Zero‐field splitting versus interelectronic distance in triplet electron spin resonance spectra of localized dinitrenes

Abstract

AbstractTriplet zero‐field splitting parameters were obtained in 2‐methyltetrahydrofuran glass at 77 K for phenylene‐1,4‐dinitrene (1), biphenyl‐4,4′‐dinitrene (2), (E)‐1,2‐bis(4′‐nitrenophenyl)ethene (3), 1,4‐bis(4′‐nitrenophenyl)buta‐1,3‐diene (4) and 1,8‐bis(4′‐nitrenophenyl)octa‐1,3,5,7‐tetraene (5). The results were (1) |D/hc| = 0·169 cm−1 |E/hc| = 0·004 cm−1, (2) |D/hc| = 0·189 cm−1, |E/hc| = 0·00 cm−1, (3) |D/hc| = 0·122 cm−1, |E/hc| = 0·00 cm−1, (4) |D/hc| = 0·0865 cm−1, |E/hc| = 0·00 cm−1 and (5) |D/hc| = 0·0442 cm−1, |E/hc| = 0·00 cm−1. All these biradicals are ground‐state singlets. Based on the observed decrease in triplet signal intensities as temperature decreases. The substantial magnitudes of |D/hc| for 3–5, despite the large distance between localized nitrene electrons, is much more than can be explained by a simple dipolar interaction between localized electrons, and is attributed at least partly to spin polarization effects on the π‐electron clouds of these systems.