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The Cyano Nitronyl Nitroxide Radical: Experimental and Theoretical Evidence for the Fourth Case of the McConnell‐I Mechanism
Author(s) -
Hirel Catherine,
Luneau Dominique,
Pécaut Jacques,
Öhrström Lars,
Bussière Guillaume,
Reber Christian
Publication year - 2002
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 - 10.1002/1521-3765(20020715)8:14<3157::aid-chem3157>3.0.co;2-f
Subject(s) - chemistry , nitroxide mediated radical polymerization , antiferromagnetism , crystallography , tetragonal crystal system , radical , atomic orbital , molecular orbital , spin (aerodynamics) , molecule , crystal structure , condensed matter physics , physics , monomer , organic chemistry , radical polymerization , quantum mechanics , electron , thermodynamics , polymer
The nitronyl nitroxide 2‐cyano‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide ( 1 ) crystallises in the tetragonal P $\bar 4$ 2 1 m space group with a =7.4050(7), c =8.649(1) Å. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953(2) Å, between the NO groups and the bridging carbon atoms of the O‐N‐C‐N‐O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temperature‐dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2–300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by considering a two‐dimensional square array of spin S =1/2 antiferromagnetically coupled ( J =−10 cm −1 and g =2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively.