Eigen-like hydrated protons traveling with a local distortion through the water nanotube in new molecular porous crystals {[MIII(H2bim)3](TMA)·20H2O}n (M = Co, Rh, Ru)

Abstract

In molecular porous crystals {[M(III)(H(2)bim)(3)](TMA)·20H(2)O}(n) (M = Co, Rh, Ru), the structural property of confined water network and the dynamics of mobile hydrated protons have been examined by the measurement of infrared spectrum and microwave conductivity. The water network undergoes first order phase transition from the ice nanotube (INT) to the water nanotube (WNT) around 200 K, while the infrared spectral features for these states are almost equivalent. Consequently, the water molecules in WNT dynamically fluctuate in the vicinity of the regulated position in INT with maintaining the O-O distance. The additional band observed around 2200 cm(-1) reveals the emergence of an Eigen-like protonic hydrate, around which the O-O distance locally shrinks to ~2.56 Å. The microwave conductivity exhibiting activation-type behavior, isotope effect and anisotropy indicates that the water nanotube is a quasi one-dimensional high proton conductor. Together with the neutron experimental results, we have clarified that the proton and protonic hole are generated by the self-dissociation in some water molecules just hydrated to the carboxylate oxygen atom of trimesic acid. The Eigen-like hydrated proton and protonic hole contribute to the intrinsic proton conduction accompanying local distortions. The carrier density dominated by the intrinsic ionic equilibrium is not large, whereas the actual mobility, which is higher than 1 × 10(-2) (cm(2)/Vs), yields the present high proton conductivity.

Anomalous Enhancement of Proton Conductivity for Water Molecular Clusters Stabilized in Interstitial Spaces of Porous Molecular Crystals

“…The formation of such hydrated protons has been studied in detail in acidic aqueous solutions (such as HCl), organic membranes, and protonated water clusters in the gas phase 19. For crystals of {[Co III (H 2 bim) 3 ] ⋅ (TMA) ⋅ 20 H 2 O} n ( 1 ; H 2 bim=2,2′‐biimidazole, TMA=trimesate), the crystal structure of the WNT and the proton‐transfer dynamics have been examined by infrared (IR) spectroscopy measurements 20. At a temperature of about 243 K, the confined WMC underwent a first‐order phase transition from a frozen ice nanotube (INT) to a melted water nanotube (WNT), while the IR spectra of the two WMCs were nearly equivalent; it was concluded that H 2 O in the WNT thermally fluctuates around defined positions in the INT.…”

“…[19] For crystals of {[Co III -(H 2 bim) 3 ]·(TMA)·20 H 2 O} n (1; H 2 bim = 2,2'-biimidazole, TMA = trimesate), the crystal structure of the WNT and the proton-transfer dynamics have been examined by infrared (IR) spectroscopy measurements. [20] At a temperature of about 243 K, the confined WMC underwent a first-order phase transition from a frozen ice nanotube (INT) to a melted water nanotube (WNT), while the IR spectra of the two WMCs were nearly equivalent; it was concluded that H 2 O in the WNT thermally fluctuates around defined positions in the INT. Meanwhile, before the melting state via the first-order phase transition of 1, the INT exhibited a broadening endothermic transition.…”

Transpiration of Water Molecules through Molecule-Based Porous Crystals with One-Dimensional Nanochannels

“…200 K. 19 The absolute value at 270 K was approximately one order of magnitude smaller than the · MW value along the c axis, as previously reported for the WMC of 3. 20,21 In accordance with the phase transition, the reduction in the · MW just below T m = 197 K (broken line) became slightly steeper than the curve of activation behaviour. In contrast, such thermal activation behaviour was never observed in the · MW perpendicular to the c axis (green solid circles), for which the absolute value was one order of magnitude smaller than the · MW parallel to the c direction at 270 K (red open circles).…”

Proton Conduction via Water Bridges Hydrated in the Collagen Film

“…A proton transfer via water networks has been widely studied, for instance, in water nanotubes and water chains confined in the hydrophilic nanochannel of molecular porous crystals [ 17 , 18 , 19 ]. The proton is affected by the size, geometry, and interfacial interaction arising from the framework molecules.…”