Trinuclear Mn(ii) complex with paramagnetic bridging 1,2,3-dithiazolyl ligands

Article abstract of DOI:10.1039/c2cc35869g

The first metal coordination complex of a radical ligand based on the 1,2,3-dithiazolyl heterocycle is reported. 6,7-Dimethyl-1,4-dioxo-naphtho[2,3-d] [1,2,3]dithiazolyl acts as a bridging ligand in the volatile trinuclear Mn(hfac)₂-Rad-Mn(hfac)₂-Rad-Mn(hfac)₂ complex (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The Mn(ii) and radical ligand spins are coupled anti-ferromagnetically (AF) resulting in an S_T = 13/2 spin ground state.

Full text of DOI:10.1039/c2cc35869g

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2012, 48, 10963–10965
www.rsc.org/chemcomm
COMMUNICATION
Trinuclear Mn(II) complex with paramagnetic bridging 1,2,3-dithiazolyl
ligandsw
a
rac,bc Michael Jennings, Alan J. Lough and
d
e
David J. Sullivan, Rodolphe Cle
´
a
Kathryn E. Preuss*
Received 13th August 2012, Accepted 12th September 2012
DOI: 10.1039/c2cc35869g
1
3
The first metal coordination complex of a radical ligand based
on the 1,2,3-dithiazolyl heterocycle is reported. 6,7-Dimethyl-
that was observed in solution EPR by Mayer in 1981.
The latter is a structural isomer of the 1,3,2-dithiazolyl-p-
1
,4-dioxo-naphtho[2,3-d][1,2,3]dithiazolyl acts as a bridging ligand in
naphthoquinone recently detected in solution EPR by Pass-
1
4
the volatile trinuclear Mn(hfac) -Rad–Mn(hfac) -Rad–Mn(hfac)
2
2
2
more. We have incorporated methyl groups in the frame-
work of ligand 1 in order to increase the sigma donor ability of
the radical and ensure its function as a ligand. This alteration
also promotes the solubility of the ligand in organic media,
facilitating coordination syntheses.
complex (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The
Mn(II) and radical ligand spins are coupled anti-ferromagnetically
(
T
AF) resulting in an S = 13/2 spin ground state.
Ligand 1 is prepared by treating 2-amino-3-bromo-6,7-
dimethyl-1,4-naphthoquinone with excess S Cl followed by
The ability to manipulate magnetic coupling between paramagnetic
species is the key to creating new materials with desirable magnetic
2
2
1
properties. One possible method is the use of organic paramagnets
reduction of the resulting dithiazolium chloride.w Purple crystals
of 1 are grown by sublimation on a preparative scale.
2
,3
as ligands: the so-called ‘‘metal–radical approach’’. An unpaired
electron on a ligand can couple strongly to unpaired electrons on a
coordinated metal ion, particularly if there is significant spin
density at the donor atom(s). If the ligand bridges multiple metal
ions, a high-spin ground state can be achieved. New paramagnetic
ligands continue to be reported, however these are often modifica-
tions of a few organic radical architectures, such as phenoxyls and
As illustrated in Fig. 2, 1 is dimerized in the solid state.
While this is expected for thiazyl radicals that have not been
1
explicitly designed to do otherwise, the dimerization motif is
5
entirely new, characterized by short intermolecular Sꢀ ꢀ ꢀO
˚
contacts (3.111(3) A). This can be rationalized by invoking
the O-radical resonance contributor. Computational analysisw
of radical 1 predicts a delocalized p* SOMO (singly occupied
molecular orbital) with a significant coefficient at atom O2
(Mulliken spin density ca. 13%; compare ca. 25% at N1). The
O-radical resonance contributor also influences the crystallo-
4
5
6
semiquinones, nitroxides and nitronylnitroxides, verdazyls, and
7
triphenylmethyls. Thiazyls and selenazyls have lately been added
8
to this list with the use of 1,3,2-dithiazolyls and 1,2,3,5-dithia-
9
–11
12
(and selenium analogues of the latter) as radical
diazolyls
2
graphic C–O bond lengths: C2–O1 (1.220(3) A
CQO double bond in a benzoquinone, whereas C9–O2
˚
) is typical for a
ligand building blocks. As Veciana recently articulated, the
advancement of ‘‘spin science’’ requires structural diversity,
and therefore it is important that new paramagnetic ligand
designs be pursued and developed. To this end, we are
reporting the first radical ligand based on the 1,2,3-dithiazolyl
heterocycle and the first trinuclear metal complex of a thiazyl
radical ligand, illustrated in Fig. 1.
˚
(
1.234(3) A) is long for this type of bond.z
The dc susceptibility measurements indicate that dimers of 1
are diamagnetic over a temperature range of 1.8 to 300 K. No
evidence for a thermally populated triplet excited state is
1
6
observed by solid state X-band EPR (150 to 300 K). The
solution EPR spectrum of 1 (CH Cl ) is a three-line pattern
hyperfine coupling to one N nucleus) with small shoulders
6
,7-Dimethyl-1,4-dioxo-naphtho[2,3-d][1,2,3]dithiazolyl 1 is
2
2
1
4
(
a derivative of the 1,2,3-dithiazolyl-p-naphthoquinone radical
1
from hyperfine coupling to two H nuclei on the naphthalene
backbone. This spectrum is adequately simulated using: aN
.46; aH = 0.32; aH = 0.53 G; g = 2.0095.w
Coordination complex 2 was prepared by treating radical 1
=
a
Department of Chemistry, University of Guelph, Guelph,
4
0
ON N1G 2W1, Canada. E-mail: kpreuss@uoguelph.ca;
Fax: (+1) 519-766-1499; Tel: (+1) 519-824-4120
CNRS, CRPP, UPR 8641, F-33600 Pessac, France
Univ. Bordeaux, CRPP, UPR 8641, F-33600 Pessac, France
185 Chelsea Avenue, London, ON N6J 3J5, Canada
b
11
with Mn(hfac) (THF)
2
2
.
Crystalline material suitable for bulk
c
analysis was grown by sublimation. The structure of 2 is shown in
Fig. 3. Atom Mn2 is located at an inversion center, thus the two
halves of the molecule are symmetry-related. The coordination
geometry about Mn2 is roughly octahedral with the two radical
ligands occupying axial positions via monodentate O-coordina-
tion. Like many monodentate O-coordinated Mn(II) complexes of
d
e
Department of Chemistry, University of Toronto, Toronto,
ON M5S 3H6, Canada
w Electronic supplementary information (ESI) available: Syntheses,
crystallography, magnetic measurements, X-band EPR, computa-
tional details, cyclic voltammetry, CIFs for
96030–896032. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2cc35869g
1 and 2. CCDC
8
1
7
nitronylnitroxides, the Mn–O bond is not in the ligand
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 10963–10965 10963

View Article Online
Fig. 1 Top: line drawing of 1 illustrating two possible resonance
contributors. Middle: singly occupied molecular orbital (SOMO) and
spin density distribution calculatedw for 1. Bottom: line drawing of 2.
Fig. 3 Single crystal X-ray structure of 2. ORTEP thermal ellipsoids
drawn at 50% probability. F atoms omitted for clarity. Top: complete
molecule; symmetry code: (ii) ꢁx, 1 ꢁ y, ꢁz. Bottom: crystal packing
between two molecules with the intermolecular Sꢀ ꢀ ꢀS contact high-
lighted by a green dashed line and the Sꢀ ꢀ ꢀO contacts by red dashed
lines; H atoms omitted for clarity.
Fig. 2 Single crystal X-ray structure of 1. Green dashed lines denote
close Sꢀ ꢀ ꢀO contacts that define the dimer. ORTEP thermal ellipsoids
drawn at 50% probability. Symmetry code: (i) 1 ꢁ x, 1 ꢁ y, ꢁz.
plane (C9–O2–Mn2, 139.0(2)1; C10–C9–O2–Mn2, 59.7(5)1).
Bidentate chelation of Mn1 places this metal ion approxi-
mately in the ligand plane.
Fig. 4 Temperature dependence of the wT product for 2 at 1000 Oe
The magnetic properties of 2 were investigated between
(
with w defined as molar magnetic susceptibility equal to M/H per
2
2
80 and 1.8 K with an applied field of 1000 Oe (Fig. 4). At
3
mole of complex 2). Black circles indicate measured data and the red
line represents best simulation obtained with the model described in
the text. Inset: M vs. H data below 8 K.
ꢁ1
80 K, the wT product is 13.1 cm Kmol . Upon cooling, the
3
ꢁ1
wT product gradually decreases to 12.4 cm Kmol at 110 K,
3
ꢁ1
then increases to a maximum of 15.5 cm Kmol at 14 K.
This thermal behaviour is consistent with significant antiferro-
magnetic (AF) coupling between the ligand and metal ion spins
leading to a ferrimagnetic arrangement of the magnetic sites.
Upon further cooling, the wT product decreases sharply to a
minimum of 4.7 cm Kmol at 1.8 K, indicating additional
3
ꢁ1
AF intermolecular interactions. From the structure of 2,
1
0964 Chem. Commun., 2012, 48, 10963–10965
This journal is c The Royal Society of Chemistry 2012

View Article Online
the magnetic data were simulated numerically using MAGPACK
and L. Ouahab, Chem. Commun., 2012, 48, 714; A. J. Tasiopoulos
and S. P. Perlepes, Dalton Trans., 2008, 5537.
18
software with the following isotropic Heisenberg Hamiltonian:
2
3
I. Ratera and J. Veciana, Chem. Soc. Rev., 2012, 41, 303.
A. Caneschi, D. Gatteschi, R. Sessoli and P. Rey, Acc. Chem. Res.,
1989, 22, 392; K. E. Vostrikova, Coord. Chem. Rev., 2008,
252, 1409; C. Train, L. Norel and M. Baumgarten, Coord. Chem.
Rev., 2009, 253, 2342; M. T. Lemaire, Pure Appl. Chem., 2004,
H = ꢁ2JMn1-Rad[SMn1 ꢂ S
+ SMn1(ii) ꢂ S
] ꢁ
rad
rad(ii)
2
J
[SMn2(S
+ S
rad rad(ii)
)], where JMn1-Rad and J
Mn2-Rad
Mn2-Rad
represent the exchange interactions between ligand 1 (S = 1/2)
and Mn1 and Mn2 (S = 5/2) spins respectively, and S is the spin
i
7
6, 277; M. T. Lemaire, Pure Appl. Chem., 2011, 83, 141.
operator of each magnetic site. Introducing inter-complex interac-
tions in the above model in the frame of the mean-field approxi-
4
A. Dei, D. Gatteschi, C. Sangregorio and L. Sorace, Acc. Chem.
Res., 2004, 37, 827; D. A. Shultz, Magn.: Mol. Mater. II, 2001, 281;
D. N. Hendrickson and C. G. Pierpont, Top. Curr. Chem., 2004,
0
mation (zJ ),y an adequate simulation of the experimental data was
2
2
34, 63; P. Chaudhuri and K. Wieghardt, Prog. Inorg. Chem.,
001, 50, 151.
obtained with JMn1-Rad/k
B
= ꢁ35(1) K, JMn2-rad/k
B
= ꢁ13(1) K,
0
zJ /k
B
= ꢁ0.17(2) K, and giso = 2.05(2), suggesting an S
T
= 13/2
5
6
D. Luneau and P. Rey, Coord. Chem. Rev., 2005, 249, 2591;
S. Kaizaki, Coord. Chem. Rev., 2006, 250, 1804.
B. D. Koivisto and R. G. Hicks, Coord. Chem. Rev., 2005,
spin ground state for complex 2. This ground state is confirmed by
M vs. H data (inset Fig. 4) and the high field magnetization at
2
49, 2612; P. K. Poddutoori, M. Pilkington, A. Alberola,
1.8 K that saturates at 13.4mB.
V. Polo, J. E. Warren and A. van der Est, Inorg. Chem., 2010,
49, 3516; M. Chahma, K. Macnamara, A. van der Est,
A. Alberola, V. Polo and M. Pilkington, New J. Chem., 2007,
31, 1973; S. D. J. McKinnon, B. O. Patrick, A. B. P. Lever and
R. G. Hicks, Chem. Commun., 2010, 46, 773.
Magnetic coupling between radical ligand and terminal Mn1
atom spins is larger than that between the radical and central
Mn2 atom spins. This is likely a result of the larger spin density
at N1 than at O2, and possibly also aided by the in-plane,
bidentate coordination motif at Mn1. Short intermolecular
7
N. Roques, N. Domingo, D. Maspoch, K. Wurst, C. Rovira,
J. Tejada, D. Ruiz-Molina and J. Veciana, Inorg. Chem., 2010,
4
9, 3482; D. Maspoch, N. Domingo, D. Ruiz-Molina, K. Wurst,
Sꢀ ꢀ ꢀO contacts like those apparent in complex 2 (2.915 and
J. M. Hernandez, F. Lloret, J. Tejada, C. Rovira and J. Veciana,
Inorg. Chem., 2007, 46, 1627; N. Roques, V. Mugnaini and
J. Veciana, Top. Curr. Chem., 2010, 293, 207.
8 W. Fujita and K. Awaga, J. Am. Chem. Soc., 2001, 123, 3601;
Y. Miyoshi, K. Takahashi, T. Fujimoto, H. Yoshikawa, M. M.
Matsushita, Y. Ouchi, M. Kepenekian, V. Robert, M. P.
Donzello, C. Ercolani and K. Awaga, Inorg. Chem., 2012, 51, 456.
9 E. M. Fatila, J. Goodreid, R. Cle
K. E. Preuss, Chem. Commun., 2010, 46, 6569.
0 N. G. R. Hearns, R. Clerac, M. Jennings and K. E. Preuss, Dalton
Trans., 2009, 3193; N. G. R. Hearns, E. M. Fatila, R. Clerac,
M. Jennings and K. E. Preuss, Inorg. Chem., 2008, 47, 10330; N. G. R.
Hearns, K. D. Hesp, M. Jennings, J. L. Korcok, K. E. Preuss and
˚
.188 A; Fig. 3) have previously been shown to mediate AF
3
coupling between a radical ligand and a neighbouring Mn(II)
ion, thereby giving rise to a high spin ground state for a pair of
9
complexes. For 2, however, the dominant intermolecular
˚
magnetic contacts appear to be the Sꢀ ꢀ ꢀS contacts (3.388 A;
Fig. 3). Non-orthogonal overlap between neighbouring radical
ligand SOMOs provides a mechanism for the AF couplings
observed between the trinuclear complexes in the solid state.
Paramagnetic ligand 6,7-dimethyl-1,4-dioxo-naphtho[2,3-d]-
´
rac, M. Jennings, J. Assoud and
1
´
´
[
1,2,3]dithiazolyl, 1, is shown to be capable of coordinating a
ˇ
C. S. Smithson, Polyhedron, 2007, 26, 2047; J. Britten, N. G. R.
Hearns, K. E. Preuss, J. F. Richardson and S. Bin-Salamon, Inorg.
Chem., 2007, 46, 3934; N. G. R. Hearns, K. E. Preuss, J. F. Richardson
and S. Bin-Salamon, J. Am. Chem. Soc., 2004, 126, 9942.
metal ion in a monodentate fashion at atom O2 and in a
bidentate chelating fashion at atoms N1 and O1. Owing to the
significant spin density at both N1 and O2, strong antiferro-
magnetic coupling is observed between the ligand and the
metal ions in both positions. The trinuclear coordination
complex 2 is the first example of metal ion coordination to a
11 M. Jennings, K. E. Preuss and J. Wu, Chem. Commun., 2006, 341.
2 J. Wu, D. J. MacDonald, R. Clerac, R. Jeon Ie, M. Jennings,
A. J. Lough, J. Britten, C. Robertson, P. A. Dube and
1
´
K. E. Preuss, Inorg. Chem., 2012, 51, 3827.
13 R. Mayer, G. Domschke, S. Bleisch and A. Bartl, Z. Chem., 1981,
1, 324.
1
,2,3-dithiadiazolyl radical and it is a very rare example of a
2
linear ‘‘oligomeric’’ radical ligand coordination complex
with more than two metal ions. This complex is robust and
volatile, such that sublimation produces pure crystalline
material on a preparative scale. The spin ground state of the
1
4 A. Decken, A. Mailman, S. M. Mattar and J. Passmore, Chem.
Commun., 2005, 2366.
15 A. Alberola, R. J. Less, C. M. Pask, J. M. Rawson, F. Palacio,
P. Oliete, C. Paulsen, A. Yamaguchi, R. D. Farley and D. M. Murphy,
Angew. Chem., Int. Ed., 2003, 42, 4782; A. Alberola, C. S. Clarke,
D. A. Haynes, S. I. Pascu and J. M. Rawson, Chem. Commun., 2005,
T
complex 2 is S = 13/2, the highest to date for any thiazyl–
metal system.
4
726; S. M. Winter, K. Cvrkalj, P. A. Dube, C. M. Robertson,
M. R. Probert, J. A. Howard and R. T. Oakley, Chem. Commun.,
009, 7306; X. Yu, A. Mailman, P. A. Dube, A. Assoud and
Funding provided to K.E.P. by NSERC (DG), CFI (LOF),
OIT, the CRC program, and the University of Guelph. R.C.
2
R. T. Oakley, Chem. Commun., 2011, 47, 4655.
thanks the University of Bordeaux, the Region Aquitaine and
´
1
6 K. V. Shuvaev, A. Decken, F. Grein, T. S. Abedin, L. K. Thompson
and J. Passmore, Dalton Trans., 2008, 4029; A. Alberola, E. Carter,
C. P. Constantinides, D. J. Eisler, D. M. Murphy and J. M. Rawson,
Chem. Commun., 2011, 47, 2532.
the CNRS for financial support.
Notes and references
1
7 A. Caneschi, D. Gatteschi, P. Rey and R. Sessoli, Inorg. Chem.,
988, 27, 1756; A. Caneschi, D. Gatteschi, J. Laugier, P. Rey,
z For 86 measured benzoquinone species, the unweighted mean CQO
1
˚
˚
bond length is 1.222 A, the median is 1.220 A with a standard
R. Sessoli and C. Zanchini, J. Am. Chem. Soc., 1988, 110, 2795;
A. Caneschi, D. Gatteschi, J. Laugier, L. Pardi, P. Rey and
C. Zanchini, Inorg. Chem., 1988, 27, 2027.
19
˚
deviation of 0.013 A, and the upper quartile is 1.231 A.
˚
y In order to take into account the inter-complex interaction, the
following definition of the susceptibility has been used:
20
1
1
8 J. J. Borra
´
s-Almenar, J. M. Clemente-Juan, E. Coronado and
s-Almenar,
B. S. Tsukerblat, Inorg. Chem., 1999, 38, 6081; J. J. Borra
´
w
Mn3Rad2
w ¼
J. M. Clemente-Juan, E. Coronado and B. S. Tsukerblat, Comput.
Chem., 2001, 22, 985.
9 CRC Handbook of Chemistry and Physics, ed. D. R. Lide, CRC
Press, Inc., Boca Raton, 1991, 72 edn.
20 C. J. O’Connor, Prog. Inorg. Chem., 1982, 29, 203; B. E. Myers,
L. Berger and S. Friedberg, J. Appl. Phys., 1969, 40, 1149.
0
2
zJ
1
ꢁ
2
2
wMn3Rad2
Ng mB
.
1
G. Aromı, D. Aguila, P. Gamez, F. Luis and O. Roubeau, Chem.
´ `
Soc. Rev., 2012, 41, 537; F. Pointillart, S. Klementieva,
V. Kuropatov, Y. Le Gal, S. Golhen, O. Cador, V. Cherkasov
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 10963–10965 10965