Bisdithiazolyl Radical Spin Ladders

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• 作者：Kristina Lekin ; Joanne W. L. Wong ; Stephen M. Winter ; Aaron Mailman ; Paul A. Dube ; Richard T. Oakley
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：February 18, 2013
• 年：2013
• 卷：52
• 期：4
• 页码：2188-2198
• 全文大小：557K
• 年卷期：v.52,no.4(February 18, 2013)
• ISSN：1520-510X

文摘

A series of four bisdithiazolyl radicals 1a鈥?b>d (R₁ = Pr, Bu, Pn, Hx; R₂ = F) has been prepared and characterized by X-ray crystallography. The crystal structure of 1a (R₁ = Pr) belongs to the tetragonal space group P4̅2₁m and consists of slipped 蟺-stack arrays of undimerized radicals packed about 4虆 centers running along the z-direction, an arrangement identical to that found for 1 (R₁ = Et; R₂ = F). With increasing chain length of the R₁ substituent, an isomorphous set 1b鈥?b>d is generated. All three compounds crystallize in the P2₁/c space group and consist of pairs of radical 蟺-stacks locked together by strong intermolecular F路路路S鈥?bridges to create spin ladder arrays. The slipped 蟺-stack alignment of radicals produces close S路路路S鈥?interactions which serve as the 鈥渞ungs鈥?of a spin ladder, and the long chain alkyl substituents (R₁) serve as buffers which separate the ladders from each other laterally. Variable temperature magnetic susceptibility measurements indicate that 1a behaves as an antiferromagnetically coupled Curie鈥揥eiss paramagnet, the behavior of which may be modeled as a weakly coupled AFM chain. Stronger antiferromagnetic coupling is observed in 1b鈥?b>d, such that the Curie鈥揥eiss fit is no longer applicable. Analysis of the full data range (T = 2鈥?00 K) is consistent with the Johnston strong-leg spin ladder model. The origin of the magnetic behavior across the series has been explored with broken-symmetry Density Functional Theory (DFT) calculations of individual pairwise exchange energies. These confirm that strong antiferromagnetic interactions are present within the ladder 鈥渓egs鈥?and 鈥渞ungs鈥? with only very weak magnetic exchange between the ladders.