Magnetic moments: The orientation of the title single‐molecule magnet was investigated by magnetic single crystal and luminescence characterization, supported by ab initio calculations, and was found to be governed by the position of the hydrogen atoms of the apical water molecules. This finding suggests that simple magneto‐structural correlations can give misleading clues for research in molecular magnetism as well as in the design of MRI contrast agents.

The first family of rare-earth-based single chain magnets is presented. Compounds of general formula [M(hfac)3(NITPhOPh)], where M = Eu, Gd, Tb, Dy, Ho, Er, or Yb, and PhOPh is the nitronyl-nitroxide radical (2,4'-benzoxo-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), have been structurally characterized and found to be isostructural. The characterization of both static and dynamic magnetic properties of the whole family is reported. Dy, Tb, and Ho compounds display slow relaxation of the magnetization, and ac susceptibility shows a thermally activated regime with energy barriers of 69, 45, and 34 K for Dy, Tb, and Ho compounds, respectively, while only a frequency-dependent susceptibility is observed for Er below 2.0 K. In Gd and Yb derivatives, antiferromagnetic interactions dominate. The pre-exponential factors differ by about 4 orders of magnitude. Finite size effects, due to naturally occurring defects, affect the static and dynamic properties of the compounds differently.

Single crystal magnetic studies combined with a theoretical analysis show that cancellation of the magnetic moments in the trinuclear Dy 3+ cluster [Dy3(µ3-OH)2L3Cl(H2O)5]Cl3, resulting in a non-magnetic ground doublet, originates from the non-collinearity of the single ion easy axes of magnetization of the Dy 3+ ions that lie in the plane of the triangle at 120 • one from each other. This gives rise to a peculiar chiral nature of the ground non-magnetic doublet and to slow relaxation of the magnetization with abrupt accelerations at the crossings of the discrete energy levels.PACS numbers: 71.79. Ej, 75.10.Jm,75.50.Xx, 75.30.Cr Molecular nanomagnetism has provided benchmark systems to investigate new and fascinating phenomena in magnetism [1,2] like magnetic memory at the molecular level [3], quantum tunneling of the magnetization [4,5], or destructive interferences in the tunneling pathways [6]. In this field rare earth ions like dysprosium(III) are currently investigated because of their large magnetic anisotropy and high magnetic moment [7]. In the course of our synthetic efforts to obtain new molecular nanomagnets based on rare-earth ions we recently obtained the trinuclear(where L is the anion of ortho-vanillin) [8], hence abbreviated as Dy 3 , which possesses an almost trigonal (C 3h ) symmetry (see Figure 1 and EPAPS for more information) [9].Preliminary powder magnetic measurements measure- Figure 1. To the best of our knowledge an experimental realization of this simple but fascinating spin structure is unprecedented.To verify our hypothesis larger crystals (of size ca. 1 mm 3 ) of one of the two compounds were grown according to [8] through very slow evaporation of the solvent. This allowed an accurate face indexing of the crystal on the X-ray diffractometer and the investigation of the magnetic anisotropy by using an horizontal sample rotator in the SQUID magnetometer (see EPAPS for experimental details) [9]. Scans in different crystallographic planes allowed us to determine the three magnetic anisotropy axes, denoted as X, Y and Z. The two structurally equivalent Dy 3 molecules in the unit cell have the Dy 3 planes almost perpendicular to Z and one side of the triangle parallel to Y (see Fig. 1). Magnetization vs. field curves along these axes are given in Figure 2a. Along X and Y a sudden jump around 8 kOe is observed while an almost linear but weaker magnetization is observed along Z. In Figure 2b the temperature dependence of the magnetization along the three axes measured at 1 kOe, and thus before the jump to saturation, are shown. The inplane X and Y directions are very similar and M tends to zero at low temperatures, confirming a non-magnetic ground state, while a weaker signal is observed along Z.The observed behaviour has been modelled using the canonical formalism of the statistical thermodynamics

Heteronuclear lanthanide terephthalate coordination polymers with the general chemical formula [Ln2–2xLn′2x(bdc)3(H2O)4]∞, for which bdc2– symbolizes benzene‐1,4‐dicarboxylate (or terephthalate) and Ln and Ln′ represent trivalent rare earth ions, were synthesized and structurally characterized. Analysis of the Y/Lu compounds by 89Y and 13C solid‐state NMR spectroscopy was carried out, and the results support the hypothesis of randomly distributed lanthanide ions. The spectroscopic and colorimetric properties of this family of compounds were investigated in detail. The resulting data demonstrate that this series of compounds presents highly tunable luminescence properties and clearly indicate that intermetallic deactivation processes play an important role in the emission mechanism. Playing with intermetallic distances allows one to tune the color and the brightness of the lanthanide emission in these coordination polymers.

Reaction in water between rare earth ions (Ln = Y, La-Tm, except Pm) and the sodium salt of terephthalic acid leads to a family of lanthanide-based coordination polymers of general formula [Ln2(C8H4O4)3(H2O)4] n with Ln = La-Tm or Y. The isostructurality of the compounds with the previously reported Tb-containing polymer is ascertained on the basis of their X-ray powder diffraction diagrams. The coordination water molecules can be reversibly removed without destroying the crystal structure for compounds involving one of the lighter lanthanide ions (La-Eu). For compounds involving one of the heavier lanthanide ions (Tb-Tm) or yttrium, a structural change occurs during the drying process. X-ray diffraction data show this new anhydrous phase corresponding to the linking of pairs of Er(III) ions through mu-carboxylate bridges. Porosity profiles calculated for the anhydrous phases of Tb(III) and Er(III) show the presence of channels with very small sections. The luminescent properties of all the compounds have been recorded and the two most luminescent polymers, namely, the europium- and the terbium-containing ones, have been studied in more detail. Tb(III)-containing compounds display large quantum yields, up to 43%. Polyvinylpyrrolidone nanoparticles doped with [Ln2(C8H4O4)3(H2O)4] n (Ln = Eu, Tb, Er) have also been synthesized and characterized. The encapsulation of the coordination polymers results in somewhat reduced luminescence intensities and lifetime, but the nanoparticles can be dispersed in water and remain unchanged in this medium for more than 20 h.

The reaction of manganese(III) acetate meso-tetraphenylporphyrin with phenylphosphinic acid provides the one-dimensional compound of formula [Mn(TPP)O2PHPh] x H2O, which crystallizes in the monoclinic C2/c space group. The chain structure is generated by a glide plane resulting in Jahn-Teller elongation axes of the MnIII octahedra that alternate along the chain. The phenylphosphinate anion transmits a sizable antiferromagnetic exchange interaction that, combined with the easy axis magnetic anisotropy of the MnIII sites, gives rise to a canted antiferromagnetic arrangement of the spins. The static single-crystal magnetic properties have been analyzed with a classical Monte Carlo approach, and the best fit parameters for the exchange and single ion anisotropy are J = -0.68(4) K and D = -4.7(2) K, respectively (using the -2JS(i)S(j) formalism for the exchange). Below 5 K the single-crystal dynamics susceptibility reveals a frequency-dependent out-of-phase signal typical of single-chain magnets. The extracted relaxation time follows the Arrhenius law with delta = 36.8 K. The dynamic behavior has been rationalized and correlated to geometrical parameters of the structure. The contribution of the correlation length to the energy barrier has been investigated, and it has been found that the characteristic length that dominates the dynamics strongly exceeds the correlation length estimated from magnetic susceptibility.

Spotting trends: Upon going from Tb(III) to Yb(III) centers in the complexes of the DOTA(4-) ligand, a reorientation of the easy axis of magnetization from perpendicular to parallel to the Ln-O bond of the apical water molecule is experimentally observed and theoretically predicted (SMM=single-molecule magnet). Only ions with an odd number of electrons show slow relaxation of the magnetization.

A mixed theoretical and experimental approach was used to determine the local magnetic anisotropy of the dysprosium(III) ion in a low-symmetry environment. The susceptibility tensor of the monomeric species having the formula [Dy(hfac)(3)(NIT-C(6)H(4)-OEt)(2)], which contains nitronyl nitroxide (NIT-R) radicals, was determined at various temperatures through angle-resolved magnetometry. These results are in agreement with ab initio calculations performed using the complete active space self-consistent field (CASSCF) method, validating the predictive power of this theoretical approach for complex systems containing rare-earth ions, even in low-symmetry environments. Susceptibility measurements performed with the applied field along the easy axis eventually permitted a detailed analysis of the temperature and field dependence of the magnetization, providing evidence that the Dy ion transmits an antiferromagnetic interaction between radicals but that the Dy-radical interaction is ferromagnetic.