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.

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.

Insights into the Spin Dynamics of Mononuclear Cerium(III) Single-Molecule Magnets

Four novel Ce^III mononuclear complexes of formulas [Ce(ntfa)₃(MeOH)₂] (1), [Ce(ntfa)₃(5,5'-Me₂bipy)] (2), [Ce(ntfa)₃(terpy)] (3), and [Ce(ntfa)₃(bipy)₂] (4), where ntfa = 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionato, 5,5'-Me₂bipy = 5,5'-dimethyl-2,2'-dipyridyl, terpy = 2,2':6',2″-terpyridine, and bipy = 2,2'-bipyridine, have been synthesized and structurally characterized with Ce^III displaying coordination numbers of 8, 8, 9, and 10, respectively. Magnetic measurements indicate that all the complexes show a field-induced single-ion magnet behavior under a small applied dc field. The magnetic analysis shows the relevance of the different spin relaxation mechanisms in the magnetic relaxation of the Ce^III compounds, with special emphasis on the local-mode process. Multiconfigurational calculations were also performed to get more information on the axiality of the compounds.

Experimental and theoretical insights into Co-Ln magnetic exchange and the rare slow-magnetic relaxation behavior of [CoII2Pr]2+ in a series of linear [CoII2Ln]2+ complexes

We herein report a series of near-linear trinuclear complexes [Co₂Ln(HL)₄(NO₃)](NO₃)₂ (where HL = (2-methoxy-6-[(E)-2'-hydroxymethyl-phenyliminomethyl]-phenolate) with Ln(III) = La (1), Ce (2), Pr (3)). For the comparative study, we have also included the recently reported analogous complexes of Gd(III), Tb(III), and Dy(III) (complexes 4-6) with the same H₂L ligand. The experimental nature of the dc magnetic susceptibilities profile and an empirical approach revealed that the magnetic exchange interaction between Co(II) and Ln(III) having <4f⁷ (complexes 2 and 3) is antiferromagnetic while the dominant interaction between Co(II) and Ln(III) having ≥4f⁷ (complexes 4-6) is ferromagnetic. Dynamic magnetic relaxation studies on complexes 1-3 revealed the field induced single-molecule magnetic (SMM) behavior of 1 and 3 with effective energy barriers of 10.65 K and 15.03 K respectively, for magnetic relaxation. To the best of our knowledge, 3d-Pr(III) based zero or field induced SMMs have not been reported to date. CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations on the X-ray structures of complexes 1-6, followed by POLY_ANISO simulations, estimated the magnetic exchange coupling constants J_Co-Ln and J_Co-Co and also rationalized our experimental findings for the dynamic magnetic properties.

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.

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.

Enhancement of magnetic relaxation properties with 3d diamagnetic cations in [ZnIILnIII] and [NiIILnIII], LnIII= Kramers lanthanides

Comparison between two series of [Ni^IILn^III] and [Zn^IILn^III] dimers reveals lower intermolecular interactions for the square-planar Ni^IIderivatives that favour an induced SIM response. Some unusual Ce^III, Nd^IIIand Yb^IIISIMs are reported.

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.

Heterometallic ZnII⁻LnIII⁻ZnII Schiff Base Complexes with Linear or Bent Conformation-Synthesis, Crystal Structures, Luminescent and Magnetic Characterization

A series of racemic, heteronuclear complexes [Zn₂Nd(ac)₂(HL)₂]NO₃·3H₂O (1), [Zn₂Sm(ac)₂(HL)₂]NO₃·3CH₃OH·0.3H₂O (2), [Zn₂Ln(ac)₂(HL)₂]NO₃·5.33H₂O (3–5) (where HL is the dideprotonated form of N,N′-bis(5-bromo-3-methoxysalicylidene)-1,3-diamino-2-propanol, ac = acetate ion, and Ln = Eu (3), Tb (4), Dy (5), respectively) with an achiral multisite coordination Schiff base ligand (H₃L) were synthesized and characterized. The X-ray crystallography revealed that the chirality in complexes is centered at lanthanide(III) ions due to two vicinally located μ-acetato-bridging ligands. The presented crystals have isoskeletal coordination units but they crystallize in monoclinic (1, 2) or trigonal crystal systems (3–5) with slightly different conformation. In 1 and 2 the Zn^II–Ln^III–Zn^II coordination core is linear, whereas in isostructural crystals 3–5 the chiral coordination cores are bent and lie on a two-fold axis. The complexes 1, 3–5 show a blue emission attributed to the emission of the ligand. For Zn^II₂Sm^III complex (2) the characteristic emission bands of f-f* transitions were observed. The magnetic properties for compounds 1, 4 and 5 are characteristic for the paramagnetism of the corresponding lanthanide(III) ions.

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 [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 new strongly paramagnetic cerium-containing microporous MOF for CO2 fixation under ambient conditions

A new microporous Ce₂NDC₃ MOF has been synthesized solvothermally and it displayed strong paramagnetism and high catalytic efficiency in CO₂ fixation under ambient conditions for the synthesis of cyclic carbonates.

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.

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.

Slow magnetic relaxation of light lanthanide-based linear LnZn2 trinuclear complexes

Four isostructural Zn(ii)–Ln(iii)–Zn(ii) trinuclear complexes were synthesized using light lanthanide ions as magnetic centers, of which Ce(iii) and Nd(iii) complexes behaved as single-molecule magnets.

Structural switching from paramagnetic to single-molecule magnet behaviour of LnZn2 trinuclear complexes

Single molecule magnet (SMM) behaviors of Zn–Ln–Zn complexes were switched by slight changing of the molecular structures.