Syntheses, crystal structures, magnetic and luminescence properties of five novel lanthanide complexes of nitronyl nitroxide radical

Modulation of Slow Magnetic Relaxation in Gd(III)-Tetrahalosemiquinonate Complexes

Incorporating lanthanoid(III)-radical magnetic exchange coupling is a possible route to improving the performance of lanthanoid (Ln) single-molecule magnets (SMMs), molecular materials that exhibit slow relaxation and low temperature quantum tunnelling of the magnetization. Complexes of Gd(III) can conveniently be used as model systems to study the Ln-radical exchange coupling, thanks to the absence of the orbital angular momentum that is present for many Ln(III) ions. Two new Gd(III)-radical compounds of formula [Gd(18-c-6)X4 SQ(NO3 )].I3 (18-c-6=18-crown-6, X4 SQ⋅- =tetrahalo-1,2-semiquinonate, 1: X=Cl, 2: X=Br) have been synthesized, and the presence of the dioxolene ligand in its semiquinonate form confirmed by X-ray crystallography, UV-Visible-NIR spectroscopy and voltammetry. Static magnetometry and EPR spectroscopy indicate differences in the low temperature magnetic properties of the two compounds, with antiferromagnetic exchange coupling of JGd-SQ ∼-2.0 cm-1 (Hex =-2JGd-SQ (SGd SSQ )) determined by data fitting. Interestingly, compound 1 exhibits slow magnetic relaxation in applied magnetic fields while 2 relaxes much faster, pointing to the major role of packing effects in modulating slow relaxation of the magnetization.

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)

A series of heterometallic carboxylate 1D polymers of the general formula [Ln^IIICd₂(piv)₇(H₂O)₂]_n·nMeCN (Ln^III = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of Cd^II instead of Zn^II under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with Ln^IIIZn₂ cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.

Enhancing Magnetic Communication between Metal Centres: The Role of s-Tetrazine Based Radicals as Ligands

Although 1,2,4,5-tetrazines or s-tetrazines have been known in the literature for more than a century, their coordination chemistry has become increasingly popular in recent years due to their unique redox activity, multiple binding sites and their various applications. The electron-poor character of the ring and stabilization of the radical anion through all four nitrogen atoms in their metal complexes provide new aspects in molecular magnetism towards the synthesis of new high performing Single Molecule Magnets (SMMs). The scope of this review is to examine the role of s-tetrazine radical ligands in transition metal and lanthanide based SMMs and provide a critical overview of the progress thus far in this field. As well, general synthetic routes and new insights for the preparation of s-tetrazines are discussed, along with their redox activity and applications in various fields. Concluding remarks along with the limitations and perspectives of these ligands are discussed.

Structures and Spectral and Magnetic Properties of a Series of Carbacylamidophosphate Pentanuclear Lanthanide(III) Hydroxo Complexes

A series of pentanuclear lanthanide complexes Ln₅L₆(μ-L)₄(μ₃-OH)₄(μ₄-OH) (Ln^III = Nd, Dy, Ho, Er, Yb; L^- = dimethyl N-benzoylamidophosphate ion, [C₆H₅C(O)-N-P(O)(OCH₃)₂]^-) was obtained by the reaction of sodium dimethyl N-benzoylamidophosphate with the corresponding lanthanide nitrates. The pentanuclear cores formed as a result of self-arrangement and their composition did not depend on the lanthanide ion. The complexes and sodium dimethyl N-benzoylamidophosphate have been characterized by single-crystal X-ray diffraction. The absorption spectra of the complexes were measured at 300 and 4 K. The dysprosium and ytterbium complexes exhibited weak emission in the visible and IR regions, respectively. Temperature dependences of magnetic susceptibility (χ_M) of the dysprosium, holmium, and erbium compounds were studied. It was found that χ_M vs T dependences were governed by the crystal field splitting effects with the Δ parameter being in the range 5-17 cm^-1. Slow magnetic relaxation was found for the dysprosium complex by ac magnetic measurements, while no significant out-of-phase signals were detected for holmium and erbium complexes.

A family of lanthanide compounds based on nitronyl nitroxide radicals: synthesis, structure, magnetic and fluorescence properties

A series of lanthanide nitronyl nitroxide radical compounds have been synthesized and characterized structurally and magnetically.

Unusual Gd-nitronyl nitroxide antiferromagnetic coupling and slow magnetic relaxation in the corresponding Tb analogue

The lanthanide-radical approach has been applied to construct three isomorphous mononuclear lanthanide complexes [Ln(hfac)3(NIT2-PyOCH3)] (Ln(III) = Gd , Tb , Er ) in which the nitronyl nitroxide radical NIT2-PyOCH3 (NIT2-PyOCH3 = 2-(3'-methoxy-2'-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) acts as a tridentate chelating ligand via the pyridyl nitrogen atom, the oxygen atom from the NO group and the oxygen atom from the methoxy group. The central lanthanide ions are nine-coordinated and their coordination geometry can be considered as an intermediate between muffin and spherical capped square antiprisms. Interestingly, an unusual antiferromagnetic interaction was observed between the Gd(iii) and the coordinated nitronyl nitroxide radical in complex . Moreover, ac magnetic susceptibilities display frequency-dependent out-of-phase signals in the case of the anisotropic Tb complex, indicating magnetic relaxation behavior.

Magnetic exchange in {GdIII–radical} complexes: method assessment, mechanism of coupling and magneto-structural correlations

Which functional is best suit to calculate Js in lanthanide–radical pairs?