Ferromagnetic S = 1 chain formed by a square Ni2S2 motif in Ni(qt)2 (qt = quinoline-8-thiolate). Magnetic properties of related compounds

Article abstract of DOI:10.1016/S0277-5387(01)00653-2

ML₂ complexes [M = Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺; L = quinolin-8-olate (q), quinoline-8-thiolate (qt)] were prepared and their magnetic properties were studied. X-ray crystal structure analysis of Ni(qt)₂ reveals that nickel(II) ions are arranged to form a one-dimensional structure with double thiolate bridges. Magnetic susceptibility measurements of Ni(qt)₂ indicate that the nickel S = 1 spins are ferromagnetically coupled within a chain. Other ML₂ showed antiferromagnetic interactions. Magnetic properties of molecular complexes of ML₂ with 7,7,8,8-tetracynanoquinodimethane (TCNQ) were also investigated. The crystal structure of Ni(qt)₂(TCNQ) was determined.

Full text of DOI:10.1016/S0277-5387(01)00653-2

Polyhedron 20 (2001) 1551–1555
www.elsevier.nl/locate/poly
Ferromagnetic S=1 chain formed by a square Ni2S2 motif
in Ni(qt)2 (qt=quinoline-8-thiolate).
Magnetic properties of related compounds
Takashi Miyake, Takayuki Ishida *, Daisuke Hashizume, Fujiko Iwasaki,
Takashi Nogami
Department of Applied Physics and Chemistry, The Uni6ersity of Electro-Communications, Chofu, Tokyo 182-8585, Japan
Received 17 September 2000; accepted 9 November 2000
Abstract
ML2 complexes [M=Fe2+, Co2+, Ni2+, Cu2+; L=quinolin-8-olate (q), quinoline-8-thiolate (qt)] were prepared and their
magnetic properties were studied. X-ray crystal structure analysis of Ni(qt)2 reveals that nickel(II) ions are arranged to form a
one-dimensional structure with double thiolate bridges. Magnetic susceptibility measurements of Ni(qt)2 indicate that the nickel
S=1 spins are ferromagnetically coupled within a chain. Other ML2 showed antiferromagnetic interactions. Magnetic properties
of molecular complexes of ML2 with 7,7,8,8-tetracynanoquinodimethane (TCNQ) were also investigated. The crystal structure of
Ni(qt)2(TCNQ) was determined. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Nickel(II) ion; Magnetic susceptibility; One-dimensional structure; Quinoline; TCNQ
1. Introduction
Recently there has been increased interest in the
studies on molecule-based magnetic metals [1–4]. We
examined the possibility of forming charge-transfer
(CT) complexes of paramagnetic ML2 [M=Mn2+
,
Fe2+, Co2+, Ni2+, Cu2+; L=8-quinolinolate (q), 8-
quinolinethiolate (qt)], since Cu(q)2 and Pd(q)2 were
reported to afford molecular complexes with 1,2,4,5-te-
tracyanobenzene (TCNB) [5]. Although their crystal
structures have been determined, their physical proper-
ties and those of their related compounds have not been
reported so far. ML2 complexes were easily obtained by
complexation of a metal dihalide with commercially
available qH or qtH·HCl. Their magnetic and electron-
donating properties were investigated. In the course of
our study, we have found that Ni(qt)2 has a nearly ideal
one-dimensional magnetic structure due to a unique
molecular assembly [6].
2. Experimental
Complexation with NiCl2·6H2O and 2 equiv. of
qtH·HCl in methanol gave Ni(qt)2 as a dark brown
powder (yield: 81%). Recrystallization of the product
from benzonitrile gave black needle-like crystals (m.p.
\300°C). The elemental analysis (C,H,N) satisfied the
formula Ni(qt)2. Fe(qt)2 and Cu(qt)2 were prepared
from FeCl2 and CuCl2·2H2O, respectively, in place of
NiCl2·6H2O, according to similar procedures. They
were obtained as a black and a brown powder, respec-
tively, and used directly for further analysis, since
Fe(qt)2 and Cu(qt)2 are practically insoluble in benzo-
* Corresponding author. Tel.: +81-424-43-5490; fax: +81-424-43-
5501.
E-mail address: ishi@pc.uec.ac.jp (T. Ishida).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00653-2

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T. Miyake et al. / Polyhedron 20 (2001) 1551–1555
Table 1
Curie constants and Weiss temperatures of M(q)2 and M(qt)2 measured at 5000 Oe
Compounds
Fe(q)2
Co(q)2
Ni(q)2
Cu(q)2
Fe(qt)2
Cu(qt)2
C (cm3 K mol−1
q (K)
)
3.23
−0.76
2.56
−12
1.28
−19
0.444
−0.71
4.76
−0.85
0.402
−2.3
nitrile, chloroform, or N,N-dimethylformamide. M(q)2
complexes (M=Fe, Co, Ni) were obtained by using qH
and the corresponding metal(II) chlorides in methanol
in the presence of catalytic amount of aqueous HCl [7].
M(q)2 (M=Fe, Co, Ni) were purified by recrystalliza-
tion from chloroform, giving a black, a brown, and a
light green powder, respectively. Cu(q)2 was purchased
from Tokyo Chemical Industry.
The molecular complex Ni(qt)2 with 7,7,8,8-tetracy-
nanoquinodimethane (TCNQ) was obtained by mixing
benzonitrile solutions containing Ni(qt)2 and TCNQ at
approximately 80°C, followed by standing at room
temperature for a month. Black platelet crystals were
precipitated and they were used for crystal structure
analysis and magnetic measurements. Molecular com-
plexes of M(q)2(TCNQ) (M=Co, Ni, Cu) were pre-
pared in chloroform, giving a green powder, a dark
green powder, and a black platelet crystalline product,
respectively.
dence of the product of magnetic susceptibility and
temperature (molT) for Ni(qt)2, measured at 500 Oe
[6]. With decreasing temperature, the molT value
monotonically increased and reached 5.07 cm3 K mol−1
at 1.8 K. Fig. 1(b) shows the magnetization curve
measured at 2.0 K. The magnetization largely exceeded
the Brillouin function of S=1. Thus the presence of
ferromagnetic interaction among the nickel(II) spins
was confirmed. No magnetic phase transition could be
found above 1.8 K.
The X-ray crystallographic analysis of Ni(qt)2 [6]
reveals a uniform one-dimensional molecular arrange-
ment. As Fig. 2 shows every nickel(II) ion is located at
an inversion center and is surrounded by two nitrogen
and two sulfur atoms at trans equatorial positions with
,
bond distances of 2.07 and 2.40 A for NiꢀN and NiꢀS,
respectively. Almost planar quinoline moieties are ar-
Elemental analysis (C,H,N) was done on a Fisons
EA-1108 by the usual combustion method. Cyclic
voltammetry was recorded on a BAS CV-50W in aceto-
nitrile with Ag/Ag+ as the reference electrode, Pt as the
working and counter electrodes and Bu4N+BF4− as
supporting electrolyte.
X-ray diffraction data of Ni(qt)2 and Ni(qt)2(TCNQ)
were collected with graphite monochromated Mo Ka
and Cu Ka radiations, respectively, on a Raxis-Rapid
IP diffractometer (Rigaku). The atomic positions were
directly solved with SIR92 [8] and refined with teXsan
[9] using all of the diffraction data.
Magnetic properties were measured on Quantum De-
sign MPMS and PPMS systems equipped with 7 and 9
T magnets, respectively. The diamagnetic contribution
of the sample itself was estimated from Pascal’s
constants.
3. Results and discussion
The magnetism of ML2, except for Ni(qt)2, simply
obeyed the Curie–Weiss law. The Curie constants and
Weiss temperatures are summarized in Table 1. The
Weiss temperatures in Table 1 are negative, indicating
the presence of antiferromagnetic interactions. On the
other hand, Fig. 1(a) shows the temperature depen-
Fig. 1. (a) Temperature dependence of the product molT for Ni(qt)2
measured at 500 Oe. The broken lines correspond to the calculated
curves based on Fisher’s equation with J/kB=11 and 3 K. (b)
Magnetization curve of Ni(qt)2 measured at 2.0 K. The Brillouin
functions of S=1, 2 and 10 are shown with broken lines.

T. Miyake et al. / Polyhedron 20 (2001) 1551–1555
1553
+794 K with g=2.27 by fitting to an analytical
expression for the magnetic susceptibility of an infinite
chain derived by Fisher [10].
The NiꢀSꢀNi angle in Ni(qt)2 is 94.3°, which is close
to 90°. The magnetic d orbitals of the S=1 nickel(II)
ion are assigned to be dx
and d . The geometry of
2
2
2
−y
z
the Ni2S2 unit favors a ferromagnetic superexchange
drawn as: dx
2ꢀp Þp ꢀd . The J value is compara-
2
2
y
z
ble to those of−syeveral oligoznuclear nickel(II) complexes
containing a cubane-like Ni4O4 core [11,12], in which
the NiꢀOꢀNi angles were designed to be a right angle.
Whereas several nickel(II) cluster complexes containing
a square Ni2S2 core have been reported, they were
diamagnetic in most cases [13,14]. Although uniform
one-dimensional nickel(II) systems showing antiferro-
magnetic interaction have been extensively studied in
connection with Haldane’s conjecture [15], those show-
ing a ferromagnetic interaction are rather limited in
halogen- [16–18] and pseudohalogen-bridged [19,20]
compounds. Thus, the complex Ni(qt)2 is the first ex-
ample of an S=1 ferromagnetic chain consisting of a
Ni2S2-type repeating motif.
Fig. 2. One-dimensional structure of Ni(qt)2. Ni and S atoms are
shaded. Selected bond lengths and angles are shown.
We examined the electron-donating properties of
ML2 by means of cyclic voltammetry. The cyclic
voltammograms of Co(q)2, Ni(q)2, Cu(q)2, Co(qt)2, and
Ni(qt)2 exhibited irreversible anodic peaks at 0.68, 0.67,
0.67, 0.51 and 0.28 V, respectively (in CH3CN; refer-
ence electrode — Ag/Ag+; scan rate — 100 mV s−1).
Their electron-donating abilities are confirmed. In par-
ticular, Ni(qt)2 is a relatively strong donor, and this
finding may be responsible for a different D/A ratio (D
and A denote donor and acceptor molecules, respec-
tively) in complexation with TCNQ as described below.
Molecular complexes of ML2 with TCNQ were ob-
tained in chloroform or benzonitrile. The elemental
analysis revealed
a
D/A ratio of 1:2 for
Co(q)2(TCNQ)2, Ni(q)2(TCNQ)2 and Cu(q)2(TCNQ)2.
On the other hand, Ni(qt)2 and TCNQ gave black
polycrystals, whose D/A composition of 1:1 was deter-
mined by means of X-ray crystal structure analysis.
The crystal of Ni(qt)2(TCNQ) belongs to a triclinic
space group P1 and the cell parameters are a=
Fig. 3. (a) ORTEP drawing of Ni(qt)2(TCNQ) at the 50% probability
level. Atomic numbering is also shown for non-hydrogen atoms. (b)
Molecular arrangement of Ni(qt)2 and TCNQ moieties in the crystal
of Ni(qt)2(TCNQ).
ranged to construct a column along the a axis. The
sulfur atom in a qt anion is deviated from the averaged
quinoline plane toward a neighboring Ni ion, in which
the axial coordination is found with a NiꢀS distance of
,
8.7345(7), b=9.7142(6), c=8.0982(8) A, h=
106.1392(2), i=100.058(3) and k=76.333(3)°. The
molecular structure of Ni(qt)2(TCNQ) is shown in Fig.
3(a). The Ni(qt)2 and TCNQ moieties are highly planar.
The nickel(II) ion is surrounded by two sulfur and two
nitrogen atoms at the trans equatorial sites with bond
,
2.60 A. The angles of SꢀNiꢀS and NiꢀSꢀNi are 85.6
and 94.4°, respectively. All of the Ni2S2 units are copla-
nar within a chain. The shortest inter-chain Ni···Ni
,
lengths of 2.175(1) and 1.913(4) A, respectively, which
,
distance is 9.85 A, which is much longer than the
are remarkably shorter than those of thiolate-bridged
Ni(qt)2 (Fig. 2). The molecular arrangement of Ni(qt)2
and TCNQ moieties is shown in Fig. 3(b). The molecu-
lar planes of Ni(qt)2 and TCNQ are parallel to each
other in a mixed stack with a rather short inter-plane
,
shortest intra-chain distance (3.67 A). There is no ap-
preciable contact between chains. Therefore the crystal
of Ni(qt)2 has almost an ideal one-dimensional struc-
ture. The observed ferromagnetic interaction is due to
the intra-chain interaction. We can estimate J/kB=
,
distance of approximately 3.35 A.

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T. Miyake et al. / Polyhedron 20 (2001) 1551–1555
Table 2
5. Supplementary material
Curie constants and Weiss temperatures of M(q)2(TCNQ)2 measured
at 5000 Oe
Crystallographic data (excluding structure factors)
for the structures of Ni(qt)2 and Ni(qt)2(TCNQ) have
been deposited with the Cambridge Crystallographic
Data Center, CCDC Nos 151618 and 151608, respec-
tively. Copies of this information can be obtained free
of charge on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Compounds
Co(q)2(TCNQ)2 Ni(q)2(TCNQ)2 Cu(q)2(TCNQ)2
C (cm3 K mol−1
q (K)
)
2.53
−1.4
1.60
−13
0.547
−0.98
In order to estimate degree of CT, the detailed
structure of the TCNQ moiety in Ni(qt)2(TCNQ) is
stated briefly. The bond lengths of C12ꢀC13,
C10ꢀC12*, C11ꢀC12 and C10ꢀC11 are 1.371(8),
Acknowledgements
,
1.446(8), 1.437(9) and 1.341(9) A, respectively. These
values are close to the corresponding values of neutral
TCNQ [21] rather than TCNQ− [22]. Thus, it is con-
cluded that Ni(qt)2(TCNQ) is a neutral p-complex, and
the magnetic interaction between the nickel(II) ions is
expected to be small due to an intervening TCNQ
molecule.
This work was supported by Grants-in-Aid for Scien-
tific Research (401/11136212, 730/11224204 and 297/
12020219) from the Ministry of Education, Science,
Sports and Culture, Japan.
The magnetic susceptibilities of M(q)2(TCNQ)2
(M=Co2+, Ni2+, Cu2+) are found to obey the
Curie–Weiss law. Dominant antiferromagnetic interac-
tions were observed, as indicated by the negative Weiss
temperatures (Table 2). Preliminary results on the mag-
netism of Ni(qt)2(TCNQ) also suggest the presence of a
weak antiferromagnetic interaction.
References
[1] T. Otsuka, A. Kobayashi, Y. Miyamoto, J. Kiuchi, N. Wada, E.
Ojima, H. Fujiwara, H. Kobayashi, Chem. Lett. (2000) 732.
[2] H. Kobayashi, A. Sato, H. Tanaka, A. Kobayashi, P. Cassoux,
Coord. Chem. Rev. 190 (1999) 921.
McConnell proposed a model for ferromagnetic spin
alignment using ionic CT salts [23]. In a normal mixed-
stack of CT solids, intermolecular spin pairing is the
result of the mixing of the ground state (D+A−) and a
singlet back-CT state of a DA pair. McConnell applied
this to a DA system where the neutral D (or A) is a
triplet molecule, and proposed that if an ionic CT pair
having a back-CT excitation to a neutral triplet state
could be built, then the D+A− pair could also be a
triplet, owing to mixing of the CT state with the neutral
state. Triplet or higher multiplet donor molecules are
required along this approach to CT-based ferromag-
nets. In the present study the degree of CT of
Ni(qt)2(TCNQ) is not sufficient for realizing the Mc-
[3] M. Clemente-Leon, E. Coronado, J.R. Galan-Mascaros, C.J
Go´mez-Garcia, C. Rovira, V.N. Laukhin, Synth. Met. 103
(1999) 2339.
[4] E. Coronado, J.R. Gala´n-Mascaro´s, C.J. Go´mez-Garcia, V.
Laukhin, Nature 408 (2000) 447.
[5] (a) P. Murray-Rust, J.D. Wright, J. Chem. Soc. (A) (1968) 247.
(b) B. Kamenar, C.K. Prout, J.D. Wright, J. Chem. Soc. (A)
(1966) 661.
[6] T. Miyake, T. Ishida, D. Hashizume, F. Iwasaki, T. Nogami,
Chem. Lett. (2000) 952.
[7] A.S. Bailey, R.J.P. Williams, J.D. Wright, J. Chem. Soc. (1965)
2579.
[8] A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C. Giaco-
vazzo, A. Guagliardi, G. Polidori, J. Appl. Crystallogr. 27 (1994)
435.
[9] Crystal Structure Analysis Package, Molecular Structure Corpo-
ration, 1985, 1999.
[10] M.E. Fisher, Am. J. Phys. 32 (1964) 343.
[11] J.A. Barnes, W.E. Hatfield, Inorg. Chem. 10 (1971) 2355.
[12] A. Escuer, M. Font-Bard´ıa, S.B. Kumar, X. Solans, R. Vicente,
Polyhedron 18 (1999) 909.
.
Connell model. Complexation with stronger acceptors
such as F4TCNQ is now under way.
[13] G.R. Brubaker, J.C. Latta, D.C. Aquino, Inorg. Chem. 9 (1970)
2608.
[14] T.B. Rauchfuss, D.M. Roundhill, J. Am. Chem. Soc. 97 (1975)
3386.
4. Summary
The ferromagnetic interaction of Ni(qt)2 has been
clarified to be operative within a linear chain structure
having a repeating motif of Ni2S2. Other complexes
ML2 obtained here showed antiferromagnetic interac-
tions. Their TCNQ complexes [Co(q)2(TCNQ)2,
Ni(q)2(TCNQ)2, Cu(q)2(TCNQ)2, and Ni(qt)2(TCNQ)]
were prepared.
[15] F.D.M. Haldane, Phys. Rev. Lett. 50 (1983) 1153.
[16] C. Dupas, J.-P. Renard, J. Chem. Phys. 61 (1974) 3871.
[17] F.W. Klaaijsen, Z. Dokoupil, W.J. Huiskamp, Physica 79B
(1975) 547.
[18] W.E. Estes, R.R. Weller, W.E. Hatfield, Inorg. Chem. 19 (1980)
26.
[19] P. Chaudhuri, T. Weyhermuller, E. Bill, K. Wieghardt, Inorg.
Chim. Acta 252 (1996) 195 (and references cited therein).

T. Miyake et al. / Polyhedron 20 (2001) 1551–1555
1555
[20] A. Escuer, R. Vicente, M.S. El Fallah, X. Solans, M. Font-Bar-
d´ıa, J. Chem. Soc., Dalton Trans. (1996) 1013.
[21] R.E. Long, R.A Sparks, K.N. Trueblood, Acta Crystallogr. 18
(1965) 932.
[22] M. Konno, Y. Saito, Acta Crystallogr., Sect. B 30 (1974)
1294.
[23] H. McConnell, Proc. Robert A. Welch Found. Conf. Chem. Res.
11 (1967) 144.
.