Inorganica Chimica Acta 359 (2006) 3790–3794
www.elsevier.com/locate/ica
Note
Two-dimensional cyanide-bridged heterobimetallic complexes based on
CpCoðCNÞ3: Syntheses, structures and magnetic properties
Zhi-Guo Gu a, Qiao-Fang Yang a, Jing-Lin Zuo a,*, Xi-Rui Zeng b,
Hong-Cai Zhou c, Xiao-Zeng You a,*
a
Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, Nanjing University,
Nanjing 210093, PR China
b
Department of Chemistry, Jinggangshan Normal College, Jian 343009, PR China
c
Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056-1465, USA
Received 14 July 2005; received in revised form 4 January 2006; accepted 16 January 2006
Available online 2 March 2006
Dedicated to D.M.P. Mingos.
Abstract
Using the half-sandwich tricyanometalate, KCpCo(CN)3 (1, Cp = cyclopentadienyl), as the building block, two new cyano-bridged
heterobimetallic complexes, [{CpCo(CN)3}2M(H2O)2] Æ 2H2O (M = FeII, 2; CoII, 3), have been synthesized and structurally characterized. Complexes 2 and 3 are isostructural. In each complex, [CpCo(CN)3] acts as a bis-monodentate bridging ligand toward the central
[M(H2O)2]2+ core through two of its three cyanide groups, which leads to a two-dimensional network layer structure with a repeating
cyclic octameric [(–M–NC–Co–CN–)]4 unit. The magnetic properties of complexes 2 and 3 have been investigated in the temperature
range of 2.0–300 K and they both show weak antiferromagnetic interaction.
2006 Elsevier B.V. All rights reserved.
Keywords: Cyanide bridged; Heterometallic complexes; Crystal structures; Magnetic properties
1. Introduction
Cyanometalates have been widely employed as building
blocks for the construction of multi-metallic assemblies
[1–3]. In recent years, half-sandwich tricyanometalates have
been proved to be versatile precursors to coordination solids of host–guest systems [4]. For example, the self-assembly
reactions between [(C5R5)M(CN)3] (R = H, Me; M = Co,
Rh) and C5Me5Mn+ (M = Rh, Ru) sources have generated
some very interesting organometallic boxes. These boxes
with easy ion-exchange properties can be potentially used
as molecular containers devices in the future.
*
Corresponding authors. Tel.: +86 25 83593893; fax: +86 25 83314502.
E-mail address: zuojl@nju.edu.cn (J.-L. Zuo).
0020-1693/$ - see front matter 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.01.024
Very recently, modified cyanometalates, [M(L)x(CN)y]n (M = first row transition metallic ion and
L = organic polydentate ligand), have been studied as multidentate ligands or linkers to prepare cyanide-bridged
bimetallic systems [5–8]. In our previous work, we have
employed the tricyanometalate precursor (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl)hydroborate) to achieve
new cyano-bridged compounds of single-chain magnet
and single-molecule magnet [9]. As an alternative way for
constructing supramolecular systems, we used the organometallic tricyanometallate, KCpCo(CN)3 (1), as the building block. Based on it, two novel two-dimensional
complexes, [{CpCo(CN)3}2M(H2O)2] Æ 2H2O (M = FeII,
2; CoII, 3), have been prepared. In this paper, we report
the crystal structures and physical properties of these polymeric metal complexes.
Z.-G. Gu et al. / Inorganica Chimica Acta 359 (2006) 3790–3794
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2. Experimental
Table 2
Selected bond lengths and angles in complex 2
2.1. Syntheses
Bond lengths (Å)
Co(1)–C(1)
Co(1)–C(3)
Co(1)–C(12)
Co(1)–C(14)
C(1)–N(1)
Fe(1)–N(3)#2
Ammonium iron (II) sulfate hexahydrate and cobalt (II)
nitrate hexahydrate were purchased from commercial
sources and used as received. KCpCo(CN)3 (1) is synthesized as described previously [10].
2.1.1. [{CpCo(CN)3}2Fe(H2O)2] Æ 2H2O (2)
A mixture of methanol and water (1:1, 10 ml) was gently
layered on the top of a solution of (NH4)2Fe(SO4)2 Æ 6H2O
(39 mg, 0.1 mmol) in water (3 ml). A solution of KCpCo(CN)3 (48 mg, 0.2 mmol) in methanol (3 ml) was added
carefully as a third layer. Orange block crystals were
obtained after two weeks, washed with ethanol and ether,
dried in air. Yield: 49%. Anal. Calc. (%) for C16H18Co2FeN6O4: C, 17.99; H, 1.70; N, 39.33. Found: C, 17.94; H,
1.66; N, 39.39%.
2.1.2. [{CpCo(CN)3}2Co(H2O)2] Æ 2H2O (3)
To a methanolic solution (5 ml) of KCpCo(CN)3 (48 mg,
0.2 mmol), a water solution (5 ml) of Co(NO3)2 Æ 6H2O
(29 mg, 0.1 mmol) was added. The mixture was stirred at
room temperature for 2 min. After filtering, slow evaporation of the filtrate in air afforded orange plate-like crystals.
Yield: 41%. Anal. Calc. (%) for C16H18Co3N6O4: C, 17.99;
H, 1.70; N, 39.33. Found: C, 17.91; H, 1.65; N, 39.41%.
Bond angles ()
Co(1)–C(1)–N(1)
Co(1)–C(3)–N(3)
C(1)–Co(1)–C(2)
C(1)–N(1)–Fe(1)
N(1)–Fe(1)–N(3)#2
O(1)–Fe(1)–N(3)#2
1.8729(15)
1.8826(16)
2.0544(19)
2.0737(18)
1.146(2)
2.2302(14)
179.14(14)
177.84(15)
90.91(7)
173.19(13)
86.39(5)
90.40(5)
Co(1)–C(2)
Co(1)–C(11)
Co(1)–C(13)
Co(1)–C(15)
Fe(1)–N(1)
Fe(1)–O(1)
Co(1)–C(2)–N(2)
C(1)–Co(1)–C(3)
C(2)–Co(1)–C(3)
C(3)–N(3)–Fe(1)#4
O(1)–Fe(1)–N(1)
1.8751(16)
2.0673(19)
2.0658(18)
2.0680(18)
2.1357(13)
2.0831(12)
175.45(15)
90.68(6)
95.41(7)
162.95(13)
90.06(5)
Symmetry transformations used to generate equivalent atoms: #2 x,
y + 1/2, z + 1/2; #4 x + 2, y 1/2, z + 1/2.
2.2. Physical measurements
The IR spectra were taken on a Nicolet-170SX FT-IR
spectrophotometer with KBr pellets in the range 4000–
400 cm1. Elemental analyses for C, H, N were performed
on a Perkin–Elmer 240 C analyzer. Variable-temperature
magnetic susceptibility data were collected using a
Quantum Design MPMS SQUID magnetometer. The
experimental susceptibilities were corrected for the diamagnetism of the constituent atoms (Pascal’ tables).
2.3. Crystal data collection and refinement
Table 1
Crystal and refinement data for complexes 2 and 3
Formula
Formular weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a ()
b ()
c ()
Z
V (Å3)
Dcalc (g cm3)
T (K)
k (Å)
l(mm1)
F(0 0 0)
h Range ()
h k l Range
Collected
Unique
Parameters
Goodness-of-fit
R1 (I > 2r(I))
wR2 (I > 2r(I))
(D map) maximum/
minimum [e Å3]
2
3
C16H18Co2FeN6O4
532.07
monoclinic
P21/c
9.4327(5)
11.4588(6)
10.2838(5)
90
114.5640(10)
90
2
1010.95(9)
1.748
293(2)
0.71073
2.365
536
2.37–28.28
8 6 h 6 12,
15 6 k 6 14,
13 6 l 6 10
7354
2512
150
1.082
0.0219
0.0237
0.410/0.347
C16H18Co3N6O4
535.16
monoclinic
P21/c
9.426(2)
11.314(3)
10.270(2)
90
114.322(4)
90
2
998.0(4)
1.781
293(2)
0.71073
2.500
538
2.37–28.05
12 6 h 6 11,
14 6 k 6 14,
13 6 l 6 10
5935
2345
149
0.925
0.0417
0.0635
0.645/0.410
The well-shaped single crystals of 2 and 3 were selected
for X-ray diffraction study on a Siemens (Bruker) SMART
CCD diffractometer using graphite monochromated Mo Ka
radiation (k = 0.71073 Å). Cell parameters were retrieved
using SMART software and refined using SAINT on all observed
reflections. Data were collected using the following strategy:
606 frames of 0.3 in x with / = 0, 435 frames of 0.3 in x
with / = 90, and 235 frames of 0.3 in x with / = 180. An
additional 50 frames of 0.3 in x with / = 0 were collected
to allow for decay correction. The highly redundant data
sets were reduced using SAINT and corrected for Lorentz
and polarization effects. Absorption corrections were
applied using SADABS supplied by Bruker. The structures
were solved by direct methods using the program SHELXL97 and refined on F2 by full-matrix least-squares procedures
using SHELXTL software. All non-hydrogen atoms were
anisotropically refined. All H atoms were located theoretically and not refined. Crystallographic data and refinement
for the complexes are presented in Table 1 and selected bond
distances and angles in Table 2, respectively.
3. Results and discussion
3.1. IR spectra
In general, the bridging and terminal cyanide groups are
usually differentiated by the positions of the corresponding
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Z.-G. Gu et al. / Inorganica Chimica Acta 359 (2006) 3790–3794
C„N stretching absorption bands. The bridging cyanide
ligands lead to a shift to high wavenumbers. At room temperature, in the solid infrared spectrum of the precursor
complex KCpCo(CN)3, only one C„N stretching
(2119 cm1) has been observed. However, the C„N
stretching frequencies are located at 2129 and 2156 cm1
for 2, and 2136 and 2157 cm1 for 3, which are consistent
with the presence of terminal and bridging cyanide ligands.
The diamagnetic result of magnetic measurements shows
the low-spin character of the cobalt(III) ion in the complex
KCpCo(CN)3 (1).
3.2. Crystal structures
Complexes 2 and 3 are isostructural and no detailed
descriptions are presented here for 3. The asymmetric unit
of the structure of 2 together with the atomic labeling
scheme is given in Fig. 1. The central Fe(II) ion is sixcoordinated with two oxygen atoms of water in trans
position and four cyanide nitrogen atoms, taking a
FeN4O2 distorted octahedral environment. The bond
length of Fe–O(w) is 2.083(1) Å. To form the network,
two Fe–NC–Co bonding modes are utilized: the bending
mode [Fe(1)–N(3A)–C(3A)] (Fe(1)–N(3A), 2.2302(14) Å;
Fe(1)–N(3A)–C(3A), 162.95(13)) and relatively linear
mode [Fe(1)–N(1)–C(1)] (Fe(1)–N(1), 2.1357(13) Å;
Fe(1)–N(1)–C(1), 173.19(13)). The cobalt atom has a distorted octahedral geometry, completed by Cp ligand and
three carbon atoms from cyanide groups. Each
[CpCo(CN)3] provides two cyanide groups to coordinate
with two Fe(II), another cyanide group is free. The average Co–C(cyano) bond lengths are 1.878(2) Å for the
bridging cyanide groups and 1.8751(16) Å for the terminal
cyanide group. The Co–C–N angles for both terminal and
bridging cyanide groups are somewhat bent from linearity
[175.45(15)–179.14(14)]. The shortest intramolecular
Fe Fe, Fe Co distances are 7.698(4) and 5.145(2) Å.
As shown in Fig. 2a and 2b, the two-dimensional network structures are spread over the bc plane of the unit cell
with a repeating cyclic octameric [(–Fe–NC–Co–CN–)]4
unit. The center of the octameric ring is occupied by the
Fig. 1. Perspective drawing of the asymmetric unit of complex 2 showing
the atom numbering. Thermal ellipsoids are drawn at the 50% probability
levels. The hydrogen atoms and solvents are omitted for clarity.
Fig. 2a. A view of a fragment of 2D network structure of 2 along the aaxis. The crystallization water molecule and the hydrogen atoms have
been omitted for clarity.
Fig. 2b. A schematic view of a fragment of 2D structure of 2 along the
a-axis where only the metal atoms and the cyanide bridges (full line) are
included.
two Cp sandwiches. Namely, the layer structure is stacked
along the a-axis, and the water molecules of crystallization
are located between the 2D Co and Fe layers. It is noteworthy that 2 is the first example of a 2D layered cyano-bridged
complex constructed from organometallic tricyanometallate. The coordinated water is linked to the terminal cyanide
nitrogen atom of the other layer through a hydrogen bond
(O(1)–H N(2), 3.020(2) Å, symmetry code: 1 + x, y, z).
The oxygen atom of lattice water is hydrogen bonded to
the water coordinated to the Fe atom (O(1)–H O(2),
2.628(2) Å, symmetry code: 1 + x, 1/2 y, 1/2 + z) and
the carbon atom of Cp (C(11)–H O(2), 3.398(3) Å, symmetry code: 1 x, y, 1 z). The bridging cyanide nitrogen atom N(3) and the terminal cyanide nitrogen atom
N(2) are also linked to the lattice water molecule (O(2)–
H N(3), 3.207(3) Å, symmetry code: 1 + x, 1/2 y,
Z.-G. Gu et al. / Inorganica Chimica Acta 359 (2006) 3790–3794
1/2 + z; O(2)–H N(2), 2.834(2) Å, symmetry code: x, y,
1 + z). The three-dimensional structure is formed through
these hydrogen-bonding interactions.
3.3. Magnetic properties
Recently, CoFe Prussian blue analogues have been
investigated as photo-induced magnets by Hashimoto
et al. They proposed the explanation of this phenomenon
as: the presence of diamagnetic low-spin Co(III)–Fe(II)
pairs in these compounds and a photoinduced electron
transfer from Fe(II) to Co(III) to give Co(II)–Fe(III) magnetic pairs [11]. However, compound 2 consists of low spin
Co(III) and high spin Fe(II) ions, which is obviously different from the above systems. The temperature dependence
of vMT for complex 2 is shown in Fig. 3. At room temperature, vMT is equal to 3.40 cm3 mol1 K, which is higher
than spin-only one high spin Fe(II) value 3.00 cm3 mol1 K
(S = 2). It is almost independent of temperature in the
range of 50–300 K but decreases with further lowering of
temperature up to the minimum value of 2.50 cm3 mol1 K
at 2 K, indicating that antiferromagnetic interaction
between the Fe(II) ions dominates the magnetic properties
of complex 1. The higher vMT value is suggested as the
presence of the orbital contribution.
Taking into account the molecular theory, the theoretical expression of the magnetic susceptibility of the FeII–
FeII (S1 = S2 = 2) is:
vFe ¼ Ng2 b2 S Fe ðS Fe þ 1Þ=3kT
ð1Þ
vM ¼ vFe =ð1 2vFe zj0 =Ng2 b2 Þ
ð2Þ
The best fit to the above experimental data gives
zj 0 =P
0.124(3) cm1, g = 2.141(2).
P The agreement factor
R = [(vMT)obsd (vMT)cald]2/ [(vMT)obsd]2 is 1.0 · 105.
Therefore, the antiferromagnetic interaction between the
high-spin iron(II) ions through Fe–NC–Co–CN–Fe pathway is very weak but cannot be neglected.
As shown in Fig. 4, complex 3 exhibits similar magnetic
behavior. The result, plotted as vMT versus T, shows that
the value for vMT decreases from 2.547 cm3 mol1 K at
300 K to 1.288 cm3 mol1 K at 2 K. The high-temperature
vMT value obtained is much larger than the spin-only value
expected for one S = 3/2 spin (1.875 cm3 mol1 K). This
deviation is the result of the first-order orbital momentum
displayed by high-spin Co(II) ions in octahedral surrounding. Moreover, in addition to the symmetry lowering due to
the deformation of the octahedral coordination sphere of
the Co ions, the coupling of the first-order orbital momentum with the spin momentum partially removes the degeneracy of the ground state and the excited state.
The theoretical expression for the molar susceptibility of
the CoII–CoII(S1 = S2 = 3/2) is given in Eq. (3) [12]. It considers the paramagnetic behavior for the independent CoII
ions found in the molecular formula. Possible weak interactions between the Co(II) sites within the network are considered through a Curie–Weiss parameter h
N l2B g2Co 1 1 þ 9e2D=kT
vM ¼
kðT hÞ 3 4ð1 þ e2D=kT Þ
2 1 þ ð3kT =4DÞð1 e2D=kT Þ
þ
þ TIP
ð3Þ
3
1 þ e2D=kT
Best fit to the experimental data in the temperature domain
2–300 K leads to g = 2.603, D = 76.2 cm1, h =
3.753
K, TIP = 0.00518.PThe agreement factor R =
P
[(vMT)obsd (vMT)cald]2/ [(vMT)obsd]2 is 1.0 · 106.
The small h value is consistent with weak antiferromagnetic
interactions between the Co(II) ions through the diamagnetic NC–CoIII–CN bridges.
2.6
/ em u m ol
-1
1.0
3.0
2.8
0.8
0.6
0.4
0.2
0.0
0
2.6
50
100
150
200
250
0.20
2.4
0.15
-1
1.2
c M / em u mol
c MT / emu K mol -1
1.4
3.2
cM
-1
3.4
cMT / emu K mol
3793
2.2
0.10
0.05
2.0
0.00
300
0
50
100
T/K
150
200
250
300
T/K
1.8
2.4
0
50
100
150
200
250
300
T/K
Fig. 3. The temperature dependence of magnetic susceptibilities in the
forms of vMT vs. T and vM vs. T (inset) of 2. The red line corresponds to
the best-fit curves using the parameters described in the text. (For
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
0
50
100
150
200
250
300
T/K
Fig. 4. The temperature dependence of magnetic susceptibilities in the
forms of vMT vs. T and vM vs. T (inset) of 3. The red line corresponds to
the best-fit curves using the parameters described in the text. (For
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
3794
Z.-G. Gu et al. / Inorganica Chimica Acta 359 (2006) 3790–3794
Acknowledgements
This work was supported by the National Natural
Science Foundation of China (20531040 and 90501002).
J.-L. Zuo thanks the Program for New Century Excellent
Talents in University of China (NCET-04-0469).
[5]
Appendix A. Supplementary data
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre as Supplementary Publication Nos. CCDC-278133 and -278134 for complexes 2 and 3, respectively. Copies of this information may
be obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK, fax: +44 1223
336 033, e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk). Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.ica.2006.01.024.
[6]
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