Molecular Rotor of Cs2([18]crown-6)3in the Solid State Coupled with the Magnetism of [Ni(dmit)2]

Intra-host π-π interactions in crown ether complexes revealed by cryogenic ion mobility-mass spectrometry

Cryogenic ion mobility-mass spectrometry was performed to investigate the relative abundance of conformers of dinaphtho-24-crown-8 (DN24C8) complexes with alkali metal cations M+ (M = Li, Na, K, Rb, and Cs). The "closed" conformers of M+(DN24C8) with short distances between two naphthalene rings in the crown ethers were predominantly observed for all complexes at 86 K. The two noncovalent interactions, host-guest and intra-host interactions, were analyzed separately by density functional theory calculations to reveal the origin of the stability of the closed conformers. As a result, it was revealed that the intra-host π-π interactions have a more critical role in determining the stability of the conformers than the host-guest interactions. The closed conformers of M+(DN24C8) also have wider regions of the π-π interactions than those of the M+(dibenzo-24-crown-8) complexes.

Photo-responsive functional materials based on light-driven molecular motors

In the past two decades, the research and development of light-triggered molecular machines have mainly focused on developing molecular devices at the nanoscale. A key scientific issue in the field is how to amplify the controlled motion of molecules at the nanoscale along multiple length scales, such as the mesoscopic or the macroscopic scale, or in a more practical perspective, how to convert molecular motion into changes of properties of a macroscopic material. Light-driven molecular motors are able to perform repetitive unidirectional rotation upon irradiation, which offers unique opportunities for responsive macroscopic systems. With several reviews that focus on the design, synthesis and operation of the motors at the nanoscale, photo-responsive macroscopic materials based on light-driven molecular motors have not been comprehensively summarized. In the present review, we first discuss the strategy of confining absolute molecular rotation into relative rotation by grafting motors on surfaces. Secondly, examples of self-assemble motors in supramolecular polymers with high internal order are illustrated. Moreover, we will focus on building of motors in a covalently linked system such as polymeric gels and polymeric liquid crystals to generate complex responsive functions. Finally, a perspective toward future developments and opportunities is given. This review helps us getting a more and more clear picture and understanding on how complex movement can be programmed in light-responsive systems and how man-made adaptive materials can be invented, which can serve as an important guideline for further design of complex and advanced responsive materials.

A Poling-Free Supramolecular Crown Ether Compound with Large Piezoelectricity

Supramolecular host-guest ferroelectrics based on solution processing are highly desirable because they are generally created with intrinsic piezoelectricity/ferroelectricity and do not need further poling. Poly(vinylidene fluoride) (PVDF) in the electric-active beta phase after stretching/annealing still shows no piezoelectric response unless poled. Although many supramolecular host-guest ferroelectrics have been discovered, their piezoelectricity is relatively small. Based on H/F substitution, we reported a supramolecular host-guest compound [(CF₃-C₆H₄-NH₃)(18-crown-6)][TFSA] (CF₃-C₆H₄-NH₃ = 4-trifluoromethylanilinium, TFSA = bis(trifluoromethanesulfonyl)ammonium) with a remarkable piezoelectric response of 42 pC/N under no poling condition. The introduction of F atoms increases phase transition temperature, polar axes, second harmonic generation (SHG) intensity, and piezoelectric coefficient d₃₃. To our knowledge, such a large piezoelectric performance of [(CF₃-C₆H₄-NH₃)(18-crown-6)][TFSA] makes its d₃₃, piezoelectric voltage coefficient g₃₃, and mechanical quality factor Q_m the highest among the reported supramolecular host-guest ferroelectric compounds and even larger than the values of PVDF. This work provides inspiration for optimizing piezoelectricity on molecular materials.

Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules

Using Na-encapsulated benzo[18]crown-6 (Na)(B18C6) as a counter cation, we successfully magnetically isolated a fluoride-bridging Dy dinuclear complex {[(PW₁₁O₃₉)Dy(H₂O)₂]₂F} (Dy₂POM) with lacunary Keggin ligands. (Na)(B18C6) formed two types of tetramers through C-H⋯O, π⋯π and C-H⋯π interactions, and each tetramer aligned in one dimension along the c-axis to form two types of channels. One channel was partially penetrated by a supramolecular cation from the ±a-axis direction, dividing the channel in the form of a "bamboo node". Dy₂POM was spatially divided by this "bamboo node," which magnetically isolated one portion from the other. The temperature dependence of the magnetic susceptibility indicated a weak ferromagnetic interaction between the Dy ions bridged by fluoride. Dy₂POM exhibited the magnetic relaxation characteristics of a single-molecule magnet, including the dependence of AC magnetic susceptibility on temperature and frequency. Magnetic relaxation can be described by the combination of thermally active Orbach and temperature-independent quantum tunneling processes. The application of a static magnetic field effectively suppressed the relaxation due to quantum tunneling.

Solvent Dependence of Crystal Structure and Dielectric Relaxation in Ferromagnetic [MnCr(oxalate)3]− Salt

[MnCr(oxalate)3]− possesses a two-dimensional ferromagnetic network that is an ideal system for the construction of multifunctional molecular materials based on ferromagnetism. This is because additional functions, such as ferroelectricity, can...

Dynamics of proton, ion, molecule, and crystal lattice in functional molecular assemblies

Dynamic molecular processes, such as short- or long-range proton (H⁺) and ion (M⁺) motions, and molecular rotations in electrical conducting and magnetic molecular assemblies enable the fabrication of electron-H⁺ (or M⁺) coupling systems, while crystal lattice dynamics and molecular conformation changes in hydrogen-bonded molecular crystals have been utilised in external stimuli responsive reversible gas-induced gate opening and molecular adsorption/desorption behavior. These dynamics of the polar structural units are responsible for the dielectric measurements. The H⁺ dynamics are formed from ferroelectrics and H⁺ conductors, while the dynamic M⁺ motions of Li⁺ and Na⁺ involve ionic conductors and coupling to the conduction electrons. In n-type organic semiconductors, the crystal lattices are modulated by replacing M⁺ cations, with cations such as Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The use of polar rotator or inversion structures such as alkyl amides, m-fluoroanilinium cations, and bowl-shaped trithiasumanene π-cores enables the formation of ferroelectric molecular assemblies. The host-guest molecular systems of ESIPT fluorescent chromic molecules showed interesting molecular sensing properties using various bases, where the dynamic transformation of the crystal lattice and the molecular conformational change were coupled to each other.

Magnetostructural relationships in [Ni(dmit)2]- radical anions

This work explores the relationship between the magnetic properties of salts based on [Ni(dmit)2]- radicals and different arrangements that these radicals can adopt in the crystals, induced by the packing constrains imposed by the counterions. Our analysis is based on difference dedicated configuration interaction calculations on models containing two neighbouring [Ni(dmit)2]- units with different interaction patterns. The amplitude and sign of these through-space interactions can be rationalized on the basis of a valence-only model that essentially analyzes the effective interactions between the atoms carrying the electronic density of singly occupied orbitals (SOMOs). Despite the simplicity of the model, it provides simple rules to predict the nature and the expected amplitude (strong/medium/weak) of the leading interactions in systems based on these [Ni(dmit)2]- radicals.

Molecular motion of halogenated ethylammonium/[18]crown-6 supramolecular ions in nickel dithiolate magnetic crystals

Supramolecular cations, consisting of ethylammonium derivatives (X–CH₂CH₂–NH₃⁺) complexed with [18]crown-6, were incorporated into [Ni(dmit)₂]⁻ crystals in order to promote molecular motion.

Magnetism, dielectrics and ion conduction in two polymorphs of a heteroleptic bis(dithiolato)nickelate molecular solid

A new heteroleptic compound [triethylpropylammonium][Ni(dmit)(mnt)] with two crystal polymorphs, which show different magnetic and dielectric properties, has been reported.

3D supramolecular chiral crystal structures of radical anion salts of (−)-NDI-Δ and possible magnetic phase diagrams

Supramolecular chiral crystals of radical anion salts of a triangular chiral electron acceptor, (−)-naphthalene diimide (NDI)-Δ, were electrochemically grown in propylene carbonate electrolyte solutions in the presence of cyclic multidentate ligands.

A Rotorlike Supramolecular Assembly, {[K(18-crown-6)]PbI3}∞, with a Reversible Breaking-Symmetry Phase Transition near Room Temperature

A rotorlike supramolecular crystal, {[K(18-crown-6)]PbI₃}_∞, is composed of a linear [PbI₃]_∞ chain acting as a stator and [K(18-crown-6)]⁺ cations fastened to the [PbI₃]_∞ chain and K-I bond like rotators and axes, respectively. A reversible breaking-symmetry phase transition occurs at ∼305 K. Variable-temperature ¹H NMR spectra and dielectrics were used for the dynamic analysis of [K(18-crown-6)]⁺ cations in the crystal.

Selective Ion Exchange in Supramolecular Channels in the Crystalline State

Artificial ion channels are of increasing interest because of potential applications in biomimetics, for example, for realizing selective ion permeability through the transport and/or exchange of selected ions. However, selective ion transport and/or exchange in the crystalline state is rare, and to the best of our knowledge, such a process has not been successfully combined with changes in the physical properties of a material. Herein, by soaking single crystals of Li₂ ([18]crown-6)₃ [Ni(dmit)₂ ]₂ (H₂ O)₄ (1) in an aqueous solution containing K⁺ , we succeeded in complete ion exchange of the Li⁺ ions in 1 with K⁺ ions in the solution, while maintaining the crystalline state of the material. This ion exchange with K⁺ was selectively conducted even in mixed solutions containing K⁺ as well as Na⁺ /Li⁺ . Furthermore, remarkable changes in the physical properties of 1 resulted from the ion exchange. Our finding enables not only the realization of selective ion permeability but also the development of highly sensitive biosensors and futuristic ion exchange agents, for example.

The effect of amorphization on the molecular motion of the 2-methylimidazolate linkers in ZIF-8

We investigated the effect of amorphization on the mobility of the organic linkers in a metal–organic framework.

A high temperature reversible phase transition in a supramolecular complex of 15-crown-5 with tetraphenylboron sodium

High temperature (391 K) reversible phase transition and large thermal hysteresis (19 K) was observed in 15-crown-5 clathrates: [Na(15-crown-5)][BPh₄] (15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane, NaBPh₄ = sodium tetraphenylboron).

Supramolecular self-assembly for designing non-centrosymmetric crystals based on Keggin polyoxometallates and crown ether

POM based non-centrosymmetric inorganic–organic hybrids are designed by gradually introducing asymmetry into the building units.

A room temperature reversible phase transition containing dielectric switching of a host-guest supramolecular metal-halide compound

Following our recent findings on dielectric materials, we synthesized a new host-guest supramolecular metal-halide compound, [(2-AMPD)(18-crown-6)]CuCl₄ (1, 2-AMPD = 2-aminomethylpiperidinium). Systematic characterization techniques such as variable-temperature crystal structure analyses, differential scanning calorimetry (DSC) measurements, temperature-dependent dielectric measurements and powder X-ray diffraction (PXRD) measurements demonstrate that 1 undergoes a reversible phase transition at room temperature, accompanied by switchable dielectric responses and remarkable anisotropy along three different crystallographic axes. The structural phase transition mechanism is triggered by the order-disorder transition of the 18-crown-6 molecules. We believe that these findings might further promote the application of a host-guest inclusion compound in the field of switchable dielectric materials.

Photoluminescent-dielectric duple switch in a perovskite-type high-temperature phase transition compound: [(CH3)3PCH2OCH3][PbBr3]

A perovskite-type high-temperature phase transition compound, ([(CH₃)₃PCH₂OCH₃][PbBr₃], 1), displays a remarkable bistable photoluminescent-dielectric duple switching behavior.

Coronene-based charge-transfer complexes

Recent developments in the arena of charge-transfer complexes composed of the D 6h-symmetric polycyclic aromatic hydrocarbon, coronene, are highlighted with emphasis on the structural and physical properties of these complexes. Because of the dual electron-donating and -accepting abilities of coronene, this group involves structurally-defined four cation salts and three anion salts. The Jahn-Teller distortions and in-plane motion of coronene molecules in the solids, both of which are closely associated with the high symmetry of coronene molecules, and syntheses of clathrate-type complexes are also presented.

Synthesis, Ion Recognition Ability, and Metal-Assisted Aggregation Behavior of Dinuclear Metallohosts Having a Bis(Saloph) Macrocyclic Ligand

Macrocyclic molecule 1 that has two saloph coordination sites was designed and synthesized. The macrocycle 1 was easily converted into the corresponding metallohosts 2 and 3 by the reaction with nickel(II) and palladium(II), respectively. As expected from the molecular structure of these metallohosts having an 18-crown-6-like cavity, the nickel(II) metallohost 2 showed excellent binding affinity toward Na(+), Ca(2+), and Sr(2+) to give 1:1 host-guest complexes. Preorganization effect due to the extremely rigid metal-containing macrocycle was suggested to be a major factor for the strong binding. Larger cations such as K(+), Rb(+), Cs(+), and Ba(2+) gave higher aggregated host-guest complexes such as 22M, 23M2, and 24M3. Density functional theory calculations revealed that smaller metal ions do not occupy the center of each macrocycle in the sandwich structures 22M, while larger Cs(+) simultaneously interacts with all the 12 oxygen donor atoms. On the basis of the interaction energy calculations, the preference for 2·Na over 22Na can be explained by destabilization of 22Na due to the elongated Na-O bonds and repulsive three-body interactions. When the ionic radius of the guest ion increases (K(+), Rb(+), Cs(+)), this destabilization becomes less significant and the formation of sandwich complexes 22M is favored. Such aggregation would significantly affect the physical and chemical properties of the metal complexes due to the interplane interactions between the metal centers.

Phase transition metal–crown ether coordination compounds tuned by metal ions

(15-Crown-5)(BiCl₃) and (15-crown-5)(SbCl₃) are discovered to show phase transitions above room temperature, where the phase transition temperature relates to the metal center.

Bistable N–H⋯N hydrogen bonds for reversibly modulating the dynamic motion in an organic co-crystal

Bistable N–H⋯N hydrogen bonds enable the modulation of the dynamic molecular motion by slowing down the fast rotation in 1,2-diazabicyclo(2.2.2)octane bis(thiourea).

Control of molecular rotor rotational frequencies in porous coordination polymers using a solid-solution approach

Rational design to control the dynamics of molecular rotors in crystalline solids is of interest because it offers advanced materials with precisely tuned functionality. Herein, we describe the control of the rotational frequency of rotors in flexible porous coordination polymers (PCPs) using a solid-solution approach. Solid-solutions of the flexible PCPs [{Zn(5-nitroisophthalate)x(5-methoxyisophthalate)1-x(deuterated 4,4'-bipyridyl)}(DMF·MeOH)]n allow continuous modulation of cell volume by changing the solid-solution ratio x. Variation of the isostructures provides continuous changes in the local environment around the molecular rotors (pyridyl rings of the 4,4'-bipyridyl group), leading to the control of the rotational frequency without the need to vary the temperature.

Observation of a magnetic phase transition but absence of an electrical response in a new two-dimensional mixed-valence nickel-bis-dithiolene molecular crystal

A two-dimensional mixed-valence molecular crystal of [Ni(dmit)₂]₃⁻ shows a magnetic phase transition at ca. 77 K but absence of an electrical response in the same temperature interval.

Rotation of a bulky triptycene in the solid state: toward engineered nanoscale artificial molecular machines

We report the design and dynamics of a solid-state molecular rotor with a large triptycene rotator. With a cross-section and surface area that are 2 and 3 times larger than those of the phenylene rotators previously studied in the solid state, it is expected that van der Waals forces and steric hindrance will render the motion of the larger triptycene more difficult. To address this challenge, we used a rigid and shape-persistent stator in a dendritic structure that reaches ca. 3.6 nm in length. Using variable-temperature solid-state (2)H NMR spectroscopy, we determined a symmetric three-fold rotational potential with a barrier of 10.2 kcal/mol and a pre-exponential factor of 1.1 × 10(10) s(-1), which correspond to ca. 4600 Brownian jumps per second in the solid state at 300 K.