A Discrete Nickel Cubane with [Ni4O4] Cluster: Synthesis, Structure, and Magnetic Property

Article abstract of DOI:10.1002/zaac.201500772

The tetranuclear nickel cluster {[Ni₄(L)₄(C₂H₅OH)₄]·7H₂O} (1) was synthesized based on the tridentate Schiff base ligand H₂L = 1-phenyl-3-[(2-hydroxyphenyl)imino]-1-butanone. The

Full text of DOI:10.1002/zaac.201500772

Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201500772
A Discrete Nickel Cubane with [Ni4O4] Cluster: Synthesis, Structure, and
Magnetic Property
Qi-Long Zhang,*[a][‡] Zhi-Lei Wu,*[b][‡] Hong Xu,[a] Bin Zhai,[b] Yu-Fang Wang,[b]
Guang-Wei Feng,[a] and Ya-Li Huang[a]
Keywords: Tetranuclear clusters; Nickel; Schiff bases; Ferromagnetic interactions; Thermal stability
Abstract. The tetranuclear nickel cluster {[Ni4(L)4(C2H5OH)4]· a discrete [Ni4O4] cluster. Magnetic studies indicate that ferromagnetic
7H2O} (1) was synthesized based on the tridentate Schiff base ligand
H2L = 1-phenyl-3-[(2-hydroxyphenyl)imino]-1-butanone. The struc-
ture of 1 was determined by single-crystal X-ray diffraction. It exhibits
interactions exist within compound 1. Furthermore, thermogravimetric
analysis and PXRD patterns in various solvents reveal thermal and
solvent stability of compound 1.
Supporting Information) (Scheme 1), prepared by condensa-
tion of benzoylacetone and 2-aminophenol, was selected to
construct Ni cluster with the following considerations: (1) The
acylhydrazone Schiff-base ligands with polydentate N,O-donor
are especially favorable for the construction of polynuclear
transition metal complexes.[12] (2) Similar ligands have been
selected to synthesize many structurally and magnetically
interesting transition metal complexes. Herein, the structure
and magnetic properties of a discrete cubane-like [Ni4]
cluster{[Ni4(L)4(C2H5OH)4]·7H2O} (1) are reported.
Introduction
In the past decades, the design and construction of clusters
have been extensively concerned not only because of their in-
triguing structural diversity,[1] but also due to their potential
applications in electronic, optical, catalytic, and magnetic ma-
terials among others.[2] Up to now, many different kinds of
transition metallic clusters have been studied, such as {Co3},[3]
{Ni4},[4] {Zn8},[5] {Cu10},[6] {Mn12},[7] or {Fe18},[8] of which
some polynuclear clusters display interesting structure types
and properties. Among the reported clusters, the tetranuclear
cubane like {M4O4} clusters (M = Cu, Ni, Co, etc.) are of
particular interest because of their versatile magnetic proper-
ties,[9] in particular, for the {Ni4O4} clusters, in which the in-
tracluster magnetic interactions can be fine-tuned by using
multidentate bridging ligand. In order to construct polynulear
complexes, polydentate ligands, especially Schiff-base ligands
have been widely explored. For example, Tandon et al. pre-
pared two novel hexanuclear nickel clusters by use of different
Schiff-base ligands in 2012.[10] Moreover, Das et al. synthe-
sized a series of di-, tri-, and tetranuclear NiII compounds
based on two tridentate Schiff-base ligands.[11]
Scheme 1. Structure of the ligand H2L.
Results and Discussion
In this contribution, a tridentate Schiff-base 1-phenyl-3-[(2-
hydroxyphenyl)imino]-1-butanone (H2L, synthesis is given in
Description of the Structure
The crystal structure of the compound 1 is shown in
Figure 1. Single-crystal X-ray diffraction analyses reveal that
1 crystallizes in the monoclinic system with a Pbca space
group. As shown in Figure 1a, four crystallographically inde-
pendent Ni atoms, four L2– ligands, and four ethanol molecules
exist in the asymmetric unit. Eight alternately arranged oxygen
and Ni atoms form a distorted cubane-like {Ni4O4} cluster
(Figure 1b), in which each Ni atom is coordinated by four oxy-
gen atoms and one nitrogen atom from different L2– ligands
and one oxygen atom from ethanol molecule. The bond lengths
of Ni–O and Ni–N are in the range of 1.961–2.235 and 1.992–
2.000 Å, respectively (Table 3), which is comparable to the
* Prof. Dr. Q.-L. Zhang
Fax: +86-851-88174017
E-Mail: gzuqlzhang@126.com
* Prof. Dr. Z.-L. Wu
Fax: +86-370-2592844
E-Mail: wuzhilei03@163.com
[a] Department of Chemistry
Guizhou Medical University
Guizhou,Guiyang 550004, P. R. China
[b] Department of Chemistry & Chemical Engineering
Shangqiu Normal University
Shangqiu, 476000, P. R. China
[‡] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201500772 or from the au-
thor.
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Figure 1. (a) Coordination environments of the Ni atoms in 1 (30% probability level of thermal ellipsoids. Hydrogen atoms are omitted for
clarity). (b) Principal structure of the coordination sphere of four nickel(II) ions in 1.
similar Ni clusters previously reported.[13] The Ni–O–Ni
angles in {Ni4O4} cluster are in the range of 91.73(8)–
101.49(10)° (Table 2), all of which play an important part in
determining the intracluster magnetic exchange interactions.
All the Ni atoms are six coordinated with a distorted octahedral
coordination polyhedron, in which three oxygen atoms act as
bridges to connect the other remaining three Ni atoms. Up to
now, many NiII cluster-based compounds have been previously
reported,
such
as
{Ni2}clusters,[14]
liner-shaped
{Ni3}clusters,[15] triangle-shaped {Ni3}clusters linked by μ3-O
atom,[16] rhombus-shaped {Ni4}clusters,[17] cubane-like
{Ni4}clusters,[18] {Ni5}clusters with rectangular symmetry,[19]
{Ni6} clusters constructed by two {Ni3}clusters and so
on,[10,20] all of which exhibit various magnetic behaviors.
Powder X-ray Diffraction
Figure 2. Thermogravimetric analysis (TGA) curve of compound 1.
Powder X-ray diffraction analysis of compound 1 was car-
ried out to confirm the purity and solvent stability of the sam-
ple. As shown in Figure S1 (Supporting Information), the ex-
perimental PXRD patterns of 1 immersed in various solvents
(such as H2O, CH3OH, CH3CH2OH, butyl alcohol, petroleum
ether, cyclohexane) are similar to the simulated ones from sin-
gle crystal data, indicating that compound 1 possess excellent
solvent stability.
Magnetic Properties
The magnetic susceptibility measurement of 1 was carried
out in a 1 KOe external field in the temperature range of
2–300 K, and the plot of χMT vs. T is shown in Figure 3.
The observed χMT value of 1 at room temperature is
4.19 cm3·K·mol–1, which is slightly higher than the expected
value 4 cm3·K·mol–1 for four uncoupled NiII ions with g = 2.
With decreasing temperature, the χMT value remains nearly
constant until 100 K, and then increases sharply to a maximum
value of 5.99 cm3·K·mol–1 at 9.5 K. Further cooling tempera-
ture, χMT value decline to 4.72 cm3·K·mol–1 at 2 K. The mag-
Thermal Analysis
Thermal gravimetric analysis (TGA) of 1 was performed in netic behavior reveals that predominant ferromagnetic interac-
a nitrogen atmosphere in the temperature range of 25–800 °C tion exists between adjacent NiII ions. The fit of 1/χM vs. T
(Figure 2). At the beginning, about 8.02% weight loss was above 10 K using the Curie-Weiss equation χM = C/(T – θ)
observed below 95 °C, which corresponds to the free water gives the Curie constant C = 4.12 cm3·K·mol–1 and Weiss con-
molecules in the lattice (calcd: 8.85%). Due to the hydrogen stant θ = 3.18 K, and the positive θ value further proves the
bonding interaction in 1, the coordinated ethanol molecules are predominant ferromagnetic interaction between NiII ions.
difficult to remove at low temperature. As shown in Figure 2, Amongst the similar cubane-shaped [Ni4O4] compounds, the
the coordinated ethanol molecules leave at about 350 °C. Sub- interaction between two central nickel atoms can be mediated
sequently, the whole structure starts to decompose, revealing by μ3-O bridges and ligands. For example, Meyer’s group re-
that 1 also has high thermal stability.
ported two discrete [Ni4O4] clusters {[NiL1(MeOH)]4 and
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[NiL(H2O)]4, H2L1
= pyrazole-based tridentate {ONO} reveal that Ni1–Ni4 and Ni2–Ni3 exhibit antiferromagnetic in-
ligand} with different μ3-O bridges, exhibiting different mag- teraction within the {Ni4O4} cluster, while the other nickel
netic properties.[18a] Furthermore, Das et al. synthesized a one- pairs show stronger ferromagnetic exchange with the strength
dimensional chain based on [Ni4O4] cluster.[18b] Comparably, J2 = 2.59 cm–1, which is in consistent with the difference of
1 is a discrete tetranuclear nickel cluster with ethanol as μ3-O Ni–O–Ni angles in the crystal structure. The ferromagnetic in-
bridges, displaying similar magnetic behavior like that of teraction is observed when the Ni–O–Ni angle is lower than
[Ni(μ3-Cl)Cl(HL)]4, NiL1(MeOH)]4, and [Ni(μ3-OH)Cl(HL)]4 98°, and antiferromagnetic interaction is found when the Ni–
(HL = 2-methyl-1-(pyridin-2-yl)propan-2-ol).[12]
O–Ni angle is larger than 98°. For 1, five of twelve Ni–O–Ni
angles are above 98°, and the bigger positive J2 value are full
agreement with the ferromagnetic behavior observed in 1.
Conclusions
The discrete cubane-like {Ni4O4} cluster 1 was prepared
and characterized. The compound displays excellent thermal
and solvents stability. Magnetic studies indicate that ferromag-
netic interactions exist between adjacent NiII atoms of 1. This
work is aimed to provide more information for designing novel
clusters with interesting physical and chemistry properties.
Experimental Section
Materials and Physical Methods: Chemical reagents were purchased
commercially and were used as received without further purification.
Elemental analyses of C, N, and H were performed with an EA1110
CHNS-0 CE elemental analyzer. 1H NMR spectra were recorded at
25 °C with a Bruker Avance 400 spectrometer. IR (KBr pellet) spectra
were recorded with a Nicolet Magna 750FT-IR spectrometer. Thermo-
gravimetric measurements were carried out in a nitrogen stream with
a Netzsch STA449C apparatus with a heating rate of 10 K·min–1. Dif-
fraction studies on single crystals were conducted with a Bruker
SMART APEX II CCD diffractometer applying graphite-monochro-
matized Mo-Kα radiation (λ = 0.71073 Å). X-ray powder diffraction
(XRPD) was carried out with a RIGAKU DMAX2500 apparatus. Vari-
able-temperature magnetic susceptibility measurements were per-
formed with a MPMS Multivu device.
–1
Figure 3. Plots of the χMT vs. T and χM vs. T for compound 1. The
solid red lines represent the fit for plots of χMT vs. T and Curie-Weiss
fit for χM vs. T of compound 1, respectively.
–1
In order to investigate the magnetic behavior of this tetra-
nuclear nickel cluster, the structure can be simplified to a
model for quantifying the magnetic interactions (Figure 4). It
has been reported that the exchange interactions in similar
Ni4O4 cubanes is dependent on the Ni–O–Ni angle.[9e] Accord-
ing to the X-ray structure and Ni–O–Ni angles for each of
interacting Ni pairs in 1, the skeleton of the Ni4O4 is not an
ideal cube arrangement, but a reduced tetragonal symmetry, so
an lower symmetry Heisenberg Hamiltonian model is em-
ployed to fit the magnetic susceptibility data, in which two
coupling constants J1 and J2 are involved:[21]
{[Ni4(L2–)4(C2H5OH)4]·7H2O} (1): An ethanol solution (20 mL) of
Ni(O2CCH3)2·4H2O (0.25 g, 1 mmol) was added to CHCl3 solution
(20 mL) of H2L (1.01g, 4 mmol). The resulting solution was refluxed
for 3 h. Slow evaporation of this reaction mixture at room temperature
in air afforded the complex as dark brown crystalline material. The
material was collected by filtration, and washed several times with
methanol and water respectively, and dried in air. Yield 0.38 g (53%).
C72H76N4Ni4O12: calcd. C 60.72; H 5.38; N 3.93%; found: C 60.78;
H 5.36; N 3.95%. IR (KBr): ν˜ = 3422 (m), 2922 (w), 1582 (s), 1479
(vs), 1400 (vs), 1263 (m), 1185 (w), 1108 (w), 1022 (w), 745 (m), 701
(m), 572(w), 434 (w) cm–1.
H = –2J1(S1S4 + S2S3) –2J2(S1S2 + S2S4 + S3S4 + S1S3)
(1)
X-ray Crystallographic Studies: Single crystals of complex 1 with
appropriate dimensions were chosen under an optical microscope and
quickly coated with high vacuum grease (Dow Corning Corporation)
before being mounted on a glass fiber for data collection. Intensity
data collection was carried out with a Siemens SMART diffractometer
equipped with a CCD detector using Mo-Kα monochromatized radia-
tion (λ = 0.71073 Å) at 293(2) K. The absorption correction was based
on multiple and symmetry-equivalent reflections in the data set using
the SADABS program. The structure was solved by direct methods
and refined anisotropically by full-matrix least-squares techniques
based on F2 using the SHELXTL-97 and SHELXTL-97 programs.[22]
Figure 4. Model for magnetic analysis of compound 1.
The best fitting results based on Equation (1) are g = 2.00,
J1 = –0.55 cm–1, and J2 = 2.59 cm–1. The negative J1 value All the non-hydrogen atoms were refined anisotropically. The
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hydrogen atoms were assigned one common isotropic displacement
Crystallographic data (excluding structure factors) for the structure in
parameter and included in the final refinement in calculated positions this paper have been deposited with the Cambridge Crystallographic
using the riding model approximation by use of geometrical restrains.
The crystallographic data of compound 1 are shown in Table 1. Se-
lected bond angles and lengths are listed in Table 2 and Table 3.
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the
depository number CCDC-695202 for 1 (Fax: +44-1223-336-033;
E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
Table 1. Crystallographic data for 1.
Supporting Information (see footnote on the first page of this article):
Powder X-ray diffraction (PXRD) patterns, IR spectra and crystallo-
graphic data.
1
Empirical formula
Formula weight
Temperature /K
Crystal system
Space group
a /Å
C72H76N4Ni4O12
1424.21
293(2)
orthorhombic
Pbca
20.910(2)
23.662(3)
28.047(3)
13877(3)
8
Acknowledgements
This work was supported by the Joint Fund of Guizhou Province of
P. R. China (No. [2014]7090) and the Youth Foundation of Guizhou
Provincial Department of Education (No. [2015]415).
b /Å
c /Å
Volume /Å3
Z
Dcalc /g·cm–3
Absorption coefficient /mm–1
F(000)
1.363
1.131
5952
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0.0408
0.22ϫ0.21ϫ0.20
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Ni(3)–O(2)–Ni(1)
Ni(1)–O(3)–Ni(2)
Ni(1)–O(3)–Ni(4)
Ni(2)–O(3)–Ni(4)
Ni(2)–O(5)–Ni(4)
Ni(2)–O(5)–Ni(3)
Ni(4)–O(5)–Ni(3)
Ni(3)–O(8)–Ni(1)
Ni(3)–O(8)–Ni(2)
Ni(1)–O(8)–Ni(2)
97.83(9)
100.81(10)
93.39(10)
98.50(10)
100.87(10)
92.68(9)
97.28(9)
101.13(10)
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N(2)–Ni(1)
N(3)–Ni(2)
N(4)–Ni(3)
O(1)–Ni(4)
O(2)–Ni(1)
O(2)–Ni(3)
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O(3)–Ni(4)
O(4)–Ni(1)
1.999(3)
2.000(3)
1.992(3)
1.985(3)
1.971(3)
2.197(2)
2.061(2)
2.055(2)
2.045(2)
2.084(2)
2.205(2)
1.979(3)
O(5–Ni(2)
O(5–Ni(3)
O(5–Ni(4)
O(6–Ni(2)
O(7–Ni(3)
O(8–Ni(1)
O(8–Ni(2)
O(8–Ni(3)
O(9–Ni(2)
O(10–Ni(4)
O(11–Ni(1)
O(12–Ni(3)
2.051(3)
2.235(2)
2.085(2)
1.961(3)
1.967(3)
2.112(2)
2.226(3)
2.049(3)
2.132(3)
2.098(3)
2.107(3)
2.134(3)
Z. Anorg. Allg. Chem. 2016, 414–418
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Received: November 17, 2015
Published Online: March 4, 2016
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