Probing through-space and through-bond magnetic exchange couplings in a new benzotriazinyl radical and its metal complexes

Article abstract of DOI:10.1039/c9dt01918a

The synthesis and characterization of a new chelating benzotriazinyl radical (Rad₂) are described. Crystallographic studies coupled with SQUID magnetometry on Rad₂ reveal the presence of discrete radical pairs which are antiferromagnetically coupled. The reaction of Rad₂ with the 3d transition metal complexes M(hfac)₂·xH₂O (hfac^- = hexafluoroacetylacetonate) led to mononuclear metal complexes of general formula M(hfac)₂(Rad₂) [M = Zn(ii) (1); Ni(ii) (2) and Co(ii) (3)] whose structures have been determined by single crystal X-ray diffraction. Compounds 1-3 are isostructural and crystallize in the monoclinic space group P2₁/n with two molecules in the asymmetric unit. In the case of the Zn(ii) complex (1) through-space intermolecular radical?radical antiferromagnetic exchange interactions via π??π? contacts are observed, whereas strong intramolecular through-bond metal-radical ferromagnetic interactions [J = +59.3(9) cm^-1] are observed for the Ni(ii) complex (2). For the Co(ii) complex (3), computational and magnetic studies reveal substantial zero field splitting and ferromagnetic metal-radical interactions.

Full text of DOI:10.1039/c9dt01918a

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Nasani, S. Roy, S. T. S., A. Mondal and J. M. Rawson, Dalton Trans., 2019, DOI: 10.1039/C9DT01918A.
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DOI: 10.1039/C9DT01918A
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Probing through-space and through-bond magnetic exchange
couplings in a new benzotriazinyl radical and its metal complexes
Received 00th January 20xx,
Accepted 00th January 20xx
Rajendar Nasani,‡a Thulaseedharan Nair Sailaja Sidharth,§‡a Subhadip Roy,a Arpan Mondal,a Jeremy
M. Rawson,*b and Sanjit Konar*a
DOI: 10.1039/x0xx00000x
The synthesis and characterization of a new chelating benzotriazinyl radical (Rad2) are described. Crystallographic studies
coupled with SQUID magnetometry on Rad2 reveal the presence of discrete radical pairs which are antiferromagnetically
coupled. Reaction of Rad2 with the 3d transition metal complexes M(hfac)2·xH2O (hfac− = hexafluoroacetylacetonate) led
to mononuclear metal complexes of general formula M(hfac)2(Rad2) [M = Zn(II) (1); Ni(II) (2) and Co(II) (3)] whose
structures have been determined by single crystal X-ray diffraction. Compounds 1– 3 are isostructural and crystallize in the
monoclinic space group P21/n with two molecules in the asymmetric unit. In the case of the Zn(II) complex (1) through-
space intermolecular radical···radical antiferromagnetic exchange interactions via π*···π* contacts are observed, whereas
strong intramolecular through-bond metal-radical ferromagnetic interactions [J = +59.3(9) cm-1] are observed for the Ni(II)
complex (2). For the Co(II) complex (3), computational and magnetic studies reveal substantial zero field splitting and
ferromagnetic metal-radical interactions.
www.rsc.org/
ligands often give strong intramolecular metal-radical
exchange (Jintra/k) such that the complexes’ spin ground state is
often fully populated at/near room temperature. Conversely
through-space intermolecular exchange between molecules
has been less extensively explored but is typically only evident
Introduction
The development of molecule-based magnetic materials has
relied heavily on magnetic exchange-coupling between
paramagnetic metals centers (d- or f-based electrons) typically
via diamagnetic ligands. The sign and magnitude of such
magnetic super-exchange interactions for d-block metals is
well understood through Goodenough-Kanamori rules.1 While
one and two atom bridges such as O2- and CN- prove effective
exchange coupling ligands, exchange coupling via diamagnetic
ligands over more extended distances is typically weak. An
alternative strategy is to implement the use of bridging
paramagnetic ligands where strong metal-ligand exchange can
lead to high spin molecules irrespective of whether the
at low temperature and often modelled using
a
phenomenological Weiss constant, (where | | << |Jintra/k|)
θ
θ
and typically |θ|< 2 K. For example, Preuss’ studies7 on
through-bond and through-space space exchange in
Mn(hfac)2(boadtda) revealed strong intramolecular exchange
(Jintra/k = -39 K) and weaker through-space interactions,
propagated via close S···O intermolecular contacts (Jinter/k = -
2.5 K). Conversely a McConnell I mechanism8a via a π···π orbital
overlap is proposed for through-space ferromagnetic
interactions in Ni(hfac)2(boadtda).8b One approach to
deconvolute contributions from intramolecular exchange,
intermolecular exchange and other effects (such as residual
orbital angular momentum and zero field splitting) and
unambiguously probe such through-space exchange in metal-
radical complexes is to use complexes in which the metal ion is
diamagnetic (commonly d0, low spin d6 or d10), thereby
providing a direct probe for the strength of through-space
exchange.
coupling is ferro- or antiferro-magnetic.2
A number of
paramagnetic ligands have been explored of which nitroxide,
nitronyl nitroxide, verdazyl and dithiadiazolyl radicals have
been particularly well documented (Scheme 1a,b).3–6 These
a Department of Chemistry, Indian Institute of Science Education and Research
Bhopal, Bhopal Bypass Road, Bhauri, Bhopal 462 066, India. E-mail:
skonar@iiserb.ac.in; Fax: +91-755-6692392; Tel: +91-755-6692339.
b
Department of Chemistry & Biochemistry, The University of Windsor, 401 Sunset
Ave., Windsor, ON, CANADA, N9B 3P4; E-mail: jmrawson@uwindsor.ca
The 1,2,4-benzotriazinyl radicals (Blatter radicals) comprise
an interesting family from the viewpoint of their ease of
preparation, functionalization, transformations of functional
groups and robust air and moisture stability.9–12 In the solid
state, they tend to adopt slipped π−stacked structures. The
magnetic properties of these radicals appear particularly
†Electronic supplementary information (ESI) available: Cyclic voltammetry, plots of
M vs H/T for complexes 2 and 3, computational details and a summary Table of
crystallographic data. CCDC 1882619–1882622. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/x0xx00000x
‡Both the authors have equal contribution to this work.
§Undergraduate Researcher.
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sensitive to their solid state structure and exhibit a diverse sodium sulfide, and 4-trifluoromethyl aniline which generated
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range of magnetic properties including abrupt spin transitions the corresponding pyridylthioamide species (
(between paramagnetic and diamagnetic phases),13 the pyridylthioamide with phenyl hydrazine gave
DOI: 1A0.)1.01379R/Ce9aDcTt0io1n918oAf
antiferromagnetic exchange11c,g,12a,h,14 and ferromagnetic pyridylamidrazone ( ).18 The ring closure and oxidation of the
B
interactions11b,f,15 depending on the subtle differences in purified amidrazone was accomplished by a combination of
molecular arrangement along the stacking direction. Pd/C and 1,8-diazabicycloundec-7-ene in air to obtain the
Functionalization at the C7 position of the parent Blatter radical Rad2
.
The product was purified using column
followed by recrystallization and
radical with a trifluoromethyl11b,15b or thienyl11f group serves a chromatography
dual purpose, enhancing the oxidative stability of the characterized by elemental analysis, IR and EPR spectroscopy,
benzotriazinyl framework as well as favoring a 1D columnar cyclic voltammetry, magnetic measurements and single-crystal
alignment. Recently, Morgan et al. reported the coordinating X-ray diffraction.
Blatter
radical,
1-phenyl-3-(pyrid-2-yl)-1,4-dihydro-1,2,4-
benzotriazin-4-yl (Rad1, Scheme 1c) with a bipyridine-like N,N′-
chelating pocket and its coordination complexes
M(hfac)2(Rad1) (M = Mn, Fe, Co, Ni, Cu).16 Magnetic studies
revealed that in Rad1 the radical pairs are strongly
antiferromagnetically coupled and are essentially diamagnetic
below 100 K;16a Cu(II) and Ni(II) complexes showed
intramolecular ferromagnetic exchange consistent with orbital
orthogonality rules whereas Mn(II) and Fe(II) complexes
showed antiferromagnetic exchange.16
NH2
CF3
F
3C
S
A
Na .9H
2S 2O
Sulphur
N
N
H
N
H2NNHPh
DBU
Pd/C
HN
F
3C
N
F
3C
N
N
N
N
H
N
N
N
N
(c)
N
O
(a)
(b)
N
Rad2
N
B
R
N
7
1
2 N
pyvd
O
4
N
N
S
Scheme 2. Synthetic route of Rad2.
N
N
N
S
=
=
CF3
Electrochemical studies on Rad2 reveal an oxidation and a
reduction process (Figure S1, Supporting Information)
comparable with other benzotriazinyls11h with a large window
of redox stability (-0.85 – +0.31 V vs Fc/Fc+ reference
electrode) permitting it to react with a range of transition
metals in common oxidation states without electron transfer.
Reaction of Rad2 with the hydrated salts M(hfac)2·xH2O
Rad
Rad
boadtda
1 (R H);
2 (R
)
Scheme 1. Representative chelating paramagnetic ligands; the (a) pyridyl-verdazyl, (b)
4-benzoxazolyl-dithiadiazolyl and the (c) benzotriazinyl radicals Rad1 and Rad2.
In order to increase the robustness of the radical moiety,
the current study was aimed to functionalize the parent
ligating benzotriazinyl framework (Rad1) by the trifluoromethyl
group (-CF3) at the C7 position (Rad2) to prevent any undesired
oxidation products and to establish how such functionalization
affects the solid-state structure and magnetic response.
Herein, we describe the synthesis and characterization of Rad2
and, despite the electron-withdrawing nature of the CF3 group,
we show that it can act as a chelating ligand to yield an
isostructural series of d-block complexes of composition
(where M = Zn(II) (1), Ni(II) (2) and Co(II) (3
), hfac−:
hexafluoroacetylacetonate) in dichloromethane afforded
complexes of general formula M(hfac)2(Rad2).
EPR studies
EPR spectra for Rad2 and Zn(hfac)2(Rad2) were recorded on a
Bruker EMX-MicroX-band EPR spectrometer equipped with a
variable temperature unit providing access to temperatures in
the range 100–300 K. The solid state EPR spectra of Rad2
revealed a strong temperature dependence (Figure 1). At high
temperature (300 K) the spectrum appeared as a broad singlet
with limited resolution of additional features. At 100 K there
was some evidence for exchange coupling reflected in
absorption to either side of the central line and some better
resolution of features in the 150–200 K region. The EPR
spectrum at 150 K was simulated as a single component EPR
spectrum with both hyperfine coupling and zero field splitting.
In general the isotropic hyperfine coupling in solution (aiso) is
M(hfac)2(Rad2) [M = Zn(II) (1), Ni(II) (2) and Co(II) (3
); hfac− =
hexafluoroacetylacetonate]. The through-bond and through-
space interactions were examined through variable-
temperature magnetic susceptibility measurements and
theoretical calculations were carried out to probe both the
metal-radical and radical···radical exchange coupling.
Results and Discussion
Synthetic considerations
The benzotriazinyl radical Rad2 was prepared via a multistep
route (Scheme 2) starting from the readily available picoline,
2 | J. Name., 2012, 00, 1-3
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Figure 1. (a) Variable temperature solid state EPR spectra of Rad2; (b) EPR spectrum of Rad2 at 150 K with simulation (gx = 2.0075, gy = 2.0070, gz = 2.0055; aNz(1) = 22 G, 2 x
aNz(2,3) = 14 G, D = 0.00055 cm-1, E = 0.0001 cm-1, ∆Hpp = 2.8 G (Gaussian)); (c) EPR spectrum of Rad2 at 200 K with simulation (gx = 2.0075, gy = 2.0070, gz = 2.0055; aNx(1) = 6
G, aNy(1) = 6 G, aNz(1) = 9 G, 2 x aNx(2,3) = 4.5 G, 2 x aNy(2,3) = 4.5 G, aNz(2,3) = 6 G, D = 0.00095 cm-1, E = 0.00007 cm-1).
related to the principal components of the hyperfine coupling
(ax, ay and az) by Eqn. 1:
aiso = 1/3 (ax + ay + az)
Eqn. 1
For π radicals the hyperfine coupling to one component is
large and the other two components which sit in the nodal
plane of the singly occupied molecular orbital (SOMO) are near
zero. The non-zero component of the hyperfine is then ~ 3 aiso
.
As a starting point for simulating the solid state EPR spectrum
of Rad2, we used the isotropic hyperfine coupling parameters
forthe closely related “super stable” Blatter radical, 1,3-
diphenyl-7-trifluoro-methyl-1,4-dihydro-1,2,4-benzotriazin-4-
yl.11b This radical is identical to Rad2 except that the pyridyl
ring at the 3-position in Rad2 is replaced by a phenyl group.
Here, the solution EPR spectrum implemented three 14N
hyperfine coupling constants of 7.62, 4.95 and 4.56 G. The
corresponding non-zero anisotropic parameters are expected
to be in the region of 22.86, 14.85 and 13.68 G respectively.
Refined parameters to simulate the anisotropic spectrum of
Rad2 were 22.0, and 2 × 14.0 G in excellent agreement with
expectation. A small additional zero field splitting term D =
0.00055 cm-1 was included and provided a very good fit to all
features in the EPR spectrum. EPR simulations were
undertaken using PIP through the PIP4WIN interface.19 On
warming from 150 K to 200 K there are subtle changes to the
solid state EPR spectrum of Rad2 associated with an increase in
the zero field splitting parameter D and an averaging of the
hyperfine coupling across the three components. The
temperature evolution of the spectral resolution is likely due
to the temperature dependence of the relaxation rates which
are sensitive to distance and therefore coupled to thermal
lattice expansion effects upon warming.20
Figure 2. Variable temperature solid state EPR studies on Zn(hfac)2(Rad2).
Description of the crystal structures and molecular packing
topology of the benzotriazinyl radical (Rad2) and M(hfac)2(Rad2)
(M
=
Zn(II) (1), Ni(II) (2) and Co(II) (3), hfac:
hexafluoroacetylacetonate)
The benzotriazinyl radical Rad2 crystallizes in the triclinic space
group P-1 with one molecule in the asymmetric unit (Figure S2,
Supporting Information). The bond lengths and bond angles
are largely unexceptional and similar to the values reported for
other related benzotriazinyl systems. The phenyl ring (ring I:
formed by C21, C23, C24, C25, C26) makes a dihedral angle of
56.47o with the spin-bearing triazinyl ring (ring II: formed by
N1, C1, C6, N2, N3, C7) and the dihedral angle between the
pyridyl ring (ring III: formed by C8, C9, C10, C11, C12, N4) and
the triazinyl ring II is 8.51o. Two Rad2 molecules are located
about the crystallographic inversion center leading to a
supramolecular dimer linked through N···H interactions (2.691
Å) (Figure 3). These interactions fix the two triazinyl rings in an
essentially eclipsed configuration with a centroid···centroid
distance of 3.375 Å [the degree of slippage,13a longitudinal
Variable temperature solid state EPR spectra of
Zn(hfac)2(Rad2) (Figure 2) were rather featureless but revealed
the emergence of a weak absorption slightly to low field of the
central resonance, consistent with the presence of thermal
population of excited high spin states. In contrast, we were
(
φ
1)= 29.40o and latitudinal (
substantially longer compared to the centroid···centroid
distance of 3.256 Å (
1= 38.01o, 2= 9.39o) between two
φ
2)= 9.12o]. This distance is
unable to observe EPR spectra for complexes
2 and 3 under
the limited conditions available (100 – 300 K, X-band).
φ
16a
φ
triazinyl rings in Rad1
.
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those built from the molecules having the largestVsieowliAdrticalenOgnlelin2e2
DOI: 10.1039/C9DT01918A
of intermolecular contacts–pair with Ω=16.1%. Even when
considering the topology in terms of dimers, the packing
description does not change and these π-π dimers similarly
adopt the bcu-x type net (Figure 4).
To realize the difference in molecular packing, topological
analysis of the molecular packing of the reported Rad1
molecule16a has been undertaken which has a CN (coordination
number) of 17. The topology of the 17-c underlying net is not
contained in the Topos Topological Database (Figure 5) and
this net can be described as a {354.473.59} net. Rad1 also
comprises a π-π dimer motif and a topological analysis based
on π-π dimer repeat units generates an underlying 14T3 net of
supramolecular dimers in the standard representation.
Figure 3. Structure of Rad2 highlighting intermolecular C-H···N (a) and
π···π
stacking (b) interactions which generate supramolecular dimers.
Topological analysis of the molecular packing21 reveals that
the molecule has a CN (coordination number) of 14, a common
number for neighboring molecules in molecular crystals22 and
the topological motif of the molecular packing can be
described by a net of the bcu-x type (14-coordinate extended
body-centered packing) as shown in Figure 4.
Figure 5. The underlying net of molecular packing and environment of the (a) molecule
and (b) its dimer in the crystal structure of compound Rad1. Surrounding (a) seventeen
molecules and (b) fourteen dimers are highlighted depending on the solid angle of
intermolecular contact (Ω≥ 8% - pink; 8%> Ω≥ 3% - yellow; Ω< 3% - green). The atoms
of the central molecule are colored according to the color scheme presented in the
legend. Pink, yellow and green spheres represent the centers of (a) molecules within
the 17-c uninodal underlying net and (b) dimers within the 14-c uninodal underlying
net.
Crystal structures of M(hfac)2(Rad2) (M = Zn(II) (
1) Ni(II) (2)
and Co(II) ( )) are isostructural and crystallize in the monoclinic
3
space group P21/n with two molecules in the asymmetric unit
which exhibit similar molecular geometries. Given the
isostructural nature of the compounds, the structure of
Figure 4. (a) The environment of the molecule and underlying net of molecular packing
in the crystal structure of compound Rad2. The solid angle (Ω) has been used as a
criterion serving as a weight factor proportional to the strength of the intermolecular
contact.22 The surrounding fourteen molecules are highlighted depending on the solid
angle of intermolecular contact (Ω≥ 9% - pink; 9%> Ω≥ 4% - yellow; Ω< 4% - green). The
atoms of the central molecule are colored according to the color scheme presented in
the legend. Black edges present the underlying net of centers of molecules with
topology bcu-x. (b) Uninodal underlying net of the bcu-x topological type describing the
packing of the molecular dimers formed by Rad2 molecules.
Zn(hfac)2(Rad2) (
example. In , each six-coordinate Zn(II) center adopts a
1) is described in detail as a representative
1
distorted {ZnN2O4} octahedral coordination geometry that is
filled by one N,N′-chelating Rad2 moiety and two hfac ligands.
The two molecules in the asymmetric unit form two similar but
crystallographically different centrosymmetric dimer pairs
linked through C-H···O contacts between the pyridyl C-H and
the hfac O atom (C-H···O = 2.65 Å and 2.62 Å for the two
crystallographically independent molecules) and π···π
interactions (Figure 6).
Aforementioned, π-π dimers can be observed within the
crystal packing. An alternative description of the molecular
packing can be considered as the packing of these
supramolecular π-π dimers. The corresponding dimers are
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Table 1. List of non-valence contacts between molecules in structure Rad2 and for ZA1/ZA2 molecules in M(hfac)2(Rad2) (M = Zn(II) (1), Ni(II) (2) and Co(II) (3))
Type of
contact
Number of contacts
Surface area, Å2
Fraction of total area
Rad2
1
2
3
Rad2
1
2
3
Rad2
1
2
3
ZA1/ZA2
122/114
ZA1/ZA2
112/112
ZA1/ZA2
121/111
ZA1/ZA2
ZA1/ZA2
ZA1/ZA2
ZA1/ZA2
37.3/35.2
ZA1/ZA2
37.4/34.5
ZA1/ZA2
38.4/35.1
H-F
F-F
36
3
93.88
3.76
64.39
28.84
_
256.25/251.55
174.90/153.14
73.16/70.82
46.80/78.88
41.96/39.85
40.64/57.72
15.76/16.25
15.35/17.13
14.02/15.03
2.78/6.71
245.99/233.03
164.54/147.37
73.98/68.12
44.81/72.93
38.52/38.46
41.37/56.87
15.5/15.47
13.40/17.84
14.22/14.5
2.38/5.01
267.59/251.86
23.5
0.9
16.1
7.2
_
72/69
92/98
68/102
20/20
25/33
33/33
33/36
21/23
5/9
69/68
84/90
65/95
20/20
25/33
32/32
30/37
22/24
3/9
71/64
91/97
68/102
20/20
30/40
28/30
31/34
22/24
4/8
181.10/154.24
74.73/71.78
44.72/79.39
38.77/37.28
41.01/63.36
14.61/14.20
13.67/16.77
14.70/15.35
2.58/5.63
25.5/21.4
10.7/9.9
6.8/11.0
6.1/5.6
5.9/8.1
2.3/2.3
2.2/2.4
2.0/2.1
0.4/0.9
0.4/0.4
0.3/0.7
25.0/21.8
11.2/10.1
6.8/10.8
5.9/5.7
6.3/8.4
2.4/2.3
2.0/2.6
2.2/2.1
0.4/0.7
0.3/0.3
0.2/0.4
26.0/21.5
10.7/10.0
6.4/11.1
5.6/5.2
5.9/8.8
2.1/2.0
2.0/2.3
2.1/2.1
0.4/0.8
0.3/0.4
0.2/0.7
C-H
F-C
92
42
_
O-H
H-H
N-C
C-C
N-H
F-O
N-N
N-F
67
30
50
32
_
121.00
14.55
22.52
48.18
_
30.3
3.6
5.6
12.1
_
2
2/2
2/2
2/2
1.82
0.48
2.90/2.60
2.05/2.29
2.19/2.61
0.5
0.1
4
4/8
5/9
4/10
1.87/4.83
1.53/2.89
1.71/4.90
and nine ZA2 (Figure 7a). The second crystallographically
independent molecule (ZA2) is surrounded by 15 molecules
(nine ZA1 and six ZA2) (Figure 7b). In total, the 15,17-
coordinated net is of a previously unknown topological type
with point symbol for net (340.457.58)(347.470.519) (Figure 7c).
Figure 6. Structure of Zn(hfac)2(Rad2) highlighting intermolecular C-H···O (a) and π···π
stacking (b) interactions which generate supramolecular dimers.
These π···π interactions in the supramolecular dimer
[Zn(hfac)2(Rad2)]2 are rather different from those in Rad2 itself.
In the latter eclipsing of the benzotriazinyl framework is
observed whereas in the complexes 1–3 the molecules are
now slipped so that there is overlap of the triazinyl and pyridyl
rings (via an inversion centre). While the supramolecular dimer
in Rad2 locates the two benzotriazinyl rings over each other, in
[Zn(hfac)2(Rad2)]2 the benzotriazinyl ring is located over the
pyridyl ring with centroid···centroid distances of 3.718 Å and
3.605
independent supramolecular dimers. The corresponding
distances are 3.729 Å & 3.622 Å in Ni(hfac)2(Rad2) ( ) and
3.788 Å & 3.629 Å in Co(hfac)2(Rad2) ( ).
From a topological perspective, the complete molecular
packings of complexes are similar if intermolecular
contacts with solid angles more than 0.4% are considered. The
packing comprises two crystallographically different molecules
of the same composition which are defined as ZA1 and ZA2.
ZA1 has intermolecular contacts with 17 molecules – eight ZA1
Å
respectively for the two crystallographically
2
3
Figure 7. The environment of molecules ZA1 (a) and ZA2 (b) in the crystal structure of
compound Zn(hfac)2(Rad2) (2) is shown as a representative example. Surrounding ZA1
and ZA2 molecules are highlighted by pink and yellow, respectively. The atoms of the
central molecule are colored according to the color scheme presented in the legend. (c)
The underlying net of molecular packing in 2. Orange and purple balls represent
centroids of two non-equivalent ZA1 and ZA2 molecules, respectively.
1–3
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ARTICLE
Journal Name
Furthermore, the role of intermolecular interactions in the
solid-state packing of Rad2 and complexes
probed in a quantitative fashion by means of Voronoi-Dirichlet spin and g = 2.00) and
polyhedral analysis using the Dirichlet routine within antiferromagnetic interactions between Zn(hfac)2(Rad2
ToposPro.21c The non-valence interactions governing the molecules (Figure 9). The onset of a significant downturn in
crystal packings in Rad2 and complexes are listed in Table MT upon cooling below 50 K is indicative of antiferromagnetic
1. For Rad2, despite the presence of only three fluorine atoms, interactions in . Given the mononuclear nature of the S = ½
numerous interatomic contacts of types F···H, F···F, and F···C Zn(II) benzotriazinyl complex ( ), this behavior is attributed to
are present. In total, they comprise 31.6% of the total surface through-space intermolecular interactions between radicals.
area of interatomic contacts. However, the contacts N···N, The structure of reveals each radical forms a single nearest
C···C and N···C, responsible for π-π stacking, are also strong neighbor π-π contact between radical ligands. However, initial
since they are responsible for intermolecular interactions attempts to model the magnetism of as a simple exchange
(Table 1) with large solid angles. In the case of complexes coupled dimer (Eqn. 2) failed to fit the data across the entire
The magnetism of Zn(hfac)2(Rad2) (
1–3 has been behaviour with C = 0.379 cm mol K (consistent with an S = ½
1
) revealed Curie-Weiss
View Article Online
DOI: 10.1039/C9DT01918A
3
-1
θ
= -6.4 K consistent with weak
)
1
–3
χ
1
1
1
1
1–3,
the fluorine atoms again produce the most numerous temperature range. Use of a Bleaney-Bowers model23 for each
interatomic contacts of types F···H, F···Fand F···C between of the two independent dimmers (Eqn. 3) provided an
molecules (Table 1). The N···N, C···C and N···C contacts improved fit to the data with g = 2.006 (fixed) and two
responsible for π-π stacking, appear to be less important in different J values; J1 = -2 K and J2 = -38 K.
these three structures.
Ĥ = -2J1Ŝ1Ŝ2– 2J2Ŝ3Ŝ4
Eqn. 3
Magnetic studies
The large variation in J between the two crystallographically
independent dimers reflects sensitivity in orbital overlap, a
phenomenon previously seen for π-stacked radicals.13a The
formation of supramolecular dimers with a singlet ground
state and thermally accessible triplet is also reflected in the
emergence of additional features in the EPR spectrum above
120 K, consistent with a thermally accessible spin triplet (vide
supra). It is clear from these studies that through-space
In Rad2, the room temperature value of
is consistent with an S = ½ radical with the decrease in
χ
MT ~ 0.363 cm3mol-1K
MT
upon cooling reflecting weak antiferromagnetic exchange
coupling between spins (Figure 8). A plot of 1/ vs T in the high
χ
χ
temperature region (T > 50 K) reflected Curie-Weiss behavior
with C = 0.379 cm3mol-1K (consistent with that expected for an
S = ½ radical of 0.375 cm3mol-1K) and
θ
= -9.4 K. The Weiss
constant is indicative of weak antiferromagnetic interactions
between spins. The structure of Rad2 comprises
exchange coupling through the presence of
π∗···π∗
a
interactions mediated by McConnell I mechanism8a between
paramagnetic ligands is likely at the origin of the observed
exchange coupling.
supramolecular dimer in which triazinyl rings are associated in
a face-to-face π-π interaction. Assuming this is the dominant
exchange pathway (z = 1) then application of the mean field
model (θ = 2zJS(S+1)/3k) affords J/k ~ -8 K. A subsequent single
parameter fit to the Bleaney-Bowers model23 for an S = ½
dimer (Eqn. 2) with fixed g value (2.006) afforded J/k = -13(1)
K.
Ĥ = -2JŜ1Ŝ2
Eqn. 2
The weak antiferromagnetic nature of the exchange coupling
in Rad2 contrasts with Rad1 which was reported to be
diamagnetic below 100 K.16a This can be attributed to the CF3
group which weakens the π···π stacking between the spin-
bearing triazinyl rings, leading to reduced orbital overlap and a
resultant decrease in exchange coupling.
Figure 9. Temperature dependence of χMT for two Zn(hfac)2(Rad2) (1) molecules.
The χMT value for the Ni(II) complex (2
) is 1.97 cm3mol-1K
at room temperature (Figure 10) which is slightly larger than
the calculated spin only value of one radical and one Ni(II) ion
(1.8 cm3mol-1K). Upon decreasing the temperature
χMT
increases up to 2.24 cm3mol-1K at 60K which suggests strong
ferromagnetic interaction between the radical and the metal
centre. Further cooling leads to a reduction in χMT of 1.24
cm3mol-1K at 2 K which could arise from zero field splitting
(ZFS) effects or intermolecular antiferromagnetic exchange to
neighbouring molecules. In addition, the field dependence of
magnetization was measured by varying dc field from 0 – 7 T at
Figure 8. Temperature dependence of χMT (a) and 1/χ (b) for Rad2. The dotted line
corresponds to the model for exchange-coupled radicals with J/k = -13 K.
6 | J. Name., 2012, 00, 1-3
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ARTICLE
2 K, 4 K, 6 K, 8 K, and 10 K (Figure S3, Supporting Information). reported a net ferromagnetic interaction in other semi-
View Article Online
At low field and temperature (2 K) the magnetization increases quinone radical complexes.30 Work by PDreOuI:s1s0.a10n3d9/HC9icDkTs01h9a1v8eA
slowly to a value of 2.9 µB at the highest applied field without respectively described a net ferromagnetic exchange coupling
saturation. For a well-isolated magnetic ground state, the M vs for both dithiadiazolyl and verdazyl radicals coordinated to
H/T curves at these different temperatures should be Co(II)31, reflecting the complexity of the situation.
superimposable. This is not the case for complex
the presence of low lying excited states. A fit of the complex
2
, reflecting The magnetic susceptibility of the cobalt benzotriazinyl radical
is 3.52 cm3 mol-1K at room temperature (Figure 11)
3
experimental susceptibility to an isotropic exchange increasing up to 3.74 cm3 mol-1K upon cooling to 70 K before
Hamiltonian (Eqn. 4) with the radical g-factor fixed at 2.006 decreasing again to 0.79 cm3 mol-1K at 2.0 K. The high
and taking into account a generic mean field term to model temperature behaviour is consistent with ferromagnetic
either ZFS or intermolecular exchange was performed within interactions between radical and Co(II) centers, while the
PHI.24
decrease at low temperature could be due to depopulation
effects within the ST = 2 ground spin state or intermolecular
Eqn. 4 exchange coupling. Additionally, the field dependence of the
magnetization plot (Figure S4, Supporting Information) shows
Ĥ = -2JŜNiŜRad2
This afforded J = +59.3(9) cm-1, gNi = 2.326(2) and a mean field the magnetization does not saturate even at low temperature
exchange term, zJ′ = -0.178(6) cm-1. The g value is not and a large applied field, again indicating the presence of low-
dissimilar to values for other octahedral Ni2+ ions (typical g lying excited states. To extract useful parameters for the
values in the vicinity of 2.25).25 The positive J value is magnetism of
3, we implemented a Hamiltonian (Eqn. 5) to
consistent with ferromagnetic exchange between radical and take into account intramolecular exchange (Ja) between the
Ni2+ ions based on the orbital orthogonality of the ligand π - radical and Co(II) and an additional intermolecular exchange
system and the metal eg set (Figure 10, inset).26 The small term (Jb) to take into account through-space radical-radical
value of zJ′ is consistent with small ZFS effects or weak exchange. Additional D and E parameters were included to
intermolecular exchange.
take into account zero field splitting effects for Co(II):
Ĥ = −2ꢀa�ꢁCo 1)ꢁ
+ ꢁ
)ꢁ
)� − 2ꢀb�ꢁrad 1)ꢁrad 2)� +
( ( (
(
(
)
(
rad 1
Co 2 rad 2
2
ꢂ
�
ꢁꢃ2ꢄ − 13 ꢁꢃ2
�
+ E i=1(ꢁꢅ2 − ꢁꢆ2 ) +
2
ꢃ=1
∑
∑
2
∑
ꢇꢈ. ꢉ. ( ꢃ=1 ꢁꢃ). ꢊCo
+
2
∑
ꢇꢈ. ꢉ. ( ꢃ=1 ꢁꢃ). ꢊrad
Eqn. 5
Given the large number of variables, we undertook a series of
computational studies to find an initial set of parameters from
which to undertake fitting of the experimental data. We
performed density functional theory (DFT) and ab initio
calculations followed by CASSCF+RASSI-SO+SINGLE_ANISO
method by MOLCAS 8.2 software package (Supporting
Information).32 The exchange coupling constant was calculated
using the method of Yamaguchi.33 The DFT calculations
afforded Ja (+72.7 cm-1) and Jb (-3.1 cm-1). In addition, the
CASSCF+RASSI-SO+SINGLE_ANISO calculations yielded g = 2.3
and D = +33.7 cm-1 and E = -4.5 cm-1 for the CoII ion. The
Figure 10. Temperature dependence of χMT for Ni(hfac)2(Rad2) (2) [Red line is the best
fit to the experimental data (circles) using the Hamiltonian described in the text]. Inset:
Mutually orthogonal nature of the Ni dz2 and dx2-y2 orbitals and the N π system.
simulated χmT vs T data for 3 using these computed values
The magnetism of high spin octahedral cobalt(II) complexes
is complex due to unquenched orbital angular momentum
associated with the 4T term, leading to significant anisotropy in
g-tensor and an Ising-like spin.27 For π-based radicals
coordinated to the t2g5eg2 Co(II) configuration the interaction of
the radical with the metal π-type (t2g) set is expected to be
clearly replicate well the salient features of the magnetic data
(blue). Subsequent curve-fitting of the both temperature
dependence of the experimental magnetic data and the M vs
H data within PHI, using these computed values as the starting
point for refinement gave refined values in good agreement
with computation. The best fit (red line) gives Ja = +71 cm-1, Jb
= -3.01 cm-1, D = +21 cm-1, E = -4.5 cm-1 and gCo= 2.3 while grad
was fixed at 2.0. The large and positive D and g > 2 values
obtained for Co(II) are comparable with data reported for
other octahedral Co(II) ions.34 Additional ac susceptibility data
antiferromagnetic whereas the metals’
σ-type (eg) electrons
are mutually orthogonal like Ni(II) and are anticipated to
propagate a ferromagnetic term. Typically the presence of a
non-zero overlap integral is predicted to generate a net
antiferromagnetic interaction between Co(II) and the radical
ligand.28 However, several studies have commented upon the
unexpectedly small antiferromagnetic exchange for Co(II)
semiquinone derivatives29 while Hendrickson and co-workers
were measured on complex
3 but no frequency dependence of
the ac response was observed in the out-of-phase signal in
either zero field or with an external applied field of 2000 Oe,
reflecting the absence of slow relaxation phenomena in 3.
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benzotriazinyl radicals.12d,f As the calculations are highly
View Article Online
DOI: 10.1039/C9DT01918A
sensitive on the choice of basis set and functional,
multiconfigurational approaches are required to accurately
reproduce the value of J.12f,36 However, multiconfigurational
approaches are extremely computationally demanding and
often qualtitative models have been used for
understanding.12f
a basic
Figure 11. Temperature dependence of χMT for Co(hfac)2(Rad2) (3). The blue line is the
computed temperature dependence, based on computed values, while the red line is
the best fit using optimized parameters (see text).
Figure 12. (a) SOMO of the Blatter radical Rad2; (b) side view of spin density
distribution of the radical pairs as calculated using UB3LYP/6-311+G (blue = α; green =
β)
Theoretical calculations
For the Zn(II) complex (1) the Weiss constant (θ = -6.4 K)
was consistent with weak antiferromagnetic exchange. From
the mean field approximation23 (Eqn. 7), the average nearest
neighbour exchange coupling can be estimated as J/k = -12.8
cm-1 (z = number of nearest-neighbour exchange interactions):
To gain insight into the magnetic exchange coupling between
radicals in Rad2 and between metal and radical in complexes
and we performed density functional theory (DFT)
1
2
,
calculations in combination with broken symmetry (BS)
approach to obtain information on both metal-radical (Ja) and
radical…radical (Jb) exchange couplings within the ORCA 4.0
software package.35 Calculations implemented the hybrid
functional B3LYP with TZVP basis set for Zn and Ni and 6-
311G* for other atoms. The tight SCF convergence criteria
were employed throughout the calculation. For the S = ½
θ = 2zJ S(S+1)/3k
Eqn. 7
, the
For each crystallographically independent molecule of
1
nearest neighbour
π···π interactions between coordinated
Rad2 ligands was identified and the exchange couplings for the
two pairs were computed. The calculated coupling constant J1
was -2.9 cm-1 (-4.1 K) for the pair of zinc(II) complex molecules
with a centroid···centroid distance of 3.718 Å whereas J2 was
found around -3.5 cm-1 (-5.1 K) with a centroid···centroid
distance of 3.605 Å. These computed exchange couplings are
in qualitative agreement with the experimental observation of
two different antiferromagnetic exchange couplings, albeit
under-estimating the strength of the interaction. An
examination of the spin density distribution within one of the
two crystallographically independent complexes reflects the
superposition of positive (α) spin density between triazinyl and
pyridyl rings (Figure 13).
radical Rad2 and the zinc complex
via the ··· interaction between nearest-neighbour
1, the exchange couplings
π
π
benzotriazinyl radicals (Figures 3 and 6b respectively) were
computed using the method of Yamaguchi33 where the
exchange coupling is determined from the energies (E) and
expectation values (<S2>) of the triplet and broken symmetry
singlet states:
−(ꢋꢌ−ꢋꢍꢎꢎ
<ꢏ2>ꢌ−<ꢏ2>ꢍꢎꢎ
)
J =
Eqn. 6
For the benzotriazinyl radical Rad2, there is substantial
positive ( ) spin density on the triazinyl ring and the
α
superposition of these areas of positive spin density (Figure
12b) on neighbouring molecules is expected to lead to an
antiferromagnetic through-space coupling based on the
McConnell I mechanism.8a These were confirmed by DFT
calculations based on single point calculations based on the
crystallographic coordinates for Rad2 which predict
a
substantial antiferromagnetic interaction (J = -89 cm-1 or J/k-
128 K) within the π-stacked dimer, consistent with that
predicted based on the simple orbital overlap model described
above. While the computed exchange coupling clearly reflects
the correct sign of J, it over-estimates the value of J in relation
to the experimental fit to the magnetic data (J/k = -13 K). It is
important to mention here that discrepancies between J
values
experimental magnetic susceptibility and
calculation is
derived
from fitting the
theoretical
Figure 13. Side view of spin density distribution in molecule pair in complex 1 (blue = α;
green = β)
a
persistent problem in the family of
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In the case of the Ni(II) complex
ARTICLE
, a ferromagnetic metal- Anal. Calcd (%): C, 55.31; H, 3.21; N, 9.92; S, 11.36. Found (%):
2
View Article Online
radical exchange coupling was computed (Ja = +116 cm-1) C, 55.45; H, 3.10; N, 10.02; S, 11.44. LR-LDCOMI:S1:0m.10/3z9/(C%9)D: T2081291.08A4
which was in qualitative agreement with the estimate of J from [M]+ (100%), 283 [M+H]+ (14%).
fitting of the experimental data (+59 cm-1). The radical···radical
exchange coupling constant was estimated by replacing Preparation
paramagnetic Ni(II) by diamagnetic Zn(II) and computing the (trifluoromethyl)phenyl)picolinohydrazonamide (B)
corresponding intermolecular exchange coupling between Compound was synthesized according to the literature
nearest-neighbour radicals. This was found to be very weakly procedure.18 Compound
(10 mmol) was dispersed in
antiferromagnetic (Jb = -3.1 cm-1 = -4.4 K), comparable with absolute ethanol (10 ml) and heated to boiling on an oil bath.
that computed for the isostructural zinc complex, , albeit a Subsequently phenyl hydrazine (10 mmol) was added
little larger than the mean field term extracted from modelling dropwise to the boiling solution with constant stirring.
of
N'-phenyl-N-(4-
B
A
1
of the magnetic data.
Evolution of hydrogen sulphide occurred. Reaction was
continued for 1 hour to obtain a clear orange liquid, which was
then cooled in an ice bath to afford a pale yellow solid. The
solid was separated by filtration and washed with cold ethanol
Conclusions
to obtain
B as yellow crystals. Yield 30 %. FT-IR (KBr pellet,
400−4000 cm−1): 3372 (s), 3205 (m), 3099 (w), 3052 (w), 3021
(w), 2943 (w), 2646 (w), 2570 (w), 2338 (w), 1984 (w), 1926
(w), 1884 (w), 1773 (w), 1708(w), 1602 (m), 1581(w), 1485 (m),
1432 (m), 1408 (w), 1324 (s), 1245 (s), 1162 (s), 1104 (s), 1063
(s), 996 (m), 885 (m), 826 (s), 784 (s), 744 (s), 694 (s), 659(w),
695 (w), 587 (s), 488(s). Elem. Anal. Calcd (%): C, 64.04; H,
4.24; N, 15.72. Found (%): C, 63.95; H, 4.29; N, 15.68. LR-LCMS:
m/z (%): 356.20 [M]+ (100%), 357.13 [M+H]+ (20%), 358.22
[M+2]+ (5%).
In summary, a new benzotriazinyl radical (Rad2) and three
neutral mononuclear metal complexes of general formula
M(hfac)2(Rad2) (where M = Zn(II) (1), Ni(II) (2) and Co(II) (3);
hfac−= hexafluoroacetylacetonate) have been prepared and
chacterized by single crystal X-ray diffraction. These three
complexes are isomorphous and the Zn(II) complex (1) allows
unambiguous determination of the radical…radical magnetic
exchange coupling (antiferromagnetic), whereas both the Ni(II)
and Co(II) complexes (2 and 3) afforded ferromagnetic metal-
radical exchange coupling. Further work is continuing to
pursue other paramagnetic metal complexes in which both
through-bond metal-ligand and through space ligand…ligand
exchange coupling may give rise to long range magnetic order.
Preparation of 1-phenyl-3-(pyridin-2-yl)-7-(trifluoromethyl)-
1,4-dihydrobenzo[e][1,2,4]triazine (Rad2)
A slightly modified version of the literature procedure was
employed.
B (435 mg, 1.22 mmol) was dissolved in
dichloromethane (20 ml) followed by addition of 1,8-
diazabicycloundec-7-ene (230 mg, 1.53 mmol) and 10% Pd/C
(20 mg). The reaction mixture was stirred at room
temperature until thin layer chromatography (1:4
hexane:dichloromethane) showed the absence of starting
material and the presence of a new fast-running dark
compound. The reaction contents were filtered through a
celite bed and solvents were evaporated under reduced
pressure and the residue purified by flash chromatography
Experimental section
Materials and methods
All chemicals and solvents were of reagent grade,
commercially available and used as received. Elemental Micro
vario Cube elemental analyzer was used for elemental analysis
of the complexes. FT-IR spectra (4000–400 cm–1) were
performed on KBr pellets with a Perkin Elmer Spectrum BX
spectrometer. The magnetic data of all compounds were
(dichloromethane) followed by recrystallization from
a
hexane:dichloromethane mixture at -30 oC to afford brown
needle-shaped crystals of Rad2. Yield: 220 mg (51 %), m.p.150
oC. FT-IR (KBr pellet, 400−4000 cm−1): 3061 (m), 2924 (w), 1743
(w), 1651 (m), 1590 (s), 1520 (m), 1486 (s), 1416 (s), 1366 (w),
1322 (s), 1276 (w), 1166 (s), 1102 (s), 1069(m), 1032 (w), 997
(w), 902 (m), 874 (m), 806 (w), 788 (w), 753 (m), 787 (s), 695
(m), 640 (m), 497 (w), 454 (w). Elem. Anal. Calcd (%): C, 64.59;
H, 3.42; N, 15.86. Found (%): C, 63.67; H, 3.47; N, 15.81. LR-
LCMS: m/z (%): 353.20 [M]+ (40%), 354.10 [M+H]+ (100%),
355.10 [M+2]+ (30%).
carried out using
a Quantum Design SQUID MPMS3
magnetometer in an applied static dc field of 1000 Oe in the
range 2–300 K. The experimental data were corrected for
diamagnetism based on Pascal’s constants as well as a
diamagnetic contribution for sample holder.
Preparation
of
N-(4-(trifluoromethyl)phenyl)pyridine-2-
carbothioamide (A)
The procedure utilized the literature procedure17 but using 4-
trifluoromethyl aniline used instead of 3,5-dichloroaniline. The
compound was purified by repeated recrystallization from
methanol. Yield 60 %. FT-IR (KBr pellet, 400−4000 cm−1): 3474
(w), 3162 (m), 3050 (w), 1908 (w), 1670 (w), 1618 (m), 1591
(m), 1536 (s), 1439 (s), 1364 (m), 1329 (m), 1282 (w), 1229 (w),
1190(m), 1150 (m), 1108 (m), 1067 (m), 1042 (w), 993 (w), 837
(s), 765 (s), 738 (w), 686 (w), 621 (m), 589 (m), 509 (m). Elem.
Preparation of M(hfac)2(Rad2) (M= Zn(II) (1), Ni(II) (2) and
Co(II) (3)
In a typical synthesis, a solution of benzotriazinyl radical Rad2
(5.30 mg, 0.015 mmol) in dichloromethane (10 mL) was slowly
added to an equimolar solution of Zn(hfac)2·2H2O (7.7 mg,
0.015 mmol) in dichloromethane (10 mL). An immediate color
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ARTICLE
Journal Name
change was observed from brown to purple and the reaction available from PLATON.41 Moreover, in the complexes
View Article Online
mixture was stirred at room temperature for 1 h. The M(hfac)2(Rad2) (1-3
) there are minor dDisOoIr:d10e.r10i3n9/Cso9DmTe019-C18FA3
corresponding complex was obtained as purple powder by groups which was treated using standard techniques.
evaporation and was recrystallized by slow diffusion of Complete lists of the applied restraints, the original diffraction
pentane into a chloroform solution to yield large crystals of file as well as the model itself are embedded in the deposited
Zn(hfac)2(Rad2).
CIF files. Crystallographic data and refinement details for Rad2
The preparation of
2
and
3
followed a similar procedure and complexes M(hfac)2(Rad2) have been summerized in Table
using M(hfac)2·xH2O, assuming x ~ 0 based on Karl-Fischer S1 (Supporting Information).
titration (x < 2%); quantities implemented: Co(hfac)2 (0.015
mmol, 7.1 mg) and Ni(hfac)2 (0.015 mmol, 7.1 mg).
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
Zn(hfac)2(Rad2) (
1). Purple crystals, Yield: 32%; FT-IR (KBr
pellet, 400−4000 cm−1): 1657 (s), 1649 (s), 1614 (w), 1599 (w),
1570 (m), 1560 (m), 1529 (m), 1485 (s), 1429 (w), 1417 (w), S.K. acknowledges SERB(CRG/2018/000072), Government of
1392 (w), 1342 (w), 1324 (w), 1284 (w), 1261 (s), 1209 (s), India and IISER Bhopal for generous financial support. J.M.R.
1147 (s), 1094 (w), 1074 (w), 1051 (w), 1022 (w), 999 (w), 950 would like to thank NSERC for financial support. R.N. and S.R.
(w), 908 (w), 894 (w), 842 (w), 796 (m), 760 (m), 751 (m), 742 are grateful to SERB, Government of India (file numbers
(w), 736 (w), 691 (w), 668 (m), 651 (w), 636 (w), 622 (w), 585 PDF/2015/0001032 and PDF/2017/001188, respectively) for
(m), 526 (w), 508 (w). Elem. Anal. Calcd (%) for National Postdoctoral fellowships. T.S.S thanks to DST-INSPIRE,
C29H14F15N4O4Zn: C, 41.82; H, 1.69; N, 6.73. Found (%): C, India for fellowship. A.M. is thankful to IISER Bhopal for PhD
41.78; H, 1.73; N, 6.79.
fellowship. We also acknowledge high performance computing
(HPC) facility of IISER Bhopal being utilized for computational
Ni(hfac)2(Rad2) (2). Purple crystals, Yield: 28%; FT-IR (KBr pellet, work.
400−4000 cm−1): 1651 (s), 1641 (s), 1601 (w), 1593 (w), 1568 (m),
1554 (m), 1525 (m), 1489(s), 1427 (w), 1417 (w), 1395 (w) 1344 (w),
References
1319 (w), 1286 (w), 1254 (s), 1214 (s), 1153 (s), 1099 (w), 1077 (w),
1042 (w), 1030 (w), 990 (w), 943 (w), 911 (w), 896 (w), 846 (w), 799
(m), 763 (m), 752 (m), 745 (w), 737 (w), 687(w), 669 (m), 651 (w),
636 (w), 626 (w), 589 (m), 528 (w), 510 (w). Anal. Calcd (%) for
C29H14F15N4O4Ni: C, 42.16; H, 1.71; N, 6.78. Found (%): C, 42.12; H,
1.68; N, 6.82.
1
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1553 (m), 1528 (w), 1505 (m), 1487 (s), 1455 (m), 1491 (s),
1362 (m), 1339 (w), 1321(w) 1286 (m), 1258 (s), 1206 (s), 1158
(m), 1146 (s), 1102 (w), 1074 (w), 1059 (w), 1025(w), 998 (w),
947 (w), 909 (w), 895 (w), 842 (w), 799 (m), 763 (w), 750 (m),
737 (w), 686 (w), 664 (m), 653 (w), 638 (w), 624 (w), 586 (m),
530 (w), 510 (w). Anal. Calcd (%) for C29H14F15N4O4Co: C, 42.15;
H, 1.71; N, 6.78. Found (%): C, 42.10; H, 1.77; N, 6.76.
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X-ray crystallography
Intensity data were collected on a Bruker APEX-II CCD
diffractometer using
a graphite monochromated Mo-Kα
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ARTICLE
Journal Name
View Article Online
DOI: 10.1039/C9DT01918A
A
new
benzotriazinyl
radical,
1-phenyl-3-(pyridin-2-yl)-7-
(trifluoromethyl)-1,4-dihydrobenzo[e][1,2,4]triazine (Rad2) and three
isomorphous metal complexes of general formula M(hfac)2(Rad2)
(where M= Zn(II) (1), Ni(II) (2) and Co(II) (3); hfac−
=
hexafluoroacetylacetonate) have been isolated as stable crystalline
solids and fully characterized, including by single crystal X-ray
diffraction. The Zn(II) complex allows unambiguous determination of
the radical…radical magnetic exchange coupling (antiferromagnetic),
whereas both the Ni(II) and Co(II) complexes afforded ferromagnetic
metal-radical exchange coupling.
12 | J. Name., 2012, 00, 1-3
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