2-(4,5,6,7-Tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1- H-imidazole-3-oxide-1-oxyl, A Hydrogen-Bonded Organic Quasi-1D Ferromagnet

详细信息    查看全文

• 作者：Hidenori Murata ; Yuji Miyazaki ; Akira Inaba ; Armando Paduan-Filho ; Valdir Bindilatti ; Nei Fernandes Oliveira Jr. ; Zeynep Delen ; Paul M. Lahti
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：January 9, 2008
• 年：2008
• 卷：130
• 期：1
• 页码：186 - 194
• 全文大小：619K
• 年卷期：v.130,no.1(January 9, 2008)
• ISSN：1520-5126

文摘

The title radical (F4BImNN) is a stable nitronylnitroxide that forms hydrogen-bonded NH···ONchains in the solid state. The chains assemble the F4BImNN molecules to form stacked contacts betweenthe radical groups, in a geometry that is expected to exhibit ferromagnetic (FM) exchange based on spinpolarization (SP) models. The experimental magnetic susceptibility of F4BImNN confirms the expectation,showing 1-D Heisenberg chain FM exchange behavior over 1.8-300 K with an intrachain exchange constantof J_chain/k = +22 K. At lower temperatures, ac magnetic susceptibility and variable field heat capacitymeasurements show that F4BImNN acts as a quasi-1-D ferromagnet. The dominant ferromagnetic exchangeinteraction is attributable to overlap between spin orbitals of molecules within the hydrogen-bonded chains,consistent with the SP model expectations. The chains appear to be antiferromagnetically exchange coupled,giving cusps in the ac susceptibility and zero field heat capacity at lower temperatures. The results indicatethat the sample orders magnetically at about 0.7 K. The magnetic heat capacity ordering cusp shifts tolower temperatures as external magnetic field increases, consistent with forming a bulk antiferromagneticphase below a Néel temperature of T_N(0) = 0.72 K, with a critical field of H_c 1800 Oe. The interchainexchange is estimated to be zJ/k (-)0.1 K.