Discrete polynuclear manganese nanorods: Syntheses, crystal structures and magnetic properties

Article abstract of DOI:10.1039/c4ra07015a

Shape-anisotropic nanomaterials with uniform lengths and widths have attracted much interest but few of them are involved in self-assembled manganese complexes. The combination of two redox-active acylthiosemicarbazide ligands with Mn³⁺cations leads to two discrete polynuclear Mn nanorods, pentanuclear [Mn₅(L3)₆][Mn_0.7(DMF)_1.4(H₂O)_2.8] (1a) and trinuclear Mn₃(L4)₃·2DMF (2), whose L3 and L4 represent N-(5-(2-hydroxyphenyl)-1,3,4-oxadiazol-2-yl)benzamide and N-(5-(2-hydroxyphenyl)-1,3,4-oxadiazol-2-yl)-propionamide, respectively, which are in situ synthesized from their acylthiosemicarbazide derivatives in the presence of Mn³⁺cations, while the latter are reduced into divalent ones in rod-like moieties. For each pentanuclear anion in 1a, the charge is balanced by a solvated trivalent manganese cation, which can be replaced by two tetramethylammonium cations to yield pure valence compound 1b. Moreover, the magnetic studies reveal all of them possess antiferromagnetic properties. This journal is

Full text of DOI:10.1039/c4ra07015a

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Discrete polynuclear manganese nanorods:
syntheses, crystal structures and magnetic
Cite this: RSC Adv., 2014, 4, 40958
properties†
a
a
a
ab
a
*
*
Chang-Cang Huang
Jian-Jun Liu, Yao Wang, Shu-Ting Wu, Mei-Jin Lin,
and Wen-Xin Daia
Shape-anisotropic nanomaterials with uniform lengths and widths have attracted much interest but few of
them are involved in self-assembled manganese complexes. The combination of two redox-active
acylthiosemicarbazide ligands with Mn3+ cations leads to two discrete polynuclear Mn nanorods,
pentanuclear [Mn5(L3)6][Mn0.7(DMF)1.4(H2O)2.8] (1a) and trinuclear Mn3(L4)3$2DMF (2), whose L3 and L4
represent N-(5-(2-hydroxyphenyl)-1,3,4-oxadiazol-2-yl)benzamide and N-(5-(2-hydroxyphenyl)-1,3,4-
oxadiazol-2-yl)-propionamide,
respectively,
which
are
in
situ
synthesized
from
their
acylthiosemicarbazide derivatives in the presence of Mn3+ cations, while the latter are reduced into
divalent ones in rod-like moieties. For each pentanuclear anion in 1a, the charge is balanced by a
solvated trivalent manganese cation, which can be replaced by two tetramethylammonium cations to
yield pure valence compound 1b. Moreover, the magnetic studies reveal all of them possess
antiferromagnetic properties.
Received 12th July 2014
Accepted 26th August 2014
DOI: 10.1039/c4ra07015a
www.rsc.org/advances
attributed to their highly redox activities during crystallizations.
To prevent forming the mixed complexes with mixed valences
Introduction
that are difficult crystallized, redox-active organic ligands are
suggested to be used.
One-dimensional magnetic nanomaterials (nanorods and
nanowires) have attracted much interest in the past decades
due to their potential applications in molecular switches,1 data-
storage devices,2 site-specic drug release.3 The shape anisot-
ropy in one-dimensional nanostructures can result in a signif-
icantly increased coercivity, which can be tuned by adjusting the
aspect ratio.4 However, synthetic challenges remain in creating
such one-dimensional magnetic nanomaterials with uniform
lengths and widths, which limits their scope for applications.
Supramolecular self-assembly is an emerging method for the
synthesis of nanostructures.5 In the past decades, a great variety
of polynuclear rod-like complexes of transition metals,
including cobalt, nickel, copper and iron, have been prepared,
and their shape-dependent properties evaluated.6 Manganese,
divalent or trivalent cation, contains an unpaired electron in
their complexes, which makes it an ideal candidate for
magnetic materials.7 To our surprise, so far only few examples
involved in manganese rod-like complexes,8 which may
Acylthiosemicarbazide derivatives are an attractive class of
multidentate ligands for the polynuclear complexes.9 At the
same time, they are also redox-active compounds.10 According
to the literature reported by Li and coworkers,11 the acylth-
iosemicarbazide derivatives can undergo a ring closure process
to form 2-amino-1,3,4-oxadiazole derivatives in the presence of
metal oxidants. Thus, we selected such redox-active acylth-
iosemicarbazide as the parent core for our organic ligands. To
increase their coordination dentations, the 2-hydroxyl phenyl
and the second acyl groups have been incorporated into the
acylthiosemicarbazide core, which is anticipated to afford the
tetradentate oxadiazol ligands aer the ring closure reactions.
Analysis of the formed oxadiazol ligands reveals they can at least
chelate with three manganese cations on the same line
(Scheme 1). Herein, we indeed report two novel discrete poly-
nuclear manganese nanorods (1a and 2) by combining trivalent
manganese cations with two acylthiosemicarbazide ligands,
N-(2-(2-hydroxybenzoyl)hydrazinecarbonothioyl)benzamide
aCollege of Chemistry, Fuzhou University, 350116, China. E-mail: meijin_lin@fzu.edu.
cn; cchuang@fzu.edu.cn; Tel: +86 591 2286 6143
(L1)
and
N-(2-(2-hydroxybenzoyl)hydrazine-carbonothioyl)
bState Key Laboratory of Structural Chemistry, Fujian Institute of Research on the
propionamide (L2), respectively. In both nanorods, the
manganese cations are reduced into the divalent ones, while the
later ligands have transformed into their oxadiazol derivatives
(L3 and L4) through a ring closure reaction in the presence of
the oxidizer trivalent manganese cations. Interestingly, the
complex 1a bearing pentanuclear anionic nanorods is a mixed
Structure of Matter, CAS, 350002, China
† Electronic supplementary information (ESI) available: The detailed single
crystal structures, characterization of L1 and L2, PXRD and bond length lists of
complex of 1a, 1b and 2 as well as HRMS. CCDC 1009186–1009188. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c4ra07015a
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DMSO-d6, ppm): d ¼ 13.72 (s, 1H), 12.00 (s, 1H), 11.96 (s, 1H),
11.88 (s, 1H), 8.02–7.00 (m, 9H). IR (KBr disk, n cmꢂ1): 3410 (m),
3200 (m), 2950 (m), 1670 (s), 1523 (s), 1487 (m), 1280 (s), 1232
(m), 812 (s), 675 (m). HRMS (ESIꢂ) m/z calculated for
C
15H13N3O3S: 315.07; found: 314.06.
Synthesis of L2. L2 was prepared in a similar procedure as L1
by replacing benzoyl chloride with propionyl chloride. Yield:
70%. 1H NMR (400 MHz, DMSO-d6, ppm): d ¼ 13.41 (s, 1H),
11.85 (s, 2H), 11.66 (s, 1H), 7.97–7.00 (m, 4H), 2.47 (q, J ¼ 8 Hz
2H), 1.06 (t, J ¼ 8 Hz, 3H). IR (KBr disk, n cmꢂ1): 3386 (w), 3262
(w), 3115 (s), 2982 (w), 1694 (s), 1622 (s), 1528 (m), 1474 (s), 1440
(s), 1203 (s), 1154 (s), 750 (s). HRMS (ESIꢂ) m/z calculated for
Scheme 1 The in situ syntheses of oxadiazole ligands from their
acylthiosemicarbazide derivatives in the presence of Mn3+. For clear
explanation, a possible coordination pattern of such oxadiazole ligands
is given.
C
11H13N3O3S: 267.07; found: 266.06.
Synthesis of 1a. A portion of Mn(acac)3 (0.071 mg, 0.2 mmol)
valence compound possessing a black appearance, whose
solvated trivalent manganese counter-cations can be replaced
by tetramethylammonium cations to generate a yellow pure
valence compound 1b.
and L1 (0.032 g, 0.1 mmol) were dissolved in 10 mL DMF, a drop
of triethylamine was added and the solution was stirred for 3 h
at room temperature. The resulting dark solution was ltered
and the ltrate was le to stand at room temperature for about
one month, during which time black crystals were produced in
25% yield based on Mn. Selected IR (KBr, cmꢂ1): 3150 (w), 2978
(w), 1650 (s), 1603 (s), 1484 (m), 1434 (m), 1265 (m), 1054 (m),
746 (s), 678 (s).
Synthesis of 1b. A portion of 1a (0.230 g, 0.10 mmol) and
tetramethylammonium chloride (0.109 g, 1 mmol) were dis-
solved in 5 mL DMF, and the clear solution was allowed to stand
at ambient temperature for 10 days to give yellow single crystals
of 1b. Selected IR (KBr, cmꢂ1): 3342 (w), 3187 (m), 2985 (m),
1673 (s), 1625 (s), 1497 (m), 1454 (s), 1273 (m), 1158 (m), 745 (s),
665 (m).
Synthesis of 2. A portion of Mn(acac)3 (0.071 mg, 0.2 mmol)
and L2 (0.027 g, 0.1 mmol) were dissolved in 10 mL DMF, a drop
of triethylamine was added and the solution was stirred for 3 h
at room temperature. The resulting dark solution was ltered
and the ltrate was le to stand at room temperature for about
one month, during which time yellow crystals were produced in
18% yield based on Mn. Selected IR (KBr, cmꢂ1): 3248 (w), 3154
(w), 3052 (m), 2992 (m), 2948 (m), 2875 (w), 1666 (m), 1607 (s),
1558 (s), 1509 (s), 1484 (s), 1405 (s), 1332 (m), 1268 (s), 1096 (m),
973 (w), 860 (m), 752 (m), 614 (w).
Experimental
Materials and measurements
N,N0-Dimetbylformamide (DMF, 99%), benzoyl chloride (99%),
propionyl chloride (99%), potassium thiocyanate (analytical
reagent grade), acetonitrile (analytical reagent grade), diethyl
ether (analytical reagent grade), salicylhydrazide (99%), triethyl-
amine (analytical reagent grade), tetramethylammonium chlo-
ride (98%) and manganese(III) acetylacetonate (Mn(acac)3, 98%)
were obtained from commercial suppliers. All chemicals and
reagents were used as received unless otherwise stated. 1H NMR
spectra were recorded with a Bruker Avance 400 MHz NMR
spectrometer. Chemical shis are given in parts per million
1
(ppm) and referred to TMS as internal standard. H coupling
constants J are given in Hertz (Hz). Powder X-ray diffraction
(PXRD) intensities were recorded on a Rigaku MiniFlex-II X-Ray
˚
diffractometer with Cu Ka radiation (l ¼ 1.5406 A) in the
angular range of 2q ¼ 5–50ꢀ at 293 K. Mass spectra were
recorded on a Thermo Fisher Scientic LCQ Fleet system. High-
resolution mass spectra (HRMS) were acquired on the Thermo
Scientic Exactive Plus Mass spectrometer equipped with an
electrospray ionization (ESI) source. Magnetic susceptibility
measurements for 1a and 1b were carried out on a Quantum
Design MPMS XL7 SQUID magnetometer in the 2–300 K
temperature range under magnetic eld of 5000 Oe. Magnetic
susceptibility data for 2 were collected over the temperature
range of 2–300 K in magnetic eld of 1000 Oe on a MPMS
(SQUID)-XL magnetometer.
X-ray diffraction analysis
Suitable single crystals of 1a, 1b and 2 were mounted on glass
bers for the X-ray measurement. Diffraction data were
collected on a Rigaku-AFC7 equipped with a Rigaku Saturn CCD
area-detector system. The measurement was made by using
˚
graphic monochromatic Mo Ka radiation (l ¼ 0.71073 A) at 113
K under a cold nitrogen stream. The frame data were integrated
and absorption correction using a Rigaku CrystalClear program
Synthesis
Synthesis of L1. Under the argon, benzoyl chloride (1.41 g, package.12 All calculations were performed with the SHELXTL-
10.0 mmol) was added to a solution of potassium thiocyanate 97 program package,13 and structures were solved by direct
(1.46 g, 15 mmol) in acetonitrile (30 mL), and the mixture was methods and rened by full-matrix least-squares based on F2.
stirred for 3 hours at 70 ꢀC, and then ltered affording a yellow The non-hydrogen atoms were rened anisotropically. The
ltrate. A portion of salicylhydrazide (1.52 g, 10.0 mmol) was hydrogen atoms were located by geometrical calculations except
added to the ltrate, and then further stirred for 3 hours at 70 ꢀC for those on the water molecules which were located from the
to give a white precipitate, which was collected and rinsed with difference Fourier syntheses. For the 1a and 1b, some included
diethyl ether (2 ꢁ 30 mL). Yield: 85%. 1H NMR (400 MHz, solvents were disorder and thus their contributions were
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Table 1 Crystal data and structure refinement parameters for 1a, 1b, and 2a,b
Complexes
1a
1b
2
Crystal size (mm)
Empirical formula
Formula weight
Crystal system
Space group
0.38 ꢁ 0.25 ꢁ 0.20
0.35 ꢁ 0.26 ꢁ 0.24
C98H78Mn5N20O18
2098.50
Monoclinic
P21/c
11.879(2)
31.352(6)
16.426(3)
90
0.23 ꢁ 0.18 ꢁ 0.15
C39H47Mn3N11O14
1058.70
Monoclinic
P21/c
11.609(2)
21.154(4)
18.246(4)
90
100.68(3)
90
4403.4(15)
4
C94.2H69.4Mn5.7 N19.4O22.8
2151.05
Monoclinic
P21/c
12.205(2)
33.209(7)
14.952(3)
90
94.15(3)
90
6045(2)
2
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
g (ꢀ)
94.25(3)
90
6101(2)
3
˚
V (A )
Z
2
Dc (g cmꢂ3
)
1.182
0.644
2191
1.142
0.566
2150
1.597
0.927
2180
m(Mo Ka) (mmꢂ1
F(000)
)
Collected reections
Independent reections
Goodness-of-t on F2
R1a, wR2b (I > 2s(I))
R1a, wR2b (all data)
48 925
13760
1.098
0.0924, 0.2551
0.1132, 0.2740
42 602
10 702
1.107
0.0728, 0.1832
0.0885, 0.1932
36833
10073
1.219
0.0639, 0.1147
0.0737, 0.1186
a
b
2
R1 ¼ S||Fo| ꢂ |Fc||/S|Fo|. wR2 ¼ [Sw(Fo ꢂ Fc2)2/Sw(Fo2)]1/2
.
subtracted from the data using SQUEEZE from the PLATON and L1 at ambient temperature. The single crystal X-ray
package of crystallographic soware (Table 1).14
diffraction analysis revealed that it is crystallized in the mono-
clinic space group P21/c. In the crystalline 1a, each smallest
repetitive unit contains one pentanuclear Mn anion and one
solvated Mn cation with around 70% occupancy. In the penta-
nuclear anionic parts, each Mn cation adopts a distorted octa-
hedral coordination geometry to coordinate with three L3
ligands arranged along the same direction in a helical pattern
through the formation of Mn–O or Mn–N bonds with a distance
Results and discussions
Synthesis
As mentioned above, acylthiosemicarbazide derivatives have
been reported to be cyclized into their corresponding oxadiazoles
by metal or metal-free oxidants at elevated temperatures. Indeed,
in our case, the organic ligands L1 and L2 are oxidized into
oxadiazole building blocks L3 and L4 in the presence of Mn3+ to
yield the nal polynuclear nanorods whose manganese are
reduced into divalent cations (for details, see the single-crystal
structural description part in the following). The formation of
oxadiazole building blocks as well as polynuclear nanorods is
conrmed by the high-resolution mass spectral studies. For
example, the HRMS of 1a in N,N-dimethylformamide at 293 K
shows a divalent anionic m/z peak at 975.04 and monovalent
anionic m/z peak at 1950.08 (Fig. S5, ESI†), which correspond to
theoretical distributions of polynuclear rod-like [Mn5(L3)6]2ꢂ and
[Mn5(L3)6]ꢂ anions. It is also worthy pointing out that such in situ
synthesis of oxadiazole ligands is supposed to play a key role in
the formation of the nal crystalline products since no target
crystalline materials were obtained by the direct combination of
L3 or L4 with Mn2+ or Mn3+. Moreover, the addition of a catalytic
amount of triethylamine to crystallization solutions is to facilitate
deprotonation of acylthiosemicarbazide derivatives during cycli-
zation reactions.
˚
˚
in the range 2.13–2.18 A and 2.21–2.25 A. Alternatively, each L3
ligand interconnects three Mn cations to form a [Mn2(L3)3]
dinuclear unit, which is self-coupled in a head–head model to
yield the nal pentanuclear clusters by sharing one Mn cation
˚
(Mn1) through Mn–O bonds (dMn–O ¼ 2.16–2.18 A) between
Mn1 and O atoms from phenolate groups of oxadiazole building
block L3. In pentanuclear clusters, the distances of Mn1 and
˚
Mn2, Mn2 and Mn3 are around 3.03 and 4.01 A, respectively,
while the angle of Mn1–Mn2–Mn3 is around 179.3ꢀ, which
indicates the clusters is rod-like. Interestingly, the size of such
rod-like polynuclear clusters is within the range of the nano-
meter, thus they are nanorods. Considering all the bond lengths
of Mn–N and Mn–O bonds fall in the range of those for the
divalent Mn cations, a conjecture can be drawn that all the Mn
cations in the pentanuclear rod-like anions are divalent. As a
result, the charges of the whole rod-like anions are divalent.
Indeed, the anionic nature of such pentanuclear nanorods is
supported by the coexistence of solvated Mn cations in crystals
(Fig. 1). For the cationic moieties, each Mn cation (Mn4) is
surrounded by four O atoms from four crystalline waters in the
square plane and two carbonyl O atoms from two DMF mole-
cules in the axial directions. Around 70% occupancy observed in
X-ray diffraction for the solvated Mn cation indicates that their
Single-crystal structural descriptions
Single crystals of 1a suitable for X-ray diffraction analysis were
obtained by slow evaporation of a DMF solution of Mn(acac)3
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Fig. 1 Side view of the crystal structure of 1a (a), as well as top view of the molecular structure of 1a (b) (magenta Mn, blue N, red O, and black C).
H atoms have been omitted for clarity.
Fig. 2 Side view of the crystal structure of 1b (a), as well as top view of the molecular structure of 1b (b) (magenta Mn, blue N, red O, and black C).
H atoms have been omitted for clarity.
Mn cations are trivalent, which is conrmed by the black that complex 2 is also crystallized in the monoclinic space group
appearance of crystal 1a and the further experiment that each P21/c, only one neutral trinuclear cluster composed of three Mn
solvated Mn cation can be replaced by two monovalent tetra- cations, three L4 ligands, three coordinated water and two free
methylammonium cations (see below).
DMF molecules have been observed. From the yellow appear-
In general, the complex of Mn2+ is light color (yellow), ance of crystalline 2 (Fig. S12, ESI†), the Mn cations are
however, 1a is black. This may be attributed to the Mn4 is a supposed to be divalent. Similar as those in 1a and 1b, each
trivalent cation in solvated Mn cations, which rstly can be Mn2+ cation in crystal 2 also adopting a distorted octahedral
deduced from their bond lengths and angles. In order to coordination geometry, is saturated by three O atoms and three
conrm our deduction, colourless tetramethylammonium N atoms, or six O atoms from three L4 ligands through Mn–O or
˚
˚
chloride was selected as a proof-of-concept cation to replace the Mn–N bonds (dMn–O ¼ 2.14–2.19 A and dMn–N ¼ 2.22–2.27 A)
aforementioned solvated Mn4 cations owing to its close struc- (Fig. 3). In other words, three L4 ligands arrange along the same
tural sizes. Co-crystallization of complex 1a with tetramethyl- direction to bridge three Mn2+ cations to form a pinwheel-like
ammonium chloride in DMF resulted in yellow prismatic trinuclear coordination rod with a size close to 1 nm, where
crystals of 1b aer several days (Fig. S12, ESI†). Single-crystal X-
ray diffraction analysis reveals that the anionic pentanuclear
rod-like units in crystalline 1b remain their structural features
as in 1a. However, the counter-cation of solvated Mn4 moieties
are indeed replaced by two tetramethylammonium cations
(Fig. 2), which corroborates our conjecture that the rod-like
pentanuclear Mn nanorods are divalent anions, while the Mn
cations in the solvated Mn4 units are +3 valence.
When the benzamide group in acylthiosemicarbazide ligand
L3 is replaced by a exible propionamide unit, similar combi-
nation of L4 with Mn(acac)3 under the same conditions affords
the yellow crystalline materials 2 suitable for X-ray diffraction
analysis. Although the single crystal structural analysis revealed
Fig. 3 Side view of the crystal structure of 2 (a), as well as top view of
the molecular structure of 1a (b) (magenta Mn, blue N, red O, and black
C). H atoms have been omitted for clarity.
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the distances between the neighboring two Mn2+ cations are
The variable-temperature magnetic susceptibility of crystal-
˚
˚
around 3.02 A and 4.06 A, respectively, and the angle of three line 2 was investigated in the range of 2.0–300 K with a 1 kOe
Mn2+ cations (Mn1–Mn2–Mn3) is ca. 177.6ꢀ. Different from 1a, appliedꢂ1eld. The magnetic properties of 2 in the form of cMT
the le three coordination sites of the Mn1 cation that inter- and cM versus T plots are shown in Fig. 4c. At room temper-
connects with three phenolate O atoms are terminated by three ature, cMT is equal to 13.06 cm3 K molꢂ1, which is close to
O atoms from three water molecules. As a result, these trinu- theoretical value for three non-interacting Mn2+ with S ¼ 5/2
clear clusters cannot further be self-coupled to generate higher (13.125 cm3 K molꢂ1 with g ¼ 2.0). The cMT value decreases
nuclear rod-like complexes.
gradually from room temperature to 11.16 cm3 K molꢂ1 at 100 K
and then sharply to 5.01 cm3 K molꢂ1 at 2 K. The above data
were tted with Curie–Weiss law with C ¼ 14.28 cm3 K molꢂ1
and q ¼ ꢂ28.28 K, which indicates antiferromagnetic coupling
between Mn cations in 2. By analyzing the magnetism of
complexes 1a, 1b, and 2, we can conclude that these compounds
are antiferromagnetic coupling between Mn2+ cations. Similar
magnetic phenomena have already been observed linear poly-
nuclear complex with Mn2+ cations.15
Magnetic properties
The magnetic measurements were carried out using a crystal-
line sample, whose phase purity was conrmed by powder X-ray
diffraction (Fig. S6–S8, ESI†). The temperature-dependent
magnetic susceptibility of crystalline 1a and 1b were investi-
gated in the range of 2.0–300 K with a 5 kOe applied eld (Fig. 4a
and b). The magnetization versus eld plot at 2.0 K is depicted in
Fig. S13.† The cMT product of 1a at 300 K is 22.96 cm3 K molꢂ1
,
which is slight lower than that for 0.7 Mn3+ (SMn3+ ¼ 2) and ve
Mn2+ (SMn2+ ¼ 5/2) cations magnetically noninteracting (cMT ¼
23.975 cm3 K molꢂ1 with g ¼ 2.0). With decreasing temperature,
the cMT value decreases slowly and reaches 14.88 cm3 K molꢂ1
at 10 K, aer which it drops abruptly to a minimum value of
10.40 cm3 K molꢂ1 at 2.0 K. The temperature dependence of
molar susceptibility in the temperature range 50–300 K is well
tted by the Curie–Weiss law with C ¼ 24.58 cm3 K molꢂ1 and q
Conclusions
In conclusion, we have demonstrated that the combination of
two redox-active acylthiosemicarbazide ligands with trivalent
manganese cations results in two discrete polynuclear manga-
nese nanorods, whose organic building blocks are oxadiazol
derivatives that are in situ synthesized from the added acylth-
iosemicarbazide ligands via a ring closure reaction in the
presence of the oxidants trivalent manganese cations, while the
latter are reduced into divalent ones in rod-like moieties. For
the pentanuclear complex, the rod-like anions are balanced by
the solvated trivalent manganese cations, which can be replaced
by tetramethylammonium cations to generate a pure valence
compound. In addition, the magnetic studies reveal all of three
complexes possess antiferromagnetic properties, which may
nd applications in various directions.
¼
ꢂ20.50
K which indicates antiferromagnetic coupling
between Mn cations.
For complex 1b, the magnetic behavior upon cooling is
slightly different from complex 1a. Value of cMT at 300 K is
21.19 cm3 K molꢂ1, which is a bit smaller than expected for ve
non-interacting Mn(II) with S ¼ 5/2 (21.875 cm3 K molꢂ1). The
decline slope for cMT ꢃ T curve of complex 1b in the range of
300 K to 10 K is similar to complex 1a. A minimum cMT value
ꢂ1
(8.44 cm3 K molꢂ1) exists at 2 K. Curve of cM vs. T follows
Curie–Weiss law above 50 K, with Curie constant C ¼ 22.94 cm3
K molꢂ1 and Weiss constant q ¼ ꢂ26.08 K, which indicates the
antiferromagnetic property of complex 1b.
Acknowledgements
We thank Prof. Jun-Dong Wang and Prof. Xin Fang for their
useful discussions. This work has been supported by National
Natural Science Foundation of China (21202020, 21273037),
Doctoral Fund of Ministry of Education of China
(20123514120002), Natural Science Foundation of Fujian Prov-
ince (2014J01040 and 2014J01045), and Science & Technical
Development Foundation of Fuzhou University (2012-XQ-10 and
2013-XQ-14).
Notes and references
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T. Nakamura, M. Matsumoto and H. Shigekawa, J. Am.
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Fig. 4 Temperature dependence curves cMT vs. T (-) and cMꢂ1 vs. T
(C) for complex 1a (a), 1b (b) and 2 (c).
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