Synthesis, structure and magnetic properties of a novel nickel(II) radical heterospin complex with salicylaldoxime

Article abstract of DOI:10.1002/zaac.200700012

A novel heterospin complex containing both Ni^II and nitroxide radical ligands: [Ni(salox)₂(NIT4Py)₂] (1) (salox = salicylaldoxime, NIT4Py = 2-(4′-pyridyl)-4,4,5,5- tetramethylimidazoline- 1-oxyl-3-oxide) has been synthesized and structurally characterized. The structure consists of neutral Ni(salox)₂-(NIT4Py)₂ moieties bridged by intermolecular hydrogen bonds, forming a one-dimensional chain structure. Magnetic measurements show intramolecular antiferromagnetic interactions between NIT4Py and Ni²⁺ ion.

Full text of DOI:10.1002/zaac.200700012

DOI: 10.1002/zaac.200700012
Synthesis, Structure and Magnetic Properties of a Novel Nickel(II) Radical
Heterospin Complex with Salicylaldoxime
Yue Maa, Wei Zhangb,c, Gong-Feng Xua, Kazuyoshi Yoshimurab, Dai-Zheng Liaoa,*, Zong-Hui Jianga,
and Shi-Ping Yana
a Tianjin/P. R. China, Nankai University, Department of Chemistry
b Kyoto/Japan, Kyoto University, Department of Chemistry, Graduate School of Science and c Research Center for Low Temperature
and Materials Sciences
Received September 22nd, 2006; revised December 15th, 2006.
Abstract. A novel heterospin complex containing both NiII and
nitroxide radical ligands: [Ni(salox)2(NIT4Py)2] (1) (salox
salicylaldoxime, NIT4Py 2-(4Ј-pyridyl)-4,4,5,5- tetramethyl-
ming a one-dimensional chain structure. Magnetic measurements
show intramolecular antiferromagnetic interactions between
NIT4Py and Ni2ϩ ion.
ϭ
ϭ
imidazoline-1-oxyl-3-oxide) has been synthesized and structurally
characterized. The structure consists of neutral Ni(salox)2-
(NIT4Py)2 moieties bridged by intermolecular hydrogen bonds, for-
Keywords: Nickel; Salicylaldoxime; Nitronyl nitroxide radical; Cry-
stal structure; Magnetic properties
Introduction
actions between the Ni2ϩ ion and NIT4Py, and forms one-
dimensional chain structure with hydrogen bonding link-
ages.
Pyridyl-substituted nitroxide radicals have attracted con-
siderable attention in recent years in the design and con-
struction of molecular magnetic materials. These stable and
easy coordinating radicals can act not only as good building
blocks for metal ions but also spin carriers themselves [1,
2]. By using the pyridyl-substituted nitroxide radicals as
NIT4Py [3Ϫ10], NIT3Py [11-16], NIT2Py [17Ϫ19], a great
many of novel heterospin functional materials exhibiting
interesting magnetic behaviors, optical properties and a var-
iety of structural topology have been obtained and studied.
On the other hand, 3d transition-metal complexes based
on phenolic oximes derived from salicylaldehydes have also
been greatly studied because of their analytical and biologi-
cal importance [20Ϫ24], as well as their function in the
hydrometallurgical processes for Cu2ϩ and Ni2ϩ ions based
on solvent extraction [25]. However, pyridyl-substituted
nitroxide radicals as co-ligand for M(salox)2 has never been
reported to the best of our knowledge. In this work we util-
ized NIT4Py as the co-ligand for M(salox)2 fragment, and
obtained a heterospin complex [Ni(salox)2(NIT4Py)2] with
three paramagnetic centers (NIT4Py -Ni- NIT4Py). The
complex shows intramolecular antiferromagnetic inter-
Experimental Section
General
All starting materials were analytical grade and used without
further purification. Elemental analysis for C, H and N were car-
ried out on a Perkin-Elmer elemental analyzer (model 240). The
infrared spectrum was obtained on a Bruker Tensor 27 Fourier
transform infrared spectroscopy in the 4000Ϫ400 cmϪ1 regions,
using KBr pellets. Variable temperature magnetic susceptibility
measurements were carried out on a SQUID MPMS5 magnet-
ometer between 2.0Ϫ300 K in a magnetic field of 5000 Oe. The
molar magnetic susceptibility was corrected from the sample holder
and diamagnetic contributions (Ϫ3.0ϫ10Ϫ4 cm3 molϪ1) of all con-
stituent atoms by using Pascal’s constants.
Synthesis
2-(4Ј-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide NIT4Py
[26] and Ni(salox)2(py)2 [27] were prepared according to previous
published methods.
Preparation of [Ni(salox)2(NIT4Py)2]
* Prof. Dai Zheng Liao
Department of Chemistry
Nankai University
Tianjin 300071/P.R. China
Tel.: ϩ86-22-23509957
fax: ϩ86-22-23502779
E-mail: coord@nankai.edu.cn
Ni(salox)2(py)2 (25 mg, 0.05 mmol) and NIT4Py (23.4 mg,
0.1 mmol) were dissolved in 5 ml CH2Cl2 and stirred for 1 hours
at RT. The clear solution was then placed in a tube and layered
with n-hexane (5 ml), staying without disturbance. After one week,
dark blue crystals suitable for X-ray structure analysis were ob-
tained (yield 60 %). Anal. Calcd for C38H44N8NiO8: C, 57.09; H,
Z. Anorg. Allg. Chem. 2007, 633, 657Ϫ660
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
657

Y. Ma, W. Zhang, G.-F. Xu, K. Yoshimura, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan
Table 1 Summary of crystallographic data for complex 1.
Empirical formula
Formula weight
Temperature /K
C38H44N8NiO8
799.52
294(2)
˚
Wavelength /A
0.71073
Crystal system, space group
monoclinic, P21/c
9.401(4)
10.750(5)
19.137(8)
90
91.888(8)
90
1932.9(14)
2, 1.374
˚
a /A
˚
b /A
˚
c /A
Ͱ /°
β /°
γ /°
3
˚
Volume /A
Z, Calculated density /(Mg / m3)
Absorption coefficient /mmϪ1
F(000)
0.564
840
Crystal size /mm3
θ Range /°
0.24 x 0.20 x 0.14
2.13 to 25.01
Ϫ10 Յ h Յ 11, Ϫ12 Յ k Յ 12,
Ϫ18 Յ l Յ 22
Limiting indices
Reflections collected / unique
Absorption correction
Max./min. transmission
Refinement method
9606 / 3393 [R (int) ϭ 0.0815]
Semi-empirical from equivalents
0.9252 and 0.8765
Full-matrix least-squares on F2
1.055
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
Largest diff. peak and hole
R1 ϭ 0.0557, ωR2 ϭ 0.1263
3
˚
0.529 and Ϫ0.426 e. A
˚
Table 2 Selected bond lengths /A and angles /° for complex 1.
Ni(1)-O(1)#1
Ni(1)-O(1)
Ni(1)-N(1)#1
Ni(1)-N(1)
Ni(1)-N(2)
1.980(3)
1.980(3)
2.003(4)
2.003(4)
2.174(4)
Ni(1)-N(2)#1
O(3)-N(4)
O(4)-N(3)
O(2)-N(1)
O(1)-C(1)
2.174(4)
1.282(4)
1.287(5)
1.410(4)
1.310(5)
Fig. 1 ORTEP drawing of 1 with 30 % thermal ellipsoids.
O(1)#1-Ni(1)-O(1)
O(1)#1-Ni(1)-N(1)#1
O(1)-Ni(1)-N(1)#1
O(1)#1-Ni(1)-N(1)
O(1)-Ni(1)-N(1)
N(1)#1-Ni(1)-N(1)
O(1)#1-Ni(1)-N(2)
O(1)-Ni(1)-N(2)
N(1)#1-Ni(1)-N(2)
N(1)-Ni(1)-N(2)
O(1)#1-Ni(1)-N(2)#1
O(1)-Ni(1)-N(2)#1
180.0
N(1)#1-Ni(1)-N(2)#1
N(1)-Ni(1)-N(2)#1
N(2)-Ni(1)-N(2)#1
C(1)-O(1)-Ni(1)
C(7)-N(1)-Ni(1)
O(2)-N(1)-Ni(1)
C(8)-N(2)-Ni(1)
C(12)-N(2)-Ni(1)
O(4)-N(3)-C(13)
O(4)-N(3)-C(17)
O(3)-N(4)-C(13)
O(3)-N(4)-C(14)
91.12(14)
88.88(14)
179.998(1)
127.5(3)
128.0(3)
118.8(3)
121.0(3)
123.1(3)
125.2(4)
122.1(4)
124.8(4)
121.6(4)
91.61(14)
88.39(14)
88.39(14)
91.61(14)
179.999(1)
90.05(14)
89.95(14)
88.88(14)
91.12(14)
89.95(14)
90.05(14)
CCDC No 611021. Copies of this information can be obtained
free of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: ϩ44-1223-336-033; email:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk)
Results and Discussion
Symmetry transformations, #1 Ϫxϩ1,Ϫyϩ1,Ϫzϩ1
Crystal Structure of 1
The ORTEP drawing of 1 is shown in Figure 1. Ni2ϩ ion is
located on an inversion center and adopts distorted octa-
hedral geometry, completed by two deprotonated phenolic
oxygen atoms (O1, O1A) and two nitrogen atoms (N1,
N1A) both from salicylaldoxime ligands, forming the basal
plane O1-N1-O1A-N1A (with the bond lengths of NiϪO1,
5.55; N, 14.02 %; Found: C, 57.25 H, 5.45; N, 13.94 %. IR (KBr
disc, cmϪ1): (1644 w δOH, 1184 m 908 s νNϪO, 1311 s, 998 s νCϪO
1370 s νNϪO
,
)
X-ray crystallography
2ϩ
˚
1.980(3), NiϪN1, 2.003(4) A), the Ni ion is absolutely
X-ray diffractions were measured on an APEX II CCD area detec-
˚
coplanar with the basal plane with a displacement of 0 A.
tor equipped with a graphite-monochromated MoKͰ radiation
˚
(λ ϭ 0.71073 A). A summary of crystallographic data is given in
While the axial positions are occupied by two nitrogen
atoms (N2, N2A) from pyridyl rings of NIT4Py radicals
Table 1. The structure was solved by direct methods using
SHELXS-97 program and refined with SHELXL-97 [28, 29] by
full-matrix least-squares techniques on F2. All non-hydrogen atoms
were refined anisotropically, while the hydrogen atoms were located
geometrically and refined isotropically. The selected bond lengths
and angles are listed in Tables 2.
˚
(with the bond length of NiϪN2, 2.174(4) A). The dihedral
angle between pyridine ring and nitroxide group
(O3ϪN4ϪC13ϪN3ϪO4) in the radical is 46.9°.
The intermolecular hydrogen bonds between O2
(from oximic) and O4 (from NIT4Py) connect the
Ni(salox)2(NIT4Py)2 moieties to form a 1-D chain, as
shown in Figure 2, with the bond length of O2···O4,
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
658
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 657Ϫ660

Synthesis, Structure and Magnetic Properties of a Novel Nickel(II) Radical Heterospin Complex with Salicylaldoxime
molecular antiferromagnetic interactions between Ni(II)
ions and NIT4Py (ii) intermolecular interactions between
Ni(salox)2(NIT4Py)2 moieties and/or the zero-field splitting
(ZFS) of Ni2ϩ ion (S ϭ 1).
Considering all the above, using the spin Hamiltonian
ˆ
ˆ
ˆ
ˆ
ˆ
H ϭ Ϫ2J(SNi·SRad1 ϩ SNi·SRad2) and Van Vleck equation,
a theoretical expression of the magnetic susceptibility can
be derived as Eq. (1) [1].
Fig. 2 Packing diagram for [Ni(salox)2(NIT4Py)2], a 1-D chain
formed by intermolecular hydrogen bond interactions. Hydrogen
atoms are omitted for clarity.
4J
2J
g221 ϩ g211 5 exp
4J
ϩ g210 exp
΂ ΃
΂ ΃
2Nβ2
kT
kT
χtri ϭ
k(TϪθ)
Ϫ2J
2J
΄
΅
3 ϩ 5 exp
ϩ exp
ϩ 3 exp
΂ ΃
΂ ΃
΂ ΃
kT
kT
kT
The molecular gs,s* factors (S* ϭ SR1 ϩ SR2, S ϭ SNi
S*) have been related to the local gR and gNi and shown
ϩ
as follows:
1
2
1
2
g21
g11
ϭ
ϭ
gRad
ϩ
ϩ
gNi
gNi
1
2
1
2
gRad
(1)
g10 ϭ gNi , gRad ϭ 2
J is the magnetic exchange coupling constant between
Ni2ϩ ion and NIT4Py. A weiss constant θ is included to
describe phenomenologically the decrease of χMT at low
temperature, which is caused by intermolecular magnetic in-
teractions in 1 and/or zero-field splitting (ZFS) of Ni2ϩ ion
(S ϭ 1) [31]. The best fitting parameters were obtained as,
Fig.
3
Temperature dependence of the molar susceptibility
(χM, ∆) and χMT, o versus T
˚
2.920 A. There are also intramolecular hydrogen bond inter-
actions between phenolic oxygen O1 and oximic oxygen O2
from two salicylaldoximes in one Ni(salox)2(NIT4Py)2
J ϭ Ϫ2.51 cmϪ1, gNi ϭ 2.10, θ ϭ Ϫ0.40 K, R ϭ 4.6ϫ10Ϫ3
2
(R value is defined as R ϭ Σ[(χM)obs Ϫ (χM)calc
]
/
˚
Σ[(χM)obs]2). The fitted J value Ϫ2.51 cmϪ1 is similar as
those in other NiII-NIT4Py complexes (Ϫ3.45 and
Ϫ5.0 cmϪ1) [4, 5], which confirms the weak intramolecular
antiferromagnetic coupling between NiII and NIT4Py.
The gNi value is also in the range of gNi in NiII-NIT4Py
systems (2.05-2.16) [5, 6]. θ ϭ Ϫ0.40 K shows the
existence of intermolecular magnetic interactions between
Ni(salox)2(NIT4Py)2 moieties and/or zero-field splitting
(ZFS) of Ni2ϩ ion (S ϭ 1).
moiety (O2···O1, 2.730 A).
Magnetic Properties
Variable temperature magnetic susceptibility measurements
were carried out with a SQUID MPMS5 magnetometer in
the temperature range 2.0Ϫ300 K at a magnetic field of
5000 Oe. The magnetic properties of 1 in the forms of both
χMT versus T and χM versus T plots are presented in Figure
3. At room temperature, the χMT is 1.87 cm3 molϪ1 K,
which is slightly higher than the value (1.75 cm3 molϪ1 K)
expected for an uncoupled system with one Ni2ϩ ion (S ϭ
1) and two NIT4Py (S ϭ 1/2), probably due to the mixing
of an angular momentum from an excited state of Ni2ϩ ion
(3T2g) via spin-orbit coupling. For the plot of χMT versus
T, at higher temperature the χMT decreases very slowly with
the decrease of the temperature, while at lower temperature
χMT decreases sharply to 0.11 cm3 K molϪ1 around 2.0 K.
In the case of χM versus T, the χM increases with the de-
crease of the temperature until getting a maximum at 7 K,
then decreases sharply down with the temperature decreas-
ing. All the above magnetic behaviors suggest the existence
of antiferromagnetic interaction in the system [30].
The antiferromagnetic coupling between NiII atom and
NIT4Py can be explained by a spin polarization mechanism
of the π-electrons and the orthogonality of 3d magnetic or-
bital of Ni2ϩ ion and the 2pπ orbital on the pyridine rings,
which have also been used to explain the magnetic proper-
ties of other pyridyl-substituted nitroxide radical-metal
complexes [32Ϫ34]. Owing to spin polarization by the posi-
tive spin of radical center (Scheme 1), the sign alternation
of spin density leads to significant negative spin density at
N atom of pyridine. Furthermore, as the crystal structure
shows in Figure 1, NIT4py radicals coordinate to Ni2ϩ ion
via the axial positions, consequently, 2pπ orbital at the ni-
2Ϫy2
trogen of the pyridine ring and the magnetic orbital dx
and dz of Ni2ϩ ion have no significant overlap. Thus, their orthog-
2
From the structural features of complex 1, the following
magnetic interactions can exist in the system, (i) intra-
onality leads to the same negative spin density at Ni2ϩ ion as that
on N atom of pyridine, while the spin sign of radical center is posi-
Z. Anorg. Allg. Chem. 2007, 657Ϫ660
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
659

Y. Ma, W. Zhang, G.-F. Xu, K. Yoshimura, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan
[4] H.-H. Wei, H.-Y. Wong, G.-H. Lee, Y.-J. Wang, Chin. Chem.
Soc. 1996, 43, 253.
[5] L.-Y. Wang, Z.-L. Liu, D.-Z.Liao, Z.-H. Jiang, S.-P. Yan, In-
org. Chem. Commun. 2003, 6, 630.
[6] A. Caneschi, F. Ferraro, D. Gattaschi, P. Rey, R. Sessoli, Inorg.
Chem. 1990, 29, 4217.
[7] M. Ogita, Y. Yamamoto, T. Suzuki, S. Kaizaki, Eur. J. Inorg.
Chem. 2002, 886.
[8] I. Dasna, S. Golhen, L. Ouahab, O. Pena, N. Daro, J. P. Sutter,
New J. Chem. 2000, 24, 903.
[9] Z.-L. Liu, L.-C. Li, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, Crystal
Growth Design 2005, 5, 783.
[10] D.-Z. Gao, J. Chen, S.-P. Wang, Y. Song, D.-Z. Liao, Z.-H.
Jiang, S.-P. Yan, Inorg. Chem. Commun. 2006, 9, 132.
[11] Y.-H. Chung, H.-H. Wei, Inorg. Chem. Commun. 1999, 2, 269.
[12] T. Okuno, K. Kuwamoto, W. Fujita, K. Awaga, W. Nakanishi,
Polyhedron 2003, 22, 2311.
[13] L.-C. Li, Z.-L. Liu, S. S. Turner, D.-Z. Liao, Z.-H. Jiang, S.-
P. Ya n, New J. Chem. 2003, 27, 752.
[14] K. Okada, O. Nagao, H. Mori, M. Kozaki, D. Shiomi, K.
Sato, T. Takui, Y. Kitagawa, K. Yamaguchi, Inorg. Chem.
2003, 42, 3221.
[15] D.-Q.Zhang, L. Ding, W. Xu, H. M. Hu, D.-B. Zhu, Y.-H,
Huang, D.-C. Fang Chem. Commun. 2002, 44.
[16] F. Lanfranc de Panthou, E. Belorizky, R. Calemczuk, D. Lu-
neau, C. Marcenat, E. Ressouche, P. Turek, P. Rey, J. Am.
Chem. Soc. 1995, 117, 11247.
[17] C.-J. Lee, H.-H. Wei, G.-H. Lee, Y. Wang, Inorg. Chem. Com-
mun. 2000, 3, 690.
[18] Y. Yamamoto, T. Suzuki, S. Kaizaki, Dalton Trans. 2001, 2943.
[19] Z.-L. Liu, Z.-L.Lu, D.-Q. Zhang, Z.-H. Jiang, L.-C. Li, C.-M.
Liu, D.-B. Zhu, Inorg. Chem. 2004, 43, 6620.
[20] M. E. Keeney, K. Osseo-Asare, K. A.Woode, Coord. Chem.
Rev. 1984, 59, 141.
Scheme 1
[21] H. Elo, P. Lumme, Inorg. Chim. Acta 1987, 136, 149.
[22] M. Lalia-Kantouri, M. Hartophylles, P. D. Jannakoudakis, G.
P. Voutsas, Z. Anorg. Allg. Chem. 1995, 621, 645.
[23] V. Yu. Kukushkin, D. Tudela, A. J. L. Pombeiro, Coord. Chem.
Rev. 1996, 156, 333.
tive, then the antiferromagnetic interaction between Ni2ϩ ion and
NIT4Py will occur.
In summary, we have studied
stituted nitronyl nitroxides complex with salicylaldoxime
[Ni(salox)2(NIT4Py)2]. The complex forms one-dimensional chain
structure with hydrogen bonding linkages, and shows intramolecu-
lar antiferromagnetic interactions between the Ni2ϩ ion and
NIT4Py.
a
new NiII-pyridyl-sub-
[24] M. Lalia-Kantouri, A. Hatzidimitriou, M. Uddin, Polyhedron
1999, 18, 3441.
´
[25] V. M. Hultgren (nee Jones), I. M. Atkinson, R. L. Beddoes,
D. Collison, C. D. Garner, Helliwell, L. F. Lindoy, P. A.
Tasker, Chem. Commun. 2001, 573.
[26] M. S. Davis, K. Morokuma, R. W. Kreilick, J. Am. Chem. Soc.
1972, 94, 5588.
[27] V. Romano, F. Maggio, T. Pizzino, J. Inorg. Nucl. Chem. 1971,
33, 2611.
[28] G. M. Sheldrick, SHELXS-97: Program for the Solution of
Crystal Structures, University of Gottingen, Germany 1997.
[29] G. M. Sheldrick, SHELXL-97: Program for the Refinement
of Crystal Structures, University of Gottingen, Germany 1997.
[30] S. Hatscher, H. Schilder, H. Lueken, W. Urland, Pure Appl.
Chem. 2005, 77, 497.
Acknowledgements. This project was supported by the National
Natural Science Foundation of China (No.20471031, No.
20631030, No.20331010, and No.20571045) and Natural Science
Key Foundation of Tianjin. This study was also partly supported
by
a Grant-in-Aid for Science Research on Priority Area,
“Invention of anomalous quantum materials“, from the Ministry
of Education, Science, Sports and Culture of Japan (Grant No.
16076210).
[31] A. Caneschi, A. Dei, C. P. Mussari, D. A. Shultz, L. Sorace,
K. E. Vostrikova, Inorg. Chem. 2002, 41, 1086.
References
[32] H. M. McConnell, J. Chem. Phys. 1963, 39, 1910.
[33] J. Cirujeda, M. Mas, E. Molins, F. L. de Panthou, J. Laugier,J.
G. Park, C. Pauson, P. Rey, C. Rovira, J. Veciana, J. Chem.
Soc., Chem. Commun. 1995, 709.
[34] O. Kahn, J. Galy, Y. Journaux, J. Jaud, I. Morgenstern-
Badarau, J. Am. Chem. Soc. 1982, 104, 2165.
[1] O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993.
[2] A. Caneschi, D. Gatteschi, P. Rey, R. Sessoli, Acc. Chem. Res.
1989, 22, 392.
[3] H.-B. Zhou, S.-P. Wang, W. Dong, Z.-Q. Liu, Q.-L. Wang, D.-
Z. Liao, Z.-H. Jiang, S.-P. Yan, P. Cheng, Inorg. Chem. 2004,
43, 4552.
660
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 657Ϫ660