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Magnetic Interactions through a Nonconjugated Framework Observed in Back‐to‐Back Connected Triazinyl–Nitroxyl Biradical Derivatives
Author(s) -
Takahashi Yusuke,
Matsuhashi Ryo,
Miura Youhei,
Yoshioka Naoki
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201800163
Subject(s) - intramolecular force , antiferromagnetism , crystallography , chemistry , ring (chemistry) , nitroxyl , magnetic susceptibility , bond length , spin (aerodynamics) , crystal structure , stereochemistry , condensed matter physics , photochemistry , organic chemistry , physics , thermodynamics
Three hetero‐biradical derivatives, with the structure of a back‐to‐back connected benzotriazinyl and tetramethyl or tetraethylisoindoline N ‐oxyl sharing a common benzo ring, 3‐ tert ‐butyl‐1‐phenyl‐1,4,6,8‐tetrahydro‐6,6,8,8‐tetramethyl‐pyrrolo[4,5‐ g ]‐1,2,4‐benzotriazin‐4‐yl‐7‐oxyl ( 1‐ t Bu ), 1,3‐diphenyl‐1,4,6,8‐tetrahydro‐6,6,8,8‐tetramethyl‐pyrrolo[4,5‐ g ]‐1,2,4‐benzotriazin‐4‐yl‐7‐oxyl ( 1‐Ph ), and 3‐ tert ‐butyl‐1‐phenyl‐1,4,6,8‐tetrahydro‐6,6,8,8‐tetraethyl‐pyrrolo[4,5‐ g ]‐1,2,4‐benzotriazin‐4‐yl‐7‐oxyl ( 2‐ t Bu ), were synthesized and characterized by single‐crystal X‐ray analyses, variable‐temperature magnetic susceptibility studies, and DFT calculations. Temperature dependences of the magnetic susceptibilities of 1‐ t Bu , 1‐Ph , and 2‐ t Bu exhibit broad maxima at 70, 71, and 43 K, respectively. Although these radical derivatives form a columnar or chained assembly in the solid state, magnetic measurements of diluted samples in the polymer matrices and computational results imply that the magnetic properties of the polycrystalline sample can be explained by a two‐spin system with an intramolecular antiferromagnetic interaction. The magnetic behavior can be reproduced by using the Bleaney–Bowers model, with 2 J =−80.0 cm −1 for 1‐ t Bu , 2 J =−77.1 cm −1 for 1‐Ph , and 2 J =−48.9 cm −1 for 2‐ t Bu . The moderately strong intramolecular antiferromagnetic interactions can be interpreted by a through‐bond interaction through the nonconjugated framework and/or through‐space interactions based on molecular orbital theory. The strong distance dependency between the N−O spin site and vinylic carbon atoms indicates that the orbital interaction plays an important role in the intramolecular magnetic interaction. The reduced magnetic interaction in 2‐ t Bu relative to those of 1‐ t Bu and 1‐Ph can be attributed to restricted rotation of the tetraethyl group.