Numerous molecular compounds in which a paramagnetic Ln(III) ion is in interaction with a second spin carrier such as a transition metal ion or an organic radical have been described. However, except for the isotropic Gd(III) ion, very little is known concerning the nature (ferro-or antiferromagnetic) and mechanism of the interaction involving a Ln(III) ion. This study addresses the problem of the interaction between the Ln(III) ions displaying spin-orbit coupling and an organic radical. The magnetic properties of a series of isostructural compounds, {Ln(organic radical) 2 (NO 3 ) 3 }, comprising a Ln(III) ion (Ln ) Ce to Dy) surrounded by two N,O-chelating aminoxyl radicals (3-nitronyl nitroxide-4,5-dimethyltriazole) have been investigated. The experimental approach used to get insight into the {Ln-Radical} coupling occurring within these compounds is based on the knowledge of the intrinsic paramagnetic contribution of the metal ion. This contribution has been deduced from the corresponding {Ln(Nitrone) 2 (NO 3 ) 3 } derivatives (Nitrone stands for 3-N-tert-butylnitrone-4,5-dimethyltriazole), where the Ln(III) ion is now in a diamagnetic surrounding. A simple mathematical difference of the magnetic susceptibilities of {Ln(organic radical) 2 (NO 3 ) 3 } and the corresponding {Ln(Nitrone) 2 -(NO 3 ) 3 } derivatives then permitted the nature of the correlations within the {Ln(organic radical) 2 (NO 3 ) 3 } compounds to be established. Moreover, these results have been confirmed by the field dependence of the magnetization for each derivative. A systematic investigation of the isostructural series of compounds allowed the evolution of these interactions to be compared as a function of the electronic configuration of the 4f orbitals. For the Ln(III) with 4f 1 to 4f 5 electronic configurations the {Ln-organic radical} interaction is antiferromagnetic. Conversely, this interaction was found to be ferromagnetic for the configurations 4f 7 to 4f. 10 These interactions have been clearly indicated for each Ln(III).

A redox active dinuclear complex [Yb(tta)(2)(L(1))(L(2))](2)·1.4(CH(2)Cl(2)) displays single molecule magnet behaviour with M(J) = ±7/2 ground state. The anisotropic barrier Δ is evaluated by the three dc data fit, ac analysis and emission spectrum demonstrating the correlation between magnetic and optical properties.

The influence of nuclear spin on the magnetic hysteresis of a single-molecule is evidenced. Isotopically enriched Dy(III) complexes are synthesized and an isotopic dependence of their magnetic relaxation is observed. This approach is coupled with tuning of the molecular environment through dilution in an amorphous or an isomorphous diamagnetic matrix. The combination of these approaches leads to a dramatic enhancement of the magnetic memory of the molecule. This general recipe can be efficient for rational optimization of single-molecule magnets (SMMs), and provides an important step for their integration into molecule-based devices.

The [Dy(tta)3(L)] complex behaves as a single ion magnet both in its crystalline phase and in solution. Experimental and theoretical magnetic anisotropy axes perfectly match and lie along the most electro-negative atoms of the coordination sphere. Both VSM and MCD measurements highlight the robustness of the complex, with persistence of the memory effect even in solution up to 4 K.

We noted in the experimental section that one of the reported crystal structures, {Pr(Nitrone) 2 (NO 3 ) 3 }, may be better described in the noncentrosymmetric space group P1 than in the centrosymmetric space group P1 h; this choice was based on better classical quality criterions in the former. Nevertheless, following discussions with careful readers we acknowledge and from consideration based on atomic displacement parameters we believe that this crystal structure is more likely to be centrosymmetric. However, nothing discussed in the article is modified by such a correction.

The syntheses and structural and physical characterization of the compounds [Cu(bipy)(2)](2)[Mo(CN)(8)].5H(2)O. CH(3)OH (1) with bipy = 2,2'-bipyridine and M(II)(2)[Mo(IV)(CN)(8)].xH(2)O (2 with M = Cu, x = 7.5; 3 with M = Mn, x = 9.5) are presented. 1 crystallizes in the triclinic space group P1; (a = 11.3006(4) A, b = 12.0886(5) A, c = 22.9589(9) A, alpha = 81.799(2) degrees, beta = 79.787(2) degrees, gamma = 62.873(2) degrees, Z = 2). The structure of 1 consists of neutral trinuclear molecules in which a central [Mo(CN8)](4-) anion is linked to two [Cu(bipy)2](2+) cations through two cyanide bridges. 2 crystallizes poorly, and hence, structural information has been obtained from the wide-angle X-ray scattering (WAXS) technique, by comparison with 3 and Fe(II)(2)(H(2)O)(4)[Mo(IV)(CN)(8)].4H(2)O whose X-ray structure has been previously solved. 2, 3, and Fe(II)(2)(H(2)O)(4)[Mo(IV)(CN)(8)].4H(2)O form extended networks with all the cyano groups acting as bridges. The magnetic properties have shown that 1 and 2 behave as paramagnets. Under irradiation with light, they exhibit important modifications of their magnetic properties, with the appearance at low temperature of magnetic interactions. For 1 the modifications are irreversible, whereas they are reversible for 2 after cycling in temperature. These photomagnetic effects are thought to be caused by the conversion of Mo(IV) (diamagnetic) to Mo(V)(paramagnetic) through a photooxidation mechanism for 1 and a photoinduced electron transfer in 2. These results have been correlated with the structural features.

Paramagnetic metal complexes that display a total spin ground state higher than that of the metal ion alone are interesting building blocks for the construction of molecular magnetic materials. Here we describe the synthesis and the magnetic properties of three such lanthanide complexes with two organic radicals as ligands, [Ln(nittrz) ] occurs between the paramagnetic metal center (S Gd 7/2) and the ligands (S rad1 S rad2 1/2) that gives rise to an S 9/2 ground state. The molecular structure of this compound has been determined by X-ray diffraction.

The structure and dehydration behavior of the porous 3D coordination polymer {[La2(adipate)3(H2O)4]6H2O} n are described. Each La3+ is coordinated by nine oxygen atoms belonging to five carboxylate ligands and to two water molecules. Large infinite interconnected channels filled with hydrogen-bonded water molecules are formed in the structure. Upon heating, this compound transforms reversibly into a nonporous lower hydrate.