Single-molecule magnet behaviour in polynuclear assembly of trivalent cerium ions with polyoxomolybdates

New series of mononuclear β-diketonate cerium(III) field induced single-molecule magnets

Five new β-diketonate Ce3+ mononuclear complexes, [Ce(Btfa)3(H2O)2] (1), [Ce(Btfa)3(phen)] (2), [Ce(Btfa)3(bipy)] (3), [Ce(Btfa)3(terpy)] (4) and [Ce(Btfa)3(bathophen)(DMF)] (5), where Btfa- = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate, phen = 1,10-phenanthroline, bipy = 2,2'-bipyridyl, terpy = 2,2':6',2''-terpyridine and bathophen = 4,7-diphenyl-1,10-phenanthroline, have been synthesized and structurally characterized through X-ray diffraction of single crystals. The central Ce3+ atom displays a coordination number of 8 for 1, 2 and 3 and of 9 for 4 and 5. Under a 0 T external magnetic field, none of the given compounds exhibits single molecule magnet (SMM) behaviour. However, a small magnetic field, between 0.02 and 0.1 T, is enough for all the compounds to exhibit slow relaxation of the magnetization. A comprehensive magnetic analysis, with experimental magnetic data and ab initio calculations, was undertaken for all the complexes, and the study highlights the significance of the different spin relaxation mechanisms that must be considered for a Ce3+ lanthanide ion.

Spin dynamics phenomena of a cerium(III) double-decker complex induced by intramolecular electron transfer

Switchable spin dynamic properties in single-molecule magnets (SMMs) via an applied stimulus have applications in single-molecule devices. Many SMMs containing heavy lanthanoid ions with strong uniaxial magnetic anisotropy have been reported to exhibit SMM characteristics in the absence of an external magnetic field. On the other hand, SMMs containing light lanthanoid cerium(III) (Ce3+) ions exhibit field-induced slow magnetic relaxation. We investigated the chemical conversion of a diamagnetic Ce4+ ion (4f0) to a paramagnetic Ce3+ ion (4f1) in Ce-phthalocyaninato double-decker complexes (TBA+[Ce(obPc)2]- (1) and TBA+[Ce(Pc)2]- (2)) which exhibit field-induced SMM behaviour due to a 4f1 system. The phthalocyaninato ligands with electron-donating substituents (obPc2- = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato) in 1 have a significant effect on the valence state of the Ce ion, which is reflected in its magnetic properties due to the mixed valence state of the Ce ion. Given that Ce double-decker complexes with π-conjugated ligands undergo intramolecular electron transfer (IET) to the Ce ion mixed valence state, characterised by a mixture of 4f0 and 4f1 configurations, we examined the dynamic disorder inherent in IET influencing magnetic relaxation.

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Oxalate-bridging NdIII-based arsenotungstate with multifunctional NIR-luminescence and magnetic properties

Oxalate bridged Nd-based arsenotungstate, K₁₄Na₆H₄[{(As₂W₁₉O₆₇(H₂O))Nd(H₂O)₂}₂(C₂O₄)]·64H₂O (1), was obtained from the reaction of K₁₄[As₂W₁₉O₆₇(H₂O)], oxalic acid, and NdCl₃·6H₂O in mildly acidic aqueous solution. The polyanion exhibits a dimeric structure in which the fully deprotonated oxalate ligands bridge two Nd^III cations and the arsenotungstate anions act as blocking ligands. The photoluminescence (PL) spectrum of 1 shows the characteristic emission peak of Nd^III in the near-infrared (NIR) region. However, the O → W charge-transfer transitions of arsenotungstate cannot effectively sensitize the emission of Nd^III cations as confirmed by the emission spectrum, due to the mismatch of the energy gap between ³T_1u → ¹A_1g (21.57 × 10³ cm^-1) of arsenotungstate components and ⁴F_3/2 → ⁴I_9/2 (11.43 × 10³ cm^-1) of Nd^III cations. Magnetic studies of 1 demonstrate its field-induced single-molecule magnet (SMM) behavior. Direct current magnetic susceptibility studies imply the weak ferromagnetic couplings present between the two neighboring Nd^III cations. In addition, the synergy between the coordination configuration of Nd^III cations and the intramolecular magnetic interaction was discussed.

Single-Ion Anisotropy and Intramolecular Interactions in CeIII and NdIII Dimers

This article reports the syntheses, characterization, structural description, together with magnetic and spectroscopic properties of two isostructural molecular magnets based on the chiral ligand N,N'-bis((1,2-diphenyl-(pyridine-2-yl)methylene)-(R,R/S,S)-ethane-1,2-diamine), L1, of general formula [Ln2(RR-L1)2(Cl6)]·MeOH·1.5H2O, (Ln = Ce (1) or Nd (2)). Multifrequency electron paramagnetic resonance (EPR), cantilever torque magnetometry (CTM) measurements, and ab initio calculations allowed us to determine single-ion magnetic anisotropy and intramolecular magnetic interactions in both compounds, evidencing a more important role of the anisotropic exchange for the NdIII derivative. The comparison of experimental and theoretical data indicates that, in the case of largely rhombic lanthanide ions, ab initio calculations can fail in determining the orientation of the weakest components, while being reliable in determining their principal values. However, they remain of paramount importance to set the analysis of EPR and CTM on sound basis, thus obtaining a very precise picture of the magnetic interactions in these systems. Finally, the electronic structure of the two complexes, as obtained by this approach, is consistent with the absence of zero-field slow relaxation observed in ac susceptibility.

Field supported slow magnetic relaxation in a quasi-one-dimensional copper(ii) complex with a pentaheterocyclic triphenodioxazine

A new copper(ii) complex (I) was obtained by the reaction of a sterically crowded 2,4-di-(tert-butyl)-9-chloro-benzo[5,6][1,4]oxazine[2,3-b]phenoxazine bridging ligand with Cu(ii) hexafluoroacetylacetonate.

Field-induced slow magnetic relaxation in low-spin S = 1/2 mononuclear osmium(v) complexes

Photochemical reactions of (PPh4)[OsVI(N)(L)(CN)3] (NO2-OsN) with piperidine and pyrrolidine afforded two osmium(v) hydrazido compounds, (PPh4)[OsV(L)(CN)3(NNC5H10)] ([PPh4]1) and (PPh4)[OsV(L)(CN)3(NNC4H8)] ([PPh4]2), respectively. Their structures consist of isolated, mononuclear distorted octahedral osmium anions that are well-separated from each other by PPh4+. Their low spin S = 1/2 and L = 1 ground state was confirmed by magnetometry and DFT calculations. Interestingly, both compounds exhibit slow magnetic relaxation under a bias dc-field. These osmium(v) complexes are potentially useful building-blocks for the construction of molecule-based architectures with interesting magnetic properties. In contrast, the structurally related (PPh4)[OsIII(L)(CN)3(NH3)] ([PPh4]3), which also has a low-spin S = 1/2 ground state but with a different electronic configuration (5d5), does not exhibit slow magnetic relaxation, due to the absence of any orbital moment (L = 0). Furthermore, the structurally different osmium(v) hydrazido compound reported by Meyer, [OsV(tpy)(Cl)2(NNC5H10)](PF6) (4[PF6]), also does not exhibit slow magnetic relaxation due possibly to a change in magnetic anisotropy from axial for [PPh4]1 and [PPh4]2 to planar.

A single-ion single-electron cerrous magnet

Herein, we present monometallic Ln(iii) complexes [L₃Ln(NO₃)₃] [where Ln = Ce (1) and La (2)] assembled from a simple reaction of the respective lanthanide nitrate hydrate and a bulky phosphonic diamide ^tBuPO(NHⁱPr)₂ ligand (L), where complex 1 behaves as a single-ion single-electron magnet under a small applied magnetic field. The Ce(iii) ion occupies a nine-coordinate distorted muffin-like coordination environment. The combination of direct and Raman process dominates the relaxation dynamics in 1 under the applied dc field. The low-temperature measurements performed with oriented crystals on a micro-SQUID setup exhibits strong tunnelling at zero-field, consistent with the theoretical results where strong mixing of the ground state with higher excited m_J levels is detected and also throws additional insights on the relaxation dynamics of 1. Ab initio calculations have been performed to understand the origin of anisotropy and models have been proposed for future directions.

Slow magnetic relaxation in a {EuCu5} metallacrown

A {Eu^IIICu₅} metallacrown displays field-induced slow magnetic relaxation, in which the Eu^III with diamagnetic ground state enhances the relaxation rates.

Slow magnetic relaxation in Ni–Ln (Ln = Ce, Gd, Dy) dinuclear complexes

Unusual magnetic behaviour is observed in compounds with three Cl ligands in fac-mode coordination to dysprosium, cerium and even gadolinium.

Closing the Circle of the Lanthanide-Murexide Series: Single-Molecule Magnet Behavior and Near-Infrared Emission of the NdIII Derivative

Up to now, even if murexide-based complexometric studies are performed with all 3d or 4f ions, the crystal structures of the light-lanthanide derivatives of the lanthanide-murexide series are unknown. In this work, we report the crystal structure of the NdIII derivative named NdMurex. Contrary to all known complexes of the 3d or 4f series, a dimeric compound was obtained. As for its already reported DyIII and YbIII parents, the NdIII complex responsible for the color-change behaves as a single-molecule magnet (SMM). This behavior was observed on both the crystalline (NdMurex: Ueff = 6.20(0.80) K, 4.31 cm−1; τ0 = 2.20(0.92) × 10−5 s, Hdc = 1200 Oe) and anhydrous form (NdMurexAnhy: Ueff = 6.25(0.90) K, 4.34 cm−1; τ0 = 4.85(0.40) × 10−5 s, Hdc = 1200 Oe). The SMM behavior is reported also for the anhydrous CeIII derivative (CeMurexAnhy: Ueff = 5.40(0.75) K, 3.75 cm−1; τ0 = 3.02(1.10) × 10−5 s, Hdc = 400 Oe). The Near-Infrared Emission NIR emission was observed for NdMurexAnhy and highlights its bifunctionality.

Structural diversity and photo-physical and magnetic properties of dimeric to 1D polymeric coordination polymers of lighter lanthanide(iii) dinitrobenzoates

Single crystal diffraction studies reveal the formation of the following 10 new complexes of lighter Ln(iii) ions with general formulas {[Ln(μ2-L1)3·(H2O)2]·H2O}n (Ln = Nd (1) and Eu (2)), [Nd(μ2-L2)2·(CH3COO)·(H2O)2]n (3), [Ln2(μ2-L2)5·(L2)·(H2O)4]n (Ln = Sm (4), Ce (5), and Pr (6)), [La2(μ2-L2)6·(H2O)3·(DMF)]n (7) (DMF = dimethylformamide), [Ln(μ2-L2)2·(L2)·(H2O)3]2 (Ln = Eu (8) and Gd (9)) and [Gd(L2)·(CH3COO)2·(H2O)2]2 (10), where L1 and L2 are anions of 3,5- and 2,4-dinitrobenzoic acid, respectively. Complexes 1-7 are 1D coordination polymers, while 8-10 are dinuclear complexes. The luminescence properties of Nd(iii) and Eu(iii) analogues displayed metal-centred emission with L1 exhibiting weak but more efficient sensitization than L2. A study of the magnetic properties of the compounds clearly demonstrated the field-induced single ion magnet behaviour of the Nd(iii) compounds 1 and 3. Their behaviour has been compared to previously reported analogous Nd(iii) complexes and the role of the lattice solvent and polymorphism on the magnetic behaviour has been evaluated.

A novel trigonal propeller-shaped hybrid tri-neodymium-polyoxometalate exhibiting single-molecule magnet behavior

A trigonal propeller-shaped hybrid polyoxometalate (POM) (NH₂Me₂)₃{[Nd(Mo₄O₁₃)(DMF)₄]₃(BTC)₂}·8DMF (1; BTC = 1,3,5-benzenetricarboxylate) has been synthesized and structurally characterized. The planar {Mo₄} segment is tailored from the precursor Lindqvist polyoxoanion [Mo₆O₁₉]^2- firstly, and plays a key role in the reassembly of 1. Furthermore, the magnetic studies reveal that 1 shows single-molecule magnet (SMM) behavior.

A series of Ln2 complexes based on an 8-hydroxyquinoline derivative: slow magnetization relaxation and photo-luminescence properties

A series of Ln₂ complexes display slow magnetization relaxation and photo-luminescence properties.

Regulating the luminescent and magnetic properties of rare-earth complexes with β-diketonate coligands

By introducing different β-diketonate coligands, Dy₂ complexes exhibit different SMM behaviors.

A [Ce21] keplerate

The solvothermal reaction between Ce(NO₃)₃·6H₂O, 2-amino-isobutyric acid, 2-hydroxy-1-naphthaldehyde and 2-amino-2-methyl-1,3-propanediol in MeOH, in the presence of base, leads to the formation of a unique [CeCe ] keplerate cage.

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)₃Mn≡N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation.

Crystal structure of hexa-kis-(di-methyl-formamide-κO)manganese(II) deca-kis-(di-methyl-formamide)-1κ(5) O,2κ(5) O-[μ-octa-deca-tungstodiphosphato(V)-κO:κO']dimanganate(II) di-methyl-formamide disolvate

The crystal structure of the title compound, [Mn(C3H7NO)6][{Mn(C3H7NO)5}2(μ-P2W18O62)]·2C3H7NO, reveals that the Wells-Dawson-type polyanion [P2W18O62](6-), through terminal O atoms from the belts, bridges two Mn(II) octa-hedral complexes. In the complex anion [{Mn(dmf)5}2(μ-P2W18O62)](2-), located around a twofold rotation axis, the Mn(II) ions are coordinated by five O atoms from di-methyl-formamide (dmf) ligands and to a terminal O atom from the [P2W18O62](6-) polyanion. Another Mn(II) ion, located on an inversion centre, is coordinated by six O atoms from the dmf ligands and forms the [Mn(dmf)6](2+) cation. The crystal components are connected through numerous weak C-H⋯O hydrogen bonds to construct a three-dimensional network.

An unprecedented zero field neodymium(iii) single-ion magnet based on a phosphonic diamide

A pseudo-D_5h symmetric Nd(iii)-complex exhibits zero-field SIM behavior as a result of a strong axial crystal field, stabilization of the rare m_J = |±9/2〉 ground state, and small transverse anisotropy.

Unprecedented hexagonal bipyramidal single-ion magnets based on metallacrowns

Two novel Ln(iii) (Ln = Ce or Nd) complexes based on [15-MC-6] (MC = metallacrown) and phosphine oxide are reported. Both of them feature a hexagonal bipyramidal LnO₈ geometry (D_6h) and behave as single-ion magnets.

A series of organic–inorganic hybrid materials consisting of flexible organic amine modified polyoxomolybdates: synthesis, structures and properties

A series of hybrid materials consisting of Tris[(2-pyridyl)methyl]amine modified polyoxomolybdates were obtained and some complexes have efficient photocatalytic activities to degrade pararosaniline hydrochloride dye molecules.