Layered Zn2[Co(CN)6](CH3COO) double metal cyanide: A two-dimensional DMC phase with excellent catalytic performance

Article abstract of DOI:10.1039/c9sc00527g

Double metal cyanides (DMCs) are well known, industrially applied catalysts for ring opening polymerization reactions. In recent years, they have been studied for a variety of catalytic reactions, as well as other applications, such as energy storage and

Full text of DOI:10.1039/c9sc00527g

View Article Online
View Journal
Chemical
Science
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C. Marquez, A.
Simonov, M. T. Wharmby, C. Van Goethem, I. F.J. Vankelecom, B. Bueken, A. Krajnc, G. Mali, D. De Vos
and T. De Baerdemaeker, Chem. Sci., 2019, DOI: 10.1039/C9SC00527G.
This is an Accepted Manuscript, which has been through the
Volume
7 Number 1 January 2016 Pages 1–812
Royal Society of Chemistry peer review process and has been
accepted for publication.
Chemical
Science
Accepted Manuscripts are published online shortly after
www.rsc.org/chemicalscience
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2041-6539
EDGE ARTICLE
Francesco Ricci et al.
Electronic control of DNA-based nanoswitches and nanodevices
rsc.li/chemical-science

Page 1 of 9
PleaseCdhoemnoictaal dScjuiesntcme argins
View Article Online
DOI: 10.1039/C9SC00527G
Journal Name
ARTICLE
Layered Zn2[Co(CN)6](CH3COO) double metal cyanide: a two-
dimensional DMC phase with excellent catalytic performance†
Carlos Marquez,a Arkadiy Simonov,b Michael T. Wharmby,c Cédric Van Goethem,a Ivo Vankelecom,a
Received 00th January 20xx,
Accepted 00th January 20xx
Bart Bueken,a Andraz Krajnc,d Gregor Mali,d Dirk De Vos*a and Trees De Baerdemaeker*a
̌
DOI: 10.1039/x0xx00000x
Double metal cyanides (DMCs) are well known, industrially applied catalysts for ring opening polymerization reactions. In
recent years, they have been studied for a variety of catalytic reactions, as well as other applications, such as energy storage
and Cs sorption. Herein, a new, layered DMC phase (L-DMC), Zn2[Co(CN)6](CH3COO).4H2O, was synthesized. The structure,
which crystallizes in the monoclinic space group P21/m, consists of positively charged {Zn2Co(CN)6}+ DMC layers linked
through acetate groups and presents a new layered structure to the family of double metal cyanides. L-DMC proved to be a
reusable and stable catalyst that exhibited a higher activity than the benchmark DMC catalyst in two important applications:
hydroamination of phenylacetylene with 4-isopropylaniline and polymerization of 1,2-epoxyhexane.
www.rsc.org/
compounds, which for DMC-catalyzed reactions of these
molecules signifies that the reaction takes place on the outer
surface.7 Therefore, many strategies have been suggested in
Introduction
Double metal cyanides (DMCs) are inorganic coordination
polymers containing two metal atoms connected by cyanide
groups. They have been used industrially as solid catalysts for
the ring opening polymerization of epoxides since the 1960s,1-3
and their potential as Lewis acid catalysts for other organic
transformations such as co-polymerization of epoxides and
CO2,4,5 hydroamination,6-8 transesterification9 and coupling
reactions10,11 has recently been uncovered. DMCs can generally
be described as polynuclear transition metal cyanides with the
structural formula Mu[M’(CN)n]v.xH2O (M and M’ are two metal
cations), which often crystallize with a cubic unit cell.12 The
common u-v combination 3-2 can be described as a rock salt
type structure consisting of alternating M2+ and [M’(CN)6]3- ions.
The charge imbalance between these ions produces vacancies
that occur at one in three [M’(CN)6]3- sites.13-15 Even though the
cubic phase is the most common, the occurrence of other
phases, for example a monoclinic and a rhombohedral phase for
Zn3[Co(CN)6]2, has also been observed.16,17
order to increase the accessibility and availability of the
catalytically active sites. For example, we recently showed that
by dispersing the catalytically active Zn3[Co(CN)6]2 DMC on
silica, its activity can be vastly improved in hydroamination and
epoxide polymerization reactions because of the increased
accessibility of the active sites.8 Furthermore, Robertson et al.18
proposed layered Co(H2O)2[M’(CN)4] DMCs (M’= Ni, Pd or Pt) as
high surface area catalysts for the propylene oxide (PO)
homopolymerization and PO/CO2 copolymerization. In this
case, the activity of the Co[M’(CN)4] system still remained lower
than that of the Zn3[Co(CN)6]2 DMCs. Layered materials, such as
layered double hydroxides (LDHs), layered metal-organic
frameworks (MOFs) and clay minerals, are generally of wide
interest because of their highly tunable properties and wide
range of potential applications, including in catalysis,19-22 energy
storage,23,24 and CO2 capture.25,26 Additionally, their potential
for modification through, for instance, exfoliation has been
extensively investigated in the case of clays, layered zeolite
precursors or layered double hydroxides.27-35
In all the aforementioned phases, however, the pores are too
narrow to allow the diffusion of the majority of aromatic
During our investigation of Zn3[Co(CN)6]2 DMCs, we discovered
single crystals of a phase that was not cubic, but instead,
consisted of positively charged DMC layers linked by acetate
anions. To the best of our knowledge, such a cationic, layered
DMC structure has not yet been reported in the literature.
Given the known catalytic activity of other Zn3[Co(CN)6]2 DMCs
– cubic,36 monoclinic,16 or (partially) amorphous37-39 – we were
motivated to synthesize this layered DMC phase as a powder to
investigate its catalytic properties. Herein, we report the
synthesis, structure, physicochemical characterization and
catalytic activity of this layered DMC (L-DMC). Moreover, the
advantages of L-DMC over the benchmark DMC catalyst will be
demonstrated for two important catalytic applications of DMCs:
a.Centre for Surface Chemistry and Catalysis, KU Leuven, Celestijnenlaan 200F,
3001 Leuven, Belgium. Email: dirk.devos@kuleuven.be;
trees.debaerdemaeker@kuleuven.be.
b.Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford
OX1 3QR, United Kingdom.
c. Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg,
Germany.
d.Department of Inorganic Chemistry and Technology, National Institute of
Chemistry, Hajdrihova 19, 1001 Ljubljana, Slovenia.
†Electronic Supplementary Information (ESI) available: Characterization (XRD
1
patterns, SEM and TEM images, N2 sorption isotherms, FTIR spectra, H MAS NMR
spectra, TG-MS profiles) of the synthesized DMCs and L-DMC and catalytic data of
the synthesized DMCs. Stability, recycling and hot filtration test of L-DMC. See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 2 of 9
ARTICLE
Journal Name
hydroamination of phenylacetylene and 4-isopropylaniline, and crystal cooled to a temperature of -173°C. The structure was
View Article Online
DOI: 10.1039/C9SC00527G
epoxide polymerization of 1,2-epoxyhexane.
solved using SUPERFLIP and refined using tools available within
the Crystals and Olex2 suites.44-46 High-resolution synchrotron
powder X-ray diffraction data were collected at beamline P02.1,
PETRA III (DESY, Hamburg, Germany) at a wavelength of λ =
0.20738 Å using a PerkinElmer area detector.47 The as-prepared
L-DMC powder sample was loaded into a 0.5 mm borosilicate
glass capillary tube and data were collected for 60 s in Debye-
Scherrer geometry. Raw two-dimensional detector images were
integrated using the DAWN suite, using a bin size of 0.005° 2θ.48
Indexing, Pawley fitting and Rietveld refinement of the powder
diffraction data were performed using the routines of TOPAS-
Academic V5.49-51 Chemically sensible restraints were applied to
the C-N, C-C, C-O, Co-C, Zn-N and Zn-O distances. The metal
ratio of the L-DMC was determined with ICP-OES using a Varian
720-ES equipped with a double-pass glass cyclonic spray
chamber, a Sea Spray concentric glass nebulizer and a high
solids torch. Samples were digested in a 7:3 (v:v) solution of
HNO3-HCl and heated to 200°C in a microwave oven for 2 h, as
reported by Lee et al.52 Fourier-transform infrared (FTIR)
spectra of KBr wafers (1 wt.% of DMC) were collected on a
Bruker IFS 66 v/S Vacuum FTIR spectrometer (resolution 4 cm-1).
Solid state nuclear magnetic resonance experiments (SSNMR)
were performed on a 600 MHz Varian spectrometer, equipped
with a 1.6 mm triple-resonance magic-angle spinning (MAS)
probe. Larmor frequencies were 599.44 MHz for 1H and 150.74
MHz for 13C nuclei, and the spectral axes of the recorded spectra
were referenced with respect to the signals of
tetramethylsilane. The sample was spun at MAS rate of 40 kHz.
The 1H MAS NMR spectrum was collected using Hahn-echo
sequence with 90° and 180° pulses of 1.5 µs and 3.0 µs,
respectively, and inter-pulse delay of 25 µs. 16 scans were
accumulated with a recycle delay of 5 s. The 1H-13C cross-
polarization (CP) MAS NMR spectrum was recorded by first
exciting protons and transferring polarization to carbon nuclei
using the ramped-amplitude CP block with a duration of 5 ms.
10 000 scans were accumulated with the recycle delay of 1 s.
During the acquisition, high-power XiX heteronuclear
decoupling was applied. N2 physisorption isotherms were
collected on a Micromeritics 3Flex Surface Analyzer at -196°C.
Before the measurements, the samples were evacuated at
150°C for 16 h. The specific surface area (SBET) was determined
using the BET method in a p/p0 range from 0.004 to 0.03. The
specific external surface area (Sext) and the micropore volume
(Vmicro) were obtained using t-plot analysis. In order to estimate
the micropore size distribution (MPSD), Ar physisorption
isotherms were collected under similar conditions and the
MPSD was estimated using the Horvath–Kawazoe (HK) method.
Scanning electron microscopy (SEM) images were taken using a
JEOL-6010LV SEM. Prior to imaging, samples were coated with
a Pd/Au layer using a JEOL JFC-1300 autofine coater under Ar
plasma for 10 s. Transmission electron microscopy (TEM; High
angle annular dark field, HAADF) images and Energy-dispersive
X-ray spectroscopy (EDX) maps were recorded with a JEOL ARM-
200F TEM with a probe Cs corrector operated at 200 kV. Before
imaging, the samples were suspended in ethanol and dropped
onto a Cu grid (300 Mesh, Pacific Grid Tech, USA) coated with a
Experimental section
Synthesis of single-crystal L-DMC
Single crystals of L-DMC were grown from silica gel using a
modification of the technique reported in references 40 & 41.
The silica gel was formed by mixing 2.5 mL of a 1.37 M aqueous
solution of Na2SiO3 with 2.5 mL of a 0.0125 M aqueous solution
of zinc acetate dihydrate and 5 mL of an aqueous acetic acid
solution (2 M), and leaving the solution to stand overnight.
Subsequently, a K3[Co(CN)6] solution (3 mL, 0.0833 M) was
layered on top of the gel and the crystals were left to grow for
three days.
Optimized synthesis of L-DMC (powder)
Zinc acetate dihydrate (Zn(CH3COO)2.2H2O, 3 mmol) was
dissolved in 20 mL of a 4 M solution of acetic acid. The solution
was stirred and heated to 80°C in an oil bath before dropwise
addition of 10 mL of an aqueous solution containing 1.5 mmol
of K3[Co(CN)6]. The reaction was immediately removed from the
bath and the precipitate was recovered by centrifugation,
washed three times with distilled water and dried at 80°C under
vacuum (587 mg, 82% yield).
Synthesis of benchmark DMC (DMC-PTMEG)
The benchmark DMC catalyst (DMC-PTMEG) was synthesized
with tert-butanol (tBuOH) as complexing agent and
poly(tetramethylene ether) glycol (PTMEG) as co-complexing
agent following literature procedures.6-8,42 This material has
been reported to be the most active compared to other
Zn3[Co(CN)6]2 DMCs prepared by co-precipitation for
intermolecular hydroamination of amines and alkenes or
alkynes and ring opening polymerization reactions.6,42 ZnCl2
(15 mmol) and PTMEG (1.5 mmol) were dissolved in 150 mL of
water. To this, 15 mL of a 0.1 M aqueous solution of K3[Co(CN)6]
t
was added dropswise. BuOH (37.5 mL) was added to the
reaction mixture, which was subsequently stirred for 3 h at
room temperature. The final solid was recovered by
centrifugation and washed three times with a 50:50 mixture of
water:tBuOH, and then dried at 60°C overnight.
Characterization
High-throughput powder X-ray diffraction (PXRD) data were
recorded on a Malvern PANalytical Empyrean diffractometer
equipped with a PIXcel3D solid state detector using a Cu anode
(CuKα1,2 radiation) in transmission geometry (1.3-45°2θ range;
0.013°step size), or on a STOE Stadi MP diffractometer (in
transmission mode) using an image plate detector and focusing
Ge(111) monochromator (CuKα1 radiation) over a range of
5-60°2θ. All PXRD patterns were recorded at room
temperature. Single-crystal X-ray diffraction measurements
were performed at beamline I19 (Diamond Light Source,
Oxfordshire, UK)43 using a wavelength of λ = 0.6889 Å with the
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Table 1. Summary of crystallographic results from Rietveld refinement of L-DMC.
Lacey carbon layer. Thermogravimetric mass spectrometry (TG-
MS) analysis measurements were carried out on a NETZSCH STA
449 F3 Jupiter® thermal analyzer coupled with a Hiden HPR-20
EGA gas analysis system with a heating rate of 10°C/min under
air atmosphere.
View Article Online
DOI: 10.1039/C9SC00527G
Co(CN)6Zn2(CH3COO).4H2O
Composition
Space group (crystal system)
P21/m (monoclinic)
12.3804(3)
7.50396(16)
8.4883(2)
a / Å
b / Å
c / Å
Catalytic reactions
β / °
85.3299(19)
785.97(4)
2.36 / 1.31
0.652
Cell volume / Å3
Rwp / RBragg
χ2
Epoxide polymerization. Before reaction, the catalysts were
activated at 80°C under vacuum overnight. Glass reaction vials
were loaded with the catalyst (5 mol% Zn), 1,2-epoxyhexane
(2 mmol) and diethyleneglycol (DEG, 0.2 mmol). The vials were
then placed in an aluminum block at 110°C and stirred at
500 rpm using a magnetic stirring bar. After reaction, 2.5 mL of
carbon disulfide were added, and the catalyst was recovered by
centrifugation. The supernatant was collected in 10.00 mm
quartz cells for near-infrared measurements performed on a
Cary 5000 UV-VIS-NIR spectrophotometer. The epoxide
conversion was determined by the absorbance of the sample at
2220 nm, by correlating it to the concentration of
1,2-epoxyhexane remaining in the product mixture after
reaction using a calibration curve. The TOF of the Zn sites was
Rietveld plot for the final cycles of refinement is presented in
Figure 1.
The structure crystallizes in the monoclinic space group P21/m
and is shown in Figure 2. The asymmetric unit consists of two
symmetry independent Zn atoms and one Co atom, four
cyanide groups (labelled CN20 to 23, with each C and N atom
numbered accordingly), acetate and three water molecules
(represented as isolated O atoms Ow1, Ow11 and Ow12). Zn1 is
tetrahedrally coordinated to three N atoms from two symmetry
independent cyanide groups (twice to CN20 and once to CN21)
calculated as mol of epoxyhexane consumed per mol of Zn per and one O atom of the acetate (O10). By contrast, Zn2 has an
octahedral coordination environment consisting of three N
atoms of two independent cyanide groups (twice CN22, once
CN23), one O atom from an acetate group (O11) and two water
molecules (Ow1). Co1 is also octahedrally coordinated by six
Catoms, two from CN20 and CN22 and one from each of the
other cyanide groups. The metal polyhedra are linked together
through cyanide groups to form a puckered-layered structure in
the ab-plane, in which two octahedrally coordinated Zn2 sites
and one tetrahedral Zn1 site define a pocket, into which an
octahedrally coordinated Zn2 from the underlying layer
projects. The layers are coordinatively bonded together through
an acetate group in the apical position of the tetrahedral Zn1,
which bridges to the octahedral Zn2 in the layer below. Two
capping water molecules (Ow1) project from this octahedral
Zn2 site into the interstitial region where they form a H-bonding
network with two further water molecules (Ow11 and Ow12),
with O…O distances in the range 2.827(19)- 3.054(16) Å.
It should be noted that the powder pattern reported by Zhang
et al.53 of a DMC obtained by ball milling K3[Fe(CN)6] and zinc
acetate (complex 2 in reference 50) is qualitatively similar to the
diffraction pattern of L-DMC. We therefore suggest that the
structure they observed during ball milling is an Fe(CN)6
analogue of our layered phase. Furthermore, from the FTIR
spectrum of their complex 2, they found that acetate should be
coordinated to Zn, which is in agreement with our structure and
FTIR analysis (vide infra).
hour.
Intermolecular hydroamination. Before reaction, the catalysts
were activated at 80°C under vacuum overnight. Glass reaction
vials were loaded with the catalyst (50 mol% Zn),
phenylacetylene (0.5 mmol), 4-isopropylaniline (1 mmol),
tetradecane (1 mmol) as internal standard and dry toluene
(1 mL) as solvent. The vials were then placed in an aluminum
block at 110°C and stirred at 500 rpm using a magnetic stirring
bar. After reaction, the catalyst was recovered by centrifugation
and the liquid supernatant was analyzed by GC (Shimadzu 2014
GC equipped with a FID detector and a CP-Sil 5 CB column) and
GC-MS (Agilent 6890 gas chromatograph, equipped with a
HP-5MS column, coupled to a 5973 MSD mass spectrometer).
After the reaction, the catalyst was dried under vacuum and
characterized by PXRD. Recycling tests were performed after re-
activation of the sample for 16 h before each run. The turnover
frequency (TOF) of the Zn sites was calculated as mol of
hydroamination product formed per mol of Zn per hour.
Results and discussion
Structure solution and refinement
The structure of the crystals grown using slow diffusion in a
silica gel was solved by single crystal X-ray diffraction. While all
non-H atoms could be found, the quality of the data was too low
to allow satisfactory structure refinement. Through further
synthesis optimization (vide infra), we were able to obtain a
phase pure microcrystalline powder of the L-DMC. Synchrotron
powder diffraction data were collected and successfully refined
by the Rietveld method. Details of the crystallographic
parameters of the final refinement are given in Table 1 and a
Synthesis optimization
To understand the formation mechanism of L-DMC, the single
crystal synthesis conditions were modified and the structural
changes were followed by high-throughput PXRD and both SEM
and TEM (Table 2 and Figures S1-4). To begin with, ZnCl2 ‒ the
most common zinc source in the synthesis of Zn3[Co(CN)6]2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

PleaseCdhoemnoictaal dScjuiesntcme argins
Page 4 of 9
View Article Online
DOI: 10.1039/C9SC00527G
Journal Name
ARTICLE
Fig. 1 Final Rietveld plot for the refinement of L-DMC. Data collected at beamline P02.1, PETRA III (DESY, Hamburg, Germany); λ = 0.20738 Å.
Fig. 2 Crystal structure of L-DMC (left) and polyhedral view showing the stacking of the layers in L-DMC (right). Red, blue, light grey, dark grey and black spheres
represent O, N, C, Zn and Co atoms, respectively. H atoms were omitted for clarity.
DMCs36 ‒ was replaced by Zn(CH3COO)2.2H2O. To favor slow consisted of a mixture of phases, as evidenced by its PXRD
crystal formation, the Zn(CH3COO)2.2H2O aqueous solution was pattern and SEM images (Figures S1 and S3). When the
cooled down using an ice bath. The resulting solid, DMC-1, concentration of the acetic acid solution was increased from
exhibited a PXRD pattern (Figure S1) that resembled that of 2 M to 4 M, we obtained a solid (DMC-3) with a PXRD pattern
L-DMC. However, SEM images revealed the presence of two very similar to that of L-DMC. Nevertheless, TEM images
phases with different morphologies (Figure S2), which suggests revealed that the synthesized solid was not phase pure (Figure
̅
that DMC-1 actually consists of a mixture of the cubic (퐹푚3푚
)
S4), as two different morphologies (with two different metal
and the layered phase (monoclinic, P21/m). In an attempt to ratios) were discerned. Only after increasing the crystallization
ensure the incorporation of acetate ions, the synthesis was temperature to 80°C, phase pure L-DMC was finally obtained.
repeated with Zn(CH3COO)2.2H2O dissolved in a 2 M solution of This synthesis temperature has also been used to crystallize a
acetic acid instead. This yielded a solid, DMC-2, that also
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 4
Please do not adjust margins

Page 5 of 9
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Table 2. Overview of synthesis conditions of L-DMC and other synthesized DMC samples.
View Article Online
DOI: 10.1039/C9SC00527G
Synthesis conditions
Sample
name
Crystallization
Temperature
80°C
Ice bath
Ice bath
Ice bath
80°C
Acid
concentration
4 Ma
Zn source
L-DMC
DMC-1
DMC-2
DMC-3
DMC-4
DMC-5
DMC-6
Zn(CH3COO)2.2H2O
Zn(CH3COO)2.2H2O
Zn(CH3COO)2.2H2O
Zn(CH3COO)2.2H2O
ZnCl2
-
2 Ma
4 Ma
4 Ma
Zn(CF3COO)2
Zn(CH3COO)2.2H2O
80°C
Ice bath
4 Ma
4 Mb
a Acetic acid. b Trifluoroacetic acid.
rhombohedral Zn3[Co(CN)6]2 phase, in which all Zn atoms adopt
a tetrahedral coordination.36,54 Additionally, we studied the
effect of the presence of acetate ions during the synthesis. To
that end, we replaced Zn(CH3COO)2.2H2O by other zinc salts,
such as ZnCl2 and Zn(CF3COO)2 while keeping the acetic acid
concentration at 4 M (DMC-4 and DMC-5, respectively). The
pattern of DMC-4 exhibits reflections that are readily assigned
to the rhombohedral phase, while the pattern of DMC-5 shows
reflections typical of both a rhombohedral and a cubic
structure. Substitution of acetic acid by trifluoroacetic acid
(DMC-6) also produced a cubic DMC. These results indicate the
importance of both the presence of acetic acid in the synthesis
solution and the use of Zn(CH3COO)2.2H2O as Zn source to form
the desired layered structure, since the acetate ions are needed
to balance the positive charge of the {Zn2[Co(CN)6]}+ layers and
ensure their linkage. The other studied anions most likely do not
have the appropriate geometry to form the desired 2D structure
and incomplete hydrolysis of Zn acetate might be necessary to
avoid formation of the cubic structure. Furthermore, the
electronic properties of the anions, in all likelihood, also play a
crucial role in the synthesis of the layered phase. In this sense,
CF3COO- may bind too poorly to Zn, as it offers low electron
density, and thus it can be easily displaced by water, forming a
cubic structure.
In an attempt to delaminate the layered structure, the
optimized synthesis of L-DMC was slightly modified. Before final
isolation (final washing step), the solid was dispersed in an
aqueous miscible organic solvent (AMOS) for 16 h.55 The
structural changes that occurred during the AMOS dispersion
procedure were followed by high throughput powder X-ray
diffraction (Figure S5). No significant changes were observed in
the patterns of L-DMC after washing with the solvents (acetone,
methanol, ethanol, acetonitrile and acetaldehyde). This
suggests that no exfoliation took place and that the L-DMC
structure was maintain, confirming its chemical stability.
Fig. 3 TEM images of L-DMC
.
typical of a two-dimensional (2D) geometry, with many of the
flakes randomly aggregated. Moreover, HAADF-STEM images
and EDX mapping of L-DMC (Figure S6) confirm a homogeneous
distribution of Zn and Co throughout the structure with a Zn:Co
molar ratio of 2.0. The FTIR spectra of L-DMC (Figure S7) exhibits
all the bands associated with DMCs,54 as well as two additional
bands around 1550 cm-1 and 1450 cm-1 attributed to the
asymmetric and symmetric vibrations of –COO-, respectively.56-
58
The presence of such bands in the FTIR spectra is in
agreement with the solved crystal structure. Moreover, the
band attributed to the stretching vibrations of the C≡N bond is
observed at 2190 cm-1, a red shift compared to the ν(C≡N)
frequency in the spectrum of cubic Zn3[Co(CN)6]2 DMC
complexes (2200 cm-1), indicating the influence of the acetate
anions on the electronic environment of Zn. 1H-13C CPMAS NMR
spectrum of L-DMC (Figure 4) exhibits two well resolved signals
of acetate at about 184 and 22 ppm (belonging to carboxyl and
methyl groups, respectively), and four partly overlapped signals
between 125 and 140 ppm, which can be assigned to carbon
nuclei of the four crystallographically distinct cyanide groups.
Characterization
From ICP-OES analysis of L-DMC, a Zn:Co molar ratio of 2.0 was
obtained, which corresponds with the theoretical composition
of L-DMC ‒ Zn2[Co(CN)6](CH3COO).4H2O. TEM images were
collected at different regions to corroborate the phase purity of
L-DMC (Figure 3). All images show a flake-like morphology,
Fig. 4 1H-13C CPMAS NMR spectrum of L-DMC (thick black line – measured; thin red line
– decomposition into individual contributions).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 6 of 9
ARTICLE
Journal Name
This is in excellent agreement with the proposed structure of The second application, the hydroamination reaction, is a 100%
View Article Online
1
L-DMC. Note that signal intensities in the H-13C CPMAS NMR atom efficient route towards the DpOrIo: 1d0u.1c0t3io9/nC9SoCf005f2in7Ge
spectrum do not properly reflect the abundancies of individual chemicals,64,65 thus representing a greener alternative over
species in the crystals, because the efficiency of polarization other important C-N bond forming reactions, like the Buchwald-
transfer from protons is very different to carbon nuclei within Hartwig amination. Furthermore, the formation of undesired

CH3,
(Figure S8) resolves a stronger signal of water molecules at 4.2 product under these reaction conditions. Zn-based Lewis acid
ppm and a weaker signal of the CH3 groups of acetate at 1.7 DMCs have been found to be superior catalysts for this reaction,
 CN
COO- or groups. 1H MAS NMR measurement products is limited, as only acetophenone was formed as a side

ppm, and thus additionally confirms that L-DMC comprises showing a higher selectivity to the hydroamination product
coordinating water molecules. TG-MS analysis of L-DMC than materials that contain Brønsted acid sites.6,7,65,66 Figure 5
(Figure S9) showed two marked mass decays: a first decay (bottom) shows the conversion of phenylacetylene and the
before 100°C (~10% mass loss) attributed to the elimination of yield of the desired hydroamination product obtained with
water, and a second decay between 320 and 390°C (~35% mass DMC-PTMEG and L-DMC, and the kinetic data for L-DMC are
loss) corresponding to the decomposition of CN. Since the presented in Figure S12. The higher catalytic activity of L-DMC
TG-MS analysis was performed under air flow, the cyanide (TOFL-DMC=0.87 compared to TOFDMC-PTMEG=0.23) can be
ligands were removed as (CN)2, and the observed CO2 evolution attributed to a combination of the easier accessibility of the
indicates the decomposition of acetate as no acetic acid
desorption was observed before this temperature. After the
analysis, the recovered powder exhibited an intense green
color, which is indicative of the formation of Zn1-xCoxO oxides
(cobalt green). The N2 adsorption isotherm at -196°C of cubic
100
0.5 h
Zn3[Co(CN)6]2 DMCs is a Type I isotherm with no hysteresis loop,
2 h
typical of purely microporous materials. In contrast, the
80
isotherm of L-DMC, presented in Figure S10, shows a small
hysteresis loop.59,60 The high initial N2 uptake at low p/p0 is
attributed to the filling of micropores, while the slope in the
60
0.25 to 0.35 range indicates the presence of a considerable
external surface area (Sext) in agreement with the small
crystallite size and plate-like morphology.61 Analysis of the N2
40
sorption isotherm of L-DMC results in a BET surface area (SBET
)
20
0
of 784 m2/g and a Sext of 123 m2/g, which are both higher than
those obtained for DMC-PTMEG (Table S1). Furthermore, the
MPSD was estimated from the Ar adsorption-desorption
isotherms. Horvath−Kawazoe (HK) pore size analyses disclose
differences in the microporous nature of both materials (Figure
S11). While DMC-PTMEG exhibits a relatively narrow MPSD,
centered around 6.7 Å, the MPSD of L-DMC shows the presence
of three micropore systems with maxima around 6, 10 and 11 Å.
This evidences the different geometries between L-DMC and
the common, cubic DMC structure.
DMC-PTMEG
L-DMC
100
80
60
40
20
0
4 h
24 h
Catalytic reactions
The advantages of L-DMC over the benchmark DMC catalyst are
evident in two important DMC applications: ring opening
polymerization of 1,2-epoxyhexane and intermolecular
hydroamination of phenylacetylene with 4-isopropylaniline. For
the ring opening polymerization ‒ one of the most important
applications of DMCs62,63 ‒ a significant increase in the 1,2-
epoxyhexane conversion is observed when L-DMC is employed
as catalyst (Figure 5, top). In fact, almost full conversion is
achieved after only 0.5 h reaction time (92%), which represents
a vast improvement over the 61% conversion obtained with
DMC-PTMEG. Furthermore, the initial TOF obtained with L-DMC
is 1.5 higher than that obtained with DMC-PTMEG (TOFL-DMC=6.2
and TOFDMC-PTMEG=4.1).
DMC-PTMEG
L-DMC
Fig. 5 Catalytic activity results for L-DMC and DMC-PTMEG. Top: Epoxide polymerization
(Reaction conditions: 2 mmol of 1,2-epoxyhexane, 0.2 mmol of DEG, 5 mol% Zn, 110°C).
Bottom: Intermolecular hydroamination. Circles represent phenylacetylene conversion
and bars represent yield of the hydroamination product (Reaction conditions: 0.5 mmol
of phenylacetylene, 1 mmol of 4-isopropylaniline,
tetradecane, 50 mol% Zn, 110°C).
1 mL of toluene, 1 mmol of
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 9
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
catalytic sites and the changed coordination environment of the G.07811.18N; C.V.G. and I.V.: grant no. G.0256.14N) and for a
View Article Online
Zn atoms in the structure. Additionally, the effect of the Postdoctoral Fellowship (T.D.B.
&
BD.BO.)I:.10A.10.K3.9/Ca9nSdC00G52.M7G.
presence of acetate ions in the structure of L-DMC on its high acknowledge the financial support by the Slovenian Research
catalytic activity cannot be disregarded, since it has been found Agency (research core funding No. P1-0021). Funding for the
to enhance the performance of DMC catalysts for other organic TEM through Hercules project AKUL/13/19 is kindly
reactions.11 Nevertheless, in order to fully disclose their acknowledged. The authors are grateful to Prof. Jin Won Seo
involvement in the reaction mechanism, further studies are (KU Leuven) for TEM support, to Prof. Andrew L. Goodwin
required.
(Oxford) for the use of resources and discussions, to the
As observed in both catalytic activity tests, the differences in beamline staff of I19 (Diamond Light Source, MT13639) for help
activity exhibited by the DMCs highlight the advantages of and assistance, to Kwinten Janssens (KU Leuven) for the
L-DMC
.
The catalyst L-DMC also exhibits
a
higher collection of additional FTIR data, and to Guangxia Fu and João
hydroamination activity than the other synthesized DMCs and Marreiros for Ar physisorption support.
other Lewis acid catalysts (Table S2 and S3). Furthermore,
recycling tests, PXRD and FTIR characterization after three
hydroamination runs show the high stability and reusability of
Notes and references
L-DMC as a solid catalyst (Figures S13-S15). The leaching of
active species from the solid catalysts was studied by a hot
filtration test (Figure S16). To this end, the catalyst was removed
from the hot reaction mixture after 0.5 h reaction time
(phenylacetylene conversion, ~24%). The clear supernatant (in
the absence of solid catalysts) was allowed to react for an
additional 19.5 h reaction time, after which no increase in
phenylacetylene conversion was detected. This indicates that
no leaching of catalytically active species from the solid occurs
during the reaction under the studied conditions.
1
2
3
4
Milgrom, J. US3278457 A, 1966.
Belner, R. J. US3278458; 1966
Herold, R. J. US3278459 A, 1966.
Y. Dienes, W. Leitner, M. G. J. Muller, W. K. Offermans, T.
Reier, A. Reinholdt, T. E. Weirich and T. E. Muller, Green
Chem., 2012, 14, 1168-1177.
5
6
J. Langanke, A. Wolf, J. Hofmann, K. Bohm, M. A. Subhani, T.
E. Muller, W. Leitner and C. Gurtler, Green Chem., 2014, 16
,
1865-1870.
A. Peeters, P. Valvekens, F. Vermoortele, R. Ameloot, C.
Kirschhock and D. De Vos, Chem Commun., 2011, 47, 4114-
4116.
7
8
A. Peeters, P. Valvekens, R. Ameloot, G. Sankar, C. E. A.
Kirschhock and D. E. De Vos, ACS Catal., 2013, 3, 597-607.
C. Marquez, M. Rivera-Torrente, P. P. Paalanen, B. M.
Weckhuysen, F. G. Cirujano, D. De Vos and T. De
Baerdemaeker, J. Catal., 2017, 354, 92-99.
R. Srivastava, D. Srinivas and P. Ratnasamy, J. Catal., 2006,
241, 34-44.
Conclusions
In summary, we have successfully synthesized and
characterized a new 2D layered DMC phase, L-DMC, consisting
of positively charged {Zn2[Co(CN)6)}+ layers connected through
acetate anions. L-DMC was more active than the benchmark
DMC catalyst in both the ring opening polymerization of
1,2-epoxyhexane and in the intermolecular hydroamination of
phenylacetylene and 4-isopropylaniline. Furthermore,
recycling, PXRD, FTIR and hot filtration tests demonstrated the
good reusability and stability of L-DMC. This represents, to the
best of our knowledge, the first two-dimensional DMC based on
the catalytically active Zn-Co metal combination. The successful
synthesis and excellent catalytic properties of L-DMC may lead
to new studies focused on exploring further modifications
through, for instance, intercalation of other molecules or
pillaring, in order to fine-tune its physicochemical properties.
9
10 C. Marquez, F. G. Cirujano, C. Van Goethem, I. Vankelecom, D.
De Vos and T. De Baerdemaeker, Catal. Sci. Technol., 2018, 8,
2061-2065.
11 C. Marquez, F. G. Cirujano, S. Smolders, C. Van Goethem, I.
Vankelecom, D. De Vos and T. De Baerdemaeker, Dalton
Trans., 2019, 48, 3946-3954.
12 A. Ludi and H. U. Güdel, in Inorganic Chemistry. Structure and
Bonding, Springer, Berlin, Heidelberg, 1973, pp. 1-21.
13 P. Valvekens and D. De Vos, in New Materials for Catalytic
Applications, Elsevier, Amsterdam, 2016, pp. 1-12.
14 S. H. Byun, H. S. Seo, S. H. Lee, C-S. Ha and I. Kim. Macromol.
Res., 2007, 15, 393-395.
15 S. S. Kaye and J. R. Long, J. Am. Chem. Soc., 2005, 127, 6506-
6507.
16 J. C. Wojdeł, S. T. Bromley, F. Illas and J. C. Jansen, J. Mol.
Model., 2007, 13, 751-756.
17 J. Roque, E. Reguera, J. Balmaseda, J. Rodríguez-Hernández, L.
Reguera and L. F. del Castillo, Microporous Mesoporous
Mater., 2007, 103, 57-71.
Conflicts of interest
There are no conflicts to declare.
18 N. J. Robertson, Z. Qin, G. C. Dallinger, E. B. Lobkovsky, S. Lee
and G. W. Coates, Dalton Trans., 2006, 0, 5390–5395.
19 C. G. Silva, Y. Bouizi, V. Fornes and H. Garcia, J. Am. Chem. Soc.,
2009, 131, 13833-13839.
20 F. Gándara, B. Gomez-Lor, E. Gutiérrez-Puebla, M. Iglesias, M.
A. Monge, D. M. Proserpio and N. Snejko, Chem.
Mater., 2008, 20, 72-76.
21 G. Fan, F. Li, D. G. Evans and X. Duan, Chem. Soc. Rev., 2014,
43, 7040-7066.
22 J. Helsen, J. Chem. Educ., 1982, 59, 1063-1065.
23 T. An, Y. Wang, J. Tang, Y. Wang, L. Zhang and G. Zheng, J.
Colloid Interface Sci., 2015, 445, 320-325.
Acknowledgements
This project has received funding from the European Union's
Horizon 2020 research and innovation programme under the
Marie Sklodowska-Curie grant agreement No 641887 (project
acronym: DEFNET). D.D.V. thanks KU Leuven for the Metusalem
grant CASAS. F.W.O. Vlaanderen (Research Foundation
Flanders) is thanked for project funding (D.D.V.: grant no.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 8 of 9
ARTICLE
Journal Name
24 X. Liu, C. Shi, C. Zhai, M. Cheng, Q. Liu and G. Wang, ACS Appl. 56 E. A. Secco and G. G. Worth, Can. J. Chem., 19V8ie7w, A6r5tic,le2O5n0li4ne-
Mater. Interfaces, 2016,
8
, 4585-4591.
2508.
25 Z-H. Xuan, D-S. Zhang, Z. Chang, T-L. Hu and X-H. Bu, Inorg. 57 N. Masciocchi, E. Corradi, A. Sironi, G. DMOoI:r1e0t.t1i0, 3G9./CM9iSnCe0l0li5a2n7Gd
Chem., 2014, 53, 8985-8990.
P. J. Porta, Solid State Chem., 1997, 131, 252-262.
26 M. K. Ram Reddy, Z. P. Xu, G. Q. (Max) Lu and J. C. Diniz da 58 D. C. Pereira, D. L. A. de Faria and V. R. L. Constantino. J. Braz.
Costa, Ind. Eng. Chem. Res., 2006, 45, 7504-7509. Chem. Soc., 2006, 17, 1651-1657.
27 T. J. Pinnavaia, M-S. Tzou, S. D. Landau and R. H. Raythatha, J. 59 M. Thommes, K. Kaneko, A. V. Neimark, J. P. Olivier, F.
Mol. Catal., 1984, 27, 195-212.
28 K. Suzuki, T. Mori, K. Kawase, H. Sakami and S. Iida, Clays Clay
Miner., 1988, 36, 147-152.
29 U. Díaz and A. Corma, Dalton Trans., 2014, 43, 10292-10316.
30 K. Varoon, X. Zhang, B. Elyassi, D. D. Brewer, M. Gettel, S. 61 W. J. Roth, B. Gil, W. Makowski, B. Marszalek and P. Eliasova,
Rodriguez-Reinoso, J. Rouquerol and K. S. W. Sing, Pure Appl.
Chem., 2015, 87, 1051–1069.
60 A. Gil, S. A. Korili and M. A. Vicente, Catal. Rev.: Sci. Eng., 2008,
50, 153–221.
Kumar, J. A. Lee, S. Maheshwari, A. Mittal, C-Y Sung, M.
Cococcioni, L. F. Francis, A. V. McCormick, K. A. Mkhoyan and 62 G. Trott, P. K. Saini and C. K. Williams, Phil. Trans. R. Soc. A,
M. Tsapatsis, Science, 2011, 334, 72-75.¶ 2016, 374, 20150085.
31 A. Corma, V. Fornes, S. B. Pergher, Th. L. M. Maesen and J. G. 63 S. Lee, S. T. Baek, K. Anas, C-S. Ha, D-W. Park, J. W. Lee and I.
Buglass, Nature, 1998, 396, 353-356. Kim, Polymer, 2007, 48, 4361-4367.
Chem. Soc. Rev., 2016, 45, 3400-3438.
32 A. Corma, U. Diaz, M. E. Domine and V. Fornés, Angew. Chem., 64 T. E. Müller, K. C. Hultzsch, M. Yus, F. Foubelo, M. Tada, Chem.
2000, 112, 1559-1561.
33 A. Corma, V. Fornés and U. Díaz, Chem. Commun., 2001,
2642-2643.
Rev., 2008, 108, 3795-3892.
65 J. Penzien, T. E. Müller, J. A. Lercher, Micropor. Mesopor.
Mater., 2001, 48, 285-291.
0
,
34 H. Liang, F. Meng, M. Cabán-Acevedo, L. Li, A. Forticaux, L. 66 J. C. Penzien, C. Haessner, A. Jentys, K. Kohler, T. E. Muller and
Xiu, Z. Wang and S. Jin, Nano Lett., 2015, 15, 1421-1427.
35 L. Li, R. Ma, Y. Ebina, N. Iyi and T. Sasaki, Chem.
Mater., 2005, 17, 4386-4391.
J. A. Lercher, J. Catal., 2004, 221, 302-312.
36 J. Kuyper and G. Boxhoorn, J. Catal., 1987, 105, 163-174.
37 Y-J. Huang, G. R. Qi and L. S. Chen, Appl. Catal. A, 2003, 240
,
263-271.
38 I. Kim, K. Anas, S. Lee, C-S. Ha and D-W. Park, Catal. Today,
2008, 131, 541-547.
39 X-H. Zhang, Z-J. Hua, S. Chen, F. Liu, X-K. Sun and G-R. Qi, Appl.
Catal. A, 2007, 325, 91-98.
40 Z. Blank, D. M. Speyer, W. Brenner and Y. Okamoto, Nature,
1967, 216, 1103-1104.
41 R. Z. LeGeros and J. P. LeGeros, J. Cryst. Growth, 1972, 13/14
,
476-480.
42 I. Kim, J. T. Ahn, C-S. Ha, C. S. Yang and I. Park, Polymer, 2003,
44, 3417-3428.
43 D. R. Allan, H. Nowell, S. A. Barnett,M. R.Warren, A.Wilcox, J.
Christensen, L. K. Saunders, A. Peach, M. T. Hooper, L. Zaja, S.
Patel, L. Cahill, R. Marshall, S. Trimnell, A. J. Foster, T. Bates, S.
Lay, M. A. Williams, P. V. Hathaway, G. Winter, M. Gerstel and
R. W. Wooley, Crystals, 2017, 7, 336.
44 L. Palatinus and G. Chapuis, J. Appl. Cryst., 2007, 40, 786-790.
45 P. W. Betteridge, J. R. Carruthers, R. I. Cooper, K. Prout and D.
J. Watkin, J. Appl. Crystallography, 2003, 36, 1487.
46 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K.
Howard and H. Puschmann, J. Appl. Cryst., 2009, 42, 339-341.
47 A.-C. Dippel, H.-P. Liermann, J. T. Delitz, P. Walter, H. Schulte-
Schrepping, O. H. Seeck and H. Franz, J. Synchrotron Rad.,
2015, 22, 675-687.
48 M. Basham, J. Filik, M. T. Wharmby, P. C. Y. Chang, B. El
Kassaby, M. Gerring, J. Aishima, K. Levik, B. C. A. Pulford, I.
Sikharulidze, D. Sneddon, M. Webber, S. S. Dhesi, F.
Maccherozzi, O. Svensson, S. Brockhauser, G. Naray and A. W.
Ashton, J. Synchrotron Rad., 2015, 22, 853-858.
49 G. S. Pawley, Appl. Crystallogr. 1981, 14, 357-361.
50 H. M. Rietveld, J. Appl. Cryst., 1969, 2, 65-71.
51 A. A. Coelho, J. Appl. Cryst., 2018, 51, 210–218.
52 Y. Lee, S. Kim, J. K. Kang and S. M. Cohen, Chem. Commun.,
2015, 51, 5735-5738.
53 W. Zhang, Q. Lin, Y. Cheng, L. Lu, B. Lin, L. Pan and N. Xu,
J. Appl. Polym. Sci., 2012, 2, 977-985.
54 C. P. Krap, B. Zamora, L. Reguera and E. Reguera, Micropor.
Mesopor. Mater., 2009, 120, 414-420.
55 Q. Wang and D. O’Hare, Chem. Commun., 2013, 49, 6301-
6303.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Chemical Science
View Article Online
DOI: 10.1039/C9SC00527G