Windmill-type mixed-metal clusters containing Schiff-base ligands as an efficient catalyst for cyclohexene oxidation

Article abstract of DOI:10.1039/c7nj02359f

Two new mixed-metal clusters {CuM₂(H₂O)₂[Cu(C₁₄H₁₆N₂O₃)Cl]₆}·H₂O (M = Mn 1, Zn 2) based on Schiff-base ligands were designed and synthesized by the reaction of 1,2-cyclohexanediamine-N,N′-bis-(3-carboxylsalicylide), copper chloride and zinc chloride or manganese chloride under solvothermal conditions. They were characterized by various techniques including single-crystal X-ray diffraction, powder X-ray diffraction (XPRD), elemental analysis, TG analysis, IR and UV-visible spectroscopy. Compounds 1 and 2 are isostructural, and display an interesting windmill-type structure built from a trinuclear mixed-metal center [CuM₂(CO₂)₆(H₂O)₂] (M = Mn 1, Zn 2) linked with six [CuLCl] (L = C₁₄H₁₆N₂O₃) units. The oxidation of cyclohexene catalysed by 1 and 2 as heterogeneous catalysts was investigated and showed high activity. In addition, a magnetic study indicates that antiferromagnetic interactions exist in compound 1.

Full text of DOI:10.1039/c7nj02359f

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Windmill-type mixed-metal clusters containing schiff-base ligands
as efficient catalyst for cyclohexene oxidation
Received
00th January
20xx,
Xiaoqin Li, Dan Ma, Bingran Cao, Ying Lu*
Two new mixed-metal clusters {CuM2(H2O)2[Cu(C14H16N2O3)Cl]6}·H2O (M = Mn 1, Zn 2) based on Schiff-base ligands were
designed and synthesized by the reaction of 1,2-cyclohexanediamine-N,N’-bis-(3-carboxylsalicylide), copper chloride and
zinc chloride or manganese chloride under solvothermal conditions. They were characterized by various techniques
including single-crystal X-ray diffraction, powder X-ray diffraction (XPRD), elemental analysis, TG analysis, IR and UV-visible
spectroscopy. Compounds 1 and 2 are isostructural, which display an interesting windmill-type structure built by a
trinuclear mixed-metal center [CuM2(CO2)6(H2O)2] (M = Mn 1, Zn 2) linking with six [CuLCl] (L = C14H16N2O3) units. The
oxidation of cyclohexene catalysed by 1 and 2 as heterogeneous catalysts were investigated and showed high activity. In
addition, magnetic study indicates that antiferromagnetic interactions exist in compound 1.
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Schiff-base ligands possessing attractive structural features have
been found to be intriguing ligands and were extensively studies in
coordination chemistry.11-12 They mainly refer to a class of organic
Introduction
Polymetallic cluster generated by assembling coordinatively
unsaturated metal sites (CUMs) and organic ligands have attracted
significant attention in recent years since it has proved to be very
efficient in post-synthesis modification and various gases sorption.1
More importantly, since CUMs can strongly interact with organic
molecules in catalysis, polymetallic cluster containing CUMs always
were endowed with excellent catalytic performances in a variety of
catalytic reactions such as cyanosilylation of aldehydes, oxidation of
hydrocarbons and sulphides.2-4 Design polymetallic cluster
containing CUMs as well metal-organic frameworks based on them
ligands containing amine or azomethine, which are usually obtained
by condensation reaction of aldehydes or ketones and amine.
Schiff-base ligands can coordinate with diverse metals in various
oxidation states through amine nitrogen or oxygen. Moreover, they
can be functionalized by the incorporation of additional functional
groups such as carboxyl, pyridyl and alkoxy groups. Hence, they
have become a versatile building block for the design and syntheses
of metal-organic complexes or frameworks with fascinating
structures and attractive properties in magnetism, luminescence
and catalysis.13-15 Actually, the metal center chelated by schiff-base
ligand is usually coordinatively unsaturated, which endows metal-
schiff-base complexes with excellent catalytic performance in
homogeneous and heterogeneous oxidation reactions.16-17
Recently, employing schiff-base ligand to construct metal-organic
complexes or frameworks have become an effective way to get
metal-organic complexes or frameworks with CUMs. In 2013, Ali et
al prepared a hydroperoxo–copper(II) complex of N4O2 donor Schiff
base, which was found to be an efficient catalyst for the oxidation
of aromatic hydrocarbons to the corresponding aldehyde and
alcohol in 2 : 1 mole ratio with TON∼300.18 In 2014, Pombeiro et al
have reported a series of mixed-ligand dinuclear Mn(II,II) complexes
of three different hydrazone Schiff bases, which show remarkable
catalytic activity towards microwave assisted oxidation of
alcohols.19
have become
a powerful way for achieving multifunctional
materials bearing remarkable catalytic activity. In 1999, Williams et
al. reported the preparation and structure of Cu3(btc)2 (HKUST-1) in
which two Cu2+ coordination sites were filled with two water
molecules.5 Later on, extensive research on its catalytic activity in
cyanosilylation of benzaldehyde, Friedlaönder reaction and olefins
cyclopropanation was made.6-8 Also, MIL-101(Cr) containing latent
catalytic CUMs was reported and its wide applications as catalyst in
cyanosilylation of aldehydes, selective oxidation of tetralin and
oxidation of alkenes were evaluated by Kaskel, Ahn and
Kholdeeva.9-10
Based on the features of polymetallic cluster and metal-schiff-
base complexes, connecting them through the additional functional
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oxygen; blue, nitrogen; sea green, chlorine; pink, manganese; sky blue, copper,
respectively; H atoms are omitted for clarity.
groups (carboxyl and pyridyl et al) in schiff-base ligand might
generate polynuclear metal-organic complexes with abundant
CUMs, which would be appealing catalysts for various organic
reactions. This idea stimulates us to design and synthesize new
polynuclear metal-organic complexes by using schiff-base ligands
with carboxyl groups. At the present work, we selected a schiff-base
ligand 1,2-cyclohexanediamine-N,N’-bis-(3-carboxylsalicylide), in
which carboxylate groups is in the para position of the hydroxyl
groups, to react with copper chloride and zinc chloride or
manganese chloride under solvothermal conditions. We
successfully synthesized two nonanuclear metal-organic clusters
{CuM2(H2O)2[Cu(C14H16N2O3)Cl]6}·H2O (M = Mn 1, Zn 2), which are
constructed by a trinuclear mixed-metal center [CuM2(CO2)6(H2O)2]
(M = Mn 1, Zn 2) and six [CuLCl] (L = C14H16N2O3) units connected
through carboxylate groups. The ligand L came from the hydrolysis
of 1,2-cyclohexanediamine-N,N’-bis-(3-carboxylsalicylide) during
the synthetic process (Scheme S1). Compounds 1 and 2 were
characterized by single-crystal X-ray diffraction, powder X-ray
diffraction (XPRD), elemental analysis, TG analysis, IR and UV-visible
spectroscopy. Moreover, the oxidation of cyclohexene catalysed by
1 and 2 as heterogeneous catalysts were investigated.
are 1.898 Å (Cu1–O1), 2.155 Å (Cu2–O3), 1.995Å (Cu1–N1), 1.958Å
(Cu1–N2) and 2.284
Å (Cu1–Cl1). While the Mn1 center in
[CuMn2(CO2)6(H2O)2] unit displays a tetrahedral geometry defined
by three carboxylate oxygen atoms from three distinct schiff-base
ligands with Mn-O distance of 1.972 Å and one oxygen atom from
coordinated water molecule with Mn-O distance of 2.170 Å.
As given in Fig. 2a, in 1, each Cu1 center has a weak interaction
with the chloride atom in the adjacent [CuLCl] unit (Cu···Cl 2.8761
Å) owing to Jahn–Teller effect.20a The Cu–Cl···Cu interactions among
windmill-type clusters lead to the formation of a 3D network as
show in Fig. 2b.
Results and discussion
Description of Structure
Fig. 2 (a) View of weak interactions of Cu···Cl due to Jahn-Teller effect. (b) View of 3D
structure of the compound 1 along the c axis.
As single-crystal X-ray diffraction studies revealed, compounds 1
and 2 are essentially isostructural and crystallize in the R-3 group.
Taking compound 1 as an example, the detailed description of the
structure is given as follows. As shown in Fig. 1, the mixed-metal
cluster is constructed by six [CuLCl] units and one trinuclear metal
center [CuMn2(CO2)6(H2O)2] linked through carboxylate groups. The
trinuclear metal center is surrounded by six [CuLCl] moieties,
exhibiting a novel windmill-type structure. In 1, there are two
distinct copper coordination environments: one (Cu1) is located in
the [CuLCl] unit, which adopts an square-planer geometry defined
by two nitrogen and one oxygen atoms from the schiff-base ligand
and one chloride atom; the other (Cu2) is situated in the center of
the [CuMn2(CO2)6(H2O)2] unit, which exhibits an octahedral
coordination geometry with six carboxylate oxygen atoms from six
distinct schiff-base ligands. The Cu–O, Cu–N and Cu–Cl bond lengths
FT-IR spectroscopy, UV-visible Spectra and TG analyses
The FT-IR spectra of the compounds 1 and 2 were recorded in the
range from 400 to 4000 cm-1 (Fig. S1, S2). The υ(C=N) vibration
bonds in compounds 1 and 2 are found at 1610 cm-1 which red shift,
suggesting coordination of azomethine. For 1 and 2, there are
characteristic bands at 3296 cm-1 and 3207 cm-1 corresponding to
the vibrations of the N-H bonds. The stretch vibration absorption
peak of the -CO2 at 1642 cm-1 is found. The peak at 1250 cm-1 of 1
and 2 is assigned to –Ph–O asymmetric stretch vibration. The
appearance of characteristic frequencies from 650-900 cm-1 are
confirmed to be the –Ph(C-H) vibrations.20b
The UV-vis spectra of compounds 1 and 2 were measured ranging
from 200 to 800 nm in solid state at room temperature (Fig. S3). In
the ultraviolet region, compound 1 possesses two absorption bonds
at 245 and 342 nm and compound 2 has two absorption bonds at
251 and 359 nm, which are assigned as ligand-centered absorption
of π→π* or n→π* transiꢀons. In the visible region, both
compounds 1 and 2 exhibit a broad absorption band centered at
628 nm, which is attributed to d-d transitions of coordinated metal
ions.
To explore the thermal stability of compounds
1 and 2,
thermogravimetric analyses (TGA) were performed. As exhibited in
Fig. S4, the TG curves of compounds 1 and 2 show successive
weight loss in the variable temperature ranging from 30 ℃ to 1000
℃. For 1, the first weight loss from 30 to 290 ℃ is 2.16 %
Fig. 1 (a) View of coordination environment and numbers of Mn1, Cu1, Cu2. (b) The
structure of {CuMn2(H2O)2[Cu(C14H16N2O3)Cl]6}·H2O. Atoms labelled gray, carbon; red,
2 | J. Name., 2012, 00, 1-3
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Fig. 3 Yield versus time curves for cyclohexene oxidation catalyzed by 1. Reaction
conditions: cyclohexene (0.236 mmol), t-BuOOH (1.250 mmol), octane (0.074 mmol: as
an internal), catalyst 1 (0.004 mmol) , T = 70 ℃.
corresponding to the removal of coordinated water and crystal
water (Calcd 2.26 %). The second weight loss of 43.61 % from 290
to 428 ℃ is assigned to the decomposition of four L (Calcd 43.63
%). The last weight loss from 428 to 1000 ℃ is 20.83 % attributed to
the loss of two L (Calcd 21.81 %). For 2, the first weight loss from 30
washing process. The catalysts were characterized by PXRD after
being recycled 3 times. The PXRD patterns of the recycled catalyst
to 293 ℃ is 4.34 % corresponds to the release of the coordinated corresponds well to that of the freshly prepared catalyst, proving
the stability of catalyst after catalytic runs (Fig. S8, S9). In addition,
for comparison, the mononuclear copper complex CuLCl was also
prepared according to the literature procedures (Fig.S10, S11).20a,23
And the oxidation of cyclohexene catalysed by it was also explored
with the conversion reached 67.93 % after 12 h (Fig. S12).
water and crystal water (Calcd 2.25 %). The following weight loss of
61.36 % occurred from 293 to 1000 ℃ could be related to the
disintegration of L (Calcd 64.87%).
Heterogeneous catalytic oxidation of cyclohexene
Oxidation of cyclohexene was one of the most significant catalytic
oxidations in organic chemistry, which attracted extensive concern
all the time.21 Metal-Schiff-base complexes are always regarded as
effective catalysts in olefin oxidation.22 Therefore, the liquid-phase
cyclohexene oxidation was investigated in the presence of
compounds 1 and 2 as catalyst, respectively (Scheme1).
To affirm the heterogeneous nature of the catalytic reaction, a
hot filtration experiment was carried out: the solid heterogeneous
catalysts 1 and 2 were removed from hot solution by filtering after
3h of the reaction with the conversion reaching to 46.01% and
33.41%. It is obvious that there is no further conversion of
cyclohexene after the catalyst was removed, demonstrating that
metal ions leaching from the catalyst (if any) are not responsible for
the observed activity (Fig. 4, S6). Also, the atomic absorption
spectroscopy (AAS) was applied to analyse the filtrate. Not a bit of
metal ions are determined, which indicated a high stability of
catalysts 1 and 2.
Scheme1 Oxidation of cyclohexene.
The catalytic experiments were performed in CH2Cl2 at 70 °C
using tert-butyl hydroperoxide (TBHP) as the oxidant. The
experimental data demonstrates that 1 and 2 are efficient catalysts
for the oxidation of cyclohexene. For 1, the maximum substrate
conversion reached 80.72% against 73.18% of 2 after 12 h (Fig. 3,
S5). Furthermore, it is noteworthy that the conversion rose
dramatically in the first four hours up to 56.23% for 1 and 45.33%
for 2. The heterogeneous catalysts were easily separated from the
reaction systems by
a centrifugation process. The recovered
catalysts were reused in successive two runs with only slightly
decreased substrate conversion (Fig. S7). The reason for the slightly
lower is likely to be the loss of catalyst during the separation and
Fig. 4 Conversion versus time curves for oxidation of cyclohexene with 1 as catalyst
(square) and filtration of 1 (circle).
In consideration of antecedent mechanism studies and the main
product
tert-butyl-2-cyclohexenyl-1-peroxide,
a
plausible
mechanism pathway has been put forward.21b, 24-26
As shown in scheme 2, in the first step, the t-BuOOH is likely to
preferentially utilize its terminal oxygen to coordinate with
coordinatively unsaturated Cu (II) ions. With the electron
transferring, the weak O-O bond breaks out, accelerating the
disintegration of THBP into tert-butoxy radicals (t-BuO˙) and it also
creates HO-Cu(III) species in the meanwhile. Then, the tert-butoxy
radical (t-BuO˙) possibly attracts one hydrogen atom from
cyclohexene resulting in a 3-cyclohexenyl radical and t-BuOH. The
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HO-Cu(III) species might release a hydroxyl radical (OH˙) and hand, the hydrogen atom of t-BuOOH may be captured by hydroxyl
recover to original catalyst which can be reused again. On the other
Scheme 2 Proposed mechanism of cyclohexene oxidation.
Fig. 5 Temperature dependence of magnetic susceptibility χm (black) and the molar
radial to lead to a water molecule and a t-BuOO˙ radical which
magnetic susceptibility and temperature χmT (blue) for 1; (inset) The temperature
might react with 3-cyclohexenyl radical to gain the major product
dependence of reciprocal magnetic susceptibility 1/χm, producted by fitting with Curie-
tert- butyl-2-cyclohexenyl-1-peroxide. Furthermore, the tert-butyl-
Weiss law [χm = C/(T-θ)].
2-cyclohexenyl-1-peroxide may transform into 2-cyclohexen-1-one
θ = -10.53 K. The negative Weiss constant suggests the presence of
antiferromagnetic interactions in 1.
as by-product due to its poor thermostability.
Magnetic properties of 1 and 2
For 2, the χm versus T plot is similar to 1, strating at 0.01 cm3
mol−1 at 300 K and increasing to 1.78 m3 mol−1 at 2 K. The value of
χmT at room temperature is 4.39 (cm3 K mol-1), which is expected
The magnetic susceptibility data of compound 1 and 2 was acquired
in the variable temperature ranging from 2 to 300 K under an
applied filed of 1000 Oe. The plots χm, χmT and 1/χm vs T are shown
in Fig. 5 and Fig. 6. For 1, the value of χm increases gradually from
0.03 cm3 mol−1 at 300 K to 0.25 cm3 mol−1 at 50 K, exponentially to
the maximum of 3.66 cm3 mol−1 at 2 K. The χmT vs T plot decreases
continuously with the decreasing temperature, revealing the
characteristic of antiferromagnetic interactions. The room
temperature value of χmT is 14.54 (cm3 K mol-1), which is slight
higher than the theoretical value of 11.38 (cm3 K mol-1) expected
from seven CuII ions and two MnII ions (MnII: S = 5/2, g = 2; CuII: S =
1/2, g = 2).27-28 This may be attributed to the important orbital
contribution. The 1/χm vs T curve complys well with Curie-Weiss
law, leading to Curie constant C = 14.99 cm3 K mol-1 and Weiss
constant
for
seven
CuII
ions
(2.63
cm3
K
mol-1
assuming g = 2). This value declines with cooling, reaching the
minimum value of 2.80 (cm3 K mol-1) at 20 K, and then increases at
lower temperature. The slightly rise of χmT under low temperature
may ascribe to the presence of intermolecular exchange interaction.
29
The plot of 1/χm vs T better obeys Curie-Weiss law with Curie
constant C = 4.97 cm3 K mol-1 and Weiss constant θ = -52.67 K.
Fig. 6 Temperature dependence of magnetic susceptibility χm (black) and the molar
magnetic susceptibility and temperature χmT (blue) for 2; (inset) The temperature
dependence of reciprocal magnetic susceptibility 1/χm, producted by fitting with Curie-
Weiss law [χm = C/(T-θ)].
Experimental
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AAS was performed with the contents of Cu and Zn are 17.5 μg/L
and 6.0 μg/L revealed that the molar ratio of Cu and Zn is 3 : 1.
Materials and methods
The Schiff base ligand 1,2-cyclohexanediamine-N,N’-bis-(3-
Anal. Calcd. for C84H102Cl6Cu7Zn2N12O21
8.86, Cu 18.63, Zn 5.41 % found by ICP: C 41.51, H 4.20, N 6.92, Cl
8.77, Cu 18.22, Zn 5.26 %.
2: C 41.93, H 4.24, N 6.99, Cl
carboxylsalicylide) was prepared according to the literature
procedures. 30 It was obtained in a 1:2 molar ratio by condensation
of 1,2-cyclohexanediamine and 3-formyl-4-hydroxybenzoic acid
which was synthesized by refluxing 4-hydroxybenzoic acid with
chloroform under alkaline environment. Other chemicals were
purchased from commercial sources and used without any
purification.
；
Catalytic oxidation of cyclohexene
The catalytic oxidation of cyclohexene was carried out in a 15 mL
round-bottomed flask equipped with a magnetic stirrer bar and a
reflux water condenser. To this flask, 24 μL of cyclohexene in 7 mL
FT-IR spectra were recorded on an Alpha Centaurt FT/IR
spectrophotometer ranged from 400 cm-1 to 4000 cm-1 by using KBr
pellets. Thermogravimetric analyses (TGA) were performed on a
Perkin-Elmer TGA instrument heating from room temperature to
CH2Cl2 and catalyst
1 or 2 (10 mg) were charged into and octane (12
μL) as an internal standard. The oxidant tert-butyl hydroperoxide
(THBP) was added finally to start the reaction. The mixture was
then heated at 70
℃ and refluxed. Aliquots of the reaction solution
1000
℃ in N2 atmosphere at the rate of 10 ℃
min-1. Powder X-ray
was taken out periodically and then subjected to gas
chromatographic. The oxidative products were validated by
comparing the retention times with the standard samples. In
general, after each cycle, the catalyst was separated from the
reaction mixture by centrifugation. It was then washed with CH2Cl2
for several times and dried at room temperature. Later, it was
reused in the identical experimental procedures under the same
circumstances.
diffraction (PXRD) data were obtained by using a Rigaku D/max-
2550 diffractometer with Cu-Ka radiation. Elemental analyses (C, H,
N) were carried out on a Perkin-Elmer 2400 CHN elemental
analyzer. Copper, zinc and manganese analyses were made with a
PlASMA-SPEC(I) ICP atomic emission spectrometer in a JEOL JEM
2010-F TEM (200 kV) equipped with a high resolution pole piece.
UV−vis diffuse reflectance spectra (UV−vis/DRS) were recorded on a
Cary 7000 UV−vis-NIR Universal Measurement Spectrophotometer.
The GC analyses were carried out on Agilent 7820A-GC System
using DB-5 chromatographic column with 30 m × 0.32 mm × 0.25
μm. The magnetic susceptibility measurements were performed on
Table 1 Crystallographic data for compounds 1 and 2.
Compound
Formula
1
2
a
superconducting quantum interference device (SQUID)
magnetometer (Quantum Design, MPMS-5) in variable
temperature (2–300 K) at 1000 Oe magnetic field. AAS
was performed on SpectrAA-220Fs Atomic Absorption
Spectrometer (VARIAN, USA).
C84H102Cl6Cu7Mn2
N12O21
2383.21
Trigonal
22.3264(3)
22.3264(3)
16.4388(6)
90
C84H102Cl6Cu7Zn2
N12O21
a
Mr
2404.11
Trigonal
22.2759(3)
22.2759(3)
16.4697(6)
90
Crystal system
a
a
b
c
(Å)
(Å)
(Å)
(o)
Synthesis of {CuMn2(H2O)2[Cu(C14H16N2O3)Cl]6}·H2O (1)
A mixture of 1,2-cyclohexanediamine-N,N -bis-(3-carboxylsalicylide)
α
β
γ
(o)
90
90
’
(o)
120
7096.4(3)
3
120
7077.6(3)
3
(41 mg, 0.1 mmol), CuCl2·2H2O (34 mg, 0.2 mmol) and MnCl2·4H2O
(20 mg, 0.1 mmol) in the mixed solvent of DMF (3 mL), toluene (1
mL) and distilled water (1 mL) was stirred for 30 minutes, and
adjusted pH to about 7 with tetrabutyl ammonium hydroxide, then
transformed to and sealed in a 10 mL Teflon-lined autoclave,
heated at 90 oC for three days. It was gradually cooled to room
temperature at a rate of 5 oC / h. The products were obtained as
black block-like crystals with the yield of 58% (based on L). Copper
and manganese analyses performed on AAS revealed the molar
ratio of Cu and Mn was approximately 3 : 1 with the contents of Cu
and Mn are 18.8 μg/L and 5.3 μg/L. Anal. Calcd. for
V / Å3
Z
D
T
calc, mg/m3
/K
1.673
293(2)
1.692
293(2)
Final
R
indices
R
1 = 0.0511,
wR2 = 0.1285
1 = 0.0707,
wR2 = 0.1470
R
1 = 0.0653,
wR2 = 0.1808
1 = 0.0792,
wR2 = 0.1934
a,b
[
I
>2sigma(
I)]
R
indices
R
R
aR1= Σ||Fo| - |Fc||/Σ|Fo|;
bwR2 = {Σ[w(Fo2 – Fc2)2]/Σ[w(Fo2)2]}1/2
.
C84H102Cl6Cu7Mn2N12O21
1: C 42.29, H 4.28, N 7.05, Cl 8.94, Cu 18.80,
X-Ray crystallography
Mn 4.62 % found by ICP: C 42.81, H 4.32, N 7.12, Cl 8.85, Cu
；
18.31, Mn 4.47 %.
The single crystal X-ray diffraction was carried out on a Bruker Apex
CCD diffractometer. And the data was collected by Mo-Ka
Synthesis of {CuZn2(H2O)2[Cu(C14H16N2O3) Cl]6}·H2O (2)
monochromated radiation (
solved by a direct method and refined by full matrix least-squares
method on F2 using the SHELXL-97. For compounds
and , all the
λ= 0.71073 A). The structure was
The synthetic procedure of compound
2 was similar to compound 1
1
2
except that MnCl2·4H2O was replaced by ZnCl2 (15mg, 0.1mmol).
The green block-like crystals were formed in 45% yield (based on L).
hydrogen atoms attached to nitrogen, carbon and oxygen atoms
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7
8
9
E. Pérez-Mayoral and J. Čejka, ChemCatChem., 2011, 3,157–
159.
A. Corma, M. Iglesias, F. X. Llabrés i Xamena and F. Sanchez,
Chem–Eur. J., 2010, 16, 9789–9795.
(a) G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J.
Dutour, S. Surble and I. Margiolaki, Science., 2005, 309,
2040–2042; (b) A. Henschel, K. Gedrich, R. Kraehnert and S.
Kaskel, Chem. Commun., 2008, 4192–4194.
were fixed in ideal positions. A summary of the crystallographic
data and structural determination for compounds
1
and
2
is
provided in Table 1. CCDC-1558060 for and 1558061 for
1
2
contains the supplementary crystallographic data for this paper.
This data can be obtained free of charge from the Cambridge
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Table of contents entry
Windmill-type mixed-metal clusters containing schiff-base
ligands as efficient catalyst for cyclohexene oxidation
Xiaoqin Li, Dan Ma, Bingran Cao, Ying Lu*
Two new mixedꢀmetal clusters {CuM2(H2O)2[Cu(C14H16N2O3)Cl]6}·H2O (M = Mn 1,
Zn 2) were synthesized and the properties of cyclohexene oxidation have been
investigated.