Synthesis, structures and magnetic properties of copper (II) and cobalt (II) complexes containing pyridyl-substituted nitronyl nitroxide and 3,5-dinitrobenzoate

Article abstract of DOI:10.1016/j.poly.2009.12.039

Four new metal-radical complexes - [Cu(NIT3Py)₂(DTB)₂] 1, [Co(NIT3Py)₂(DTB)₂(CH₃OH)₂] 2, [Cu(NIT4Py)₂(DTB)₂(H₂O)₂] 3, [Co(NIT4Py)₂(DTB)₂(H₂O)₂] 4, (NIT3Py = 2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], NIT4Py = 2-(4^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], DTB = 3,5-dinitrobenzoic anion) have been synthesized by using transition metal ions, nitronyl nitroxide radicals as spin carriers, and incorporating 3,5-dinitrobenzoic acid (DTB) as a coligand. The structures of 1-4 were determined by X-ray single-crystal analyses. Complex 1 has a square planar geometry, where the Cu(II) ion is located in the central site of the rectangle and two radicals and two DTBA ligands are trans-coordinated to the Cu(II) ion. The other three complexes (2-4) have similar structures, in which two radicals, two DTBA ligands and two solvent molecules act as terminal ligands to form six coordinate distorted octahedrons. The magnetic behaviors of these compounds indicate that antiferromagnetic exchanges exist between the radical ligands and the metal ions, and their magnetic properties are explained by their structures and a magnetic exchange mechanism.

Full text of DOI:10.1016/j.poly.2009.12.039

Polyhedron 29 (2010) 1387–1392
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structures and magnetic properties of copper (II)
and cobalt (II) complexes containing pyridyl-substituted nitronyl nitroxide
and 3,5-dinitrobenzoate
b
c
Chen-Xi Zhang a, , Yu-Ying Zhang , Ya-Qiu Sun
*
a College of Science, Tianjin University of Science and Technology, Tianjin 300457, People’s Republic of China
b Department of Chemistry, NanKai University, Tianjin 300071, People’s Republic of China
c Department of Chemistry, Tianjin Normal University, Tianjin 300387, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new metal-radical complexes - [Cu(NIT3Py)2(DTB)2] 1, [Co(NIT3Py)2(DTB)2(CH3OH)2] 2, [Cu(NIT4-
Py)2(DTB)2(H2O)2] 3, [Co(NIT4Py)2(DTB)2(H2O)2] 4, (NIT3Py = 2-(30-pyridyl)-4,4,5,5-tetramethylimidazo-
line-1-oxyl-3-oxide], NIT4Py = 2-(40-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], DTB = 3,
5-dinitrobenzoic anion) have been synthesized by using transition metal ions, nitronyl nitroxide radicals
as spin carriers, and incorporating 3,5-dinitrobenzoic acid (DTB) as a coligand.
The structures of 1–4 were determined by X-ray single-crystal analyses. Complex 1 has a square planar
geometry, where the Cu(II) ion is located in the central site of the rectangle and two radicals and two
DTBA ligands are trans-coordinated to the Cu(II) ion. The other three complexes (2-4) have similar struc-
tures, in which two radicals, two DTBA ligands and two solvent molecules act as terminal ligands to form
six coordinate distorted octahedrons. The magnetic behaviors of these compounds indicate that antifer-
romagnetic exchanges exist between the radical ligands and the metal ions, and their magnetic proper-
ties are explained by their structures and a magnetic exchange mechanism.
Received 12 October 2009
Accepted 30 December 2009
Available online 28 January 2010
Keywords:
Crystal structure
Nitronyl nitroxide metal complexes
Copper(II)/3,5-dinitrobenzoate complexes
Cobalt(II)/3,5-dinitrobenzoate complexes
Magnetism
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
In the different geometric structures of Cu(II)-nitronyl nitroxide
heterospin systems, the overlap between the Cu(II) magnetic
*
orbital and the magnetic orbital of the radical is favored or for-
p
In the field of molecular-based magnetic materials, much atten-
tion has been paid to the coordination of paramagnetic metal ions
with nitronyl nitroxide radicals in terms of the ‘‘metal-organic”
strategy [1,2]. By employment of this strategy, a large number of
metal-radical complexes with various structures have been syn-
thesized and magnetically characterized. Some of these complexes
exhibit single molecule magnet (SMM) behavior [3] or single chain
magnet (SCM) behavior [4].
However, the disadvantage of nitronyl nitroxides is that they
are weak Lewis bases; they prefer to coordinate to acidic metal
centers, such as hexafluoroacetylacetonato- or trifluoroacetato-
metal complexes as starting materials. This has led to the develop-
ment of functionalized nitronyl nitroxide radicals in which a strong
coligand is incorporated. This way has proved to be particularly
productive, allowing the coordination of most metal ions without
the requirement of electron-withdrawing ancillary ligands. Among
them, nitroxides substituted with pyridine groups have the advan-
tage of forming stable chelate complexes with the support of the
auxiliary substitute groups [5–8].
bidden, thus quite different magnetic behaviors (ferromagnetic
and antiferromagnetic interactions) are expected [7,9]. Co(II)-nitro-
nyl nitroxide compounds have been investigated rarely due to a
large spin-orbital coupling, although the Co(II) ion is a very effective
spin carrier [4,12]. Fundamental magneto-structural correlation
studies of Cu(II) and Co(II) nitronyl nitroxides are necessary
[9–14], especially for investigating how the structural factors affect
the metal-radical interactions. Such investigations are necessary
not only for understanding the magnetic exchange mechanism be-
tween the metal and organic radical but also for guiding the design
of new organic radical ligands for the development of novel molec-
ular magnetic materials. On the other hand, 3,5-dinitrobenzoic acid
(DTB), containing a carboxylic group, can coordinate to metal ions
with a great flexibility in the chemical design of molecular assem-
blies [15–18].
Along this line, taking advantage of the abilities of both
nitroxide radicals and DTB (the 3,5-dinitrobenzoic anion) to
coordinate to transition metals, we have synthesized four metal-
radical complexes: [Cu(NIT3Py)2(DTB)2] 1, [Co(NIT3Py)2(DTB)2-
(CH3OH)2] 2, [Cu(NIT4Py)2(DTB)2(H2O)2]
(DTB)2(H2O)2] 4.
3 and [Co(NIT4Py)2-
* Corresponding author. Tel.: +86 22 23500383; fax: +86 22 23502082.
E-mail addresses: zcx@tust.edu.cn, zcx@mail.nankai.edu.cn (C.-X. Zhang).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.12.039

1388
C.-X. Zhang et al. / Polyhedron 29 (2010) 1387–1392
Table 1
Crystallographic and refinement data for complexes 1, 2, 3 and 4.
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C38H38CuN10O16
954.32
C40H46CoN10O18
1013.80
C38H42CuN10O18
990.36
C38H42CoN10O18
985.75
triclinic
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
7.129(11)
8.7646(16)
10.962(2)
12.626(2)
10.123(3)
10.198(3)
10.810(3)
78.517(4)
10.110(4)
10.290(3)
10.656(4)
79.004(5)
b (Å)
c (Å)
11.892(19)
12.567(16)
87.85(3)
a
(°)
75.387(4)
b (°)
75.644(15)
88.98(4)
1031(3)
75.736(4)
75.486(4)
1114.4(4)
85.848(5)
85.374(4)
1088.2(5)
87.806(5)
85.999(6)
1085.1(6)
c
(°)
V (Å3)
Z
1
1
1
1
Calculated density (g cm3)
Absorption coefficient (mmꢀ1)
Crystal size (mm)
h Range for data collection (°)
Reflections collected
Independent reflection
1.536
0.616
0.32 ꢃ 0.26 ꢃ 0.22
1.77–25.00
2441
1.511
0.474
1.511
0.590
1.508
0.484
0.20 ꢃ 0.16 ꢃ 0.14
1.96–26.41
6445
4502 [R(int) = 0.0147]
R1 = 0.0514, wR2 = 0.1449
0.18 ꢃ 0.14 ꢃ 0.12
2.02–26.45
6388
4436 [R(int) = 0.0325]
R1 = 0.0517, wR2 = 0.0921
0.35 ꢃ 0.25 ꢃ 0.20
2.02–26.42
6324
4406 [R(int) = 0.0166]
R1 = 0.0360, wR2 = 0.0819
2433 [R(int) = 0.1088]
Final R indices [I > 2r(I)]
R1a = 0.0803, wR2b = 0.1831
a
R1
wR2
=
R
=
||Fo|ꢀ|Fc||/
R|Fo|.
b
2
R
{[w(Fo ꢀFc2)2]/
R
[wFo2]2}1/2
.
Herein the synthesis, X-ray structures and magnetic properties
of these complexes are reported.
Table 2
Selected bond lengths (Å) and angles (°) for complexes 1–4.
Complex 1
Complex 2
Cu(1)–O(3)
Cu(1)–N(1)
N(2)–O(1)
O(2)–N(3)
O(3)–Cu(1)–N(1)
C(13)–O(3)–Cu(1)
C(1)–N(1)–Cu(1)
1.974(6)
2.001(7)
1.265(9)
1.31(1)
90.5(2)
105.2(5)
123.7(6)
Co(1)–O(3)
Co(1)–N(1)
Co(1)–O(9)
N(2)–O(1)
O(3)–Co(1)–N(1)
O(3)–Co(1)–O(9)
N(1)–Co(1)–O(9)
1.963(2)
2.024(2)
2.404(4)
1.268(3)
91.14(9)
83.4(1)
2. Experimental
2.1. General
All reagents were purchased from commercial sources and
were used as received. Elemental analyses for carbon, hydrogen
and nitrogen were carried out on a Model 240 Perkin-Elmer
elemental analyzer. The infrared spectra were recorded on a
Shimadzu IR spectrophotometer model 408 in the 4000–
600 cmꢀ1 region, using KBr pellets. The UV–Vis spectra were
91.9(1)
Complex 3
Cu(1)–O(3)
Cu(1)–N(1)
Cu(1)–O(9)
Complex 4
Co(1)–O(3)
Co(1)–N(1)
Co(1)–O(9)
1.995 (2)
2.020(2)
2.317(2)
1.277(3)
92.53(8)
89.46(8)
92.59(9)
2.079(1)
2.146(2)
2.095(2)
1.285(2)
92.27(6)
89.69(5)
85.90(6)
N(2)–O(1)
N(2)–O(1)
recorded on
800 nm regions. Temperature dependent magnetic susceptibili-
ties were measured on MPMS-7 SQUID magnetometer.
a UV-2101 PC spectrophotometer in the 190–
O(3)–Cu(1)–N(1)
O(3)–Cu(1)–O(9)
N(1)–Cu(1)–O(9)
O(3)–Co(1)–N(1)
O(3)–Co(1)–O(9)
N(1)–Co(1)–O(9)
a
Diamagnetic corrections were made with Pascal’s constants
for all constituent atoms.
NIT4Py. Anal Calc. for C38H42CuN10O18: C, 46.06; H, 4.24; N,
14.14. Found: C, 45.90; H, 4.16; N, 14.32%. IR (KBr, cmꢀ1): 3104,
1625, 1538, 1454, 1383, 1343, 1312, 1161, 1066, 868, 820, 729,
543.
Blue crystals of [Co(NIT4Py)2(DTB)2(H2O)2] 4 were prepared in a
manner similar to that of 2 only by replacing NIT3Py with NIT4Py.
AnalCalc. for C38H42CoN10O18: C, 46.29; H, 4.26; N, 14.21. Found: C,
46.42; H, 4.37; N, 14.23%. IR (KBr, cmꢀ1): 3014, 2906, 1609, 1538,
1454, 1379, 1347, 1169, 1066, 911, 864, 725, 547.
2.2. Synthesis
2-(30-Pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide
and 2-(40-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide
were prepared according to the literature method [19,20].
[Cu(NIT3Py)2(DTB)2] 1 was synthesized by adding 5 mL aque-
ous solution of potassium 3,5-dinitrobenzoate (0.101 g, 0.4 mmol)
into a mixed solution of Cu(OAc)2ꢁH2O (0.040 g, 0.2 mmol) and
NIT3Py (0.094 g, 0.4 mmol) in 15 mL methanol. The mixture was
stirred for 1 h and then filtered, and the clear blue filtrate was kept
at room temperature for three days. Green crystals were obtained.
Anal. Calc. for C38H38CuN10O16: C, 47.80; H, 3.98; N, 14.68. Found:
C, 47.26; H, 4.16; N, 14.72%. IR (KBr, cmꢀ1): 3096, 1621, 1541,
1454, 1423, 1387, 1343, 1169, 1070, 868, 725, 543.
2.3. X-ray crystallographic study
Single crystal X-ray diffraction measurements were carried out
on a Bruker Smart 1000 diffractometer equipped with graphite-
Blue crystals of [Co(NIT3Py)2(DTB)2(CH3OH)2] 2 were prepared
in a manner similar to that of 1 only by replacing Cu(OAc)2ꢁH2O
with Co(OAc)2ꢁH2O. Anal Calc. for C40H46CoN10O18: C, 47.38; H,
4.54; N, 13.82. Found: C, 47.21; H, 4.58; N, 13.90%. IR (KBr,
cmꢀ1): 3096, 1652, 1541, 1454, 1423, 1371, 1343, 1169, 1082,
915, 868, 725, 543.
monochromated Mo K
lected at room temperature by the u–
a
radiation (k = 0.71073 Å). Data were col-
scan technique in the
x
range 2.27° ꢂ h ꢂ 25.02°. The collected data were reduced by using
the program SAINT [21] and empirical absorption correction was
done by using the SADABS program [22]. The structures were solved
with direct methods of SHELXS-97 [23]. The H atoms were assigned
with common isotropic displacement factors and included in the
final refinement by using geometrical restraints. A full-matrix
Blue crystals of [Cu(NIT4Py)2(DTB)2(H2O)2] 3 were prepared in
a manner similar to that of 1 only by replacing NIT3Py with

C.-X. Zhang et al. / Polyhedron 29 (2010) 1387–1392
1389
Fig. 1. The molecular structure of the complex [Cu(NIT3Py)2(DNB)2], 1 (hydrogen atoms have been omitted for clarity).
Fig. 2. The molecular structure of the complex [Co(NIT3Py)2(DTB)2(CH3OH)2], 2 (hydrogen atoms have been omitted for clarity).
least-squares refinement on F2 was carried out using SHELXL-97 [24].
All non-hydrogen atoms were readily located and refined with
3. Results and discussion
anisotropic thermal parameters; R1 =
R
(||F0|ꢀ|Fc||)/
R|F0| and
3.1. Description of the crystal structures
wR2 = (
R
(|F0|2ꢀ|Fc|2)2/(
R
w|F0|2)2, respectively. Crystal data and se-
lected structural parameters were summarized in Tables 1 and 2,
respectively.
For complexes 1, 2, 3 and 4, the metal atoms are located on
inversion centers. All compounds are in the triclinic space group

1390
C.-X. Zhang et al. / Polyhedron 29 (2010) 1387–1392
Fig. 3. The molecular structure of the complex [Cu(NIT4Py)2(DTB)2(H2O)2], 3 (hydrogen atoms have been omitted for clarity).
ꢀ
P1. For all compounds, either square planar or octahedral coordina-
tion geometries are adopted.
The crystal structure of complex 2 is illustrated in Fig. 2. The
Co(II) ion adopts an octahedral coordination arrangement. Two
nitrogen atoms (N1, N1A) from the pyridine rings of the NIT3Py
ligands, with a Co–N bond length of 2.024(2) Å, and two oxygen
atoms (O3, O3A) from two DTB anions, with a Co–O bond
length of 1.963(2) Å, form the equatorial plane of the octahedral
geometry. The axial positions of the octahedron are occupied by
two oxygen atoms (O9, O9A) from two methanol molecules,
with a Co–O bond distance of 2.404(4) Å, which is significantly
longer than the basal distances. The fragment O1–N2–C6–N3–
O2 is nearly planar too, but forms a dihedral angle of 40.4°
with the plane of the pyridine ring. The N2–O1 distance
(1.268(3) Å) is similar to N–O distances already reported in
An ORTEP drawing of complex 1 is shown in Fig. 1. The Cu(II)
ion is four-coordinated in a square planar CuN2O2 coordination
environment, in which the coordination sites are occupied by
two nitrogen atoms (N1, N1A) from NIT3Py anions and two oxygen
atoms (O3,O3A) from NTB anions. The Cu–N and Cu–O bond
lengths (2.001(7) and 1.974(6) Å) are comparable with those ob-
served in other Cu- NIT3Py complexes [7,28]. The N2–O1 distance
(1.265(9) Å) is intermediate among those observed in copper com-
plexes with coordinated NIT3Py radicals [7,9]. The fragment O1–
N2–C6–N3–O2 is nearly planar, and forms a dihedral angle of
35.8° with the plane of the pyridine ring.
Fig. 4. The molecular structure of the complex [Co(NIT4Py)2(DTB)2(H2O)2], 4 (hydrogen atoms have been omitted for clarity).

C.-X. Zhang et al. / Polyhedron 29 (2010) 1387–1392
1391
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
analogous cobalt complexes with coordinated NIT3Py radicals
[28,30].
Complex 3 and 4 are isostructural and an ORTEP drawings of
complexes 3 and 4 are shown in Figs. 3 and 4. The metal ion is lo-
cated at an inversion center and adopts a distorted octahedral
geometry.
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
The equatorial plane is formed by two nitrogen atoms from the
pyridine rings of NIT4Py ligands and two oxygen atoms from two
DTB anions. Two water molecules occupy the apical positions for
3. However, two oxygen atoms from two DTB anions and two oxy-
gen atoms from two water molecules form the base plane, with
two nitrogen atoms from the pyridine rings of NIT4Py ligands oc-
cupy the apical positions for 4. The axial distortion in complex 3 in-
volves the Co–O9 axis whereas that in complex 4 involves the Co–
N1 axis. The metal-N (pyridine) bond distances are 2.020(2) and
2.146(2) Å for 3 and 4, respectively. The metal-O(DTB) bond dis-
tances are 1.995(2) for 3 and 2.079(1) Å for 4, whereas the me-
tal-O(water) bond distances are 2.317(2) and 2.095(2) Å for 3
and 4, respectively. Thus, similarly to complex 2, complexes 3
and 4 have an axially distorted octahedral geometry. The axial dis-
tortion in complexes 2 and 4 are significantly different in magni-
0
50
100
150
200
250
300
T / K
Fig. 5. Experimental and calculated variations of
[Cu(NIT3Py)2(DTB)2], 1.
vM (s) and
v
MT ( ) versus T for
r
32° with the N(1)–Cu(1)–N(1A) plane, and the angle between the
N(1)–Cu(1)–N(1A) plane and the plane of the pyridine ring is 39°.
tude, with
2
(2.404(4) Å) being more distorted than
4
*
p mag-
These geometrical parameters favor a weak overlap of the
(2.095(2) Å). The axial distortion in complex 2 involves the Co–
O9 axis whereas that in complex 4 involves the Co–N1 axis. These
differences maybe are caused by the different kinds of coordinated
solvent molecules (methanol and water molecules) and radicals
(NIT3Py and NIT4Py). Both the fragments O1–N2–C6–N3–O2 for
complex 3 and O1–N2–C6–N3–O2 for complex 4 are nearly planar,
but dihedral angles of 12.5° and 7.1° are observed for complexes 3
and 4 with the plane of the pyridine ring, respectively. In the rad-
ical ligand, the oxyl bond lengths, the N2–O1 distances 1.277(3)
and 1.285(2) Å, are similar to N–O distances already reported in
analogous complexes with coordinated NIT4Py radicals [7,31].
netic orbital of the radical with the dx2 magnetic orbital of the
Cu(II) ion. This is the origin of the weak antiferromagnetic Cu(II)-
nitroxide interaction.
ꢀy2
The weak antiferromagnetic interaction between Cu(II) and
NIT4Py in compound 3 can be explained by McConnell’s mecha-
nism [25], which is shown in Scheme 1. According to this model,
a spin distribution would induce a contrary spin on the adjacent
atom due to the spin polarization. In the radical ligand, the spin
distribution arising from intramolecule spin polarization of the
adjacent atoms leads to alternating positive and negative spin den-
sity on the carbon backbone of the radical ligand. A large positive
spin density is located on the NO groups, while a large negative
spin density is located on the sp2 carbon atom bridging two NO
groups, and the alternative delocalization takes place over the pyr-
idine ring due to the spin polarization. This in turn induces a neg-
ative spin density on the nitrogen atom of NIT4Py [26,27]. The
O(7)–N(2)–C(6)–N(3)–O(8) mean plane containing the unpaired
electron of the radical makes an angle of 44.8° with the N(1)–
Cu(1)–N(1A) plane. Compared with complex 1, the large overlap
3.2. Magnetic properties and discussion
The magnetic susceptibilities,
were measured in the 2–300 K region at 10000 G. A typical plot
of MT and vM versus T is shown in Fig. 5. The other plots are
shown in the Supplementary material.
The
vM, for complexes 1, 2, 3 and 4
v
v
MT value at room temperature is 1.09 cm3 molꢀ1 K for
complex 1 and 1.07 cm3 molꢀ1 K for complex 3, which are lower
than the spin-only value expected for two S = 1/2 and one S = 1/2
uncoupled spin systems (1.12 cm3 molꢀ1 K). When the systems
*
p
of the
magnetic orbital of the radical with the dx2
magnetic
ꢀy2
orbital of the planar Cu(II) ion leads to a stronger antiferromagnetic
Cu(II)-nitroxide interaction (J = ꢀ8.89 cmꢀ1). The relevant struc-
tural and magnetic data of some Cu(II)-nitroxide complexes are
listed in Table 3. It can be seen that when the angle between the
O(1)–N(2)–C(6)–N(3)–O(2) plane of the radical and the plane of
the pyridine ring is large, an antiferromagnetic exchange interac-
tion is expected, as for the copper complexes with coordinated
NIT3Py radicals, however, when the angle between the O(1)–
N(2)–C(6)–N(3)–O(2) plane of the radical and the plane of the pyr-
idine ring is small, a weak antiferromagnetic exchange interaction
is obtained, as for the copper complexes with coordinated NIT4Py.
are cooled down, the
vMT value decreases, which implies the exis-
tence of weak antiferromagnetic spin exchange interactions both
in complex 1 and complex 3.
The magnetic data were fitted into the isotropic model
ˆ
ˆ
ˆ
ˆ ˆ
H = ꢀ2J(SCuSR + SCuSR), where J is the interaction parameter be-
tween two paramagnetic centers. For radical–Cu(II)–radical com-
plexes, the theoretical expression of the magnetic susceptibility is
ꢀ
ꢁ
Nb2g2 1 þ expðꢀ2J=kTÞ þ 10expðJ=kTÞ
vM
¼
4kT 1 þ expðꢀ2J=kTÞ þ 2expðJ=kTÞ
The best-fitted parameters were J = ꢀ3.18 cmꢀ1, g = 1.99, R = 1.52 ꢃ
10ꢀ3 for 1 and J = ꢀ8.89 cmꢀ1, g = 1.98, R = 1.71 ꢃ 10ꢀ4 for 3, where
_
+
_
+
Â
Ã
2
2
O
N
O
N
R is defined as R ¼
R
ð
vMÞobs ꢀ ðvMÞcalc
=R
ð
vMÞobs
.
Those above results indicate that an antiferromagnetic ex-
change exists between the radical and metal ion.
Cu
N
N
We found the intramolecular metal-radical magnetic couplings
varied over a considerably wide range with relatively small struc-
tural modifications. This leads to an insight of the magneto-struc-
ture relationship.
N
N
.
.
O
O
In the compound 1, the O(1)–N(2)–C(6)–N(3)–O(2) mean plane
containing the unpaired electron of the radical makes an angle of
Scheme 1. The spin polarization mechanism for intramolecular magnetic coupling
in the compound 3.

1392
C.-X. Zhang et al. / Polyhedron 29 (2010) 1387–1392
Table 3
metry are used to explain the magnetic properties of the four
complexes. The values of the dihedral angles between the pyridyl
ring and the nitroxide group of the radical would affect the magnetic
properties in the four complexes. Although only weak antiferromag-
netic interactions were observed in these compounds, our effort is to
obtain single molecule magnets or single chain magnets with nitro-
nyl nitroxide radicals. It is known that small changes in the coordi-
nation of the nitronyl nitroxide radicals and metal ions have a large
influence on the magnetic properties of complexes. To realize our
purpose, we are working on the synthesis of complexes with differ-
ent metal ions and nitronyl nitroxide radical ligands.
Selected structural and magnetic parameters for Cu-NIT3Py and Cu-NIT4Py
compounds.
Compound
da (°)
J (cmꢀ1
)
Reference
Cu(NITm-Py)2(N3)2(DMSO)2
Cu(NITmPy)2(tp)
[Cu(Cl2CHCO2)2(NITmPy)2(H2O)2]
Cu(NIT3Py)2(DTB)2]
28.6
6.4
24.91
35.8
30.9
29.96
29.61
20.65
12.5
3.61
17.0
12.0
ꢀ3.18
[28]
[32]
[7]
this work
[29]
[29]
[29]
[7]
this work
Cu(NITpPy)2(NO3)2
ꢀ14.1 0.1
ꢀ16.7 0.6
ꢀ17.0 0.2
ꢀ13
Cu(NITpPy)2(CH3COO)2
Cu(NITpPy)2[N(CN)2]2ꢁ(H2O)2
[Cu(Cl3CCO2)2(NITpPy)2(H2O)]
[Cu(NIT4Py)2(DTB)2(H2O)2]
ꢀ8.89
a
Acknowledgements
d is defined by the pyridine ring and ONCNO plane.
This work was supported by the National Natural Science Foun-
dation of China (No. 20771081 and No. 20771083)
The
v
MT value at room temperature is 2.65 cm3 molꢀ1 K for
complex 2, which is close to the spin-only expected value for
two S = 1/2 and one S = 3/2 uncoupled spin systems (2.63 cm3
Appendix A. Supplementary data
molꢀ1 K). The
v K
MT value at room temperature is 2.83 cm3 molꢀ1
for complex 4, which is higher than the spin-only expected value
for two S = 1/2 and one S = 3/2 uncoupled spin systems
CCDC 629452, 629664, 746732 and 746733 contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.
html. Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.poly.2009.12.039.
(2.63 cm3 molꢀ1 K). When the systems are cooled down, the
vMT
value decreases. This implies the existence of weak antiferromag-
netic spin exchange interactions both in complexes 2 and 4.
ˆ
The magnetic data were fitted into the isotropic model H = ꢀ2J
ˆ
ˆ
ˆ ˆ
(SCoSR + SCoSR), where J is the interaction parameter between two
paramagnetic centers. For radical–Co(II)–radical complexes, the
theoretical expression of the magnetic susceptibility is
References
[1] A. Caneschi, D. Gatteschi, A. Grand, J. Laugier, L. Pardi, P. Rey, Inorg. Chem. 27
(1988) 1031.
[2] H. Oshio, T. Watanabe, A. Ohto, T. Ito, H. Masuda, Inorg. Chem. 35 (1996) 472.
[3] J.-X. Xu, Y. Ma, D.-Z. Liao, G.-F. Xu, J. Tang, C. Wang, N. Zhou, S.-P. Yan, P. Cheng,
L.-C. Li, Inorg. Chem. 48 (2009) 8890.
ꢀ
ꢁ
Nb2g2 10 þ expðꢀ5J=kTÞ þ 10expðꢀ2J=kTÞ þ 35expð3J=kTÞ
vM
¼
4kT
2 þ expðꢀ5J=kTÞ þ 2expðꢀ2J=kTÞ þ 3expð3J=kTÞ
[4] N. Ishil, Y. Okamura, S. Chiba, T. Nogami, T. Ishida, J. Am. Chem. Soc. 130 (2008)
24.
The best-fitted parameters were J = ꢀ1.57 cmꢀ1
, g = 2.01,
[5] L.-C. Li, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, J. Chem. Soc., Dalton Trans. 1 (2002) 1.
[6] A. Cogne, J. Laugier, D. Luneau, P. Rey, Inorg. Chem. 39 (2000) 5510.
[7] H.-H. Lin, H.-H. Wei, G.-H. Lee, Y. Wang, Polyhedron 20 (2001) 3057.
[8] H. Oshio, T. Watanabe, A. Ohto, T. Ito, T. Ikoma, S.Tero-Kubota, Inorg. Chem. 36
(1997) 3014.
[9] Y. Ma, D.-Z. Gao, W. Zhang, K. Yoshimura, D.-Z. Liao, Z.-H. Jiang, S.-P. Yang,
Inorg. Chim. Acta 14 (2006) 359.
[10] K. Hayakawa, D. Shiomi, T. Ise, K. Sato, T. Takui, J. Mater. Chem. 16 (2006) 4146.
[11] J.Tao, Y.-Z. Zhang, Y.-L. Bai, O. Sato, Inorg. Chem. 45 (2006) 4877.
[12] L.-Y. Wang, B. Zhao, C.-X. Zhang, Z.-H. Jiang, D.-Z. Liao, S.-P. Yan, Inorg. Chem.
42 (2003) 5804.
R = 2 ꢃ 10ꢀ5 for 2 and J = ꢀ2.62 cmꢀ1, g = 2.02, R = 8.58 ꢃ 10ꢀ5 for
2
2
4, where R is defined as R ¼
R
½ðvMÞobs ꢀ ðvMÞcalcꢄ =
R
ð
vMÞobs
.
Those above results indicate that an antiferromagnetic ex-
change exists between the radical and metal ion.
For both complexes 2 and 4, the magnetic exchange interactions
between the Co(II) ion and the radicals are weak, which indicates
the pyridine ring is not a suitable linker to transmit the magnetic
interaction. Based on the orbital symmetry of the Co (II) ion of 2
[13] R.-N. Liu, L.-C. Li, X.-Y. Xing, D.-Z. Liao, Inorg. Chim. Acta 362 (2009) 2253.
[14] J.-Y. Zhang, C.-M. Liu, D.-Q. Zhang, S. Gao, D.-B. Zhu, Inorg. Chim. Acta 360
(2007) 3553.
[15] R.P. Sharma, A. Singh, P. Branado, V. Felix, P. Venugopalan, J. Mol. Struc. 921
(2009) 227.
[16] D.-X. Hu, P.-K. Chen, F. Luo, L. Xue, Y. Che, L.-M. Zheng, Inorg. Chim. Acta 360
(2007) 4077.
[17] X. Wang, Y. Guo, E. Wang, L. Duan, X. Xu, C. Hu, J. Mol. Struc. 691 (2004) 171.
[18] Z.-L. Wang, L.-H. Wei, M.-X. Li, J.-P. Wang, J. Mol. Struc. 879 (2008) 150.
[19] E.F. Ullman, J.H. Osiecki, D.G.B. Boocock, R. Darcy, J. Am. Chem. Soc. 94 (1974)
7049.
[20] E.F. Ullman, L. Call, J.H. Osiecki, J. Org. Chem. 35 (1970) 3623.
[21] Siemens, SMART and SAINT, Area Detector Control and Integration Software,
Siemens Analytical X-ray System, Inc, Madison, WI, 1996.
[22] G.M Sheldrick, SADABS Program for Empirical Absorption Correction of Area
Dectector Data, University of Göttingen, Germany, 1996.
[23] G.M Sheldrick, SHELXS 97 Program for the Solution of Crystal Structure,
University of Göttingen, Germany, 1997.
and 4, its two magnetic orbitals with
r symmetry (dx2 , dz2 ) are
ꢀy2
*
p ) of the radical and would in-
orthogonal to the magnetic orbital (
duce a ferromagnetic interaction, while its one magnetic orbital
with symmetry (either of dxy, dxz, dyz) is able to overlap with
p
the magnetic orbital of the radical to cause antiferromagnetic cou-
pling. Meantime, due to the conjugation between the pyridine ring
and the plane defined by five-atom fragment ONCNO, the unpaired
electrons of the nitroxide radicals can delocalize onto the pyridine
ring. The observed antiferromagnetic coupling in 2 and 4 can be
*
attributed to the good overlap of the
ical with the magnetic orbital with
p
p
magnetic orbital of the rad-
symmetry of the Co (II) ion.
Therefore, spin both on the Co (II) ion and the radical is expected
to interact magnetically through the -conjugated system, which
leads to an antiferromagnetic interaction.
p
[24] G.M Sheldrick, SHELXL 97 Program for the Crystal Structure Refinement,
University of Göttingen, Germany, 1997.
[25] H.M. McConnell, J. Chem. Phys. 39 (1963) 1910.
[26] T. Shimada, T. Ishida, T. Nogami, Polyhedron 24 (2005) 2593.
[27] H. Kumada, A. Sakane, N. Koga, H. Iwamura, J. Chem. Soc., Dalton Trans. (2000)
911.
[28] Y.-H. Xu, X.-N. Qu, H.-B. Song, L.-C. Li, Z.-H. Jiang, D.-Z. Liao, Polyhedron 26
(2007) 741.
[29] I. Dasna, S. Golhen, L. Ouahab, M. Fettouhi, O. Pena, N. Daro, J.-P. Sutter, Inorg.
Chim. Acta 326 (2006) 37.
[30] S.-P. Wang, D.-Z. Gao, Y. Song, Z.-Q. Liu, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, Inorg.
Chim. Acta 359 (2006) 505.
4. Conclusion
We have successfully obtained four new metal-radical
complexes of the formula [Cu(NIT3Py)2(DTB)2] 1, [Co(NIT3Py)2-
(DTB)2(CH3OH)2] 2, [Cu(NIT4Py)2(DTB)2(H2O)2] 3 and [Co(NIT4-
Py)2(DTB)2(H2O)2] 4. For the four complexes, the crystal structural
analyses indicate that the two radical ligands are coordinated to
the metal ions via the nitrogen atoms of the pyridine rings to form
three spin complexes. All the complexes show weak antiferromag-
netic interactions. A spin polarization mechanism and orbital sym-
[31] L. Zhang, L.-C. Li, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, P.-W. Shen, Inorg. Chim. Acta
320 (2001) 41.
[32] L.-C. Li, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, Inorg. Chim. Acta 357 (2004) 405.