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We report four new complexes based on a {LnIII6} wheel structure, three of which possess a net toroidal magnetic moment. The four examples consist of {TbIII6} and {HoIII6} wheels, which are rare examples of non DyIII based complexes possessing a toroidal magnetic ground state, and a {DyIII6} complex which improves its toroidal structure upon lowering the crystallographic symmetry from trigonal (R3‾) to triclinic (P1‾). Notably the toroidal moment is lost for the trigonal {ErIII6} analogue. This suggests the possibility of utilizing the popular concept of oblate and prolate electron density of the ground state MJ levels of lanthanide ions to engineer toroidal moments. High symmetry and dipolar coupling are key criteria for engineering toroidal moments in ring/wheel species, the oblate nature of the electron density of the LnIII ion also play a significant role while lowering of the crystallographic symmetry helps to improve the toroidal properties. [ABSTRACT FROM AUTHOR]

We report the synthesis, structure and magnetic properties of the first 4d–4f single-molecule magnet. The complex [RuIII2DyIII2(OMe)2(O2CPh)4(mdea)2(NO3)2] displays a butterfly type core, with an anisotropy barrier of 10.7 cm−1. Ab initio and DFT calculations provide insight into the observed magnetic behaviour. [ABSTRACT FROM AUTHOR]

The syntheses, structures, and magnetic properties of two heterometallic CuII-LnIII (LnIII = Gd, Tb, and Dy) families, utilizing triethanolamine and carboxylate ligands, are reported. The first structural motif displays a nonanuclear {CuII2LnIII7} metallic core, while the second reveals a hexadecanuclear {CuII4LnIII12} core. The differing nuclearities of the two families stem from the choice of carboxylic acid used in the synthesis. Magnetic studies show that the most impressive features are displayed by the {CuII2GdIII7} and {CuII4GdIII12} complexes, which display a large magnetocaloric effect, with entropy changes -Sm = 34.6 and 33.0 J kg-1 K-1 at T = 2.7 and 2.9 K, respectively, for a 9 T applied field change. It is also found that the {CuII4DyIII12} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K. [ABSTRACT FROM AUTHOR]

Four isostructural [Ni2Ln2(CH3CO2)3(HL)4(H2O)2]3+(Ln3+=Dy ( 1), Tb ( 2), Ho ( 3) or Lu ( 4)) complexes and a dinuclear [NiGd(HL)2(NO3)3] ( 5) complex are reported (where HL=2-methoxy-6-[( E)-2′-hydroxymethyl-phenyliminomethyl]-phenolate). For compounds 1- 3 and 5, the Ni2+ ions are ferromagnetically coupled to the respective lanthanide ions. The ferromagnetic coupling in 1 suppresses the quantum tunnelling of magnetisation (QTM), resulting in a rare zero dc field Ni-Dy single-molecule magnet, with an anisotropy barrier Ueff of 19 K. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of four related heterometallic complexes of formulas [DyIII2CoIII2(OMe)2(teaH)2CO2CPh)4(MeOH)4](NO3)2-MeOH•H2O (1a) and [DyIII2CoIII2(OMe)2-(teaH)2(O2CPh)4(MeOH)2(NO3)2]•MeOH•H2O (1b), [DylII2CoIII2(OMe)2(dea)2(O2CPh)4(MeOH)4](NO3)2 (2), [DyIII2CoIII2(OMe)2(mdea)2(O2CPh)4(NO3)2] (3), and [DyIII2CoIII2(OMe)2(bdea)2(O2CPh)4(MeOH)4](NO3)2• 0.5MeOH•H2O (4a) and [DyIII2CoIII2(OMe)2(bdea)2-(O2CPh)4(MeOH)2(NO3)2]•MeOH•1.5H2O (4b) are reported (teaH3 = triethanolamine, deaH2 = diethanolamine, mdeaH2 = N-methyldiethanolamine, and bdeaH2 = N-n-butyldiethanolamine). Compounds 1 (? 1a and 1b) and 4 (? 4a and 4b) both display two unique molecules within the same crystal and all compounds display a butterfly type core, with the DyIII ions occupying the central body positions and the diamagnetic CoIII ions the outer wing-tip sites. Compounds 1--4 were investigated via direct current and alternating current magnetic susceptibility measurements, and it was found that each complex displayed single-molecule magnet (SMM) behavior. All four compounds display unique coordination and geometric environments around the DyIII ions and it was found that each displays a different anisotropy barrier. Ab initio calculations were performed on 1--4 and these determined the low lying electronic structure of each DyIII ion and the magnetic interactions for each cluster. It was found that there was a strong correlation between the calculated energy gap between the ground and first excited states of the single-ion ligand-field split DyIII levels and the experimentally observed anisotropy barrier. Furthermore, the transverse g factors found for the DyIII ions, defining the tunnelling rates within the ground Kramers doublets, are largest for 1, which agrees with the experimental observation of the shortest relaxation time in the high-temperature domain for this complex. The magnetic exchange between the DyIII ions revealed overall antiferromagnetic interactions for each compound, derived from the dominant dipolar exchange resulting in nonmagnetic ground states for 1--4. The diamagnetic ground states coupled with small tunneling gaps resulted in quantum tunneling time scales at zero field of between 0.1 and >1.5 s. [ABSTRACT FROM AUTHOR]

Abstract: Four isostructural heterometallic octanuclear complexes have been synthesized of general formulae [CoII 4LnIII 4(OH)4(chp)10(acac)6]·solv (Ln=Y (1), Gd (2), Tb (3) and Dy (4); solv=0.5MeCN for 1, 2 and 4 and Et2O for 3), where Hchp=6-chloro-2-hydroxypyridine and acac− =acetylacetonate. A fifth complex of formula [CoII 11DyIII 6(OH)14(chp)14(piv)8(NO3)4(MeCN)4]·2H2O (5) was also isolated using the Hchp ligand with pivalic acid as a co-ligand. X-ray crystallographic studies reveal that complexes 1–4 all display a central planar butterfly motif consisting of the four LnIII ions, with the CoII ions “capping” around the periphery of the butterfly. Compound 5 displays a complex metallic core with an unusual disc-like motif capped by two non-planar butterfly units. DC magnetic susceptibility measurements for the {CoII 4LnIII 4} family of compounds (1–4) reveals that the diamagnetic Y analogue {CoII 4YIII 4} (1) displays antiferromagnetic exchange interactions between the Co–Co ions. An overall decrease in the susceptibility (χMT) is then observed upon lowering the temperature for {CoII 4GdIII 4} (2) and {CoII 4TbIII 4} (3), while the {CoII 4DyIII 4} (4) complex displays a decrease before a small increase at the lowest temperatures measured, indicating a ferrimagnetic ground state. AC susceptibility measurements reveal an absence of any SMM behaviour for 1–3 but show the onset of slow magnetic relaxation below 4K in the case of 4. The DC and AC behaviour of complex 5 {CoII 11DyIII 6} follows a similar profile to compound 4 revealing a small increase in χ M T at low temperatures, with the observation of possible SMM behaviour as observed via low temperature ‘tails’ of peaks in the out-of-phase susceptibilities. [Copyright &y& Elsevier]

Three new heterometallic complexes with formulas of [DyIII2CoIII2(OMe)2(teaH)2(acac)4(N03)2] (l), [DyIII2CoIII2(OH)2- (teaH)2(acac)4(N03)2]-4H20 (2), and [DyIII2CoIII2(OMe)2(mdea)2-(acac)4(N03)2] (3) were characterized by single-crystal X-ray dinxaction and by dc and ac magnetic susceptibility measurements. All three complexes have an identical "butterfly"-type metallic core that consists of two DyIII ions occupying the "body" position and two diamagnetic low-spin DyIII ions occupying the outer "wing-tips". Each complex displays single-molecule magnet (SMM) behavior in zero applied magnetic field, with thermally activated anisotropy barriers of 27, 28, and 38 K above 7.5 K for 1--3, respectively, as well as observing a temperature-independent mechanism of relaxation below S K for 1 and 2 and at 3 K for 3, indicating fast quantum tunneling of magnetization (QTM). A second, faster thermally activated relaxation mechanism may also be active under a zero applied dc field as derived from the Cole--Cole data. Interestingly, these complexes demonstrate further relaxation modes that are strongly dependent upon the application of a static dc magnetic field. Dilution experiments that were performed on 1, in the {YIII2CoIII2} diamagnetic analog, show that the slow magnetic relaxation is of a single-ion origin, but it was found that the neighboring ion also plays an important role in the overall relaxation dynamics. [ABSTRACT FROM AUTHOR]

Two new potential single molecule magnets [Mn10O3(O2CCH3)6(tea)(teaH)3(teaH2)3][NO3]2.3H2O (1) and [Mn18(N3)12O12(tea)2(teaH)4(OMe)(MeOH)].2MeOH.H2O.Et2O (2) have been synthesised using manganese(II) nitrate, the tripodal ligand triethanolamine (teaH3) and co-ligands such as acetate for 1 and azide for 2. Both compounds are mixed-valent with 1 consisting of 4 Mn(II) and 6 Mn(III) ions and 2 consisting of 3 Mn(II) and 15 Mn(III) ions. Complex 1 has a near planar Mn7(II/III) disc-like core with 3 Mn(II) ions positioned on the periphery of the disc, forming a star-like geometry. Complex 2 contains a hexa-capped truncated tetrahedral core. Variable temperature DC magnetic susceptibility data collected in 2, 1, 0.1 and 0.01 T fields, and in the 2-300 K temperature range, for 1 and 2, indicate a large ground spin-state for both compounds. Using a new approach to calculating the DCM vs. H isotherms (or isofieldM vs. H/T curves) by means of the thermal population of Zeeman levels generated from a group of closely spaced S states (within 9 cm-1 of ground), the ground S of 1 is 10. The ZFS term, D, is close to zero. For 2, the magnetisation isotherms, and low temperature susceptibilities, point to a ground state spin of 21/2 with many closely spaced spin states (probably from 17/2 to 35/2) close in energy, the lowest Zeeman level energies of which change as the field increases. AC magnetic susceptibility data show frequency-dependent out-of-phase signals indicating both clusters are possibly single molecule magnets. Extrapolation of the in-phase component, X'MT, to 0 K suggests spin ground state of S = 10 for 1 and 21/2 for 2, in agreement with the DC data. [ABSTRACT FROM AUTHOR]