Synthesis, structure and spectroscopic properties of two new trinuclear nickel(II) clusters possessing solvent effect

Article abstract of DOI:10.1016/j.saa.2009.08.037

Two solvent-induced trinuclear nickel(II) clusters, [{NiL(CH₃OH)}₂(OAc)₂Ni]·2CH₃OH (I) and [{NiL(C₂H₅OH)}₂(OAc)₂Ni]·2C₂H₅OH (II), have been synth

Full text of DOI:10.1016/j.saa.2009.08.037

Spectrochimica Acta Part A 74 (2009) 719–725
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, structure and spectroscopic properties of two new trinuclear nickel(II)
clusters possessing solvent effect
Wen-Kui Donga,∗, Xiao Chena, Yin-Xia Suna, Yu-Hua Yanga, Li Zhaoa, Li Xua, Tian-Zhi Yub
a School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, China
b Key Laboratory of Opto-Electronic Technology and Intelligent Control (Lanzhou Jiaotong University), Ministry of Education, Lanzhou 730070, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two solvent-induced trinuclear nickel(II) clusters, [{NiL(CH3OH)}2(OAc)2Ni]·2CH3OH (I)
Received 29 November 2008
Received in revised form 2 August 2009
Accepted 4 August 2009
and [{NiL(C2H5OH)}2(OAc)2Ni]·2C2H5OH (II), have been synthesized by the reaction of
a
new Salen-type bisoxime chelating ligand of 5,5ꢀ-di(N,Nꢀ-diethylamino)-2,2ꢀ-[(1,3-propylene)
dioxybis(nitrilomethylidyne)]diphenol (H2L) with nickel(II) acetate tetrahydrate in different sol-
vents. Clusters I and II were characterized by elemental analyses, IR spectra, UV–vis absorption spectra,
TG–DTA and X-ray diffraction methods. In clusters I (or II), there are two ligand moieties (which provide
N2O2 donors), two acetate ions, two coordinated methanol (or ethanol) molecules and two crystallizing
methanol (or ethanol) molecules, which result in the formation of three slightly distorted octahedral
geometries around Ni(II) ions. Interestingly, nickel(II) ions in the structures of clusters I and II are all
six-coordinated geometry, but clusters I and II are grown up in different solvent. Right because of this,
solvent effect cause to their different crystal structures.
Keywords:
Ni(II) cluster
Synthesis
Structure
Spectroscopic properties
Solvent effect
© 2009 Published by Elsevier B.V.
1. Introduction
2. Experimental
Investigation of the structures of transition metal complexes
bearing Salen-type ligand or its derivatives have been the main
focus of considerable recent research interest, due to their appli-
cations in organometallic chemistry, important nonlinear optical
materials [1] and interesting magnetic materials [2,3]. Some of
these complexes usually possess homogeneous catalysis, which
have been used as catalysts for organic reactions [4], models of
reaction centers of metalloenzymes [5]. So, the study on Salen-
type ligands and their nickel(II) complexes are still the aim of
our many current investigations [6–9]. In this paper, we report
the synthesis, characterization and crystal structures of a new
Salen-type bisoxime ligand, 5,5ꢀ-di(N,Nꢀ-diethylamino)-2,2ꢀ-[(1,3-
propylene)dioxybis(nitrilomethylidyne)]diphenol (H2L), and its
corresponding trinuclear nickel clusters [{NiL(CH3OH)}2(OAc)2Ni]·
2CH3OH (I) and [{NiL(C2H5OH)}2(OAc)2Ni]·2C2H5OH (II) possess-
ing solvent effect.
2.1. Materials
4-(N,Nꢀ-Diethylamine)-2-hydroxybenzaldehyde was purchased
from Acros Organics and recrystallized from ethanol. 1,3-
Bis(aminooxy)propane was synthesized according to the method
reported earlier [10]. The other reagents and solvents were analyt-
ical grade reagents from Tianjin Chemical Reagent Factory.
2.2. Methods
Elemental analysis for Ni was detected by an IRIS ER/S·WP-
1 ICP atomic emission spectrometer. C, H and N analyses were
carried out with a GmbH VariuoEL V3.00 automatic elemental
analyzer. IR spectra were recorded on a VERTEX70 FT-IR spec-
trophotometer, with samples prepared as KBr (500–4000 cm−1
)
and CsI (100–500 cm−1) pellets. UV–vis absorption spectra were
recorded on a Shimadzu UV-2550 spectrometer. 1H NMR spectra
were recorded on a Mercury-400BB spectrometer at room temper-
ature using CDCl3 as a solvent. TG–DTA analyses were carried out on
a ZRY-1P thermal analyzer at a heating rate of 3 ◦C/min. X-ray sin-
gle crystal structures were determined on a Bruker Smart APEX CCD
area detector. Melting point was measured by the use of a micro-
scopic melting point apparatus made in Beijing Taike Instrument
Limited Company, and the thermometer was uncorrected. Molar
conductance value measurements were carried out on a model
∗
Corresponding author. Tel.: +86 931 4938703; fax: +86 931 4956512.
E-mail address: dongwk@mail.lzjtu.cn (W.-K. Dong).
1386-1425/$ – see front matter © 2009 Published by Elsevier B.V.
doi:10.1016/j.saa.2009.08.037

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DDS-11D type conductivity bridge using 1.0 × 10−3 mol dm−3 solu-
52.9%. Anal. calcd for C58H90N8Ni3O16 (%): C, 52.32; H, 6.81; N, 8.42;
Ni, 13.22. Found: C, 52.21; H, 6.86; N, 8.49; Ni, 13.17.
tion in chloroform at 25 ◦C.
2.5. Synthesis of cluster II
2.3. Synthesis of the ligand H2L
5,5ꢀ-Di(N,Nꢀ-diethylamino)-2,2ꢀ-[(1,3-
propylene)dioxybis(nitrilomethylidyne)]diphenol
Cluster II was prepared by the same method as that of cluster
I except changing from methanol to ethanol. Dark-green rhom-
bohedral crystals were isolated after two weeks following the
solvent was partially evaporated. Yield 21.7 mg, 46.9%. Anal. calcd
for C62H98N8Ni3O16 (%): C, 53.67; H, 7.12; N, 8.08; Ni, 12.69. Found:
C, 53.74; H, 7.19; N, 7.99; Ni, 12.61.
(H2L)
was
prepared by the modification of the reported method
[11,12]. To an ethanol solution of 4-(N,Nꢀ-diethylamine)-2-
hydroxybenzaldehyde (388.4 mg and 2.01 mmol) was added an
ethanol solution of 1,3-bis(aminooxy)propane (106.1 mg and
1.00 mmol). The mixture solution was stirred at 55 ◦C for 3 h.
After cooling to room temperature, the precipitate was filtered,
and washed successively with ethanol and ethanol/hexane (1:4),
respectively. The product was dried under vacuum, and obtained
2.6. X-ray crystallography
The single crystals of H2L, clusters I and II with approx-
imate dimensions of 0.50 × 0.21 × 0.10, 0.49 × 0.40 × 0.37 and
0.31 × 0.30 × 0.28 mm were placed on a Bruker Smart diffrac-
tometer equipped with Apex CCD area detector. The diffraction
was collected using a graphite monochromated Mo K␣ radiation
(ꢀ = 0.71073 Å) at 293(2), 298(2), 298(2) K, respectively. The struc-
tures were solved by using the program SHELXS-97 [13] and Fourier
difference techniques, and refined by full-matrix least-squares
method on F2 using SHELXL-97 [14]. Details of the data collec-
tion and refinements are given in Table 1. All hydrogen atoms were
added theoretically.
268.47 mg of colorless microcrystal. Yield 58.8%. m.p. 85–86 ◦C. 1
H
NMR (400 MHz, CDCl3) 1.17 (t, J = 7.2 Hz, 12H), 2.10 (t, J = 6.4 Hz,
2H), 3.36 (dd, J = 7.2 Hz, 8H), 4.23 (t, J = 6.4 Hz, 4H), 6.22 (dd,
J = 2.4 Hz, 4H), 6.94 (t, J = 4.6 Hz, 2H), 8.06 (s, 2H), 9.89 (s, 2H). Anal.
calcd. for C25H36N4O4 (%): C, 65.76; H, 7.95; N, 12.27. Found: C,
65.63; H, 7.99; N, 12.21.
Colorless needle-shaped crystals of H2L suitable for X-ray crystal
analysis were grown up from the ethanol solution by slow evapo-
ration of the solvent at room temperature.
2.4. Synthesis of cluster I
3. Results and discussion
A solution of nickel(II) acetate tetrahydrate (24.9 mg and
0.10 mmol) in methanol (10 ml) was added dropwise to a solu-
tion of H2L (45.7 mg and 0.10 mmol) in acetonitrile (10 ml) at room
temperature. The color of the mixing solution turned to green
immediately, and then continuing stirs for 4 h at room tempera-
ture. The mixture solution was filtered and the filtrate was allowed
to stand at room temperature for about one week, the solvent was
partially evaporated and obtained several green prismatic single
crystals suitable for X-ray crystallographic analysis. Yield 23.5 mg,
3.1. Molar conductances
Clusters I and II are soluble in chloroform, DMF, DMSO,
but not soluble in acetone, ethanol, methanol, ethyl acetate
and hexane. Molar conductance values of clusters
I and II
at 25 ◦C of 10−3 mol dm−3 chloroform solutions are 0.4 and
0.5 ꢁ−1 cm2 mol−1, respectively, indicating that clusters I and II are
non-electrolyte [15]. These imply that all the acetate groups in clus-
Table 1
Crystal data and structure refinement for H2L, clusters I and II.
H2L
I
II
Empirical formula
Formula weight
Temperature (K)
C25H36N4O4
456.58
293(2)
C58H90Ni8N3O16
1331.51
298(2)
C62H98N8Ni3O16
1387.61
298(2)
Wavelength (Å)
Crystal system, space group
0.71073
Monoclinic, C2/c
0.71073
Triclinic, P-1
0.71073
Triclinic, P-1
Unit cell dimensions (Å, ◦
)
a
b
c
29.922(3)
4.9686(5)
16.8353(17)
99.345(2)
12.6579(15)
13.4477(16)
21.541(2)
12.5101(10)
12.6121(14)
13.2552(16)
67.4280(10)
ˇ
88.648(3)
Volume (Å3)
2469.7(4)
4, 1.228
0.084
984
3256.0(6))
2, 1.358
0.928
1412
1742.5(3)
1, 1.322
0.870
738
Z, Calculated density (Mg/m3)
Absorption coefficient (mm−1
F (0 0 0)
)
Crystal size (mm)
0.50 × 0.21 × 0.10
0.49 × 0.40 × 0.37
0.31 × 0.30 × 0.28
ꢂ range for data collection (◦)
Limiting indices
1.38–25.01
1.80–25.01
1.67–25.00
−35 ≤ h ≤ 31, −5 ≤ k ≤ 5, −11 ≤ l ≤ 20
5817/2164
14 ≤ h ≤ 15, −15 ≤ k ≤ 15, −19 ≤ l ≤ 25
17,051/11,292
−14 ≤ h ≤ 14, −12 ≤ k ≤ 14, −15 ≤ l ≤ 14
9117/6056
Reflections collected/unique
[Rint = 0.0668]
[Rint = 0.0312]
[Rint = 0.0304]
Completeness to ꢂ
100% (ꢂ = 25.01◦)
Semi-empirical from equivalents
0.9917 and 0.9592
Full-matrix least-squares on F2
2164/0/152
98.5% (ꢂ = 25.01◦)
Semi-empirical from equivalents
0.7252 and 0.6591
Full-matrix least-squares on F2
11292/0/773
98.7% (ꢂ = 25.01◦)
Semi-empirical from equivalents
0.7927 and 0.7742
Full-matrix least-squares on F2
6056/0/422
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
1.002
1.013
1.011
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole (e Å−3
R1 = 0.0555, wR2 = 0.1297
R1 = 0.1648, wR2 = 0.1836
0.186 and −0.146
R1 = 0.0736, wR2 = 0.1820
R1 = 0.1392, wR2 = 0.2388
0.931 and −0.950
R1 = 0.0668, wR2 = 0.1581
R1 = 0.1152, wR2 = 0.1968
0.664 and −0.810
)

W.-K. Dong et al. / Spectrochimica Acta Part A 74 (2009) 719–725
721
Fig. 2. UV–vis absorption spectra of H2L, clusters I and II.
Fig. 1. Infrared absorption spectra of H2L, clusters I and II.
3.4. Thermal properties
Thermal decomposition process of cluster I can be divided into
four stages. The first stage is at 40–55 ◦C. The TG curve shows that
the weight loss corresponding to this temperature range is 5.1% that
roughly coincides with the value of 4.8%, calculated for the loss of
two crystallizing methanol molecules from the outer of cluster I.
The second stage starts from 86 to 94 ◦C with the weight loss of
5.0%, which corresponds to the loss of two methanol molecules
which takes part in coordination to the nickel atoms. The third
stage degradation temperature is in the range of 202–248 ◦C with
the mass loss of 9.3%, in which two coordinated acetate ions are
removed with theoretical loss of 8.9%. The solid remains stable up to
329 ◦C and the fourth weight loss starts at around 335–347 ◦C with
decomposition of the compound. The TG curve shows around 81.9%
weight loss at 365 ◦C indicating the complete removal of organic
part of the compound. The main product was NiO with a residual
value of 18.1% (theoretical residual value was 16.8%).
ters I and II are always held in the coordination sphere in solution
or solid state.
3.2. IR spectra
IR spectra of H2L and its clusters I and II are given in Fig. 1. IR
spectra indicate that clusters I and II have similar structures. The
free ligand H2L exhibits Ar–O and C N stretching bands at 1298 and
1599 cm−1, respectively, which are shifted to lower frequencies by
ca. 54 and 16 cm−1 upon complexation. This lowering of energy
results from the M–O and M–N interaction upon complexation and
is similar to that reported for nickel(II) clusters [16]. In addition,
O–H stretching bands can be found at 3431 (or 3427) cm−1 in clus-
ter I (or II), providing the evidence for existence of crystallizing
methanol (or ethanol) molecules.
Thermal decomposition of cluster II also occurs in four stages.
The initial weight loss occurs in the range 46–68 ◦C. The TG curve
shows that weight loss corresponding to this temperature range is
7.2% consistent with 6.6%, calculated for loss of two crystallizing
ethanol molecules. The second stage is 88–97 ◦C with weight loss
of 7.0%, which corresponds to the loss of two ethanol molecules
coordinated to Ni. The third stage degradation temperature is in
the range 230–256 ◦C with mass loss of 9.1%, in which two coor-
dinated acetate ions decompose with theoretical loss of 8.5%. The
solid remains stable up to 340 ◦C and the fourth weight loss starts at
around 346–357 ◦C with further decomposition of the compound.
The TG trace of cluster II shows 82.2% weight loss at 377 ◦C indicat-
ing complete removal of organic fragments and NiO with a residual
value of 17.8% (theoretical residual value was 16.1%).
The far-infrared spectra of clusters I and II are also obtained
in the region 500–100 cm−1 in order to identify frequencies due
to the Ni–O and Ni–N bonds. The IR spectrum of cluster I (or
II) shows vibrational absorption frequencies at 496 (or 496) and
422 (or 426) cm−1, which are assigned to ␯(Ni–N) and ␯(Ni–O),
respectively. These assignments are consistent with the literature
frequency values [17–19].
3.3. UV–vis absorption spectra
UV–vis absorption spectra of the ligand (H2L) and its cor-
responding trinuclear nickel(II) clusters I and II in the dilute
chloroform solutions at 298 K are shown in Fig. 2. The spectral
shapes of clusters I and II are similar to each other, and different
from the shape of the ligand (H2L). The absorption spectrum of the
free ligand (H2L) shows absorption peaks at 337 nm. This is the
characteristic peak for any Salen-type ligands due to ␲–␲* transi-
tions [20,21]. Noteworthy is that there is a broad absorption around
373 nm, which is seen in the corresponding Salen analogues. The
absorption is ascribed to the keto-NH form of Salen-type com-
pounds [12,22]. Compared with the absorption peak of ligand, the
corresponding absorption peak of clusters I and II is observed at 345
and 346 nm, respectively, which is bathochromically shifted by ca.
8 and 9 nm, indicating that the coordination of Ni(II) ions with L2−
units. Noteworthy is that the same of UV–vis absorption spectra
of clusters I and II can clearly indicate the similar structure of the
clusters.
3.5. Crystal structures and solvent effect
3.5.1. Ligand H2L
The crystal structure of H2L was determined by X-ray crys-
tallography. The H2L is sufficiently stable to resist scrambling of
the C N bonds, which may be ascribed to lower reactivity of
the oxime C N bonds toward nucleophiles. The molecule adopts
a V-shaped conformation, the dihedral angle between the two
halves of the molecule being 89.77(4)◦. There is one half-molecule
in the asymmetric unit, with a crystallographic twofold rota-
tion axis passing through the central C atom (Figs. 3 and 4).
The oxime groups and phenolic alcohols have trans-conformation,
and there is a strong intramolecular hydrogen bond, O2–H2· · ·N1

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W.-K. Dong et al. / Spectrochimica Acta Part A 74 (2009) 719–725
Fig. 3. The molecule structure of H2L with the atom numbering. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level.
Fig. 4. Packing diagram of H2L along b-axis. H atoms are omitted for clarity.
Fig. 5. The molecule structure of cluster I with the atom numbering. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level. Each of the nickel atoms
sit in an octahedral geometry.

W.-K. Dong et al. / Spectrochimica Acta Part A 74 (2009) 719–725
723
Fig. 6. Packing diagram of cluster I along a-axis. H atoms are omitted for clarity.
space group C2/c, and the unit cell contains two crystallographically
independent but chemical identical trinuclear clusters, molecules
A and B (Fig. 5). Both molecules A and B consist of three nickel(II)
ions, two L2− units, two acetate ions, two coordinated methanol
molecules and two crystallizing methanol molecules. In molecule
A, the terminal nickel atom (Ni2) is six-coordinated by two nitro-
gen atoms (N1 and N2) and two oxygen atoms (O3 and O4) in the
N2O2 moieties of the ligand, one oxygen atom (O6) from the bridg-
ing acetate anion and one oxygen atom (O7) from the coordinated
ethanol molecule. Consequently, around Ni2 atom is a slightly dis-
torted octahedral geometry. In addition, the central nickel (Ni1)
(d(O2–H2) = 0.820 Å, d(H2· · ·N1) = 1.918 Å, d(O2· · ·N1) = 2.640(2) Å,
O2–H2· · ·N1 = 146.35◦) involving the hydroxy group and adjacent
oxime N atoms [9].
3.5.2. Clusters I and II
Two new clusters I and II, possessing coordinated methanol and
ethanol molecules, respectively, have been synthesized success-
fully through changing of solvent, which can help to study the influ-
ence of solvent effect in the formation and structure of the clusters.
X-ray crystallographic analysis of cluster I reveals a symmet-
ric trinuclear structure. It crystallizes in the monoclinic system,
Fig. 7. The molecule structure of cluster II with the atom numbering. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level. Each of the nickel
atoms sit in an octahedral geometry.

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W.-K. Dong et al. / Spectrochimica Acta Part A 74 (2009) 719–725
Table 2
Intermolecule H-bond (Å, ◦) details for clusters I and II.
D–H· · ·A
d(D–H)
d(H· · ·A)
∠DHA
d(D· · ·A)
Cluster I
O7–H7· · ·O16i
O14–H14· · ·O15
O15–H15· · ·O12ii
O16–H16· · ·O5iii
0.820
0.820
0.820
0.820
1.802
1.792
1.892
1.911
175.04
176.72
169.15
170.71
2.620
2.611
2.702
2.724
Cluster II
O7–H7· · ·O8iv
0.820
0.821
1.832
1.969
171.85
169.18
2.646
2.779
O8–H8· · ·O5v
Symmetry codes: (i) x, y, z − 1; (ii) −x + 1, −y, −z + 1; (iii) −x + 2, −y, −z + 1; (iv) −x + 1,
−y + 1, −z + 2; (v) x, y, z − 1.
coordination sphere is completed by four ␮-phenoxo oxygen atoms
(O3, O4, O3# and O4#) from two [NiL] chelates, and both of oxy-
gen atoms (O5 and O5#) from two acetate anions which adopts a
familiar ␮O–C–O fashion [9,23,24], and also constitute octahedral
geometry. Compared with molecule A, molecule B is similar in the
structural features but distinct in some bond distances and angles.
Furthermore, the trinuclear structure is stabilized by two ␮-acetato
ligands, which neutralize the whole charge of cluster I (Fig. 6).
The single crystal structures of clusters I and II are isomorphous
and isostructural, so the structural features of cluster II are very
similar to those of cluster I except the difference of coordinated
solvent molecules (Fig. 7). Noticeably is that the structure of cluster
II only contains a trinuclear cluster.
Intermolecular hydrogen bonds are existed and given in Table 2.
In cluster I, there are four strong hydrogen bonds (include
molecules A and B), O7–H7· · ·16, O14–H14· · ·O15, O15–H15· · ·O12
and O16–H16· · ·O5, but only two hydrogen bonds exist in cluster
II, O7–H7· · ·O8 and O8–H8· · ·O5. Every O atom from crystallizing
methanol or ethanol molecules exhibits obviously strong inter-
molecular interactions with two nearest O atoms, one from acetate
anion and one from coordinated methanol or ethanol molecule at
same time.
Fig. 8. Packing diagram of cluster II along b-axis. H atoms are omitted for clarity.
molecules than the coordinated methanol molecules. So, it is easily
found solvent effect on clusters I and II cause to their differences in
crystal structures (Fig. 8).
4. Conclusions
Based on the data, description and discussion above, a new
Salen-type bisoxime chelating ligand, 5,5ꢀ-di(N,Nꢀ-diethylamino)-
2,2ꢀ-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol (H2L),
and its two solvent-induced trinuclear nickel(II) cluster,
[{NiL(CH3OH)}2(OAc)2Ni]·2CH3OH (I) and [{NiL(C2H5OH)}2(OAc)2
Ni]·2C2H5OH (II), have been synthesized and structurally charac-
terized. Molar conductance values of clusters I and II in chloroform
indicate that clusters I and II is non-electrolyte and all the acetate
groups in clusters I and II are held in the coordination sphere. In IR
spectra of clusters I and II, O–H stretching bands are found at 3431
and 3427 cm−1, implying existence of crystallizing and coordinated
methanol and ethanol molecules, respectively. UV–vis spectra
clearly indicated the structures of two clusters are similar and
different from the ligand (H2L). X-ray crystal structures reveal that
the structural features of clusters I and II are very similar except
the difference of coordinated solvent molecules. Interestingly, the
existence of solvent effect on clusters I and II cause to their slight
differences in crystal structures.
3.5.3. Solvent effect
Comparing clusters I and II, the ratio of ligands and the nickel(II)
ions are both 2:3. Every terminal Ni atom forms two six-membered
rings with two salicylaldoxime moieties and the acetates adopt
familiar role to reinforce the structures by the bridging between the
adjacent nickel(II) ions. Here, solvent effect on the nickel(II) clus-
ters cause to their different crystal structures, in which methanol
(or ethanol) molecules are coordinated to Ni2 and Ni4 in cluster I
(or Ni2 in cluster II) [25].
5. Supplementary material
It is clearly revealed the influence of solvent effect in selected
bond distances (Å) and bond angles (◦) for clusters I and II. In cluster
I, the distance from O7 (coordinated methanol molecule) to plane
of N1–N2–O3–O4 is 2.072(2) Å and O7–Ni2 is 2.138(2) Å, so we con-
firm that Ni2 is not coplanar with N1–N2–O3–O4 plane and slightly
deviates toward O6 from the acetate anion. The dihedral angle of
N1–Ni2–O3 and N2–Ni2–O4 is 6.24(3)◦ (molecules A), and the dihe-
dral angle of N5–Ni4–O10 and N6–Ni4–O11 is 6.55(3)◦ (molecules
B).
Cluster II shows distance from O7 (coordinated ethanol
molecule) to plane of N1–N2–O3–O4 (2.068(3) Å) is shorter than
O7–Ni2 (2.133(2) Å). As same as cluster I, Ni2 is also not copla-
nar with N1–N2–O3–O4 plane and slightly deviates toward O6
from the acetate anion. And the dihedral angle of N1–Ni2–O3 and
N2–Ni2–O4 is 4.92(2)◦.
Crystallographic data for the structure analyses have been
deposited with the Cambridge Crystallographic Data Center, CCDC
Nos: 684103 for H2L, 652648 for cluster I and 684102 for II. Copies
of these information may be obtained free of charge from the
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (e-mails:
linstead@ccdc.cam.ac.uk; deposit@ccdc.cam.ac.uk, direct line: +44
1223 762910; tel.: +44 1223 336408; fax: +44 1223 336033).
Acknowledgements
This work was supported by the Foundation of the Education
Department of Gansu Province (No. 0904-11) and the ‘Jing Lan’ Tal-
ent Engineering Funds of Lanzhou Jiaotong University, which are
gratefully acknowledged.
The appearance of Ni2 deviates toward O6 in clusters I and II
may be attributed to electrostatic attraction of acetate anion. Fur-
ther, the dihedral angle of two planes (N1–Ni2–O3 and N2–Ni2–O4)
in cluster II (4.92(2)◦) is smaller than that in cluster I (6.24(3)◦
or 6.55(3)◦), due to larger steric hindrance of coordinated ethanol
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2009.08.037.

W.-K. Dong et al. / Spectrochimica Acta Part A 74 (2009) 719–725
725
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