Encapsulation of a CrIII single-ion magnet within an FeII spin-crossover supramolecular host

Single functional molecules are regarded as future components of nanoscale spintronic devices. Supramolecular coordination chemistry provides unlimited resources to implement multiple functions to individual molecules. A novel coordination [Fe2] helicate exhibiting spin-crossover is demonstrated to be ideally suited to encapsulate a [Cr(ox)3]3@ complex anion (ox=oxalate), unveiling for the first-time single ion slow relaxation of the magnetization for this metal. Apossibility of tuning the dynamics of this relaxation as well as the performance of the CrIII center as qubit arises from the observation that metastable high spin FeII centers from the host can be generated by irradiation with green light at low temperature

Guest-, light- and thermally-modulated spin crossover in [Fe-2(II)] supramolecular helicates

A new bis(pyrazolylpyridine) ligand (H2L) has been prepared to form functional [Fe-2(H2L)(3)](4+) metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe-2(H2L)(3)]X(PF6)(2)center dot xCH(3)OH (1, x = 5.7 and X = Cl; 2, x = 4 and X = Br), X@[Fe-2(H2L)(3)]X(PF6)(2)center dot yCH(3)OH center dot H2O (1a, y = 3 and X = Cl; 2a, y = 1 and X = Br) and X@[Fe-2(H2L)(3)](I-3)(2)center dot 3Et(2)O (1b, X = Cl; 2b, X = Br). Their structure and functional properties are described in detail by single-crystal X-ray diffraction experiments at several temperatures. Helicates 1a and 2a are obtained from 1 and 2, respectively, by a single-crystal-to-single-crystal mechanism. The three possible magnetic states, [LS-LS], [LS-HS], and [HS-HS] can be accessed over large temperature ranges as a result of the structural non-equivalence of the FeII centers. The nature of the guest (Cl- vs. Br-) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS-HS] or [HS-HS] states are generated through irradiation. All helicates (X@[Fe-2(H2L)(3)])(3+) persist in solution

A ferric guest inside a spin crossover ferrous helicate

A designed dimetallic Fe(II) helicate made with biphenylenebridged bispyrazolylpyridine ligands and exhibiting a process of spin crossover at temperatures above ambient is shown to encapsulate an S = 5/2 tris-oxalato Fe(III) ion. The spin relaxation dynamics of this guest are strongly reduced upon encapsulatio

A probe of steric ligand substituent effects on the spin crossover of Fe(II) complexes

Identifying and quantifying the individual factors affecting the temperature and properties of the spin crossover in transition metal complexes is a challenging task, because many variables are involved. While the most decisive factor is the crystal field imparted by ligands around the active metal center, some less common actors are intramolecular steric repulsions or non-covalent interactions. A series of three Fe(ii) complexes of 1,3bpp derivatives of (2-(pyrazol-1-yl)-6-(1H-pyrazol-3-yl)pyridine) have been prepared and characterized crystallographically to probe these effects: [Fe(1,3bpp)2](ClO4)2 (1), [Fe(met1,3bpp)2](ClO4)2 (2) and [Fe(dimet1,3bpp)2](ClO4)2 (3). The ligands exhibit none, one or two methyl substituents on the pyrazol-1-yl heterocycle. These groups exert a dramatic effect on the SCO temperature in the solid state, and, most significantly, in solution (with TSCO (3) > TSCO (1) > TSCO (2)). Extensive DFT calculations have unveiled the origin of these effects which lie in the intramolecular non-covalent or steric interactions rather than resulting from crystal field effects

Coordination [CoII2] and [CoIIZnII] helicates showing slow magnetic relaxation

The slow magnetic relaxation of CoII ions in the elusive intermediate geometry between the trigonal prism and antiprism has been studied on the new [Co2L3]4+ and [CoZnL3]4+ coordination helicates [L is a bis(pyrazolylpyridine) ligand]. Solution paramagnetic 1H NMR and solid-state magnetization measurements unveil single-molecule-magnet behavior with small axial anisotropy, as predicted previously

Bimetallic Intersection in PdFe@FeOx-C Nanomaterial for Enhanced Water Splitting Electrocatalysis

Supported Fe-doped Pd-nanoparticles (NPs) are prepared via soft transfor-mation of a PdFe-metal oraganic framework (MOF). The thus synthesized bimetallic PdFe-NPs are supported on FeOx@C layers, which are essential for developing well-defined and distributed small NPs, 2.3 nm with 35% metal loading. They are used as bifunctional nanocatalysts for the electro-catalytic water splitting process. They display superior mass activity for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), both in alkaline and acid media, compared with those obtained for benchmarking platinum HER catalyst, and ruthenium, and iridium oxide OER catalysts. PdFe-NPs also exhibit outstanding stability against sintering that can be explained by the protecting role of graphitic carbon layers provided by the organic linker of the MOF. Additionally, the superior electrocatalytic performance of the bimetallic PdFe-NPs compared with those of monometallic Pd/C NPs and FeOx points to a synergetic effect induced by Fe-Pd interactions that facilitates the water splitting reaction. This is supported by additional characterization of the PdFe-NPs prior and post electrolysis by TEM, XRD, X-ray photoelectron spectroscopy, and Raman revealing that dispersed PdFe NPs on FeOx@C promote interactions between Pd and Fe, most likely to be Pd-O-Fe active centers

MOF-mediated synthesis of supported Fe-doped Pd nanoparticles under mild conditions for magnetically recoverable catalysis

Metal-organic framework (MOF)-driven synthesis is considered as a promising alternative for the development of new catalytic materials with well-designed active sites. This synthetic approach is used here to gradually transform a new bimetallic MOF, with Pd and Fe as the metal components, by the in situ generation of aniline under mild conditions. This methodology results in a compositionally homogeneous nanocomposite formed by Fe-doped Pd nanoparticles that, in turn, are supported on iron oxide-doped carbon. The nanocomposite has been fully characterized by several techniques such as IR and Raman spectroscopy, TEM, XPS, and XAS. The performance of this nanocomposite as an heterogeneous catalyst for hydrogenation of nitroarenes and nitrobenzene coupling with benzaldehyde has been evaluated, proving it to be an efficient and reusable catalyst

Spin crossover supramolecular coordination compounds: design, synthesis and properties

[eng] The results obtained in this thesis demonstrate the importance of supramolecular chemistry for the design of potential new SCO clusters. Starting from synthesizing the suitable ligands with suitable functional groups, novel host-guest systems could be obtained where the guest play a major role in tuning the physical properties of the guest. Two bis-pyrazolylpyridine lignads, H2L4 and H2L6 were designed and prepared to achieve the assembly of transition metal ions in a triple-stranded helicate fashion where the central cavity can encapsulate different counterions depending on the size of this cavity. The N-H groups found in these ligands which usually directed toward the internal cavity help in the encapsulation of hydrogen acceptor anions. 13 iron-based compounds have been crystallized and studied adding significantly to the helical SCO compounds in the literature. The crystal structure for all the compounds were resolved, which allowed for an extensive study of supramolecular interactions and the influence of these interactions on the magnetic properties of the compounds. The first part of the thesis deals with spin-crossover dinuclear triple-stranded helicates compounds with encapsulated halide ions using H2L4. Six of such helicates with different encapsulated halide or counter ions were synthesized: Cl⊂[Fe2(H2L4)3]Cl(PF6)2·5.7CH3OH (1) Br⊂[Fe2(H2L4)3]Br(PF6)2·4CH3OH (2) Cl⊂[Fe2(H2L4)3]Cl(PF6)2·3CH3OH·1H2O (1a) Br⊂[Fe2(H2L4)3]Br(PF6)2·1CH3OH·1H2O (2a) Cl⊂[Fe2(H2L4)3](I3)3·3(Et2O) (3) Br⊂[Fe2(H2L4)3](I3)3·3(Et2O) (4) These isostructural compounds consist of triple-stranded helicates that encapsulate halide ion inside their cavity. The main difference is the kind of outer counterions and lattice solvents which affect dramatically the magnetic properties of these compounds as a result of changing the supramolecular interactions. Changing the halide ion from chloride to bromide in 1 and 2, respectively, shift the spin transition by 30 K. The SCO occur here from [HS-LS] to [HS-HS] upon heating. Compounds 1a and 2a are the water solvate helicates that produced from single-crystal to single-crystal exchange by exposing the crystals to the ambient water. This exchange leads to important changes; the {X⊂ [Fe2(H2L4)3]}3+ helicate are now symmetric and the two Fe centers are crystallographically identical. This change in the solvent affects dramatically the SCO behavior of the helicates. Two-step SCO from [LS-LS] à [HS- LS]à [HS-HS] states was observed in the bulk magnetic studies. Compounds 3 and 4 consists of {X⊂ [Fe2(H2L4)3]}3+ triple-stranded helicates similar to the one seen in previous helicates where the counter ions are now three triodide (I3-) linear ions occupying the outer space formed between the helical strands and the solvent is ether. In these complexes the iron centers remain in the HS state through all the temperatures. The change of the solvents used in the reaction yielded different supramolecular compounds using the same ligands H2L4. Dimerized mononuclear helicates {X⊂[Fe(H2L4)3]2}3+ was prepared where a halide ion is encapsulated inside the cavity formed by the intercalating dimers. Five dimerized triple-stranded helicates are presented in this thesis: Cl⊂[Fe(H2L4)3]2(OH)(PF6)2·H2O (5). Cl⊂[Fe(H2L4)3]2(FeCl4)3·2C3H6O·4C7H8 (6). Br⊂[Fe(H2L4)3]2(OH)(PF6)2·H2O (7). I⊂[Fe(H2L4)3]2(PF6)2.23(I)0.21(I3)0.56·2CH3OH (8) I⊂[Fe(H2L4)3]2(I)2(I3)0.6(OH)0.4·0.6H2O·2CH3OH·2C3H6O (9) In every mononuclear helicate, one pyrazolyl-pyridine side of each ligand is not coordinated to any metal ion. The SCO behavior of the dimer is also affected by the nature of the halide ions which make hydrogen bonding with the N-H groups of the pyrazole rings. Using the ligand H2L6, the encapsulation of [M(III)(ox)3]3- (M = Fe and Cr; ox = oxalate) metal complexes inside the helical cavity of [Fe2(H2L6)3]4+ was achieved. Two of such triple-stranded helicates are presented in this thesis: Fe(C2O4)3⊂[Fe2(H2L6)3](BF4)·4CH3OH·3.7H2O (10). Cr(C2O4)3⊂[Fe2(H2L6)3](BF4)·1.4CH3OH·6H2O (11). The Fe(II) ions of the helicate exhibit SCO behavior and LIESST effect in the case of the encapsulated chromium oxalate complex. Interestingly, the guest [Cr(III)(ox)3]3- exhibits SIM-like behavior at low temperatures. This is the first example where a host- guest system exhibits both LIESST effect and SIM behavior.[spa] Dos ligandos bis-pyrazolylpyridine, H2L4 y H2L6 fueron diseñados y preparados para sintetizar ensamblajes con iones de metales de transición en forma de helicatos de cadena triple donde la cavidad central puede encapsular diferentes contraiones en función del tamaño de esta cavidad. 13 compuestos a base de hierro se han cristalizado y estudiado, con la adición de manera significativa de compuestos helicoidales con SCO de la literatura. La estructura cristalina de todos los compuestos fueron resueltas, lo que permitió un amplio estudio de las interacciones supramoleculares y la influencia de estas interacciones sobre las propiedades magnéticas de los compuestos. La primera parte de la tesis trata de compuestos helicoidales dinucleares de cadena triple presentando transición de espín con iones haluro encapsulados utilizando H2L4. Estos compuestos isoestructurales consisten en helicatos de cadena triple que encapsulan iones haluro dentro de su cavidad. La principal diferencia es el tipo de contraiones exteriores y disolventes de cristalización que afectan dramáticamente las propiedades magnéticas de estos compuestos, como resultado de cambiar las interacciones supramoleculares. El cambio del ión haluro, de cloruro a bromuro, da un cambio de la transición de espín de unos 30 K. En los complejos metanólicos, la SCO se producen por calentamiento, a partir de [HS-LS] a [HS-HS], donde los estados de espín mixtos se consigue gracias a diferente distorsión alrededor de los iones metálicos, como resultado de diferentes enlaces de hidrógeno supramolecular cerca de los dos. Los helicatos con agua se producen a partir de una transformación cristal-cristal, mediante la exposición de los cristales a agua a temperatura ambiente. Este cambio en el disolvente afecta dramáticamente el comportamiento del SCO. Dos pasos en el SCO ([LS-LS] à [HS-LS] à [HS-HS]) se observarón en los estudios magnéticos. El cambio de los aniones a triyoduro (I3-) estabilizan el estado HS en todas las temperaturas medidas. El cambio en los disolventes utilizados en la reacción produjo diferentes compuestos supramoleculares utilizando el mismo ligando H2L4. Diferente helicatos mononucleares dimerizados {X⊂[Fe(H2L4)3]2}3+ fueron preparado donde se encapsula un ion haluro dentro de la cavidad formada por los dímeros intercalantes. En cada helicato mononuclear, un lado pirazolilo-piridina de cada ligando no se coordina a ningun ion metálico. El comportamiento de SCO del dímero también se ve afectada por la naturaleza de los iones haluro que forman con los enlaces de hidrógeno con los grupos N-H de los anillos de pirazol. Utilizando el ligando H2L6, se logró la encapsulación de complejos metálios de tipo [M(III)(ox)3]3- (M = Fe y Cr; ox = oxalato) dentro de la cavidad helicoidal [Fe2(H2L6)3]4+. Los iones Fe (II) del helicato exhiben SCO y efecto LIESST en el caso del complejo de cromo oxalato encapsulado. Curiosamente, el invitado [Cr(III)(ox)3]3- presenta un comportamiento de SIM a bajas temperaturas. Este es el primer ejemplo en el que un sistema hospedador-huésped exhibe tanto efecto LIESST y comportamiento SIM

Polynuclear Fe(II) complexes: Di/trinuclear molecules and coordination networks

We review here the recent progress made in the synthesis of spin crossover (SCO) Fe(II) coordination complexes with two or three metal atoms, as well as coordination polymers, with the main focus on that in the last five years. We discuss these as well as their magnetic properties to derive magnetostructural correlations. This manuscript is organized through the ligand types that serve to produce the various coordination systems presented. The ligand structure and essential SCO parameters of the complexes are gathered in comprehensive figures and tables. This review illustrates the richness and key parameters of coordination chemistry to develop multiple architectures with the desired properties involving this fascinating phenomeno

Synthesis, characterization and antimicrobial activity of zinc(II) ibuprofen complexes with nitrogen-based ligands

<p>Metal carboxylate complexes possess different carboxylate coordination modes, e.g. monodentate, bidentate, and bridging bidentate. Five Zn(II) complexes were prepared and characterized in order to examine their coordination modes in addition to their biological activity. The syntheses were started by preparation of [Zn(ibup)₂(H₂O)₂] (<b>1</b>). Then, different nitrogen-donor ligands reacted with <b>1</b> to produce [Zn(ibup)₂(2-ampy)₂] (<b>2</b>), [Zn(ibup)(2-ammethylpy)] (<b>3</b>), [Zn(ibup)(2,2′-bipy)] (<b>4</b>), and [Zn₂(ibup)₄(2-methylampy)₂] (<b>5</b>) (ibup = ibuprofen, 2-ampy = 2-aminopyridine, 2-ammethylpy = 2-aminomethylpyridine, 2,2′-bipy = 2,2′-bipyridine, 2-methylampy = 2-(methylamino)pyridine). IR, ¹H NMR, ¹³C{¹H}-NMR and UV–vis spectroscopies were used for characterization. The crystal structures of <b>2</b> and <b>5</b> were determined by single-crystal X-ray diffraction. Investigation of <i>in vitro</i> antibacterial activities for the complexes against Gram-positive (<i>Micrococcus luteus</i>, <i>Staphylococcus aureus</i> and <i>Bacillus subtilis</i>) and Gram-negative (<i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i> and <i>Proteus mirabilis</i>) bacteria were done using agar well-diffusion method. Complex <b>1</b> showed antibacterial activity against Gram-positive bacteria. Complexes <b>2</b> and <b>3</b> did not exhibit antibacterial activity. Complex <b>4</b> showed antibacterial activity and was chosen for further studies to determine the inhibition zone diameter for different concentrations and to set the minimum inhibitory concentration. The antibacterial activity against most of the bacteria was minimized as a result of the complexation of zinc ibuprofen with 2,2′-bipy in <b>4</b>.</p