Two novel 3D-MOFs (Ca-TATB and Co-HKUST): Synthesis, structure and characterization

Article abstract of DOI:10.1016/j.ica.2018.03.014

We report X-ray crystallographic investigations of two novel metal–organic frameworks (MOFs) by using 4,4′,4′'-s-triazine-2,4,6-triyltribenzoic acid [H₃TATB] ligand with Ca metal for 1 and 1,3,5 benzene tri-carboxylic acid [H₃BTC] ligand with Co metal for 2 respectively. The compound [Ca₆(TATB)₄(H₂O)(DMA)₄] (1); (where DMA = dimethylacetamide); was successfully synthesized in a sealed tube at 110 °C for 72 h and shows the formation of a 3D network with embedded 1D channels which are occupied by solvent molecules. The structure of the compound 1 is relatively new and its structural differences with the reported Cu-TATB compounds are noteworthy. The compound Co-HKUST (2) was synthesized by solvothermal method at 140 °C for 72 h. Paddlewheel secondary building units are used to construct Co-HKUST (2) which is isostructural analogue of HKUST-1 enriching the series which consists of Cr, Fe, Ni, Zn, Mo, and Ru analogues. Both 1 and 2 are metastable MOFs characterized by complementary techniques namely powder X-ray diffraction and FTIR analysis.

Full text of DOI:10.1016/j.ica.2018.03.014

Accepted Manuscript
Research paper
Two novel 3D-MOFs (Ca-TATB and Co-HKUST): Synthesis, structure and
characterization
Subba R. Marri, Neha Chauhan, Ranjay K Tiwari, Jitendra Kumar, J.N. Behera
PII:
S0020-1693(17)31425-1
https://doi.org/10.1016/j.ica.2018.03.014
ICA 18159
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 September 2017
21 January 2018
9 March 2018
Please cite this article as: S.R. Marri, N. Chauhan, R.K. Tiwari, J. Kumar, J.N. Behera, Two novel 3D-MOFs (Ca-
TATB and Co-HKUST): Synthesis, structure and characterization, Inorganica Chimica Acta (2018), doi: https://
doi.org/10.1016/j.ica.2018.03.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Two novel 3D-MOFs (Ca-TATB and Co-HKUST): Synthesis, structure and
characterization
Subba R. Marria,b, Neha Chauhana,b, Ranjay K Tiwaria,b, Jitendra Kumara,b and J. N.
Beheraa,b*
a
School of Chemical Sciences, National Institute of Science Education and Research
(NISER), Bhubaneswar 751005.
b Homi Bhabha National Institute, Mumbai, India
E-mail: jnbehera@niser.ac.in
Key words: Ca(II)-MOF / 3D Framework / 1D Channel / Paddel wheel / Co-HKUST
Abstract:
We report X-ray crystallographic investigations of two novel metal-organic frameworks
(MOFs) by using 4,4',4''-s-triazine-2,4,6-triyltribenzoic acid [H3TATB] ligand with Ca metal
for 1 and 1,3,5 benzene tri-carboxylic acid [H3BTC] ligand with Co metal for 2 respectively.
The compound [Ca6(TATB)4(H2O)(DMA)4] (1); (where DMA = dimethylacetamide); was
successfully synthesized in a sealed tube at 110 °C for 72 h and shows the formation of a 3D
network with embedded 1D channels which are occupied by solvent molecules. The structure
of the compound 1 is relatively new and its structural differences with the reported Cu-TATB
compounds are noteworthy. The compound Co-HKUST (2) was synthesized by Hydro/solvo
thermal method at 140 °C for 72h. Paddlewheel secondary building units are used to
construct Co-HKUST (2) which is isostructural analogue of HKUST-1 enriching the series
which consists of Cr, Fe, Ni, Zn, Mo, and Ru analogues. Both 1 and 2 are metastable MOFs

characterized by complementary techniques namely powder X-ray diffraction and FTIR
analysis.
Introduction:
The synthesis and applications of metal-organic frameworks (MOFs) have surpassed many
boundaries and exceptionally well defined MOF structures with unique applications like
catalysis, clean energy sources, gas storage, proton conduction etc. have been reported in the
literature.[1-4] The basic assembling unit for MOF is a metal ion sometimes referred as node
and a ligand which can have rigid, semi-rigid or flexible skeleton. Structural variants of
multitude of ligands have been utilized for assembling MOF system which contributes
significantly towards our understanding regarding the salient issues in MOF synthesis with
desired properties.[5-8] Undoubtedly, transition metal ions are the most studied metal
systems for the construction of MOF structures because of the inherent magnetic, electronic,
photo physical properties and structural diversities.[9-12] However, recent trends have also
seen the use of alkali and alkaline earth metal ions as the building blocks for MOF
synthesis.[13, 14] The use of s-block elements like magnesium and calcium offers significant
advantages in terms of toxicity, environment friendly nature and large abundance which
make them an economically benign alternative to the transition metal ions.[15-18]
Furthermore, the light weight and higher propensity to interact with adsorbed gas molecules
makes them promising candidate for achieving MOF materials with high adsorption
coefficient per unit weight.[19] Subsequently, number of magnesium based coordination
networks with permanent porosity have been reported in the literature.[20-22] Similarly,
natural processes for CO2 fixation by Ca2+ have prompted the investigation towards the
synthesis of Ca-based MOF systems.[23, 24]

Keeping these facts in mind, we have synthesized Ca-TATB (H3TATB = 4, 4', 4''-s-triazine-
2, 4, 6-triyltribenzoic acid) complex under solvothermal conditions in a sealed tube. TATB
ligand has been used for the construction of MOF systems with high porosity where the
triazine ring systems is believed to enhance the gas adsorption properties due to Lewis basic
character of ring nitrogen atoms towards CO2 and similar gasses.[8, 25-30] However, no
alkaline metal-TATB complex has been reported in the literature to the best of our
knowledge. Herein, we present successful synthesis, structural description and
characterization of a novel [Ca6(TATB)4(H2O)(DMA)4] complex (1) with 1D channels in this
article.
The paddlewheel carboxylates [M(O2CR)4] (where M = Cu or Zn and R= aromatic ring) have
been successfully used for assembling of porous networks.[31, 32] The most celebrated
among those MOFs was a synthesis of the cubic copper trimesate (HKUST-1) [31] with a
framework formula of [Cu3(BTC)2(H2O)3] (BTC = benzene-1,3,5-tricarboxylate) that features
dicopper (II, II) paddlewheel SBUs. This structure still serves as a benchmark material in
both stability and gas uptake capacity. Recently, a [Mo3(BTC)2] 3-D porous network based
on quadruply-bonded dimolybdenum paddlewheel units has been obtained[33] and proved to
be isomorphous to the copper analogue. There are two very attractive features of these
MOFs: (i) the metal Lewis-acidic sites available for coordination by donor substrates are
located on the interior of the pore walls; (ii) the materials can be activated (including the
removal of axially-coordinated molecules) without loss of the basic framework skeleton.
Compared to the vast report on MOF synthesis and its structural characterization, fewer MOF
structures are known to form an isostructural series. In this regard, HKUST-1 stands out as an
emblematic example where isostructural series with other transition metal ions which include
Cr[34, 35], Fe[36], Ni[37], Zn[32], Mo[33], and Ru[38] analogues are known.[39] The Co
analogue from the series has not been reported so for. The efforts to synthesize Co-HKUST-1

analogue has resulted in structural variants of Co-BTC system [40, 41] as reported but they
were not isostructural to HKUST-1 and lacks the paddlewheel arrangement which is the
signature feature of the above series. Herein, we report the Co-HKUST (2) which is
isostructural with analogue of HKUST-1. Both 1 and 2 are metastable MOFs characterized by
complementary techniques namely powder X-ray diffraction and FTIR analysis.
Experimental Section
Materials and methods: All the chemicals were purchased from standard chemical suppliers
and used without further purification. Infrared spectra were recorded on a Perkin Elmer FT-
IR spectrometer equipped with an attenuated total reflectance accessory. Powder X-ray
diffraction data were collected on a Bruker D8 Advance with DAVINCI design fitted with
HTK 16 temperature chamber X-ray powder diffractometer using Cu Kα radiation (λ =
1.5418 Å). Single crystal structure determination by X-ray diffraction was performed on a
Bruker Smart Apex II diffractometer equipped with an Oxford Cryostream low-temperature
device and a fine focus sealed-tube X-ray source (Mo Kα radiation, λ = 0.71073 Å, graphite
monochromated) operating at 50 kV and 30 mA.
Synthesis of 2, 4, 6-tri-p-tolyl-s-triazine (A): Compound A was prepared by adopting the
reported procedure.[42, 43] Briefly, p-tolunitrile (1.45 mL, 12.15 mM) was added slowly to
trifluoromethane sulfonic acid (5 g). The mixture was stirred for 13 h under nitrogen.
Afterwards, the reaction mixture was poured on crushed ice followed by neutralization with
aqueous ammonia which gave white color precipitate. The precipitate was collected by
filtration and washed with water and acetone. A was recrystallized from toluene which
yielded 1.35 g (95 %) of A. 1H-NMR (400 MHz, CDCl3): δ = 8.65 ppm (d, J = 8.2 Hz, 6H),

7.37(d, J = 8.2 Hz, 6H), 2.48 (s, 9H); MS (ESI)(m/z):[M+H]+ calc. for C24H22N3, 352.1800,
found 352.1801.
Synthesis of 4, 4', 4''-s-triazine-2, 4, 6-triyltribenzoic acid (H3TATB, (B)): Compound A
(1.0 g, 2.8 mM), acetic acid (24.85 mL) and H2SO4 (1.58 mL) were taken in a 100 mL flask
and stirred for 5 min. After heating the mixture to 50 °C, chromium trioxide (2.58 g)
dissolved in a mixture of acetic acid (5 mL) and H2SO4 (5 mL) was added slowly. The dark
brown slurry was stirred overnight followed by the filtration of the reaction mixture. The
residue was collected and re-dissolved in 2N NaOH and filtered to remove any insoluble
impurity. The final product was obtained by acidifying the solution with 6N HCl which gave
B (H3TATB) as a white precipitate in 60% yield. 1H-NMR (400 MHz, DMSO-d6) δ = 8.80
ppm (d, J = 8.5 Hz, 6H), 8.18 (d, J = 8.5 Hz, 6H); MS (ESI)(m/z):[M-H]‾ calc. for
C24H14N3O6, 440.0800, found 440.0100.
Synthesis of Ca-TATB MOF Ca6(TATB)4(H2O)(DMA)4, (1):. Ca(NO3)2.4(H2O) (0.060 g,
0.25 mM) and H3TATB (0.073 g, 1.65 mM) were dissolved in 1 mL of DMA and stirred for
15 min. The clear solution was transferred to a glass tube of 10 mm, frozen in liq. N2 and
sealed under vacuum. The tube was placed at 110 °C for 72 h. Colorless rod shaped crystals
of 1 were formed in 40% yield. Anal Calc. (Found) for [Ca6(TATB)4(H2O)(DMA)4] with
6DMA molecules: C 56.66 (55.91); H 4.89 (5.03); N 10.69 (10.33).
Synthesis of Co3(BTC)2 (2): Dark blue octahedral crystals of 2 suitable for X-ray diffraction
study were obtained in a phase pure form when CoCl2 (0.095 g, 0.733 mM) and BTC (0.062
g, 0.295 mM) were stirred in 1.5 mL of DMF for 10 minutes, and the resulting reaction
mixture was transferred into a 15 mL PTFE-lined acid digestion bomb and heated at 140 °C
for 72 h. Yield was ca 70%.

Single-Crystal Structure Determination: Suitable single crystals of both the compounds 1
and 2 were carefully selected under a polarizing microscope and mounted at the tip of the thin
glass fibre using cyanoacrylate (super glue) adhesive. Single crystal structure determination
by X-ray diffraction was performed on a Bruker Kappa Apex-II diffractometer equipped with
a normal focus, 2.4 kW sealed-tube X-ray source (Mo-Kα radiation, = 0.71073 Å) operating
at 50 kV and 30 mA. Structures were solved by the direct method using SHELXS-97 and
refined on F2 by a full-matrix least-squares technique using the SHELXTL-PLUS[44]
programs package. An empirical absorption correction based on symmetry equivalent
reflections was applied using SADABS.[45] Non-coordinated solvent molecules in the
structure were highly disordered and were impossible to refine using conventional discrete
atom models. To resolve these issues, the contribution of solvent electron density was
removed by the SQUEEZE routine in PLATON.[46] The graphic programs DIAMOND[47]
and ORTEP[48] were used to draw the structures. Non-hydrogen atoms were refined
anisotropically. In the refinement, hydrogens were treated as riding atoms using the SHELXL
default parameters. During refinement, water hydrogen atoms were located on Fourier map
however, constrain was applied to fix the positions. In compound 1, the coordinated
dimethylacetamide (DMA) solvent molecules were showing disorder hence constrained were
applied to fix the position of atoms in the molecule. In the check-cif report ‘A’ level alerts are
present related to the solvent molecules. Details of crystal structure refinement parameters for
both 1 and 2 given in Table 1.
Table 1.Crystal structure refinement parameters for both 1 and 2
Parameter
Formula
Mr
1
2
C112H86Ca6N16O29
2360.45
C6H2CoO5
213.01

Monoclinic
crystal system
Cubic
space group
P21
Fm-3m
a/Ǻ
b/Ǻ
c/Ǻ
/°
/°
/°
15.0283(10)
29.0847(18)
16.2929(12)
90
26.4954(6)
26.4954(6)
26.4954(6)
90
92.800(4)
90
90
90
V/Ǻ3
7113.0(8)
2
18599.9(7)
48
Z
calc (gcm-3)
1.102
0.913

λ(MoKα) [Å]
0.71073
0.291
0.71073
1.095
/ mm-1 μ(cm-1)
 range (deg)
1.43 to 25.46
47820
1.54 to 24.49
29868
reflections collected
unique reflections [ R(int)] 25302 [0.0755]
835 [0.0614]
835 / 0 / 39
1.180
data/restraints/parameters
GOF on F2
25302 / 42 / 1453
0.972
R1 and R2 [I>2σ(I)]
0.0925, 0.2311
0.1410, 0.2540
0.0591, 0.1891
0.0677, 0.1991
0.838 and -0.490
R1 and R2 (all data)
largest residual peaks (e.Ǻ-
1.046 and -0.868
3
)
CCDC no
1449204
1417645
Results and Discussion:
1 and 2 were synthesized by the solvothermal method and formulated on the basis of single
crystal X-ray diffraction. Unfortunately, both the compounds are air sensitive and unstable.
The solvent is playing major role in the synthesis of MOF, which can act as structure
directing agent and sometime it coordinates with metal site and enhancing the stability of
MOF. Generally, the formamide are good solvent for carboxylate and nitrogen based ligand
which dissolve the ligands (Carboxylate and N based ligands) due to the high polarity nature

of formamide solvents. While heating the reaction mixture in formamide solvent, the solvent
decomposed and form in-situ protonated amine which helps in neutralising the charge
balance of anionic framework, balancing the pH of the reaction mixture solution and activate
the Carboxylate ligand by the deprotonation[49]. Attempt to get single crystal of Ca-MOF
using DMF and DEF as a solvent, were unsuccessful. Thus, we used DMA as a solvent which
shows slow rate of evaporation, binding ability with metal and play crucial role in the
formation of single crystal of Ca-MOF.
Structure analysis of [Ca6(TATB)4(H2O)(DMA)4] (1):
Single crystals of compound 1 suitable for X-ray crystallographic studies were grown under
solvothermal condition in a sealed tube. Attempts to grow the crystal under conventional
solvothermal conditions using Teflon liner did not result in any crystal formation which
indicates the use of sealed tube is crucial for the formation of crystalline phase. X-ray
diffraction analysis revealed that 1 crystallizes in a monoclinic crystal system with space
group P21 which have a 3D-network. The asymmetric unit of 1 consists of six
crystallographically unique Ca(II) ions neutralized by twelve carboxylates group contributed
by four crystallographically unique TATB ligands. Apart from this, four dimethylacetamide
(DMA) solvent molecules and one aqua ligand were also found to be coordinated with the
metal centres where the aqua ligand is bridging two calcium centres. The asymmetric unit of
1 is shown in the Figure S1.
The four unique ligands present in the asymmetric unit were assigned suffix A, B, C and D to
differentiate their coordination behaviors. It has been observed that each ligand binds to
seven Ca(II) ions invoking different coordination modes from carboxylate moiety. Two
carboxylate groups of TATB anion labelled as A and C binds in a η1,η2-μ2 manner whereas
the third carboxylate showed η2,η2-μ3 coordination mode as shown in Figure S3a and S3c.

Further, two carboxylate groups of TATB anion labelled as B and D exhibit η1-μ2 mode and
the remaining carboxylate group has η1,η2-μ3 coordination mode as shown in Figure S3b and
S3d. The detailed description of various bond length and bond angles is provided as Table S2
in supporting information.
Six crystallographically unique Ca(II) ions are also encountered in the crystal lattice. Out of
six Ca(II) ions, four Ca(II) ions (namely Ca1, Ca2, Ca4 and Ca5) have octahedral geometries
where the equatorial plane is consists of four carboxylate oxygen from different TATB
ligands and the axial site is composed of DMA solvent molecule and either carboxylate
moiety (Ca1 and Ca2) from TATB ligand or aqua ligand (Ca3 and Ca4) (Figure S4). The
remaining two Ca(II) ions (namely Ca3 and Ca6) are having bicapped trigonal prismatic
coordination environment which consists of eight oxygen atoms where the equatorial plane is
composed of six oxygen atom coming from three carboxylate groups which are coordinating
in a chelate fashion invoking bidentate coordination mode whereas the two axial sites are
occupied by oxygen atoms contributed by carboxylate group of two different TATB ligands
as shown in Figure S4.
The subtle changes in the coordination geometry of metal ions and the coordination mode of
the carboxylate moiety resulted in a 3D network with occupied solvent DMA molecules
(Figure 1a). The calcium ions are interconnecting with each other along c-axis as shown in
Figure 1b and 1c. Thus, the interconnected Ca(II) ions facilitate the formation of hexagonal
1D channels along c-axis embedded within the 3D network.[50-52] The calcium ions Ca1
and Ca2 are bridged together by three carboxylate groups offering (η1-μ2) coordination mode.
Similar connectivity with two carboxylate bridge was also found for Ca4 and Ca5 but in this
case, interestingly, an aqua ligand is involved in bridging the Ca(II) ions while
simultaneously providing hydrogen bonding interactions to the coordinated carboxylate
moieties (The H-bonding and short contact interactions has been provided in Table S1).

Figure 1: Crystal lattice of Ca6(TATB)4(H2O)(DMA)4 (1) showing the void space (part of the
ligand and solvent molecules are omitted for clarity); (b) Another view of the Ca-O
connectivity; (c) Formation of 3D lattice as a result of Ca-carboxylate connectivity along c-
axis.
Figure 2: (a) A 3D lattice showing presence of 1D channels in Ca6(TATB)4(H2O)(DMA)4
(1); (b) Position of unique ligands in the construction of unidirectional pore wall along c-axis.
(Different color highlights the crystallographically unique ligands).

The porous channel extends along c-axis where the channel walls are composed by ligands as
shown in Figure 2. The 3D lattice was further stabilized by π-π stacking interactions as
shown in Figure S5. The two ligands are slightly displaced from each other, however, the
distance between rings A and B is 3.5316(2) Å and between C and D is 3.7785(2) Å which
are in the acceptable range for such interactions.[53]
The noted example of TATB with copper (PCN-6) consists of two identical interwoven net
where the TATB ligand is involved in the formation of dicopper tetracarboxylate
paddlewheel SBUs with axial aqua ligands where each SBU connects four TATB ligands and
each TATB ligand interconnects three SBUs to form a tetrahedral-octahedron.[42, 43] The
planarity of TATB ligand and its susceptibility to form π-π stacking has been attributed for
the formation of interwoven structure[42, 43] in sharp contrast to the structurally similar
examples of HKUST-1 [31] which employs planar but smaller 1,3,5-benzenetricarboxylic
acid (BTC) and MOF-14[54] which was constructed using 4,4',4''-benzene-1,3,5-
triyltribenzoate (BTB) ligand which has similar structure as of TATB but is essentially non-
planar due to steric interaction and results in a completely different (3, 4)-connected Pt3O4-
type topology. Similarly, copper coordination with m-TATB; meta-isomer of TATB, is
reported which again shows the formation of paddlewheel arrangement with two identical
interwoven nets.[55] In case of current investigation, we have found that all four
crystallographically unique TATB ligand are essentially non-planar and the dihedral angle
between centre and three peripheral rings range from 2.68° to 27.54° (2.68, 9.56 and 10.911°
for ligand with suffix A; 13.60, 22.34 and 23.64° for ligand with suffix B; 3.50; 16.16 and
18.79° for ligand with suffix C and 11.49, 11.79 and 27.54° for ligand with suffix D) with the
carboxylate moiety deviating further from the planarity. The deviation of carboxylate group
from planarity and the variable geometrical shapes adopted by Ca(II) ions can be attributed
for the formation of lower symmetry structure in this case.

Structure analysis of Co3(BTC)2, (2):
Dark blue single crystals of compound 2 with composition Co3(BTC)2 was synthesized by
hydro/solvo thermal method. The structure of 2 was solved by single-crystal X-ray diffraction
with space group of Fm-3m having unit cell dimension of 26.4954(6) Å. The crystal structure
of 2 is composed of Co2(COO)4 paddlewheels units with cobalt dimers as four connectors and
benzene-1,3,5-tricarboxylate (BTC) as three connectors (Figure S2). Each paddlewheel unit
is locked by four carboxyl groups from four equivalent BTC linkers and each linker connects
three paddlewheel unit forming a three-dimensional frame work with (3, 4)-connected net
(Figure 3). Such obstacles are commonly observed in MOF chemistry.[31, 32, 36, 39] The
topology of the framework can be regarded as the twisted boracite type which is isostructural
to that of Cu-BTC (HKUST-1).[31] The crystallographically equivalent Co atoms in a
paddlewheel unit are five-coordinated with square-pyramidal geometry form four equatorial
carboxyl oxygen atoms and an axial water molecule. The axial water molecules are directed
from the cobalt atoms to the interior portion of the nanopore. As the solvent molecules reside
inside the pore, they are completely disorder in the crystal and thus, difficult to locate using
X-ray diffraction techniques. The Co…Co distance in the paddlewheel cluster averages to
2.9432 (18) Å, slightly more than the Cu…Cu distance (2.628 (2) Å) in its copper analogue.
The Co-O carboxylate bond lengths are 2.010(3) Å where as Co-O aqua bond lengths are
2.215(6) Å. Bond valence sum (BVS) calculations[56] using and ro (Co-O) of 1.692 Å gave a
valence sum of 1.98 for Co. As 2 is squeezed to remove the solvent molecules we are unable
to know the H-bonding pattern between the solvent molecules and the oxygen of BTC unit.

Figure 3: Crystal lattice view of (3, 4)-connected framework of 2.(a) showing HKUST-1 type
of topology (b and c) crystal lattice of 2 having two different internal void space which is
shown different color sphere (c) crystallographic unit cell having 12 Co···Co paddlewheel
motif. (Color code: oxygen = red; Carbon = gray and Cobalt = Teal) Co1-O1=2.010(3), Co1-
O2=2.215(6); Co1-Co1=2.9432(18)17.
The Co(BTC) is isostructural with the highly stable Cu-HHKUST-1, the Cu has d9 system
and hence it forms square planar geometry, and the coordination environment of the two Cu
satisfy with the eight oxygens (four oxygen for one Cu ions) from four BTC unit and water
molecule. When we activated the Cu-HKUST-1, the axial position of the water molecules
removed from the polymer and the square-pyramidal Cu comes in the highly stable Cu
square-planar geometry due to the high ligand field stabilization energy[57]. Whereas, the Co
is stable in octahedral and tetrahedral geometry. In case of Co(BTC), Co appears to have
square-pyramidal geometry like Cu-HKUST-1 but it is unstable and structure gets collapsed

when the axial solvent molecules are removed. The use of amide solvent with ketone
carbonyl group (DMA), instead of those with a formamide group (DMF or DEF) is essential
for making the process more effective. For solvent with a ketonic carbonyl group such as
DMA, the additional alkyl substituents might lead to an electron donating effect that
strengthen the coordination of the carbonyl group to the metal ion.
Unfortunately, both the polymers are unstable at room temperature. The crystals were
collected from the mother liquor and the PXRD data was recorded. The polymers get
decomposed slowly after removing from the mother liquor and hence the intensity of the
peaks diminish and extra peaks were observed in the higher angle of the PXRD pattern as
shown in the Figure S6 and S8. Thus, we were unable to perform the gas adsorption studies
for the complexes because of its susceptibility to collapse into an unknown phase. For the
compound 1, PXRD data was collected periodically over a period of 5 days to study the
stability of product at ambient conditions. From the PXRD pattern; given in Figure S7a, it
can be seen that the sample is stable up to 3 days in mother liquor, which then starts
collapsing after this time and gets converted to an unknown phase as indicated by PXRD
pattern of 1 after 5 days. We also carried out solvent exchange experiments for compound 1
to remove the strongly coordinating high boiling point DMA solvent molecules with solvents
having low boiling point (like methanol and acetonitrile). The material was immersed in the
solvent (methanol or acetonitrile) which were repeatedly changed with fresh batch for 3 days.
After the experiment, the crystal quality deteriorated and we are unable to perform X-ray
crystallographic examination. The PXRD analysis of the isolated material after solvent
exchange suggested good agreement with the simulated pattern however it is noteworthy to
highlight that the peak intensity significantly diminished as can be seen form Figure S7b. As
per the classification, such materials can be considered as first generation porous
coordination polymers since the porosity collapses irreversibly after guest removal.[58] Both

the complexes were characterized by FTIR (Figure S9 and S10), where the characteristic
peaks centered around 3400 cm-1 is due to the O-H stretch of water and peak around 3000
cm-1 is due to the aromatic C-H stretch. The characteristic peak of carboxylate group
coordinated with metal ion is around 1610-1400 cm-1. The peaks at 1000 cm-1 and 700 cm-1
are absorption peaks for disubstituted aromatic benzene and triazine core, with C=C and C=N
functionality which further confirms the formation of 1 and peak at 1100 cm-1 and 741 cm-
1corresponds to the C=C of aromatic benzene which further confirms the formation of 2.
Conclusions
We have successfully synthesized and characterized two novel MOFs by using alkaline earth
and transition metal atoms by changing different organic ligands. From the single crystal X-
ray analysis suggest that Ca-TATB compound; [Ca6(TATB)4(H2O)(DMA)4] (1) formed with
porous three dimensional network structure with one dimensional channels. These channels
are occupied by solvent molecules. The structural differences to the reported Cu-TATB
compound are noteworthy. Along with this compound we also synthesized Co-HKUST
which is isostructural with analogue of HKUST-1. The framework of the compound 2 formed
with paddlewheel Co2 units and BTC linkers. Both the compounds were well characterized
by complementary techniques like PXRD and FTIR. Unfortunately, both the complexes were
decomposed after removing from the mother liquor.
CCDC contains the supplementary crystallographic data for this paper with a deposition
numbers of CCDC 1449204 (1) and 1417645 (2). These data can be obtained free of charge
at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.) +44-1223/336-033; E-
mail: deposit@ccdc.cam.ac.uk].

Supporting Information (see footnote on the first page of this article): Asymmetric units, π-π
stacking interactions, PXRD data and FTIR spectra as pictures, H-bonding interactions,
complete bond lengths and bond angles as table and X-ray crystallographic data in CIF
format has been given as supporting information.
Acknowledgements
We thank Single Crystal CCD X-ray facility at NISER-Bhubaneswar. SM and RT thank
NISER Bhubaneswar for senior research fellowship and JK thank NISER Bhubaneswar for
postdoctoral fellowship. This work is supported by the Council of Scientific and Industrial
Research (CSIR), New Delhi, Govt. of India for the award of a research grant
(01(2808)/14/EMR-II).
References
[1]
[2]
[3]
L.J. Murray, M. Dinca, J.R. Long, Hydrogen storage in metal-organic frameworks, Chem. Soc.
Rev., 38 (2009) 1294-1314.
Y. Cui, Y. Yue, G. Qian, B. Chen, Luminescent Functional Metal–Organic Frameworks, Chem.
Rev., 112 (2012) 1126-1162.
S.S. Nagarkar, S.M. Unni, A. Sharma, S. Kurungot, S.K. Ghosh, Two-in-One: Inherent
Anhydrous and Water-Assisted High Proton Conduction in a 3D Metal–Organic Framework,
Angew. Chem. Int. Ed., 53 (2014) 2638-2642.
[4]
[5]
J. Lee, O.K. Farha, J. Roberts, K.A. Scheidt, S.T. Nguyen, J.T. Hupp, Metal-organic framework
materials as catalysts, Chem. Soc. Rev., 38 (2009) 1450-1459.
Z. Zhang, Y. Zhao, Q. Gong, Z. Li, J. Li, MOFs for CO2 capture and separation from flue gas
mixtures: the effect of multifunctional sites on their adsorption capacity and selectivity,
Chem. Commun., 49 (2013) 653-661.
[6]
A.M. Plonka, D. Banerjee, J.B. Parise, Effect of Ligand Structural Isomerism in Formation of
Calcium Coordination Networks, Cryst. Growth Des., 12 (2012) 2460-2467.

[7]
[8]
Y.-F. Song, L. Cronin, Postsynthetic Covalent Modification of Metal–Organic Framework
(MOF) Materials, Angew. Chem. Int. Ed., 47 (2008) 4635-4637.
J. Kim, S.-T. Yang, S.B. Choi, J. Sim, J. Kim, W.-S. Ahn, Control of catenation in CuTATB-n
metal-organic frameworks by sonochemical synthesis and its effect on CO2 adsorption, J.
Mater. Chem., 21 (2011) 3070-3076.
[9]
L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P. Van Duyne, J.T. Hupp, Metal–Organic
Framework Materials as Chemical Sensors, Chem. Rev., 112 (2012) 1105-1125.
Q.-L. Zhu, Q. Xu, Metal-organic framework composites, Chem. Soc. Rev., 43 (2014) 5468-
[10]
5512.
[11]
R. Ricco, L. Malfatti, M. Takahashi, A.J. Hill, P. Falcaro, Applications of magnetic metal-
organic framework composites, J. Mater. Chem. A, 1 (2013) 13033-13045.
[12]
[13]
M.C. So, G.P. Wiederrecht, J.E. Mondloch, J.T. Hupp, O.K. Farha, Metal-organic framework
materials for light-harvesting and energy transfer, Chem. Commun., 51 (2015) 3501-3510.
W.-X. Lim, A.W. Thornton, A.J. Hill, B.J. Cox, J.M. Hill, M.R. Hill, High Performance Hydrogen
Storage from Be-BTB Metal–Organic Framework at Room Temperature, Langmuir, 29 (2013)
8524-8533.
[14]
[15]
T. Kundu, S.C. Sahoo, R. Banerjee, Alkali earth metal (Ca, Sr, Ba) based thermostable metal-
organic frameworks (MOFs) for proton conduction, Chem. Commun., 48 (2012) 4998-5000.
L. Cooper, T. Hidalgo, M. Gorman, T. Lozano-Fernandez, R. Simon-Vazquez, C. Olivier, N.
Guillou, C. Serre, C. Martineau, F. Taulelle, D. Damasceno-Borges, G. Maurin, A. Gonzalez-
Fernandez, P. Horcajada, T. Devic, A biocompatible porous Mg-gallate metal-organic
framework as an antioxidant carrier, Chem. Commun., 51 (2015) 5848-5851.
S.R. Miller, E. Alvarez, L. Fradcourt, T. Devic, S. Wuttke, P.S. Wheatley, N. Steunou, C.
Bonhomme, C. Gervais, D. Laurencin, R.E. Morris, A. Vimont, M. Daturi, P. Horcajada, C.
Serre, A rare example of a porous Ca-MOF for the controlled release of biologically active
NO, Chem. Commun., 49 (2013) 7773-7775.
[16]

[17]
[18]
D. Banerjee, J.B. Parise, Recent Advances in s-Block Metal Carboxylate Networks, Cryst.
Growth Des., 11 (2011) 4704-4720.
A.E. Platero-Prats, M. Iglesias, N. Snejko, Á. Monge, E. Gutiérrez-Puebla, From
Coordinatively Weak Ability of Constituents to Very Stable Alkaline-Earth Sulfonate
Metal−Organic Frameworks, Cryst. Growth Des., 11 (2011) 1750-1758.
Y.Y. Sun, K. Lee, Y.-H. Kim, S.B. Zhang, Ab initio design of Ca-decorated organic frameworks
for high capacity molecular hydrogen storage with enhanced binding, Appl. Phys. Lett., 95
(2009) 033109.
[19]
[20]
[21
M. Dincǎ, J.R. Long, Strong H2 Binding and Selective Gas Adsorption within the Microporous
Coordination Solid Mg3(O2C-C10H6-CO2)3, J. Am. Chem. Soc., 127 (2005) 9376-9377.
] A. Mallick, S. Saha, P. Pachfule, S. Roy, R. Banerjee, Selective CO2 and H2 adsorption in a
chiral magnesium-based metal organic framework (Mg-MOF) with open metal sites, J.
Mater. Chem., 20 (2010) 9073-9080.
[22]
[23]
[24]
D. Saha, T. Maity, S. Koner, Alkaline earth metal-based metal-organic framework:
hydrothermal synthesis, X-ray structure and heterogeneously catalyzed Claisen-Schmidt
reaction, Dalton Trans., 43 (2014) 13006-13017.
D. Banerjee, Z. Zhang, A.M. Plonka, J. Li, J.B. Parise, A Calcium Coordination Framework
Having Permanent Porosity and High CO2/N2 Selectivity, Cryst. Growth Des., 12 (2012) 2162-
2165.
A. Mallick, E.-M. Schon, T. Panda, K. Sreenivas, D.D. Diaz, R. Banerjee, Fine-tuning the
balance between crystallization and gelation and enhancement of CO2 uptake on
functionalized calcium based MOFs and metallogels, J. Mater. Chem., 22 (2012) 14951-
14963.
[25]
S. Ma, D. Yuan, J.-S. Chang, H.-C. Zhou, Investigation of Gas Adsorption Performances and
H2 Affinities of Porous Metal-Organic Frameworks with Different Entatic Metal Centers,
Inorg. Chem., 48 (2009) 5398-5402.

[26]
[27]
D. Feng, K. Wang, J. Su, T.-F. Liu, J. Park, Z. Wei, M. Bosch, A. Yakovenko, X. Zou, H.-C. Zhou,
A Highly Stable Zeotype Mesoporous Zirconium Metal–Organic Framework with Ultralarge
Pores, Angew. Chem. Int. Ed., 54 (2015) 149-154.
Y.K. Park, S.B. Choi, H. Kim, K. Kim, B.-H. Won, K. Choi, J.-S. Choi, W.-S. Ahn, N. Won, S. Kim,
D.H. Jung, S.-H. Choi, G.-H. Kim, S.-S. Cha, Y.H. Jhon, J.K. Yang, J. Kim, Crystal Structure and
Guest Uptake of a Mesoporous Metal–Organic Framework Containing Cages of 3.9 and 4.7
nm in Diameter, Angew. Chem. Int. Ed., 46 (2007) 8230-8233.
[28]
[29]
[30]
J. Park, D. Feng, H.-C. Zhou, Structure-Assisted Functional Anchor Implantation in Robust
Metal–Organic Frameworks with Ultralarge Pores, J. Am. Chem. Soc., 137 (2015) 1663-1672.
J. Li, H.-R. Fu, J. Zhang, L.-S. Zheng, J. Tao, Anionic Metal–Organic Framework for Adsorption
and Separation of Light Hydrocarbons, Inorg. Chem., 54 (2015) 3093-3095.
B. Zheng, Z. Yang, J. Bai, Y. Li, S. Li, High and selective CO2 capture by two mesoporous
acylamide-functionalized rht-type metal-organic frameworks, Chem. Commun., 48 (2012)
7025-7027.
[31]
[32]
S.S. Chui, A Chemically Functionalizable Nanoporous Material [Cu3(TMA)2(H2O)3]n,
Science, 283 (1999) 1148-1150.
J.I. Feldblyum, M. Liu, D.W. Gidley, A.J. Matzger, Reconciling the Discrepancies between
Crystallographic Porosity and Guest Access As Exemplified by Zn-HKUST-1, J. Am. Chem. Soc.,
133 (2011) 18257-18263.
[33]
[34]
M. Kramer, U. Schwarz, S. Kaskel, Synthesis and properties of the metal-organic framework
Mo3(BTC)2 (TUDMOF-1), J. Mater. Chem., 16 (2006) 2245-2248.
L.J. Murray, M. Dinca, J. Yano, S. Chavan, S. Bordiga, C.M. Brown, J.R. Long, Highly-Selective
and Reversible O2 Binding in Cr3(1,3,5-benzenetricarboxylate)2, J. Am. Chem. Soc., 132
(2010) 7856-7857.
[35]
K. Sumida, J.-H. Her, M. Dincă, L.J. Murray, J.M. Schloss, C.J. Pierce, B.A. Thompson, S.A.
FitzGerald, C.M. Brown, J.R. Long, Neutron Scattering and Spectroscopic Studies of Hydrogen

Adsorption in Cr3(BTC)2—A Metal−Organic Framework with Exposed Cr2+ Sites, J. Phys.
Chem. C, 115 (2011) 8414-8421.
[36]
[37]
L. Xie, S. Liu, C. Gao, R. Cao, J. Cao, C. Sun, Z. Su, Mixed-Valence Iron(II, III) Trimesates with
Open Frameworks Modulated by Solvents, Inorg. Chem., 46 (2007) 7782-7788.
P. Maniam, N. Stock, Investigation of Porous Ni-Based Metal–Organic Frameworks
Containing Paddle-Wheel Type Inorganic Building Units via High-Throughput Methods, Inorg.
Chem., 50 (2011) 5085-5097.
[38]
[39]
H. Noei, O. Kozachuk, S. Amirjalayer, S. Bureekaew, M. Kauer, R. Schmid, B. Marler, M.
Muhler, R.A. Fischer, Y. Wang, CO Adsorption on a Mixed-Valence Ruthenium Metal–Organic
Framework Studied by UHV-FTIR Spectroscopy and DFT Calculations, J. Phys. Chem. C, 117
(2013) 5658-5666.
C.R. Wade, M. Dinca, Investigation of the synthesis, activation, and isosteric heats of CO2
adsorption of the isostructural series of metal-organic frameworks M3(BTC)2 (M = Cr, Fe, Ni,
Cu, Mo, Ru), Dalton Trans., 41 (2012) 7931-7938.
[40]
[41]
O.M. Yaghi, H. Li, T.L. Groy, Construction of Porous Solids from Hydrogen-Bonded Metal
Complexes of 1,3,5-Benzenetricarboxylic Acid, J. Am. Chem. Soc., 118 (1996) 9096-9101.
M.A. Nadeem, M. Bhadbhade, J.A. Stride, Four new coordination polymers constructed
from benzene tricarboxylic acid: synthesis, crystal structure, thermal and magnetic
properties, Dalton Trans., 39 (2010) 9860-9865.
[42]
[43]
D. Sun, S. Ma, Y. Ke, D.J. Collins, H.-C. Zhou, An Interweaving MOF with High Hydrogen
Uptake, J. Am. Chem. Soc., 128 (2006) 3896-3897.
W. Gao, F. Xing, D. Zhou, M. Shao, S. Zhu, Novel MOFs with tetrahedral cavity assembled
from 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid (H3TATB), Inorg. Chem. Commun., 14 (2011)
601-605.
[44]
G.M. Sheldrick, SHELXTL-PLUS Program for Crystal Structure Solution and Refinement,
University of Gottingen, Gottingen, Germany.

[45]
[46]
[47]
[48]
[49]
G.M. Sheldrick, SADABS Siemens Area Correction Absorption Program, University of
Göttingen, Göttingen, Germany1994.
A. Spek, Single-crystal structure validation with the program PLATON, J. Appl. Crystallogr.,
36 (2003) 7-13.
W.T. Pennington, DIAMOND-Visual crystal structure information system, J. Appl.
Crystallogr., 32 (1999) 1028-1029.
L.J. Farrugia, ORTEP-3 for Windows-a version of ORTEP-III with a Graphical User Interface
(GUI), J. Appl. Crystallogr., 30 (1997) 565-565.
R. Seetharaj, P.V. Vandana, P. Arya, S. Mathew, Dependence of solvents, pH, molar ratio and
temperature in tuning metal organic framework architecture, Arabian Journal of Chemistry,
DOI https://doi.org/10.1016/j.arabjc.2016.01.003(2016).
[50]
[51]
T.-T. Luo, H.-C. Wu, Y.-C. Jao, S.-M. Huang, T.-W. Tseng, Y.-S. Wen, G.-H. Lee, S.-M. Peng, K.-
L. Lu, Self-Assembled Arrays of Single-Walled Metal–Organic Nanotubes, Angew. Chem. Int.
Ed., 48 (2009) 9461-9464.
S.R. Caskey, A.G. Wong-Foy, A.J. Matzger, Dramatic Tuning of Carbon Dioxide Uptake via
Metal Substitution in a Coordination Polymer with Cylindrical Pores, J. Am. Chem. Soc. , 130
(2008) 10870-10871.
[52]
[53]
K.M. Ok, J. Sung, G. Hu, R.M.J. Jacobs, D. O'Hare, TOF-2:ꢀ A Large 1D Channel Thorium
Organic Framework, J. Am. Chem. Soc., 130 (2008) 3762-3763.
Z.-H. Liu, C.-Y. Duan, J. Hu, X.-Z. You, Design, Synthesis, and Crystal Structure of a cis-
Configuration N2S2-Coordinated Palladium(II) Complex:ꢀ Role of the Intra- and
Intermolecular Aromatic-Ring Stacking Interaction, Inorg. Chem., 38 (1999) 1719-1724.
B. Chen, M. Eddaoudi, S.T. Hyde, M. O'Keeffe, O.M. Yaghi, Interwoven Metal-Organic
Framework on a Periodic Minimal Surface with Extra-Large Pores, Science, 291 (2001) 1021-
1023.
[54]

[55]
[56]
Z. Guo, J. Yu, G. Li, Z. Si, H. Guo, H. Zhang, A three-dimensional metal-organic framework
based on a triazine derivative: syntheses, structure analysis, and sorption studies,
CrystEngComm, 11 (2009) 2254-2256.
I.D. Brown, D. Altermatt, Bond-valence parameters obtained from a systematic analysis of
the Inorganic Crystal Structure Database, Acta Crystallographica Section B, 41 (1985) 244-
247.
57]
M. Bosch, M. Zhang, H.-C. Zhou, Increasing the Stability of Metal-Organic Frameworks,
Advances in Chemistry, 2014 (2014) 8.
[58]
S. Horike, S. Shimomura, S. Kitagawa, Soft porous crystals, Nat Chem, 1 (2009) 695-704.

Graphical abstract
We report two novel 3D MOFs with composition [Ca6(TATB)4(H2O)(DMA)4] (1) and
Co3(BTC)2 (2). The Compound 1 was synthesized in sealed tube shows a formation of 3D
netwrok with 1D channel where as compound 2 was synthesized by solvothermal method
formed as 3D framework with Co2(COO)4 paddlewheels units. Both the compounds
charactrized well by complementry techniques like Powder X-ray diffraction and FTIR
analysis

Highlights

[Ca6(TATB)4(H2O)(DMA)4] (1) Formed with porous three dimensional network structure
with one dimensional channels.
 Ca(II) ion MOFs are extremely rare compared to the commonly used vast transition metal
ions.
 Such Ca-MOF could provide cheaper materials which are biocompatible.

In case of [Ca6(TATB)4(H2O)(DMA)4] (1), we have found that all four crystallographically
unique TATB ligand are essentially non-planar and the dihedral angle between centre and
three peripheral rings range from 2.68° to 27.54°.


There are attractive features of BTC based MOFs, the metal Lewis-acidic sites available
for coordination by donor substrates are located on the interior of the pore walls.
Co3(BTC)2 (2) has paddlewheel type 3D porous framework which is isostructural analogue
of HKUST-1(Cu-HKUST-1).