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Agradecimentos: We acknowledge financial support from Brazilian agencies: Fapesp, Faperj, Capes and Cnpq Abstract: In this work we present scanning heat flow measurements in the series of compounds Dy1-xGdxCo2 (x = 0, 0.1, 0.2, 0.3) which reveal a first order character in the magnetic transition for x = 0 and 0.1. The isothermal entropy change obtained for a magnetic field variation from 0 to 2T shows good agreement with the calculations based on a model Hamiltonian that takes into account the crystal field, magnetoelastic, exchange and Zeeman interactions. The maximum entropy change varies from 7.0 J/kg K (DyCo2) to 1.8 J/kg K (Dy0.7Gd0.3Co2) under a 2T magnetic field variation. The refrigerant cooling power (RCP) varies from 97 J/kg to 67 J/kg across the series. The entropy shows a strong correlation with the transition temperature regardless the transition type FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO - FAPERJ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

The reactions of hydrated lanthanide(III) [Ln(III)] nitrates and salicylideneaniline (salanH) have provided access to two families of mononuclear complexes depending on the reaction solvent used. In MeCN, the products are [Ln(NO3)3(salanH)2(H2O)]&middot, MeCN, and, in MeOH, the products are [Ln(NO3)3(salanH)2(MeOH)]&middot, (salanH). The complexes within each family are proven to be isomorphous. The structures of complexes [Ln(NO3)3(salanH)2(H2O)]&middot, MeCN (Ln = Eu, 4&middot, MeCN_Eu, Ln = Dy, 7&middot, MeCN_Dy, Ln = Yb, 10&middot, MeCN_Yb) and [Ln(NO3)3(salanH)2(MeOH)]&middot, (salanH) (Ln = Tb, 17_Tb, Ln = Dy, 18_Dy) have been solved by single-crystal X-ray crystallography. In the five complexes, the LnIII center is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms from the two monodentate zwitterionic salanH ligands, and one oxygen atom from the coordinated H2O or MeOH group. The salanH ligands are mutually &ldquo, cis&rdquo, in 4&middot, MeCN_Eu, 7&middot, MeCN_Dy and 10&middot, MeCN_Yb while they are &ldquo, trans&rdquo, in 17_Tb and 18_Dy. The lattice salanH molecule in 17_Tb and 18_Dy is also in its zwitterionic form with the acidic H atom being clearly located on the imine nitrogen atom. The coordination polyhedra defined by the nine oxygen donor atoms can be described as spherical tricapped trigonal prisms in 4&middot, MeCN_Dy, and 10&middot, MeCN_Yb and as spherical capped square antiprisms in 17_Tb and 18_Dy. Various intermolecular interactions build the crystal structures, which are completely different in the members of the two families. Solid-state IR data of the complexes are discussed in terms of their structural features. 1H NMR data for the diamagnetic Y(III) complexes provide strong evidence that the compounds decompose in DMSO by releasing the coordinated salanH ligands. The solid complexes emit green light upon excitation at 360 nm (room temperature) or 405 nm (room temperature). The emission is ligand-based. The solid Pr(III), Nd(III), Sm(III), Er(III), and Yb(III) complexes of both families exhibit LnIII-centered emission in the near-IR region of the electromagnetic spectrum, but there is probably no efficient salanH&rarr, LnIII energy transfer responsible for this emission. Detailed magnetic studies reveal that complexes 7&middot, MeCN_Dy, 17_Tb and 18_Dy show field-induced slow magnetic relaxation while complex [Tb(NO3)3(salanH)2(H2O)]&middot, MeCN (6&middot, MeCN_Tb) does not display such properties. The values of the effective energy barrier for magnetization reversal are 13.1 cm&minus, 1 for 7&middot, MeCN_Dy, 14.8 cm&minus, 1 for 17_Tb, and 31.0 cm&minus, 1 for 18_Dy. The enhanced/improved properties of 17_Tb and 18_Dy, compared to those of 6_Tb and 7_Dy, have been correlated with the different supramolecular structural features of the two families. The molecules [Ln(NO3)3(salanH)2(MeOH)] of complexes 17_Tb and 18_Dy are by far better isolated (allowing for better slow magnetic relaxation properties) than the molecules [Ln(NO3)3(salanH)2(H2O)] in 6&middot, MeCN_Tb and 7&middot, MeCN_Dy. The perspectives of the present initial studies in the Ln(III)/salanH chemistry are discussed.

Magnetic and thermal hysteresis (difference in magnetic properties on cooling and heating) have been studied in polycrystalline Dy (dysprosium) between 80 and 250 K using measurements of the reversible Villari effect and alternating current (AC) susceptibility. We argue that measurement of the reversible Villari effect in the antiferromagnetic phase is a more sensitive method to detect magnetic hysteresis than the registration of conventional B(H) loops. We found that the Villari point, recently reported in the antiferromagnetic phase of Dy at 166 K, controls the essential features of magnetic hysteresis and AC susceptibility on heating from the ferromagnetic state: (i) thermal hysteresis in AC susceptibility and in the reversible Villari effect disappears abruptly at the temperature of the Villari point; (ii) the imaginary part of AC susceptibility is strongly frequency dependent, but only up to the temperature of the Villari point; (iii) the imaginary part of the susceptibility drops sharply also at the Villari point. We attribute these effects observed at the Villari point to the disappearance of the residual ferromagnetic phase. The strong influence of the Villari point on several magnetic properties allows this temperature to be ranked almost as important as the Curie and Néel temperatures in Dy and likely also for other rare earth elements and their alloys. This work was supported by the Spanish Ministerio de Economía y Competitividad, project MAT2014-56116-C04-01-R and by the Government of the Russian Federation (Grant 074-U01) through the ITMO Fellowship and Professorship Program.

The atomic volume of rare earth metal dysprosium (Dy) has been measured up to high pressures of 35 GPa and low temperatures between 200 and 7 K in a diamond anvil cell using angle dispersive X-ray diffraction at a synchrotron source. The hexagonal close-packed (hcp), alpha-Samarium (α-Sm), and double hexagonal close-packed (dhcp) phases are observed to be stable in Dy under high-pressure and low-temperature conditions achieved in our experiments. Dy is known to undergo magnetic ordering below 176 K at ambient pressure with magnetic ordering Néel temperature (TN) that changes rapidly with increasing pressure. Our experimental measurement shows that Dy has near-zero thermal expansion in the magnetically ordered state and normal thermal expansion in the paramagnetic state for all the three known high pressure phases (hcp, α-Sm, and dhcp) to 35 GPa. This near-zero thermal expansion behavior in Dy is observed below the magnetic ordering temperature TN at all pressures up to 35 GPa.

Тетрарні сполуки Er2,34Се(Pr)0,66Ge1,28S7 утворюються у квазіпотрійних системах Er2S3 – R2S3 – GeS2 (R – Ce, Pr) за температури 770 К. Рентгенівським методом порошку встановлено, що ці сполуки кристалізуються у структурному типі – Dy3Ge1,25S7 (просторова група P63). У структурі тетрарних сполук атоми статистичної суміші (Er + R) утворюють тригональні антипризми [(Er + R)7S], які вкладаються сферично навколо октаедрів [Ge26S], наступна сфера навколо цих антипризм складається з [Ge14S]-тетраедрів., Quaternary compounds Er2.34Се(Pr)0.66Ge1.28S7 are formed in the quasi-ternary systems Er2S3–R2S3–GeS2 (R–Ce, Pr) at 770 K. The structure of these compounds was determined from data sets obtained from homogeneous samples weighing 0.8 g recorded at a DRON 4-13 X-ray diffractometer, CuKα radiation, in the range of 10°≤2θ≤100°, scan step 0.05°, 20 s exposure at each point. The computation of the crystal structure of the quaternary compounds Er2.34Се(Pr)0.66Ge1.28S7 was peformed using WinCSD software package. It was determined by powder method that these compounds crystallize in the Dy3Ge1.25S7 structure type (space group P63). The new compounds are formed by substituting Dy atoms in the Dy3Ge1.25S7 structure with atoms of the statistical mixture (2.34 Er + 0.66 Се) or (2.34 Er + 0.66 Pr): r(Dy+3) = 0.0910 nm, averaged radius r(Rr+3 + Ce+3) = 0.0916 nm, r(Er+3 + Pr+3) = 0.0912 nm (was calculated on the basis of the REM content of the statistical mixture). The replacement of Ce atoms with Pr atoms leads to a decrease in the unit cell parameters which is explained mainly by a corresponding decrease in the atomic radii of the above elements. The unit cell contains 22.5 atoms. The coordinates of the atoms and the isotropic displacement parameters have satisfactory values. The 2a site contain Ge2 atoms with 0.28 occupation ratio.The atoms of the statistical mixture (Er + R) form in the structure of the quaternary compounds trigonal antiprisms [(Er + R)7S] that are spherically embedded around the [Ge26S] octahedral; the next sphere around these antiprisms is composed of the [Ge14S] tetrahedra. One of the features of such crystal structure is the formation of two-dimensional networks of sulfur atoms parallel to ab plane. The Er2.34Се(Pr)0.66Ge1.28S7 compounds have mixed covalent ionic nature. The closest packing of sulfur atoms in the Er2.34Се(Pr)0.66Ge1.28S7 structure contains one octahedral void and two tetrahedral voids per unit cell; these are occupied by Ge2 and Ge1 atoms, respectively. A row of prismatic voids that are occupied by the mixture (Er + R) is located between the rows of octahedral and tetrahedral voids. This arrangement of atoms in the structure forms the particular properties of these materials that will be a promising object for the study of physical properties.

Treballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2019, Tutora: Saskia Speed Castro, Five compounds have been synthesized in this work: [Co4(μ3-py2C(OH)O)4(4-Br-3-CF3-PhNCN)2 (PhCOO)2] (1), [Co4(μ2-py2C(OH)O)2(μ3-py2C(OCH3)O)2(μ2-4-Cl-PhNCN)2(4-Cl-PhNCN)2] (2), [Co(py2C(OH)O)(py2C(OCH2CH3)O)][NO3]·3H2O (3), [Zn2Tb(μ2-py2C(OCH2CH3)O)3(μ3-py2C(OCH2CH3)O) (NO3) (H2O)][Tb(NO3)5] (4) and [Dy5Co4(py2C(OH)O)4(μ3-py2CO2)4(μ4-py2CO2)2(O)2(H2O)6(NO3)2][NO3]5 (5). The metal ions of the five compounds are connected through oxo-bridges from the Di(2-pyridil) ketone derivatives formed after solvolysis and a posterior deprotonation. In addition the Co(II) atoms of compound 2 are connected by two R-phenylcyanamides in the end-on coordination mode. The magnetic susceptibility measurements were performed for compounds 1, 2, 4 and 5. Compound 1 and 2 exhibit a ferromagnetic coupling between the Co(II) metal ions. Compound 4 shows paramagnetic behaviour and 5 exhibit weak antiferromagnetic coupling between the Dy(II) ions. Compounds 1, 2 and 5 show SMM (Single Molecular Magnet) behaviour. The relaxation time of magnetization hasn’t been calculated.

The synthesis and structural characterization of two benzoquinone-bridged dinuclear rare-earth complexes [BQ(MCl2·THF3)2] (BQ = 2,5-bisoxide-1,4-benzoquinone; M = Y (1), Dy (2)) are described. Of these reported metal complexes, the dysprosium analogue 2 is the first discrete bridged dinuclear lanthanide complex in which both metal centres reside in pentagonal bipyramidal environments. Interestingly, both complexes undergo significant thermal expansion upon heating from 120 K to 293 K as illustrated by single-crystal X-ray and powder diffraction experiments. AC magnetic susceptibility measurements reveal that 2 does not show the slow relation of magnetization in zero dc field. The absent of single-molecule behaviour in 2 arises from the rotation of the principal magnetic axis as compared to the pseudo-C5 axis of the pentagonal bipyramidal environment as suggested by ab initio calculations. The cyclic voltammetry and chemical reduction experiments demonstrated that complexes 1 and 2 can be reduced to radical species containing [BQ3˙−]. This study establishes efficient synthetic strategy to make bridged redox-active multinuclear lanthanide complexes with a pentagonal bipyramidal coordination environment that are potential precursors for single-molecule magnets. peerReviewed