High resolution electron paramagnetic resonance spectroscopy of quintet pyridyl-2,6-dinitrene in solid argon: Magnetic properties and molecular structure

Abstract

The high resolution X-band electron para magnetic resonance (EPR) spectrum of quintet pyridyl-2,6-dinitrene was recorded after the photolysis of 4-amino-2,6-diazido-3,5-dichloropyridine in solid argon matrix at 15 K. This spectrum represents a new type of powder EPR spectra that are characteristic for quintet spin states with zero-field splitting parameters |E(q)/D(q)| approximately 1/4. All EPR lines of the quintet dinitrene were unambiguously assigned based on the eigenfield calculations of the Zeeman energy levels and angular dependencies of resonance magnetic fields. Owing to the high resolution of the experimental EPR spectrum, zero-field splitting parameters of the quintet dinitrene were determined with a high accuracy: D(q)=0.2100+/-0.0005 cm(-1) and E(q)=-0.0560+/-0.0002 cm(-1). These parameters provide correct information regarding the molecular angle Theta and distance r between two triplet sites in the molecule of quintet dinitrene. The measured molecular angle Theta=114.2 degrees+/-0.2 degrees is in excellent agreement with results of the density functional theory calculations. The analysis of the magnetic parameters shows that the spin population on the nitrene units in the quintet dinitrene is greater than that on the nitrene unit in the triplet nitrene.

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

“…The parameter R(min) equals to 0.18 mT for ESR lines y 1 , x 1 , y 2 , and A. This fact indicates that the terms involving higher powers of S z , S x , and S y in the magnetic spin Hamiltonian (9), are negligibly small. This quintet dinitrene is the major product after brief irradiation of triazide 1.…”

“…4, 9 In particular, two intense lines at 47.9 and 362 mT correspond to the most intense y 1 and y 2 transitions of such dinitrenes. 9 The exact analytical solution of spin Hamiltionian (9) for S = 2, g = 2.0023, H(y 1 ) = 47.9 mT, H(y 2 ) = 362 mT, and ν 0 = 9.10729 GHz yields |D q1 | = 0.289 cm −1 and |E q1 | = 0.057 cm −1 (for details, see supplementary material 16 ).…”

“…The optimal EPR spectra of the molecules Q-1, Q-2, and S-1 in Figs. 1-5 were calculated at isotropic g-factor g = g e in spin Hamiltonian (9), where S is an operator corresponding to effective spin and the g-tensor reflects a molecular anisotropy in the Zeeman term. Usually the high-spin electronic states of purely organic molecules, such as Q-3 to Q-10 and S-2 FIG.…”

“…12 In argon matrices, this dinitrene showed D q = 0.210 cm −1 and E q = 0.056 cm −1 . 9 The largest magnetic anisotropy among quintet dinitrenes was reported for axially symmetric dinitrene Q-10 (D q = 0.340 cm −1 , E q = 0.011 cm −1 ). 13 The origin of so large value of D q for this dinitrene remains still unclear.…”

Selective Reactions on the Azido Groups of Aromatic Polyazides

“…6,7,9,10,[43][44][45][46][47][48][49][50] Thus, for instance, the photolysis of azide 12 in organic solids at 77 K allowed us to obtain and investigate a new heterospin quintet system, carbenonitrene 40 (Scheme 18). 43…”