A computational study of the Dougherty model for the prediction of high-spin states in organic chemistry

During the last two decades, growing interest in the field of material chemistry has been focused on the synthetic design of organic high‐spin molecules for use as novel magnetic materials. Conjugated radicals based on the bis(pyrazolyl)pyridine core are very attractive in principle, since they per se combine optical, chelating and magnetic properties on a single molecular entity. The functionalisation of this core via the bis(4′‐formyl) derivatives with Ullman radicals results in novel functional biradicals, which may further be used for supramolecular architectures. In this paper we describe the synthesis, structure and properties of 2,6‐bis[4′‐(3‐oxo‐1‐oxyl‐4,4,5,5‐tetramethylimidazolin‐2‐yl)pyrazol‐1′‐yl]pyridine (Pz2PyNN) and 2,6‐bis[4‐(1‐oxyl‐4,4,5,5‐tetramethylimidazolin‐2‐yl)pyrazolyl]pyridine (Pz2PyIN). The two biradicals can clearly be differentiated by UV/Vis, IR and EPR spectroscopy. The optical absorptions of the blue Pz2PyNN appear around λmax= 610 nm (ϵ ≈︁ 1700 M−1 cm−1) while for Pz2PyIN the orange‐red colour arises from absorptions at λmax= 468 nm (ϵ ≈︁ 1400 M−1 cm−1). A triplet ground state for the bis(nitronylnitroxide) Pz2PyNN with ΔES‐T ≈︁ 11.8 ± 4.8 cm−1 can be deduced from the EPR studies because of the increase of the double integrated intensity times temperature at very low temperatures, indicating complete population of the triplet state. For the related bis(iminonitroxide) Pz2PyIN a much smaller (at least one order of magnitude lower) singlet−triplet energy gap with an upper limit of 0.7 cm−1 has been derived (0.7 ⪖ ΔES‐T ⪖ −0.07 cm−1). The new multifunctional biradicals represent the first example of high‐spin molecules in the bis(pyrazolyl)pyridine family. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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2,6‐Bis(pyrazolyl)pyridine Functionalised with Two Nitronylnitroxide and Iminonitroxide Radicals

Zoppellaro

Geies

Enkelmann

et al. 2004

Eur J Org Chem

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Synthesis, Optical Properties and Magnetic Studies of 2,6‐Bis(pyrazolylmethyl)pyridine Functionalized with Two Nitronyl Nitroxide Radicals

et al. 2008

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The synthesis, optical properties, spin‐polarization path and magnetic ground‐state studies of a novel nitronyl nitroxide biradical system based on the 2,6‐bis(pyrazolylmethyl)pyridine unit is reported. Besides the presence of σ conjugation and a non‐alternant pathway for spin polarization through the core as a coupling unit, the through‐bond ferromagnetic interaction between spin carriers, although weak (0.06 cm–1 < ΔEST = 2J/kB < 0.6 cm–1), is preserved. It vanishes (2J/kB ≈ 0) upon coordination with Zn2+ metal ions, but is restored upon Zn2+ depletion with EDTA. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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Electron‐spin resonance (ESR) characterization of quintet spin‐state bis‐nitroxide‐bearing cyclopentane‐1,3‐diyl diradicals

Omokawa

Hatano

Abe

2014

J of Physical Organic Chem

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High-spin organic molecules have attracted much attention as spin sources for magnetic materials. In this paper, a novel high-spin organic molecule was designed according to a logical strategy. A 2,2-dimethylcyclopentane-1,3-diyl diradical unit was utilized as a spin source and a spin-bridged fragment. In addition, nitroxides were introduced as spin sources. Quintet electron-spin resonance (ESR) signals, which were attributed to the 1,3-di(3′-nitoroxyphenyl)-2,2-dimethylcyclopentane-1,3-diyl tetraradical (TR), were observed in a 2-methyltetrahydrofuran glassy matrix at 80 K after the photodenitrogenation of a newly synthesized azoalkanes AZ. A simulation of the signal provided the zero-field splitting parameters D (|D|/hc = 0.0127 cm À1) and E (|E|/hc = 0.0014 cm À1) for the quintet state of the tetraradical TR. The parameter D of the quintet state of TR was found similar to those of the previously reported quintet spin states of tetraradical TR1 with two cyclobutane-1,3-diyl units (0.0190 cm À1) and TR2 with two 2,2-dimethylcyclopentane-1,3-diyl diradicals (0.0116 cm À1).

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A computational study of the Dougherty model for the prediction of high-spin states in organic chemistry

Cited by 5 publications

References 9 publications

2,6‐Bis(pyrazolyl)pyridine Functionalised with Two Nitronylnitroxide and Iminonitroxide Radicals

2,6‐Bis(pyrazolyl)pyridine Functionalised with Two Nitronylnitroxide and Iminonitroxide Radicals

Synthesis, Optical Properties and Magnetic Studies of 2,6‐Bis(pyrazolylmethyl)pyridine Functionalized with Two Nitronyl Nitroxide Radicals

Electron‐spin resonance (ESR) characterization of quintet spin‐state bis‐nitroxide‐bearing cyclopentane‐1,3‐diyl diradicals

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