A Pressure Induced Structural Dichotomy in Isostructural Bis-1,2,3-thiaselenazolyl Radical Dimers

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• 作者：Kristina Lekin ; Alicea A. Leitch ; John S. Tse ; Xuezhao Bao ; Richard A. Secco ; Serge Desgreniers ; Yasuo Ohishi ; Richard T. Oakley
• 刊名：Crystal Growth & Design
• 出版年：2012
• 出版时间：September 5, 2012
• 年：2012
• 卷：12
• 期：9
• 页码：4676-4684
• 全文大小：668K
• 年卷期：v.12,no.9(September 5, 2012)
• ISSN：1528-7505

文摘

The pressure dependence of the crystal and molecular structure of the bis-1,2,3-thiaselenazolyl radical dimer [1b]₂ has been investigated over the range 0鈥?1 GPa by powder diffraction methods using synchrotron radiation and diamond anvil cell techniques. At ambient pressure, the dimer consists of a pair of radicals linked by a hypervalent 4-center 6-electron S---Se鈥揝e---S 蟽-bond in an essentially coplanar arrangement. The dimers are packed in cross-braced slipped 蟺-stack arrays running along the x-direction of the monoclinic (space group P2₁/c) unit cell. Pressurization to 11 GPa causes the unit cell dimensions a and c to undergo a slow but uniform compression, while the b-axis is slightly elongated. There is virtually no change in the molecular structure or in the slipped 蟺-stack crystal architecture. This behavior is in marked contrast to that of the isostructural radical dimer [1a]₂, where the basal fluorine is replaced by hydrogen. Pressurization of this latter material induces a phase change near 4鈥? GPa, characterized by a sharp contraction in a and c, and a correspondingly large increase in b. At the molecular level, the transition is associated with a buckling of the 蟽-bonded dimer to a more conventional 蟺-bonded arrangement. Geometry optimized DFT band structure calculations on [1b]₂ replicate the observed structural changes and indicate that compression widens both the valence and conduction bands but does not induce band gap closure until >13 GPa. This result is consistent with the measured thermal activation energy for conduction E_act, which indicates that a metallic state requires pressures > 10 GPa.