Tunable High-Pressure Field Operating on a Cationic Biphenyl Derivative Intercalated in Clay Minerals

Makoto Tominaga,Yukihiro Nishioka,Yasutaka Suzuki,Jun Kawamata,Seiji Tani

doi:10.1038/s41598-017-08064-0

Abstract

We propose a methodology for applying a pseudo uniaxial pressure to an organic molecule under ordinary temperature and pressure, namely by intercalation into smectites. The pseudo pressure on a biphenyl derivative (BP) was estimated from the averaged dihedral angle around the central bond of BP. In a high hydrostatic pressure field, biphenyl takes a planar conformation. In the interlayer space of synthetic saponite (SSA), the averaged dihedral angle of BP at a loading level of 27% versus the cation exchange capacity was ~26.3°, which indicates that the pseudo pressure applied to BP in the SSA interlayer space corresponds to 0.99 GPa. The high pseudo-pressure field in the interlayer space of SSA was also confirmed by absorption measurements. The dihedral angle around the central bond of the biphenyl moiety decreased to enhance the planarity of the molecule, mainly in response to the electrostatic force that operates between the negatively charged SSA layer and the interlayer cation. The pseudo pressure operating on BP in the smectite interlayer space could be controlled by varying the smectite layer charge density and/or the BP loading level. By using this methodology, controllable pseudo high-pressure properties of organic molecules can be obtained at ordinary temperatures and pressures.

Highlights

The principle force that flattens a cationic organic molecule in the interlayer space of a smectite is the electrostatic force between the exchangeable inorganic cations and/or intercalated organic cations and the anionic sites of the smectite layer[12]
The average dihedral angle about the central bond of a biphenyl moiety in a biphenyl derivative (BP) that is confined in the smectite interlayer space was estimated from the molecular thickness that corresponds to the gallery height estimated by X-ray diffraction (XRD)
Gallery heights of hybrid films fabricated at various loading levels of BP versus the cation exchange capacity (CEC), which indicates the amount of exchangeable cations per unit weight, with synthetic saponite (SSA) or montmorillonite (Mont) as host smectites were estimated by XRD

Summary

Introduction

The principle force that flattens a cationic organic molecule in the interlayer space of a smectite is the electrostatic force between the exchangeable inorganic cations and/or intercalated organic cations and the anionic sites of the smectite layer[12]. When a molecule with a thickness larger than the gallery height of the smectite is intercalated under specific conditions (which depend on the type of intercalated species, humidity and other factors), the uniaxial force applies to the molecule. We regard this uniaxial force as a pseudo uniaxial pressure. The uniaxial force, that is, the pseudo uniaxial pressure applied to one molecule, decreases as the number of molecules per unit area increases It is possible for intercalated organic molecules to experience a tunable pseudo-high-pressure field by varying the charge density or loading level. The absorption spectrum of BP in methanol at an isotropic hydrostatic pressure was measured with a diamond anvil cell

Methods

Results

Conclusion