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The valence shell of the gadolinium element corresponds to 4f7 5d1 6s2, so that the trivalent GdIII 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 CuII–GdIII complexes can only be reproduced if the 5d Gd orbitals are taken into account in the active space. 155Gd Mössbauer isomer shifts of 3d–Gd complexes, L1CuGd(NO3)3, L1NiGd(NO3)3·acetone, L2Cu(acetone)Gd(NO3)3, L2Ni(H2O)2Gd(NO3)3 where L1 and L2 are hexadentate Schiff base ligand, are almost unchanged (0.62–0.64 mm s−1 relative to 155Eu/SmPd3 source) though the values are slightly smaller than a typical ionic compound GdF3 (0.67 mm s−1). The very similar isomer shift values of the 3d–Gd complexes indicate that there is no change in the small electron density of the 6s orbital and that the spin delocalization or spin polarization concerns the 5d Gd orbitals, in agreement with the crystal structure and Mössbauer spectrum of the Gd complex of nitrogen-coordinating tridentate ligand PrnTBP, [Gd(PrnTBP)3](OTf)3. Thus the observed 155Gd Mössbauer isomer shifts of 3d–Gd complexes give an experimental proof for the participation of 5d Gd orbitals to the magnetic interaction in these 3d–Gd complexes. [ABSTRACT FROM AUTHOR]

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]3+ or -trinuclear [Ni–Ln–Ni]3+ 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. For instance, the presence of one chelating nitrato ligand is already sufficient to impede an increase in the nuclearity, while the replacement of nitrato ligands by chloride anions still yields dinuclear Ni–Ln complexes. This experimental result evidences the role of protic solvents. In contrast, the use of lanthanide salts, soluble in non-protic solvents, allows the isolation of dinuclear [Ni–Ln]3+ or trinuclear cationic [LNi–Ln–NiL]3+ complexes, depending on the Ni/Ln ratio. A further synthetic step can be overtaken by the reaction of a Ni–Ln complex, soluble in a non-protic solvent, with a LM complex (M = Cu, Zn). By doing so, a heterotrinuclear complex made of three different metal ions, two distinct 3d ions and a 4f one, has been isolated and structurally characterized. Note that the Ni coordination number decreases from 6 to 5 on going from the dinuclear complex to the trinuclear one. Also, the replacement of water molecules by chloride ligands in the hexacoordinate Ni complexes induces a net increase of the positive zero-field splitting parameter D to 20 cm−1, which is supported by ab initio calculations. Although the Ni–Ln (Ln = Gd, Tb, Dy) magnetic interactions are ferromagnetic, the corresponding trinuclear complexes are devoid of SMM properties in the absence of an applied magnetic field. [ABSTRACT FROM AUTHOR]

We report the syntheses, structural determination and magnetic properties of a few 3d Schiff base metal complexes resulting from the reaction of preformed 3d Schiff base metal complexes with MCl2 salts (M = Cu, Ni, Mn). Different behaviors can occur, from a metal exchange reaction to coordination of M ions and chloride anions or, in the presence of alkaline ions, to formation of tetrachlorocuprate entities that behave as counter-anions in the final structures. So use of o-vanillin-derived Schiff base ligands possessing two coordination sites of different sizes allows isolation of a genuine dicopper complex entity involving a highly non symmetric diphenoxo bridge characterized by a central Cu–O2–Cu core possessing very different Cu–O bond lengths and Cu–O–Cu angles. Use of o-vanillin as a chelating ligand in place of o-vanillin-derived Schiff base ligands furnishes a supplementary degree of freedom in the syntheses of new complexes. The two o-vanillin ligands can rearrange to yield cubane complexes or give heterodinuclear complexes. DFT calculations demonstrate that in the genuine non-symmetric diphenoxo bridge, the two different bridging pathways have to be taken into consideration to explain the resulting weak antiferromagnetic interaction in the dicopper complex, an interaction resulting from non-negligible antagonistic antiferro- and ferromagnetic interactions. [ABSTRACT FROM AUTHOR]

The preparation of non-symmetric Schiff base ligands possessing one oxime function that is associated to a second function such as pyrrole or phenol function is first described. These ligands, which possess inner N4 or N3O coordination sites, allow formation of cationic or neutral non-symmetric CuII or NIII metallo-ligand complexes under their mono- or di-deprotonated forms. In presence of Lanthanide ions the neutral complexes do not coordinate to the LnIII ions, the oxygen atom of the oxime function being only hydrogen-bonded to a water molecule that is linked to the LnIII ion. This surprising behavior allows for the isolation of LnIII ions by non-interacting metal complexes. Reaction of cationic NiII complexes possessing a protonated oxime function with LnIII ions leads to the formation of original and dianionic (Gd(NO3)5)2- entities that are well separated from each other. This work highlights the preparation of well isolated mononuclear LnIII entities into a matrix of diamagnetic metal complexes. These new complexes complete our previous work dealing with the complexing ability of the oxime function toward Lanthanide ions. It could open the way to the synthesis of new entities with interesting properties, such as single-ion magnets for example. [ABSTRACT FROM AUTHOR]

Ester-functionalized bicompartmental Schiff base ligands and their 3d-Ln complexes (3d = NiII, CuII, or ZnII and Ln = GdIII, TbIII, or DyIII) are reported. The Themodularity of the Schiff base structure (i.e., symmetric ester group compared with dissymmetric ester group) is illustrated to highlight the possibility offered by the ester for facile functionalization at the periphery of the ligand, in addition to its electron-withdrawing effect on the complexing core. The introduction of a chiral pool (i.e., a menthyl group) at the ester functions led to a transfer of chirality to the coordination sphere of the Ln in the solid state. Several 3d-4f complexes were found to crystallize as (NO3-)- or (OH-)-bridged compounds. Crystal structures and magnetic behaviors are reported for all of the 3d-4f complexes. [ABSTRACT FROM AUTHOR]

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 (L2− is the di-deprotonated form of the N2O2 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. The Zn ions are pentacoordinate in all cases, linked to the N2O2 atoms from L, and the apical position of the Zn coordination sphere is occupied by a water molecule or bromide or chloride ions. These resulting complexes, formulated (LZnX)-Dy-(LZnX), are tricationic with X=H2O and monocationic with X=Br or Cl. They behave as field-free single-molecule magnets (SMMs) with effective energy barriers ( Ueff) for the reversal of the magnetization of 96.9(6) K with τ0=2.4×10−7 s, 146.8(5) K with τ0=9.2×10−8 s, and 146.1(10) K with τ0=9.9×10−8 s for compounds with ZnOH2, ZnBr, and ZnCl motifs, respectively. The Cole-Cole plots exhibit semicircular shapes with α parameters in the range of 0.19 to 0.29, which suggests multiple relaxation processes. Under a dc applied magnetic field of 1000 Oe, the quantum tunneling of magnetization (QTM) is partly or fully suppressed and the energy barriers increase to Ueff=128.6(5) K and τ0=1.8×10−8 s for 1, Ueff=214.7 K and τ0=9.8×10−9 s for 2, and Ueff=202.4 K and τ0=1.5×10−8 s for 3. The two pairs of largely negatively charged phenoxido oxygen atoms with short DyO bonds are positioned at opposite sides of the Dy3+ ion, which thus creates a strong crystal field that stabilizes the axial MJ=±15/2 doublet as the ground Kramers doublet. Although the compound with the ZnOH2 motifs possesses the larger negative charges on the phenolate oxygen atoms, as confirmed by using DFT calculations, it exhibits the larger distortions of the DyO9 coordination polyhedron from ideal geometries and a smaller Ueff value. Ab initio calculations support the easy-axis anisotropy of the ground Kramers doublet and predict zero-field SMM behavior through Orbach and TA-QTM relaxations via the first excited Kramers doublet, which leads to large energy barriers. In accordance with the experimental results, ab initio calculations have also shown that, compared with water, the peripheral halide ligands coordinated to the Zn2+ ions increase the barrier height when the distortions of the DyO9 have a negative effect. All the complexes exhibit metal-centered luminescence after excitation into the UV π-π* absorption band of ligand L2− at λ=335 nm, which results in the appearance of the characteristic DyIII (4F9/2→6H J/2; J=15/2, 13/2) emission bands in the visible region. [ABSTRACT FROM AUTHOR]

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. From Gd to Ho, the complexes [(LCu)2Ln(NO3)3(H2O)] are still trinuclear, with a supplementary water molecule linked to the Ln ion but the CuII and LnIII ions are only bridged by the oximato (N-O) pair, the phenoxo oxygen atom being hydrogen-bridged to the Ln-coordinated water molecule. Then, with heavier Ln ions, dinuclear [(LCu)Ln(NO3)3(H2O)2] complexes are characterized. The magnetic study demonstrates that the oximato bridge is responsible for the antiferromagnetic character of the Cu-Gd interaction, with JCuGd = -0.63 cm-1 in [(LCu)2Gd(NO3)3(H2O)], in contrast to the ferromagnetic Cu-Gd interaction induced by the single oxygen atom phenoxo bridge. [ABSTRACT FROM AUTHOR]

Condensation of 3-hydroxysalicylaldehyde with 2,4,6-trimethyl-1,3-phenylenediamine gives the ligand N,N′-bis(3-hydroxysalicylidene)-2,4,6-trimethyl-m-phenylenediamine (H4L). The dinuclear zinc(ii) complex [Zn(H2L)]2 (1) and the tetranuclear copper(ii) square complex [{Cu(H2L)}4(THF)] (2) were synthesized and structurally characterized by single crystal X-ray diffraction. In 1, the ZnII ions are bridged by two H2L molecules and they adopt a tetrahedral geometry. The coordination geometry of the copper atoms in 2 is either square planar or square pyramidal, each metal atom being bound to the NO donor sets of two Schiff base ligands and, in one case, to an extra THF molecule. The arrangement of the tetranuclear complexes in the crystal lattice results in the formation of square channels. Variable temperature magnetic measurements on 2 evidence significant long-range ferromagnetic interactions between the four CuII centres leading to an S = 2 ground state with J1 = +5.81, J2 = +2.36, J3 = +1.73 and J4 = +2.37 cm−1. DFT calculations have been carried out in order to corroborate the experimental fitting and ascertain the origin of this ferromagnetic behaviour. [ABSTRACT FROM AUTHOR]

Abstract: The template effect involves two main effects, first the “kinetic template effect”, in which a metal ion is able to hold two reactive functions in a position that allows a reaction to occur, followed by the “thermodynamic template effect” that favours the formation of a thermodynamically more stable product resulting from the reaction. Through the preparation of a non symmetric Schiff base, we highlight the primordial role of the “kinetic template effect”. Very often, this kinetic effect is not easy to evidence, the resulting complex being too reactive to be isolated. In the present example, the use of an ambidentate ligand, pyrrole carboxaldehyde, has been quite interesting. Reaction of a cationic copper complex possessing a primary amine function coordinated to the copper ion with pyrrole carboxaldehyde can yield two different complexes, depending on the reaction conditions. In absence of a base, the structural determination shows that the copper ion is linked in apical position to the carbonyl oxygen atom of pyrrole carboxaldehyde and the two reactive aldehyde and amine functions are unable to react, as a consequence of their mutual coordination to copper. On the contrary, addition of a base to the reaction mixture induces deprotonation of the pyrrole function followed by its coordination to copper ion, leaving free the carbonyl carbon atom that can be positioned in the vicinity of the primary amine function, thus facilitating the formation of a new imine function. The resulting thermodynamically stable complex is characterized by X-ray diffraction. [Copyright &y& Elsevier]

Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear CuIILnIIICuII (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H2L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the CuII and LnIII ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η2: η1: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a JCuGd interaction equal to −1.25 cm−1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction. [ABSTRACT FROM AUTHOR]

Abstract: Salen-type Schiff base ligands possess a N2O2 coordination site able to chelate transition metal ions. Reaction of such a ligand with FeCl3·6H2O leads to the formation of a genuine dinuclear L3Fe2 complex in which the ligand plays a double role. The structural determination confirms that each iron ion is wrapped up by a chelating tetradentate ligand while the third one ensures a bridge in between the two Fe ions and completes to six the metal coordination sphere. Such a bridge implies a non planar coordination of the chelating ligands and induces helicity around each metal ion. Crystals are true racemates made of homochiral Λ–Λ and Δ–Δ pairs. The magnetic study confirms the absence of a spin exchange interaction through the saturated diamino chain and the presence of an axial single ion zero field splitting (ZFS) D equal to −0.7cm−1. The Mössbauer spectra show a unique asymmetric quadrupole-split doublet with isomer shift values, δ, of 0.342(2), 0.438(2) and 0.450(2)mms−1, and quadrupole splittings, ΔE Q, of 0.826(4), 0.836(4) and 0.827(4)mms−1 at 293, 80 and 4.5K, respectively. These values are in agreement with a high-spin iron(III) site in a N3O3 ligand environment. [Copyright &y& Elsevier]

Examines the crystal and molecular structures of dinuclear complexes deriving from hexadentate Schiff bases. Occurrence of weak iron (Fe)-gadolinium ferromagnetic exchange interaction; Derivation of single ion zero-field splitting of the Fe; Magnetic properties of the bimetallic complexes.

Studies two original dinuclear (CuII, GdIII) complexes deriving from polydentate nonsymmetrical Schiff base ligands. Previous difference in the length of the diamino chain; Crystallization; Cell parameters; Formation of a double bridge through a phenolato oxygen atom and an oximato pair; Non-planar bridging network; Antiferromagnetic interaction.

A strictly heterodinuclear Cu-Tb complex [LCu(O2COMe)Tb(thd)2] made with a Schiff base L, thd, and monomethylcarbonate ligands [L2- = N,N′-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato); thd = tetramethylheptanedionato] behaves like a single-molecule magnet. The monomethylcarbonate ligand, which appears during the reaction pathway, bridges the Cu and Tb ions. [ABSTRACT FROM AUTHOR]

Abstract: Heterotrimetallic {3d–5d–4f} compounds have been prepared by assemblage of {W(CN)8}3− and {LMe2NiLn}3+ units, with Ln=Y (1) and La (2). These have been found to exhibit different supramolecular organizations. A chain structure is formed for Ln=Y, whereas La leads to a hexanuclear aggregate. The investigation of the magnetic behavior for these compounds revealed ferromagnetic W–Ni interaction with J =20cm−1 for 2. [Copyright &y& Elsevier]

Four heterodinuclear (H20)2NiL-Ln(N03)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 P21, as the previously described (H2O)2NiL-Gd(NO3)3 equivalent All four complexes are ferromagnetjcally coupled. If this behavior is clearly shown by the XMT increase at low temperature in the case of the Ni--Tb and Ni--Dy complexes, it necessitates the preparation of the Zn--Er and Zn--Yb equivalent entities to be evidenced in the case of the Ni--Er and Ni--Yb complexes. Out-of-phase susceptibility signals are found in the four cases, but the SMM behavior is neither confirmed, nor completely studied because of die presence of fast quantum tunnelling at zero field. Thorough ab initio multiconfiguration calculations are carried out, achieving a realistic account of ligand field effects, exchange coupling and magnetic anisotropy in the discussed systems. The calculations reveal the ferromagnetic intercenter exchange coupling, the interplay with spin--orbit effects leading to a Ising-like scheme of the lowest levels. The ab initio simulation of the magnetic susceptibility is in semiquantitative agreement with experimental data, certifying the reasonableness of the theoretical treatments in obtaining valuable information for the interacting mechanisms. The anisotropy is accounted for by drawing polar diagrams of state-specific magnetization functions, obtained by handling of the data resulting from ah initio calculations including the spin--orbit effects. Supplementary, Density Functional Theory (DFT) calculations are carried out, presenting new methodological clues and assessments. The DFT is not perfectly adequate for lanthanide systems because of orbital pseudodegeneracy issues. However, we show that in particular circumstances the DFT can be partly used, succeeding here in mimicking different orbital configurations of the Ni--Tb system. The DFT seems to offer reasonable estimations of exchange coupling parameters, while it remains problematic in the complete account of Ligand Field splitting. The Paper presents unprecedented methodological advances and correlations with phenomenological and heuristic interpretation of experimental data, taking into focus relevant d-f systems constructed with a prototypical binucleating ligand. [ABSTRACT FROM AUTHOR]