Cooperativity of dynamics of 18-crown-6 molecule forming one-dimensional chain in Cs2(18-crown-6)3[Ni(dmit)2]2

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.

Multirotations of (Anilinium)([18]Crown-6) Supramolecular Cation Structure in Magnetic Salt of [Ni(dmit)2]−

A solid-state dynamic supramolecular structure consisting of (anilinium)([18]crown-6) was arranged as the cation in a salt of [Ni(dmit)2]- (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate). With the ammonium moiety of anilinium located within the cavity of [18]crown-6, a hydrogen-bonded supramolecular structure is formed, with an orthogonal arrangement between the pi plane of anilinium and the mean O6 plane of [18]crown-6. In this supramolecular cation, both anilinium and [18]crown-6 act as dynamic units with different rotational modes in the solid state. The uniform stacks of cations form an antiparallel arrangement, thus producing a layer structure. Sufficient space for the 180 degree flip-flop motion of the phenyl ring and the rotation of [18]crown-6 was observed in the cation layer. Thermally activated 180 degree flip-flop motions, with a frequency of 6 MHz at room temperature and an activation energy of 31 kJ mol(-1), were confirmed by temperature-dependent 2H NMR spectra of ([D5]anilinium)-([18]crown-6)[Ni(dmit)2]. A double-minimum potential for the molecular rotation of anilinium, with a barrier of approximately 40 kJ mol(-1), was indicated by ab initio calculations. The wide-line 1H NMR spectra indicated a thermally activated rotation of [18]crown-6 at temperatures above 250 K. Therefore, multiple molecular motions of the 180 degree flip-flop motion of the phenyl ring and the rotation of [18]crown-6 occur simultaneously in the solid state. The temperature-dependent dielectric constants revealed that the molecular motion of [18]crown-6, other than the flip-flop motion, dominates the dielectric response in the measured temperature and frequency range.

One-dimensional correlation in the dipolar Ising crystal tricyclohexylmethanol: crystal structure revisited and heat capacity

The crystal structure of an organic weak-ferroelectrics, tricyclohexylmethanol (TCHM), was re-examined by single-crystal x-ray diffraction at room temperature. TCHM forms a dimer through hydrogen bonding at the centre of the dimer, where two hydroxyl groups are arranged in tandem and their direction is disordered in two possible orientations, which brings about a dipolar Ising nature. The heat capacity measured by adiabatic calorimetry from 6 to 400 K shows three anomalies including fusion at 368 K. The entropy of the ferroelectric transition is 1.9 J K(-1) mol(-1), supporting the order-disorder mechanism of dimer dipoles. A broad anomaly at 348 K is related to the breakage of the intra-dimer hydrogen bond. Detailed analysis of the temperature dependence of heat capacity due to the phase transition showed the presence of a broad hump in the excess heat capacity around 160 K. The temperature dependences of the excess heat capacity and the existing dielectric constant can be analysed in terms of a highly anisotropic Ising model.

Supramolecular Rotor: Adamantylammonium([18]crown-6) in [Ni(dmit)2]- Salt

Adamantylammonium (ADNH3+) was complexed with [18]crown-6, forming a supramolecular cation of (ADNH3+)([18]crown6), which was introduced into a [Ni(dmit)2]- salt as a supramolecular rotor. The cation layers were alternately arranged with [Ni(dmit)2]- layers in the crystal, in which the molecular rotation of (ADNH3+)([18]crown-6) was confirmed from the temperature-dependent solid-state 1H NMR.

Formation of p-Phenylenediamine−Crown Ether−[PMo12O40]4- Salts

Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)3[PMo12O40]3- forms a one-electron-reduced Keggin cluster of [PMo12O40]4-, bearing a S = 1/2 spin, while proton transfer from the proton donor of (H+)3[PMo12O40]3- to the proton acceptor of PPD yielded mono- and diprotonated cations of 4-aminoanilinium (HPPD+) and p-phenylenediammonium (H2PPD2+). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD2+)(crown ethers) were successfully introduced into three new alpha-[PMo12O40]4- salts of (H2PPD2+)2([12]crown-4)4[PMo12O40]4- (1), (HPPD+)4([15]crown-5)4[PMo12O40]4- (2), and (HPPD+)2(H2PPD2+)([18]crown-6)4[PMo12O40]4- (3) as the countercation. The protonated states of PPD and molecular-assembly structures of the supramolecular cations depended on the size of the crown ethers. In salt 3, a novel mixed-protonated state of HPPD+ and H2PPD2+ was confirmed to be complexed in the cation structure. According to the changes in the cation structures, the anion arrangements were modulated from those of the two-dimensional layer for salt 1 to the isolated cluster for salts 2 and 3. The temperature-dependent magnetic susceptibilities of salts 1-3 were consistent with the isolated spin arrangements of [PMo12O40]4-. The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent Mo(V) to hexavalent Mo(VI) ions within the [PMo12O40]4- cluster. Temperature-dependent electron spin resonance spectra of salt 2 revealed the delocalization-localization transition of the S = 1/2 spin at 60 K. The spin on the [PMo12O40]4- cluster was localized on a specific Mo(V) site below 60 K, which was thermally activated with an activation energy of 0.015 eV.