Article
Inorganic Chemistry, Vol. 48, No. 19, 2009 9403
molecule-based magnetic materials, transition metal com-
plexes with a coordinating cyano group have been a
major subject of intensive study.19-25 Nevertheless, in
contrast to the fact that there are a number of reports on
Mnþ(NtC-R)m-type molecule-based magnets, relatively
few studies have been reported regarding their isoelectro-
nic carbon analogues, the transition metal acetylides
Mnþ(CtC-R)mm-, because most of the transition metal
acetylides are easily decomposed under the existence of
oxygen or water.26-28 Recently, efforts to design new
transition metal acetylides have led to the development of
air- and water-stable paramagnetic acetylides,29-37 where
multidentate ligands protect the complexes from decom-
position. These stable transition metal acetylides show inter-
esting optical and electrochemical properties and strong
intramolecular spin-spin interactions and have consi-
derable promise as molecule-based bulk magnets. However,
to our knowledge, no attempt has succeeded in construct-
ing the molecule-based magnets by using transition metal
acetylides.
and weak-ferromagnet containing
acetylide.
a transition metal
In this paper, we report on the preparations, the crystal
structures, and the magnetic properties of the transition
metal acetylide based magnets. Among the several kinds of
stable transition metal acetylides, we employed the chro-
mium complex [CrCyclam(CtC-R)2]þ (R = 3-thiophene,
Ph; Cyclam= 1,4,8,11-tetraazacyclotetradecane) as a mag-
netic cation because its large magnetic moment (S=3/2) is
suitable for producing a strong intermolecular exchange
interaction and bringing a magnetic transition. Meanwhile,
the nickel dithiolate [Ni(mdt)2]- (mdt=1,3-dithiole-4,5-di-
thiolate) was used as a paramagnetic counteranion. Transi-
tion metal dithiolate anions are known to have a large
π-orbital perpendicular to the molecular plane, which en-
hances intermolecular orbital overlaps, resulting in the
strong intermolecular exchange interaction.38 The obtained
new materials, [CrCyclam(CtC-3-thiophene)2][Ni(mdt)2]
(1) and [CrCyclam(CtC-Ph)2][Ni(mdt)2](H2O) (2), are, as
far as the authors know, the first examples of a ferrimagnet
Experimental Section
Synthesis. [CrCyclam(CtC-Ph)2]OTf (OTf = trifluoro-
methanesulfonate) and (C4H9)4N[Ni(mdt)2] were prepared
according to literature methods.35,39-41 [CrCyclam(CtC-3-
thiophene)2]OTf H2O was synthesized by the same method
3
where 3-ethynylthiophene was used rather than phenylace-
tylene (yield: 55%, anal. calcd for C23H32Cr1F3N4O4S3: C,
43.59; H, 5.09; N, 8.84; S, 15.18%, Found: C, 43.22; H, 5.07;
N, 8.69; S, 14.99%). Thin plate crystals of 1 and small needle
crystals of 2 were precipitated by mixing a solution of
[CrCyclam(CtC-3-thiophene)2]OTf H2O or [CrCyclam-
3
(CtC-Ph)2]OTf (40 mg) in 1,2-dichloroethane (30 mL) with
a solution of (C4H9)4N[Ni(mdt)2] (40 mg) in chlorobenzene
(25 mL) within a day, where solvents were used without any
purification. In the case of 2, the yield can be increased by
adding a small portion of water, while the crystal size
becomes smaller. Typical crystal sizes are ca. 0.15 ꢀ 0.15 ꢀ
0.005 mm3 for 1 and 0.4 ꢀ 0.04 ꢀ 0.005 mm3 for 2.
(24) Miyasaka, H.; Madanbashi, T.; Sugimoto, K.; Nakazawa, Y.;
ꢀ
Wernsdorfer, W.; Sugiura, K.; Yamashita, M.; Coulon, C.; Clerac, R.
Single-Crystal X-ray Diffraction. X-ray diffraction measure-
ments were carried out on a Rigaku AFC-7R four-circle dif-
fractometer (fine focus type) with a Mercury CCD area detector
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at 293 K, using Mo KR radiation (λ = 0.7107 A). The structures
were solved using direct methods (SIR2004)42 then refined with
a full-matrix least-squares method (SHELXL-97).43 An absorp-
tion correction based on Ψ-scan was introduced. All non-
hydrogen atoms were refined anisotropically, while hydrogen
atoms were placed in their calculated positions and refined using
the riding model. Crystallographic data are summarized in
Table 1. Full bond lengths and bond angles, atomic coordinates,
and complete crystal structure results are provided as Support-
ing Information.
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Magnetic Susceptibility Measurements. DC and AC magnetic
susceptibilities were measured using
a Quantum-Design
MPMS-XL7 SQUID magnetometer for randomly oriented
single crystals encapsulated in aluminum capsules. Diamagnetic
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