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An ionic-liquid-containing 2D coordination polymer was synthesized via a solvent-free reaction. The material exhibited incongruent melting at 112 °C, forming a solid–liquid mixture; further heating to 240 °C led to complete melting. Upon cooling, the melt transformed into a solid–liquid mixture, from which the coordination polymer was gradually recovered at ambient temperature. Rapid cooling (>200 °C s⁻¹) of the melt resulted in complete vitrification at −28 °C.

Salts containing the merocyanine form of a pyridinium-fused spiropyran ([6′-MC]X; X = I and PF6) were prepared, and their crystal structures were determined. In addition, the photochromic propertie...

The salts of cationic spiropyran with various anions ([PSP]X; X = I, NO3, SCN, BF4, ClO4, PF6, CF3BF3, OTf, and BPh4) were prepared, and their crystalline-state photochromism and crystal structures...

The structure of the title compound, H3O+·C2F6NO4S2 −·C12H24O6 or [H3O+·C12H24O6][N(SO2CF3)2 −], which is an ionic liquid with a melting point of 341–343 K, has been determined at 113 K. The asymmetric unit consists of two crystallographically independent 18-crown-6 molecules, two hydronium ions and two bis(trifluoromethanesulfonyl)amide anions; each 18-crown-6 molecule complexes with a hydronium ion. In one 18-crown-6 molecule, a part of the ring exhibits conformational disorder over two sets of sites with an occupancy ratio of 0.533 (13):0.467 (13). One hydronium ion is complexed with the ordered 18-crown-6 molecule via O—H...O hydrogen bonds with H2OH...OC distances of 1.90 (6)–2.19 (7) Å, and the other hydronium ion with the disordered crown molecule with distances of 1.85 (6)–2.36 (6) Å. The hydronium ions are also linked to the anions via O—H...F hydrogen bonds. The crystal studied was found to be a racemic twin with a component ratio of 0.55 (13):0.45 (13).

We synthesized novel 4,4′-diamino-2,2′-bipyridine (dabpy) complexes of Cu(II), Co(III), and Ni(II), and determined their molecular structures by single-crystal XRD analysis. As a result, we found that [Cu(dabpy)2]2+ had a four-coordinated Cu center and distorted square-planar geometry, while the Co(III) and Ni(II) complexes contained six-coordinated metal centers and exhibited an octahedral geometry. The prepared complexes were investigated as co-catalysts for H2 evolution from aqueous media in the presence of erythrosin B as a photosensitizer. Notably, the Cu(II) complex demonstrated a much higher co-catalyst activity than the corresponding Co(III) and Ni(II) species. Additionally, the H2 evolution mechanism and the redox potentials of the metal dabpy complexes were elucidated using electrochemical studies, and it was found that the reduction of protons to H2 was accompanied by a Cu(II)/Cu(I) redox reaction. In addition, it was suggested that the high co-catalyst activity of the Cu(II) complex was due to the low protonation-induced overpotential compared to those of Co(III) and Ni(II). Furthermore, the photo-sensitized H2 evolution activity of the metal complex/K2PtCl4 mixed systems were shown to exceed that of the K2PtCl4-only control system. The Cu(II) complex was found to be low-cost and effective co-catalyst for homogeneous H2 evolution system.

In this work, the effect of substituents on the valence states of biferrocenium salts was investigated in order to explore the valence control of ionic molecular materials. Reactions of 1′,1‴-disubstituted biferrocene derivatives (R2-bifc) and fluoro tetracyanoquinodimethanes (Fn-TCNQ; n = 1, 2, 4) produced single crystals of six salts (1–6), most of which were either monovalent ([D]+[Am]−; m = 1–3) or divalent ([D]+[Am]−) salts. (Et2-bifc)(F1-TCNQ)2 (1) was a mixed-stack monovalent salt, whereas the corresponding F2-TCNQ salt was a divalent salt. (MeO2-bifc)(F1-TCNQ)2 (2) was a monovalent salt because of the small Madelung energy of its segregated-stack structure, despite the low redox potential of the donor. (MeS2-bifc)(2,6-F2-TCNQ)2 (3) was a mixed-stack salt with an apparent intermediate valence state ([D]1.5+[A2]1.5–), containing [D]2+ and [D]+ in a 1:1 ratio. Its valence state, which is intermediate between those of corresponding salts with F1-TCNQ and 2,5-F2-TCNQ, is probably related to the unsymmetrical crystalline environment. (Bu2-bifc)(F1-TCNQ)3 (4) was a divalent salt with a segregated-stack structure, whereas the corresponding TCNQ salt was monovalent. (R2-bifc)(F4-TCNQ) [R = Bu (5), I (6)] were monovalent salts. Their magnetic susceptibilities were found to be consistent with their valence states. These results demonstrated that the valence control of biferrocenium salts could be achieved via the fluorine substitution of acceptors and crystal engineering.

The valence state of ionic molecular solids composed of biferrocene derivatives (D) and tetracyanoquinodimethane (TCNQ) derivatives (A), either monovalent ([D](+)[A(2)](-)) or divalent ([D](2+)[A2](2-)), can be controlled by changing the redox potentials and molecular volumes of the components.

Introduction of asymmetry into charge-transfer complexes composed of axially ligated iron phthalocyanines was achieved. In the obtained crystals of TPP[FeIII(Pc)(CN)Cl]2, TPP[FeIII(Pc)(CN)Br]2, and TPP[FeIII(Pc)BrCl]2 (TPP = tetraphenylphosphonium and Pc = phthalocyanine), the axial positions of the iron atoms were occupied by 50/50 ratios of the ligands CN/Cl, CN/Br, and Br/Cl, respectively. The crystal structures of the obtained CT complexes were isostructural to those composed of the symmetric analogues of the type [FeIII(Pc)L2] (L = CN, Cl or Br); the [FeIII(Pc)LL′] units formed regular one-dimensional chains along the c-axis following the symmetry of the P42/n space group. Despite forming similar regular chains to the symmetric systems, the electrical resistivities and activation energies were enhanced in the obtained CT complexes compared to those in symmetric systems, indicating that the charge-ordered states were stabilised by the introduction of asymmetry. More specifically, the dielectric relaxation behaviour of the inhomogeneous disordered TPP[FeIII(Pc)(CN)Cl]2 probably suggests that a dipole moment was induced in this material.

There are various thermochromic materials, though liquid thermochromic materials are less common. To produce functional thermochromic liquids, we have designed ionic liquids based on cationic nickel complexes with ether side chains, [Ni(acac)(Me2NC2H4NR1R2)]Tf2N ([1]Tf2N: R1 = C3H6OEt, R2 = Me, [2]Tf2N: R1 = C3H6OMe, R2 = Me, [3]Tf2N: R1 = R2 = C3H6OMe), where acac = acetylacetonate and Tf2N = (F3CSO2)2N−. The side chains (R1, R2) can moderately coordinate to the metal center, enabling temperature-dependent coordination equilibrium in the liquid state. [1]Tf2N is a liquid at room temperature. [2]Tf2N is obtained as a solid (Tm = 352.7 K) but remains liquid at room temperature after melting. [3]Tf2N is a solid with a high melting point (Tm = 422.3 K). These salts display thermochromism in the liquid state, colored red at high temperatures and orange, light blue, or bluish green at lower temperatures, exhibiting concomitant changes in the magnetic properties. This phenomenon is based on temperature-dependent equilibrium between a square-planar diamagnetic species and a paramagnetic species with intramolecular ether coordination.

We reported previously that ionic liquids containing cationic solvatochromic metal–chelate complexes exhibit vapochromic and solvatochromic properties, changing color upon coordination of different solvents. To control the solvent response by intramolecular coordination, an ether side chain was introduced into the cation as an additional flexible coordination site, and ionic liquids of the formula [Cu(acac){Me2NCH2CH2NMe(CH2)nOMe}][Tf2N] {[1][Tf2N]: n = 3, [2][Tf2N]: n = 4; acac = acetylacetonato, Tf2N = (F3CSO2)2N–} were synthesized. The melting points of [1][Tf2N] and [2][Tf2N] were 44.1 °C and 49.8 °C, respectively. X-ray crystal-structure determination revealed intramolecular coordination of the side chain in [1][Tf2N] and its absence in [2][Tf2N] in the solid state. The addition of 1 and 2 mol-equiv. of dimethyl sulfoxide to [1][Tf2N] produced ionic liquids with Tm = 28.6 °C and –12.0 °C, respectively. To investigate the potential competition between side-chain coordination and solvent coordination, the solvatochromism of these salts was investigated in various solvents. Although the d–d transition energy of [2][Tf2N] varies linearly with the donor number (DN) of a solvent, that of [1][Tf2N] is nearly constant in solvents with a DN smaller than that of methanol owing to intramolecular coordination. This demonstrates the control of solvent response by intramolecular coordination sites.

Transparent photochromic films were conveniently prepared by incorporating two different cationic diarylethenes into an ion-exchange Nafion film. The colorless films changed to dark blue or violet upon UV light irradiation, and subsequently switched to colorless under visible light. The films exhibited high photochromic durability compared with that in solution. The diarylethene molecules were also significantly more stable to photochromic reaction in the Nafion film than in the solution state.

To understand the structural features and intermolecular interactions of photoreactive organometallic ionic liquids (ILs), ILs containing cationic Ru sandwich complexes [Ru(C5H5){C6H3(OC3H6CN)3}]X (1a: X = (FSO2)2N−, 1b: X = (CF3SO2)2N−) were synthesized. Thereafter, their thermal properties and crystal structures were investigated. The melting points of these ILs were determined to be 87 and 79 °C, respectively. In the former crystal, the cation and anion were alternately arranged and the crystal undergoes a phase transition with ordering of the anion at −155 °C. In the latter crystal, the cations formed columnar arrangements through π–π interactions, with the anions located between the columns. In this crystal, the anions were extensively disordered even at −173 °C. The supercooled liquid of 1a exhibited a photochemical transformation into an amorphous coordination polymer, similar to the IL with longer substituents, though the reaction rate was considerably lower.

Multistimuli-responsive polymer films incorporating cationic spiropyran are demonstrated based on a Nafion membrane. The films exhibit color changes between yellow and red under photoirradiation, temperature changes, and application of pressure. These characteristic behaviors are based on the stabilization of the zwitterionic merocyanine cation in the polar environment of Nafion.

Ionic liquids comprising cationic Pd II complexes with SNS-pincer ligands ([Pd(L SNS )Me] + ([ 1 ] + ) and [Pd(L SNS )Cl] + ([ 2 ] + ); L SNS = 2,6-bis( n -butylthiomethyl)pyridine) and bis(trifluoromethanesulfonyl)amide (Tf 2 N) or tetrafluoroborate (BF 4 ) anions were prepared, and the effect of ancillary ligands on their thermal properties and solvent polarities were investigated. [ 1 ]Tf 2 N and [ 2 ]Tf 2 N were liquids and exhibited glass transitions at −47 °C and −23 °C, and their solvent polarity parameters ( E N T ) were 0.51 and 0.46, respectively. [ 1 ]BF 4 and [ 2 ]BF 4 were solids with melting points of 73.2 °C and 141.5 °C, respectively. X-ray structure determination of [ 2 ]BF 4 revealed a structure with alternating ionic and non-polar alkyl chain layers.

N-R1-N′-R2-4,4′-Bipyridinium and N-R1-4,4′-bipyridinium salts containing ferrocenyl substituents were prepared as donor–acceptor compounds (R1 = ferrocenyl, ferrocenylphenyl; R2 = ferrocenyl, ferrocenylphenyl, phenyl, methyl). Platinum(II)-bridged diferrocene compounds were prepared by using the N-R1-4,4′-bipyridinium ligands. These compounds display multistage redox properties. The redox potentials of the ferrocenyl and bipyridinium moieties in these compounds are independently affected by molecular modifications, which indicates that conjugation between the donor and acceptor moieties is less effective. Single-crystal X-ray diffraction analyses revealed large twist angles between the two moieties in the solid state. The compounds exhibit broad charge-transfer absorption bands in the range 450–800 nm. No electronic communication was observed between the terminal ferrocenes in the diferrocene complexes.

A series of ionic liquids containing cationic ruthenium complexes ([Ru(C5H5)(C6H5R)]+) were prepared, and their thermal properties were investigated (R = C4H9 (1a), C8H17 (1b), OCH2OCH3 (2a), O(CH2CH2O)2CH3 (2b), O(CH2)3CN (3a), O(CH2)6CN (3b), CO(CH2)2CH3 (4a), CO(CH2)6CH3 (4b)). Bis(trifluoromethanesulfonyl)amide (TFSA) and bis(fluorosulfonyl)amide (FSA) were used as counter anions. These ionic liquids were colorless and stable toward air and light. These salts exhibited glass transitions upon cooling from the melt (Tg = −82 °C to −55 °C), and the glass transition temperatures of the salts increased as the polarity of the substituents increased (alkyl cyano > carbonyl > ether. The viscosities, solvent polarities, and refractive indices of the salts of 1a and 2a were also evaluated. Hexafluorophosphate (PF6) salts were also prepared, which were solids with high melting points (Tm = 65–127 °C). X-ray crystal structure analyses of these salts revealed the importance of intermolecular contacts involving the ring hydrogens. The PF6 salt of 2a exhibited an order–disorder phase transition.

To develop solvent-recognition films, Nafion membranes incorporating cationic nickel-chelate complexes, that is, [Ni(L(1))(L(2))](+) (HL(1) = acetylacetone, 2,2,6,6-tetramethyl-3,5-heptanedione; L(2) = N,N-diethylethylenediamine, N-butyl-N,N',N'-trimethylethylenediamine), were prepared. Immersion of the films in various solvents effected the color changes varying from red to pale blue green depending on the donor number of the solvents. The color change is based on an equilibrium shift between square-planar and solvent-coordinated octahedral geometries of the cations. The degree of the color change depended on the affinity of the incorporated complex to the solvent molecules. The films were robust and exhibited a reversible solvent response. The films exhibited thermochromism when a small amount of appropriate solvents were incorporated and changed from pale blue green at low temperatures to red at high temperatures.

Decamethyl- and octamethyl-ferrocenium salts of FnTCNQ (n = 1, 2) were prepared and their crystal structures characterized. The 2,5-F2TCNQ salts [Fe(C5Me5)2](2,5-F2TCNQ) (1) and [Fe(C5Me4H)2](2,5-F2TCNQ) (2) exhibit one-dimensional …[D]+[A]−[D]+[A]−… mixed-stack structures, while the salts with polar acceptors [Fe(C5Me5)2][A] (A = F1TCNQ (3), 2,3-F2TCNQ (4), 2,6-F2TCNQ (5)) and [Fe(C5Me4H)2][A] (A = 2,3-F2TCNQ (6), 2,6-F2TCNQ (7)) consist of [D]+[A2]2−[D]+ units involving a diamagnetic dimer of the acceptors. These salts are isomorphous to the corresponding TCNQ salts. 1 and 2 exhibit small ferromagnetic interactions at low temperatures. 1 undergoes an antiferromagnetic phase transition at TN = 3.9 K, which is higher than TN = 2.1 K of the metamagnetic polymorph of [Fe(C5Me5)2](TCNQ).

Charge-transfer salts composed of biferrocene derivatives and Xn–TCNQ (X = F, Cl; n = 1, 2; TCNQ = tetracyanoquinodimethane) were prepared and crystallographically characterized. All nine salts exhibited a 1:2 donor/acceptor (D/A) ratio consisting of mixed-valence biferrocenium cations and anions with acceptor dimers. The packing patterns were correlated to the donor substituents. On the basis of the π–π interactions of the cations, the observed structures were classified into three categories: segregated-stack structures for the biferrocenium and dibromo-biferrocenium salts, mixed-stack structures [···(DA2)n···] for the diiodo-biferrocenium salts, and intermediate structures [···(DDA2A2)n···] for the bromo-biferrocenium salts.

Charge-transfer salts of biferrocene derivatives bearing branched-alkyl substituents [1′-R1-1‴-R2-1,1″-biferrocene; R1 = R2 = isopropylthio (D1), isopropyl (D2), isobutyl (D3), neopentyl (D4), and R1 = isobutyl and R2 = neopentyl (D5)] were prepared and crystallographically characterized. F2- and F4-tetracyanoquinodimethane (TCNQ) produced salts with D/A ratios of 1:3 ([D1][F2TCNQ]3, [D2][F2TCNQ]3), 1:2 ([D2][F4TCNQ]2, [D3][F4TCNQ]2), 2:3 ([D1]2[F4TCNQ]3), and 1:1 ([D2][F4TCNQ], [D4][F2TCNQ], [D4][F4TCNQ], [D5][F4TCNQ]). [Ni(mnt)2] produced a 1:1 salt [D3][Ni(mnt)2]. Although the biferrocenium salts reported to date contain only monocations, the cation valence in these salts decreases as the donor/acceptor ratio increases; the 1:3 and 1:2 salts contain biferrocenium dications, the 1:1 salts contain mixed-valence biferrocenium monocations, and the intermediate 2:3 salt contains both the dication and monocation. The packing structures of the salts differ significantly despite being composed of donors and ac...

Five-coordinate copper(II) complexes [Cu(L)Cl]X bearing alkylimidazole-containing tripodal ligands were prepared, where L = bis(2-dimethylaminoethyl)-((1-alkylimidazol-2-yl)methyl)amine and X = bis(trifluoromethanesulfonyl)amide (Tf2N) and PF6. The salts with hexyl ([1]X), propyl ([2]X), and methyl ([3]X) substituents in the ligand were prepared, of which [1]Tf2N and [2]Tf2N were ionic liquids with high viscosity at room temperature. X-ray crystal structure determination at low temperature revealed that the coordination geometry around the metal ion in [3]Tf2N was distorted trigonal bipyramidal, whereas that in [2]PF6 was close to square pyramidal. UV-vis absorption spectra of these salts were consistent with the coordination structures.

Crystal structures and thermal properties of cobaltocenium salts with bis(perfluoroalkylsulfonyl)amide (C(n)F2(n+1)SO2)2N anions [n = 0 (1), 1 (1 a), 2 (1 b), 3 (1 c), and 4 (1 d)] and the 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonylamide anion (2) were investigated. In these solids, the cations are surrounded by four anions around their C5 axis, and stacking of these local structures forms two kinds of assembled structures. In the salts with even n (1, 1 b, and 1 d), the cation and anion are arranged alternately to form mixed-stack columns in the crystal. In contrast, in the salts with odd n (1 a and 1 c), the cations and anions independently form segregated-stack columns. An odd-even effect was also observed in the sum of the phase-change entropies from crystal to melt. All of the salts exhibited phase transitions in the solid state. The phase transitions to the lowest-temperature phase in 1, 1 a, and 2 are accompanied by order-disorder of the anions and symmetry lowering of the space group, which results in the formation of an ion pair. Solid-state (13)C NMR measurements on 1 a and 1 b revealed enhanced molecular motions of the cation in the higher-temperature phases.

Alkyloctamethylferrocenium salts with the Tf2N anion ([Fe(C5Me4C(n)H(2n+1))(C5Me4H)][Tf2N]; Tf2N = bis(trifluoromethanesulfonyl)amide) were prepared, and their ionic liquid properties, thermal properties, crystal structures, and magnetic properties were investigated. The melting points of the Tf2N salts were near room temperature, and decreased with increasing alkyl chain length up to n = 8 and then increased. The salts with PF6 and NO3 anions were also prepared. The melting points of the PF6 salts were higher than 100 °C. Most of these salts exhibited phase transitions in the solid state. The sum of the entropies of the melting and solid phase transitions was nearly independent of the alkyl chain length for salts with short alkyl chains, whereas those for salts with longer alkyl chains (n≥ 10 for Tf2N salts, n≥ 6 for PF6 salts) increased with increasing alkyl chain length. Crystal structure determinations revealed that the short chain salts form simple alternately packed structures of cations and anions in the solid state, and that the long chain salts form lamellar structures, in which the alkyl chains are aligned parallel between the layers. The effects of magnetic fields on the crystallization of the paramagnetic ionic liquids were investigated, and revealed that the Tf2N salts with n = 4 exhibited magnetic orientation when solidified under magnetic fields. The magnetic orientation was shown to be a bulk phenomenon, and the importance of the magnetic anisotropy of the crystal structure was suggested in comparison with the response of other Tf2N salts.

A series of copper(II) solvatochromic complexes [Cu(acac)(N^N)(ligand)]BPh4 (acac = acetylacetonato; N^N = 1,10-phenanthoroline (1), 2,2′-bipyridyl (2); ligand = HMPA, pyridine, DMSO, DMF, MeOH, acetone, and MeCN) have been synthesized and their coordination geometries were crystallographically investigated. The solvent-coordinated cations, adopting a five-coordinate square-pyramidal structure, formed head-to-tail dimers via π⋯π interactions. Solid-state absorption studies revealed that their d–d transition energies are correlated with the donor number of the axial ligands. A linear correlation was found between the d–d transition energies and the Cu–O (axial ligands) distances in the solid-state, revealing the role of the coordination environment on the d–d transition energies in the copper(II) solvatochromic complexes.

The structural change associated with the first-order phase transition ( T C = 155.1 K) in a mixed-stack charge-transfer complex (octamethylferrocene)(2,3-dichloro-1,4-naphthoquinone) 2 was investigated crystallographically. X-ray structure determination at 90 K revealed that the transition is associated with the order-disorder of the C 5 Me 4 H ring in octamethylferrocene. In the low temperature phase, tripling of the unit cell occurred, accompanied by a change in spacegroup from P 2 1 /c to P −1, and every third octamethylferrocene molecule twists out of the plane to minimize steric interactions.

Sandwich compounds often exhibit various phase transitions, including those to plastic phases. To elucidate the general features of the phase transitions in metallocenium salts, the thermal properties and crystal structures of [Fe(C5 Me5 )2 ]X ([1]X), [Co(C5 Me5 )2 ]X ([2]X), and [Fe(C5 Me4 H)2 ]X ([3]X) have been investigated, where the counter anions (X) are Tf2 N (=(CF3 SO2 )2 N- ), OTf (=CF3 SO3- ), PF6 , and BF4 . The Tf2 N salts commonly undergo phase transitions from an ordered phase at low temperatures to an anion-disordered phase, followed by a plastic phase and finally melt at high temperatures. All these salts exhibit a phase transition to a plastic phase, and the transition temperature generally decreases with decreasing cation size and increasing anion size. The crystal structures of these salts comprise an alternating arrangement of cations and anions. About half of these salts exhibit phase transitions at low temperatures, which are mostly correlated with the order-disorder of the anion.

Vapor- and gas-responsive ionic liquids (ILs) comprised of cationic metal-chelate complexes and bis(trifluoromethanesulfonyl)imide (Tf(2)N) have been prepared, namely, [Cu(acac)(BuMe(3)en)][Tf(2)N] (1 a), [Cu(Bu-acac)(BuMe(3)en)][Tf(2)N] (1 b), [Cu(C(12)-acac)(Me(4)en)][Tf(2)N] (1 c), [Cu(acac)(Me(4)en)][Tf(2)N] (1 d), and [Ni(acac)(BuMe(3)en)][Tf(2)N] (2 a) (acac = acetylacetonate, Bu-acac = 3-butyl-2,4-pentanedionate, C(12)-acac = 3-dodecyl-2,4-pentanedionate, BuMe(3)en = N-butyl-N,N',N'-tetramethylethylenediamine, and Me(4)en = N,N,N',N'-trimethylethylenediamine). These ILs exhibited reversible changes in color, thermal properties, and magnetic properties in response to organic vapors and gases. The Cu(II)-containing ILs are purple and turn blue-purple to green when exposed to organic vapors, such as acetonitrile, methanol, and DMSO, or ammonia gas. The color change is based on the coordination of the vapor molecules to the cation, and the resultant colors depend on the coordination strength (donor number, DN) of the vapor molecules. The vapor absorption caused changes in the melting points and viscosities, leading to alteration in the phase behaviors. The IL with a long alkyl chain (1 d) transitioned from a purple solid to a brown liquid at its melting point. The Ni(II)-containing IL (2 a) is a dark red diamagnetic liquid, which turned into a green paramagnetic liquid by absorbing vapors with high DN. Based on the equilibrium shift from four- to six-coordinated species, the liquid exhibited thermochromism and temperature-dependent magnetic susceptibility after absorbing methanol.

Ion-pair compounds of phenyl-substituted viologen dications with [M(mnt)2] dianions were prepared and characterized. (Benzyl viologen)[M(mnt)2] (M = Cu (1), Ni (2), Pt (3)) and (phenyl viologen)[Cu(mnt)2] (4) exhibited mixed-stack crystal structures, whereas (dinitrophenyl viologen)[Cu(mnt)2] (5) exhibited no π–π interactions. Magnetic susceptibility measurements revealed that 1 exhibits a ferromagnetic exchange interaction (Weiss constant θ = +0.9 K), possibly mediated by the diamagnetic cation. Antiferromagnetic interactions were observed for 4 (θ = −2.0 K) and 5 (θ = −2.9 K), whereas 2 and 3 were diamagnetic. Absorption bands assignable to charge transfer were observed in the mixed-stack salts in the visible to near-infrared region.

Charge-transfer (CT) complexes of ferrocenes with 1,4-quinone derivatives were investigated. Deca- and octamethylferrocene complexes with 1,4-naphthoquinone derivatives were prepared and structurally characterized; these were neutral 1:2 DA complexes with mixed-stack structures. The formation of complexes with 1,4-benzoquinones was examined by applying solvent-drop grinding. CT energies and phase transitions in these neutral and other ionic complexes were investigated. Their electronic states are discussed on the basis of the phase diagrams derived for mixed-stack ferrocene-based CT complexes, taking into account their dependence on the DA ratio, dimensionality, and intermolecular interactions.

Organometallic charge-transfer salts composed of decamethyl-, octamethyl-, and dimethylferrocene with N,N′-dicyano-1,4-benzoquinonediimine (DCNQI) derivatives were prepared. [Fe(C5Me5)2][(MeO)2DCNQI] (1) and [Fe(C5Me4H)2][Me2DCNQI] (2) were 1:1 DA salts with mixed-stack structures, whereas [Fe(C5Me4H)2][(MeO)2DCNQI]2 (3) and [Fe(C5MeH4)2][DCNQI]2 (4) were 1:2 DA salts. 3 exhibited a segregated-stack structure, in which charge separation was observed in the acceptor column. 1 became a metamagnet below TN = 5.0 K, whereas the other salts were paramagnets. Valence states and charge-transfer (CT) transitions in these complexes are discussed based on the neutral–ionic (NI) phase diagram.

An ionic molecular crystal of (1',1'''-dineopentylbiferrocene)(F1TCNQ)3 exhibits a first-order phase transition from a monovalent state (D(+)A3(-)) to a divalent state (D(2+)A3(2-)) at around 120 K. The transition was successfully controlled by modulation of the redox potentials using FnTCNQ (n = 0-2) and by chemical-pressure effects.

[Dineopentyl-biferrocene]2[Cl1TCNQ]7, which has an unprecedented high donor-acceptor ratio of 2 : 7, contains a linear paramagnetic hexamer of Cl1TCNQ. Both the donor and acceptor molecules exhibit charge disproportionation in the crystal through mutual electrostatic interactions.

We proposed a thermoresponsive light scattering device that utilizes the surface behavior between polyimide and an ionic liquid-water mixture exhibiting lower critical solution temperature (LCST)-type phase separation. The LCST behavior for an ionic liquid device utilizing the polyimide with and without alkyl side chains was investigated. In the here-reported ionic liquid device that utilized the polyimide with alkyl side chains, [nBu4P][CF3COO] droplets were generated by phase separation—they were predominantly formed at the alkyl surface by a surface pinning effect. A stable transmittance in the opaque state could be obtained with this device. In contrast, an ionic liquid device using polyimide without alkyl side chains deteriorated transmittance in the opaque state because there was no surface pinning effect. Additionally, the viewing angle, contrast ratio, and heat cycle testing of this ionic liquid device with polyimide with alkyl side chains were also investigated. The results indicated that no parallax was obtained and that the ionic liquid device has a stable transmittance (verified by heat cycle testing). This unique device is expected to find use in the smart window applications that are activated by temperature changes.We proposed a thermoresponsive light scattering device that utilizes the surface behavior between polyimide and an ionic liquid-water mixture exhibiting lower critical solution temperature (LCST)-type phase separation. The LCST behavior for an ionic liquid device utilizing the polyimide with and without alkyl side chains was investigated. In the here-reported ionic liquid device that utilized the polyimide with alkyl side chains, [nBu4P][CF3COO] droplets were generated by phase separation—they were predominantly formed at the alkyl surface by a surface pinning effect. A stable transmittance in the opaque state could be obtained with this device. In contrast, an ionic liquid device using polyimide without alkyl side chains deteriorated transmittance in the opaque state because there was no surface pinning effect. Additionally, the viewing angle, contrast ratio, and heat cycle testing of this ionic liquid device with polyimide with alkyl side chains were also investigated. The results indicated that no para...

A series of ionic liquids containing cationic ruthenium complexes ([Ru(C5H5)(C6H5R)](+)) were prepared, and their thermal properties were investigated (R = C4H9 (1a), C8H17 (1b), OCH2OCH3 (2a), O(CH2CH2O)2CH3 (2b), O(CH2)3CN (3a), O(CH2)6CN (3b), CO(CH2)2CH3 (4a), CO(CH2)6CH3 (4b)). Bis(trifluoromethanesulfonyl)amide (TFSA) and bis(fluorosulfonyl)amide (FSA) were used as counter anions. These ionic liquids were colorless and stable toward air and light. These salts exhibited glass transitions upon cooling from the melt (Tg = −82 °C to −55 °C), and the glass transition temperatures of the salts increased as the polarity of the substituents increased (alkylethercyanocarbonyl). The decomposition temperatures decreased in the order of alkylcyanocarbonylether. The viscosities, solvent polarities, and refractive indices of the salts of 1a and 2a were also evaluated. Hexafluorophosphate (PF6) salts were also prepared, which were solids with high melting points (Tm = 65–127 °C). X-ray crystal structure analyses of these salts revealed the importance of intermolecular contacts involving the ring hydrogens. The PF6 salt of 2a exhibited an order–disorder phase transition.

Nafion films incorporating cationic nickel complexes [Ni(II)(acac)(R4en)](+) (acac = acetylacetonato, R4en = tetraalkylethylenediamine) that exhibit chromic behavior in response to temperature changes and solvent molecules in the vapor and liquid phases have been prepared.

A paramagnetic ferrocenium-based ionic liquid that exhibits a magnetic memory effect coupled with a liquid–solid phase transformation has been developed. Based on field alignment of the magnetically anisotropic ferrocenium cation, the magnetic susceptibility in the solid state can be tuned by the weak magnetic fields (

Metal-containing ionic liquids comprising cationic Pd(II) chelate complexes and the bis(trifluoromethanesulfonyl)amide (Tf2N) anion were prepared: [Pd(acac)(Me4en)]Tf2N (1), [Pd(acac)(BuMe3en)]Tf2N (2), and [Pd(C8-acac)(Me4en)]Tf2N (3) (acac = 2,4-pentanedionate, C8-acac = 3-octyl-2,4-pentanedionate, Me4en = N,N,N',N'-tetramethylethylenediamine, BuMe3en = N-butyl-N,N',N'-trimethylethylenediamine). These salts were yellow solids with melting points of 85.2 °C, 71.1 °C, and 62.3 °C, respectively. During cooling from the liquid state, complex 1 exhibited crystallization, whereas 2 and 3 exhibited only glass transitions at approximately -40 °C. X-ray structure determination revealed that the cations in 1 and 3 form dimer-like arrangements and that there were no direct contacts between the charged moieties of the cations and anions in the solid state.

We report on the discovery of ferromagnetic behavior below \(T_{\text{C}} = 41\) K in CeIr3B2 single crystals by means of magnetization, electrical resistivity, and specific heat measurements. The ferromagnetic transition temperature is unusually high despite the lack of magnetic elements except Ce, which is the second highest transition temperature recorded after CeRh3B2 (\(T_{\text{C}}\sim 120\) K). The ferromagnetic ordered moment is estimated to be \(\mu_{\text{s}}\sim 0.04\) \(\mu_{\text{B}}\)/Ce at 1.8 K, which lies in the \(c\)-plane of a monoclinic crystal structure. A structural phase transition from monoclinic to hexagonal occurs approximately at 395 K upon heating. The similarity and difference in physical properties between CeIr3B2 and CeRh3B2 are discussed.

A thermochromic magnetic ionic liquid containing a cationic iron(III) Schiff-base complex has been developed, whose color and magnetic moment change with temperature because of spin crossover in the liquid state. This spin-crossover behavior closely resembles that of a solid having the same cation.

Decamethylferrocenium salts with perfluoroalkylsulfonate anions ( C n F 2 n + 1 SO 3 − ; n = 1, 4, and 8) and perfluoroalkylcarboxylate anions ( C n F 2 n + 1 CO 2 − ; n = 1–4) were prepared to investigate the effects of the anion on the thermal behaviors of the salts. Differential scanning calorimetry (DSC) measurements revealed that all the salts exhibited phase transitions in the solid state. Salts with an octamethylferrocenium cation or decamethylcobaltocenium cation exhibited different phase sequences from those of the corresponding decamethylferrocenium salts. Structural changes associated with the phase transitions were investigated crystallographically for two salts. The phase transition in [Fe(C 5 Me 5 ) 2 ](CF 3 SO 3 ) at −121.6 °C was accompanied by ordering of the cation conformations into eclipsed and staggered conformations in different ratios. The unit cell volume became six times larger and the space group changed from P mn2 1 to P 1 in the low-temperature phase. The phase transition in [Fe(C 5 Me 5 ) 2 ](C 3 F 7 CO 2 ) at −115 °C was not accompanied by any change in the unit cell or the space group ( P 2 1 / c ). The libration or displacements of the anions that existed in the high-temperature phase was suppressed in the low-temperature phase, associated with a slight rotational displacement of the molecules. Anions with longer perfluoroalkyl chains exhibited disorder in the solid state even at low temperatures.

Butyl- and hexyloctamethylferrocenium salts with bis(trifluoromethylsulfonyl)amide (TFSA) and tetracyanoethylene (TCNE) were prepared, and their thermal properties were investigated by differential scanning calorimetry (DSC) measurements. The TFSA salts were ionic liquids with melting points of 34.4 °C and 27.7 °C, respectively. The TCNE salts were prepared by annealing the mixture of alkyloctamethylferrocene and TCNE. These salts exhibited high melting points of 100.2 °C and 80.9 °C, respectively; they were thermally unstable at higher temperatures. A butyloctamethylferrocenium salt with PCNP (pentacyanopropenide), obtained by a reaction with TCNE under ambient conditions, was crystallographically characterized. The structure was severely disordered, consisting of alternately stacked cations and anions.

A perchlorate salt of ferrocenylphenyltetrazole has been prepared and characterized crystallographically. In the crystal, tape-like one-dimensional molecular arrangements are formed by weak CH⋯N intermolecular hydrogen bonds between the tetrazole moieties (H⋯N distance: 2.49 A). A layer-like structure was formed, composed of neutral layers of phenyltetrazole moieties and ionic layers of ferrocenium moieties and anions.