Jean-Pascal Sutter

Analytical Determination of the {Ln–Aminoxyl Radical} Exchange Interaction Taking into Account Both the Ligand‐Field Effect and the Spin–Orbit Coupling of the Lanthanide Ion (Ln=DyIII and HoIII)

Numerous compounds in which a paramagnetic LnIII ion is in an exchange interaction with a second spin carrier, such as a transition metal ion or an organic radical, have been described. However, except for GdIII, very little has been reported about the magnitude of the interactions. Indeed, for these ions both the ligand-field effects and the exchange interactions between the magnetic centers become relevant in the same temperature range; this makes the analysis of the magnetic behavior of such compounds more difficult. In this study, quantitative analyses of the thermal variations of the static isothermal initial magnetic susceptibility measured on powdered samples of the [Ln(NO3)3-[organic radical]2] (Ln = DyIII and HoIII) compounds were performed. The ligand-field effects on the Ln ions were taken into account, and the exchange interactions within a molecule were treated exactly within an appropriate Racah formalism. Values of the intramolecular [Ln-aminoxyl radical] exchange parameter have thus been rigorously deduced for both the Dy Kramers and Ho non-Kramers ion-based compounds. Ferromagnetic [Ln-radical] interactions are found for both the Dy and Ho derivatives with J = 8 cm(-1) and J = 4.5 cm(-1), respectively.

Enhanced Ion Anisotropy by Nonconventional Coordination Geometry: Single-Chain Magnet Behavior for a [{FeIIL}2{NbIV(CN)8}] Helical Chain Compound Designed with Heptacoordinate FeII

Nonconventional heptacoordination in combination with efficient magnetic exchange coupling is shown to yield a 1-D heteronuclear {Fe(II)Nb(IV)} compound with remarkable magnetic features when compared to other Fe(II)-based single chain magnets (SCM). Cyano-bridged heterometallic {3d-4d} and {3d-5d} chains are formed upon assembling Fe(II) bearing a pentadentate macrocycle as the blocking ligand with octacyano metallates, [M(CN)(8)](4-) (M = Nb(IV), Mo(IV), W(IV)). X-ray diffraction (single-crystal and powder) measurements reveal that the [{(H(2)O)Fe(L(1))}{M(CN)(8)}{Fe(L(1))}](infinity) architectures consist of isomorphous 1-D polymeric structures based on the alternation of {Fe(L(1))}(2+) and {M(CN)(8)}(4-) units (L(1) stands for the pentadentate macrocycle). Analysis of the magnetic susceptibility behavior revealed cyano-bridged {Fe-Nb} exchange interaction to be antiferromagnetic with J = -20 cm(-1) deduced from fitting an Ising model taking into account the noncollinear spin arrangement. For this ferrimagnetic chain a slow relaxation of its magnetization is observed at low temperature revealing a SCM behavior with Delta/k(B) = 74 K and tau(0) = 4.6 x 10(-11) s. The M versus H behavior exhibits a hysteresis loop with a coercive field of 4 kOe at 1 K and reveals at 380 mK magnetic avalanche processes, i.e., abrupt reversals in magnetization as H is varied. The origin of these characteristics is attributed to the combination of efficient {Fe-Nb} exchange interaction and significant anisotropy of the {Fe(L(1))} unit. High field EPR and magnetization experiments have revealed for the parent compound [Fe(L(1))(H(2)O)(2)]Cl(2) a negative zero field splitting parameter of D approximately = -17 cm(-1). The crystal structure, magnetic behavior, and Mossbauer data for [Fe(L(1))(H(2)O)(2)]Cl(2) are also reported.

Synthesis and Magnetic Behavior of Rare-Earth Complexes with N,O-Chelating Nitronyl Nitroxide Triazole Ligands: Example of a [GdIII{Organic Radical}2] Compound with anS=9/2 Ground State

A ferromagnetically coupled gadolinium–radical compound is described. A series of three lanthanide complexes of general formula [Ln(organic radical)2(NO3)3] (Ln =Y3+, La3+, and Gd3+, shown on the right) have been synthesized. With the paramagnetic GdIII a ferromagnetic interaction with the ligands was found, which gives rise to a S = 9/2 ground-state spin.

Preparation, crystal structures, and magnetic features for a series of dinuclear (Ni(II)Ln(III)) Schiff-base complexes: evidence for slow relaxation of the magnetization for the Dy(III) derivative

A series of dinuclear [Ni(II)Ln(III)] Schiff-base complexes (using a Schiff-base dicompartmental ligand derived from o-vanillin [H(2)valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)]) with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and a hydroxo-bridged tetranuclear [Ni(II)Yb(III)] are reported. The crystal structures have been solved for 10 dinuclear complexes revealing four arrangements for the dinuclear units, which are modulated by the coordinated solvent molecules and the nitrato-anion interactions. The magnetic behaviors have been investigated, and the nature of the Ni(II)-Ln(III) exchange interaction has been emphasized by comparison with the behavior of the related [Zn(II)Ln(III)] derivatives. This allowed for establishing that the interaction within these compounds is antiferromagnetic with the 4f ions of the beginning of the Ln series and turns ferromagnetic from Gd(III) toward the end of the series. AC susceptibility investigations clearly show the occurrence of slow relaxation processes of the magnetization close to 2 K for the dinuclear [Ni(II)Dy(III)] complex.

Origin of the Magnetic Anisotropy in Heptacoordinate Ni-II and Co-II Complexes

The nature and magnitude of the magnetic anisotropy of heptacoordinate mononuclear Ni(II) and Co(II) complexes were investigated by a combination of experiment and ab initio calculations. The zero-field splitting (ZFS) parameters D of [Ni(H(2)DAPBH)(H(2)O)(2)](NO(3))(2)⋅2 H(2)O (1) and [Co(H(2)DAPBH)(H(2)O)(NO(3))](NO(3)) [2; H(2)DAPBH = 2,6-diacetylpyridine bis- (benzoyl hydrazone)] were determined by means of magnetization measurements and high-field high-frequency EPR spectroscopy. The negative D value, and hence an easy axis of magnetization, found for the Ni(II) complex indicates stabilization of the highest M(S) value of the S = 1 ground spin state, while a large and positive D value, and hence an easy plane of magnetization, found for Co(II) indicates stabilization of the M(S) = ±1/2 sublevels of the S = 3/2 spin state. Ab initio calculations were performed to rationalize the magnitude and the sign of D, by elucidating the chemical parameters that govern the magnitude of the anisotropy in these complexes. The negative D value for the Ni(II) complex is due largely to a first excited triplet state that is close in energy to the ground state. This relatively small energy gap between the ground and the first excited state is the result of a small energy difference between the d(xy) and d(x(2)-y(2)) orbitals owing to the pseudo-pentagonal-bipyramidal symmetry of the complex. For Co(II), all of the excited states contribute to a positive D value, which accounts for the large magnitude of the anisotropy for this complex.

Further insight into the mechanism of the palladium induced carbocyclisation of aryl rings.

Abstract The depalladation of several cyclopalladated compounds, containing two inserted diphenlacetylenes in the PdC bond has been acheived by treatment with either a neutral coordinating ligand such as pyridine, triphenylphosphine or maleic anhydride. This has afforded carbocyclic compounds where one or two of the aryl groups of the butadienyl chain have been annulated as a result of CC bond formation. These demetallation reactions could be performed under rather mild conditions which enabled the characterisation of an intermediate which in turn provided valuable information about the mechanism of the palladium mediated carbocyclisation reaction.

Synthesis, X-ray crystal structures and magnetic properties of Cu(II)(NITpPy)2[N(CN)2]2·solv (NITpPy=nitronyl nitroxide radical, solv=H2O or CH3CN). From discrete molecules to 2-D polymeric coordination compounds

Abstract The synthesis, X-ray crystal structures and magnetic properties of five new copper(II) complexes containing nitroxide radicals Cu(NITpPy)2(NO3)2 (1), Cu(NITpPy)2(CH3COO)2 (2), Cu(NITpPy)2[N(CN)2]2·(H2O)2 (3), Cu(NITpPy)2[N(CN)2]2·3CH3CN (4) and Cu(NITpPy)2[N(CN)2]2·2CH3CN (5) are reported. Compounds 1–3 consists of discrete molecules in the solid state, but in compounds 4 and 5 the Cu(NITpPy)22+ units are connected through N(CN)2− bridging ligands in μ2 coordination developing, respectively, into one-dimensional and two-dimensional polymeric networks. For all compounds, the magnetic properties have been investigated and antiferromagnetic interactions dominate at low temperature.

Ferromagnetic interactions in Mn(II) coordination complex containing nitronyl nitroxide radical and silver–dicyanide anion: structure and magnetic studies of MnII(NITpPy)2[Ag(CN)2]2

Abstract A new complex of formula, Mn(NITpPy)2[Ag(CN)2]2, where NITpPy stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, was synthesized and characterized structurally and magnetically. The Mn atom is in a distorted octahedral geometry. It is coordinated to two organic radicals and [Ag(CN)2]− anions. Each [Ag(CN)2]− unit is μ2 bridging between two adjacent Mn ions yielding infinite 1D chains. Intramolecular ferromagnetic interactions are observed but antiferromagnetic interactions dominate at very low temperature.

1-D hydrogen-bonded organization of hexanuclear {3d-4f-5d} complexes: evidence for slow relaxation of the magnetization for [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2] with Ln = Tb and Dy

Heterometallic {3d-4f-5d} aggregates with formula [{LMe2Ni(H2O)Ln(H2O)4.5}2{W(CN)8}2]·15H2O, (LMe2 stands for N,N′-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato) Schiff-base ligand) with Ln = Gd, Tb, Dy, have been obtained by reacting bimetallic [LMe2Ni(H2O)2Ln(NO3)3] and Cs3{W(CN)8} in H2O. The hexanuclear complexes are organized in 1-D arrays by means of hydrogen bonds established between the solvent molecules coordinated to Ln and the CN ligands of an octacyanometallate moiety. The X-ray structure was solved for the Tb derivative. Magnetic behavior indicates ferromagnetic {W–Ni} and {Ni–Ln} interactions (JNiW = 18.5 cm−1, JNiGd = 1.85 cm−1) as well as ferromagnetic intermolecular interactions mediated by the H-bonds. Dynamic magnetic susceptibility studies reveal slow magnetic relaxation processes for the Tb and Dy derivatives, suggesting SMM type behavior for these compounds.

M(hfac)2(TTF–py)2 (M = CuII, MnII; hfac = hexafluoroacetylacetonate and TTF–py = 4-(2-tetrathiafulvalenyl-ethenyl)pyridine): a new approach for π–d interactions in conducting and magnetic molecule based materials

Abstract The new coordination complexes M(hfac)2(TTF–py)2 (M = CuII, MnII) in which the paramagnetic transition metal and the organic donor are covalently linked through delocalized π system are prepared aiming with a new approach for the occurrence of π–d interactions in conducting and magnetic molecule based materials. The structures, magnetic properties and electrochemical properties were investigated. X-ray structure analysis revealed its structure is favorable for electrical conductivity.