Zero-field splitting parameters of quintet 2,6-dinitrenopyridines

The zero field splitting parameters of two 2,6-dinitrenopyridines were estimated to be |D/hc| ≅ 0.19–0.20 cm−1 and |E/hc| ≅ 0.064–0.066 cm−1 by lineshape simulation of frozen solution X-band ESR spectra. This large ratio of |E/D| is consistent with a dominating dipolar interaction between the two nitrene units having a relative interaction vector angle of about 114°–116°. UB3LYP/6-31G* computations of 2,6-dinitrenopyridine predict a very similar interaction vector angle. These results are quite different from analogous results observed for meta-dinitrenobenzenes. The experimental zero-field splitting (zfs) and computational results indicate that the ESR spectroscopy of 2,6-dinitrenopyridines are dominated by the one-center interactions between unpaired electrons on the nitrene units (the triplet mononitrene zfs), and the relative geometry of interaction between the mononitrenes caused by the molecular geometry of the dinitrenopyridine (the interaction vector angle). Copyright © 2006 John Wiley & Sons, Ltd.