Molecular Conformations and Magnetic Parameters of the Compact Trimethylenemethane-Type Triplet Diradical

Molecular Conformations and Magnetic Parameters of the Compact Trimethylenemethane-Type Triplet Diradical Full article

Journal

The Journal of Physical Chemistry A
ISSN: 1089-5639

Output data

Year: 2013, Volume: 117, Number: 33, Pages: 8065-8072 Pages count : 8 DOI: 10.1021/jp405572n

Authors

Misochko Eugenii Ya. ¹ , Korchagin Denis V. ¹ , Akimov Alexander V. ¹ , Masitov Artem A. ¹ , Tolstikov Svyatoslav E. ² , Tretyakov Evgeny V. ² , Ovcharenko Victor I. ²

Affiliations

1	Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation
2	International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Institutskaya Street 3a, 630090 Novosibirsk, Russian Federation

The ESR spectrum of compact nitroxide (NO)-substituted nitronyl nitroxide (NN) triplet diradical N-tert-butyl-N-oxidanyl-2-amino-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (1) was recorded in solid argon matrix at 15 K. The zero-field splitting (ZFS) parameters of 1 were derived from the recorded ESR spectrum: |D| = 0.0248 cm–1 and E = 0.0025 cm–1. Quantum chemical calculations have been performed using DFT and multiconfigurational ab initio (CAS) methods in order to establish equilibrium geometries of the conformational isomers resulting from twisted conformations of NO and NN moieties. The ZFS parameters of 1 were calculated at these levels of theory to test validity of the calculated structures. The calculation results were analyzed using the measured ZFS parameters and magnetic and structural data from the previous studies (Suzuki, S.; et al. J. Am. Chem. Soc.2010, 132, 15908; Tretyakov, E. V.; et al. Russ. Chem. Bull.2011, 60, 2608). It was found that the ab initio method is most successful for accurate predictions of molecular and magnetic parameters. Diradical 1 has only one stable enantiomeric pair in pseudoeclipsed conformations. The two chiral isomers exist in racemic crystals 1 and in solid matrices with molecular parameters close to those attributed to a free molecule. The analysis of the spin density distribution suggests that one unpaired electron occupies NO group at the equilibrium geometry, whereas the torsion of NO group governs the spin density distribution of the second unpaired electron on a conjugated fragment in NN group. The increase in planarity by torsion of NO group enhances the trimethylenemethane-type properties and, therefore, gives rise to larger ferromagnetic exchange interaction. More planar equilibrium geometry and greater (three times) exchange interaction constant J were predicted for hypothetical diradical 1a, where bulky tert-butyl group is replaced by a methyl group in the nitroxide fragment.

Misochko E.Y. , Korchagin D.V. , Akimov A.V. , Masitov A.A. , Tolstikov S.E. , Tretyakov E.V. , Ovcharenko V.I.
Molecular Conformations and Magnetic Parameters of the Compact Trimethylenemethane-Type Triplet Diradical
The Journal of Physical Chemistry A. 2013. V.117. N33. P.8065-8072. DOI: 10.1021/jp405572n WOS Scopus

Published print:

Aug 22, 2013

Web of science:	WOS:000323593700044
Scopus:	2-s2.0-84883200391

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