Pressure-Induced Magnetic Switching and Linkage Isomerism in K0.4Fe4[Cr(CN)6]2.8·16H2O: X-ray Absorption and Magnetic Circular Dichroism Studies

Pressure-induced single-crystal-to-single-crystal nitrite ligand isomerisation accompanied by a piezochromic effect

High-pressure structural study of a piezochromic crystal of a rare di-exo-nitrito nickel(II) complex supported by computational analysis is presented. The examined system is not photoswitchable, however, in the 0-6.2 GPa pressure range the crystal undergoes two phase-transitions accompanied by a colour change and the nitrite ligand isomerisation, which is unique.

Pressure-controlled magnetism in 2D molecular layers

Long-range magnetic ordering of two-dimensional crystals can be sensitive to interlayer coupling, enabling the effective control of interlayer magnetism towards voltage switching, spin filtering and transistor applications. With the discovery of two-dimensional atomically thin magnets, a good platform provides us to manipulate interlayer magnetism for the control of magnetic orders. However, a less-known family of two-dimensional magnets possesses a bottom-up assembled molecular lattice and metal-to-ligand intermolecular contacts, which lead to a combination of large magnetic anisotropy and spin-delocalization. Here, we report the pressure-controlled interlayer magnetic coupling of molecular layered compounds via chromium-pyrazine coordination. Room-temperature long-range magnetic ordering exhibits pressure tuning with a coercivity coefficient up to 4 kOe/GPa, while pressure-controlled interlayer magnetism also presents a strong dependence on alkali metal stoichiometry and composition. Two-dimensional molecular interlayers provide a pathway towards pressure-controlled peculiar magnetism through charge redistribution and structural transformation.

Single-Crystal to Single-Crystal Transformation of a Spin-Crossover Hybrid Perovskite via Thermal-Induced Cyanide Linkage Isomerization

Linkage isomers involving changes in the bonding mode of ambidentate ligands have potential applications in data storage, molecular machines, and motors. However, the observation of the cyanide-linkage-isomerism-induced spin change (CLIISC) effect characterized by single-crystal X-ray diffraction remains a considerable challenge. Meanwhile, the high-spin and low-spin states can be reversibly switched in spin-crossover (SCO) compounds, which provide the potential for applications to data storage, switches, and sensors. Here, a new perovskite-type SCO framework (PPN)[Fe{Ag(CN)₂}₃] (PPN⁺ = bis(trisphenylphosphine)iminium cation) is synthesized, which displays the unprecedented aging and temperature dependences of hysteretic multistep SCO behaviors near room temperature. Moreover, the thermal-induced cyanide linkage isomerization from Fe^II-N≡C-Ag^I to Fe^II-C≡N-Ag^I is revealed by single-crystal X-ray diffraction, Raman, and Mössbauer spectra, which is associated with a transition from the mixed spin state to the low-spin state and a dramatic volume shrinkage. Considering the wide use of cyanogen in magnetic systems, the association of CLIISC and SCO opens a new dimension to modulate the spin state and realize a colossal negative thermal expansion.

Toward Quantitative Magnetic Information from Transition Metal K-Edge XMCD of Prussian Blue Analogs

Two series of Prussian blue analogs (PBA) were used as model compounds in order to disentangle the information contained in X-ray magnetic circular dichroism (XMCD) at the K-edges of transition metals. The number of 3d electrons on one site of the bimetallic cyanide polymer has been varied by associating to the [Fe(CN)₆]^3- or the [Cr(CN)₆]^3- precursors various divalent metal ions A²⁺ (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, and Cu²⁺). The compounds were studied by X-ray diffraction and SQUID magnetometry, as well as by X-ray absorption spectroscopy and XMCD at the K-edges of the A²⁺ transition metal ion. The study shows that the 1s → 4p contribution to the A K-edge XMCD signal can be related to the electronic structure and the magnetic behavior of the probed A²⁺ ion: the shape of the signal to the filling of the 3d orbitals, the sign of the signal to the direction of the magnetic moment with respect to the applied magnetic field, the intensity of the signal to the total spin number S_A, and the area under curve to the Curie constant C_A. The whole study hence demonstrates that PBAs are particularly well-adapted for understanding the information contained in the transition metals K-edge XMCD signals. It also offers new perspectives toward the full disentangling of the information contained in these signals and access to new insights into materials magnetic properties.

Pressure Tunable Electronic Bistability in Fe(II) Hofmann-like Two-Dimensional Coordination Polymer [Fe(Fpz)2Pt(CN)4]: A Comprehensive Experimental and Theoretical Study

A comprehensive experimental and theoretical study of both thermal-induced spin transition (TIST) as a function of pressure and pressure-induced spin transition (PIST) at room temperature for the two-dimensional Hofmann-like SCO polymer [Fe(Fpz)₂Pt(CN)₄] is reported. The TIST studies at different fixed pressures have been carried out by magnetic susceptibility measurements, while PIST studies have been performed by means of powder X-ray diffraction, Raman, and visible spectroscopies. A combination of the theory of elastic interactions and numerical Monte Carlo simulations has been used for the analysis of the cooperative interactions in TIST and PIST studies. A complete (T, P) phase diagram for the compound [Fe(Fpz)₂Pt(CN)₄] has been constructed. The critical temperature of the spin transition follows a lineal dependence with pressure, meanwhile the hysteresis width shows a nonmonotonic behavior contrary to theoretical predictions. The analysis shows the exceptional role of the total entropy and phonon contribution in setting the temperature of the spin transition and the width of the hysteresis. The anomalous behavior of the thermal hysteresis width under pressure in [Fe(Fpz)₂Pt(CN)₄] is a direct consequence of a local distortion of the octahedral geometry of the Fe(II) centers for pressures higher than 0.4 GPa. Interestingly, there is not a coexistence of the high- and low-spin (HS and LS, respectively) phases in TIST experiments, while in PIST experiments, the coexistence of the HS and LS phases in the metastable region of the phase transition induced by pressure is observed for a first time in a first-order gradual spin transition with hysteresis.

A comprehensive experimental and theoretical study of both thermal-induced spin transition as a function of pressure and pressure-induced spin transition at room temperature for the two-dimensional Hofmann-like SCO polymer [Fe(Fpz)₂Pt(CN)₄] is reported. A complete (T, P) phase diagram for compound [Fe(Fpz)₂[Pt(CN)₄] has been constructed. The critical temperature of the spin transition follows a lineal dependence with pressure, meanwhile the hysteresis width shows a nonmonotonic behavior contrary to theoretical predictions.

Pressure and temperature dependences of the canting angle and increase in the magnetic ordering temperature, Tc(P), for the weak ferromagnet Li+[TCNE]˙- (TCNE = tetracyanoethylene)

The hydrostatic pressure dependence of the magnetic ordering temperature, T_c(P), for the interpenetrating, diamondoid lattice-structured, weak ferromagnet (= canted antiferromagnet) Li⁺[TCNE]˙^- (TCNE = tetracyanoethylene) reversibly increases from 20.9 to 23.4 K at 9.73 kbar, an increase of 12% with a rate of increase, dT_c/dP, of 0.27 K kbar^-1. The 5 T magnetization increased by 672% from 186 emu Oe mol^-1 at ambient pressure to an average of 1440 emuOe mol^-1 upon application of pressure. The remanent magnetization initially increases 30% from 10.8 to 14.0 emuOe mol^-1 from ambient to 0.06 kbar, and increases further by 6% to a maximum of 14.8 emuOe mol^-1 at 0.56 kbar before declining by 22% to 11.5 emuOe mol^-1 at 9.73 kbar. The pressure-dependent coercive field, H_cr(P), initially decreases by 42% from 31.1 Oe at ambient pressure to 18 Oe at 0.06 kbar, then increases to 52 Oe at 9.73 kbar. The canting angle, α, increases by 28% from 0.52° to 0.66° at 0.06 kbar, then decreases by 23% to 0.51° at 9.73 kbar, as well as increases by 2% from 0.536° to 0.548° from 1.8 to 2.5 K, before decreasing by 79% to 0.117° at 19 K. The interlattice interactions are attributed to be the primary exchange mechanism. Thus, α(T) and α(P) have similar dependencies that are attributed to a competition between an increase and a decrease in the intra- and interlayer C⋯N interlattice separations as the temperature and pressure increases.

Pressure Dependence of the Magnetic Ordering Temperature (Tc) for the Na2Mn[Mn(CN)6] Noncubic Prussian Blue Analogue

The pressure dependence of the magnetic properties of rhombohedral Na₂Mn[Mn(CN)₆] up to 10 kbar has been studied. The magnetic ordering temperature, T_c, for Na₂Mn[Mn(CN)₆] reversibly increases with increasing applied hydrostatic pressure, P, by 9.0 K (15.2%) to 68 K at 10 kbar with an average rate of increase, dT_c/dP, of 0.86 K/kbar. The magnetization at 50 kOe and remanent magnetization, M_r(H), remain constant with an average value of 13,100 ± 200 and 8500 ± 200 emuOe/mol. The coercive field H_cr increases by 12% from 13,400 to 15,000 Oe. The increase and rate of increase of T_c for rhombohedral Na₂Mn[Mn(CN)₆] are reduced with respect to monoclinic A₂Mn[Mn(CN)₆] (A = K and Rb), but they are still greater than those of cubic Cs₂Mn[Mn(CN)₆]. This is attributed to the compression of the MnNC framework bonding without decreasing ∠Mn^II-N≡C, maintaining the unit cell in accord with cubic A = Cs at lower applied pressures, and not due to reduction in ∠Mn^II-N≡C, which correlates with increasing T_c that is reported for A = K and Rb as well as Cs at higher applied pressures.

Intrinsic Effect of Pyridine-N-Position on Structural Properties of Cu-Based Low-Dimensional Coordination Frameworks

Metal-organic assemblies have received significant attention for catalytic and other applications, including gas and energy storage, due to their porosity and thermal/chemical stability. Here, we report the synthesis and physicochemical characterization of three metallosupramolecular assemblies consisting of isomeric ambidentate pyridyl-β-diketonate ligands L1–L3 and Cu(II) metal ions. It has been demonstrated that the topology and dimensionality of generated supramolecular aggregates depend on the location of the pyridine nitrogen donor atom in L1–L3. This is seen in characterization of two distinct 2D polymeric assemblies, i.e., [Cu(L1)₂]_n and [Cu(L2)₂]_n, in which both β-diketonate and pyridine groups are coordinated to the Cu(II) center, as well as in characterization of the mononuclear 1D complex Cu(L3)₂, in which the central atom is bound only by two β-diketonate units.

Solid-state 1D → 3D transformation of polynitrile-based coordination polymers by dehydration reaction

In crystal structures of two chain coordination polymers [M(tcnopr3OH)₂(H₂O)₂] (M = Ni^II and Co^II; tcnopr3OH^- = [(NC)₂CC(O(CH₂)₃OH)C(CN)₂]^-) based on a N,O or N,N'-bridge polynitrile ligand, the parallel chains are connected via, respectively, C[triple bond, length as m-dash]NH-O and O-HO hydrogen bonds between uncoordinated functional groups of the ligand and coordinated water molecules. Upon heating, both solids undergo dehydration accompanied by degradation of their single crystals. Powder X-ray diffraction showed that non-isostructural triclinic single crystals transformed to isostructural monoclinic compounds. The solid-state reaction yielded 3D coordination polymers [M(tcnopr3OH)₂] (M = Ni^II and Co^II) based on a N,N',O-connected tcnopr3OH^-. Although previously tens of complexes based on tcnopr3OH and similar anions were synthesized and X-ray characterized, none of these contain a tridentate polynitrile ligand. Thus, this study provides evidence that solid-state reactions allow obtaining novel coordination modes of polynitrile ligands. The possible pathways for the transformation of H-bonded networks to 3D coordination polymers are discussed on the basis of the topological approach. Applicability of the topological approach to predict possible networks of solid-state reaction products based on the crystal structures of initial compounds is demonstrated.

How to Quench Ferromagnetic Ordering in a CN-Bridged Ni(II)-Nb(IV) Molecular Magnet? A Combined High-Pressure Single-Crystal X-Ray Diffraction and Magnetic Study

High-pressure (HP) structural and magnetic properties of a magnetic coordination polymer {[NiII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Ni2Nb) are presented, discussed and compared with its two previously reported analogs {[MnII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Mn2Nb) and {[FeII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Fe2Nb). Ni2Nb shows a significant decrease of the long-range ferromagnetic ordering under high pressure when compared to Mn2Nb, where the pressure enhances the Tc (magnetic ordering temperature), or to Fe2Nb exhibiting a pressure-induced spin crossover. The different HP magnetic responses of the three compounds were rationalized and correlated with the structural models as determined by single-crystal X-ray diffraction.

The Effect of Pressure on Magnetic Properties of Prussian Blue Analogues

We present the review of pressure effect on the crystal structure and magnetic properties of Cr(CN)6-based Prussian blue analogues (PBs). The lattice volume of the fcc crystal structure space group Fm 3 ¯ m in the Mn-Cr-CN-PBs linearly decreases for p ≤ 1.7 GPa, the change of lattice size levels off at 3.2 GPa, and above 4.2 GPa an amorphous-like structure appears. The crystal structure recovers after removal of pressure as high as 4.5 GPa. The effect of pressure on magnetic properties follows the non-monotonous pressure dependence of the crystal lattice. The amorphous like structure is accompanied with reduction of the Curie temperature (TC) to zero and a corresponding collapse of the ferrimagnetic moment at 10 GPa. The cell volume of Ni-Cr-CN-PBs decreases linearly and is isotropic in the range of 0–3.1 GPa. The Raman spectra can indicate a weak linkage isomerisation induced by pressure. The Curie temperature in Mn2+-CrIII-PBs and Cr2+-CrIII-PBs with dominant antiferromagnetic super-exchange interaction increases with pressure in comparison with decrease of TC in Ni2+-CrIII-PBs and Co2+-CrIII-PBs ferromagnets. TC increases with increasing pressure for ferrimagnetic systems due to the strengthening of magnetic interaction because pressure, which enlarges the monoelectronic overlap integral S and energy gap ∆ between the mixed molecular orbitals. The reduction of bonding angles between magnetic ions connected by the CN group leads to a small decrease of magnetic coupling. Such a reduction can be expected on both compounds with ferromagnetic and ferrimagnetic ordering. In the second case this effect is masked by the increase of coupling caused by the enlarged overlap between magnetic orbitals. In the case of mixed ferro–ferromagnetic systems, pressure affects μ(T) by a different method in Mn2+–N≡C–CrIII subsystem and CrIII–C≡N–Ni2+ subsystem, and as a consequence Tcomp decreases when the pressure is applied. The pressure changes magnetization processes in both systems, but we expect that spontaneous magnetization is not affected in Mn2+-CrIII-PBs, Ni2+-CrIII-PBs, and Co2+-CrIII-PBs. Pressure-induced magnetic hardening is attributed to a change in magneto-crystalline anisotropy induced by pressure. The applied pressure reduces saturated magnetization of Cr2+-CrIII-PBs. The applied pressure p = 0.84 GPa induces high spin–low spin transition of cca 4.5% of high spin Cr2+. The pressure effect on magnetic properties of PBs nano powders and core–shell heterostructures follows tendencies known from bulk parent PBs.

Electrically switchable magnetic exchange in the vibronic model of linear mixed valence triferrocenium complex

A vibronic model for the electric field control of antiferromagnetic exchange is developed for the linear mixed-valence triferrocenium complex Fe(iii)–Fe(ii)–Fe(iii), which is proposed as possible molecular candidate for the implementation of a quantum logic gate.

Effect of the Metal Ion on the Enantioselectivity and Linkage Isomerization of Thiosemicarbazone Helicates

The effect of the metal ion and ligand design on the enantioselectivity and linkage isomerization of neutral cobalt and zinc bisthiosemicarbazone metallohelicates has been investigated in this work. The electrochemical synthesis has afforded the enantioselective formation of chirally pure cobalt helicates, and the ΛΛ isomer of a single enantiomer has been crystallized as only product for the cobalt methyl-substituted thiosemicarbazone helicate. Interestingly linkage isomers have been formed from zinc ethyl-substituted thiosemicarbazone helicate enantiomers for the first time. The co-existence of these isomers has been evaluated from the point of view of both experimental results and computational calculations.

Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers

Materials that demonstrate long-range magnetic order are synonymous with information storage and the electronics industry, with the phenomenon commonly associated with metals, metal alloys or metal oxides and sulfides. A lesser known family of magnetically ordered complexes are the monometallic compounds of highly anisotropic d-block transition metals; the ‘transformation' from isolated zero-dimensional molecule to ordered, spin-canted, three-dimensional lattice being the result of through-space interactions arising from the combination of large magnetic anisotropy and spin-delocalization from metal to ligand which induces important intermolecular contacts. Here we report the effect of pressure on two such mononuclear rhenium(IV) compounds that exhibit long-range magnetic order under ambient conditions via a spin canting mechanism, with T_c controlled by the strength of the intermolecular interactions. As these are determined by intermolecular distance, ‘squeezing' the molecules closer together generates remarkable enhancements in ordering temperatures, with a linear dependence of T_c with pressure.

Materials that demonstrate long-range magnetic order are synonymous with information storage. Here, the authors report the effect of pressure on two mononuclear rhenium compounds that exhibit long-range magnetic order under ambient conditions via a spin canting mechanism, where T_c is proportional to pressure.

The nature of chemical bonding in actinide and lanthanide ferrocyanides determined by X-ray absorption spectroscopy and density functional theory

The electronic properties of actinide cations are of fundamental interest to describe intramolecular interactions and chemical bonding in the context of nuclear waste reprocessing or direct storage. The 5f and 6d orbitals are the first partially or totally vacant states in these elements, and the nature of the actinide ligand bonds is related to their ability to overlap with ligand orbitals. Because of its chemical and orbital selectivities, X-ray absorption spectroscopy (XAS) is an effective probe of actinide species frontier orbitals and for understanding actinide cation reactivity toward chelating ligands. The soft X-ray probes of the light elements provide better resolution than actinide L3-edges to obtain electronic information from the ligand. Thus coupling simulations to experimental soft X-ray spectral measurements and complementary quantum chemical calculations yields quantitative information on chemical bonding. In this study, soft X-ray XAS at the K-edges of C and N, and the L2,3-edges of Fe was used to investigate the electronic structures of the well-known ferrocyanide complexes K4Fe(II)(CN)6, thorium hexacyanoferrate Th(IV)Fe(II)(CN)6, and neodymium hexacyanoferrate KNd(III)Fe(II)(CN)6. The soft X-ray spectra were simulated based on quantum chemical calculations. Our results highlight the orbital overlapping effects and atomic effective charges in the Fe(II)(CN)6 building block. In addition to providing a detailed description of the electronic structure of the ferrocyanide complex (K4Fe(II)(CN)6), the results strongly contribute to confirming the actinide 5f and 6d orbital oddity in comparison to lanthanide 4f and 5d.

Local Lattice Distortions in Mn[N(CN)2]2 under Pressure

We combined synchrotron-based infrared spectroscopy, Raman scattering, and diamond anvil cell techniques with complementary lattice dynamics calculations to reveal local lattice distortions in Mn[N(CN)2]2 under compression. Strikingly, we found a series of transitions involving octahedral counter-rotations, changes in the local Mn environment, and deformations of the superexchange pathway. In addition to reinforcing magnetic property trends, these pressure-induced local lattice distortions may provide an avenue for the development of new functionalities.

New insights into the compressibility and high-pressure stability of Ni(CN)2: a combined study of neutron diffraction, Raman spectroscopy, and inelastic neutron scattering

Nickel cyanide is a layered material showing markedly anisotropic behaviour. High-pressure neutron diffraction measurements show that at pressures up to 20.1 kbar, compressibility is much higher in the direction perpendicular to the layers, c, than in the plane of the strongly chemically bonded metal-cyanide sheets. Detailed examination of the behaviour of the tetragonal lattice parameters, a and c, as a function of pressure reveal regions in which large changes in slope occur, for example, in c(P) at 1 kbar. The experimental pressure dependence of the volume data is fitted to a bulk modulus, B0, of 1050 (20) kbar over the pressure range 0-1 kbar, and to 124 (2) kbar over the range 1-20.1 kbar. Raman spectroscopy measurements yield additional information on how the structure and bonding in the Ni(CN)2 layers change with pressure and show that a phase change occurs at about 1 kbar. The new high-pressure phase, (Phase PII), has ordered cyanide groups with sheets of D4h symmetry containing Ni(CN)4 and Ni(NC)4 groups. The Raman spectrum of phase PII closely resembles that of the related layered compound, Cu1/2Ni1/2(CN)2, which has previously been shown to contain ordered C≡N groups. The phase change, PI to PII, is also observed in inelastic neutron scattering studies which show significant changes occurring in the phonon spectra as the pressure is raised from 0.3 to 1.5 kbar. These changes reflect the large reduction in the interlayer spacing which occurs as Phase PI transforms to Phase PII and the consequent increase in difficulty for out-of-plane atomic motions. Unlike other cyanide materials e.g. Zn(CN)2 and Ag3Co(CN)6, which show an amorphization and/or a decomposition at much lower pressures (~100 kbar), Ni(CN)2 can be recovered after pressurising to 200 kbar, albeit in a more ordered form.

Synergistic photomagnetic effects in coordination polymer heterostructure particles of Hofmann-like Fe(4-phenylpyridine)2[Ni(CN)4]·0.5H2O and K0.4Ni[Cr(CN)6]0.8·nH2O

A coordination polymer heterostructure exhibits light-switchable magnetism with the photoevent in one component influencing the magnetization of the other.

Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet

Photomagnetic compounds are usually achieved by assembling preorganized individual molecules into rationally designed molecular architectures via the bottom-up approach. Here we show that a magnetic response to light can also be enforced in a nonphotomagnetic compound by applying mechanical stress. The nonphotomagnetic cyano-bridged Fe(II)-Nb(IV) coordination polymer {[Fe(II)(pyrazole)4]2[Nb(IV)(CN)8]·4H2O}n (FeNb) has been subjected to high-pressure structural, magnetic and photomagnetic studies at low temperature, which revealed a wide spectrum of pressure-related functionalities including the light-induced magnetization. The multifunctionality of FeNb is compared with a simple structural and magnetic pressure response of its analog {[Mn(II)(pyrazole)4]2[Nb(IV)(CN)8]·4H2O}n (MnNb). The FeNb coordination polymer is the first pressure-induced spin-crossover photomagnet.

High pressure induced charge transfer in 3d–4f bimetallic photomagnetic materials

A non-hydrostatic pressure induces ligand to metal charge transfer on the iron site of a 3d–4f photomagnetic material.

Reversible stimulus-responsive Cu(i) iodide pyridine coordination polymer

A coordination polymer based on CuI double chains with substituted pyrimidine is a dynamic and reversible material very sensible to both physical and chemical stimuli.

Core-shell Prussian blue analogue molecular magnet Mn(1.5)[Cr(CN)6]·mH2O@Ni(1.5)[Cr(CN)6]·nH2O for hydrogen storage

Core-shell Prussian blue analogue molecular magnet Mn1.5[Cr(CN)6]·mH2O@Ni1.5[Cr(CN)6]·nH2O has been synthesized using a core of Mn1.5[Cr(CN)6]·7.5H2O, surrounded by a shell of Ni1.5[Cr(CN)6]·7.5H2O compound. A transmission electron microscopy (TEM) study confirms the core-shell nature of the nanoparticles with an average size of ∼25 nm. The core-shell nanoparticles are investigated by using x-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and elemental mapping, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy. The Rietveld refinement of the XRD pattern reveals that the core-shell compound has a face-centered cubic crystal structure with space group Fm3m. The observation of characteristic absorption bands in the range of 2000-2300 cm(-1) in IR spectra corresponds to the CN stretching frequency of Mn(II)/Ni(II)-N≡C-Cr(III) sequence, confirming the formation of Prussian blue analogues. Hydrogen absorption isotherm measurements have been used to investigate the kinetics of molecular hydrogen adsorption into core-shell compounds of the Prussian blue analogue at low temperature conditions. Interestingly, the core-shell compound shows an enhancement in the hydrogen capacity (2.0 wt % at 123 K) as compared to bare-core and bare-shell compounds. The hydrogen adsorption capacity has been correlated with the specific surface area and TGA analysis of the core-shell compound. To the best of our knowledge, this is the first report on the hydrogen storage properties of core-shell Prussian blue analogue molecular magnet that could be useful for hydrogen storage applications.

Solid-state magnetic switching triggered by proton-coupled electron-transfer assisted by long-distance proton-alkali cation transport

Acidity of water molecules coordinated to Co ions in CoFe Prussian blue analogues (PBA) has been used to reversibly activate the Co(III)Fe(II) ↔ Co(II)Fe(III) electron transfer. The study of the structure and the electronic structure shows that the process implies an original PCET reaction between a solid-state porous coordination polymer and hydroxide ions in solution. The PCET reaction spreads throughout the solid network thanks to a long-range H(+) and Rb(+) transport within the pore channels of PBA taking advantage of the hydrogen-bonding network of zeolitic water molecules acting as proton wires.

Spin crossover iron(II) coordination polymer chains: syntheses, structures, and magnetic characterizations of [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II), Pt(II), aqin = quinolin-8-amine)

New Fe(II) coordination polymeric neutral chains of formula [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II) (1) and Pt(II) (2)) (aqin = Quinolin-8-amine) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, and magnetic measurements. The crystal structure determinations of 1-2 reveal in both cases a one-dimensional structure in which the planar [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion acts as a μ2-bridging ligand, and the two aqin molecules as chelating coligands. Examination of the intermolecular contacts in the two compounds reveals that the main contacts are ascribed to hydrogen bonding interactions involving the amine groups of the aqin chelating ligands and the nitrogen atoms of the two non bridging CN groups of the [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion. The average values of the six Fe-N distances observed respectively at room temperature (293 K) and low temperature (120 K), that is, 2.142(3) and 2.035(2) Å for 1, and 2.178(3) and 1.990(2) Å for 2, and the thermal variation of the cell parameters (performed on 2) are indicative of the presence of an abrupt HS-LS spin crossover (SCO) transition in both compounds. The thermal dependence of the product of the molar magnetic susceptibility times the temperature (χmT), in cooling and warming modes, confirms the SCO behavior at about 145 and 133 K in 1 and 2, respectively, and reveals the presence of a small thermal hysteresis of about 2 K for each compound.