FULL PAPER
DOI: 10.1002/chem.201202795
A New Family of Trinuclear Nickel(II) Complexes as
Single-Molecule Magnets
Rituparna Biswas,[a] Yumi Ida,[b] Michael L. Baker,[c] Saptarshi Biswas,[a] Paramita Kar,[a]
Hiroyuki Nojiri,[c] Takayuki Ishida,*[b] and Ashutosh Ghosh*[a]
Abstract: Three new trinuclear nickel
(II) complexes with the general compo-
consistent with the magnetic anisotropy
expected from the coordination struc-
ture of each nickel ion. Temperature-
dependent magnetic measurements in-
dicated ferromagnetic coupling leading
to an S=3 ground state with 2J/k=17,
17, and 28 K for 1, 2, and 3, respective-
ly, with the nickel atoms in an approxi-
mate equilateral triangle. The high-fre-
quency EPR spectra in combination
with spin Hamiltonian simulations that
include zero-field splitting parameters
DNi/k=ꢁ5, ꢁ4, and ꢁ4 K for 1, 2, and
3, respectively, reproduced the EPR
spectra well after a anisotropic ex-
change term was introduced. Aniso-
tropic exchange was identified as Di,j/
k=ꢁ0.9, ꢁ0.8, and ꢁ0.8 K for 1, 2, and
3, respectively, whereas no evidence of
single-ion rhombic anisotropy was ob-
served spectroscopically. Slow relaxa-
tion of the magnetization at low tem-
peratures is evident from the frequen-
cy-dependence of the out-of-phase ac
susceptibilities. Pulsed-field magnetiza-
tion recorded at 0.5 K shows clear
steps in the hysteresis loop at 0.5–1 T,
which has been assigned to quantum
tunneling, and is characteristic of
single-molecule magnets.
sition
[Ni3L3(OH)(X)]ACTHUNGTERNNU(G ClO4) have
been prepared in which X=Clꢁ (1),
ꢁ
OCNꢁ (2), or N3 (3) and HL is the tri-
dentate N,N,O donor Schiff base ligand
2-[(3-dimethylaminopropylimino)me-
thyl]phenol. Single-crystal structural
analyses revealed that all three com-
plexes have a similar Ni3 core motif
with three different types of bridging,
namely phenoxido (m2 and m3), hy
ido (m3), and m2-Cl (1), m1,1-NCO (2), or
m1,1-N3 (3). The nickel(II) ions adopt a
compressed octahedron geometry.
ACHTUNGTNERdNUNG rox-
ACHTUNGTRENNUNG
Single-crystal magnetization measure-
ments on complex 1 revealed that the
pseudo-three-fold axis of Ni3 corre-
sponds to a magnetic easy axis, being
Keywords: EPR spectroscopy
·
magnetic properties · nickel · Schiff
bases · X-ray diffraction
Introduction
barrier (D) in the majority of SMMs results mainly from the
spin ground state (S) and the uniaxial anisotropy of the mol-
ecule.[4] The magnetic anisotropy has to be of the Ising-type,
that is, the zero-field splitting parameter (D) must be nega-
tive to ensure that the m= ꢀS states are the lowest in
Single-molecule magnets (SMMs) have attracted considera-
ble interest in recent years owing to their potential applica-
tions in information storage and quantum computing at the
molecular level.[1–3] These systems exhibit slow relaxation of
their magnetization and function as a magnet below their
blocking temperature (TB). The origin of the anisotropic
energy and the m=0 state the highest (for integer spin; for
1
noninteger spin m= ꢀ = would be the highest).[5] A signifi-
2
cant barrier to the reversal of the magnetic moment results
in a hysteresis of the magnetization that is of purely molecu-
lar origin.[2a,b,6,7] An interesting feature of these molecules is
that they show quantum tunneling of magnetization
(QTM).[7b,8] High-frequency electron paramagnetic reso-
nance (HF-EPR) is a useful tool for determining the sign
and magnitude of the D value of such magnetic clusters.[9]
Since the discovery of the first SMM behavior of the
[a] R. Biswas, S. Biswas, P. Kar, A. Ghosh
Department of Chemistry, University College of Science
University of Calcutta
92, A.P.C. Road, Kolkata 700 009 (India)
[b] Y. Ida, T. Ishida
dodeca
ACHTUNGTRENNUNG
Department of Engineering Science
The University of Electro-Communications
Chofu, Tokyo, 182-8585 (Japan)
G
derivatives of such Mn12 species have been synthesized and
investigated.[11] Continuing effort is being devoted to the
synthesis and characterization of new polynuclear clusters
that display slow magnetic relaxation below a certain TB
and have potential practical applications. Although most of
the homometallic SMMs contain MnIII,[12] other metal ions
such as VIII,[13] FeIII,[14] CoII,[15] or NiII[5a,16] have also been
found to be very promising. In general, SMM behavior is
[c] M. L. Baker, H. Nojiri
Institute of Material Research, Tohoku University
Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan)
Supporting information for this article is available on the WWW
the [Ni3L3(OH)X]+ cations of 2 and 3, IR and electronic absorption
spectra of 1–3, magnetism data for 2 and 3, and CIF files.
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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