Three-dimensional cobalt(II) and cadmium(II) MOFs containing 1,4-naphthalenedicarboxylate: Catalytic activity of Cd-MOF

Article abstract of DOI:10.1016/j.poly.2015.12.022

Three-dimensional (3D) cobalt(II) and cadmium(II) metal-organic frameworks (MOFs) bearing rigid 1,4-naphthalenedicarboxylate (1,4-NDC) linkers were prepared and their solid-state structures were characterized by X-ray crystallography. Both Co-MOF and Cd-M

Full text of DOI:10.1016/j.poly.2015.12.022

Accepted Manuscript
Three-Dimensional Cobalt(II) and Cadmium(II) MOFs Containing 1,4-Naph-
thalenedicarboxylate: Catalytic Activity of Cd-MOF
In-Hwan Choi, Youngmee Kim, Do Nam Lee, Seong Huh
PII:
S0277-5387(15)00772-X
http://dx.doi.org/10.1016/j.poly.2015.12.022
POLY 11721
DOI:
Reference:
Polyhedron
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11 December 2015
Please cite this article as: I-H. Choi, Y. Kim, D.N. Lee, S. Huh, Three-Dimensional Cobalt(II) and Cadmium(II)
MOFs Containing 1,4-Naphthalenedicarboxylate: Catalytic Activity of Cd-MOF, Polyhedron (2015), doi: http://
dx.doi.org/10.1016/j.poly.2015.12.022
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Three-Dimensional Cobalt(II) and Cadmium(II) MOFs Containing 1,4-
Naphthalenedicarboxylate: Catalytic Activity of Cd-MOF
In-Hwan Choi,a Youngmee Kim,b Do Nam Lee,*c and Seong Huh*a
aDepartment of Chemistry and Protein Research Center for Bio-Industry, Hankuk University of Foreign Studies,
Yongin 17035, Korea. Fax: +82-31-330-4566 E-mail: shuh@hufs.ac.kr
bDepartment of Chemistry and Nano Sceince, Ewha Womans Univeristy, Seoul 03760, Korea.
cDivision of General Education (Chemistry), Kwangwoon Univeristy, Seoul 01897, Korea. Fax: +82-2-940-
5677 E-mail: donamlee@hanmail.net
Abstract
Three-dimensional (3D) cobalt(II) and cadmium(II) metal-organic frameworks bearing rigid
1,4-naphthalenedicarboxylate (1,4-NDC) linkers were prepared and their solid-state
structures were characterized by X-ray crystallography. Both Co-MOF and Cd-MOF
exhibited isostructural frameworks. 1,4-NDC ligands bridge the metal ions in
chelating/bridging and simple bridging modes to form a 1D chains, and these 1D chains are
interconnected by 1,4-NDC to form 3D frameworks with the formula of [M2(1,4-
NDC)2(DMF)2] (M = CoII or CdII). The as-prepared Cd-MOF was found to be catalytically
active for the cyanosilylation reaction of aromatic aldehydes with nitro substituent in varying
positions in the presence of trimethylsilyl cyanide to afford cyanohydrin trimethylsilyl ethers
in a shape and size selective manner. The catalytic reaction is thought to have mainly
occurred inside the Cd-MOF micropores which were generated through the partial
dissociation of DMF ligands near the surfaces of Cd-MOF, where openly accessible
coordination sites are available once the labile DMF ligands dissociate from CdII ions. The
as-prepared Co-MOF did not exhibit catalytic activities for the same reaction.
Keywords: Metal-organic framework; 1,4-Naphthalenedicarboxylate; MOF catalysis; Cyanosilylation;
Shape selectivity
1

1. Introduction
Since the first report of MOF-5 by Yaghi and coworkers [1], a large number of metal-
organic frameworks have been disclosed. The chemical functionalities of the interior surfaces
of MOFs are often strongly dependent on the type and nature of the polytopic organic
bridging linkers which effectively interconnect different metal ion-based nodes [2]. The
geometry and symmetry of these organic bridging linkers also influence the final topological
networks of the resultant MOFs. Among the known ditopic organic bridging linkers, 2,6-
naphthalenedicarboxylate (2,6-NDC) has often been employed as the bridging linker because
it is commercially available and its geometry and molecular dimension are adequate for the
production of novel MOF structures: In-MOF [3] with an anionic framework, Zn-MOFs
(IRMOF-8 [4]), Cr-MOF [5] with MIL-101 topology, [M3(2,6-NDC)3(DMF)4]n [6] type of
MOFs with MnII, FeII, and CoII ions, Mg-MOF (TUDMOF-2 and TUDMOF-3) [7], Cd-MOF
with an additional 4-pyridinecarboxylate linker [8], Al-MOF (MIL-69) [9], and MOFs
containing rare-earth elements such as EuIII, TbIII, and CeIII [10].
In contrast, the commercially available geometrical isomer, 1,4-naphthalenedicarboxylate
(1,4-NDC), was less explored for the preparation of MOFs, presumably because 1,4-NDC has
a much shorter dimension of two carboxylate groups than 2,6-NDC (Scheme 1). Despite its
smaller dimension of two carboxylate groups which will bind two different metal ion centers,
the perfectly linear angle between these two carboxylate groups compared to 2,6-NDC will
benefit the generation of new topologically interesting MOF systems. The backbone structure
of 1,4-NDC is exactly the same as that of the more commonly used 1,4-benzenedicarboxylate
(1,4-BDC), which is a bridging linker found in MOF-5. Nevertheless, the extra phenyl ring in
1,4-NDC usually leads to different secondary building units (SBUs) and framework
structures compared to the MOFs prepared from 1,4-BDC. A few examples of MOF contain
1,4-NDC without other ditopic N-donor co-ligands: Zn6(1,4-NDC)5(OH)2(DMF)2·4DMF
containing hexanuclear SBU (MOF-48) [11], Al(OH)(1,4-NDC) of MIL-53 topology [12],
In(OH)(1,4-NDC)·2H2O and HIn(1,4-NDC)2·2H2O·1.5DMF [13]. Therefore, we predicted
that new functional MOFs based on 1,4-NDC linkers with various metal ions would be
possible.
2

Scheme 1. Structural comparison of 2,6-NDC, 1,4-NDC, and 1,4-BDC anionic ditopic linkers.
MOFs can be utilized as efficient heterogeneous catalytic systems when either Lewis
acidic metal centers or Lewis acidic/basic functional ligands act as catalytic sites for organic
transformations. Generally, the Lewis acidic metal centers are available due to the presence
of openly accessible metal sites or defects in the frameworks [14]. There are several excellent
review articles summarizing recent MOF-based catalytic systems for various organic
transformations [15-17]. One of the most valuable MOF-based catalytic systems may be the
cyanosilylation reaction between aldehydes and trimethylsilyl cyanide because the resulting
products, cyanohydrins, are very useful intermediate compounds for fine chemicals and
pharmaceuticals [18, 19].
In this report, we present two isostructural 1,4-NDC-based three-dimensional (3D)
MOFs: Co-MOF and Cd-MOF. Co-MOF was obtained as very small single crystals while
Cd-MOF was hierarchically grown as single crystals. The crystal structures of both 3D MOFs
and the shape-selective catalysis of Cd-MOF for cyanosilylation reaction of aromatic
aldehydes are also reported.
2. Experimental
2.1. General Methods
1,4-Naphtalenedicarboxylic acid (1,4-H2NDC) was purchased from TCI. All other
commercially available starting materials and solvents were purchased from Sigma-Aldrich
and TCI and were used without further purification.
2.2. Preparation of [Co2(1,4-NDC)2(DMF)2]
3

A mixture of Co(NO3)2·6H2O (0.145 g, 0.5 mmol) 1,4-H2NDC (0.216 g, 1.0 mmol)
dissolved in 10 mL of DMF was sealed in a Teflon-lined high pressure bomb and stored at
130 °C for 48 h. The mixture was cooled to room temperature and the violet colored crystals
were retrieved by filtration and washed with DMF. The crystals were air-dried overnight
(0.160 g, 46%). Anal. calcd. for C30H26Co2N2O10 (692.39): C, 52.04; H, 3.78; N, 4.05. Found:
C, 51.94; H, 3.93; N, 4.08.
2.3. Preparation of [Cd2(1,4-NDC)2(DMF)2]
A mixture of Cd(NO3)2·4H2O (0.154 g, 0.5 mmol) 1,4-H2NDC (0.216 g, 1.0 mmol)
dissolved in 10 mL of DMF was sealed in a Teflon-lined high pressure bomb and stored at
130 °C for 48 h. The mixture was cooled down to room temperature and the ivory colored
crystals were retrieved by filtration and washed with DMF. The crystals were air-dried
overnight (0.204 g, 60%). Anal. calcd. for C30H26Cd2N2O10 (799.33): C, 45.08; H, 3.28; N,
3.50. Found: C, 44.67; H, 3.21; N, 3.70.
2.4. Cyanosilylation of Aldehydes
A mixture of the as-prepared Cd- MOF catalyst (0.020 g, 0.0125 mmol), an aldehyde of
choice (1.0 mmol, 4-nitrobenzaldehyde 0.151 g; 3-nitrobenzaldehyde 0.151 g; 2-
nitrobenzaldehyde 0.151 g) and trimethylsilyl cyanide (0.125 mL, 1.0 mmol) in dry toluene
(10 mL) was heated at 50 °C with constant stirring for 72 h. After cooling to room
temperature, the MOF solids were filtered off and the filtrate was evaporated until dry under
high vacuum. The dried residue was completely dissolved in a mixture of CDCl3 and
acetone-d6 and 1,1,2,2-tetrachloroethane (106 µL, 1 mmol) as a standard for calibration was
added to the solution. The reaction conversions were determined from the ratio of proton
signal of cyanohydrins at around 5.65 ppm and a signal from 1,1,2,2-tetrachloroethane at 5.95
ppm based on 1H NMR measurements.
2.5. Physical Measurements
NMR spectra were recorded on a Bruker Ascend 400 (400.13 MHz for 1H) spectrometer.
1H chemical shifts were referenced to the proton resonance resulting from protic residue in
deuterated solvent. The N2 and CO2 adsorption-desorption analyses were performed on a
4

Belsorp-miniII (BEL Japan) at 77 K and 196 K, respectively. The as-prepared MOF samples
were dried at 150 °C or 180 °C for 2 h prior to measurement. Powder X-ray diffraction
patterns were obtained using a Rigaku MiniFlex (30 kV, 15 mA, step size 0.02°). SEM
images of gold-coated Cd-MOF were obtained on a Coxem CX-100S (accelerating voltage,
20 kV). Thermogravimetric analysis was carried out on a TGA Q5000 (TA Instruments)
under a nitrogen atmosphere. FT-IR spectra in attenuated total reflection (ATR) mode were
obtained on a Jasco FT/IR-4100 spectrometer. Elemental analysis was performed at the
Organic Chemistry Research Center, Sogang University (Seoul, Korea) using EA1112 (CE
Instruments, Italy).
2.6. X-ray Crystallography
The X-ray diffraction data for Co-MOF were collected on a Bruker D8 Venture
diffractometer equipped with a Cu IµSTM microfocus sealed-tube X-ray source (λ = 1.54178
Å), and the diffraction data for Cd-MOF were collected on a Bruker APEX-II diffractometer.
Each crystal was mounted on a glass fiber. The CCD data were integrated and scaled using
the Bruker-SAINT software package, and the structure was solved and refined using
SHEXTL V6.12. All hydrogen atoms were placed in the calculated positions. The
crystallographic data for the Co-MOF and Cd-MOF compounds are listed in Table 1. The
selected bond distances are listed in Table 2. Structural information was deposited at the
Cambridge Crystallographic Data Center (CCDC reference numbers are 961436 for Co-MOF
and 961437 for Cd-MOF).
3. Results and Discussion
Co-MOF and Cd-MOF were prepared by thermal reactions of 1,4-H2NDC ligand with
Co(NO3)2·6H2O and Cd(NO3)2·4H2O, respectively, in dimethylformamide (DMF). Solid-
state structures of both MOFs are very similar to the general formula [M2(1,4-NDC)2(DMF)2]
(M = CoII or CdII) (Table 1 and 2). Both Co-MOF and Cd-MOF crystallized in the P21/c
space group, and the asymmetric unit consists of two metal ions, two 1,4-NDC, and two
mutually cis-positioned DMF ligands. Both Co-MOF and Cd-MOF have similar cell
dimensions, but the crystal quality of Cd-MOF gave us low quality data. The optical
microscopic image of Cd-MOF is given in Fig. 1a. The morphology of the Cd-MOF crystals
5

is that of thin tapered needles which are grown from the same single root crystal. Also, the
surfaces were not smooth. The surface structure of the crystals of Cd-MOF further
investigated by scanning electron microscopy (SEM) indicated that many small particles
covered the surfaces of rod shaped crystals (Fig. 1b and 1c). Thus, although we tried the
preparation of Cd-MOF many times to obtain good single crystals with smooth surfaces,
when preparing Cd-MOF, the same type of crystals were always obtained. Unexpectedly,
however these crystals gave us diffraction data and we successfully solved the structure.
Therefore, the crystals are thought to be a rare example of hierarchically ordered MOF.
Otherwise, we could not have obtained a valid crystal structure. Because smaller crystals
uniformly surround the rod shaped crystals as shown in Fig. 1c, the smaller crystals
presumably epitaxially overgrew on the surfaces of the larger crystals [20].
1,4-NDC ligands bridge metal ions in chelating/bridging and simple bridging modes to
form 1D chains, and these 1D chains are interconnected by 1,4-NDC ligands to form 3D
frameworks (Fig. 2). There are two asymmetric metal ions with different coordination
geometries: a metal ion adopted octahedral geometry, bound by four carboxylate oxygen
atoms and two DMF oxygen atoms, and that of the other metal ion adopted pseudo-
tetrahedral geometry, bound by two chelating carboxylates and two carboxylate oxygen
atoms (Fig. 3). Two DMF ligands coordinate to only one of the two available metal ions in a
mutually cis-positioned manner.
The purity of the bulk samples was checked by powder X-ray diffraction (PXRD)
analysis. The PXRD patterns of the bulk as-prepared MOFs were compared with the
simulated patterns based on the data obtained from X-ray crystallography as given in Fig. 4.
The diffraction patterns of the as-prepared MOFs were in good agreement with those shown
in the simulated data. Thus, the as-prepared MOFs are pure phases.
Thermogravimetric analysis (TGA) clearly suggested that the two DMF ligands in both
as-prepared MOFs could be completely removed when suitably evacuated as shown in Fig. 5.
As-prepared Co-MOF completely lost DMF ligands at 291 °C as shown in Fig. 5a. The
corresponding first derivative curve indicates that a series of heat absorption occurred at 247,
278, and 463 °C. The first two heat absorption can be attributed to the removal of DMF
ligands while the last heat absorption can be attributable to the decomposition of 1,4-NDC
ligand. The as-prepared Cd-MOF exhibited heat absorption at 286, 379, and 432 °C as
6

depicted in Fig. 5b. The first heat absorption can be considered as complete removal of DMF
ligands. Thus, the thermal stabilities of the two MOFs are slightly different.
Although PLATON analysis shows that the as-prepared MOFs are nonporous [21], the
removal of the two DMF ligands would provide not only open metal sites but also void
spaces. As depicted in Fig. 2, 1,4-NDC ligands are located alternately to leave no solvent
accessible voids. This type of packing of 1,4-NDC ligands differs from the known grid-type
of MOF having a mononuclear metal center and 1,4-BDC or N-donor based ditopic co-ligand.
On the other hand, the porosity of the evacuated MOFs was estimated to be 29.6% for Co-
MOF and 32.6% for Cd-MOF due to the removal of the two DMF ligands. The drying of the
as-prepared Co-MOF at 180 °C under vacuum for 2 h afforded a DMF-free sample as
evidenced by Fourier-transform infrared (FT-IR) absorption spectroscopy. The absorption
band at 1653 cm-1 for as-prepared Co-MOF can be attributed to the characteristic C=O
stretching mode of the coordinated DMF ligands. The value is shifted into a lower
wavenumber region upon coordination to CoII metal ion compared with that of free DMF
molecule, 1667 cm-1. The C=O stretching band of DMF ligands almost disappeared in the
dried Co-MOF as depicted in Fig. 6. Despite this spectral change, the values of 1599 and
1407 cm-1 for ν(COOasym) and ν(COOsym) of 1,4-NDC linkers in as-prepared Co-MOF
remained without significant changes after drying. Furthermore, the FT-IR bands
corresponding to the naphthyl ring were also observed for dried Co-MOF at 1534, 1461, 1360,
1262, 1212 and 775 cm-1. These results clearly suggest that the Co-1,4-NDC connectivity
remained intact after the uncoordination of labile DMF ligands.
The gas sorption measurements were taken to investigate the permanent porosity of both
MOFs. The N2 adsorption-desorption analyses of the evacuated MOFs at 180 °C or 230 °C
did not show any meaningful sorption data at 77 K. Nevertheless, we also checked the CO2
sorption of the evacuated samples to test the CO2 sorption abilities of both MOFs at 196 K.
Several flexible CO2-selective MOFs exhibited CO2 sorption abilities despite their low
sorption of N2 gases [22-25]. In both cases, however no meaningful sorption of CO2 was
observed. The reason for this nonporosity may be attributed to either the collapse of
frameworks or structural change into nonporous frameworks after the removal of the two
labile DMF ligands which coordinate to the single metal ion. As the DMF ligands were
eliminated, the coordination number of M(2) ion shown in Fig. 3a changed from six to four
7

and the stability of this metal center may not be high. Thus, we measured the PXRD patterns
of the evacuated Co-MOF and Cd-MOF as shown in Fig. 4, and found that the evacuated
MOFs almost lost their original crystallinity. Very weak diffraction planes of (020) and (040)
were observed for both MOFs. Thus, neither of the MOFs showed permanent porosity upon
evacuation due to the framework collapse.
Although neither of the MOFs exhibited meaningful sorption of N2 and CO2 due to their
low porosities, the as-prepared Cd-MOF could be catalytically active for aldol-type reactions
because it contains acidic Cd(II) ions with labile DMF ligands [26, 27]. Thus, we checked the
catalytic activity of Cd-MOF for the cyanosilylation reaction of aromatic aldehydes with
trimethylsilyl cyanide (TMSCN) in the presence of a catalytic amount of the as-prepared Cd-
MOF (Fig. 7). The resulting cyanohydrins are very useful organic intermediate compounds
for pharmaceuticals [18]. Three different aromatic aldehyde substrates were chosen for the
comparison of reactivities: 4-nitrobenzaldehyde (4-NBA), 3-nitrobenzaldehyde (3-NBA), and
2-nitrobenzaldehyde (2-NBA). The corresponding reaction conversions are summarized in
Fig. 7. We also examined the catalytic activities of as-prepared Co-MOF under the same
reaction conditions. Unlike the Cd-MOF, however Co-MOF did not show significant
activities for all three substrates.
Duan and co-workers recently reported a catalytically active porous lanthanide MOF, Tb-
TCA, where H3TCA is tricarboxytriphenylamine, in which Lewis acidic openly accessible
metal centers were available [28]. They investigated the catalytic activities of Tb-TCA for
cyanosilylation reaction of 4-NBA, 3-NBA, and 2-NBA under the same experimental
conditions. Interestingly, the conversions were increased in the order of 2-NBA (78%) > 3-
NBA (59%) > 4-NBA (47%). They attributed the highest conversion of 2-NBA to the
potential bidentate chelating ability of 2-NBA substrate to Tb ion compared with other NBA
substrates. In general, 2-NBA and 4-NBA undergo faster reaction than 3-NBA in solution
because of the favorable electronic effect of the 2- or 4-positioned electron-withdrawing nitro
substituent. However, if the reaction mainly occurs inside the micropores, the reactivity trend
could be altered due to the substrate shape and/or size-selection effect of the confined space
[29-31]. For instance, Fujita and coworkers revealed that porous 2D CdII network, [Cd(4,4’-
bpy)2](NO3)2 (4,4’-bpy = 4,4’-bipyridine), displayed substrate shape/size-dependent catalytic
cyanosilylation [26]. The reaction conversion of 3-tolualdehyde (19%) was less than that of
8

2-tolualdehyde (40%). Furthermore, while 1-naphthaldehyde and 2-naphthaldehyde gave
good conversions of 62% and 84%, respectively, the more sterically demanding substrate, 9-
anthraldehyde, did not produce any product. Long and coworkers also demonstrated that
microporous MnII-containing MOF, Mn3[(Mn4Cl)3(BTT)8(CH3OH)10]2 (H3BTT = 1,3,5-
benzenetristetrazol-5-yl), displayed substrate-size dependent cyanosilylation reaction [32].
Both benzaldehyde (98%) and 1-naphthaldehyde (90%) gave higher conversions than 4-
phenoxybenzaldehyde (19%) and 4-phenylbenzaldehyde (18%).
In our case, 4-NBA (49%) exhibited a higher conversion than 3-NBA and 2-NBA under
the same reaction conditions. 2-NBA having an electronically favorable 2-positioned nitro
group only exhibited negligible conversion (~ 1%), implying that the reaction mainly
occurred inside the MOF pores. The reaction conversion of 2-NBA was even lower than 3-
NBA. Each benzaldehyde contains nitro substituents at systematically varied positions as
depicted in Fig. 8. The shape and dimensions are also indicated in Fig. 8. The molecular
shapes of both 3-NBA and 2-NBA approximate a square geometry, while 4-NBA displays a
rectangular geometry. The physical dimension of 2-NBA is slightly larger than that of 3-NBA.
This difference may account for the higher reaction conversion of 3-NBA than 2-NBA.
Therefore, the reaction conversions are strongly dependent on both the shape and dimension
of the aldehyde substrates. In order to further confirm that the reaction actually occurs inside
the Cd- MOF micropores, we analyzed the Connolly surface of DMF-free Cd-MOF as shown
in Fig. 9. The shape of the accessible micropores is a flat rectangular geometry along the b-
axis as depicted in Fig. 9b and 9c. Thus, 4-NBA is the most suited substrate for the catalytic
reaction. The pores along the c-axis are not fully accessible as depicted in Fig. 9d and 9e.
Although the framework of evacuated Cd-MOF collapsed, the as-prepared Cd-MOF in
solution may provide catalytic CdII active sites through partial dissociation of DMF ligands.
This partial dissociation of DMF ligands near the surfaces of Cd-MOF particles may prevent
the framework collapse. Therefore, the catalytic cyanosilylation reaction mainly occurs on
the surfaces of Cd-MOF. It is interesting to note that such surface reaction is still sufficient to
lead to substrate shape- and size-dependent catalysis.
4. Conclusion
9

New 3D Co-MOF and Cd-MOF containing rigid 1,4-NDC bridging ligands were
prepared and structurally characterized. Both 3D MOFs are isostructural and contain two
asymmetric metal ions with different coordination geometries. One metal ion adopted
octahedral bound by four carboxylate oxygen atoms and two DMF oxygen atoms, and the
other adopted pseudo-tetrahedral bound by two chelating carboxylates and two carboxylate
oxygen atoms. Two DMF ligands coordinate to only one of the two available metal ions in a
mutually cis-positioned manner. These two DMF ligands could be thermally removed under
vacuum to lead MOFs with openly accessible Lewis acidic metal sites. Single crystals of Cd-
MOF exhibited rare hierarchical particle morphology. Small crystals epitaxially overgrew on
a large crystal. The as-prepared Cd-MOF displayed catalytic activity in cyanosilylation of
aromatic aldehydes due to the acidic metal centers once the labile DMF ligands dissociate
from CdII ions in solution. The heterogeneous cyanosilylation reaction mainly occurred inside
the Cd-MOF micropores along the b-axis generated through the partial dissociation of DMF
ligands near the surfaces of Cd-MOF. The reaction yields were strongly dependent on the
shape and dimension of the aldehyde substrates.
Acknowledgments
The Basic Science Research Program through the National Research Foundation of Korea
(NRF), funded by the Ministry of Education, Science and Technology (NRF-20110008018,
2013R1A1A2006914, 2015R1D1A1A01058136), and the Gyeonggi Regional Research
Center (GRRC) Program of Gyeonggi Province (GRRC-HUFS-2015-B04), and Financial
support from Kwangwoon University in the year 2015 are gratefully acknowledged.
Appendix A. Supplementary material
CCDC 961436 and 961437 contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
10

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12

Table 1. Crystallographic Data for Co-MOF and Cd-MOF.
Co-MOF
Cd-MOF
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Space group
a (Å)
C30H26Co2N2O10
692.39
C30H26Cd2N2O10
799.33
100(2)
170(2)
1.54178
0.71073
P21/c
P21/c
7.0771(2)
19.3930(7)
19.6397(6)
90.00
7.2030(14)
19.888(4)
19.968(4)
90.00
b (Å)
c (Å)
α (°)
β (°)
97.168(2)
90.00
94.94(3)
90.00
γ (°)
Volume(Å3)
2674.41(15)
4
2849.9(10)
4
Z
Density (calc.) (Mg/m3)
Absorption coeff. (mm-1)
Crystal size (mm3)
Reflections collected
Independent reflections
1.720
1.863
10.305
1.556
0.10 × 0.03 × 0.02
16209
0.15 × 0.08 × 0.02
16490
2062 [R(int) = 0.0745]
6272 [R(int) = 0.1488]
Data/restraints/parameters
2062 / 7 / 401
1.043
1272 / 15 / 363
0.996
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Largest diff. peak and hole
(e.Å-3)
R1 = 0.0401, wR2 = 0.0935
R1 = 0.0508, wR2 = 0.0994
0.796 and -0.536
R1 = 0.1307, wR2 = 0.3200
R1 = 0.2101, wR2 = 0.3519
3.944 and -1.869
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Table 2. Selected Bond Distances for Co-MOF and Cd-MOF.
Co-MOF
Cd-MOF
M-Ocarboxylate
M-ODMF
2.008(4)-2.279(4)
2.105(5), 2.2112(7)
3.845, 3.876
2.232(14)-2.379(10)
2.248(13), 2.262(17)
3.925, 4.024
M···M
14

Figure Captions
Fig. 1. Optical microscopy image of Cd-MOF (a). SEM images of hierarchical Cd-MOF
crystals at different magnifications. Image (c) is the enlarged view of the square
outlined area of (b).
Fig. 2. Framework structure of Co-MOF and Cd-MOF containing 1,4-NDC shown along the
a-axis. Hydrogen atoms are omitted for clarity.
Fig. 3. Asymmetric unit of Co-MOF and Cd-MOF (a). Crystal structure of the asymmetric
unit of Co-MOF with atomic labelling scheme (b). Displacement ellipsoids are shown
at the 50% probability level. All hydrogen atoms were omitted for clarity. Symmetry
operations: (i) -x, 0.5+y, 0.5-z, (ii) -x, -0.5+y, 0.5-z, (iii) -1+x, y, z, (iv) 1+x, y, z, (v)
1+x, 1.5-y, 0.5+z, and (vi) -1+x, 1.5-y, -0.5+z.
Fig. 4. Comparison of the PXRD patterns of the as-prepared MOFs, simulated data, and dried
MOFs. Co-MOF (a) and Cd-MOF (b).
Fig. 5. TG curves and their first derivatives for the as-prepared Co-MOF (a) and Cd-MOF
(b).
Fig. 6. FT-IR spectra of the as-prepared Co-MOF (solid line in blue) and evacuated Co-MOF
(dotted line in red).
Fig. 7. Substrate-dependent reaction conversions in the cyanosilylation reaction of aromatic
aldehydes catalyzed by the as-prepared Cd-MOF. Reaction conditions: as-prepared
Cd-MOF, 20 mg; substrate, 1.0 mmol; TMSCN, 1.0 mmol; 50°C (3 d).
Fig. 8. Comparison of the molecular dimensions of aldehyde substrates. In order to estimate
the physical dimensions of these molecules, we chose two suitable atoms and
calculated their center-to-center distance using Chem3D then added their van der
Waals radii.
Fig. 9. Connolly surface of DMF-free Cd-MOF probed with a probe radius of 1.0 Å along the
a-axis (a), the same Connolly surface viewed down the b-axis (b), and c-axis (d). The
corresponding ball-and-stick framework structures (c, e). Grey and green colors in (a),
(b), and (d) indicate the exterior and interior of the surface, respectively.
15

Fig. 1
16

Fig. 2
17

Fig. 3
18

Fig. 4
19

Fig. 5
20

Fig. 6
21

Fig. 7
Fig. 8
22

Fig. 9
23

Graphical Abstract
Three-Dimensional Cobalt(II) and Cadmium(II) MOFs Containing 1,4-
Naphthalenedicarboxylate: Catalytic Activity of Cd-MOF
In-Hwan Choi, Youngmee Kim, Do Nam Lee*, and Seong Huh*
3D metal-organic frameworks with the formula of [M2(1,4-NDC)2(DMF)2] (M = CoII or CdII)
were formed, and the as-prepared Cd-MOF was found to be catalytically active for the
cyanosilylation reaction of aromatic aldehydes with nitro substituent in varying positions in
the presence of trimethylsilyl cyanide to afford cyanohydrin trimethylsilyl ethers in a shape
and size selective manner.
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