(Me4 cyclam) mean plane, whereas for M=Co it lies in the Co(Me4 cyclam) mean plane and thus perpendicular to the Co-Nazido direction. These orientations match one of the possible solutions experimentally provided by single-crystal cantilever torque magnetometry. To rationalize the geometry and its impact on the orientation of the anisotropy tensor axis, calculations were carried out on model complexes [NiII (NCH)5 ]2+ and [CoII (NCH)5 ]2+ by varying the geometry between square pyramidal and trigonal bipyramidal. The geometry of the complexes was found to be the result of a compromise between the electronic configuration of the metal ion and the structure-orienting effect of the Me4 cyclam macrocycle. Moreover, the orientation of the anisotropy axes is mainly dependent on the geometry of the complexes.

The experimental investigation of the molecular magnetic anisotropy in crystals in which the magnetic centers are symmetry related, but do not have a parallel orientation has been approached by using torque magnetometry. A single crystal of the orthorhombic organometallic Cp*ErCOT [Cp*=pentamethylcyclopentadiene anion (C5Me5(-)); COT=cyclooctatetraenedianion (C8H8(2-))] single-molecule magnet, characterized by the presence of two nonparallel families of molecules in the crystal, has been investigated above its blocking temperature. The results confirm an Ising-type anisotropy with the easy direction pointing along the pseudosymmetry axis of the complex, as previously suggested by out-of-equilibrium angular-resolved magnetometry. The use of torque magnetometry, not requiring the presence of magnetic hysteresis, proves to be even more powerful for these purposes than standard single-crystal magnetometry. Furthermore, exploiting the sensitivity and versatility of this technique, magnetic anisotropy has been investigated up to 150 K, providing additional information on the crystal-field splitting of the ground J multiplet of the Er(III) ion.

We present here a reaction scheme to connect TbPc2 single-molecule magnets into 1D architectures using acyclic diene metathesis. To investigate the impact of the bonding through aliphatic chains on the magnetic properties of TbPc2, we isolate and characterize the dimeric species obtained as one of the products of the reaction. Remarkably, the magnetic properties are only slightly modified after the formation of the bond between molecules, enlightening the great potential of this reaction scheme.

The magnetic properties of the pentacoordinate [M

We report here the determination of the helical spin structure of three Ln-based chiral chains of the formula [Ln(Hnic)(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and Er) by means of cantilever torque magnetometry. While the Dy and Er derivatives are strongly axial (easy-axis and easy-plane anisotropy, respectively), the Tb derivative is characterized by a remarkable rhombicity. In agreement with these findings, alternating-current susceptibility reveals slow magnetic relaxation only in the Dy derivative. Dilution of DyIII ions in the diamagnetic Y-based analogue shows that the weak ferromagnetic intrachain interactions do not contribute significantly to the energy barrier for the reversal of magnetization, which is better described as a single-ion process. Single crystals of the two enantiomers of the Dy derivative have also been investigated using hard X-ray synchrotron radiation at the L-edge of the metal revealing optical activity although with negligible involvement of the 4f electrons of the ...

Spotting trends: Upon going from TbIII to YbIII centers in the complexes of the DOTA4- ligand, a reorientation of the easy axis of magnetization from perpendicular to parallel to the Ln-O bond of the apical water molecule is experimentally observed and theoretically predicted (see picture; SMM = single-molecule magnet). Only ions with an odd number of electrons show slow relaxation of the magnetization. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim., This work was supported by the European Research Council through the AdG “NoINanoMaS” (grant number 267746), by the Italian MIUR (PRIN 2008), Spanish research project MAT2011-27233-C02-02, Région Bretagne, Rennes Métropole, and by the Italian CINECA through the award number HP10AI85MB, 2011.

Cantilever torque magnetometry is used to elucidate the orientation of magnetic molecules in thin films. The technique allows depth-resolved investigations by intercalating a layer of anisotropic magnetic molecules in a film of its isotropic analogues. The proof-of-concept is here demonstrated with the single-molecule magnet TbPc2 evidencing also an exceptional long-range templating effect on substrates coated by the organic molecule perylene-3,4,9,10-tetracarboxylic dianhydride.

A multitechnique investigation of an evaporable vanadyl spin system with long-lived quantum coherence that self-assembles on gold., Electronic spins in different environments are currently investigated as potential qubits, i.e. the logic units of quantum computers. These have to retain memory of their quantum state for a sufficiently long time (phase memory time, Tm) allowing quantum operations to be performed. For molecular based spin qubits, strategies to increase phase coherence by removing nuclear spins are rather well developed, but it is now crucial to address the problem of the rapid increase of the spin–lattice relaxation rate, T1–1, with increasing temperature that hampers their use at room-temperature. Herein, thanks to the combination of pulsed EPR spectroscopy and AC susceptometry we evidence that an evaporable vanadyl complex of formula VO(dpm)2, where dpm– is the anion of dipivaloylmethane, presents a combination of very promising features for potential application as molecular spin-qubit. The spin–lattice relaxation time, T1, studied in detail through AC susceptometry, decreases slowly with increasing temperature and, more surprisingly, it is not accelerated by the application of an external field up to several Teslas. State-of-the art phase memory times for molecular spin systems in protiated environment are detected by pulsed EPR also in moderate dilution, with values of 2.7 μs at 5 K and 2.1 μs at 80 K. Low temperature scanning tunnel microscopy and X-ray photoelectron spectroscopy in situ investigations reveal that intact molecules sublimated in ultra-high vacuum spontaneously form an ordered monolayer on Au(111), opening the perspective of electric access to the quantum memory of ensembles of spin qubits that can be scaled down to the single molecule.

International audience; We report here a study about the magnetic anisotropy of the LnTRENSAL complexes (Ln = Tb, Dy, Er) performed by using cantilever torque magnetometry and electron paramagnetic resonance. For all of the compounds, we extracted a set of crystal-field parameters to obtain the energy-level splitting of the ground-state multiplet.

Single-crystal torque magnetometry performed on weakly-coupled polynuclear systems provides access to a complete description of single-site anisotropy tensors. Variable-temperature, variable-field torque magnetometry was used to investigate triiron(III) complex [Fe3La(tea)2(dpm)6] (Fe3La), a lanthanum(III)-centred variant of tetrairon(III) single molecule magnets (Fe4) (H3tea = triethanolamine, Hdpm = dipivaloylmethane). Due to the presence of the diamagnetic lanthanoid, magnetic interactions among iron(III) ions (si = 5/2) are very weak (0.1 cm(−1)) and the magnetic response of Fe3La is predominantly determined by single-site anisotropies. The local anisotropy tensors were found to have Di0 and to be quasi-axial with |Ei/Di| ~ 0.05. Their hard axes form an angle of approximately 70° with the threefold molecular axis, which therefore corresponds to an easy magnetic direction for the molecule. The resulting picture was supported by a High Frequency EPR investigation and by DFT calculations. Our study confirms that the array of peripheral iron(III) centres provides substantially noncollinear anisotropy contributions to the ground state of Fe4 complexes, which are of current interest in molecular magnetism and spintronics.

In this chapter, data of thermal conductivity (κ) and integrated conductivity (I*) are presented in the form of tables. Data are divided into three categories. 1. Very low temperature data (100 mK–2 K), 2. Low temperature data (4–300 K), 3. Data about crystalline materials for which a fit in a limited range of temperature is proposed.

In this chapter useful tables containing data of thermal contraction below room temperature of several materials, most of them used in cryogenic applications, are reported together with the coefficient of thermal expansion at 293 K. The values of thermal contraction are referred at the length of the sample at 293 K.

The methods to measure the thermal conductivity at low temperature are described: the steady-state techniques, (Sect. 2.2); the 3ω technique (Sect. 2.3); and the thermal diffusivity measurement (Sect. 2.4). Each of these techniques has its own advantages as well as its inherent limitations, with some techniques more appropriate to specific sample geometry, such as the 3ω technique for thin films which is discussed in detail in Sect. 2.4.2. The radial flux method is reported in Sect. 2.2.4, the laser flash diffusivity method in Sect. 2.4.1 and the “pulsed power or Maldonado technique” in Sect. 2.3.2.

Thermal expansion measurements in the high temperature range have been thoroughly explored, and various experimental methods are available even as commercial instrumentation, measurements at cryogenic temperatures have been confined to the field of high-precision laboratory experiments, needing large experimental efforts and expenses, and often also suffering from intrinsic limitations. All techniques used for the measurements of thermal expansion can be divided into two categories, namely: absolute methods and relative methods. While in the former the linear changes of dimension of the sample are directly measured at various temperature, in the latter the coefficient of thermal expansion is determined through comparison with a reference materials of known thermal expansion. A lot of experimental set-ups are described in Sect. 2.1, while Sect. 2.2 some examples of measurements performed at very low temperatures are listed.

In this chapter experimental data for materials of common use in cryogenics are reported, in particular, approximate integrated data useful for a rough estimation of the power necessary to cool down a system. Specific heat data are divided into two groups of tables: (1) very-low temperature data of c p (below about 4 K) given by a fit when possible (Sect. 3.2). (2) low temperature of c p (approximately 4–300 K) of specific heat c p and H*(integral of c p ) (Sect. 3.3).

This chapter is devoted to the description of calorimetric techniques used to measure heat capacity of solids: pulse heat calorimetry (Sect. 2.3), relaxation calorimetry (Sect. 2.4), dual slope calorimetry (Sect. 2.5), a.c. calorimetry (Sect. 2.6), differential scanning calorimetry (Sect. 2.7). Examples of measurements of heat capacity are reported in Sects. 2.3 and 2.4.