Large magnetic anisotropy in mononuclear metal complexes

This review examines mononuclear metal complexes with high magnetic anisotropy and the theoretical approaches used to rationalize their magnetic properties. Electronic structure calculations based on CASSCF (or CASPT2/NEVPT2) methods provide a quantitative agreement of the zero- field splitting parameters either for mononuclear transition metal complexes or for equivalent lanthanide systems. To produce a more qualitative tool for predicting the magnetic anisotropy of metal complexes, we have developed a set of simple models. For transition metal systems, a simple model based on the splitting of the d orbitals, considering the coordination mode of the metal and its electronic configuration, is enough to qualitatively predict the system's magnetic anisotropy. A similar approach does not work with the f orbitals of the lanthanide complexes. As an alternative, we studied the electrostatic field generated by the ligands and found that this magnitude controls the shape and the orientation of the anisotropic electron density. This procedure allows us to rationalize and to predict whether the system will have a strong axial character, and also to determine the direction of the magnetic moment

Spin-phonon coupling and slow-magnetic relaxation in pristine ferrocenium

We report the spin dynamic properties of non-substituted ferrocenium complexes. Ferrocenium shows a field-induced single-molecule magnet behaviour in DMF solution while cobaltocene lacks slow spin relaxation neither in powder nor in solution. Multireference quantum mechanical calculations give a non-Aufbau orbital occupation for ferrocenium with small first excitation energy that agrees with the relatively large measured magnetic anisotropy for a transition metal S=1/2 system. The analysis of the spin relaxation shows an important participation of quantum tunnelling, Raman, direct and local-mode mechanisms which depend on temperature and the external field conditions. The calculation of spin-phonon coupling constants for the vibrational modes shows that the first vibrational mode, despite having a low spin-phonon constant, is the most efficient process for the spin relaxation at low temperatures. In such conditions, vibrational modes with higher spin-phonon coupling constants are not populated. Additionally, the vibrational energy of this first mode is in excellent agreement with the experimental fitted value obtained from the local-mode mechanism

Influence of the disposition of the anisotropy axes into the magnetic properties of Mn-III dinuclear compounds with benzoato derivative bridges

The two new Mn-III dinudear compounds [{Mn-(H2O)(phen)}(2)(mu-4-CH3C6H4COO)(2)(mu-O)](ClO4)(2)center dot 3CH(3)CN center dot H2O (1.3CH(3)CN center dot H2O) and [{Mn(H2O)(phen)}(mu-O)](mu-2-BrC6H4COO)(2){Mn(NO3)(phen)}]NO3 (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn-III ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the Mn-III ions (D-Mn and E-Mn) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local D-Mn 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Delta, in absolute value is increased

Metal-Organic Nanocapsules with Functionalized s-Heptazine Ligands

A metalloorganic capsule was synthesized where the ligand is a derivative of heptazine with three carboxylic groups that are coordinated to CuII cations, forming paddle-wheel motifs. Each nanocapsule is neutral, with 12 CuII centers and 8 ligands adopting a rhombicuboctahedron shape. It has almost 3 nm diameter, and the main intermolecular interactions in the solid are π··· π stacking between the C6N7 heptazine moieties. The nanocapsules can form monolayers deposited on graphite as observed by atomic force microscopy, which confirms their stability in solution

Dysprosium-based complexes with a flat pentadentate donor: a magnetic and ab initio study

The reactivity of the well-known pentadentate N3O2 Schiff base H2L (2,6-bis(2-hydroxyphenyliminomethyl)pyridine) towards a lanthanoid metal, in this case DyIII, has been investigated for the first time. This reactivity markedly depends on the pH of the medium and, accordingly, two different complexes, [Dy(HL)(NO3)2]·H2O (1·H2O) and [Dy(L)(NO3)(EtOH)(H2O)]·2H2O (2·2H2O), could be isolated from dysprosium(III) nitrate and H2L. In addition, reaction of H2L with dysprosium(III) chloride in methanol yields [Dy(HL′)2][Dy(L)(Cl2)] (3), where H2L′ ((6-(2-hydroxyphenyliminomethyl)-2-methoxyhydroxymethyl)pyridine) is an N2O2 hemiacetal donor derived from the partial hydrolysis of the H2L ligand, and subsequent addition of the methanol solvent to the carbonyl group. This latter reaction has been firstly observed for a lanthanoid metal. Single crystal X-ray diffraction studies of 1·1.15Py·0.3CH3C6H5, 2·2H2O and 3 show that the Schiff base is acting as a nearly flat pentadentate donor in all the cases, this behaviour being independent of the deprotonation degree of the phenolic oxygen atoms, both mono- or bisdeprotonated. Complexes 1·1.15Py·0.3CH3C6H5 and 2·2H2O show DyN3O6 cores, with distorted geometries closer to spherical tricapped trigonal prism or spherical capped square antiprism for 1·1.15Py·0.3CH3C6H5 and 2·2H2O, respectively. In the case of 3, the [Dy(HL′)2]+ cation shows a dysprosium ion in an N4O4 triangular dodecahedron environment, while the [Dy(L)(Cl2)]− anion displays a DyN3O2Cl2 core with distorted pentagonal bipyramidal geometry. Moreover, attempts to dilute 1·H2O with yttrium yielded single crystals of (Et3NH)[Dy0.09Y0.91(L)(NO3)2] (4), where the Schiff base shows a similar pentadentate coordination mode. Dynamic magnetic studies of 1·H2O, 2·2H2O and 3 show that 2·2H2O and 3 present field-induced slow relaxation of the magnetisation, with Ueff barriers of 46.1(9) and 31.0(7) K for 2·2H2O and 3, respectively, while 1·H2O does not exhibit frequency-dependent peaks of the out of phase susceptibility, even in the presence of an external dc magnetic field. By contrast, the dilute sample 4 behaves as a SIM at zero dc field, with an energy barrier of ca. 49 K. Ab initio calculations using CASSCF methods including spin–orbit effects qualitatively support the obtained magnetic results, indicating that axiality is not the only factor that should be taken into account in order to increase effective energy barriers.Authors thank the Spanish Ministerio de Innovación, Ciencia y Universidades (PGC2018-102052-B-C21, PGC2018-093863-B-C21 and MDM-2017-0767) for financial support. J. C. V thanks Xunta de Galicia for his Ph.D. fellowship. E. R. thanks Generalitat de Catalunya for an ICREA Academia award and for the SGR2017-1289 grant, and S. G. C. for a Beatriu de Pinòs grant. The authors acknowledge computer resources, technical expertise and assistance provided by the CSUC.S

Dinuclear CoIIYIII vs Tetranuclear Co2IIY2III complexes: The effect of increasing molecular size on magnetic anisotropy and relaxation dynamics

The authors acknowledge financial support from Ministerio de Economía y Competitividad (MINECO) for Project CTQ2014-56312-P. The authors also acknowledge a Maria de Maeztu grant (MDM-2017-0767) and thank Ministerio de Educación, Cultura y Deporte for projects PGC2018-093863-B-C21 and PGC2018-102052-B-C21, the Junta de Andalucía (FQM-195) and the Project of excellence P11-FQM-7756, the University of Granada and the Generalitat de Catalunya (SGR2017-1289). M. A. P. thanks MINECO for a Juan de la Cierva Incorporation contract (IJCI-2014-19485). E. R. thanks the Generalitat de Catalunya for an ICREA Academia fellowship and CSUC for computational resources. S. G.-C. thanks Generalitat de Catalunya for a Beatriu de Pinós Fellowship (2017 BP 00080). The HFEPR studies were supported by the NHMFL, which is funded by the National Science Foundation (Cooperative Agreement DMR 1157490) and the State of Florida. The authors thank Dr. A. Ozarowski (NHMFL) for his EPR software SPIN.A new CoII2YIII2 complex with the formula [{Co(u-L)Y(NO3)}2(u-CO3)2]·2CH3OH·2H2O (where H2L = N,N’,N”-trimethyl-N,N”-bis(2-hydroxy-3-methoxy-5-methylbenzyl) diethylenetriamine) has been prepared and its structure solved by single-crystal X-Ray diffraction. The tetranuclear structure is formed by the connection of two [Co(μ-L)Y(NO3)] dinuclear units through two carbonate bridging ligands, which exhibit a tetradentate coordination mode. The CoII ion exhibits a slightly distorted octahedral CoN3O3 coordination environment. From direct-current magnetic data a large and positive axial anisotropy parameter was extracted (D = +82.62 cm-1) and its sign unambiguously confirmed by HFEPR spectra and ab initio calculations. The extracted D value is rather larger than those previously reported for the analogous CoIIYIII dinuclear complexes, which agrees with the fact that the CoII ion in the CoII2YIII2 complex exhibits the lower distortion from the octahedral geometry in this family of CoIInYIIIn complexes. Dynamic ac magnetic measurements show that the reported compound presents field-induced slow relaxation for magnetization reversal, through a combination of direct and Raman processes. Magnetic measurements on the diluted magnetic counterpart (Zn/Co = 10/1) show the persistence of these processes, pointing out their single-ion origin. The Raman relaxation process for the Co2Y2 complex is faster that those observed for the CoY dinuclear counterparts. This fact and the existence of the persistent direct process at low temperature could be because the former molecule is larger and flexible than the latter ones.Maria de Maeztu grant MDM-2017-0767Ministerio de Educación, Cultura y Deporte PGC2018-093863-B-C21, PGC2018-102052-B-C21Junta de Andalucía FQM-195, P11-FQM-7756University of GranadaMinisterio de Economía y Competitividad CTQ2014-56312-P, IJCI-2014-19485Generalitat de Catalunya SGR2017-1289, 2017 BP 00080National Science Foundation DMR 115749

Clinical effectiveness of convalescent plasma in hospitalized patients with COVID-19: a systematic review and meta-analysis

Aims: Given the variability of previously reported results, this systematic review aims to determine the clinical effectiveness of convalescent plasma employed in the treatment of hospitalized patients diagnosed with COVID-19. Methods: We conducted a systematic review of controlled clinical trials assessing treatment with convalescent plasma for hospitalized patients diagnosed with SARS-CoV-2 infection. The outcomes were mortality, clinical improvement, and ventilation requirement. Results: A total of 51 studies were retrieved from the databases. Five articles were finally included in the data extraction and qualitative and quantitative synthesis of results. The overall risk of bias in the reviewed articles was established at low-risk only in two trials. The meta-analysis suggests that there is no benefit of convalescent plasma compared with standard care or placebo in reducing the overall mortality and the ventilation requirement. However, there could be a benefit for the clinical improvement in patients treated with plasma. Conclusion: Current results led to assume that the convalescent plasma transfusion cannot reduce the mortality or ventilation requirement in hospitalized patients diagnosed with SARS-CoV-2 infection. More controlled clinical trials conducted with methodologies that ensure a low risk of bias are still needed. The reviews of this paper are available via the supplemental material section.Fil: Abeldaño Zuñiga, Roberto Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de la Sierra Sur; MéxicoFil: González Villoria, Ruth Ana María. Universidad de la Sierra Sur; MéxicoFil: Elizondo, María Vanesa. Universidad Catolica de Cuyo. Facultad de Ciencias Medicas. Instituto de Investigacion En Ciencias Biomedicas.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Osorio, Anel Yaneli Nicolás. Universidad de la Sierra Sur; MéxicoFil: Gómez Martínez, David. Universidad de la Sierra Sur; MéxicoFil: Coca, Silvia Mercedes. Universidad de la Sierra Sur; Méxic

Dinuclear fluoride single-bridged lanthanoid complexes as molecule magnets: unprecedented coupling constant in a fluoride-bridged gadolinium compound

A new synthetic method allows isolating fluoride-bridged complexes Bu4N{[M(3NO2,5Br-H3L1,1,4)]2(μ-F)} (M = Dy, 1; M = Ho, 2; M = Gd, 3) and Bu4N{[Dy(3Br,5Cl-H3L1,2,4)]2(μ-F)}·2H2O, 4·2H2O. The crystal structures of 1·5CH3C6H5,·2·2H2O·0.75THF, 3, and 4·2H2O·2THF show that all of them are dinuclear compounds with linear single fluoride bridges and octacoordinated metal centers. Magnetic susceptibility measurements in the temperature range of 2–300 K reveal that the GdIII ions in 3 are weakly antiferromagnetically coupled, and this constitutes the first crystallographically and magnetically analyzed gadolinium complex with a fluoride bridge. Variable-temperature magnetization demonstrates a poor magnetocaloric effect for 3. Alternating current magnetic measurements for 1, 2, and 4·2H2O bring to light that 4·2H2O is an SMM, 1 shows an SMM-like behavior under a magnetic field of 600 Oe, while 2 does not show relaxation of the magnetization even under an applied magnetic field. In spite of this, 2 is the first fluoride-bridged holmium complex magnetically analyzed. DFT and ab initio calculations support the experimental magnetic results and show that apparently small structural differences between 1 and 4·2H2O introduce important changes in the dipolar interactions, from antiferromagnetic in 1 to ferromagnetic in 4·2H2OThe authors thank the Spanish Ministerio de Ciencia e Innovación projects (PGC2018-102052-B-C21, PGC2018-093863-B-C21, MCIN/AEI/10.13039/501100011033/FEDER “Una manera de hacer Europa”) for financial support. E.C. acknowledges Junta de Andalucía for the FEDER Andalucía project A-FQM-172-UGR18. J.C.-V. also thanks Xunta de Galicia for his Ph.D. fellowship (ED481A-2018/136)S

Insights into the Spin Dynamics of Mononuclear Cerium(III) Single-Molecule Magnets

Four novel CeIII mononuclear complexes of formulas [Ce(ntfa)3(MeOH)2] (1), [Ce(ntfa)3(5,5′-Me2bipy)] (2), [Ce(ntfa)3(terpy)] (3), and [Ce(ntfa)3(bipy)2] (4), where ntfa = 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionato, 5,5′-Me2bipy = 5,5′-dimethyl-2,2′-dipyridyl, terpy = 2,2′:6′,2″-terpyridine, and bipy = 2,2′-bipyridine, have been synthesized and structurally characterized with CeIII displaying coordination numbers of 8, 8, 9, and 10, respectively. Magnetic measurements indicate that all the complexes show a field-induced single-ion magnet behavior under a small applied dc field. The magnetic analysis shows the relevance of the different spin relaxation mechanisms in the magnetic relaxation of the CeIII compounds, with special emphasis on the local-mode process. Multiconfigurational calculations were also performed to get more information on the axiality of the compounds