Mechanism of magnetisation relaxation in M III 2 Dy III 2 (M = Cr, Mn, Fe, Al) “butterfly” complexes: How important are the transition metal ions here?

We describe the synthesis, characterisation and magnetic studies of four tetranuclear, isostructural “butterfly” heterometallic complexes: [MIII 2 LnIII 2 (m3-OH)2(p-Me-PhCO2)6(L)2] (H2 L ¼ 2,20-((pyridin-2-ylmethyl)azanediyl)bis(ethan-1-ol), M ¼ Cr, Ln ¼ Dy (1), Y (2), M ¼ Mn, Ln ¼ Dy (3), Y (4)), which extend our previous study on the analogous 5 {Fe2Dy2}, 6 {Fe2Y2} and 7 {Al2Dy2} compounds. We also present data on the yttrium diluted 7 {Al2Dy2}: 8 {Al2Dy0.18Y1.82}. Compounds dc and ac magnetic susceptibility data reveal single-molecule magnet (SMM) behaviour for complex 3 {Mn2Dy2}, in the absence of an external magnetic field, with an anisotropy barrier Ueff of 19.2 K, while complex 1 {Cr2Dy2}, shows no ac signals even under applied dc field, indicating absence of SMM behaviour. The diluted sample 8 {Al2Dy0.18Y1.82} shows field induced SMM behaviour with an anisotropy barrier Ueff of 69.3 K. Furthermore, the theoretical magnetic properties of [MIII 2 LnIII 2 (m3-OH)2(p-Me-PhCO2)6(L)2] (M ¼ Cr, 1 or Mn, 3) and their isostructural complexes: [MIII 2 DyIII 2 (m3-OH)2(p-Me-PhCO2)6(L)2] (M ¼ Fe, 5 or Al, 7) are discussed and compared. To understand the experimental observations for this family, DFT and ab initio CASSCF + RASSI-SO calculations were performed. The experimental and theoretical calculations suggest that altering the 3dIII ions can affect the single-ion properties and the nature and the magnitude of the 3dIII–3dIII, 3dIII–DyIII and DyIII–DyIII magnetic coupling, thus quenching the quantum tunneling of magnetisation (QTM) significantly, thereby improving the SMM properties within this motif. This is the first systematic study looking at variation and therefore role of trivalent transition metal ions, as well as the diamgnetic AlIII ion, on slow relaxation of magnetisation within a series of isostructural 3d–4f butterfly compounds

Assisted Self-Assembly to Target Heterometallic Mn-Nd and Mn-Sm SMMs: Synthesis and Magnetic Characterisation of [Mn7_{7}Ln3_{3}(O)4_{4}(OH)4_{4}(mdea)3_{3}(piv)9_{9}(NO3_{3})3_{3}] (Ln=Nd, Sm, Eu, Gd)**

Assisted self-assembly by using a preformed [Mn$_{6}$O$_{2}$(piv)$_{10}$(4-Me-py)$_{2}$(pivH)$_{2}$] (1) (pivH=pivalic acid) cluster leads to 3 different outcomes of the reaction with Ln(NO$_{3}$)$_{3}$ ⋅ xH$_{2}$O (Ln=Pr−Ho and Y): Mn$_{7}$Ln$_{3}$ and in some cases the inverse butterfly Mn$_{2}$Ln$_{2}$ for Ln=Pr−Eu, Mn$_{5}$Ln$_{4}$ for Ln=Tb-Ho and in the special case of Gd all three possibilities can form. Whilst the magnetic properties for the Mn$_{5}$Ln$_{4}$ systems show the expected known SMM properties, for Mn$_{7}$Ln$_{3}$ two new examples of Nd- and Sm-containing SMMs have been discovered. in an assisted self-assembly approach starting from the [Mn$_{6}$O$_{2}$(piv)$_{10}$(4-Me-py)$_{2}$(pivH)$_{2}$] cluster a family of Mn−Ln compounds (Ln=Pr−Yb) was synthesised. The reaction of [Mn$_{6}$O$_{2}$(piv)$_{10}$(4-Me-py)$_{2}$(pivH)$_{2}$] (1) with N-methyldiethanolamine (mdeaH$_{2}$) and Ln(NO$_{3}$)$_{3}$ ⋅ 6H$_{2}$O in MeCN generally yields two main structure types: for Ln=Tb−Yb a previously reported Mn$_{5}$Ln$_{4}$ motif is obtained, whereas for Ln=Pr−Eu a series of Mn$_{7}$Ln$_{3}$ clusters is obtained. Within this series the Gd$^{III}$ analogue represents a special case because it shows both structural types as well as a third Mn$_{2}$Ln$_{2}$ inverse butterfly motif. Variation in reaction conditions allows access to different structure types across the whole series. This prompts further studies into the reaction mechanism of this cluster assisted self-assembly approach. For the Mn$_{7}$Ln$_{3}$ analogues reported here variable-temperature magnetic susceptibility measurements suggest that antiferromagnetic interactions between the spin carriers are dominant. Compounds incorporating Ln=Nd$^{III}$(2), Sm$^{III}$(3) and Gd$^{III}$ (5) display SMM behaviour. The slow relaxation of the magnetisation for these compounds was confirmed by ac measurements above 1.8 K

Synthesis of Bimetallic Uranium and Neptunium Complexes of a Binucleating Macrocycle and Determination of the Solid-State Structure by Magnetic Analysis

Syntheses of the bimetallic uranium(III) and neptunium(III) complexes [(UI)2(L)], [(NpI)2(L)], and [{U(BH4)}2(L)] of the Schiff-base pyrrole macrocycles L are described. In the absence of single-crystal structural data, fitting of the variable-temperature solid-state magnetic data allows the prediction of polymeric structures for these compounds in the solid state.JRC.E.6-Actinides researc

An Undecanuclear FeIII Single-Molecule Magnet

3 pagesInternational audienceThe undecanuclear complex in [FeIII 11(μ4-O)3(μ3-O)4(L)3(μ- O2CCMe3)12]Cl 3 5MeCN has been synthesized and characterized by single-crystal X-ray crystallography. M€ossbauer spectroscopy and bulk susceptibility studies reveal that the complex has an S = 13/2 spin ground state and exhibits single-molecule-magnet behavior

Tetradecanuclear lanthanide-vanadium "nanochocolates": catalytically-active cationic heteropolyoxovanadium clusters

The synthesis, structural characterization, magnetic and catalytic properties of a new class of lanthanide-containing cationic heteropolyoxovanadium clusters with a nanochocolate-like structure are reported. The title compounds were characterized by single-crystal and powder X-ray diffraction, IR and V-51-NMR spectroscopies and magnetic susceptibility measurements

Synthesis, crystal structure, magnetic and luminescence investigations of new 2Ln3+-Sr2+ heteronuclear polymers with 2-furoic acid.

New first examples of complexes with the general formula {[Ln(2)Sr(C4H3OCOO)(8)(H2O)(4)]}(n), where Ln = La3+ (1), Pr3+ (2), Nd3+ (3), Sm3+ (4), Eu3+ (5), Gd3+ (6), Tb3+ (7), Ho3+ (8), Yb3+ (9) and Er3+ (10) have been prepared and investigated by photoluminescence spectroscopy and magnetic susceptibility measurements. The X-ray crystal structure has been determined for the {[Er2Sr(C4H3OCOO)(8)- (H2O)(4)]}(n) (10) complex, indicating that this complex is built from two crystallographic independent coordination polymers {[Er2Sr(C4H3OCOO)(8)(H2O)(4)]}(n) in the triclinic crystal system and P-1 space group. The X-ray diffraction (XRD) pattern of the samples shows that all lanthanide compounds are isostructural to 10. The luminescence spectrum of a microcrystalline sample of "2Eu-Sr" compound displays the characteristic Eu3+ (D-5(0) -> F-7(J) (J = 0-4)) metal centred transitions; also "2Nd-Sr" proved to be luminescent in the near IR. Measurements of the magnetic susceptibility for 2, 3, 5 and 10 were described using Crystal Field approac