title: Hydrogen-bond-dynamics-based switching of conductivity and magnetism: a phase transition caused by deuterium and electron transfer in a hydrogen-bonded purely organic conductor crystal.
abstract: A hydrogen bond (H-bond) is one of the most fundamental and important noncovalent interactions in chemistry, biology, physics, and all other molecular sciences. Especially, the dynamics of a proton or a hydrogen atom in the H-bond has attracted increasing attention, because it plays a crucial role in (bio)chemical reactions and some physical properties, such as dielectricity and proton conductivity. Here we report unprecedented H-bond-dynamics-based switching of electrical conductivity and magnetism in a H-bonded purely organic conductor crystal, κ-D3(Cat-EDT-TTF)2 (abbreviated as κ-D). This novel crystal κ-D, a deuterated analogue of κ-H3(Cat-EDT-TTF)2 (abbreviated as κ-H), is composed only of a H-bonded molecular unit, in which two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons with a +0.5 charge are linked by a symmetric anionic [O···D···O](-1)-type strong H-bond. Although the deuterated and parent hydrogen systems, κ-D and κ-H, are isostructural paramagnetic semiconductors with a dimer-Mott-type electronic structure at room temperature (space group: C2/c), only κ-D undergoes a phase transition at 185 K, to change to a nonmagnetic insulator with a charge-ordered electronic structure (space group: P1). The X-ray crystal structure analysis demonstrates that this dramatic switching of the electronic structure and physical properties originates from deuterium transfer or displacement within the H-bond accompanied by electron transfer between the Cat-EDT-TTF π-systems, proving that the H-bonded deuterium dynamics and the conducting TTF π-electron are cooperatively coupled. Furthermore, the reason why this unique phase transition occurs only in κ-D is qualitatively discussed in terms of the H/D isotope effect on the H-bond geometry and potential energy curve.
authors.affiliation: The Institute for Solid State Physics, The University of Tokyo , Kashiwa, Chiba 277-8581, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Ueda
authors.forename: Shota
authors.initials: S
authors.lastname: Yamada
authors.forename: Takayuki
authors.initials: T
authors.lastname: Isono
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Kamo
authors.forename: Akiko
authors.initials: A
authors.lastname: Nakao
authors.forename: Reiji
authors.initials: R
authors.lastname: Kumai
authors.forename: Hironori
authors.initials: H
authors.lastname: Nakao
authors.forename: Youichi
authors.initials: Y
authors.lastname: Murakami
authors.forename: Kaoru
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Nishio
authors.forename: Hatsumi
authors.initials: H
authors.lastname: Mori
mesh_terms: D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003903:Deuterium / Q000737:chemistry*; D004553:Electric Conductivity; D004579:Electron Transport; D006860:Hydrogen Bonding; D060328:Magnetic Phenomena; D015394:Molecular Structure; D044367:Phase Transition; D012666:Semiconductors; D013059:Spectrum Analysis, Raman
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D002396:Catechols; D003903:Deuterium; C034221:catechol