Imposing high-symmetry and tuneable geometry on lanthanide centres with chelating Pt and Pd metalloligands

Square planar Pd(II)/oximate complexes as 'metalloligands' for the directional assembly of 4f-metal ions: a new family of {Ln2Pd} (Ln = lanthanide) clusters exhibiting slow magnetization relaxation

A relatively unexplored approach in heterometallic chemistry of transition metals and lanthanides has been developed toward the controlled synthesis of a new family of linear heterotrinuclear Ln(III)-Pd(II)-Ln(III) complexes with the general formula [Ln2Pd(pao)2(NO3)6(MeOH)2(H2O)2]·[Pd(pao)2]4, where LnIII = DyIII (2), GdIII (3), ErIII (4) and YbIII (5). This strategy was based on the diamagnetic 'metalloligand' [Pd(pao)2] (1), where pao- is the anion of 2-pyridinealdoxime, containing two dangling oximate O-atoms which were trans to each other and available for binding with oxophilic lanthanide ions. Because of their trans-configuration, the [Pd(pao)2] 'metalloligand' was able to direct the binding of two {Ln(NO3)3(MeOH)(H2O)} units on opposite sites, thus yielding the reported trinuclear {Ln-Pd-Ln} clusters. Complexes 2-5 constitute a new family of trinuclear heterometallic {Ln2Pd} species, and they represent the first examples of a directional assembly approach towards the coordination of 4f-metal ions. Compounds 2 and 5 exhibit out-of-phase signals under applied dc fields of 300 and 2000 Oe, respectively, characteristics of the slow magnetization relaxation, albeit with very small energy barriers for the magnetization reversal. This was due to the combined onset of fast quantum tunneling and the weak crystal field effects induced by the coordinated ligands. The combined results highlight the potential of using the 'metal complexes as ligands' method to deliberately prepare heterometallic PdII-LnIII complexes with unique structural and interesting physicochemical (magnetic, optical, catalytic) properties.

Controlling the symmetry of hexamonodentate 3d-transition metal complexes through symmetry propagation from high-symmetry Ti-Mo and Zr-Mo clusters via hydrogen-bonding interactions

The symmetry of one of the simplest hexamonodentate complexes, [M(H2O)6]2+ (M = Fe, Co, Ni, and Zn), was controlled by tuning interactions in the second coordination sphere. Highly symmetric Ti-Mo or Zr-Mo cluster cations acted as symmetry templates, imposing a crystallographic trigonal coordination geometry in the hexamonodentate complexes through intermolecular hydrogen-bonding interactions. Magnetic measurements revealed that the ideal trigonal symmetry results in weak spin-orbit coupling for high-spin FeII complexes, despite the T-term ground state in the octahedral geometry. In contrast, high-spin CoII analogues with the T-term ground state exhibited strong spin-orbit coupling. DFT studies supported that a d6 FeII ion in the D3 symmetry has a 5A1 ground state while a d7 CoII in the same symmetry has a 4E ground state. Single-ion magnet behavior was observed in the CoII complexes. These results demonstrate that incorporating a diamagnetic, highly symmetric cluster enables precise symmetry control in single-ion magnets containing only monodentate ligands.

Sandwich d/f Heterometallic Complexes [(Ln(hfac)3)2M(acac)3] (Ln = La, Pr, Sm, Dy and M = Co; Ln = La and M = Ru)

Sandwich d/f heterometallic complexes [(Ln(hfac)3)2M(acac)3] (Ln = La, Pr, Sm, Dy and M = Co; Ln = La and M = Ru) were prepared in strictly anhydrous conditions reacting the formally unsaturated fragment [Ln(hfac)3] and [M(acac)3] in a 2-to-1 molar ratio. These heterometallic complexes are highly sensitive to moisture. Spectroscopic observation revealed that on hydrolysis, these compounds yield dinuclear heterometallic compounds [Ln(hfac)3M(acac)3], prepared here for comparison purposes only. Quantum mechanical calculations supported, on the one hand, the hypothesis on the geometrical arrangement obtained from ATR-IR and NMR spectra and, on the other hand, helped to rationalize the spontaneous hydrolysis reaction.

Tailoring single-ion magnet properties of coordination polymer C11H18DyN3O9 (Dy-CP) using the radial effective charge model (RECM) and superposition model (SPM)

We investigate Dy-based coordination polymer C11H18DyN3O9 (Dy-CP) exhibiting single-ion magnet (SIM) properties, e.g., quantum tunnelling of magnetization (QTM), magnetic anisotropy, magnetic relaxation, and effective energy barrier (Ueff). To elucidate the underlying mechanisms, crystal field parameters (CFPs) for Dy3+ ions were modelled using the radial effective charge model (RECM) and superposition model (SPM), and the computational packages SIMPRE and SPECTRE. The modelled CFPs enable the prediction of the energy levels and associated wave functions, which successfully explain the field-induced Dy-CP SIM properties. The so-calculated magnetic susceptibility and isothermal magnetization match the experimental data reasonably well. The smaller energy separations of the first (Δ0-1 ∼ 31 cm-1) and the second (Δ0-2 = 74 cm-1) excited Kramers doublets suggest small Ueff = 65 cm-1 for Dy-CP. The magnetic moments of Dy3+ ions exhibit an easy-axis type magnetic anisotropy in the ground state, but change orientation in the excited states due to mixing of states from different Kramers doublets. Low-symmetry CF components play a crucial role in connecting different |±MJ〉 states within the ground multiplet, resulting in QTM and magnetic relaxation to the ground state occurring via the excited states. The RECM and SPM calculated CFP sets are standardized employing the 3DD package to enable meaningful comparison and assessing their mutual equivalence. The results demonstrate the correlation between structural and electronic features of the molecule and site symmetry and distortion of the local coordination polyhedra with SIM properties, offering insights for rational design of new SIMs. The importance of considering low-symmetry aspects in CFP modelling for accurate predictions of magnetic properties is highlighted. This study provides deeper understanding of field-induced behaviour in rare-earth-based SIMs and approaches for rationalization of experimentally measured SIMs' properties.

Mononuclear Rare-Earth Metalloligands Exploiting a Divergent Ligand

Rare-earth tris-diketonato [RE(dike)3pyterpy] metalloligands can be prepared reacting at room temperature [RE(dike)3dme] (dme = 1,2-dimethoxyethane; dike = tta with Htta = 2-thenoyltrifluoroacetone and RE = La, 1; Y, 2; Eu, 3; Dy, 4; or dike = hfac with Hhfac hexafluoroacetylacetone, and RE = Eu, 5; Tb, 6; Yb 7) with 4'-(4‴-pyridil)-2,2':6',2″-terpyridine (pyterpy). The molecular structures of 1, 5, 6, and 7 have been studied through single-crystal X-ray diffraction showing mononuclear neutral complexes with the rare-earth ion in coordination number nine and with a muffin-like coordination geometry. [RE(tta)3pyterpy] promptly reacts with [M(tta)2dme] with formation of [Mpyterpy2][RE(tta)4]2 (M = Zn, RE = Y, 8; M = Co, RE = Dy, 9). Consistently, [Zn(hfac)2dme] reacts at room temperature with 2 equiv of pyterpy yielding [Znpyterpy2][hfac]2 10 that easily can be transformed by reaction with 2 equiv of [Eu(hfac)3] in [Znpyterpy2][Eu(hfac)4]2 11 that has been structurally characterized. Finally, 1, 2, 3, 5, and 7 metalloligands react at room temperature in few minutes with [PtCl(μ-Cl)PPh3]2 yielding the heterometallic molecular complexes [RE(dike)3pyterpyPtCl2PPh3] (dike = tta, RE = La, 12; Y, 13; Eu; 14; dike = hfac, RE = Eu, 15; Yb, 16).

Engineering Clock Transitions in Molecular Lanthanide Complexes

Molecular lanthanide (Ln) complexes are promising candidates for the development of next-generation quantum technologies. High-symmetry structures incorporating integer spin Ln ions can give rise to well-isolated crystal field quasi-doublet ground states, i.e., quantum two-level systems that may serve as the basis for magnetic qubits. Recent work has shown that symmetry lowering of the coordination environment around the Ln ion can produce an avoided crossing or clock transition within the ground doublet, leading to significantly enhanced coherence. Here, we employ single-crystal high-frequency electron paramagnetic resonance spectroscopy and high-level ab initio calculations to carry out a detailed investigation of the nine-coordinate complexes, [HoIIIL1L2], where L1 = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane and L2 = F- (1) or [MeCN]0 (2). The pseudo-4-fold symmetry imposed by the neutral organic ligand scaffold (L1) and the apical anionic fluoride ion generates a strong axial anisotropy with an mJ = ±8 ground-state quasi-doublet in 1, where mJ denotes the projection of the J = 8 spin-orbital moment onto the ∼C4 axis. Meanwhile, off-diagonal crystal field interactions give rise to a giant 116.4 ± 1.0 GHz clock transition within this doublet. We then demonstrate targeted crystal field engineering of the clock transition by replacing F- with neutral MeCN (2), resulting in an increase in the clock transition frequency by a factor of 2.2. The experimental results are in broad agreement with quantum chemical calculations. This tunability is highly desirable because decoherence caused by second-order sensitivity to magnetic noise scales inversely with the clock transition frequency.

Aluminium 8-Hydroxyquinolinate N-Oxide as a Precursor to Heterometallic Aluminium-Lanthanide Complexes

A reaction in anhydrous toluene between the formally unsaturated fragment [Ln(hfac)3] (Ln3+ = Eu3+, Gd3+ and Er3+; Hhfac = hexafluoroacetylacetone) and [Al(qNO)3] (HqNO = 8-hydroxyquinoline N-oxide), here prepared for the first time from [Al(OtBu)3] and HqNO, affords the dinuclear heterometallic compounds [Ln(hfac)3Al(qNO)3] (Ln3+ = Eu3+, Gd3+ and Er3+) in high yields. The molecular structures of these new compounds revealed a dinuclear species with three phenolic oxygen atoms bridging the two metal atoms. While the europium and gadolinium complexes show the coordination number (CN) 9 for the lanthanide centre, in the complex featuring the smaller erbium ion, only two oxygens bridge the two metal atoms for a resulting CN of 8. The reaction of [Eu(hfac)3] with [Alq3] (Hq = 8-hydroxyquinoline) in the same conditions yields a heterometallic product of composition [Eu(hfac)3Alq3]. A recrystallization attempt from hot heptane in air produced single crystals of two different morphologies and compositions: [Eu2(hfac)6Al2q4(OH)2] and [Eu2(hfac)6(µ-Hq)2]. The latter compound can be directly prepared from [Eu(hfac)3] and Hq at room temperature. Quantum mechanical calculations confirm (i) the higher stability of [Eu(hfac)3Al(qNO)3] vs. the corresponding [Eu(hfac)3Alq3] and (ii) the preference of the Er complexes for the CN 8, justifying the different behaviour in terms of the Lewis acidity of the metal centre.

Electron Paramagnetic Resonance Spectra of Pentagonal Bipyramidal Gadolinium Complexes

Gadolinium is a special case in spectroscopy because of the near isotropic nature of the 4f⁷ configuration of the +3 oxidation state. Gd³⁺ complexes have been studied in several symmetries to understand the underlying mechanisms of the ground state splitting. The abundance of information in Gd³⁺ spectra can be used as a probe for properties of the other rare earth ions in the same complexes. In this work, the zero-field splitting (ZFS) of a series of Gd³⁺ pentagonal bipyramidal complexes of the form [GdX₁X₂(L_eq)₅]ⁿ⁺ [n = 1, X = axial ligands: Cl^-, ^-O^tBu, ^-OArF₅ or n = 3, X = ^tBuPO(NHⁱPr)₂, L_eq = equatorial ligand: Py, THF or H₂O] with near fivefold symmetry axes along X¹-Gd-X² was investigated. The ZFS parameters were determined by fitting of room-temperature continuous wave electron paramagnetic resonance (EPR) spectra (at X-, K-, and Q-band) to a spin Hamiltonian incorporating extended Stevens operators compatible with C₅ symmetry. Examination of the acquired parameters led to the conclusion that the ZFS is dominated by the B₂⁰ term and that the magnitude of B₂⁰ is almost entirely dependent on, and inversely proportional to, the donor strength of the axial ligands. Surveying the continuous shape measure and the X¹-Gd-X² angle of the complexes showed that there is some correlation between the proximity of each complex to D_5h symmetry and the magnitude of the B₆⁵ parameter, but that the deformation of the X¹-Gd-X² angle is more significant than other distortions. Finally, the magnitude of B₂⁰ was found to be inversely proportional to the thermal barrier for the reversal of the magnetic moment (U_eff) of the corresponding isostructural Dy³⁺ complexes.

Direct observation of magnetoelastic coupling in a molecular spin qubit: new insights from crystal field neutron scattering data

Single-molecule magnets are promising candidates for data storage and quantum computing applications. A major barrier to their use is rapid magnetic relaxation and quantum decoherence due to thermal vibrations. Here we report a reanalysis of inelastic neutron scattering (INS) data of the candidate qubit Na9[Ho(W5O18)2]·35D2O, wherein we demonstrate for the first time that magnetic relaxation times and mechanisms can be directly observed as crystal field (CF) peak broadening in INS spectra of a lanthanoid molecular system. The magnetoelastic coupling between the lower energy CF states and phonons (lattice vibrations) is determined by the simultaneous measurement of CF excitations and the phonon density of states, encoded within the same INS experiment. This directly results in the determination of relaxation coupling pathways that occur in this molecule. Such information is invaluable for the further advancement of SMMs and to date has only been obtained from techniques performed in external magnetic fields. Additionally, we determine a relaxation rate of quantum-tunnelling of magnetisation that is consistent with previously measured EPR spectroscopy data.

Experimental assignment of long-range magnetic communication through Pd & Pt metallophilic contacts

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc)₄)(pyNO₂)]₂ (M = Ni or Co) that are linked in the solid state via metallophilic Pt⋯Pt 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 d⁸⋯d⁸ 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 Pd⋯Pd bridge is found through SQUID-magnetometry and FD-FT THz-EPR spectroscopy to be much weaker than via the Pt⋯Pt 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 Pd⋯Pd and Pt⋯Pt-systems with clear minima along this coordinate and provide estimates for the force constant for this distortion. The estimated M⋯M 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 Pd⋯Pd 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.

Unequal sensitivities of energy levels in a high-symmetry Ho3+ complex towards lattice distortions

High-resolution inelastic neutron scattering has been used to study low-energy magnetic transitions in a Ho³⁺ complex. This complex crystallises in the high-symmetry space group P4/m and has near-perfect D_4d symmetry, which has allowed for the determination of all relevant spin-Hamiltonian parameters. Static and dynamic inhomogeneity in the crystal lattice manifests as a temperature-dependent broadening of the observed magnetic excitations. By implementing distributions in the spin-Hamiltonian parameters, it is possible to reproduce with great accuracy the observed magnetic transition spectrum. This reveals the range to which extraneous perturbations of the crystal field affect low-energy electronic states, such as those involved in quantum tunnelling of magnetisation, in atomic clock transitions, or in spintronics.

Invisible strings. The first single crystal of the cTSAP form of [Eu(DOTA)(H2O)]− has an electronic structure similar to one of the reported cSAP forms

Counter ions can be used to tune the solid state structure of Eu·DOTA between the cSAP and cTSAP form, but the electronic properties does not match the observations seen in solution.

Delicate, a study of the structural changes in ten-coordinated La(iii), Ce(iii), Pr(iii), Nd(iii), Sm(iii) and Eu(iii) sulfates

A study of doped ten-coordinated structures of the lanthanide(iii) crystals series, K6[Ln2(SO4)6] (Ln(iii) = La, Ce, Pr) and K5Na[Ln2(SO4)6] (Ln(iii) = Nd, Sm, Eu) to determine luminescence from Eu(iii) in distorted host lattices.

Thiolate-Thione Redox-Active Ligand with a Six-Membered Chelate Ring via Template Condensation and Its Pt(II) Complexes

A new template condensation reaction has been discovered in a mixture of Pt(II), thiobenzamide, and base. Four complexes of the general form [Pt(ctaPh^R)₂], R = CH₃ (1a), H (1b), F (1c), Cl (1d), cta = condensed thioamide, have been prepared under similar conditions and thoroughly characterized by ¹H NMR and UV-vis-NIR spectroscopy, (spectro)electrochemistry, elemental analysis, and single-crystal X-ray diffraction. The ligand is redox active and can be reduced from the initial monoanion to a dianionic and then trianionic state. Chemical reduction of 1a with [Cp₂Co] yielded [Cp₂Co]₂[Pt(ctaPh^CH3)₂], [Cp₂Co]₂[1a], which has been similarly characterized with the addition of EPR spectroscopy and SQUID magnetization. The singly reduced form containing [1a]^1-, (nBu₄N)[Pt(ctaPh^CH3)₂], has been generated in situ and characterized by UV-vis and EPR spectroscopies. DFT studies of 1b, [1b]^1-, and [1b]^2- confirm the location of additional electrons in exclusively ligand-based orbitals. A detailed analysis of this redox-active ligand, with emphasis on the characteristics that favor noninnocent behavior in six-membered chelate rings, is included.

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

The chemistry of discrete molecular chains constituted by metals in low oxidation states, displaying metal-metal proximity and stabilized by suitable metal-bridging, assembling ligands comprising at least one soft donor atom is comprehensively reviewed; complexes with a single (hard or soft) bridging atom (e.g., μ-halide, μ-sulfide, or μ-PR₂ etc.) as well as "closed" metal arrays (that fall in the realm of cluster chemistry) are excluded. The focus is on transition metal-based systems, with few excursions to cases combining transition and post-transition elements. Most relevant supporting ligands have neutral C, P, O, or S donor (mainly, N-heterocyclic carbene, phosphine, ether, thioether) or anionic donor (mainly phenyl, ylide, silyl, phosphide, thiolate) groups. A supporting-ligand-based classification of the metal chains is introduced, using as the classifying parameter the number of "bites" (i.e., ligand bridges) subtending each intermetallic separation. The ligands are further grouped according to the number of donor atoms interacting with the metal chain (called denticity in the following) and the column of the Periodic Table to which the set of donor atoms belongs (in ascending order). A complementary metal-based compilation of the complexes discussed is also provided in a concise tabular form.

The anisotropy of the internal magnetic field on the central ion is capable of imposing great impact on the quantum tunneling of magnetization of Kramers single-ion magnets

In this work, a theoretical method, taking into account the anisotropy of the internal magnetic field (B[combining right harpoon above]int), is proposed to predict the rate of quantum tunneling of magnetization (QTM), i.e., τQTM-1, for Kramers single-ion magnets (SIMs). Direct comparison to both experimental and previous theoretical results of three typical Kramers SIMs indicates the necessity of the inclusion of the anisotropy of B[combining right harpoon above]int for accurate description of QTM. The predictions of the method here are consistent with the theory proposed by Prokof'ev and Stamp (PS). For Kramers SIMs of high magnetic axiality, the QTM rates, predicted by the method here, are almost linearly proportional to the results by the PS method. The dependence of τQTM-1 on various parameters is analyzed for model systems. The averaged magnitude of B[combining right harpoon above]int (Bave) and principal g value of the axial direction (gZ) are the parameters on which τQTM-1 is linearly dependent. The ones on which τQTM-1 is quadratically dependent are gXY, i.e., the principal g value of the transversal direction, and xaniso characterizing the anisotropy of B[combining right harpoon above]int. Compared to Bave and gZ, gXY and xaniso provide a higher order of dependence for QTM. Therefore regulation of the SMM property via introduction of desired values of gXY and xaniso ought to be a strategy more efficient than the one via Bave and gZ. Being different from the one via gXY, the strategy via xaniso to regulate the QTM has been rarely touched upon according to our best knowledge. However, this strategy could also lead to significant improvement since it is the same as gXY in the aspect of the dependence of τQTM-1.

Lanthanide Complexes with a Tripodal Nitroxyl Radical Showing Strong Magnetic Coupling

A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripodal 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 a molecular structure. Their coordination polyhedron, LnO₇N₂, can be described as a tricapped trigonal prism with symmetry not far from D_3h. The extracted value of 23 cm^-1 for the antiferromagnetic coupling of 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 applied field of 0.1 T, an effective barrier of 57 cm^-1 is found.

Ionic-caged heterometallic bismuth-platinum complex exhibiting electrocatalytic CO2 reduction

An air-stable heterometallic Bi-Pt complex with the formula [BiPt(SAc)5]n (1; SAc = thioacetate) was synthesized. The crystal structure, natural bond orbital (NBO) and local orbital locator (LOL) analyses, localized orbital bonding analysis (LOBA), and X-ray absorption fine structure (XAFS) measurements were used to confirm the existence of Bi-Pt bonding and an ionic cage of O atoms surrounding the Bi ion. From the cyclic voltammetry (CV) and controlled potential electrolysis (CPE) experiments, 1 in tetrahydrofuran reduced CO2 to CO, with a faradaic efficiency (FE) of 92% and a turnover frequency (TOF) of 8 s-1 after 30 min of CPE at -0.79 V vs. NHE. The proposed mechanism includes an energetically favored pathway via the ionic cage, which is supported by the results of DFT calculations and reflectance infrared spectroelectrochemistry data.

Magnetization Dynamics and Coherent Spin Manipulation of a Propeller Gd(III) Complex with the Smallest Helicene Ligand

A homoleptic gadolinium(III) complex with the smallest helicene-type ligand, 1,10-phenanthroline-N,N'-dioxide (phendo) [Gd(phendo)₄](NO₃)₃·xMeOH (phendo = 1,10-phenanthroline-N,N'-dioxide, MeOH = methanol), shows slow relaxation of the magnetization characteristic for Single Ion Magnets (SIM), despite negligible magnetic anisotropy, confirmed by ab initio calculations. Solid state dilution magnetic and EPR studies reveal that the magnetization dynamics of the [Gd(phendo)₄]³⁺ cation is controlled mainly by a Raman process. Pulsed EPR experiments demonstrate long phase memory times (up to 2.7 μs at 5 K), enabling the detection of Rabi oscillations at 20 K, which confirms coherent control of its spin state.

High-Pressure Crystallography as a Guide in the Design of Single-Molecule Magnets

Single-molecule magnet materials owe their function to the presence of significant magnetic anisotropy, which arises from the interplay between the ligand field and spin-orbit coupling, and this is responsible for setting up an energy barrier for magnetic relaxation. Therefore, chemical control of magnetic anisotropy is a central challenge in the quest to synthesize new molecular nanomagnets with improved properties. There have been several reports of design principles targeting such control; however, these principles rely on idealized geometries, which are rarely obtained in crystal structures. Here, we present the results of high-pressure single-crystal diffraction on the single-ion magnet, Co(SPh)₄(PPh₄)₂, in the pressure range of 0-9.2 GPa. Upon pressurization a sequence of small geometrical distortions of the central CoS₄ moeity are observed, enabling a thorough analysis of the magneto-structural correlations. The magneto-structural correlations are investigated by theoretical analyses of the pressure-dependent experimental molecular structures. We observed a significant increase in the magnitude of the zero-field splitting parameter D, from -54.6 cm^-1 to -89.7 cm^-1, which was clearly explained from the reduction of the energy difference between the essential d_xy and d_x²-y² orbitals, and structurally assigned to the change of an angle of compression of the CoS₄ moeity.

Importance of Axial Symmetry in Elucidating Lanthanide-Transition Metal Interactions

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.

Janus coordination polymer derived PdO/ZnO nanoribbons for efficient 4-nitrophenol reduction

Bimetallic coordination polymers–Zn(MAA)₂/Pd(ii) nanoribbons are prepared by employing two terminal units with distinct hard–soft properties of the smallest semi-rigid methacrylate anion to combine with two different metal ions.

Orientation mapping of Rabi frequencies in a rare-earth molecular qudit

Utilizing the S = 7/2 4f spin and the D₄ symmetry of a Gd(iii) complex, we propose and demonstrate an eight-leveled rare-earth molecular qudit, which can be coherently manipulated between adjacent energy levels with precompiled pulse durations.

Identical anomalous Raman relaxation exponent in a family of single ion magnets: towards reliable Raman relaxation determination?

The results described herein suggest that the exponent n for the temperature dependence of the Raman relaxation process in the series of solid-state diluted isostructural Ln^III SIMs should be identical.

Ln-Pt electron polarization effects on the magnetic relaxation of heterometallic Ho- and Er-Pt complexes

Heterometallic Ln-Pt complexes, with the formula [Ln₂Pt₃(H₂O)₂(SAc)₁₂] (Ln = Ho(1), Er(2); SAc = thioacetate), were synthesized. From natural bond orbital (NBO) and local orbital locator (LOL) analyses and X-ray absorption fine structure (XAFS) measurements, it was clear that the Ln-Pt interactions or electron polarization occurred. Butterfly-type hysteresis was observed for both 1 and 2. 1 and 2 underwent field-induced slow magnetic relaxation up to 4 K. These magnetic properties were induced by Ln-Pt electron polarization.

Stepwise Synthesis, Hydrogen-Bonded Supramolecular Structure, and Magnetic Property of a Co–Mn Heterodinuclear Complex

A cobalt(III)–manganese(II) heterometallic dinuclear complex, [MnII{CoIII(µ-Himn)3}Cl2(CH3OH)], was prepared by a metalloligand approach. X-ray crystallographic analysis indicated that the metalloligand [CoIII(Himn)3] underwent mer/fac geometrical isomerization upon coordination to a Mn ion. Owing to the non-coordinating N–H bonds in the [CoIII(Himn)3] moiety, the heterodinuclear complex exhibited hydrogen bond interactions with the Cl− ligand of the neighboring complex to construct two-dimensional hydrogen-bond networks. The bond distances around the Mn center and the χMT value at 300 K indicate that the Mn center is in a divalent state. The temperature dependence of the χMT product and field dependence of the magnetization showed the isotropic nature of the MnII center.

Field-induced slow magnetic relaxation in the first Dy(iii)-centered 12-metallacrown-4 double-decker

The first double-decker Ga(iii)/Dy(iii) 12-MC-4 complex has been isolated and magnetic studies revealed its SMM properties.

Descriptors of magnetic anisotropy revisited

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.

Field-induced single-molecule magnet behavior in ideal trigonal antiprismatic cobalt(ii) complexes: precise geometrical control by a hydrogen-bonded rigid metalloligand

A new cobalt(ii) complex bearing a pair of cobalt(iii) tris-chelate complexes as metalloligands was prepared. The CoII ion possesses an ideal trigonal antiprismatic geometry because of the intermolecular hydrogen-bonds between the metalloligands via counter anions. This complex exhibits slow magnetic relaxation under a dc field reminiscent of a single-molecule magnet behavior.

Chiral, Heterometallic Lanthanide–Transition Metal Complexes by Design

Achieving control over coordination geometries in lanthanide complexes remains a challenge to the coordination chemist. This is particularly the case in the field of molecule-based magnetism, where barriers for magnetic relaxation processes as well as tunneling pathways are strongly influenced by the lanthanide coordination geometry. Addressing the challenge of design of 4f-element coordination environments, the ubiquitous Ln(hfac)3 moieties have been shown to be applicable as Lewis acids coordinating transition metal acetylacetonates facially leading to simple, chiral lanthanide–transition metal heterodinuclear complexes. The broad scope of this approach is illustrated by the synthesis of a range of such complexes LnM: LnM(hfac)3(μ2-acac-O,O,O′)3 (Ln = La, Pr, Gd; M = Cr, Fe, Ga), with approximate three-fold symmetry. The complexes have been crystallographically characterized and exhibit polymorphism for some combinations of 4f and 3d metal centers. However, an isostructural set of systems spanning several lanthanides which exhibit spontaneous resolution in the orthorhombic Sohncke space group P212121 is presented here. The electronic structure and ensuing magnetic properties have been studied by EPR spectroscopy and magnetometry. The GdFe, PrFe, and PrCr complexes exhibit ferromagnetic coupling, while GdCr exhibits antiferromagnetic coupling. GdGa exhibits slow relaxation of the magnetization in applied static fields.

Slow Magnetic Relaxation in a Palladium-Gadolinium Complex Induced by Electron Density Donation from the Palladium Ion

Incorporating palladium in the first coordination sphere of acetato-bridged lanthanoid complexes, [Pd₂ Ln₂ (H₂ O)₂ (AcO)₁₀ ]⋅2 AcOH (Ln=Gd (1), Y (2), Gd_0.4 Y_1.6 (3), Eu (4)), led to significant bonding interactions between the palladium and the lanthanoid ions, which were demonstrated by experimental and theoretical methods. We found that electron density was donated from the d⁸ Pd²⁺ ion to Gd³⁺ ion in 1 and 3, leading to the observed slow magnetic relaxation by using local orbital locator (LOL) and X-ray absorption near-edge structure (XANES) analysis. Field-induced dual slow magnetic relaxation was observed for 1 up to 20 K. Complex 3 and frozen aqueous and acetonitrile solutions of 1 showed only one relaxation peak, which confirms the role of intermolecular dipolar interactions in slowing the magnetic relaxation of 1. The slow magnetic relaxation occurred through a combination of Orbach and Direct processes with the highest pre-exponential factor (τ_o =0.06 s) reported so far for a gadolinium complex exhibiting slow magnetic relaxation. The results revealed that transition metal-lanthanoid (TM-Ln) axial interactions indeed could lead to new physical properties by affecting both the electronic and magnetic states of the compounds.

Heterobimetallic Lantern Complexes and Their Novel Structural and Magnetic Properties

As the scale of microelectronic circuit devices approaches the atomic limit, the study of molecular-based wires and magnets has become more prevalent. Compounds with quasi-1D geometries have been investigated for their electronic conductivity and magnetic properties with potential use as nanoscale circuit components and information storage devices. To increase the number of compositionally tailored molecular systems available to study, we have taken a building-block, bottom-up approach to the development of improved electronic structure and magnetic properties of quasi-1D arrays. Over the past decade, a large family of asymmetric complexes that can assemble into extended arrays has resulted. Lantern (or paddle-wheel) complexes with conventional {O, O} donor carboxylates are legion, but by the use of monothiocarboxylate ligands and hard-soft Lewis acid-base principles, dozens of new lantern complexes of the form [PtM(SOCR)₄(L)] (M = Mg, Ca, Cr, Mn, Fe, Co, Ni, Zn; R = Ph (tba = thiobenzoate), CH₃ (SAc = thioacetate); L = neutral or anionic ligand) have been prepared. Depending on M and L, new intermolecular arrangements have resulted, and the magnetic properties have proven particularly interesting. In the solid state, the [PtM(SOCR)₄(L)] building blocks are sometimes isolated, sometimes form dimers, and can be induced to form infinite chains. The versatility of the lantern motif was demonstrated with a range of axial ligands to form both terminal and bridged complexes with various 3d metals and two different substituted thiocarboxylate backbone ligands. Within the dozens of crystallographically characterized compounds that make up this family of lanterns, several different structural motifs of solid-state dimerization were observed and divided into four distinct categories on the basis of their Pt···Pt and Pt···S distances and relative monomer orientations. Among all of these compounds, three novel magnetic phenomena were observed. Initially, long-range antiferromagnetic coupling between two metals more than 8 Å apart was observed in solid-state dimers formed via metallophilic Pt···Pt interactions and could induced by choice of the terminal L group. An infinite chain was prepared in [PtCr(tba)₄(NCS)]_∞ that displays ferromagnetic coupling between Cr centers with J/ k_B = 1.7(4) K. Homobimetallic quasi-1D chains of the form [Ni₂(SOCR)₄(L)]_∞ (R = Ph, CH₃; L = DABCO, pyz) were also prepared with S = 1 {Ni₂} building blocks in which the Ni centers have two different spin states with weak antiferromagnetic coupling along the chain, such that -0.18 > J/ k_B > -0.24 K. In the [Ni₂(tba)₄(quin)] derivative, a solid-state dimer forms with a bridging square conformation by interlantern Ni₂S₂ interactions and displays unusual S = 1 configurations on both Ni centers and weak antiferromagnetic coupling between them.

Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C₄) to pseudo-linear (D_4d) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting.

Slow magnetic dynamics in a family of mononuclear lanthanide complexes exhibiting the rare cubic coordination geometry

Synthesis, magnetic, and theoretical studies of a new family of mononuclear lanthanide complexes exhibiting the very rare cubic coordination geometry.

Magneto-structural correlations in a family of ReIVCuII chains based on the hexachlororhenate(iv) metalloligand

Six novel one-dimensional chloro-bridged Re^IVCu^II complexes of formula {[Cu(L)₄][ReCl₆]}_n, where L = imidazole (Imi, 1), 1-methylimidazole (Meim, 2), 1-vinylimidazole (Vim, 3), 1-butylimidazole (Buim, 4), 1-vinyl-1,2,4-triazole (Vtri, 5) and N,N'-dimethylformamide (DMF, 6) are characterised structurally, magnetically and theoretically. The structures exhibit significant differences in Cu-Cl bond lengths and Re-Cl-Cu bridging angles, resulting in large differences in the nature and magnitude of magnetic exchange interactions between the Re^IV and Cu^II ions. Theoretical calculations reveal the coupling to be primarily ferromagnetic, increasing in magnitude as the bridging angle becomes smaller and the bond lengths shorten.