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A series of novel monocyclometalated [Ir(tpy)(btp)Cl]+ complexes (Ir2-Ir5) were synthesized using 2,2':6',2″-terpyridine (tpy) and 2-(2-pyridyl)benzo[b]thiophene (btp) ligands, as well as their derivatives bearing electron-donating tert-butyl (t-Bu) and electron-withdrawing trifluoromethyl (CF3) groups. Ir2-Ir5 exhibited visible-light absorption stronger than that of the known complex [Ir(tpy)(ppy)Cl]+ (Ir1; ppy = 2-phenylpyridine). Spectroscopic and computational studies revealed that two triplet states were involved in the excited-state dynamics. One is a weakly emissive and short-lived ligand to ligand charge-transfer (LLCT) state originating from the charge transfer from the btp to the tpy ligand. The other is a highly emissive and long-lived ligand-centered (LC) state localized on the btp ligand. Interestingly, the excited state dominant with 3LLCT was completely changed to the 3LC state upon the introduction of substituents on both the tpy and btp ligands. For instance, the excited state of the parent complex Ir2 was weakly emissive (Φ = 2%) and short-lived (τ = 110 ns) in CH2Cl2; conversely, Ir5, fully furnished with t-Bu and CF3 groups, displayed intense phosphorescence with a prolonged lifetime (τ = 14 μs). This difference became increasingly prominent when the solvent was changed to aqueous CH3CN, most probably due to the 3LLCT stabilization. The predominant excited-state nature was switchable between the 3LLCT and 3LC states depending on the substituents employed; this was demonstrated through investigations of Ir3 and Ir4, bearing either the t-Bu or the CF3 group, where the complexes exhibited properties intermediate between those of Ir2 and Ir5. All of the Ir(III) complexes were tested as photosensitizers in photocatalytic H2 evolution over a Co molecular catalyst, and Ir5 outperformed the others, including Ir1, due to improvement in the following key properties: visible-light-absorption ability, excited-state lifetime, and reductive power of the one-electron-reduced species against the catalyst.

Orobanchaceae root parasitic weeds cause serious agricultural damage worldwide. Although numerous studies have been conducted to establish an effective control strategy for the growth and spread of root parasitic weeds, no practical method has been developed so far. Previously, metabolomic analyses were conducted on germinating seeds of a broomrape, Orobanche minor, to find novel targets for its selective control. Interestingly, planteose metabolism was identified as a possible target, and nojirimycin (NJ) selectively inhibited the germination of O. minor by intercepting planteose metabolism, although its precise mode of action was unclear. Here, transcriptome analysis by RNA-Seq was conducted to obtain molecular insight into the effects of NJ on germinating O. minor seeds. Differential gene expression analysis results suggest that NJ alters sugar metabolism and/or signaling, which is required to promote seed germination. This finding will contribute to understanding the effect of NJ and establishing a novel strategy for parasitic weed control.

A proton-electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi-step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric-like arrangement.

The study of transition metal clusters exhibiting fast electron hopping or delocalization remains challenging, because intermetallic communications mediated through bridging ligands are normally weak. Herein, we report the synthesis of a nanosized complex, [Fe(Tp)(CN)3]8[Fe(H2O)(DMSO)]6 (abbreviated as [Fe14], Tp−, hydrotris(pyrazolyl)borate; DMSO, dimethyl sulfoxide), which has a fluctuating valence due to two mobile d-electrons in its atomic layer shell. The rate of electron transfer of [Fe14] complex demonstrates the Arrhenius-type temperature dependence in the nanosized spheric surface, wherein high-spin centers are ferromagnetically coupled, producing an S = 14 ground state. The electron-hopping rate at room temperature is faster than the time scale of Mössbauer measurements (, Fast intermetallic electron transfer is expected in principle in nanozised transition metal complexes, but has been prevented by the bridging ligands. Here the authors synthesize a mixed-valence iron metal-ligand nanocluster with cyanide bridges, showing extended delocalized electronic structure

Kinetic control of molecular self-assembly remains difficult because of insufficient understanding of molecular self-assembly mechanisms. Here we report the formation of a metastable [Pd2L4]4+ cage structure composed of naphthalene-based ditopic ligands (L) and Pd(II) ions in very high yield (99%) under kinetic control by modulating the energy landscape. When self-assembly occurs with anionic guests in weakly cooordinating solvent then suitable intermedites and the metastable cage is formed. These conditions also prevent further transformation into the thermodynamically decomposed state. The cage formation pathways under kinetic control and the effect of the anions encapsulated on the self-assembly processes were investigated by QASAP (quantitative analysis of self-assembly process) and NASAP (numerical analysis of self-assembly process). It was found that the self-assembly with a preferred guest (BF4 -) proceeds through intermediates composed of no more components than the cage ([PdaLbXc]2a+ (a ≤ 2, b ≤ 4, X indicates a leaving ligand)) and that the final intramolecular cage-closure step is the rate-determining step. In contrast, a weaker guest (OTf-) causes the transient formation of intermediates composed of more components than the cage ([PdaLbXc]2a+ (a > 2, b > 4)), which are finally converted into the cage.

Sensitive chemo-switchable magnetic materials operating at room temperature are one of the most potential candidates for future chemical devices. Here, we report a discrete iron(III) complex that e...

An important technique to realize novel electron- and/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex-a phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.

The development and the photophysical behavior of a transparent ion-exchange membrane based on a pH-sensitive polypyridyl ruthenium(II) complex, [(bpy)2RuII(H2bpib)RuII(bpy)2](ClO4)4 (bpy = 2,2′-bipyridine, H2bpib = 1,4-bis([1,10]phenanthroline[5,6-d]-imidazol-2-yl)benzene), are experimentally and theoretically reported. The emission spectra of [(bpy)2RuII(H2bpib)RuII(bpy)2]@Nafion film were observed between pH 2 and pH 11 and showed the highest relative emission intensity at pH 5 (λmaxem = 594.4 nm). The relative emission intensity of the film significantly decreased down to 75% at pH 2 and 11 compared to that of pH 5. The quantum yields (Φ) and lifetimes (τ) showed similar correlations with respect to pH, Φ = 0.13 and τ = 1237 ns at pH 5, and Φ = 0.087 and τ = 1014 ns and Φ = 0.069 and τ = 954 ns at pH 2 and pH 11, respectively. These photophysical data are overall considerably superior to those of the solution, with the radiative- (kr) and non-radiative rate constants (knr) at pH 5 estimated to be kr = 1.06 × 105 s−1 and knr = 7.03 × 105 s−1. Density functional theory calculations suggested the contribution of ligand-to-ligand- and intraligand charge transfer to the imidazolium moiety in Ru-H3bpib species, implying that the positive charge on the H3bpib ligand works as a quencher. The Ru-Hbpib species seems to enhance non-radiative deactivation by reducing the energy of the upper-lying metal-centered excited state. These would be responsible for the pH-dependent “off-on-off” emission behavior.

To investigate the interactions of 57Fe atoms with sulfur hexafluoride SF6 molecules, in-beam Mossbauer spectra were measured for 57Mn implanted SF6 at 9 K and 65 K. Isolated 57Fe atoms or ions produced by β-decay were not trapped within the SF6 matrix. At 9 K, monomeric FeF2 and FeF3 molecules were produced by reaction of 57Fe with F atoms released by decomposition of the SF6 molecules. When the temperature of the SF6 solid was increased to 65 K, FeF4 was formed in addition to FeF2 and FeF3. Density functional calculations were performed to confirm the assignments of the candidate species identified in the Mossbauer spectra.

We successfully prepared and crystallographically characterized the first intermolecular charge-transfer (CT)-based vapochromic compound, (EV)(H3O)2[Fe(CN)6] (1-Wet, EV2+: 1,1′-diethyl-4,4′-bipyridine-1,1′-diium), an ethyl viologen-containing CT salt. 1-Wet, which is purple in color, is transformed into a brown powder (1-Dry) upon exposure to methanol vapor, drying over silica gel, or heating; 1-Dry returns to 1-Wet upon exposure to water vapor. These color changes are induced by hydration and dehydration, and gravimetric analyses suggest that 1-Dry is the dehydrated form of 1-Wet, namely, (EV)(H)2[Fe(CN)6]. Interestingly, desorption of water molecules from the oxonium ions in 1-Wet produces isolated protons (H+) that remain in 1-Dry as counter cations. Powder X-ray crystal structure analysis of 1-Dry reveals the presence of very short contacts between the nitrogen atoms of adjacent [Fe(CN)6]4– anions in the crystal. The isolated protons are trapped between the nitrogen atoms of cyanido ligands to form ve...

The iron mixed-valence complex ( n- C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ] (dto = C 2 O 2 S 2 ) exhibits a novel type of phase transition according electron transfer between Fe II and Fe III called charge transfer phase transition (CTPT). The existence of the CTPT highly depends on the 3d metal substitution with Zn, Mn, Cr, or Co for corresponding Fe site in ( n- C 3 H 7 ) 4 N[Fe II Fe III (dto) 3 ]. Here, we prepared a series of magnetically diluted complexes ( n- C 3 H 7 ) 4 N[Fe II Fe III 1− x V III x (dto) 3 ] ( x = 0–1), and carried out investigation of magnetic properties. Judging from the magnetic susceptibility measurement, there is no suppression of the CTPT unlike other 3d metal substituted cases. Moreover, 57 Fe Mossbauer spectroscopy revealed that about 60% of Fe II sites changed their spin states from high spin to low spin in case of substitution rate for x = 1.00. Since the difference of hardness and softness between metallic ions (Fe II , Fe III and V III ) and coordination sites of ligand (O or S in dto), this behavior is explained by the linkage isomerization of bridging ligand in formation process of the complex.

A molecular salt with a bulky cation and anion, (H2bipip)(H)2[Fe(CN)6] (1) (H2bipip2+: 4,4′-bipiperidine-1,1′-diium), has been prepared. The salt comprises protons (H+) as counter cations. Single-crystal X-ray structure analysis revealed that the proton is trapped between two cyanido ligands of [Fe(CN)6]4− anions, forming a very short N⋯H+⋯N hydrogen bond.

Dilute Fe and Nb codoped SrTiO3-δ (STO) perovskites were prepared by a complex formation and thermal decomposition method. The structure, magnetization properties and chemical states of Fe and Nb codoped STO perovskites were characterized by XRD, VSM and Mossbauer spectrometry. Mossbauer spectra of 57Fe and Nb codoped STO perovskites consist of paramagnetic doublet and magnetic relaxation components. The 1% Fe + 5% Nb codoped STO sample showed the smallest lattice constant and the largest ferromagnetism among 0.5–4% Fe + 5% Nb codoped STO perovskites. The most distortion of cubic STO lattice and the largest magnetic relaxation in Mossbauer spectrum were observed for the 0.5% Fe and 5% Nb codoped STO perovskite. It is considered that diluted magnetism in this system is related with the deformation of cubic structure due to defects.

The template effect is a key feature to control the arrangement of building blocks in assemblies, but its kinetic nature remains elusive compared to the thermodynamic aspects, with the exception of very simple reactions. Here we report a kinetic template effect in a self-assembled cage composed of flexible ditopic ligands and Pd(II) ions. Without template anion, a micrometer-sized sheet is kinetically trapped (off-pathway), which is converted into the thermodynamically most stable cage by the template anion. When the template anion is present from the start, the cage is selectively produced by the preferential cyclization of a dinuclear intermediate (on-pathway). Quantitative and numerical analyses of the self-assembly of the cage on the on-pathway revealed that the accelerating effect of the template is stronger for the early stage reactions of the self-assembly than for the final cage formation step itself, indicating the kinetic template effect. Thermodynamic template effects are widely used in supramolecular assembly, but kinetic template effects are less well understood. Here the contributions of thermodynamic and kinetic template effects in the self-assembly of palladium metallocages are disentangled using QASAP methodology.

Root parasitic weeds, such as Orobanche spp. and Striga spp., cause serious damage to crops. Recently, it was demonstrated that nojirimycin (NJ) selectively inhibits seed germination in these weeds. In this study, we modified the medium for Streptomyces ficellus to increase its production of NJ and evaluated the culture as an antiparasitic weed agent. We screened alternatives to Pharmamedia™, an additive in the original medium, and found that marine broth stimulated NJ production. Moreover, soluble starch-depleted medium could maintain S. ficellus NJ production. The NJ concentration reached 710 mg/L after four-day batch culture in starch-depleted marine broth medium, which was 17-fold higher than that in the Pharmamedia™ medium. The culture in the marine broth medium inhibited seed germination of Orobanche spp. and Striga spp. as effectively as a standard solution of NJ.

A transparent film allowing tunable multicolor emission based on a composite of an organometallic compound and a cation-exchange membrane has been developed, in which the cyclometallated iridium(III) complex [IrIII(4Py-ppy)3] (=tris[2-(2-pyridinyl-&kappa, N)-4-(4-pyridinyl)phenyl-&kappa, C]iridium) (1) with pH-dependent emission wavelengths has been incorporated into Nafion by cation exchange. Soaking Nafion in the solution of 1 for 24 h and exposed to buffers at pH 2, 4, and 10 resulted in maximum emission wavelengths of 587, 560, and 503 nm, respectively. The photophysical properties of 1@Nafion were also enhanced, as its maximum emission wavelength was more blue-shifted than those of 602, 564, and 503 nm in the solutions. The emission quantum yields (&Phi, ) and lifetimes (&tau, ) of 1@Nafion prepared under an acidic condition were up to &Phi, = 1.8% and &tau, = 0.11, 0.92 &mu, s, which are considerably higher than the corresponding solutions of &Phi, = 0.5% and &tau, = 0.02, 0.18 &mu, s. This is attributed to the fact that 1 is surrounded by the polymer chains of Nafion and immobilized in a relatively rigid medium, which hinders non-radiative deactivation such as thermal relaxation.

The structural properties of the iron mixed-valence complex ( n-C3H7)4N[FeIIFeIII(dto)3] (dto = dithiooxalato, C2O2S2) have been investigated by single-crystal X-ray diffraction (SCXRD) at low temperatures. ( n-C3H7)4N[FeIIFeIII(dto)3] has two-dimensional (2D) honeycomb layers consisting of alternating FeII and FeIII arrays bonded by bis-bidentate dithiooxalato ligands. Upon cooling, a superlattice structure with q = (1/3, 1/3, 0) was observed below 260 K, which corresponds to an order-disorder transition of the ( n-C3H7)4N+ ions between the honeycomb layers. The charge-transfer phase transition (CTPT) occurs at TC↑1/2 ∼ 120 K and TC↓1/2 ∼ 90 K upon heating and cooling, respectively, with an electron transfer between the FeII and FeIII ions, accompanied by a spin-state change, FeII ( S = 2; HS)-O2C2S2-FeIII ( S = 1/2; LS) ↔ FeIII ( S = 5/2; HS)-O2C2S2-FeII ( S = 0; LS). During the CTPT, the intersheet [FeIIFeIII(dto)3] distance decreased monotonously upon cooling, and an abrupt structural contraction was observed in the hexagonal 2D network. The volume contraction during the CTPT was quite small (∼0.7%), and differences in the structural distortions at the FeS6 and FeO6 sites were not found in the vicinity of the CTPT. We also calculated the orbital energies and the occupied spin states for the [Fe(O2C2S2)3] and [Fe(S2C2O2)3] octahedra in the vicinity of the CTPT by density functional theory (DFT). Because the local symmetry around the two coordinating iron ions is already lowered to trigonal symmetry, the CTPT did not cause any further deformation. This symmetry invariance resulted in an absence of orbital contributions to the total entropy change (Δ S) in the CTPT, which is in agreement with the previous heat capacity measurements. [Nakamoto, T; Miyazaki, Y; Itoi, M; Ono, Y; Kojima, N; Sorai, M. Heat Capacity of the Mixed-Valence Complex {[( n-C3H7)4N][FeIIFeIII(dto)3]}∞, Phase Transition because of Electron Transfer, and a Change in Spin-State of the Whole System. Angew. Chem., Int. Ed. 2001, 40, 4716-4719.].

Monomeric diaryliron(II) complexes, Fe(Rind)2, have been obtained by introducing fused-ring bulky “Rind” groups. For Fe(Eind)2, a significant orbital contribution of the Fe(II) ion due to the linea...

Magnetic properties of perovskite oxides, SrSn1-x Fe x O3-δ (x ≤ 0.15), substituted with nonmagnetic Ca and Ti ions were studied. XRD patterns showed the orthorhombic structure (close to tetragonal) of (Sr1-y Ca y )(Sn1-x Fe x )O3-δ and Sr(Sn1-x-y Fe x Ti y )O3-δ . The cell volumes decreased with the increase of Ca and Ti doping rates. Although Ti-substituted Sr(Sn, Fe)O3-δ showed small saturation magnetizations as compared with non-Ti substituted one, the magnetization increased a little with Ti doping rates up to 15%. On the other hand, all Ca-substituted Sr(Sn, Fe)O3-δ showed larger saturation magnetization than non-Ca substituted one. Two doublets of Fe3+ and a doublet of Fe4+ were observed in Mossbauer spectra of Ca-substituted Sr(Sn, Fe)O3-δ with weak ferromagnetism, and two sextets of high spin Fe3+ were additionally observed in Mossbauer spectra of Ca-doped Sr(Sn, Fe)O3-δ with relatively strong ferromagnetism. When Sr(Sn, Fe)O3-δ were further codoped with Ca and Ti ions, they showed the stable and enhanced ferromagnetic properties. It is considered that magnetic polarons among high spin Fe3+ species are overlapped by shrinking or deforming the crystal structure of perovskite oxides. That is the magnetism induced by a chemical pressure of perovskite oxides.

SrSn1-x-yFexSbyO3-δ was prepared by a sol-gel and thermal annealing method. The lattice parameters of SrSn0.97-xFexSb0.03O3-δ (x = 0.04-0.15) decreased with the increase of Fe doping rates. All samples showed ferromagnetic behavior together with a paramagnetic component, relatively strong ferromagnetism for SrSn0.97-xFexSb0.03O3-δ and SrSn1-xFexO3-δ with Fe doping rates over 6% and 8%, respectively The Sb doping leads to the ferromagnetic behavior for the samples with the low-concentration of Fe dopant. 119Sn Mossbauer spectra of SrSn0.92Fe0.08O3-δ and SrSn0.88Fe0.12O3-δ provided a broad doublet under a magnetic field of 0.85 T. The doublet could be analyzed as a magnetic sextet with 0.76 T. In 57Fe Mossbauer spectra of SrSn0.88Fe0.12O3-δ under zero and 0.85 T different line intensity ratios of two sextets were observed. It suggests that the magnetic spin structure of SrSn1-xFexO3-δ is transversely ferrimagnetic.

Accumulation profiles of wax esters in Euglena gracilis Z were studied under several environmental conditions. The highest amount of total wax esters accumulated under hypoxia in the dark, and C28 (myristyl-myristate, C14:0-C14:0) was prevalent among all conditions investigated. The wax ester production was almost completely suppressed under anoxia in the light, and supplying exogenous inorganic carbon sources restored wax ester fermentation, indicating the need for external carbon sources for the wax ester fermentation. 13C-labeling experiments revealed specific isotopic enrichment in the odd-numbered fatty acids derived from wax esters, indicating that the exogenously-supplied CO2 was incorporated into wax esters via the propionyl-CoA pathway through the reverse tricarboxylic acid (TCA) cycle. The addition of 3-mercaptopicolinic acid, a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, significantly affected the incorporation of 13C into citrate and malate as the biosynthetic intermediates of the odd-numbered fatty acids, suggesting the involvement of PEPCK reaction to drive wax ester fermentation. Additionally, the 13C-enrichment pattern of succinate suggested that the CO2 assimilation might proceed through alternative pathways in addition to the PEPCK reaction. The current results indicate that the mechanisms of anoxic CO2 assimilation are an important target to reinforce wax ester fermentation in Euglena.

The dilute magnetic properties of SrSn1−xFexO3 (x = 0.01 − 0.15) prepared by sol-gel and thermal decomposition methods were investigated by 57Fe Mossbauer spectrometry, magnetometry, and X-ray diffractometry. It was found that SrSnO3 doped with 2–8 % Fe show weak ferromagnetism although only paramagnetic doublets are observed in 57Fe Mossbauer spectra at room temperature (RT), whereas SrSnO3 doped with 10–15 % Fe show relatively strong ferromagnetism, and the sextets are additionally observed in the 57Fe Mossbauer spectra at RT. The weak ferromagnetism by doping 2–8 % Fe is considered to be caused by the induced magnetic defects, and the ferromagnetism by doping 10–15 % Fe are considered mainly due to the magnetic coupling between dilute Fe 3+ partially substituted at Sn 4+ sites in the orthorhombic structure of SrSnO3−δ accompanying the oxygen deficiencies. It is further remarkable that poor crystalline 8 % Fe doped SrSnO3−δ obtained by annealing at 600 ∘C shows relatively high saturation magnetization and low coercivity.

The dithiooxalato-bridged iron mixed-valence complex (n-C3H7)4N[FeIIFeIII(dto)3] (dto = dithiooxalato) undergoes a novel charge-transfer phase transition (CTPT) accompanied by electron transfer between adjacent FeII and FeIII sites. The CTPT influences the ferromagnetic transition temperature according to the change of spin configuration on the iron sites. To reveal the mechanism of the CTPT, we have synthesized the series of metal-substituted complexes (n-C3H7)4N[FeII1-xMnIIxFeIII(dto)3] (x = 0&ndash, 1) and investigated their physical properties by means of magnetic susceptibility and dielectric constant measurements. With increasing MnII concentration, x, MnII-substituted complexes show the disappearance of CTPT above x = 0.04, while the ferromagnetic phase remains in the whole range of x. These results are quite different from the physical properties of the ZnII-substituted complex, (n-C3H7)4N[FeII1-xZnIIxFeIII(dto)3], which is attributed to the difference of ion radius as well as the spin states of MnII and ZnII.

Manganese (Mn)-doped black iron oxide (Fe3O4) magnetic fluids in the system of MnxFe[Formula: see text]O4 were successfully synthesized from natural magnetite (iron sand) by using co-precipitation method at room temperature. The analyses of the small angle neutron scattering (SANS) data by applying a log-normal sphere with a mass fractal models for [Formula: see text] and [Formula: see text] and two log-normal spheres with a single mass fractal models for [Formula: see text], 0.75 and 1 revealed that the primary particles of the MnxFe[Formula: see text]O4 fluids tended to decrease from 3.8[Formula: see text]nm to 1.5[Formula: see text]nm along with the increasing fraction of Mn contents. The fractal dimension ([Formula: see text]) increased from about 1.2 to 2.7 as the Mn contents were increasing; which physically represents an aggregation of the MnxFe[Formula: see text]O4 particles in the fluids growing up from 1 to 3 dimensions to consolidate a more compact structure. The magnetization curves of the fluids exhibited an increasing saturation magnetization from [Formula: see text] to [Formula: see text], and a decreasing on [Formula: see text] and 0.75, with the maximum achievement of [Formula: see text]. These phenomena may probably be due to the combined effects, arising from cationic and dopant distributions, aggregation and its size, and also fractal dimension. Furthermore, the decrease of blocking temperature of the MnxFe[Formula: see text]O4 magnetic fluids could be associated with the reduced particle sizes, while the freezing temperature had its highest peak intensity when it collectively occurred with the blocking temperature at a similar point of about 270[Formula: see text]K.

The spin-crossover (SCO) phenomenon between a high-spin and a low-spin state has attracted much attention in the field of materials science. Among the various kinds of SCO complexes, the triazole-bridged iron(II) polymeric chain system, [Fe(II)(R-trz)3]X2·xH2O (where trz is triazole and X is the anion), exhibiting the SCO phenomenon with thermal hysteresis around room temperature, has been extensively studied from the viewpoint of molecular memory and molecular devices. In connection with this system, we have controlled the SCO phenomenon according to the characteristic properties of counter ions. In the case of X being CnH2n+1SO3−, the spin transition temperature (T1/2) increases with increasing the length (n) of the alkyl chain of the counter ion and saturates above n = 5, which is attributed to the increase in the intermolecular interaction of the alkyl chains of CnH2n+1SO3−, called the fastener effect. The hysteresis width of T1/2 decreases with increasing n, showing the even-odd, also known as parity, effect. In the cases where X is toluenesulfonate (tos: CH3C6H4SO3−) and aminobenzenesulfonate (abs: NH2C6H4SO3−), T1/2 and its hysteresis width vary drastically with the structural isomerism (ortho-, metha-, and para-substitution) of counter ions, which implies the possibility of photoinduced spin transition by means of the photoisomerization of counter ions. From this strategy, we have synthesized [Fe(II)(NH2-trz)3](SP150)2·2H2O (SP150 = N-alkylsulfonated spiropyran) and investigated the SCO phenomenon. Moreover, we have developed [Fe(II)(R-trz)3]@Nafion films exhibiting spin transition around room temperature, where the Nafion membrane behaves as a counter anion as well as a transparent substrate, and investigated the photogenerated high-spin state below 35 K. The lifetime of the photogenerated high-spin state strongly depends on the intensity of irradiated light.

Four Fe(III) spin-crossover (SCO) compounds, [Fe(HL1)2](HCl4TPA) (1-Cl), [Fe(HL1)2](HBr4TPA) (1-Br), [Fe(HL2)2](HCl4TPA) (2-Cl), and [Fe(HL2)2](HBr4TPA) (2-Br) (HL1 = 4-chloro-2-nitro-6-(1-(2-(pyridine-2-yl)hydrazono)ethyl)phenolate; HL2 = 4-bromo-2-nitro-6-(1-(2-(pyridine-2-yl)hydrazono)ethyl)phenolate; HCl4TPA = 2,3,5,6-tetrachloro-4-carboxybenzoate; and HBr4TPA = 2,3,5,6-tetrabromo-4-carboxybenzoate), were synthesized to investigate the halogen substituent change effect in salicylaldehyde 2-pyridyl hydrazone-type ligands and dicarboxylic acids in SCO complexes to the spin-transition temperature. Crystal structure analyses showed that these compounds were isostructural. In addition, a one-dimensional hydrogen–bonded column was formed by the dicarboxylic acid anion and weak hydrogen bonds between the Fe(III) complexes. From Mössbauer spectroscopy and magnetic property measurements, these compounds were confirmed to exhibit gradual SCO. The spin-transition temperature can be shifted by changing the halogen substituent in the salicylaldehyde 2-pyridyl hydrazone-type ligands and dicarboxylic acids without changing the molecular arrangement in the crystal packing.

To develop room-temperature molecule-based magnets, metal–radical approach is one of the most promising strategies. Strong magnetic interactions beyond a thermal energy of room temperature are essential for achieving such coveted materials. We have developed 2-pyridyl tert-butyl nitroxide (2pyNO) derivatives as a chelating radical ligand with a copper(II) or nickel(II) ion. The torsion angle () around M−O−N−C2py is a useful metric in describing correlation between the structure and metal–radical exchange coupling 2J (defined as H = −2JΣSi Si +1). Although we previously reported such a magneto-structural correlation, in this paper we updated the plot of 2J versus by dividing into two categories: the hexacoordinatenickel(II) and copper(II) complexes. An empirical linear correlation was formulated for both Cu and Ni categories, as 2J/k B = a + b|| with a = 503(112) K and b = –36(3) K deg–1 and with a = 449(46) K and b = –21.0(17) K deg–1, respectively. In the latter plot we confirm that the relationship can be generalized for the oxoverdazyl and dithiadiazolyl systems as well as the 2pyNO systems. The results are supported by the calculations based on the density functional theory.

A synchrotron small-angle X-ray scattering (SAXS) study on PVA/Fe3O4 magnetic hydrogels has been performed to investigate the effect of clustering on their magnetic properties. The hydrogels were prepared through freezing–thawing (F–T) processes. The structure, morphology and magnetic properties of magnetite (Fe3O4) nanoparticles (NPs) were investigated using X-ray diffractometry (XRD), transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer, respectively. In this study, SAXS data were used to reveal the structural dimensions of the magnetite and its distribution in the polymer-rich PVA and magnetic hydrogels. As calculated using the Beaucage and Teubner–Strey models, the average of the structural dimensions of the PVA hydrogels was 3.9[Formula: see text]nm (crystallites), while the average distance between crystallites was approximately 18[Formula: see text]nm. Further analysis by applying a two-lognormal distribution showed that the magnetite NPs comprised secondary particles with a diameter of 9.6[Formula: see text]nm that were structured by primary particles ([Formula: see text][Formula: see text]3.2[Formula: see text]nm). A two-lognormal distribution function has also been used in describing the size distributions of magnetite NPs in magnetic hydrogels. The clusters of magnetite NPs in the magnetic hydrogels are significantly reduced from 30.4[Formula: see text]nm to 12.8[Formula: see text]nm with decreasing concentration of the NPs magnetite from 15[Formula: see text]wt.% to 1[Formula: see text]wt.%. The saturation magnetization values of the magnetite NPs, the 15% and 1% magnetic hydrogels were 34.67[Formula: see text]emu/g, 6.52[Formula: see text]emu/g and 0.37[Formula: see text]emu/g, respectively.

The first iron complexes of high-spin iron(II) species directly coordinated to verdazyl radicals, [Fe(II)(vdCOO)2(H2O)2]·2H2O (1; vdCOO(-) = 1,5-dimethyl-6-oxo-verdazyl-3-carboxylate) and [Fe(II)(vdCOO)2(D2O)2]·2D2O (2), were synthesized. The crystal structure of 1 was investigated by single-crystal X-ray diffraction at room temperature and at 90 K. The compound crystallizes in the P1 space group with no phase transition between 300 and 90 K. The crystals are composed of discrete [Fe(II)(vdCOO)2(H2O)2] complexes and crystallization water molecules. In the complex, two vdCOO(-) ligands coordinate to the iron(II) ion in a head-to-tail arrangement and two water molecules complete the coordination sphere. The Fe-X (X = O, N) distances vary in the 2.069-2.213 Å range at 300 K and in the 2.0679-2.2111 Å range at 90 K, indicating that the iron(II) ion is in its high-spin (HS) state at both temperatures. At 300 K, one of the coordinated water molecules is H-bonded to two crystallization water molecules whereas the second one appears as loosely H-bonded to the two oxygen atoms of the carboxylate group of two neighboring complexes. At 90 K, the former H-bonds remain essentially the same whereas the second coordinated water molecule reveals a complicated behavior appearing simultaneously as tightly H-bonded to two oxygen atoms and non-H-bonded. The (57)Fe Mössbauer spectra, recorded between 300 K and 10 K, give a clue to this situation. They show two sets of doublets typical of HS iron(II) species whose intensity ratio varies smoothly with temperature. It demonstrates the existence of an equilibrium between the high temperature and low temperature forms of the compounds. The solid-state magic angle spinning (2)H NMR spectra of 2 were recorded between 310 K and 193 K. The spectra suggest the existence of a strongly temperature-dependent motion of one of the coordinated water molecules in the whole temperature range. Variable-temperature magnetic susceptibility measurements indicate an antiferromagnetic interaction (J(Fe-vd) = -27.1 cm(-1); H = -J(ij)S(i)S(j)) of the HS iron(II) ion and the radical spins with high g(Fe) and D(Fe) values (g(Fe) = 2.25, D(Fe) = +3.37 cm(-1)) for the HS iron(II) ion. Moreover, the radicals are strongly antiferromagnetically coupled through the iron(II) center (J(vd-vd) = -42.8 cm(-1)). These last results are analysed based on the framework of the magnetic orbitals formalism.