Search

A cyanido-bridged Co–W assembly showing a charge transfer–induced phase transition realized room temperature bistability and red-blue drastic color change.

A magnetic field–switchable millimeter wave switch was demonstrated based on metal substituted ε-iron oxide for 81, 94, and 140 GHz usage.

Waste heat energy could be effectively used if the accumulated thermal energy could be conserved.

Nitrosyl metal complexes (M-NO), in which nitrosyl ligands are coordinated to transition-metal ions, have been studied from the viewpoints of physiological activity, catalytic activity, and photosensitivity. The structural flexibility and electric polarization of the nitrosyl ligand are attractive characteristics. Herein we show a photoswitchable nonlinear-optical (NLO) crystal based on a dysprosium-iron nitrosyl assembly. This crystal is composed of a one-dimensional chain structure in the polar

Incorporating chiral organic ligands into cyanido-bridged FeII–NbIV assemblies synthesized chiral spin-crossover complexes, FeII2[NbIV(CN)8](L)8·6H2O (L = R-, S-, or rac-1-(3-pyridyl)ethanol: R-FeNb, S-FeNb, or rac-FeNb). Rietveld analyses based on a racemic complex of rac-FeNb indicate that the chiral complexes have a cubic crystal structure in the I213 space group with a three-dimensional cyanido-bridged FeII–NbIV coordination network. All the complexes exhibit spin crossover between the high-spin (HS) and the low-spin (LS) FeII states without thermal hysteresis. Chiral complexes of R-FeNb and S-FeNb show second harmonic generation (SHG) due to their non-centrosymmetric structure. The I213 space group provides second-order susceptibility tensor elements of χxyz, χyzx, and χzxy, which contribute to SHG. The temperature-dependent second harmonic light intensity change is due to spin crossover between FeIIHS and FeIILS.

We show an anomalous change in the phonon frequency at the magnetic phase transition on a cyanide-bridged bimetal assembly, Mn3[W(CN)8]2(pyrimidine)4·6H2O. This compound shows a frequency shift in the CN stretching mode below the magnetic phase transition temperature (TC). First-principles phonon mode calculation and molecular orbital calculation suggest that the frequency shift of the CN stretching mode is due to the competition of the magnetic energy and the elastic energy. This work demonstrates that a specific change in the phonon frequency is induced by long-range magnetic ordering in flexibly structured matter.

Tetratitanium heptoxide, Ti4O7, is known to exhibit a two-step phase transition from the charge-delocalized to charge-localized phase and the charge-disordered to charge-ordered phase around 150 K and 130 K, respectively. Herein, a nanoscopic effect of the Ti4O7 phase transition is studied. A one-step phase transition from the charge-delocalized to charge-localized phase is realized in Ti4O7 nanocrystals where the transition from the charge-disordered to charge-ordered phase is suppressed. Perturbation to the free energy by the surface energy can explain this anomalous phase transition. The present nanoscopic effect, which can control cooperativity in phase transitions, should contribute to develop advanced switching materials.

Ionic conductors serve as solid electrolytes for fuel cells and batteries, whereas polar crystals such as ferroelectrics and pyroelectrics—which are typically insulating materials—are used in electronic devices. Here we show a material that combines superionic conductivity with a polar crystal structure at room temperature. This three-dimensional anionic network is based on –Fe–N≡C–Mo– units, with Cs cations hosted in every other pore. In the resulting Cs1.1Fe0.95[Mo(CN)5(NO)]·4H2O material, the negative and positive charges of the framework and Cs+ ions, respectively, are non-symmetrically shifted in the c-axis direction of the unit cell, and spontaneous electric polarization is generated, in turn leading to second harmonic generation (SHG). Additionally, this material is a superionic conductor (with an ionic conductivity value of 4 × 10−3 S cm−1 at 318 K). Furthermore, the ionic conductivity significantly decreases under 532 nm light irradiation (from 1 × 10−3 S cm−1 to 6 × 10−5 S cm−1 at room temperature) and, when irradiation stops, returns to its original value within ~1 h. A material based on a three-dimensional –Fe–N≡C–Mo– anionic framework that hosts a Cs+ cation in every other pore has been shown to exhibit superionic conductivity, despite its polar crystal structure. It also exhibits second harmonic generation (SHG)—usually observed in insulators—and its ionic conductivity was reversibly altered under light irradiation.

The self-assembly of cobalt(II) with purine and octacyanidotungstate(V) results in the formation of the three-dimensional Co3 [W(CN)8 ]2 (purine)2 ⋅8.5H2 O (1) coordination polymer. This compound exhibits humidity-induced variation of the number of water molecules of crystallisation leading to a reversible structural phase transition and the alternation of the long-range ferromagnetic ordering temperature from TC =29 K for the pristine assembly (1) to TC =49 K for the sample stored in a low-humidity atmosphere (1-deh). This phenomenon can be attributed to a reversible change in the hydrogen-bonding network resulting in the modification of the local geometries of cobalt(II) as well as the cyanido bridges.

We report a unique synthetic route toward the multistep spin crossover (SCO) effect induced by utilizing the partial ligand transformation during the crystallization process, which leads to the inc...

Light- or electromagnetic wave-responsive magnetism is an attractive issue in spin chemistry and optical materials science. Herein we show the magnetization reversal induced by visible-light pulsed laser and the ultrafast dynamic magnetooptical effect caused by terahertz (THz) pulsed laser irradiation onto chemically synthesized magnetic films based on gallium–titanium–cobalt-substituted e-Fe2O3 (GTC-e-Fe2O3) and e-Fe2O3 nanoparticles. Visible-light pulsed laser irradiation switches the sign of the Faraday effect in GTC-e-Fe2O3 films. On the other hand, irradiating the e-Fe2O3 film with pulsed THz light induces an ultrafast Faraday rotation in an extremely short time of 400 fs. The time evolution dynamics of these ultrafast magnetooptical effects are theoretically demonstrated by stochastic Landau–Lifshitz–Gilbert calculations of a nanoparticle model that considers all motions of the individual spins. These e-iron oxide magnetic nanomaterials are expected to contribute to high-density magnetic memory medi...

Self-assembly of Er(III) ions with octacyanidotungstate(V) in the presence of pure N,N-dimethylacetamide (dma) resulted in the formation of one-dimensional zigzag chain {[ErIII(dma)5][WV(CN)8]}n (1). Coordination polymer 1 crystallizes in the non-centrosymmetric space group P21 and it exhibits second harmonic generation (SHG) effect with SH susceptibility of 5.8 × 10−11 esu. Interestingly, the treatment of 1 with small amount of water results in the generation of another complex salt [ErIII(dma)5(H2O)2]·[WV(CN)8]·dma·H2O (2) which crystallizes in centrosymmetric space groups of P21/n, disqualifying the occurrence of SHG phenomenon. On the other hand, the elimination of cyanido-bridges and formation of seven-coordinated erbium(III) centre resulted in magnetic field induced single molecule magnet (SMM) behaviour with effective energy barrier of 28.6(3) K for 2. Finally, self-assembly of Er(III) with octacyanidotungstate(V) in water/dma mixture gave a complex salt [ErIII(dma)4(H2O)3]·[WV(CN)8]·dma·3H2O (3) similar to 2. Dynamic magnetic studies reveal that 3 is also showing slow magnetic relaxation, however, the substitution of single dma by water molecule induces the change in the local geometry of Er(III) centre leading to weak SMM properties for 3.

Atomic vibrations due to stretching or bending modes cause optical phonon modes in the solid phase. These optical phonon modes typically lie in the frequency range of 102 to 104 cm−1. How much can the frequency of optical phonon modes be lowered? Herein we show an extremely low-frequency optical phonon mode of 19 cm−1 (0.58 THz) in a Rb-intercalated two-dimensional cyanide-bridged Co–W bimetal assembly. This ultralow frequency is attributed to a millefeuille-like structure where Rb ions are very softly sandwiched between the two-dimensional metal–organic framework, and the Rb ions slowly vibrate between the layers. Furthermore, we demonstrate temperature-induced and photo-induced switching of this low-frequency phonon mode. Such an external-stimulation-controllable sub-terahertz (sub-THz) phonon crystal, which has not been reported before, should be useful in devices and absorbers for high-speed wireless communications such as beyond 5G or THz communication systems., Extremely low-frequency optical phonon mode in Rb-intercalated two-dimensional cyanide-bridged Co–W bimetal assembly and its temperature- and photo-induced switching effect.

International audience; Photo-induced structural dynamics in molecular materials often involve two main components; local molecular distortions induced by the self-trapping of electronic excited state and incoherent lattice dynamics due to energy dissipation. The latter component frequently hinders clear manifestation at macroscopic scale of local self-trapped entities and their coupling to the lattice. The studied photoactive MnFe Prussian blue analogue exhibits no thermal expansion, which allows observing long-range lattice dynamics induced by the structural trapping of photo-induced charge-transfer (CT) states. The self-trapping of the photo-induced (MnFeII)-Fe-III -> (MnFeIII)-Fe-II is responsible for the emergence of various physical properties. At equilibrium, the lattice volume expansion and the ferroelastic Jahn-Teller distortion associated with the charge-transfer-based phase transition, evolve in a coupled way. Here, we use time resolved X-ray diffraction to investigate the anisotropic out-of-equilibrium lattice dynamics triggered by the self-trapping of photo-induced (MnFeII)-Fe-III -> (MnFeIII)-Fe-II CT. The observed dynamics evidence a decoupling of both types of lattice deformations in the time domain, with an impulsive lattice response driven by the local Jahn-Teller reorganization and a displacive volume expansion controlled by the long-lived photo-induced CT small-polarons, due to the population of antibonding orbitals centered on Mn-N bonds in the (a,b) lattice plane.

International audience; We study by femtosecond optical pump-probe spectroscopy the photoinduced charge transfer (CT) in the RbMnFe Prussian blue analogue. Previous studies evidenced the local nature of the photoinduced Mn Fe → Mn Fe process, occurring within less than 1 ps. Here we show experimentally that two photoswitching pathways exist, depending on the excitation pump wavelength, which is confirmed by band structure calculations. Photoexcitation of α spins corresponds to the Mn(d-d) band, which drives reverse Jahn-Teller distortion through the population of antibonding Mn-N orbitals, and induces CT within ≈190 fs. The process launches coherent lattice torsion during the self-trapping of the CT small-polaron. Photoexcitation of β spins drives intervalence Fe→Mn CT towards non-bonding states and results in a slower dynamic.

Vanadium pentacyanonitrosylmolybdate, K0.82V1.06[Mo(CN)5(NO)]·3.8H2O, is synthesized from K4[Mo(CN)5(NO)]·2H2O and VCl3 under an argon atmosphere. X-ray powder diffraction and extended X-ray absorption fine structure measurements show that the crystal structure is face-centered cubic (fcc) with a lattice constant of 10.410(8) A, where V and Mo ions are in octahedral coordination geometries. This compound shows ferrimagnetism with a high Curie temperature of 200 K, in which the magnetic spins on VII (S = 3/2) and VIII (S = 1) antiparallely align with the spins on MoI (S = 1/2).

We report a magnetic film based on crystallographically oriented metal-substituted e-iron oxide, e-Ga0.45Fe1.55O3. This film was prepared by mixing nanoparticles and a vehicle resin under an applied external magnetic field. The a-axis of the orthorhombic crystal structure with a Pna21 space group is oriented out of the plane of the film. The degree of orientation is very high with a Lotgering factor of 0.94. The angular dependence of the magnetic hysteresis loops at room temperature shows a rectangular hysteresis loop with a coercive field of 9.7 kOe and a magnetization of 30.4 emu g–1 at 7 T (tesla) when the external field is along the out-of-plane direction with respect to the plane of the film, indicating that the easy axis corresponds to the crystallographic a-axis. To understand the origin of the high degree of orientation, we calculated the magnitude of the magnetic coupling between the e-Ga0.45Fe1.55O3 magnetic nanoparticles based on the magnetic dipole–dipole interaction. The theoretical model considering uniaxial magnetic anisotropy reproduces the angular dependence of the magnetic loops well.

Ultrafast magnetic response in epsilon-iron oxide (e-Fe 2 O 3 ) nano magnet was measured by terahertz-pump optical Faraday probe measurement. Terahertz excitations induce the extremely fast response of the magnetization. The response time is within 400 fs which corresponds to the time duration of the terahertz pulses.

The self-assembly of cobalt(II) with purine and octacyanidotungstate(V) results in the formation of the three-dimensional Co

Ionic conductors serve as solid electrolytes for fuel cells and batteries, whereas polar crystals such as ferroelectrics and pyroelectrics-which are typically insulating materials-are used in electronic devices. Here we show a material that combines superionic conductivity with a polar crystal structure at room temperature. This three-dimensional anionic network is based on -Fe-N≡C-Mo- units, with Cs cations hosted in every other pore. In the resulting Cs

We report a spin crossover material based on a cyanido-bridged FeII–MoIV assembly, FeII2[MoIV(CN)8](1-(3-pyridyl)ethanol)8⋅4H2O. This compound has a cubic crystal structure in the I a 3 ¯ d space group and is composed of a three-dimensional cyanido-bridged FeII–MoIV coordination network with one crystallographic FeII site. It exhibits incomplete spin crossover, because 21% of the high-spin FeII sites (S = 2) changes to low-spin FeII sites (S = 0) in the temperature range between 200 and 50 K. Thermal hysteresis is not observed. Such an incomplete and gradual spin crossover is attributed to the elastic frustration between the high-spin and the low-spin FeII sites (e.g., alternating arrangement such as –HS–LS–HS–LS–).

The introduction of 4-bromopyridine (4-Brpy) to a self-assembled MII-[NbIV(CN)8] (M = 3d metal ion) coordination system results in the formation of three-dimensional cyanido-bridged networks, {[MII(4-Brpy)4]2[NbIV(CN)8]}·nH2O (M = Zn, n = 1, 1; M = Mn, n = 0.5, 2; M = Ni, n = 2, 3). All these compounds are coordination frameworks composed of octahedral [MII(4-Brpy)4(μ-NC)2] complexes bonded to square antiprismatic [NbIV(CN)8]4– ions bearing four bridging and four terminal cyanides. 1 and 2 crystallize in the chiral I4122 space group as the mixture of two enantiomorphic forms, named 1(+)/1(−) and 2(+)/2(−), respectively. The chirality is here induced by the spatial arrangement of nonchiral but sterically expanded 4-Brpy ligands positioned around MII centers in the distorted square geometry, which gives two distinguishable types of coordination helices, A and B, along a 4-fold screw axis. The (+) forms contain left handed helices A, and right handed helices B, while the opposite helicity is presented in the...

In the era of Big Data and the Internet of Things, data archiving is a key technology. From this viewpoint, magnetic recordings are drawing attention because they guarantee long-term data storage. To archive an enormous amount of data, further increase of the recording density is necessary. Herein a new magnetic recording methodology, "focused-millimeter-wave-assisted magnetic recording (F-MIMR)," is proposed. To test this methodology, magnetic films based on epsilon iron oxide nanoparticles are prepared and a focused-millimeter-wave generator is constructed using terahertz (THz) light. Irradiating the focused millimeter wave to epsilon iron oxide instantly switches its magnetic pole direction. The spin dynamics of F-MIMR are also calculated using the stochastic Landau-Lifshitz-Gilbert model considering all of the spins in an epsilon iron oxide nanoparticle. In F-MIMR, the heat-up effect of the recording media is expected to be suppressed. Thus, F-MIMR can be applied to high-density magnetic recordings.

Vapochromic behaviour of porous crystals is beneficial for facile and rapid detection of gaseous molecules without electricity. Toward this end, tailored molecular designs have been established for metal–organic, covalent-bonded and hydrogen-bonded frameworks. Here, we explore the hydrochromic chemistry of a van der Waals (VDW) porous crystal. The VDW porous crystal VPC-1 is formed from a novel aromatic dendrimer having a dibenzophenazine core and multibranched carbazole dendrons. Although the constituent molecules are connected via VDW forces, VPC-1 maintains its structural integrity even after desolvation. VPC-1 exhibits reversible colour changes upon uptake/release of water molecules due to the charge transfer character of the constituent dendrimer. Detailed structural analyses reveal that the outermost carbazole units alone are mobile in the crystal and twist simultaneously in response to water vapour. Thermodynamic analysis suggests that the sigmoidal water sorption is induced by the affinity alternation of the pore surface from hydrophobic to hydrophilic. Water in the atmosphere can be indicated by vapochromic systems, especially where electrical detection cannot be used. Here, the authors explore the hydrochromic behaviour of a van der Waals porous crystal with a dibenzophenazine core and multibranched carbazole dendrons, finding that the outermost carbazole units alone are mobile in the crystal upon water adsorption.

As an adsorbent of gaseous ammonia, cobalt hexacyanocobaltate (CoII3[CoIII(CN)6]2) was proved to have good sorption even at high temperatures, with thermal recyclability in sorption–desorption cycles. The maximum sorption capacities evaluated with a dual-site Langmuir model are 25.2, 18.6, 8.6, and 2.1 mmol g−1 at 20, 100, 150, and 250 °C, respectively.

Three-dimensional cyanido-bridged bimetallic assemblies [MnII(4-Xpy)4]2[NbIV(CN)8]·nH2O (4-Xpy: 4-halopyridine; X = I and n = 0, (1); X = Cl and n = 0.5, (2)) are synthesized. 1 and 2 have chiral and achiral structures, respectively. The chiral structure of 1 is composed of achiral building blocks, which lead to an enantiopure compound through a spontaneous resolution process. In the crystal structure of 1, the halogen bonds between 4-Ipy and cyanide distort the structure, lowering the crystal symmetry. Both 1 and 2 show ferrimagnetism with Curie temperatures (TC) of 22 K and 28 K, respectively. Due to the chiral and polar structure in the I41 space group, 1 exhibits SHG phenomena, while such nonlinear optical phenomena are quenched in 2 due to its centrosymmetry.

We report three-dimensional (3D) cyanido-bridged Mn–Nb and Co–Nb bimetal assemblies, Mn II 2 [Nb IV (CN) 8 ]·(L) 2 · n H 2 O ( 1 : L = 5-aminopyrimidine, n = 5; 2 : L = 5-methylpyrimidine, n = 4), and Co II 2 [Nb IV (CN) 8 ] (4-pyridinealdoxime) 8 ·2H 2 O ( 3 ). The single-crystal X-ray structural analyses show that 1 and 2 consist of isomorphic 3D cyanido-bridged network (monoclinic, P 2 1 / n ) composed of square antiprism Nb sites and distorted octahedral Mn sites. Both 1 and 2 show ferrimagnetism with Curie temperatures ( T C ) of 32 and 34 K, respectively, which is caused by the antiferromagnetic superexchange interaction between Mn II ( S = 5/2) and Nb IV ( S = 1/2) through the CN groups. 3 has a 3D cyanido-bridged network (tetragonal, I 4 1 / a ) composed of a dodecahedral Nb site and axially distorted pseudo-octahedral Co site. This compound shows ferromagnetic ordering with a T C of 18 K. Magnetization versus rotation angle of single crystal reveals that 3 has a large coercive field of 15 000 Oe as crystal is oriented to a -axis, which is due to the strong magnetic anisotropy on distorted Co II .

A cyanido-bridged Fe–Nb bimetal assembly, Fe2[Nb(CN)8](4-methylpyridine)8·2H2O, was synthesized. This compound exhibits a two-step spin-crossover phenomenon between FeII high-spin (FeIIHS, S = 2) a...

In this chapter, to obtain new ionic conductive magnetic material using octacyanometalate-based magnet, the incorporation of 4-aminopyridine as organic ligand is performed due to the capability of forming hydrogen bond. The reaction of MnII, [NbIV(CN)8], and 4-aminopyridine yielded yellow crystal formulated as Mn 3 II [NbIV(CN)8]2(4-aminopyridine)10(4-aminopyridinium)2 · 12H2O. This compound possesses non-coordinated pyridinium cation and 1-dimensional infinite hydrogen-bonding networks constructed with ligand water molecules, non-coordinated water molecules, and 4-aminopyridinium cations. Magnetic measurements revealed that the present compound shows metamagnetism with a Neel temperature of 9 K. The impedance measurement showed that the present compound exhibits super-ionic conductivity (>10−4 S cm−1) which is caused by proton conduction based on the Grotthuss mechanism. In the present material, 4-aminopyridinium cation is incorporated into the flexible octacyanidometallate-based magnetic framework and plays an important role in the formation of the hydrogen-bonding network, which leads to the observation of super-ionic conductivity.

In this chapter, the first example of light-induced spin-crossover ferromagnetism is described. This phenomenon is achieved in a three-dimensional Fe–Nb bimetallic assembly. In this compound, the spin-crossover site is introduced into cyanido-bridged metal assembly. The photo-induced magnetization is observed because of the combination of LIESST effect on spin-crossover sites, strong superexchange interaction between the magnetic centers in three-dimensional manner. The present result is the first step toward the study of the new type of photo-magnetic material.

In Chap. 2, photo-induced spin-crossover magnetism is demonstrated in iron-ocatacyanoniobate-based three-dimensional spin-crossover compound, Fe 2 II [NbIV(CN)8](4-pyridinealdoxime)8 · 2H2O. In this chapter, utilizing an advantage of spin-crossover phenomenon that can be controlled by ligand substitution, a cyanido-bridged metal assembly was synthesized using FeII, [NbIV(CN)8], and 4-methylpyridine and obtained Fe 2 II [NbIV(CN)8](4-methylpyridine)8 · 2H2O. As a result, I succeeded in observing coexistence of two step spin-crossover behavior and light-induced spin-crossover magnetization.

The rare heteroligand pentacyanidonitrosylmolybdate(I) anion was employed in the construction of d–f bimetallic cyanido-bridged {[LnIII(dmf)6][MoI(CN)5(NO)]} (Ln = Gd, 1; Eu, 2) chains crystallizing in the non-centrosymmetric Pna21 space group. 1 exhibits Gd–Mo antiferromagnetic coupling giving rise to the ferrimagnetic spin chain behaviour with the onset of magnetic ordering below 2 K, and shows high second harmonic generation (SHG) activity with SH susceptibility of 1.2 × 10−10 esu, opening a novel family of non-centrosymmetric molecule-based magnets.