Designed intramolecular blocking of the spin crossover of an Fe(II) complex

A ligand derived from 1,3bpp (2-(pyrazol-1-yl)-6-(pyrazol-3-yl)- pyridine) has been prepared to prove that the spin crossover (SCO) of an Fe(II) complex can be blocked by means of intramolecular interactions not related to the crystal field. Calculations show that the blocking is caused by the energy penalty incurred by the rotation of a phenyl ring, needed to avoid steric hindrance upon SCO

Critical assessment of the nature and properties of Fe(II) triazole-based spin-crossover nanoparticles

The shape and size of nanoparticles of the spin crossover compound [Fe(Htrz)2trz]BF4 obtained by the reverse-micelle method and using as co-surfactants dioctylsulfosuccinate and behenic acid are described hrough systematic transmission electron microscopy observations. A rod shape is systematically derived, and the rod sizes, in particular, their width, are controllable through the surfactant concentration, although a poor reproducibility is observed and ascribed to uncontrolled parameters in the micelle elaboration and microemulsion formation and ageing. The influence of synthetic parameters and nanoparticle processing on the spin crossover properties of nanoparticles is also reported, as characterized by both calorimetry and magnetic measurements. These unravel original size and environment effects. On the one hand, the hysteresis width of the thermal spin crossover exhibited by raw nanoparticles increases linearly with the rod width, until it reaches a value of 40 K, close to that of the bulk material. A similarly good correlation is found with the nanoparticle volume. On the other hand, the removal of the surfactant from the raw nanoparticles is found to systematically reduce the hysteresis width in a drastic manner, by up to 16

Designed intramolecular blocking of the spin crossover of an Fe(II) complex

A ligand derived from 1,3bpp (2-(pyrazol-1-yl)-6-(pyrazol-3-yl)-pyridine) has been prepared to prove that the spin crossover (SCO) of an Fe(II) complex can be blocked by means of intramolecular interactions not related to the crystal field. Calculations show that the blocking is caused by the energy penalty incurred by the rotation of a phenyl ring, needed to avoid steric hindrance upon SCO

Enhanced Interplay between Host–Guest and Spin-Crossover Properties through the Introduction of an N Heteroatom in 2D Hofmann Clathrates

[Image: see text] Controlled modulation of the spin-crossover (SCO) behavior through the sorption–desorption of invited molecules is an extensively exploited topic because of its potential applications in molecular sensing. For this purpose, understanding the mechanisms by which the spin-switching properties are altered by guest molecules is of paramount importance. Here, we show an experimental approach revealing a direct probe of how the interplay between SCO and host–guest chemistry is noticeably activated by chemically tuning the host structure. Thus, the axial ligand 4-phenylpyridine (4-PhPy) in the 2D Hofmann clathrates {Fe(4-PhPy)(2)[M(CN)(4)]} (PhPyM; M = Pt, Pd) is replaced by 2,4-bipyridine (2,4-Bipy), resulting in the isomorphous compounds {Fe(2,4-Bipy)(2)[M(CN)(4)]} (BipyM; M = Pt, Pd), which basically differ from the former in that they have a noncoordinated N heteroatom in the ancillary aromatic substituent, i.e., 2-pyridyl instead of phenyl. Our chemical, magnetic, calorimetric, and structural characterizations demonstrate that this subtle chemical composition change provokes outstanding modifications not only in the capability to adsorb small guests as water or methanol but also in the extent to which these guests affect the SCO characteristics

Thermal and pressure-induced spin crossover in a novel three-dimensional Hoffman-like clathrate complex

The synthesis and crystal structure of the interpenetrated metal-organic framework material Fe(bpac) 2[Ag(CN) 2] 2 (bpac = 4,4�-bis(pyridyl)acetylene) are reported along with the characterization of its spin crossover properties by variable temperature magnetometry and Mössbauer spectroscopy. The complex presents an incomplete stepped spin transition as a function of temperature that is modified upon successive thermal cycling. The pressure-induced transition has also been investigated by means of high pressure Raman spectroscopy using a diamond anvil cell. The results show that it is possible to reach the thermally-inaccessible fully low spin state at room temperature by applying hydrostatic pressure to the sample. © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique

Switchable Spin-Crossover Hofmann-Type 3D Coordination Polymers Based on Tri- and Tetratopic Ligands

[EN] Fe-II spin-crossover (SCO) coordination polymers of the Hofmann type have become an archetypal class of responsive materials. Almost invariably, the construction of their architectures has been based on the use of monotopic and linear ditopic pyridine like ligands. In the search for new Hofmann-type architectures with SCO properties, here we analyze the possibilities of bridging ligands with higher connectivity degree. More precisely, the synthesis and structure of {Fe-II(L-N3)[M-I(CN)(2)](2)}center dot(Guest) (Guest = nitro-benzene, benzonitrile, o-dichlorobenzene; M-I = Ag, Au) and {Fe-II(L-N4)[Ag-2(CN)(3)][Ag(CN)(2)]}center dot H2O are described, where L-N3 and L-N4 are the tritopic and tetratopic ligands 1,3,5-tris(pyridin-4-ylethynyl)benzene and 1,2,4,5-tetrakis(pyridin-4-ylethynyl)benzene. This new series of Hofmann clathrates displays thermo- and photoinduced SCO behaviors.We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). FJ.V.-M. thanks MINECO for a predoctoral FPI grant. We also thank Dr. Carlos Marti for helping us with ToposPro software.Valverde-Muñoz, FJ.; Muñoz Roca, MDC.; Ferrer, S.; Bartual-Murgui, C.; Real, JA. (2018). Switchable Spin-Crossover Hofmann-Type 3D Coordination Polymers Based on Tri- and Tetratopic Ligands. Inorganic Chemistry. 57(19):12195-12205. https://doi.org/10.1021/acs.inorgchem.8b01842S1219512205571

Influence of Host-Guest and Host-Host Interactions on the Spin-Crossover 3D Hofmann-type Clathrates {FeII(pina)[MI(CN)2]2·xMeOH (MI = Ag, Au)

[EN] The synthesis, structural characterization and magnetic properties of two new isostructural porous 3D compounds with the general formula {FeII(pina)[MI(CN)2]2}·xMeOH (x = 0¿5; pina = N-(pyridin-4-yl)isonicotinamide; MI = AgI and x ~ 5 (1·xMeOH); MI = AuI and x ~ 5 (2·xMeOH)) are presented. The single-crystal X-ray diffraction analyses have revealed that the structure of 1·xMeOH (or 2·xMeOH) presents two equivalent doubly interpenetrated 3D frameworks stabilized by both argentophilic (or aurophilic) interactions and interligand C¿O···HC H-bonds. Despite the interpenetration of the networks, these compounds display accessible void volume capable of hosting up to five molecules of methanol which interact with the host pina ligand and establish an infinite lattice of hydrogen bonds along the structural channels. Interestingly, the magnetic studies have shown that solvated complexes 1·xMeOH and 2·xMeOH display two- and four-step hysteretic thermally driven spin transitions, respectively. However, when these compounds lose the methanol molecules, the magnetic behavior changes drastically giving place to gradual spin conversions evidencing the relevant influence of the guest molecules on the spin-crossover properties. Importantly, since the solvent desorption takes place following a single-crystal-to-single-crystal transformation, empty structures 1 and 2 (x = 0) could be also determined allowing us to evaluate the correlation between the structural changes and the modification of the magnetic properties triggered by the loss of methanol molecules.We thank the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER funds (CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). F.J.V.-M. thanks MINECO for a predoctoral FPI grant.Valverde-Muñoz, FJ.; Bartual-Murgui, C.; Piñeiro-López, L.; Muñoz Roca, MDC.; Real, JA. (2019). Influence of Host-Guest and Host-Host Interactions on the Spin-Crossover 3D Hofmann-type Clathrates {FeII(pina)[MI(CN)2]2·xMeOH (MI = Ag, Au). Inorganic Chemistry. 58(15):10038-10046. https://doi.org/10.1021/acs.inorgchem.9b01189S1003810046581

Thermo- and photo-modulation of exciplex fluorescence in a 3D spin crossover Hofmann-type coordination polymer

[EN] The search for bifunctional materials showing synergies between spin crossover (SCO) and luminescence has attracted substantial interest since they could be promising platforms for new switching electronic and optical technologies. In this context, we present the first three-dimensional Fe-II Hofmann-type coordination polymer exhibiting SCO properties and luminescence. The complex {Fe-II(bpben)[Au(CN)(2)]}@pyr (bpben = 1,4-bis(4-pyridyl)benzene) functionalized with pyrene (pyr) guests undergoes a cooperative multi-step SCO, which has been investigated by single crystal X-ray diffraction, single crystal UV-Vis absorption spectroscopy, and magnetic and calorimetric measurements. The resulting fluorescence from pyrene and exciplex emissions are controlled by the thermal and light irradiation (LIESST effect) dependence of the high/low-spin state population of Fe-II. Conversely, the SCO can be tracked by monitoring the fluorescence emission. This ON-OFF interplay between SCO and luminescence combined with the amenability of Hofmann-type materials to be processed at the nano-scale may be relevant for the generation of SCO-based sensors, actuators and spintronic devices.This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER (CTQ2013-46275-P and CTQ2016-78341-P), Unidad de Excelencia Maria de Maeztu (MDM-2015-0538), Generalitat Valenciana (PROMETEO/2016/147) and the Swiss National Science Foundation (Project number 200021-169033).Delgado, T.; Meneses-Sánchez, M.; Piñeiro-López, L.; Bartual-Murgui, C.; Muñoz Roca, MDC.; Real, J. (2018). Thermo- and photo-modulation of exciplex fluorescence in a 3D spin crossover Hofmann-type coordination polymer. Chemical Science. 9(44):8446-8452. https://doi.org/10.1039/c8sc02677gS8446845294

{[Hg(SCN)3]2(n-L)}2-: An Efficient Secondary Building Unit for the Synthesis of 2D Iron(II) Spin-Crossover Coordination Polymers

[EN] We report an unprecedented series of two-dimensional (2D) spin-crossover (SCO) heterobimetallic coordination polymers generically formulated as {Fe-II[(He(SCN)(3))(2)](L)(x))}center dot Solv, where x = 2 for L = tvp (trans-(4,4'-vinylenedipyridine)) (1tvp), bpmh ((1E,2E)-1,2-bis(pyridin-4-ylmethylene)hydrazine) (1bpmh center dot nCH(3)OH; n = 0, 1), by eh ( (1E,2E)-1,2-bis (1-(pyridin-4-yl) ethyliden e) hydrazine) (Ibpeh center dot nH(2)O; n = 0, 1) and x = 2.33 for L = 0 0 bpbz (1,4-bis(pyridin-4-yl)benzene) (1bpbz center dot nH(2)O; n = 0, 2/ 3). The results confirm that self-assembly of Fell, [Hg-II(SCN)(4)](2-), and ditopic rodlike bridging ligands L containing 4-pyridyl moieties favors the formation of linear [Fe(mu-L)](n)(2n+) chains and in situ generated binuclear units {[Hg-II(SCN)(3)](2)(mu-L)}(2)-. The latter act as bridges between adjacent chains generating robust 2D layers. The [(FeN6)-N-II] centers are equatorially surrounded by four NCS- groups and two axial N atoms of the organic ligand L. The compound 1tvp and the unsolvated form of 1bpmh undergo complete SCO centered at T-1/2 = 177 and 226 K, characterized by the enthalpy and entropy variations Delta H = 12.3 and 10.5 kJ mol(-1) and Delta S = 69.4 and 48 J KT-1 mol(-1), respectively. The almost complete SCO of the unsolvated form of 1bpeh occurs at ca. T-1/2 = 119 K and exhibits a complete LIESST effect. Regardless of the degree of solvation, a half-spin conversion at T-1/2 < 100 K occurs for 1bpbz center dot nH(2)O, which becomes almost complete at p = 0.65 GPa. The labile solvent molecules present in 1bpmh center dot CH3OH and 1bpely center dot H2O have a dramatic influence on the corresponding SCO behavior.We thank the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). FJ.V.-M. thanks MINECO for a predoctoral FPI grant. D.Z. acknowledges support from the Natural Science Foundation of China (21671121).Zhang, D.; Valverde-Muñoz, FJ.; Bartual-Murgui, C.; Piñeiro-López, L.; Muñoz Roca, MDC.; Real, JA. (2018). {[Hg(SCN)3]2(n-L)}2-: An Efficient Secondary Building Unit for the Synthesis of 2D Iron(II) Spin-Crossover Coordination Polymers. Inorganic Chemistry. 57(3):1562-1571. https://doi.org/10.1021/acs.inorgchem.7b02906S1562157157