Single-Molecule Magnets: From Mn12-ac to dysprosium metallocenes, a travel in time

The discovery of the first Single-Molecule Magnet, Mn12-ac, in 1993 changed the perspective of how information can be stored. The current bit, occupying few hundreds of nanometers in present devices, would be minimized to tens of angstroms at molecular level. However, until a couple of years these materials could only operate at temperatures near to the absolute zero. From 1993 to date, the field of Single-Molecule Magnets (SMMs) has continuously evolved thanks to the close collaboration of chemists and physicists obtaining materials already operating above the liquid nitrogen temperature. This long journey, however, has involved the study of many different routes towards high performance SMMs, being each of them essential in order to deeply understand the quantum dynamics behind these molecules. An era of high spin 3d metal clusters was the beginning of everything, but it went through highly anisotropic low coordinate 3d compounds, lanthanide based magnets, radical bridged compounds and 3d-4f mixed systems, among others, to end up in the current state of the art dysprosium metallocenes. Furthermore, after the magnetic studies in bulk, SMM based hybrid systems are emerging for future application devices, which also involve very interesting multifunctionalities. All in all, this work aims to explain how these materials work and show the trajectory and some of the major advances that have been made during recent years in this fieldThis work was supported by the Spanish Ministerio de Innovación, Ciencia y Universidades (PGC2018 102052-B-C21) and by the University of the Basque Country (GIU 17/13). E.C. is gratefully acknowledged to the Junta de Andalucía (FQM-195 and the Project financed by FEDER funds A-FQM-172-UGR18). A.Z.-L. is grateful for his predoctoral fellowship from GV/EJ

Magnetic and Luminescent Properties of Isostructural 2D Coordination Polymers Based on 2-Pyrimidinecarboxylate and Lanthanide Ions

A couple of isostructural coordination polymers with the general formula [Ln4(pymca)4(AcO)8]n have been obtained from reactions between pyrimidine-2-carboxylate (pymca) ligand and rare-earth ions (Ln = Dy (1), Nd (2)). These two-dimensional compounds have been characterized and the crystal structures have been solved by single-crystal X-ray diffraction technique, resulting in layers along the bc plane based on pymca and acetate anions that act as bridging ligands between metal atoms. Given that pymca and acetate anions possess carboxylate and hetero-nitrogen groups, it is possible to build a coordination polymer whose metal centers have a nine coordination. Furthermore, static and dynamic magnetic measurements of compound 1 reveal the lack of single molecule-magnet (SMM) behavior in this system due to the following two effects: (i) the ligand field does not stabilize magnetic ground states well separated from excited states, and (ii) anisotropy axes are not collinear, according to results with Magellan software. On another level, luminescent properties of compounds 1 and 2 are attributed to singlet π-π* transitions centered on pymca ligand as corroborated by time-dependent density functional theory (TD-DFT) calculations.Junta de Andalucia FQM-394Red Guipuzcoana de Ciencia, Tecnologia e Innovacion OF218/2018University of Basque Country GIU 17/13Basque Government IT1005-16Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE) PGC2018-102052-A-C22 PGC2018-102052-B-C21 PGC2018-102047-B-I00European funding (ERDF)European funding (ESF)Government of the Basque Countr

A Luminescent MOF Based on Pyrimidine-4,6-dicarboxylate Ligand and Lead(II) with Unprecedented Topology

In the present work, we report on a 3D MOF of {[Pb5(μ3-OH)(μ3-NO3)3(μ6-pmdc)3]·H2O}n formula (pmdc = pyrimidine-4,6-dicarboxylate) synthesized by an oven-heated, solvent-free procedure. The large connectivity afforded by the three ligands in their coordination to lead(II) ions grows cubic building units characterized by a central Pb atom with an unusual coordination index of 12 and 6 pmdc ligands occupying the faces. These cubic units are linked to one another giving rise to a quite condensed structure that represents an unprecedented topology showing the (4·62)6(43)2(45·610)3(45·68·82)6(46·69)6(612·83) point symbol. The crystalline material has been characterized by routine physico-chemical techniques to confirm its purity, and its thermal behaviour has been also studied by thermogravimetric and thermodiffractometric analyses. The solid presents a greenish blue photoluminescent emission based on pmdc ligands, as revealed by time-dependent density-functional theory (TDDFT) calculations, which is substantially more intense than in the free H2pmdc ligand according to its improved quantum yield. The emissive capacity of the material is further analysed according to decreasing temperature of the polycrystalline sample, finding that sizeable, long-lasting phosphorescence is present.This research was funded by Gobierno Vasco/Eusko Jaurlaritza (IT1755-22, IT1722-22 and IT1500-22) and Junta de Andalucía (ProyExcel_00386 and FQM-394). This publication is also part of the I+D+i projects of PGC2018-102052-A-C22 and PGC2018-102052-B-C21 codes, funded by MCIN/ AEI/10.13039/501100011033/ and “FEDER Una manera de hacer Europa”

A metal-organic framework based on Co(II) and 3-aminoisonicotinate showing specific and reversible colourimetric response to solvent exchange with variable magnet behaviour

[EN] A versatile metal-organic system consisting of Co-based compounds that show reversible transformations between a 3D metal-organic framework (MOF) of {[Co(mu-3isoani)(2)]center dot DMF}(n) (1) formula (where 3isoani - 3-aminoisonicotinato and DMF - dimethylformamide) and a 0D monomeric [Co(3isoani)(2)(H2O)(4)] (2) complex is reported. These 1 2 transformations, triggered by the exposure of the MOF and the monomer-based compound to H2O and DMF, respectively, involve colour changes from purple (in MOF 1) to light brown (in monomeric complex 2), which imbues the system with colourimetric sensing capacity towards these solvents. Despite the high reactivity of the MOF in contact with water, it presents good thermal stability and permanent porosity with a remarkably high CO2 capture capacity at room temperature (3.35 mmol/g), which is further analysed by in situ single-crystal X-ray diffraction. Experimental magnetic properties and CASSCF/NEVPT2 calculations of all compounds reveal distinct slow magnetic relaxations for 3D and 0D compounds.This work has been funded by the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE; PGC2018-102052-A-C22, PGC2018-102052-B-C21 and PID2019-108028GBC21), University of the Basque Country (GIU20/028), Gobierno Vasco/Eusko Jaurlaritza (IT1005-16, IT1291-19) and Junta de Andalucia (FQM-394, B-FQM-734-UGR20). O.P.C. thanks his predoctoral fellowship to UPV/EHU. The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF)

Zero-Field SMM Behavior Triggered by Magnetic Exchange Interactions and a Collinear Arrangement of Local Anisotropy Axes in a Linear Co3 II Complex

A new linear trinuclear Co(II)3 complex with a formula of [{Co(μ-L)}2Co] has been prepared by self-assembly of Co(II) ions and the N3O3-tripodal Schiff base ligand H3L, which is obtained from the condensation of 1,1,1-tris(aminomethyl)ethane and salicylaldehyde. Single X-ray diffraction shows that this compound is centrosymmetric with triple-phenolate bridging groups connecting neighboring Co(II) ions, leading to a paddle-wheel-like structure with a pseudo-C3 axis lying in the Co−Co−Co direction. The Co(II) ions at both ends of the Co(II)3 molecule exhibit distorted trigonal prismatic CoN3O3 geometry, whereas the Co(II) at the middle presents an elongated trigonal antiprismatic CoO6 geometry. The combined analysis of the magnetic data and theoretical calculations reveal strong easy-axis agnetic anisotropy for both types of Co(II) ions (|D| values higher than 115 cm−1) with the local anisotropic axes lying on the pseudo-C3 axis of the molecule. The magnetic exchange interaction between the middle and ends Co(II) ions, extracted by using either a Hamiltonian accounting for the isotropic magnetic coupling and ZFS or the Lines’ model, was found to be medium to strong and antiferromagnetic in nature, whereas the interaction between the external Co(II) ions is weak antiferromagnetic. Interestingly, the compound exhibits slow relaxation of magnetization and open hysteresis at zero field and therefore SMM behavior. The significant magnetic exchange coupling found for [{Co(μ-L)}2Co] is mainly responsible for the quenching of QTM, which combined with the easy-axis local anisotropy of the CoII ions and the ollinearity of their local anisotropy axes with the pseudo-C3 axis favors the observation of SMM behavior at zero field

Iman Molekularrak: informazio unitate txikienaren bila

Nowadays, storing the highest possible amount of information in size re-duced devices is one of important concerns of society. Even though this kind of tech-nology is quite developed, the discovery of the Mn12-ac coordination compound in 1993 was considered a huge step. This is because Single Molecule Magnets (SMMs) represent the smallest information units. Therefore, new devices based on this kind of materials would enhance information storage capacity. In the present work, the most important and representative discoveries since 1993 have been summarized.; Ahalik eta informazio gehien ahalik eta espazio murritzenean gorde-tzea gizartearen gaur egungo beharra eta nahia da, aldi berean. Zentzu honetan teknolo-gia dezente aurreratua badago ere, 1993. urtean Mn12-ac koordinazio konposatua aur-kitu zenean sekulako aurrerapausoa eman zen. Izan ere, Iman Molekular (SMM, Single Molecule Magnet) deituriko konposatu hauek informazio unitatea molekula bakar ba-tera murriztea ahalbidetzen dute. Ondorioz, material hauekin sortutako gailuek askoz ere potentzial handiagoa izango lukete. Lan honetan 1993. urtetik gaur arte emandako aurrerapauso garrantzitsuenak laburbiltzen dira

Transition metal, lanthanide and mixed 3d-4f based compounds based on Mannich base ligands: a progressive magnetic study towards improved materials

658 p. eng. 196 p. euskEsta tesis se sitúa en el ámbito del magnetismo molecular. Más específicamente, se ha estudiado un gran número de compuestos de coordinación basados en metales de transición, lantánidos y mixtos 3d-4f con interesantes propiedades magnéticas como la de Imán Monomolecular (SMM, Single Molecule Magnet).Con el propósito de sintetizar los compuestos de coordinación se han empleado, mayormente, bases de Mannich compartimentales, los cuales son adecuados para la coordinación tanto a iones 3d como 4f. A lo largo de la tesis, se ha realizado un estudio magnético progresivo con el objetivo de mejorar las propiedades magnéticas de dichos compuestos. Para ello, se ha hecho uso de estrategias ya conocidas como la dilución magnética, combinación de metales paramagnéticos, modulación del campo ligando, etc. Finalmente, vistos los interesantes resultados obtenidos para algunos de los sistemas, se ha tratado de desarrollar su potencial estudiando otras propiedades como la luminiscencia y quiralidad, entre otras

An experimental and theoretical study of the magnetic relaxation in heterometallic coordination polymers based on 6-methyl-2-oxonicotinate and lanthanide(III) ions with square antriprismatic environment

Two new isostructural compounds based on 6-methyl-2-oxonicotinate (6m2onic) ligand and sodium and lanthanide(III) ions are reported. The structural and chemical characterization reveals the following chemical formula: {[Ln(6m2onic)2(μ-6m2onic)2Na(H2O)3]·8H2O}n [where Ln(III) = Dy (1Dy) and Er (2Er)]. These compounds crystallize in the form of one-dimensional arrays held together into a hydrogenbonded structure, in which 6m2onic ligands establish four O,O’ chelating rings with the lanthanide to render a distorted square antiprism (SAPR) geometry. Magnetic dc and ac susceptibility measurements confirm that 1Dy and 2Er behave as SIMs. Magnetic dilutions using Y(III) matrices have been made to achieve a Dy(III) counterpart (1Y/Dy) that presents slow magnetic relaxation under zero dc field. Under an optimized Hdc field (of 1000 Oe and 1500 Oe for 1Y/Dy and 2Y/Er, respectively), 1Y/Dy reveals the occurrence of two well-separated maxima, attributed to SR (Ueff = 65.2 K (45.3 cm−1) and τ0 = 2.76 × 10−9 s) and FR processes (Ueff = 23.2 K (16.1 cm−1) and τ0 = 1.40 × 10−8 s), whereas 2Y/Er shows a multiple relaxation pathway that considers quantum tunnelling of the magnetization (QTM), Orbach, Raman and direct mechanisms. Ab initio calculations have been carried out to support the experimental evidence and to explain the lanthanide ion-dependent behaviour deepen the understanding of the magneto-structural relationship of the SAPR environment.This work has been funded by the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE) (PGC2018- 102052-A-C22, PGC2018-102052-B-C21), University of the Basque Country (GIU20/028), Gobierno Vasco/Eusko Jaurlaritza (IT1755-22), and Junta de Andalucía (FQM-394 and B-FQM-734- UGR2). OPC thanks his predoctoral fellowship to UPV/EH

Combined experimental and theoretical investigation on the magnetic properties derived from the coordination of 6-methyl-2-oxonicotinate to 3d-metal ions

Five new compounds are reported herein starting from 2-hydroxy-6-methylnicotinic acid (H2h6mnic) and first-row transition metal ions, although H2h6mnic shows a prototropy in solution to lead to the 6-methyl-2-oxonicotinate (6m2onic) ligand that is the molecule eventually present in the compounds. The structural and chemical characterization reveals the following chemical formulae: {[MnNa(μ-6m2onic)(μ-6m2onic)(MeOH)]·HO·MeOH} (1Mn), {[MNa(μ-6m2onic)(μ-6m2onic)(μ-HO)(HO)](NO)} [M = Co (2Co) and Ni (3Ni)], 2[Cu(6m2onic)(μ-6m2onic)(MeOH)]·[Cu(6m2onic)(μ-6m2onic)]·2[Cu(6m2onic)(MeOH)]·32HO (4Cu) and {[Cu(μ-6m2onic)]·6HO} (5Cu) (where 6m2onic = 6-methyl-2-oxonicotinate). An unusual structural diversity is observed for the compounds, ranging from isolated complexes (in 4Cu), 1D arrays (in 1Mn and 5Cu) and 3D frameworks (in 2Co and 3Ni). Magnetic properties have been studied for all compounds. Analysis of the magnetic dc susceptibility and magnetization data for 4Cu and 5Cu suggests the occurrence of ferromagnetic exchange, which is well explained by broken-symmetry and CASSCF calculations. The sizeable easy-plane magnetic anisotropy present in compound 2Co allows for a field-induced magnet behaviour with an experimental effective energy barrier of 16.2 cm, although the slow relaxation seems to be best described through Raman and direct processes in agreement with the results of ab initio calculations.This work has been funded by the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE) (PGC2018-102052-A-C22, PGC2018-102052-B-C21), University of the Basque Country (GIU20/028), Gobierno Vasco/Eusko Jaurlaritza (IT1005-16, IT1291-19), and Junta de Andalucía (FQM-394 and B-FQM-734-UGR2). OPC thanks his predoctoral fellowship to UPV/EHU. The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF)

Spin canting and slow magnetic relaxation in mononuclear cobalt(ii) sulfadiazine ternary complexes

Monomeric [Co(SDZ)2phen] (1) and [Co(SDZ)(bq)Cl] (2) complexes (SDZ = sulfadiazine, phen = 1,10-phenanthroline, and bq = 2,2′-biquinoline) have been synthesized and characterized. X-ray diffraction studies indicate that SDZ acts as a bidentate ligand coordinating through the sulfonamide and the pyrimidine N atoms in both compounds. In complex 1, the coordination sphere consists of two SDZ ligands and a bis-chelating phen ligand, giving rise to a CoN6 coordination sphere. On the other hand, 2 has a CoN4Cl core, with two N-atoms from SDZ and two from the bq ligand. Both compounds have been studied by dc and ac magnetometry and shown to display slow magnetic relaxation under an optimum external dc field (1 kOe) at low temperatures. Moreover, compound 2 displays long range magnetic ordering provided by spin-canted antiferromagnetism, which has been characterized by further field-dependent magnetic susceptibility measurements, FC/ZFC curves, hysteresis loops and frequency-independent ac curves. The signs of the calculated D parameters, positive in 1 and negative in 2, have been rationalized according to the two lowest-lying transitions in the orbital energy diagrams derived from ab initio ligand field theory (AILFT). In a subsequent attempt to reveal the possible hidden zero-field SMM behaviour, Ni(II)-based 3 and Co(II)-doped Ni(II)-based (with a Ni : Co ratio of 0.9 : 0.1) heterometallic compound 2Ni were synthesized.C. V.-P. acknowledges the financial support from ANPCYT (PICT 2019-02589). D. B. S. and G. A. E. would like to thank Universidad Nacional de La Plata (UNLP) 11X/876 and X857 and CONICET. The financial support by Gobierno Vasco/Eusko Jaurlaritza (IT1755-22) is also acknowledged. The authors are thankful for the technical and human support provided by the Geochronology and Isotope Geochemistry-SGIker facility of UPV/EHU and European funding (ERDF and ESF). The authors acknowledge Dr María Mar Quesada-Moreno for insightful discussions and help with the quantum-chemical calculations, and they are also grateful to Dr Oscar Castillo for the enlightening discussions on the magnetic properties of these compounds