Abstract
Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. As a representative system, water-filled carbon nanotubes (CNTs) are generally studied, but direct observation of the crystal structure and proton transport is difficult for CNTs due to their poor crystallinity and high electron conduction. Here, we report the direct observation of a unique water-cluster structure and high proton conduction realized in a metal-organic nanotube, [Pt(dach)(bpy)Br]4(SO4)4·32H2O (dach: (1R, 2R)-(–)-1,2-diaminocyclohexane; bpy: 4,4’-bipyridine). In the crystalline state, a hydrogen-bonded ice nanotube composed of water tetramers and octamers is found within the hydrophobic nanochannel. Single-crystal impedance measurements along the channel direction reveal a high proton conduction of 10−2 Scm−1. Moreover, fast proton diffusion and continuous liquid-to-solid transition are confirmed using solid-state 1H-NMR measurements. Our study provides valuable insight into the structural and dynamical properties of confined water within 1D hydrophobic nanochannels.
Highlights
Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties
The confined water in the hydrophobic nanochannel of 1 forms unique clustered structures, which was confirmed by single-crystal X-ray diffraction (SCXRD) measurements
The high conductivity of 1 is attributed to both the high proton diffusivity within the hydrophobic nanochannel combined with the acidity of the coordinated amine protons, both of which were supported by pulsed-field gradient (PFG)-nuclear magnetic resonance (NMR) and theoretical calculations
Summary
Water confined within one-dimensional (1D) hydrophobic nanochannels has attracted significant interest due to its unusual structure and dynamic properties. To study the effect of confining water in a one-dimensional (1D) nanospace, waterfilled carbon nanotubes (CNTs) have been an attractive research focus, with interesting water-cluster formation[4,5], fast water transport[6,7], and high proton conductivity observed[8,9,10]. Such studies on the dynamics of water confinement in hydrophobic nanochannels are especially important as biomimetics[11,12] for understanding transport mechanisms in proton pumps[13] or water transport proteins[14]. We have developed a rational bottom-up synthesis of a metal-organic nanotube[18] based on the oxidative polymerisation of a square-shaped platinum complex using elemental iodine
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