High-spin organic molecules with dominant spin-orbit contribution and unprecedentedly large magnetic anisotropy

Abstract

High-spin organic molecules with dominant spin-orbit contribution to magnetic anisotropy are reported. Quintet 4-azido-3,5-dibromopyridyl-2,6-dinitrene (Q-1), quintet 2-azido-3,5-dibromopyridyl-4,6-dinitrene (Q-2), and septet 3,5-dibromopyridyl-2,4,6-trinitrene (S-1) were generated in solid argon matrices by ultraviolet irradiation of 2,4,6-triazido-3,5-dibromopyridine. The zero-field splitting (ZFS) parameters, derived from electron spin resonance spectra, show unprecedentedly large magnitudes of the parameters D: ∣D(Q1)∣ = 0.289, ∣D(Q2)∣ = 0.373, and ∣D(S1)∣ = 0.297 cm(-1). The experimental ZFS parameters were successfully reproduced by density functional theory calculations, confirming that magnetic anisotropy of high-spin organic molecules can considerably be enhanced by the "heavy atom effect." In bromine-containing high-spin nitrenes, the spin-orbit term is dominant and governs both the magnitude and the sign of magnetic anisotropy. The largest negative value of D among septet trinitrenes is predicted for 1,3,5-trinitrenobenzene bearing three heavy atoms (Br) in positions 2, 4, and 6 of the benzene ring.

The EPR Spectrum of Triplet Mesitylphosphinidene: Reassignment and New Assignment

“… The contribution of the spin‐orbit (SO) coupling to parameter D is one order of magnitude greater than the contribution of the spin–spin (SS) interaction. The main SO contribution is the SOMO→SOMO spin‐flip interaction between excited singlet and ground triplet states (Table S3). The PBE/Ahlrichs‐DZ level of theory is universal and describes the experimental results for all known triplet phosphinidenes (Table ), as well as for high‐spin nitrenes The calculated components ( A x and A y ) of hyperfine structure tensor A are similar to those obtained from the experimental spectrum, see Table . …”

“…Our interest in the EPR spectra of organic phosphinidenes was motivated by the study of the heavy‐atom effect on magnetic anisotropy as a continuation of our previous studies . Our initial EPR measurements in photolyzed frozen solutions with precursors 1 a and 1 b showed that the spectrum of photolytic product 2 (Scheme ) is significantly different from that reported in Ref.…”

“…The PBE/Ahlrichs‐DZ level of theory is universal and describes the experimental results for all known triplet phosphinidenes (Table ), as well as for high‐spin nitrenes …”

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

“…The halonitrenes FN, ClN, and BrN have the highest D values (2.46, 3.4, and ca. 17 cm −1 , respectively), as a result of large contributions of SOC. Alkoxynitrenes, R−O−N, also have very high D values (ca.…”

“…[50,78] Theh alonitrenes FN, ClN,a nd BrN have the highest D values (2.46, 3.4, and ca. 17 cm À1 ,r espectively), [79,80] as ar esult of large contributions of SOC.Alkoxynitrenes,R À O À N, also have very high D values (ca. 1.96 cm À1 ) [81] that are about 30 %h igher than predicted from the natural spin densities,t hereby implying significant contribution from SOC.T his finding can be explained by mixing of the triplet state with the zwitterionic singlet RO + =N À .I ng eneral, as erious deviation from the straight line hints at ap ossible importance of SOC.T he E values are also dependent on SOC.…”