Dodecanuclear 3d/4f-metal clusters with a 'Star of David' topology: Single-molecule magnetism and magnetocaloric properties

A family of interwoven molecular inorganic knots, shaped like the 'Star of David', was prepared by the employment of naphthalene-2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion.This work was supported by Brock University, NSERC-DG and ERA (to Th.C.S), the Ontario Trillium Foundation (graduate scholarship to D.I.A), the Fundaçao para a Ciencia e a Tecnologia (FCT, Portugal) financial support to REQUIMTE/LAQV (UID/ QUI/50006/2013), the European Synchrotron Radiation Facility (Grenoble, France) (for granting access time to the Swiss Norwegian BM01a beamline under the CH-3613 and CH-3849 research proposals), MINECO (FEDER-MAT2012-38318-C03 to M. E and postdoctoral contract to G. L), and the National Natural Science Foundation of China (grants 21371166, 21331003 and 21221061 to J. T).Peer Reviewe

Relationship between obesity and structural brain abnormality: Accumulated evidence from observational studies

Body mass index; Structural brain abnormalitiesÍndex de massa corporal; Anormalitats estructurals del cervellÍndice de masa corporal; Anomalías estructurales del cerebroWe aimed to evaluate the relationship between obesity and structural brain abnormalities assessed by magnetic resonance imaging using data from 45 observational epidemiological studies, where five articles reported prospective longitudinal results. In cross-sectional studies’ analyses, the pooled weighted mean difference for total brain volume (TBV) and gray matter volume (GMV) in obese/overweight participants was -11.59 (95 % CI: -23.17 to -0.02) and -10.98 (95 % CI: -20.78 to -1.18), respectively. TBV was adversely associated with BMI and WC, GMV with BMI, and hippocampal volume with BMI, WC, and WHR. WC/WHR are associated with a risk of lacunar and white matter hyperintensity (WMH). In longitudinal studies’ analyses, BMI was not statistically associated with the overall structural brain abnormalities (for continuous BMI: RR = 1.02, 95 % CI: 0.94–1.12; for categorial BMI: RR = 1.18, 95 % CI: 0.75–1.85). Small sample size of prospective longitudinal studies limited the power of its pooled estimates. A higher BMI is associated with lower brain volume while greater WC/WHR, but not BMI, is related to a risk of lacunar infarct and WMH. Future longitudinal research is needed to further elucidate the specific causal relationships and explore preventive measures.This work was supported by the National Natural Science Foundation of China (No. 82070851, 81870556, 81930019, 81770686, 81970591), Beijing Municipal Administration of Hospital’s Youth Program (QML20170204), Excellent Talents in Dongcheng District of Beijing

Bis(μ-2-{[2-(1,3-benzothia­zol-2-yl)hydrazinyl­idene]meth­yl}-6-meth­oxy­phenolato)bis­[dinitratodysprosium(III)] methanol disolvate

In the centrosymmetric dinuclear title compound, [Dy2(C15H12N3O2S)2(NO3)4]·2CH3OH, the two DyIII atoms are coordinated by two deprotonated 2-{[2-(1,3-benzothia­zol-2-yl)hydrazinyl­idene]meth­yl}-6-meth­oxy­phenol ligands and four nitrate ions, all of which are chelating. The crystal packing is stabilized by inter­molecular N—H⋯O hydrogen bonds and weak O—H⋯O inter­actions, forming a two-dimensional network parallel to (010)

Neutron studies of a high spin Fe19_{19} molecular nanodisc

The molecular cluster system [Fe$_{19}$(metheidi)$_{10}$(OH)$_{14}$O$_{6}$(H$_{2}$O)$_{12}$]NO$_{3}$·24H$_{2}$O, abbreviated as Fe$_{19}$, contains nineteen Fe(III) ions arranged in a disc-like structure with the total spin S = 35/2. For the first order, it behaves magnetically as a single molecule magnet with a 16 K anisotropy barrier. The high spin value enhances weak intermolecular interactions for both dipolar and superexchange mechanisms and an eventual transition to antiferromagnetic order occurs at 1.2 K. We used neutron diffraction to determine both the mode of ordering and the easy spin axis. The observed ordering was not consistent with a purely dipolar driven order, indicating a significant contribution from intermolecular superexchange. The easy axis is close to the molecular Fe1–Fe10 axis. Inelastic neutron scattering was used to follow the magnetic order parameter and to measure the magnetic excitations. Direct transitions to at least three excited states were found in the 2 to 3 meV region. Measurements below 0.2 meV revealed two low energy excited states, which were assigned to S = 39/2 and S = 31/2 spin states with respective excitation gaps of 1.5 and 3 K. Exchange interactions operating over distances of order 10 Å were determined to be on the order of 5 mK and were eight-times stronger than the dipolar coupling

Subcomponent self-assembly of circular helical Dy6_{6}(L)6_{6} and bipyramid Dy12_{12}(L)8_{8} architectures directed via second-order template effects

In situ metal-templated (hydrazone) condensation also called subcomponent self-assembly of 4,6-dihydrazino-pyrimidine, o-vanillin and dysprosium ions resulted in the formation of discrete hexa- or dodecanuclear metallosupramolecular Dy$_{6}$(L)$_{6}$ or Dy$_{12}$(L)$_{8}$ aggregates resulting from second-order template effects of the base and the lanthanide counterions used in these processes. XRD analysis revealed unique circular helical or tetragonal bipyramid architectures in which the bis(hydrazone) ligand L adopts different conformations and shows remarkable differences in its mode of metal coordination. While a molecule of trimethylamine acts as a secondary template that fills the void of the Dy$_{6}$(L)$_{6}$ assembly, sodium ions take on this role for the formation of heterobimetallic Dy$_{12}$(L)$_{8}$ by occupying vacant coordination sites, thus demonstrating that these processes can be steered in different directions upon subtle changes of reaction conditions. Furthermore, Dy$_{6}$(L)$_{6}$ shows an interesting spin-relaxation energy barrier of 435 K, which is amongst the largest values within multinuclear lanthanide single-molecular magnets

Synthesis and single-molecule magnet properties of a trimetallic dysprosium metallocene cation

The dimetallic fulvalene-bridged dysprosium complex [{Dy(Cp*)(μ-BH4)}2(Fvtttt)] (1, Cp* = C5Me5) is converted into the trimetallic borohydride-bridged species [{Dy(Cp*)(Fvtttt)}2Dy(μ-BH4)3] (2). In turn, 2 is reacted with a silylium electrophile to give [{Dy(Cp*)(μ-BH4)(Fvtttt)}2Dy][B(C6F5)4] ([3][B(C6F5)3]), the first trimetallic dysprosocenium cation. Compound [3][B(C6F5)3] can also be formed directly from 1 by adding two equivalents of the electrophile. A three-fold enhancement in the effective energy barrier from 2 to 3 is observed and interpreted with the aid ofab initiocalculations

Coupling of nitric oxide and release of nitrous oxide from rare-earth-dinitrosyliron complexes

Addition of Lewis acidic [Cp*2M]+ (M = Y, Gd) to the dinitrosyliron complexes (DNICs) [(NacNacAr)Fe(NO)2]− (Ar = mesityl, 2,6-diisopropylphenyl) results in formation of the isonitrosyl-bridged DNICs [(Cp*)2M(μ-ON)2Fe(NacNacAr)]. When Ar = 2,6-diisopropylphenyl, coupling of the NO ligands and release of N2O occur. Two factors contribute to this previously unobserved DNIC reactivity mode. First, the oxophilic rare-earth elements drive the formation of isonitrosyl bonds, forcing the DNIC nitrogen atoms into proximity. Second, the bulky substituents further squeeze the DNIC, which ultimately overcomes the barrier to NO coupling, demonstrating that N2O elimination can occur from a single iron center

Dominance of Cyclobutadienyl Over Cyclopentadienyl in the crystal field splitting in dysprosium single-molecule magnets

Replacing a monoanionic cyclopentadienyl (Cp) ligand in dysprosium single-molecule magnets (SMMs) with a dianionic cyclobutadienyl (Cb) ligand in the sandwich complexes [(η4-Cb′′′′)Dy(η5-C5Me4tBu)(BH4)]− (1), [(η4-Cb′′′′)Dy(η8-Pn†)K(THF)] (2) and [(η4-Cb′′′′)Dy(η8-Pn†)]− (3) leads to larger energy barriers to magnetization reversal (Cb′′′′=C4(SiMe3)4, Pn†=1,4-di(tri-isopropylsilyl)pentalenyl). Short distances to the Cb′′′′ ligands and longer distances to the Cp ligands in 1–3 are consistent with the crystal field splitting being dominated by the former. Theoretical analysis shows that the magnetic axes in the ground Kramers doublets of 1–3 are oriented towards the Cb′′′′ ligands. The theoretical axiality parameter and the relative axiality parameter Z and Zrel are introduced to facilitate comparisons of the SMM performance of 1–3 with a benchmark SMM. Increases in Z and Zrel when Cb′′′ replaces Cp signposts a route to SMMs with properties that could surpass leading systems