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Certain magnetic molecules and molecular-based frameworks are considered as alternative materials for cryogenic cooling due to their large magneto-caloric effect. This potential is particularly appealing for applications requiring local refrigeration, but so far no study has been aimed at making thin films of efficient molecular coolers on a typical device substrate and evaluating their cooling potential. In this work, the growth of a dense gadolinium metal–organic framework on oxide-free silicon covered by either self-assembled or covalent monolayers with carboxylic end groups is explored. A continuous coverage with nanosized crystallites of the selected gadolinium formate framework is successfully formed on covalent monolayers obtained by hydrosilylation with either undecenoic acid or undecynoic acid. The thickness of the magnetocaloric deposit can be increased by increasing the growth time, as shown by the surface densities derived through determination of the film magnetic properties. An estimation of the cooling potential of the thicker film obtained shows that it would refrigerate a 2 μm thick Si membrane from 5 to 0.8 K, by adiabatic demagnetization from 2 T to zero field. Altogether, this study demonstrates the potential of molecular cooler thin films to develop on-chip magnetic refrigeration at cryogenic temperatures., The authors acknowledge funding from the Spanish MINECO and FEDER through projects MAT2014-53961-R (GL, EN and OR), MAT2015-70868-ERC (OR), MAT2015-68204-R (GL and ME) and MAT2017-86826-R (OR and EN), as well as from the Aragon government (DGA, consolidated groups MOLCHIP E98, PLATON E31_17R and M4 E13_17R).

Magnetization, heat capacity and direct measurements of the magnetocaloric effect show that EuGd2O4 and EuDy2O4 have a remarkably large magnetocaloric effect at cryogenic temperatures, owing to their high magnetic density and low ordering temperatures. The Gd derivative orders antiferromagnetically at TN = 4.6 K, while its magnetocaloric effect largely exceeds that of the reference refrigerant Gadolinium Gallium Garnet (GGG) above 5 K. The Dy derivative undergoes two phase transitions at TC1 = 3.65 K and TC2 = 4.7 K, respectively, which are the result of a peculiar magnetic arrangement: the first Dy sublattice is parallel to the crystallographic c-axis, while the Eu sublattice makes a variable angle from 0o to 45o with the direction of the second Dy sublattice that lies in the ab-plane. EuDy2O4 has a lower magnetocaloric effect than EuGd2O4, yet larger than GGG. Both ordering mechanisms are semi-quantitatively explained within the frame of a mean-field simulation, which takes into account the magnetic anisotropy strength of the participating magnetic ions., This work has been funded by Spanish Ministry of Science and Innovation (Projects MAT2017–86019-R, MAT2017–84385-R, RTI2018–098537-B-C22), Gobierno de Aragón (Consolidated Group E11_20R) and Comunidad de Madrid (Project S2009/PPQ-1626).

ortho-Vanillin in the presence of nickel and lanthanide ions yields three types of heteronuclear NiII-GdIII complexes, ranging from dinuclear to tetranuclear defect dicubane complexes, as demonstrated by their structural determinations. These complexes are dependent on the solvents used during the reaction processes and on the retained lanthanide ions, as characterized by an increase in their Lewis acid character on moving from lighter to heavier lanthanide ions. Intramolecular ferromagnetic NiII-GdIII interactions are present in the heterodinuclear NiII-GdIII entities, whereas ferromagnetic NiII-NiII and NiII-GdIII interactions dominate above 2 K in the tetranuclear Ni-Gd compounds, devoid of any GdIII-GdIII interaction. The effect of a magnetic field on the magnetic entropy and adiabatic temperature changes is maximum near the liquid-helium boiling temperature, mainly determined by the relative weakness of the magnetic interactions., This work was n supported by Spanish MINECO through grant MAT2015-68204-R (to M. E. and G. L.) and a postdoctoral contract (to G. L.), by CNRS and MAGMANet (Grant NMP3-CT-2005-515767).

et al., The family of compounds of general formula [Ln TM (OH)(L)(OCR)(MeOH)](ClO) {[GdZn(OH)(hmp)(OCPr)](ClO) (1a); [YZn(OH)(hmp)(OCPr)](ClO) (1b); [GdCu(OH)(hmp)(OCPr)](ClO) (2a); [YCu(OH)(hmp)(OCPr)](ClO) (2b); [GdCu(OH)(hep)(OCPr)](ClO) (3a); [GdCu(OH)(Hpdm)(OCBu)](ClO) (4a); [GdCu(OH)(ea)(OCMe)](ClO) (5a); [GdNi(OH)(hmp)(OCEt)(MeOH)](ClO) (6a); [YNi(OH)(hmp)(OCEt)(MeOH)](ClO) (6b); [GdCo(OH)(hmp)(OCEt)(MeOH)](ClO) (7a); [YCo(OH)(hmp)(OCEt)(MeOH)](ClO) (7b)} can be formed very simply and in high yields from the reaction of Ln(NO)·6HO and TM(ClO)·6HO and the appropriate ligand blend in a mixture of CHCl and MeOH in the presence of a suitable base. Remarkably, almost all the constituent parts, namely the lanthanide (or rare earth) ions Ln (here Ln = Gd or Y), the transition metal ions TM (here TM = Zn, Cu, Ni, Co), the bridging ligand L (Hhmp = 2-(hydroxymethyl)pyridine; Hhep = 2-(hydroxyethyl)pyridine; Hpdm = pyridine-2,6-dimethanol; Hea = 2-ethanolamine), and the carboxylates can be exchanged while maintaining the structural integrity of the molecule. NMR spectroscopy of diamagnetic complex 1b reveals the complex to be fully intact in solution with all signals from the hydroxide, ligand L, and the carboxylates equivalent on the NMR time scale, suggesting the complex possesses greater symmetry in solution than in the solid state. High resolution nano-ESI mass spectrometry on dichloromethane solutions of 2a and 2b shows both complexes are present in two charge states with little fragmentation; with the most intense peak in each spectrum corresponding to [LnCu(OH)(hmp)(OCPr)](ClO) . This family of compounds offers an excellent playground for probing how the magnetocaloric effect evolves by introducing either antiferromagnetic or ferromagnetic interactions, or magnetic anisotropy, by substituting the nonmagnetic Zn (1a) with Cu (2a), Ni (6a) or Co (7a), respectively. The largest magnetocaloric effect is found for the ferromagnetically coupled complex 6a, while the predominant antiferromagnetic interactions in 2a yield an inverse magnetocaloric effect; that is, the temperature increases on lowering the applied field, under the proper experimental conditions. In spite of increasing the magnetic density by adding ions that bring in antiferromagnetic interactions (2a) or magnetic anisotropy (7a), the magnetocaloric effect is overall smaller in 2a and 7a than in 1a, where only four Gd spins per molecule contribute to the magnetocaloric properties., EKB thanks the EPSRC for financial support and the Velux Foundation for a Villum Visiting Professor Program grant. JS thanks the Deutsche Forschungsgemeinschaft (SCHN 615/23-1) for continuous support. Supercomputing time at the LRZ Garching (Germany) is gratefully acknowledged. GL and ME thank MINECO/FEDER (MAT2015-68204-R).

In contrast to the mainstream research on molecular refrigerants that seeks magnetically isotropic molecules, we show that the magnetic anisotropy of dysprosium acetate tetrahydrate, [{Dy(OAc)(HO)}]·4 HO (1), can be efficiently used for cooling below liquid-helium temperature. This is attained by rotating aligned single-crystal samples in a constant applied magnetic field. The envisioned advantages are fast cooling cycles and potentially compact refrigerators., We are grateful to Spanish MINECO for financial support (grand number FEDER-MAT2012-38318-C03-01) and for a postdoctoral contract (to G.L.).

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., The magnetic ordering structure of GdPO4 is determined at T=60 mK by the diffraction of hot neutrons with wavelength λ=0.4696 Å. It corresponds to a noncollinear antiferromagnetic arrangement of the Gd moments with propagation vector k=(1/2,0,1/2). This arrangement is found to minimize the dipole-dipole interaction and the crystal-field anisotropy energy, the magnetic superexchange being much smaller. The intensity of the magnetic reflections decreases with increasing temperature and vanishes at T≈0.8 K, in agreement with the magnetic ordering temperature TN=0.77 K, as reported in previous works based on heat capacity and magnetic susceptibility measurements. The magnetocaloric parameters have been determined from heat capacity data at constant applied fields up to 7 T, as well as from isothermal magnetization data. The magnetocaloric effect, for a field change ΔB=0-7T, reaches -ΔST=375.8mJ/cm3K-1 at T=2.1 K, largely exceeding the maximum values reported to date for Gd-based magnetic refrigerants., We acknowledge the Spanish MINECO for funding this research through Grant Nos. MAT2012-38318-C03-01 and MAT2013-44063-R. Research at the Oak Ridge National Laboratory for one author (L.A.B.) was sponsored by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

We report the magnetic properties and magnetic structure of the zircon-type compound GdVO4, together with the magnetic structure of the isostructural NdVO4. At T≃2.5 K, GdVO4 undergoes a phase transition to antiferromagnetic Gz, driven mainly by the exchange interactions, while the magnetic anisotropy and dipolar interactions are minor contributions. Near the liquid-helium boiling temperature, the magnetocaloric effect of GdVO4 is nearly as large as that of the structurally closely related GdPO4. It is noteworthy that GdVO4 has been recently proposed as a good passive regenerator in Gifford-McMahon cryocoolers, since adding a magnetization-demagnetization stage to the cryocooler refrigeration cycle would increase its efficiency for liquefying helium. NdVO4 is a canted Gz-type antiferromagnet and shows enhancement of the magnetic reflections in neutron diffraction below ca. 500 mK, due to the polarization of the Nd nuclei by the hyperfine field., M.E. thanks the Donostia International Physics Center (DIPC) for the support of his stay in San Sebastián. This work has been funded by the Spanish Ministerio de Economía, Industria y Competitividad through Projects No. MAT2017-86019-R and No. MAT2015-68204-R, DGA Consolidated Group E100, and Comunidad de Madrid Project S2009/PPQ1626.

et al., A solvothermal reaction between Ln(NO)·6HO (Ln: Gd, Tb and Dy), 2-hydroxy-1-naphthaldehyde, 2-OH-naphth, and ethylenediamine, en, in MeOH in the presence of a base, NEt, led to the formation of the 1D coordination polymers [Ln(L)(MeO)(MeOH)]·MeOH (Ln = Gd (1·MeOH), Tb(2), Dy (3·MeOH); HL = 1,1′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol), the Schiff-base ligand derived from the condensation of 2-OH-naphth and en), while a similar reaction in an excess of NaN yielded 1D coordination polymers [Ln(L)(N)(MeO)(MeOH)] (Ln = Gd (4), Tb (5), Dy (6)). Finally, upon replacing ethylenediamine with o-phenylenediamine, o-phen, we managed to isolate the discrete dimers [Dy(L′)(MeOH)]·2MeOH (7·2MeOH) and [Gd(L′)(MeOH)]·2MeOH (8·2MeOH) (HL′ = 1,1′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis (naphthalen-2-ol), the Schiff-base ligand from the condensation of 2-OH-naphth and o-phen). Polymers 1-3 describe one-dimensional chains, containing alternating seven- and eight-coordinate Ln metal centers, polymers 4-6 contain eight-coordinate lanthanide ions, while in both 7 and 8 the two Ln centers are eight- and seven-coordinate, adopting square antiprismatic and “piano-stool” geometry, respectively. The magnetocaloric properties of the three Gd analogues were determined from magnetic measurements, yielding the magnetic entropy change-ΔS = 21.8, 23.0 and 16.0 J kg K at T = 3.0 K on demagnetization of 7 T to 0, for 1, 4 and 8, respectively. The study of the magnetic properties also revealed that all three Dy analogues (3, 6 and 7) display out-of-phase signals, therefore suggesting slow magnetic relaxation, while such behaviour was not established in the Tb analogues., The research fund for CJM and ABC has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) – Research Funding Program: THALES. Investing in knowledge society through the European Social Fund. GL and ME thank Spanish MINECO (MAT2015-68204-R). MS, MO and TL: “Project partially supported by Wroclaw Centre of Biotechnology, programme The Leading National Research Centre (KNOW) for years 2014–2018”

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).

Layered gadolinium hydroxides have revealed to be excellent candidates for cryogenic magnetic refrigeration. These materials behave as pure 2D magnetic systems with a Heisenberg-Ising critical crossover, induced by dipolar interactions. This 2D character and the possibility offered by these materials to be delaminated open the possibility of rapid heat dissipation upon substrate deposition., We are grateful to the EU (ERC Advanced Grant SPINMOL), the Spanish MINECO (Projects MAT-2014-56143-R, CTQ-2014-59209-P and FEDER-MAT2012-38318-C03-01), and the Generalitat Valenciana (Prometeo Program and ISIC-Nano). Support from INNCIDE program through Vicerectorat d’lnvestigacio i Política Científica of the University of Valencia is also acknowledged. G. A. thanks the EU for a Marie Curie Fellowship (FP7/2013-IEF-627386). G.M.E. thanks the Spanish MINECO for a Ramón y Cajal Fellowship.

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.-- et al., The reaction of the pro-ligand H4L, which combines the complementary phenolic oxime and diethanolamine moieties within the same organic framework, with Zn(NO3)2·6H2O and Ln(NO3)3·6H2O in a basic methanolic solution generates a family of isostructural heterometallic coordination compounds of general formula [Ln6Zn2(CO3)5(OH)(H2L)4(H3L)2(H4L)]NO3·xMeOH [Ln = Gd, x = 30 (1), Ln = Dy, x = 32 (2), Ln = Sm, x = 31 (3), Ln = Eu, x = 29 (4), Ln = Tb, x = 30 (5)]. The octametallic skeleton of the cage describes a heavily distorted [GdIII6] octahedron capped on two faces by ZnII ions. The metal core is stabilised by a series of μ3- and μ4-CO32− ions, originating from the serendipitous fixation of atmospheric CO2. The magnetic properties of all family members were examined via SQUID magnetometry, with the χMT product and VTVB data of the Gd analogue (1) being independently fitted by numerical diagonalisation to afford the same best-fit parameter JGd–Gd = −0.004 cm−1. The MCE of complex 1 was elucidated from specific heat data, with the magnetic entropy change reaching a value of 22.6 J kg−1 K−1 at T = 1.7 K, close to the maximum entropy value per mole expected from six GdIII spins (SGd = 7/2), 23.7 J kg−1 K−1., S.P. thanks the Danish Ministry of Science, Innovation and Higher Education for a Sapere Aude Fellowship (10-081659), M.E. acknowledges financial support from MINECO through grant MAT2012-38318-C03-01. EKB thanks the EPSRC.

The synthesis, characterization, crystal structures and magnetic properties of isoskeletal heptanuclear disk‐like MII3LnIII4 coordination clusters with the general formula [CoII3LnIII4(µ3‐OH)6L6(CF3SO3)][(CF3SO3)5] where Ln = Gd (2), Y (3) and [NiII3LnIII4(µ3‐OH)6L6(CF3SO3)][(CF3SO3)5] where Ln = Dy (4), Gd (5), Y (6) are presented. All the compounds are stable in solution as confirmed by ESI‐MS. Magnetic studies were performed for compounds 2, 4, 5 and 6 and indicate ferromagnetic coupling while the magnetocaloric properties of 5 are characterized by ΔSm = –15.4 J kg–1 K–1 at T = 5.0 K and ΔTad = 5.9 K at T = 2.3 K, for µ0ΔH = 7 T., We thank the Engineering and Physical Sciences Research Council (EPSRC) UK National Crystallography Service at the University of Southampton for the collection of the crystallographic data for compounds 3, 4 and 4′, the Research Development Fund (RDF) (V. N. D.) and Junior Research Associate (JRA) summer fellowship (C. H.) from the University of Sussex. A. E., G. L. and M. E. thank the Ministerio de Economía, Industria y Competitividad for financial support (Projects CTQ2015-63614-P and MAT2015-68204-R) and for a postdoctoral contract (to G. L.).

The syntheses, structures, magnetic and thermodynamic properties of three related triethanolamine-based GdIII complexes are described. The smallest, a dimer ([Gd2]), can be viewed as the subunit from which the two larger complexes, a linear tetramer ([Gd2]2) and a cyclic hexamer ([Gd2]3), are composed by further deprotonation of the triethanolamine ligand. In all cases, nearest neighbour magnetic ions are weakly correlated by antiferromagnetic isotropic exchange, whose strength does not change significantly from one complex to another; J ranging from -0.10 to -0.13 cm-1. Therefore, rather than the strength of the coupling, it is the spin topology that is the dominant factor in determining the differences between the physical properties - specifically, the nuclearity and the transition from open (dimer and tetramer) to cyclic (hexamer) boundary conditions. Indeed the hexanuclear wheel reaches the continuum limit of classical Heisenberg spin chains. In terms of the magnetocaloric properties, the smaller the nuclearity, the larger the magnetic entropy and adiabatic temperature changes., EKB thanks the EPSRC for funding. SGC, GL, ER and ME thank the Spanish Ministry of Economy, Industry and Competitiveness (MAT2015-68204-R and CTQ2015-64579-C3-1-P) and for a postdoctoral grant (to GL). ER acknowledges the Generalitat de Catalunya for an ICREA Academia grant and the BSC (Barcelona Supercomputer Center) for computational resources. KSM thanks the Australian Research Council for a Discovery grant.

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 {CuII 2LnIII 7} metallic core, while the second reveals a hexadecanuclear {CuII 4LnIII 12} 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 {CuII 2GdIII 7} and {CuII 4GdIII 12} complexes, which display a large magnetocaloric effect, with entropy changes -ΔSm = 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 {CuII 4DyIII 12} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K., K.S.M. thanks the Australian Research Council (ARC) and the Australia-India Strategic Research Fund (AISRF) for support of this work. M.E. acknowledges financial support from MINECO through grant MAT2012-38318-C03-01.

In this work we study the assisted translocation of a polymer across a membrane nanopore, inside which a molecular motor exerts a force fuelled by the hydrolysis of ATP molecules. In our model the motor switches to its active state for a fixed amount of time, while it waits for an ATP molecule which triggers the motor, during an exponentially distributed time lapse. The polymer is modelled as a beads-springs chain with both excluded volume and bending contributions, and moves in a stochastic three dimensional environment modelled with a Langevin dynamics at a fixed temperature. The resulting dynamics shows a Michaelis-Menten translocation velocity that depends on the chain flexibility. The scaling behavior of the mean translocation time with the polymer length for different bending values is also investigated., The authors acknowledge funding from the Spanish MINECO and EU FEDER through projects MAT2013-44063-R (E. P.), MAT2014-53961-R (O. R., E. N., G. L.), MAT2015-70868-ERC (O. R.) and MAT2015-68204-R (M. E., G. L.), as well as for a postdoctoral contract (to G. L.).

The employment of 2-amino-isobutyric acid, Haib, and 2-hydroxy-1-naphthaldehyde, Hnaphth, in NiII/LnIII chemistry has led to the isolation and characterization of two new isostructural 3d–4f tetradecanuclear [NiII6LnIII8] clusters (Ln = GdIII, DyIII), with the Dy analogue displaying temperature and frequency dependent out-of-phase signals, and the Gd analogue showing interesting magnetocaloric properties., CJM: This work was supported by the ARISTEIA Action (Project code 84, acronym MAGCLOPT) of the Operational Programme Education and Lifelong Learning”, co-funded by ESF and National Resources. GL and ME thank Spanish MINECO (MAT2015-68204-R). MS and TL: “Project partially supported by Wroclaw Centre of Biotechnology, programme The Leading National Research Centre (KNOW) for years 2014–2018”. RI thanks the Royal Society of Edinburgh for funding.

The employment of the tetradentate ligand acenaphthenequinone dioxime (acndH2) for a first time in heterometallic CuII/LnIII (Ln = Gd and Dy) chemistry has afforded the one-dimensional coordination polymers [Cu6Gd2(acnd)6(acndH)6(MeOH)6]n (1) and [Cu6Dy2(acnd)6(acndH)6(MeOH)2]n (2), which consist of repeating {Cu6Ln2} clusters that are intermolecularly linked to each other through the oximate groups of two η2:η1:η1:μ3 acnd2– ligands. The [Cu6Ln2(μ3-NO)6(μ-NO)8]4+ core is unprecedented in heterometallic cluster chemistry and comprises two symmetry-related {Cu3Ln} subunits, each with a distorted trigonal pyramidal topology. Magnetic susceptibility studies revealed the presence of predominant ferromagnetic exchange interactions within the {Cu3Ln} subunits and weak antiferromagnetic interactions between them. As a result, the magnetic and magnetocaloric properties of the {Cu6Gd2}n compound could be rationalized in terms of two weakly coupled S = 5 spins that yield a magnetic entropy change of −ΔSm = 11.8 J kg–1 K–1 at T = 1.6 K for μ0ΔH = 7 T., This work was supported by Brock University (Chancellor’s Chair for Research Excellence, to Th.C.S), NSERC-DG and ERA (to Th.C.S), MINECO (MAT2015-68204-R 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.). This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231.

We report the synthesis and structure of a molecular {Gd7} cage of the formula (iPr2NH2)6[Gd7(μ3-OH)3(CO3)6(O2CtBu)12] which has crystallographic C3h symmetry. Low temperature specific heat and adiabatic demagnetization experiments (the latter achieving temperatures below 100 mK), lead to the observation of the effects of both intramolecular dipolar interactions and geometric spin frustration. The dipolar interaction leads to a massive rearrangement of energy levels such that specific heat and entropy below 2 K are strongly modified while magnetic susceptibility and magnetization above 2 K are not affected. The consequences of these phenomena for low temperature magnetocaloric applications are discussed., EMP thanks the Panamanian agency SENACYT-IFARHU. KZ thanks the KRG-Scholarship program in “Human Capacity Development (HCDP)”. JS thanks the Deutsche Forschungsgemeinschaft (DFG SCHN 615/20-1) for continuous support. Supercomputing time at the LRZ Garching is gratefully acknowledged. GL and ME thank Spanish MINECO (MAT2015-68204-R). We also thank EPSRC (UK) for funding an X-ray diffractometer (grant number EP/K039547/1).

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.

El pdf del artículo es la versión post-print., Coole Sache: Mit Phosphonaten wurde eine Gruppe heterometallischer 3d-4f-Käfige mit Wells-Dawson-Struktur zugänglich (siehe Bild; Gd, Dy oder Y lila, Ni cyan, P grün, O orange, C grau). Magnetische Untersuchungen offenbaren ferromagnetische Wechselwirkungen innerhalb des Oxo-zentrierten Nickel-Dreiecks sowie eine sehr große Entropieänderung im Gd-Analogon, das als Kühlmittel für ultratiefe Temperaturen genutzt werden könnte., Y.Z.Z. is grateful for the support of Marie Curie International Incoming Fellowship (EC contract no: PIIF-GA-2008-219588). M.E. acknowledges the MICINN for contracts MAT2009-13977-C03 and CSD2007-00010.

Under the terms of the Creative Commons Attribution license.-- et al., We have investigated the magnetocaloric effect in single and polycrystalline samples of quantum paraelectric EuTiO3 by magnetization and heat capacity measurements. Single crystalline EuTiO3 shows antiferromagnetic ordering due to Eu2+ magnetic moments below TN=5.6K. This compound shows a giant magnetocaloric effect around its Néel temperature. The isothermal magnetic entropy change is 49Jkg-1K-1, the adiabatic temperature change is 21 K, and the refrigeration capacity is 500Jkg-1 for a field change of 7 T at TN. The single crystal and polycrystalline samples show similar values of the magnetic entropy and adiabatic temperature changes. The large magnetocaloric effect is due to suppression of the spin entropy associated with the localized 4f moment of Eu2+ ions. The giant magnetocaloric effect, together with negligible hysteresis, suggest that EuTiO3 could be a potential material for magnetic refrigeration below 40 K., R.M. acknowledges the support of MOE Tier 1 Grant No. R144-000-308-112. J.-S.W. acknowledges the support of MOE Tier 2 Grant No. R144-000-349-112. M.E. acknowledges financial support from MINECO through Grant No. FEDER-MAT2012-38318-C03-01.

et al., The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln=Dy(1), Tb(2), and Gd (3)) and pentanuclear Ln5 complexes (Ln=Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1–6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff)=16.12(8) K and relaxation time (τo)=3.3×10−5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: −ΔSm=26.6 J kg−1 K−1 at T=2.2 K for 3 and −ΔSm=27.1 J kg−1 K−1 at T=2.4 K for 4, both for an applied field change of 7 T., We are thankful to the Department of Science and Technology, New Delhi, for financial support. S.D., A.D., S.K., and S.B. thank CSIR, India for Senior Research Fellowship. V.C. is thankful to the Department of Science and Technology for a J.C. Bose National Fellowship. EC is thankful for financial support to Ministerio de Economía y Competitividad (MINECO) for Projects CTQ-2011-24478, CTQ2014-56312-P, the Junta de Andalucía (FQM-195 and the Project of excellence P11-FQM-7756), the University of Granada financial support. M.E. acknowledges financial support from MINECO through grant MAT2012-38318-C03-01. ST thanks the Junta de Andalucía for a postdoctoral contract.

Density functional theory (DFT) studies on two polynuclear clusters, [(Cu5Gd4O2)-Gd-II-O-III(OMe)(4)(teaH)(4)(O2CC(CH3)(3))(2)(NO3)(4)] (1) and [Cu5Gd2(OH)(4)(Br)(2)-(H2L)(2)(H3L)(2)(NO3)(2)(OH2)(4)] (2), have been carried out to probe the origin of the large magnetocaloric effect (MCE). The magnetic exchange interactions for 1 and 2 via multiple pathways are estimated using DFT calculations. While the calculated exchange parameters deviate from previous experimental estimates obtained by fitting the magnetic data, the DFT parameter set is found to offer a striking match to the magnetic data for both complexes, highlighting the problem of overparameterization. Magnetostructural correlations for {Cu-Gd} pairs have been developed where both the Cu-O-Gd angles and Cu-O-Gd-O dihedral angles are found to significantly influence the magnitude and sign of the exchange constants. The magnitude of the MCE has been examined as a function of the exchange interactions, and clues on how the effect can be enhanced are discussed.

A new family of isomorphous [Cu4Ln] clusters (LnIII = Gd, Tb, Dy) with a ‘propeller’-like topology was obtained from the use of naphthalene-2,3-diol in CuII/LnIII chemistry; all complexes are ferromagnetically-coupled and display either magnetocaloric properties or SMM behavior depending on the central Ln 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), Fundação para a Ciência e a Tecnologia (FCT, Portugal) for financial support to REQUIMTE/LAQV (UID/QUI/50006/2013), the MINECO (MAT2012-38318-C03, to M. E), and the National Natural Science Foundation of China (grants 21371166, 21331003 and 21221061 to J. T).

Part III: Physics and Applications., The recent progress in molecule-based magnetic materials exhibiting a large magnetocaloric effect at liquid-helium temperatures is reviewed. The experimental methods for the characterization of this phenomenon are described. Theory and examples are presented with the aim of identifying those parameters to be addressed for improving the design of new refrigerants belonging to this class of materials. Advanced applications and future perspectives are also discussed., Financial support by the Spanish MINECO through grant MAT2012-38318-C03-01 is acknowledged.

Under the terms of the Creative Commons Attribution 3.0 Unported License., We acknowledge financial support by MINECO through Grant MAT2012-38318-C03-01.

New types of linear tetranuclear LnIII-NiII-NiII-LnIII (LnIII = Dy (1), Gd (2)) complexes have been prepared using the multidentate ligand N,N′-bis(3-methoxysalicylidene)-1,3-diaminobenzene, which has two sets of NO and OO′ coordination pockets that are able to selectively accommodate NiII and LnIII ions, respectively. The X-ray structure analysis reveals that the NiII ions are bridged by phenylenediimine groups forming a 12-membered metallacycle in the central body of the complex, whereas the LnIII ions are located at both sides of the metallacycle and linked to the NiII ions by diphenoxo bridging groups. Phenylenediimine and diphenoxo bridging groups transmit ferromagnetic exchange interactions between the two NiII ions and between the NiII and the LnIII ions, respectively. Complex 1 shows slow relaxation of the magnetization at zero field and a thermal energy barrier Ueff = 7.4 K with HDC = 1000 Oe, whereas complex 2 exhibits an S = 9 ground state and significant magnetocaloric effect (-ΔSm = 18.5 J kg-1 K-1 at T = 3 K and ΔB = 5 T). © 2014 American Chemical Society., Financial support from Ministerio de Economía y Competitividad (MINECO) for Project Nos. CTQ-2011-24478 and MAT2012-38318-C03-01, the Junta de Andalucía (No. FQM-195 and Project of Excellence No. P11-FQM-7756), and the University of Granada are acknowledged. S.T. thanks to Junta de Andalucia for a post-doctoral contract.

This work is licensed under a Creative Commons Attribution 4.0 International License., Geometric spin frustration in low-dimensional materials, such as the two-dimensional kagome or triangular antiferromagnetic nets, can significantly enhance the change of the magnetic entropy and adiabatic temperature following a change in the applied magnetic field, that is, the magnetocaloric effect. In principle, an equivalent outcome should also be observable in certain high-symmetry zero-dimensional, that is, molecular, structures with frustrated topologies. Here we report experimental realization of this in a heptametallic gadolinium molecule. Adiabatic demagnetization experiments reach ~200¿mK, the first sub-Kelvin cooling with any molecular nanomagnet, and reveal isentropes (the constant entropy paths followed in the temperature-field plane) with a rich structure. The latter is shown to be a direct manifestation of the trigonal antiferromagnetic net structure, allowing study of frustration-enhanced magnetocaloric effects in a finite system., We thank the EPSRC (UK) for funding. This work was supported by the Deutsche Forschungsgemeinschaft through Research Unit 945 and grant INST 215/363-1, and by the Spanish MINECO through grant MAT2012-38318-C03-01 and MAT2013-44063-R.

We review history, materials and underlying physics that form a background common to magnetic refrigeration and spin–lattice relaxation. To illustrate how these subjects are profoundly interrelated with each other, we describe studies performed on the molecular nanomagnets with formula [Gd(W5O18)2]9− and [Gd(P5W30O110)]12−. Each molecular unit carries a single ion of gadolinium, which is coordinated to different polyoxometalate moieties, respectively. Each Gd3+ spin is magnetically isolated and maintains thermal equilibrium with the lattice down to temperatures close to absolute zero. For T ≲ 200 mK, the spin–lattice relaxation becomes dominated by pure quantum tunneling events. We discuss these properties with a keen eye for promising applications of molecular nanomagnets, namely, as magnetic refrigerants for attaining such low temperatures and spin qubits in quantum information processing.

et al., The reaction of fac-[MIIIF3(Me3tacn)] ×x H2O with Gd(NO3)3×5H 2O affords a series of fluoride-bridged, trigonal bipyramidal {GdIII 3MIII 2} (M=Cr (1), Fe (2), Ga (3)) complexes without signs of concomitant GdF3 formation, thereby demonstrating the applicability even of labile fluoride-complexes as precursors for 3d-4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3 J kg-1 K-1 (1) and 33.1 J kg-1 K-1 (2) for the field change 7 T→0 T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe-Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close-lying excited states for successful design of molecular refrigerants., K.S.P. and S.P. thank the Danish Ministry of Science Innovation and Higher Education for an EliteForsk travel grant and a Sapere Aude Fellowship (10-081659), respectively. G.L., J.J.M., and M.E. acknowledge financial support by the Spanish MINECO through grant MAT2012-38318-C03-01. G.L. is also grateful to the EC for a Marie Curie-IEF (PIEF-GA-2011-299356). G.R. would like to thank DST, India (SR/S1/IC-41/2010; SR/NM/NS-1119/2011) for funding and IITB for HPC resources. S.K.S. thanks CSIR for a SRF fellowship.

Trabajo presentado al "The 23rd IIR International Congress of Refrigeration" celebrado del 21 al 26 de Agosto del 2011 en Praga.-- Dedicated to Alfred Werner on the 100th Anniversary of his Nobel prize in Chemistry in 1913., We study the magnetothermal properties of magnetically isotropic high-spin molecular nanomagnets containing 17 Fe3+ ions per molecule linked via oxide and hydroxide ions, packed in a crystallographic cubic symmetry. Low-temperature magnetization and heat capacity experiments reveal that each molecular unit carries a net spin ground state as large as S = 35/2 and a magnetic anisotropy as small as D = −0.023 K, while no magnetic order, purely driven by dipolar interactions, is to be expected down to very-low temperatures. These characteristics suggest that the Fe17 molecular nanomagnet can potentially be employed as a sub-Kelvin magnetic refrigerant., This work has been partially supported by Spanish MINECO through grants MAT2009-13977-C03 and PIE201060I012, the EPSRC and The Leverhulme Trust (UK).

Trabajo presentado a la V European School on Molecular Nanoscience (ESMolNa) celebrada en Cuenca (España) del 28 de octubre al 2 de noviembre de 2012., An excellent molecule-based cryogenic magnetic refrigerant, gadolinium acetate tetrahydrate, is here used to decorate selected portions of silicon substrate. By quantitative magnetic force microscopy for a variable applied magnetic field near liquid-helium temperature, the molecules are demonstrated to hold their magnetic properties intact, and therefore their cooling functionality, after their deposition. These results represent a step forward towards the realization of a molecule-based micro-refrigerating device at very low temperatures., This work was supported by the Spanish MINECO through grants CSD2007-00010, MAT2011-24284 and MAT2012-38318, by a CSIC JAE-technician fellowship (to P.G.-M.) and by an EU Marie Curie IEF (PIEF-GA-2011-299356, to G.L.).

El pdf del artículo es la versión post-print.-- et al., Playing it cool: Almost all of the constituent parts of the complex [Ln III 4M II 8(OH) 8(L) 8(O 2CR) 8]X 4, namely the lanthanide ions Ln 3+, the transition-metal ions M 2+, the bridging ligand L, the carboxylates, and the counterions X can be exchanged, thus allowing a thorough understanding of the individual contributions to the magnetocaloric effect. Example in picture: Gd purple, Cu green, O red, N blue. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., E.K.B. wishes to thank the EPSRC for funding. M.E. acknowledges contracts MAT2009-13977-C03 and CSD2007-00010. S.P. thanks the Danish Natural Science Research Council for a Sapere Aude Fellowship (10-081659).

Trabajo presentado a la 5th International Conference on Molecular Materials (MolMat) celebrada en Barcelona (España) del 3 al 6 de julio de 2012., The magnetothermal properties of a coordination polymer and a metal-organic framework (MOF) based on Gd 3+ ions are reported. An equally large cryogenic magnetocaloric effect (MCE) is found, irrespective of the dimensionality. This combined with their robustness makes them appealing for widespread magnetic refrigeration applications. © 2012 The Royal Society of Chemistry., We are grateful to MINECO (contracts MAT2009-13977-C03, MAT2011-24284 and CSD2007-00010), EC (for a Marie Curie-IEF to GL), University of Granada (for a postdoctoral fellowship to MAP), and EPRSC for funding.

The polyoxometalate clusters with formula [Gd(W 5O 18) 2] 9- and [Gd(P 5W 30O 110)] 12- each carry a single magnetic ion of gadolinium, which is the most widespread element among magnetic refrigerant materials. In an adiabatic demagnetization, the lowest attainable temperature is limited by the presence of magnetic interactions that bring about magnetic order below a critical temperature. We demonstrate that this limitation can be overcome by chemically engineering the molecules in such a way to effectively screen all magnetic interactions, suggesting their use as ultra-low-temperature coolers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work has been supported by the European Union (Project ELFOS and ERC Advanced Grant SPINMOL to EC), the Spanish MINECO (Project Consolider-Ingenio in Molecular Nanoscience, CSD2007-00010, and grants MAT2007-61584, MAT2009-13977 and MAT2011-22785), the Gobierno de Aragón (MolChip), and the Generalidad Valenciana (Prometeo Program).

The synthesis, structures, and magnetic properties of six families of cobalt–lanthanide mixed-metal phosphonate complexes are reported in this Article. These six families can be divided into two structural types: grids, where the metal centers lie in a single plane, and cages. The grids include [4 × 3] {Co8Ln4}, [3 × 3] {Co4Ln6}, and [2 × 2] {Co4Ln2} families and a [4 × 4] {Co8Ln8} family where the central 2 × 2 square is rotated with respect to the external square. The cages include {Co6Ln8} and {Co8Ln2} families. Magnetic studies have been performed for these compounds, and for each family, the maximum magnetocaloric effect (MCE) has been observed for the Ln = Gd derivative, with a smaller MCE for the compounds containing magnetically anisotropic 4f-ions. The resulting entropy changes of the gadolinium derivatives are (for 3 K and 7 T) 11.8 J kg–1 K–1 for {Co8Gd2}; 20.0 J kg–1 K–1 for {Co4Gd2}; 21.1 J kg–1 K–1 for {Co8Gd4}; 21.4 J kg–1 K–1 for {Co8Gd8}; 23.6 J kg–1 K–1 for {Co4Gd6}; and 28.6 J kg–1 K–1 for {Co6Gd8}, from which we can see these values are proportional to the percentage of the gadolinium in the core., We are gratufel for financial support provied by a Marie Curie International Incoming Fellowship (to Y.-Z.Z., EC contract no.: PIIF-GA-2008-219588), by the EPSRC (UK) and the Royal Society for a Wolfson Merit Award (to R.E.P.W.), and by the MICINN (Spain) throught contract nos. MAt2009-13977-C03 and CSD2007-00010.

Molecular nanomagnets are considered valid candidates for magnetic refrigeration at low temperatures. Designing these materials for enhanced cooling requires the control and optimization of the quantum properties at the molecular level, in particular: spin ground state, magnetic anisotropy, and presence of low-lying excited spin states. Herein, we present the theoretical framework together with a critical review of recent results, and perspectives for future developments., This work is partially funded by the Spanish Ministry for Science and Innovation through grants MAT2009-13977-C03 and CSD2007- 00010, and in the UK through the generous contributions of The Leverhulme Trust and the EPSRC.

8 páginas, 6 figuras, 1 tabla., Three high-nuclearity mixed valence manganeseII/III coordination clusters, have been synthesised, that is, [MnIII6MnII4(μ3-O)4(HL1)6(μ3-N3)3(μ3-Br)(Br)](N3)0.7/(Br)0.33 MeCN2 MeOH (1) (H3L1=3-methylpentan-1,3,5-triol), [MnIII11MnII6(μ4-O)8(μ3-Cl)4(μ,μ3-O2CMe)2(μ,μ-L2)10Cl2.34(O2CMe)0.66(py)3(MeCN)2]7 MeCN (2) (H2L2=2,2-dimethyl-1,3-propanediol and py is pyridine), and [MnIII12MnII7(μ4-O)8(μ3-η1N3)8(HL3)12(MeCN)6]Cl210 MeOH MeCN (3) (H3L3=2,6-bis(hydroxymethyl)-4-methylphenol) with high ground-spin states, S=22, 28±1, and 83/2, respectively; their magnetothermal properties have been studied. The three compounds are based on a common supertetrahedral building block as seen in the Mn10 cluster. This fundamental magnetic unit is made up of a tetrahedron of MnII ions with six MnIII ions placed midway along each edge giving an inscribed octahedron. Thus, the fundamental building unit as represented by compound 1 can be described as a Mn10 supertetrahedron. Compounds 2 and 3 correspond to two such units joined by a common edge or vertex, respectively, resulting in Mn17 and Mn19 coordination clusters. Magnetothermal studies reveal that all three compounds show interesting long-range magnetic ordering at low temperature, originating from negligible magnetic anisotropy of the compounds; compound 2 shows the largest magnetocaloric effect among the three compounds. This is as expected and can be attributed to the presence of a small magnetic anisotropy, and low-lying excited states in compound 2., S.N. gratefully acknowledges the mobility grant from MAGMANet (grant No. 515767-2) to carry out the research in Karlsruhe, Leiden and Zaragoza. M.E. thanks the Spanish Ministry for Science and Innovation for grants MAT2009-13977-C03 and CSD2007-00010.

For molecular nanomagnets, excesses of magnetic entropy at finite low temperatures are induced by degrees of freedom resulting from macroscopic degeneracies of the molecular spin states. We experimentally demonstrate that this effect can be huge and efficiently exploited for enhancing the magnetic field dependence of the adiabatic temperature change. We specifically consider the ${\text{Mn}}_{32}$ molecular nanomagnet, proving it to be an excellent magnetic refrigerant below $T\ensuremath{\approx}2\text{ }\text{K}$, due almost entirely to its spin degeneracy.

The syntheses and structures of two decametallic mixed-valent Mn supertetrahedra using 2-amino-2-methyl-1,3-propanediol (ampH(2)), two decametallic mixed-valent Mn planar discs using 2-amino-2-methyl-1,3-propanediol (ampH(2)) and 2-amino-2-ethyl-1,3-propanediol (aepH(2)), and a tetradecametallic mixed-valent Mn planar disc using pentaerythritol (H(4)peol) are reported. The decametallic complexes display dominant ferromagnetic exchange and spin ground states of S = 22, and the tetradecametallic complex displays dominant antiferromagnetic exchange and a spin ground state of S = 7 +/- 1. All display large (the former) and enormous (the latter) magnetocaloric effect-the former as a result of negligible zero-field splitting of the ground state, and the latter as a result of possessing a high spin-degeneracy at finite low temperatures-making them the very best cooling refrigerants for low-temperature applications.

We experimentally show that the magnetocaloric properties of molecule-based Prussian blue analogues can be adjusted by controlling during the synthesis the amount of intrinsic vacancies. For Cs_xNi^II_4[Cr^III(CN)_6]_(8+x)/3}, we find indeed that the ferromagnetic phase transition induces significantly large magnetic entropy changes, whose maxima shift from 68 K to 95 K by varying the number of [Cr^III(CN)_6]^3- vacancies, offering an unique tunability of the magnetocaloric effect in this complex., 6 pages, 4 figures, JEMS06

We report on the magnetocaloric properties of two molecule-based hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K, whereas the latter is a ferrimagnet below Tc=230 K. For both, we find significantly large magnetic entropy changes DSm associated to the magnetic phase transitions. Notably, our studies represent the first attempt to look at molecule-based materials in terms of the magnetocaloric effect for temperatures well above the liquid helium range., 4 pages, 6 figures

An unusually large magnetocaloric effect for the temperature region below 10 K is found for the Fe14 molecular nanomagnet. This is to large extent caused by its extremely large spin S ground-state combined with an excess of entropy arising from the presence of low-lying excited S states. We also show that the highly symmetric Fe14 cluster core, resulting in small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below T_N=1.87 K., Comment: 4 pages, 3 figures, accepted for publication in Applied Physics Letters

We report on the magnetic and thermal properties of the Fe14 molecular nanocluster. We find a huge magnetocaloric response in the temperature range below 10 K. This is to large extent caused by its very large spin ground-state combined with an excess of entropy arising from the admixture of low-lying excited S states. We also show that the high degree of symmetry of the Fe14 cluster core, resulting in a very small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below TN = 1.87 K.