Contribution of Gd Mössbauer data to the study of the magnetic interaction in heterodinuclear 3d-Gd (3d = Cu, Ni) coordination complexes.

The valence shell of the gadolinium element corresponds to 4f 5d 6s, so that the trivalent Gd ion possesses free 5d and 6s orbitals. It has been previously shown by CASSCF methods that the 5d orbitals, along with the 6s Gd orbitals, which are expected to be unoccupied, present a slight spin density and that the magnetic behaviour of Cu-Gd complexes can only be reproduced if the 5d Gd orbitals are taken into account in the active space. Gd Mössbauer isomer shifts of 3d-Gd complexes, LCuGd(NO), LNiGd(NO)·acetone, LCu(acetone)Gd(NO), LNi(HO)Gd(NO) where L and L are hexadentate Schiff base ligand, are almost unchanged (0.

Influence of ancillary ligands and solvents on the nuclearity of Ni-Ln complexes.

A Schiff base ligand resulting from the reaction of ovanillin and 2,2-dimethyl-1,3-diaminopropane allows the preparation of hetero-dinuclear [Ni-Ln] or -trinuclear [Ni-Ln-Ni] complexes. Although empirical parameters for rationalizing the strength of the ferromagnetic Ni-Gd interaction have already been discussed in several papers, no systematic study has been devoted to the control of the nuclearity of such complexes. With the help of structural determinations, we demonstrate the role of solvent and of the nature of ancillary ligands, linked to the Ln ions, in nuclearity.

Effects of the Exchange Coupling on Dynamic Properties in a Series of CoGdCo Complexes.

Reaction of 2-hydroxy3-methoxybenzaldehyde ( o-vanillin) with 1,1,1-tris(aminomethyl)ethane, Me-C(CHNH), or with N, N', N''-trimethylphosphorothioic trihydrazide, P(S)[NMe-NH], yields two tripodal LH and LH ligands which are able to give cationic heterotrinuclear [LCoGdCoL] or [LCoGdCoL] complexes. The Co ions are coordinated to these deprotonated ligands in the inner NO site, while the Gd ion is linked to three deprotonated phenoxo oxygen atoms of two anionic [LCo] or [LCo] units. Air oxidation of these trinuclear complexes does not yield complexes associating Co and Gd ions.

Ni-Ln complexes with o-vanillin as the main ligand: syntheses, structures, magnetic and magnetocaloric properties.

ortho-Vanillin in the presence of nickel and lanthanide ions yields three types of heteronuclear Ni-Gd complexes, ranging from dinuclear to tetranuclear defect dicubane complexes, as demonstrated by their structural determinations. These complexes are dependent on the solvents used during the reaction processes and on the retained lanthanide ions, as characterized by an increase in their Lewis acid character on moving from lighter to heavier lanthanide ions. Intramolecular ferromagnetic Ni-Gd interactions are present in the heterodinuclear Ni-Gd entities, whereas ferromagnetic Ni-Ni and Ni-Gd interactions dominate above 2 K in the tetranuclear Ni-Gd compounds, devoid of any Gd-Gd interaction.

Electronic Structure and Magnetic Anisotropy in Lanthanoid Single-Ion Magnets with C Symmetry: The Ln(trenovan) Series.

We report the syntheses and the magnetic characterization of a new series of lanthanide complexes, in which the Ce, Nd, Gd, Dy, Er, and Yb derivatives show single-molecule magnet behavior. These complexes, named Ln(trenovan), where Htrenovan is tris(((3-methoxysalicylidene)amino)ethyl)amine, exhibit trigonal symmetry and the Ln(III) ion is heptacoordinated. Their molecular structure is then very similar to that of the previously reported Ln(trensal) series, where Htrensal is 2,2',2″-tris(salicylideneimino)triethylamine.

Effect of Ligand Substitution around the Dy(III) on the SMM Properties of Dual-Luminescent Zn-Dy and Zn-Dy-Zn Complexes with Large Anisotropy Energy Barriers: A Combined Theoretical and Experimental Magnetostructural Study.

The new dinuclear Zn(II)-Dy(III) and trinuclear Zn(II)-Dy(III)-Zn(II) complexes of formula [(LZnBrDy(ovan) (NO3)(H2O)](H2O)·0.5(MeOH) (1) and [(L(1)ZnBr)2Dy(MeOH)2](ClO4) (3) (L and L(1) are the dideprotonated forms of the N,N'-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato and 2-{(E)-[(3-{[(2E,3E)-3-(hydroxyimino)butan-2-ylidene ]amino}-2,2-dimethylpropyl)imino]methyl}-6-methoxyphenol Schiff base compartmental ligands, respectively) have been prepared and magnetostructurally characterized. The X-ray structure of 1 indicates that the Dy(III) ion exhibits a DyO9 coordination sphere, which is made from four O atoms coming from the compartmental ligand (two methoxy terminal groups and two phenoxido bridging groups connecting Zn(II) and Dy(III) ions), other four atoms belonging to the chelating nitrato and ovanillin ligands, and the last one coming to the coordinated water molecule.

Relaxation Dynamics and Magnetic Anisotropy in a Low-Symmetry Dy(III) Complex.

The magnetic behaviour of a Dy(LH)3 complex (LH(-) is the anion of 2-hydroxy-N'-[(E)-(2-hydroxy-3-methoxyphenyl)methylidene]benzhydrazide) was analysed in depth from both theoretical and experimental points of view. Cantilever torque magnetometry indicated that the complex has Ising-type anisotropy, and provided two possible directions for the easy axis of anisotropy due to the presence of two magnetically non-equivalent molecules in the crystal. Ab initio calculations confirmed the strong Ising-type anisotropy and disentangled the two possible orientations.

Does the Sign of the Cu-Gd Magnetic Interaction Depend on the Number of Atoms in the Bridge?

Several theoretical investigations with CASSCF methods confirm that the magnetic behavior of Cu-Gd complexes can only be reproduced if the 5d Gd orbitals are included in the active space. These orbitals, expected to be unoccupied, do present a low spin density, which is mainly due to a spin polarization effect. This theory is strengthened by the experimental results reported herein.

Analysis of the Role of Peripheral Ligands Coordinated to Zn(II) in Enhancing the Energy Barrier in Luminescent Linear Trinuclear Zn-Dy-Zn Single-Molecule Magnets.

Three new Dy complexes have been prepared according to a complex-as-ligand strategy. Structural determinations indicate that the central Dy ion is surrounded by two LZn units (L(2-) is the di-deprotonated form of the N2 O2 compartmental N,N'-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato) Schiff base. The Dy ions are nonacoordinate to eight oxygen atoms from the two L ligands and to a water molecule.

On the importance of ferromagnetic exchange between transition metals in field-free SMMs: examples of ring-shaped hetero-trimetallic [(LnNi2){W(CN)8}]2 compounds.

Rare cases of genuine (i.e. field-free) SMM have been found for mixed 3d-4f-5d ring-shaped compounds with Tb(III) (Ueff/kB = 23.

Determination of magnetic anisotropy in the LnTRENSAL complexes (Ln = Tb, Dy, Er) by torque magnetometry.

We report here a study about the magnetic anisotropy of the LnTRENSAL complexes (Ln = Tb, Dy, Er) performed by using cantilever torque magnetometry and electron paramagnetic resonance. For all of the compounds, we extracted a set of crystal-field parameters to obtain the energy-level splitting of the ground-state multiplet.

Antiferromagnetic Cu-Gd interactions through an oxime bridge.

The copper complex of a polydentate non-symmetrical Schiff base ligand [LCu]2, prepared by template synthesis, has been reacted with the series of lanthanide ions. This complex used as a ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions and, according to the Ln ion, three types of complexes are obtained. From La to Eu, trinuclear [(LCu)2Ln(NO3)3] complexes with a double phenoxo-oximato bridge were isolated.

Synthesis, structural characterization, and magnetic properties of a copper-gadolinium complex derived from a hydroxybenzohydrazide ligand.

The reaction of hydroxybenzohydrazide with o-vanillin yields 2-hydroxy-N'-[(2-hydroxy-3-methoxyphenyl)methylidene]benzohydrazide (LH3), a ligand that is able to give mononuclear and tetranuclear copper complexes but also to associate copper and gadolinium ions in a Cu2-Gd2 heterotetranuclear complex. This synthesis is successful if the Gd ions, which are acidic in protic solvents, are introduced in a basic methanol solution of the mononuclear copper complex. In the absence of piperidine, the addition of Gd ions to a methanol solution of the mononuclear copper complex only yields a tetranuclear cubane-type copper complex.

Beyond the anisotropy barrier: slow relaxation of the magnetization in both easy-axis and easy-plane Ln(trensal) complexes.

We present a spectroscopic and magnetic (both static and dynamic) characterization of two isostructural Dy and Er complexes evidencing that, despite the different types of magnetic anisotropy, the two molecules show similar slow relaxation of the magnetization in a static magnetic field.

Interplay of strongly anisotropic metal ions in magnetic blocking of complexes.

The key characteristic of single-molecule magnets (SMMs) is the anisotropy-induced blocking barrier, which should be as efficient as possible, i.e., to be able to provide long magnetic relaxation times at elevated temperatures.

Field and dilution effects on the slow relaxation of a luminescent DyO9 low-symmetry single-ion magnet.

A mononuclear Dy(III) complex with a non-Schiff base compartmental ligand has been prepared and characterised by X-ray crystallography and ac magnetic susceptibility measurements. The complex exhibits SIM behaviour induced by dilution and/or magnetic field with two thermally activated relaxation processes.

Tetranuclear [Co-Gd]2 complexes: aiming at a better understanding of the 3d-Gd magnetic interaction.

Tetranuclear [Co-Gd](2) complexes were prepared by using trianionic ligands possessing amide, imine, and phenol functions. The structural determinations show that the starting cobalt complexes present square planar or square pyramid environments that are preserved in the final tetranuclear [Co-Gd](2) complexes. These geometrical modifications of the cobalt coordination spheres induce changes in the cobalt spin ground states, going from S = 1/2 in the square planar to S = 3/2 for the square pyramid environments.

Chiral crystallization of a heterodinuclear Ni-Ln series: comprehensive analysis of the magnetic properties.

Four heterodinuclear (H(2)O)(2)NiL-Ln(NO(3))(3) complexes (Ln = Tb, Dy, Er, Yb) with a double phenoxo bridge coming from the dideprotonated Schiff-base ligand are synthesized and characterized by crystal and powder X-ray diffraction studies. This series of compounds devoid of any chiral center, crystallizes in a noncentrosymmetric space group P2(1), as the previously described (H(2)O)(2)NiL-Gd(NO(3))(3) equivalent. All four complexes are ferromagnetically coupled.

Pentacoordinate Ni(II) complexes: preparation, magnetic measurements, and ab initio calculations of the magnetic anisotropy terms.

Two novel mononuclear five-coordinate nickel complexes with distorted square-pyramidal geometries are presented. They result from association of a tridentate "half-unit" ligand and 6,6'-dimethyl-2,2'-bipyridine according to a stepwise process that highlights the advantage of coordination chemistry in isolating an unstable tridentate ligand by nickel chelation. Their zero-field splittings (ZFS) were studied by means of magnetic data and state-of-the-art ab initio calculations.

Experimental evidence and DFT studies of next-nearest-neighbor magnetic interactions through diamagnetic 3d and 4d ions.

The copper template effect allows the preparation of tridentate ligands that chelate copper ions, leaving unoccupied the fourth basal coordination position and at least one axial position of the copper coordination polyhedron. Two such cationic complexes, [LCu](+) and [L(1)Cu](+) (L(-) = 2-{(E)-[(2-aminoethyl)imino]methyl}phenoxo] and L(1-) = 2-{(E)-[(2-aminopropyl)imino]methyl}phenoxo), react with diamagnetic polycyanometalate tectons such as Ni(CN)(4)(2-) or Ag(CN)(2)(-) to yield different neutral 1D complexes. In {[(LCu)(2)Ni(CN)(4)]}(n) (1) the four cyano nitrogen atoms are involved in coordination with copper ions in such a manner that each copper atom is pentacoordinated and linked to two cyano functions that occupy axial and equatorial coordination positions.

Magnetic anisotropy in Ni(II)-Y(III) binuclear complexes: on the importance of both the first coordination sphere of the Ni(II) ion and the Y(III) ion belonging to the second coordination sphere.

The synthesis of a new Ni(II)-Y(III) binuclear complex with a marked elongation axis in the first coordination sphere of the Ni(II) ion is presented. Its zero-field splitting (ZFS) is studied by means of magnetic data and state-of-the-art ab initio calculations. A good agreement between the experimental and theoretical ZFS parameter values is encountered, validating the whole approach.

Metalloligands for designing single-molecule and single-chain magnets.

2-Hydroxy-N-{2-[2-hydroxyethyl)amino]ethyl}benzamide (L¹H₃) and 2-hydroxy-N-{2-[2-hydroxybutyl)amino]ethyl}benzamide (L²H₃) ligands coordinate to copper ions to give anionic metalloligands, L¹Cu⁻ and L²Cu⁻, after deprotonation of their amide, alcohol and phenol functions. In presence of ancillary ligands as diketones, these metalloligands react with lanthanide salts to yield tetranuclear [Cu-Ln]₂ complexes while in presence of lanthanide salts alone, L¹Cu⁻ gives 1D chains of tetranuclear entities linked through the Ln ions. The micro-SQUID data evidence the SMM behavior of the tetranuclear Tb complexes and the SCM behavior of the Tb chain derivative.

A heterotrimetallic 3d-3d'-4f single chain magnet constructed from anisotropic high-spin 3d-4f nodes and paramagnetic spacers.

By connecting [LCuTb](3+) nodes with [Fe(CN)₆]³⁻ spacers a 1-D coordination polymer with slow relaxation of magnetization is obtained (L²⁻ is the N,N'-propylene-bis(3-methoxysalicylideneiminato) anion).

New binuclear Mn(II) and Fe(II) complexes supported by 1,4,8-triazacycloundecane.

Two new binuclear metal complexes supported by 1,4,8-triazacycloundecane (tacud) are reported. [Fe(2)(tacud)(2)(μ-Cl)(2)Cl(2)] (1) and [Mn(2)(tacud)(2)(μ-Cl)(2)Cl(2)] (2) are isomorphs consisting of bis(μ-chloro) bridged metal centers along with terminal chloro groups and tacud ligands. Both compounds 1 and 2 crystallize in the P1 space group.