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DOI: 10.1002/chem.201501343
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Radical Chemistry
Coordination Complexes of a Neutral 1,2,4-Benzotriazinyl Radical
Ligand: Synthesis, Molecular and Electronic Structures, and
Magnetic Properties
Ian S. Morgan,*[a] Akseli Mansikkamäki,[a] Georgia A. Zissimou,[b] Panayiotis A. Koutentis,[b]
Mathieu Rouzires,[c, d] Rodolphe ClØrac,[c, d] and Heikki M. Tuononen*[a]
Abstract: A series of d-block metal complexes of the recent-
ly reported coordinating neutral radical ligand 1-phenyl-3-
(pyrid-2-yl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1) was synthe-
sized. The investigated systems contain the benzotriazinyl
radical 1 coordinated to a divalent metal cation, MnII, FeII,
CoII, or NiII, with 1,1,1,5,5,5-hexafluoroacetylacetonato (hfac)
as the auxiliary ligand of choice. The synthesized complexes
were fully characterized by single-crystal X-ray diffraction,
magnetic susceptibility measurements, and electronic struc-
ture calculations. The complexes [Mn(1)(hfac)2] and
[Fe(1)(hfac)2] displayed antiferromagnetic coupling between
the unpaired electrons of the ligand and the metal cation,
whereas the interaction was found to be ferromagnetic in
the analogous NiII complex [Ni(1)(hfac)2]. The magnetic prop-
erties of the complex [Co(1)(hfac)2] were difficult to interpret
owing to significant spin–orbit coupling inherent to octahe-
dral high-spin CoII metal ion. As a whole, the reported data
clearly demonstrated the favorable coordinating properties
of the radical 1, which, together with its stability and struc-
tural tunability, make it an excellent new building block for
establishing more complex metal–radical architectures with
interesting magnetic properties.
Introduction
indefinitely stable under ambient conditions and cannot there-
fore be used as building blocks for practical materials. For this
reason, a bulk of the reported investigations of metal–radical
coordination complexes has employed only a limited number
of different ligands such as semiquinones,[3] nitroxides,[4] thia-
zyls,[5] and verdazyls.[6]
The design and synthesis of new molecular magnetic materials
is currently a topic of interest in materials sciences.[1] One
promising avenue is the so-called metal–radical approach that
takes advantage of strong intramolecular magnetic exchange
interactions, which result from the coordination of radical li-
gands to paramagnetic metal ions.[2] The propagation of these
interactions in the solid state through intermolecular exchange
coupling can then give rise to cooperative magnetic behavior
such as antiferro-, ferri-, or ferromagnetism. This approach has
enabled the preparation of molecule-based magnetic materials
ranging from simple one-dimensional coordination polymers
to both two- and three-dimensional metal-radical networks.[1]
Although there exists a number of open-shell ligands that
are known to coordinate to metal ions, many of them are not
Some of the most recent developments in the field of stable
radical chemistry involve 1,2,4-benzotriazinyls, also known as
“Blatter radicals”. The parent compound was synthesized in
1968,[7] but despite its inherent stability, it received only scant
attention over the following decades. During the past five
years, we have reported improved syntheses for a growing
family of 1,2,4-benzotriazinyls, simultaneously demonstrating
that the modifications to the molecular structure do not signif-
icantly influence the stability of the radicals.[8] Recently, we
published the syntheses of Blatter radicals for coordination
purposes,[8e,9] and demonstrated that 1-phenyl-3-(pyrid-2-yl)-
1,4-dihydro-1,2,4-benzotriazin-4-yl (1), which has a bidentate
chelation pocket, can act as a coordinating ligand by charac-
terizing its [Cu(hfac)2] complex (hfac=1,1,1,5,5,5-hexafluoroa-
cetylacetonato).[9] This complex possessed a strong ferromag-
netic metal–radical interaction along with weak antiferromag-
netic radical···radical couplings in
[a] Dr. I. S. Morgan, A. Mansikkamäki, Dr. H. M. Tuononen
Department of Chemistry, Nanoscience Center
University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä (Finland)
[b] G. A. Zissimou, Dr. P. A. Koutentis
Department of Chemistry, University of Cyprus
P.O. Box 20537, 1678 Nicosia (Cyprus)
the solid state.
[c] M. Rouzires, Dr. R. ClØrac
The bipyridyl-like N,N’-chelating
pocket in the benzotriazinyl radical
CNRS, CRPP, UPR 8641, 33600 Pessac (France)
[d] M. Rouzires, Dr. R. ClØrac
1 suggests that it can have a wide
Univ. Bordeaux, CRPP, UPR 8641, 33600 Pessac (France)
coordination chemistry. Thus, the
Supporting information for this article is available on the WWW under
radical is an important new
Chem. Eur. J. 2015, 21, 15843 – 15853
15843
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim